Chapter 4 PHYSIOLOGICAL BASIS OF BEHAVIOUR
Attempts have been made to explain why and how we behave in a particular way in a given situation from different standpoints. Here= dity endowment or environmental influence or the interaction of both has been made responsible for the causation and occurrence of human ‘behaviour. The cognitive factors including intelligence have bzen supposed to be potent factors in an underlying behaviour. Psychological factors like interests, attitudes, emotions and sentiments, mood, and temperament, psycho-state and mental health have also been recognised as major influensable attributes. Apart from all these factors it has been commonly agreed that behaviour in all its forms and shapes definitely has a biological or physiological base.
The mechanism of the human body not only directs the functioning of the sense organs and the process of growth and maturation but also dictates and influences the delicate and complex processes such as thinking, learning and emotional responses. Thereby, it becomes Imperative to pay attention to the mechanism of the human body for the necessary study of human behaviour. There are two important and distioct mechanisms, namely, the nervous system and ductless glands that have been adjudged to carry strong influence over human behaviour. Let us try to get an idea of these body mechanisms.
NERVOUS SYSTEM
The neuron-basic unit of the nervous system
The human body is composed of different types of cells like bone cells, muscle cells, body cells, etc. Each type, consisting of millions of tiny cells, forms a single unit which has a specialized function. The duty of carrying electrical messages from one part of the body to the other has been assigned to nerve cells. Our nervous system is made up of these nerve cells. A nerve cell with all its branches is called a neuron. This neuron is the ultimate structure and functional unit of the nervous system The number of these neurons jn a human nervous system has been estimated at 100 to 200 billion. They are basically alike in structure but appear in different lengths, sizes and shapes Gesigned for specialized functions. Within each neuron there are millions of RNA molecules, each carrying genetic instructions from the DNA.
A neuron has a nucleus, a cell body, and a cell membrane to enclose the whole cell. There are tiny fibres extending out from the cell body called dendrites. Their role is to receive messages through electrical impulses from the sense organs or adjacent neurons and carry them to the cell body. The messages from the cell body further travel the length of a nerve fibre known as the axon. A group of axon, bundled together like parallel wires in an electrical cable, 1s referred to as nerve. The axon (but certainly not all of them) is surrounded by a fatty covering called a myelin sheath. Its function is ta speed up the transmission of the messages. The messages thus transmitted are further carried to a muscle or a gland or a neighbouring nevron through the terminal branches of the nerve fibre.
These neurons or nerve tissues are spread all over the body, There are three types of neurons. The sensory neurons collect messages from inside and outside the body and carry them to the spinal cord and brain. These neurons help in the processes of sensation and perception. The motor neurons carry messages from the brain and Spinal cord to the muscles and the glands. They are responsible for physical movements and activation of glands. The inter neurons or association neurons carry messages from one neuron to another. Their specific role is to carry signals in the form of memories and thoughts and to add reflex or automatic activities.
The Neural Impulse: Neurons as we have seen are the receivers and transmitters of messages. This message is always in the form of electro-chemical impulses. Let us sce how this work is carried on by the neurons.
A neuron in its resting pusition is supposed to maintain a sort of electrical equilibrium i.e., state of polarization. It is because inside the cell membrane of the neuron, there are negatively charged ions and outside the neuron membrane there arc positively charged ions, This state of polarization may be disturbed on account of the effect of the tugger like action of a stimulus applied to the membrane. It causes a sudden change in the electrical potentiality of the neuron. It gets depolarized and a neuron or neural impulse is thus initiated.
The neural impulse is not initiated in response to every electrical message (or impulse) it receives. If the incoming message is not strong enough, it will not cause a change in its electrical potentiality and nothing will happen. The incoming message must be above a certain threshold of intensity if it is to cause a neural impulse.
In this way, a neuron will either be releasing the neural impulse to the extent it is being excited by the messages or impulses it receives or it will not be disturbed at all releasing no neural impulse. This principle is known as the all-or-none law. The law may be stated formally as under:
“The magnitude of the activity in any single neural functioning unit (neuron) is as great as it can be in that unit at that time and is independent of the magnitude of the energy exciting it, provided only that the stimulating energy is sufficiently strong to excite the neuron at all.” (Boring, Langfeld & Weld, 1948 p. 28)
How does the neuron impulse travel further from one neuron to another? There must be some connection for the flow of the current. Certainly there is. There is a fluid-filled space called the Synapse _ between the axon of the neuron and the receiving dendrite of the next. After reaching the end branches of an axon, an impulse signals the release of a chemical substance (neuro transmitter). This chemical transmitter substance is what actually travels across the pap between the two neurons. With the help of the release of a neuro-transmitter into the synapse, one neuron 1s capable of sending its message on to many other neurons. It makes possible for a single neuron to receive messages from thousands of other neurons.
The division of the human nervous system
The human nervous system can be divided into two parts: the central nervous system and the peripheral nervous system.
1. The Central Nervous System: The central nervous system is that part of the nervous system which lies within the body case formed by the skull and spine. The brain and the spinal cord constitute this system.
2. The brain: It is the control room of the huge complicated telephone system of the body. It is composed of three main divisions: the forebrain, the midbrain and the hindbrain.
3. The forebrain: The forebrain is at the very top of the brain. Its important structures are the thalamus, the hypothalamus and the cerebrum. The thalamus consists of two egg shaped structures situated in the central core Of the forebrain just over the brainstem. All sensory impulses pass through it to the higher centres. Therefore, it is usually known as the relay station. In addition, the thalamus seems to exercise some control over the automatic nervous system and also plays a role in the control of sleep and alertness.
‘Hypothalamus lies below the thalamus. It exerts a key influence on all kinds of emotional as well as motivational behaviour. Centres in the hypothalamus exercise control over the important body processes like eating, drinking, sleeping, temperature control and sex. It also exerts control over the activities of the pituitary gland which is located just below it.
The cerebrum lies at the very top of the brain. It is the most complex and largest part of the brain. It extends from the eyebrows to the middle of the skull. It is divided into two hemispheres; the left brain and right brain which controls behaviour in the right and left body sides respectively. A great mass of white matter called the corpus callosum connects these two hemispheres to each other and to the other parts of the nervous system. The cerebrum is covered by a thick layer of tightly packed neurons—called the cerebral cortex. Different areas of the cerebral cortex like sensory projection areas, motor projection areas and association areas, etc., have been found to be responsible for different functions. In this way, the cerebral cortex, also known as the new brain has the ability to perform the functions of storing sensory information, controlling body movements, coordinating all information that comes to the brain and regulating highly cognitive functions such as thinking, reasoning and problem-solving.
4. The Midbrain: The midbrain is a sort of bridge connecting the forebrain (at the top) and hindbrain (at the base). It is particularly concerned with the relaying of messages, particularly those related to hearing and sight) to higher brain centres. One of its important structures is known as recticular activating system (RAS). With the help of this structure an individual is able to decide which impulses Should register consciously and which should be repressed or rejected. Co nsequently, it helps him to concentrate on studying even with the radio set on and sleep soundly with a noisy environment.
5. The Hindbrain: The Hindbrain is situated behind and beneath the Forebrain. It rests within the brainstem, a structure that connects the upper part of the spinal cord with the lowest part of the brain. It is composed of three structures, the medulla, the pons and the cerebellum.
6. Medulla lies nearest to the spinal cord. It controls breathing and many important reflexes such as those that help us maintain our upright postures. It also regulates the highly complex processes like digestion, respiration and circulation which are necessary for the preservation of life.
The pons connects the cerebrum at the top of the brain to the topmost section of the hindbrain, the Cerebellum. It assists the breathing, transmitting impulses from the cerebellum to the higher brain regions and coordinating the activities of both sides of the brain.
The Cerebellum is composed of two circular hemispheres. It helps in performing many bodily functions. It is responsible for body balance and the coordination of body movements. Behaviours like dancing, typing and playing the piano depend on this structure.
Localization of the brain functions
As we know, there are a number of mental functions that are performed by our brain. Whether a specific function is performed by a specific part of the brain or not; and how far our mental functions are dependent on several different areas of the brain; this problem concerning localization of psycho functions in the brain has been a matter of considerable research and experimentation.
Lashley’s laws on localization
On the basis of their experiments, Franz and Lashley have provided two distinct laws on cerebral localization, namely, the law of mass action and the law of equi-potentiality.
Where the law of mass action means that the learned habits disintegrate in the ratio in which the cortex nerve fibres are destroyed, the law of equi-potentiality asserts that every point of cortex has equal potential. The potentiality of cortex destroys in the ratio the potentisality destroys.
These two laws, thus, may lead us to conclude that localization of brain functions is not possible. However, further studies and extengive research in this area have given enough evidence to prove that in human beings, while simple reflex actions are localized in sub-cortical parts of the central nervous system, all other acts of simple or higher mental functioning are carried out by the different areas of the cerebral cortex. Let us describe the localization in brief:
1. Motor Area: Motor areas of the cerebral cortex lie in the form of narrow strips just in front of the Central fissure (a large fold that extends from the top of the head to the ears). These areas belonging to each hemisphere control the movements of the body of its opposite side by telling the muscles and glands what to do. While movements of the toes, feet and legs are controlled by the centres lying at the top of this motor region the movement of the mouth and tongue are controlled by the centres located in the lower region. Movement of these parts of the body get paralysed when due to one or the other reasons. the associated motor area suffer extirpation or destruction.
2. Bodily Sensory Area: The parietal lobes of the brain are connected with body sensations such as temperature, pain and the feel of objects. The functioning of the centres located in this area is similar to that of the motor areas i.e., the centres Jocated in the upper region controls the sensations of the lower parts of the body and the centres located in the lower region control the sensations of the upper parts of the bodv.
3. Visual Area: The visual centres responsible for vision are located in the occipital lobes at the very back of each hemisphere. These centres help the individual in the matter of discriminating and identifying shape, size, distance and colour of the environmental objects. Destruction of this area in an individual may cause complete blindness in him.
4. Auditory Areas: Auditory centres are located at the side of each hemisphere in the temporal lobes. They are responsible for providing various auditory experiences in terms of identification and discrimination of various sounds stimuli present in the environment. Their loss by destruction or operation may cause ‘Cortical deafness’, state of partial deafness.
5. Speech Area: This area, responsible for the controlling and conduct of speech lies a bit below the motor area in the frontal Jobe. The destruction or damage of this area may cause speech hindrance.
6. Association Area: The largest of the association areas is located in the frontal lobe of the brain, just under the forehead, Rather than directly influencing sensory or motor responses (which is almost the function of other sensory or motor areas) they are chiefly concerned with higher cognitive functions like thinking and problemsolving. A man’s ability to order his bebaviour and direct it towards a goal depends especially on these areas.
Spinal cord
It is that part of the central nervous system which lies within the backbone. It is a rope-like structure made up of bundles of long, nearly round nerve fibres. The inside of the spinal cord has a grayish colour; while outside the coverings of myelin sheaths gives it a whitish appearance. Spinal cord’s function is two-fold. In the first place, it works a channel of communication from and to the brain. Secondly it works as an organ for effective reflex action. Let us see how it helps in performing reflex or automatic reactions.
The action like closing of the eyelid when something threatens the eye and the withdrawal of the hand when something hot or cold touches it are known as reflex actions. Such reflex acts are almost automatic in nature. They are controlled by our spinal cord. Normally the messages (sense impressions or impulses caught through the sensory nerves) are conveyed to the brain by the spinal cord and it is the brain that takes the decision. But there are times, when an immediate action is needed. Then the spinal cord gets the emergency Signal and instead of receiving orders from the brain, itself directs the motor nerves to run the muscles for necessary movement. In this way, the spinal cord helps in exercising reflex movements.
In the preceding article, we have discussed the brain and the spinal cord under two separate heads as two distinct structures. But in the real sense, there is no definite point of division between them. The spinal cord, at its upper end gets enlarged as to merge with the lower part of the brain. The point or portion of the nervous system which functions as a joint or connecting line between the spinal cord and brain is known as brainstem. Inits actual functioning it serves like a stalk that supports the whole structure of the brain.
B. THE PERIPHERAL NERVOUS SYSTEM
Thenerve tissues lying outside the bony case of the central nervous system come in the region of the pheripheral nervous system. It consists of a net-work of nerves which helps in passing the sense impressions to the Central nervous system as well as in conveying the orders of the central nervous system to the muscles. Because of these two functions, the pheripheral nervous system is sub-divided into two parts—the Somatic system and the autonomic system.
The Somatic system is both sensory and motor. In this system, sensory and motor nerves, both are found running to and from the sense receptors, muscles and the surface of the body. The autonomic system, on the other hand, is only a motor system. It consists of a number of motor nerves leading from the central nervous system for serving the blood vessels, heart glands and other internal organs of the body and regulating processes such as respiration, digestion, gland functioning and emotion.
The autonomic nervous system consists of two divisions~ the sympathetic system and the para-sympathetic system.
The sympathetic system is connected to the spinal cord on either side and carries messages to the muscles and glands particularly in stress situations to prepare for an emergency, to get ready to act quickly and strenuously. In such situations it is the sympathetic system that causes adrenal glands to start producing hormones. As a result, our blood pressure and heart rate is suddenly increased, pupils are enlarged, digestion is stopped and several bodily changes are marked.
The para-sympathetic system is connected to the brain and the lower portion of the spinal cord. It tends to be active when we are calm and relaxed. The messages conveyed by the nerve fibres of this system direct the organs to do just the opposite of what the sympathetic system had asked. In other words it directs the body organs to return to anormal state after an emergency has passed. As a result, our breathing slows down, heart goes back to beating at its normal rate, the stomach muscles relax, digestion begins again, the pupils of the eyes constrict and the blood pressure is lowered. In this way para-sympathetic system does many things, that taken together build up and conserve the body’s store of energy. In spite of their opposite nature, sympathetic and para-sympathetic divisions of the autonomic nervous system work in close co-operation for maintaining the equilibrium of the body functioning.
The influence of the nervous system on human behaviour
The nervous system, which has reached its highest point of evolutionary development in human beings plays a significant and dominant role in coordinating the activities of every structure in the body. Every bit of our behaviour, to a great extent, is controlled by Our nervous system. How we will behave in a particular situation depends upon the judgement of our brain (or our spinal cord in the Case of reflex behaviour). The sense impressions, which we receive
through our sense organs, do not bear any significance unless, they are given meaning by our nervous system. Therefore, our observations and percepticns are, by all means, controlled by the nervous system.
Our learning also, to a great extent, is controlled by the nervous system. How intelligently we react or make use of our mental powers are again decided by our nervous system, particularly the brain apparatus. The proper growth and development of nerve tissues and nervous system as a whole helps in the task of proper intellectual development. Any defect in the spinal cord or brain apparatus seriously affects the intellectual growth.
Similarly, physical as well as emotional development is: also influenced by our nervous system. Our autonomic nervous system plays a leading role in this direction. It controls the activities of involuntary processes like circulation of blood, digestion, respiration and action of the glands. The equilibrium of the body functioning is almost maintained by the sympathetic and para-sympathetic divisions of our autonomic nervous system. During emotional behaviour, specially atthe time of anger, fear and other emotional outburst nerve tissucs also cause the change in the secretion of hormones by some glands and consequently influence the emotional behaviour of an individual. Moreover, the nervous system acts as a coordinating agency for many operations inside the body and harmonizes the activities and functions of the body parts—internal as well as external.
In a nutshell, an intricate net-work of nerve cells and an elaborate brair work together coordinate the functioning of all our body systems and control all the cognitive. conative and affective aspects of our behaviour. The process of growth and development is also directly and indirectly controlled by the functioning of the nervous system and in this way, the personality of an individual is greatly influenced as well as structured through mechanisms of the nervous system.
The endocrine system
Besides the nervous system, the human body also possesses a second major coordinating and controlling system for regulating its internal mechanisms in the name of Endocrine System. This system works quite automatically by means of some specific body structures called endocrine glands. These glands are quite different from the duct glands like salivary glands which pour their secretion through ducts (litle tubes) to the body surface directly. On the other hand, the endocrine glands do not need ducts to pour the secretion. Their secretions, known aS hormones, are poured straight into the blood stream, which in turn Carries them to the body tissues. It explains the reason of naming the endocrine glands as ductless glands.
The endocrine glands lie in different areas of the body as may be seen from the figure shown.
Let us now try to understand the mechanism of these glands:
1. The Pineal Gland: This gland is situated within the brain. Whereas in lower animals, it is supposed to serve as a warning device, in the case of human beings it regulates the timing of biological functions like walking and sleeping, reproductive activities, the appearance of secondary sex characteristics and the female’s mensus cycles, etc.
2. The Pituitary Gland: The pituitary gland is situated at the base of the brain and is connected toa brain centre called the hypothalamus. It is also nimed as master gland because it produces
the largest number of different hormones, at least six in number. and affects the functioning of all other glands. This gland has a two part structure: the anterior lobe and the posterior lobe.
The anterior lobe is situated towards the front of the gland. It is controlled by the chemical messages from the blood stream. It affects the functioning of the body through the secretion of different hormones as below:
(i) It secretes thyrotropin, a thyroid stimulating hormone that controls metabolic rate or the ability of the body to adjust to temperature changes.
(ii) It produces Somatotrophic hormones which exercises great influence on the growth of bones. The under production of this hormone causes incomplete development and we have a dwarf, whereas the over production results in gigantic growth and we have a giant.
(iii) It also produces adrenocorticotrophic hormone which helps in supplementing the activities of other glands like adrenal and sex glands.
The posterior lobe situated towards the back of the gland is controlled by the nervous system. One of its hormones, Vesorressin regulates the body’s blood pressure and the amount of water in the body's cells. Oxytocin, another posterior pituitary hormone helps the uterus to contract during child-birth and also causes the mammary glands to start producing milk.
3. The Thyroid Gland: The thyroid gland is located at the base of the neck just below the larynx or voice box (in front of the wind pipe). It produces one primary hormone-thyroxin; the main constituent of which is iodine. Thyroxin plays a leading role in controlling the process of oxidation of food. It regulates the body's oxygen consumption and the rate of metabolism. The deficiency of thyroxin Causes under-activity of the thyroid gland which not only retards the growth of the body but also causes mental retardation and disorders. Over secretion of this hormone is equally harmful as it can produce hypothyroidism, a condition characterized by nervousness, high blood pressure, and fatigue.
4. The Parathyroid glands : These glands look like tiny pea-shaped organs and are located in the back surface of the thyroid and are, generally, four in number. They secrete a hormone known as patathormone which controls the level of calcium and phosphate in the blood and tissues and thus helps in counterbalancing the exciting activities of thyroxin, the thyroid hormone. The parathyroid glands remove the toxic products from the body and restore the nervous system to relative calm. Their under activity may result in muscle spasms and excitability whereas over activity can lead to muscle weakness, fatigue, lethargy and poor physical coordination.
5. The Thymus Gland : Thymus gland is located within the chest. It secretes some important hormones which help us to regulate the
lymphoid system and to develop the immune reactions of the body for fighting against diseases.
6. The Adrenal Glands : These glands, two in number, surround two kidneys separately. Each gland has two parts, an inner core called the adrenal medulla and an outer covering called the adrenal cortex.
The adrenal medulla secretes adrenalin and noradrenalin hormones that assist the body in its reaction to emergency situations especially at the time of intense fear and anger.
The adrenal cortex is known to secrete at least twenty hormones, some of which help the pituitary gland to control metabolism particularly in stress situations. Adrenal cortex along with the Gonads (the sex glands) produces androgen, a male hormone, present in both sexes. The over secretion of the hormone androgen may result in increased masculine characteristics which in the case of women may produce extremely masculine characteristics like the growth of beard and moustache.
A few other hormones of the adrenal cortex also cast great influence in terms of secondary sex characteristics and sex functioning. Their over secretion makes an individual highly active and energetic. It may also cause sexual maturity at an early age. A little girl or boy may acquire secondary sex characteristics of a mature man or woman.
7. The Pancreas: The pancreas gland is situated between the stomach and the small intestine. It secretes two hormones insulin and glucogon which work against each other to maintain a_ balanced level of sugar in our blood. In case the balance is disturbed by the over secretion or under secretion of these two hormones, it leads to the excess or deficiency of sugar in the blood. While excess of sugar causes diabetes, a disease of the pancreas, the deficiency of sugar results in hypoglycemia a condition of chronic fatigue.
8. The Gonads : The gonads are the sex glands which are different in different sexes called testes in males and ovaries in females. These sex glands work with the adrenal glands to control sexuzl development as well as sex-role behaviour. In the male the primary sex hormones produced by the testes are known as androgens. The androgens are responsible for the development of the males secondary sex characteristics like growth of beard and moustache, maturity of genitals end change in terms of distinguished male voice. In the female the primary sex hormones produced by the ovaries are known as estrogens. They are responsible for the development of female secondary sex characteristics like development of breasts, maturity of the genitals and the reproductive apparatus. In addition to this estrogens also affect the sex drive and help in pregnancy. child-birth and oursing the new-born infant.
In addition to their respective primary sex hormones—androgens and estrogens; the male and female sex glands are found to secrete some amount of estrogens and androgens. In other words both men and women produce both male and female sex hormones. This is why every male has some female in him and every female has some male in her. However, an excess amount of estrogens in the males may result in their feminization. Similarly, an excess amount of androgens in the females can develop masculine tendencies and aggressive and dominant sex role behaviour in the females. The question now may arise as to what makes aman masculine ? Is it the relative absence of female hormones? The answer lies in the relative higher level of the male hormone, testosterone in the males. It ts that hormone which counteracts the effects of his female hormones and makes him more masculine.
The functioning of all the endocrine or ductless glands, discussed above, exercise a great influence on various aspects of the growth and development of human personality. The under activity or Over activity of these glands caused by the deficiency or excess of the hormones secreted by them affects not only the growth and development of an individual but also his entire behaviour. A slight imbalance of the hormones may cause unusual restlessness, anxiety and weakness. Our physical strength. moral, thinking and reasoning powers and decision-making ability all depend upon the health of the glands. “These hormones” as Gardner Murphy puts, ‘may be regarded as bathing the nervous system, including the brain, and all the organs of the body in their own appropriate chemical juices.”’ (1968 p. 52)
in this way. endocrine system besides performing its own functions through the secretion of hormones by the different glands, may also be found to work in close cooperation with the nervous system for the development of the typical personality characteristics in an individual. In short. the biological make-up of an individual (which is determined. to a great extent, by the functioning of his nervous system and endocrine glands) is responsible for all his characteristics and ‘why’ as well as ‘how’ of his entire behaviour.
SUMMARY
Behaviour in all its forms and shapes have definitely a biological. or physiological base. There are two important and distinct body mechanisms namely the nervous system and the endocrine system that bear strong influence over human behaviour.
The human nervous system can be divided into two parts—(i) the central nervous system comprising the brain and the spinal cord and (ii) the pertpheral nervous system.
The brain has three main divisions—(a) the forebrain consisting of thalamus, hypothalamus and the cerebrum, (b) the midbrain, a sort of bridge connecting the forebrain and hindbrain and (c) the hindbrain composed of the medulla, pons and the cerebellum. Our brain as a whole with all its different structures, helps, in performing a number of mental functions. However, certain specific mental functions are performed specifically by some or other parts of the brain. This characteristic is named as localization of the brain functions.
Spinal Cord lies within the backbone. It has two functions—(i) works as a channel of communication from the brain and to the brain and (ii) works as an organ for controlling and performing reflex acts.
The peripheral nervous system consisting of a network of nerves, lying outside the bony case of central nervous system, is sub-divided Into two parts—the somatic system and the autonomic system.
In the somatic system sensory and motor nerves both are found running to and from the sense receptors muscles and the surface of the body. The autonomic nervous system (with its two divisions, the sympathetic system and the para-sympathetic system) consists of only motor nerves leading from the central nervous system to regulate the body's internal processes.
The Endocrine system works quite automatically as a coordinating and controlling agency of the body’s internal mechanisms by means of some specific body structures called endocrine or ductless glands. These glands are known to secrete specific chemical substances named as hormones. The under activity or over activity of these glands, caused by the deficiency or excess of the hormones secreted, affects the entire personality make-up of an individual. The location and functioning of these glands may be summarized as under:
Gland Location Hormones Main funtion
Peneal Within brain Serotonin and Melatonin To regulate the timing of biological function
Pituitary (master gland) Base of the brain Six types of hormones like tocin, vasopressin, etc. Affects the functioning of all other glands
Thyroid Base of the neck in front of the wind pipe Thyroxin Controls buddies oxidatation process
Parathyroid (for a number) Back surface of the thyroid Parathormone Counterbalance says activity of the thyroid
Thymus Within the chest Disease defending hormones Regulates lymphoid systems
Adrenal ( two in number) Surrounds kidneys Adrenaline and adrenocortical Meet emergency situations and regulate specific sex roles
Pancreas Between the stomach and small intestine Insulin and glucagon Balance sugar level in the blood
Gonads Testes in male and ovaries in females Androgens and Estrogens (sex hormones) Controls sex behavior
References and Suggested Readings
Berman. L; The Glands Regulating Personality, New York: The MacMillian Co.
Boring, E.C., Longfield, H.S. & Weld. H.P. (Ed,); Foundations of Psychology, New York: John Wiley & Sons, 1948.
Carlson, B.R; Physiology of Behaviour, Boston: Allyn and Bacon, 1977.
Desiderato, Otello, er al; Investigating BehaviourPrinciples of Psychology, New York: Harper & Row, 1976.
Deutsch, J.A. & Deutsch, D; Psysiological Psychology, Homewood, Illinois: Dorsey Press, 1973.
Gardner, E; Fundamentals of Neurology (6th Ed.), Philadelphia: Saunders, 1975.
Jennings, A o The Biological Basis of Human Nature, London; Faber and Faber Lid., 1930.
Kimble, D.P.; Psychology as a Biological Science (2nd ed.) Santa Monica Calif: - Goodyear, ‘1977.
Levin, M. .J.; Psychology: A Biographical Approach, New York: Mc-Graw Hill, 1978
Lewin, R; The Nervous System, New York: Anchor, 1974.
Lubar, J.F.; Readings on the Biological Foundations of Behaviour, Columbus, Ohio: Collegiate, 1975.
Milner, P.M.; Physiological Psychology, New York: Holt, Rinehart & Winston, 1970.
Murphy, G: An Introduction to Psychology (na Indian reprint), New Delhi: Oxford IBH, 1968.
Schneider, A M. & Tarshis. B; An Introduction to Physiological Psychology, New York: Random House, 1975.
Thompson, R.F.: Introduction to Bio-psychology, San Francisco, Albion, 1973, Wittrock, MC. etal; The Human Brain, Englewood Cliffs, New Jersey; Prentice Hall, 1977.
CHAPTER 5
HEREDITY AND ENVIRONMENT
There are countless species on this earth. Every species is unique in itself and can be easily distinguished through some specific characteristics. We can, thus safely identify a rabbit, peacock, cow, crow, antelope and a tiger. The members of one species detinitely resemble each other but do not bear semblance to other species and possess unique characteristics that are common to their own species.
It is true that all cows appear alike on account of their species —specific characteristics—yet we are able to distinguish our own cow from so Many Other cows and our own brother and sister from a group of children. This is because of the fact that, besides the species. —specific characteristics,—individual members of the species display a family resemblance. A child, resembles his’her brothers. sisters parents, grandparents and other members of his/her family much more than he/she would to others not related to him’her and hence can easily be distinguished from other children.
However, the offspring of one set of parents may not necessarily resemble their brothers or sisters or for that matter even their parents. They may be unlike each other in so many ways. Although each organism has so many similarities on account of the species — specific characteristics and family resemblance—it may differ widely on so many grounds and this is what makes every organism a unique creation in itself.
The question is, what makes an individual a unique creation in itself? Why does or doesn’t he resemble the members of his species, his parent organisms and the organisms produced by his parents? The answers for such similarities and variations pertaining to the individuality of an organism are contained in the terms heredity and environment. Let us try to see what contributions they have made.
What is heredity?
Heredity refers to a biological mechanism as a result of which a child obtains something in terms of specific species or ancestral characteristics by which he can trace his individuality from his ancestral stock through his parents.
Heredity, thus contributes something in the form of inheritance just as we inherit land, money and other assets or liabilities from our
parents and forefathers. Now the question may arise, when does a child inherit the specific ancestral characteristics. Let us try to answer this from the Science of genetics.
The science of genetics is concerned with the way certain characteristics are transmitted through the species and through a family to an individual organism. From a genetic angle this transmission definitely occurs at the time of the conception of the child in the womb of the mothers. Conception of child is in fact a beginning of a new life. The mechanism of conception is explained below.
The male and female reproductive organs produce germ cells. In the male their testes produce the male germ cells, the spermatozoa, while in the female, their ovaries produce the female germ cells, the ova. Normally one ovum or egg is produced in each menstrual cycle (about 28 days) by the ovaries of 4a normal woman. The production of the sperm by the testes in the male is not so confined and limited. Normally, they produce 10 million sperms per day per gram of testicular tissue from the onset of puberty till death.
Conception is the result of the union of these male and female cells and in the natural way this union occuss at the time of copulating between a man and a woman. Here asa result of coitus, the male germ ceils (millions in number) usually come in contact with the female germ cells. The male germ cells are deposited at the mouth of the uterus and try to make contact with the single ovum. Out of so many spermatozoa, in a normal case, only one sperm (single male cell) is able to establisn contact with the ovum (single female cell) situated in the ovarian duct of the mother and makes it fertile. The fertilized ovum is technically known as zygote the starting single cell structure of a new life.
Human life thus starts from a single cell produced by the union of two germ cells, one from each parent and gradually develops into a complicated composition of trillions of body cells and yet containing the same genetic material as was inherited at the time of conception.
The zygote i.e., fertilized ovum consists of a semi-fluid mass called Cytop lasm and within the cytoplasm there is a nucleus which contains the chromosomes. Chromosomes always exist in pairs. In human zygote there ase 23 pairs of chromosomes (46 individual chronosomes)* 23 of which are contributed by the father and 23 by the mother and this is why for the transmission of herditary characteristics both mother and father are said to be equal partners.
Chromosomes possess a thread like structure and are made up of vety small units called genes. It is estimated that there are more than 1000 genes in each human chromosome cell. Consequently the possibility regarding the combination of 30,000 characteristics each from mother and father, may help us to understand well the untqueness of each individual.
The number of chromosomes varies from species to species. For example. dogs have 78 chromosomes, horses 64, cows 60, fruitflies 8. and peas 7.
Regardless of their very minute size, the composition of genes has been determined in terms of “DNA” and “RNA”. DNA stands for deoxyribonucleic acid and is said to be a basic chemical substance primarily responsible for genetic inheritance. RNA stands for ribonucleic acid and it acts as an active assistant to DNA for carrying out the genetic code message from parent to offspring.
Thus, what we get from our ancestral stock through our parents at the time of fertilization of the ovum of the mother by the sperm of the father is in the form of chromosomes, genes and their respective classical constituents. This inheritance at the time of conception makes up the native capita! and endowment of an individual that is present with him in the form of the sum total of the traits potentially present in the fertilized ovum and it is this that is known as the heredity of an individual.
The role of genes
In search of hereditary functions of genes, through his experiments on garden peas and fruitflies, Gregor Mendel hypothesized that some genes are dominant and others recessive. Like chromosomes, the genes also occur in pairs. Each of the pairs is donated by one of the parents. An offspring thus may be found to derive a gene pair in one of the following forms
—a dominant gene from one of the parents and recessive gene from the other.
—dominant genes from both the parents.
—recessive genes from both the parents.
In simple meaning a dominant gene must exhibit his dominance over the recessive ones. For example if one parent furnishes a gene for brown eyes (known to be dominant) and the other providesa gene for blue (a recessive gene), the offspring will have brown eyes (characteristic of the dominant gene).
However the fact that a particular trait is recessive in one generation in no way rules out its appearance in the future. For example in the above example of the mutation between brown and blue genes resulting into brown eyes, a recessive blue gene lies in wait. If that offspring is copulated with someone with another gene for blue eyes (even if he or she may not possess blue eyes) their offspring. the third generation, might have blue eyes.
The role of genes specified as above, may thus provide us a solid support (besides the chance pairing of 23 chromosomes and 3,000 genes from the egg and sperm cells) for explaining the variations and dissimilarities in height, weight. intelligence, blood type, eye colour, and the colour and texture of the skin and hair and similar Other important characteristics found in the parents and their offsprings as well as within the offsprings of the same parents.
Determination of sex (boy or girl)
The first twenty-two pairs of chromosomes are called autosomes. These chromosomes determine the development of most of our body structures and characteristics. The remaining twenty-third nair consists of the sex chromosomes. These sex chromosomes decide the individual’s sex and other sex-linked characteristics.
There are two different types of sex chromosomes X chromosome (usually big in size) and Y chromosome (comparatively smaller than X). In the male child one member of the sex chromosome is X chromosome (contributed by the mother). In the female child both of these sex chromosomes, one from each parent, are X chromosomes.
All eggs have X chromosomes, but sperm cells may contain either type. Therefore, the mother’s role in the determination of sex is quite neutral. At the time of conception she can contribute only one type of sex chromosome i.e. X chromosome. Much depends upon the possibility of the type of sex chromosomes X or Y that may be transmitted by the snerm cell of the father. If X chromosome is transmitted the child will be female and if Y chromosome is transmitted it will result in a male child. In this way, itis not the mother but the father who is biologically more countable for determination of the sex of the child.
X X Mother X Y Father
X
X Y
Daughter X Y
X Y
Son
The twins mechanism
Life is the result of the union of two cells—male and female. In anormal case when a single ovum is fertilized by sperm cell of the male, it results in the birth of a single offspring. However, in some cases, this normal function is disturbed and there are cases of multiple births —the birth of two or more offsprings at a time. The birth of twins falls in such a category of multiple births. There are two distinct types of twins namely identical twins and fraternal twins.
1 Identical Twins : In the process of the fertilization of the ovum by the sperm, the ovum is made to split into two parts. In a normal process these parts are again united. Sometimes, however it so? happens that these two split parts fail to unite together. The result ig that each part is developed into a complete individual in the form of the pair of identical twins. The twins produced, are thus, termed identical on account of the identical nature of the genetic material (exactly the same chromosomes and genes etc.) They are found to possess almost the same somatic structure and characteristics and are definitely of the same sex. From the hereditary angle, they are supposed to be the nearest ones as far as the equal transmission of hereditary stock to the offsprings is concerned.
2. Fraternal Twins: Normally in each menstrual cycle the female Ovaries produce a single ovum that can be fertilized by a sperm cell. In an exceptional case, two ova may be produced simultaneously and be fertilized at the same time by two different sperms. It may then result in the conception of two individuals who may be grown simultaneously in the womb of the mother. These individuals are known as fraternal twins. They havea different combination of chromosomes and genes as both ova are fertilized by different sperms. Fraternal twins, therefore are sure to differ in many traits. From the hereditary point of view, they are not as near as the identical twins are, but definitely nearer than the siblings (real brothers and sisters), cousins and other relatives. Also it is not essential for them to belong to the same sex. They may have similar or opposite sex.
What is environment
‘“‘Environment’’, according to Woodworth (1948, p. 156), ‘‘covers all the outside factors that have acted on the individual since he began life.”
At the time of beginning of one’s life 1.e. fertilization of the ovum by the sperm, what happens to the child, is the transmission of ancestral traits and characteristics through chromosomes, genes and their chemical substances. The heredity, thus plays its game only at the time of conception. It does not contribute any thing after conception and does not come into the picture at all before the fertilization of the ovum. What happens afterwards, after the conception, is the game of environment. It affects the individual, his bodily structure, and all of his personality make-up and behaviour.
Environment forces can be categorised into two major heads
1. Internal environment and
2. External environment.
The environment received by the individual from his conception till his birth jin the womb of the mother (a period of about 9 months in the case of human beings) is called an internal environment. In this environment, the embryo receives the nutrition through the blood stream of his mother. The physical and mental health of the mother including his habits, attitudes and interests etc., all constitute the inner surroundings Or internal environment that affects the growth and development of the individual along with his emerging behaviour in future. After his birth what the child gets in terms of environmental influences is purely external in nature. These influences can be further divided into two parts, physical and social or cultural. The physical surroundings
and the stimuli like the earth, rivers, mountains, the type of weather and climatic conditions, the food we eat, the water we drink etc., fall into the category of physical environment while the parents, members of the family, friends and classmates, neighbours, teachers, the members of the community and society, the means of mass com munication and recreation, religious places, clubs, libraries etc., are included in those forces that provide the individual his social and cultural environment for the shaping of his personality and behaviour.
The role of heredity or environment in the development of personality and behaviour
What part heredity or environment plays in influencing the growth and development of the individual, his behaviour and other personae lity characteristics has been the subject of great controversy and extensive research all through the ages for psychologists. For tendering explanations regarding the individuality and existing variations among the individuals, they quite often resort to the studies as under.
Selective Breeding: In this method of studying inheritance. members of some specific species high or low in a particular trait copulate with other members of the species in the same position and then the genetic character of the so-produced offspring is made the subject of study.
Gregor Mendel (1822-1884) was the first to use the method of selective breeding in the investigation of the inherited traits by crossing different types of peas, a fast growing, sexually reproducing plant.
The method of selective breeding has been very useful to agriculturisis, tree planters, and commercial breeders of live-stock for improving the varieties and yields. In performing such experiments, they usually arrange selective breeding through the copulating of the members of the species that excel in the desired trait such as size. The difference between the average sizes of-the males and females in the parental generation and the average sizes of the males and females of offspring (the selection gain) are noted and then the largest offspring are bred and so on. In these experiments care is taken for maintainang the environmental factors as constant as possible. Therefore any isignificant difference between the traits of the purental generation and their subsequent offspring can be sufely attributed to heredity.
The method of selective breeding for studying inheritance although found quite useful in the case of lower planis and animals. has not been found practicable in the case of human beings. This 16 because, human copulating cannot be used for experimental purposes and one human generation lasts for so many years. However, the naturally available results of (the selective breeding in the form inbred population the tribes or isolated places where marriage and copulating is permitted within the same blood) provide many smpor tant clues for the hereditary transmission of so many traits, With the development in Genetic Science regarding artificial insemination, test tube babies and the possibility of producing a body directly from the body of a human being without sex or fertilization, etc., we may place high hopes for experimental results of the selective breedings in humans.
Twin and Family Studies
For studying the impact of heredity or environment on the development and personality characteristics of individuals, psychologists have also tried to take the help of twin and family studies.
Twins, especially identical twins, are supposed to be identical in hereditary potential. Fraternal twins, siblings, cousins, family members and other blood relations are also supposed to form a group of individuals who show a gradual diminishing resemblance about heredity characteristics but are definitely nearer to the people not related at all. Generally these studies of twins and other types of family relations often use concordance or coefficient of correlation, to ascertain whether a certain characteristic is the result of heredity or environment.
In carrying out studies of twins and family, psychologists have adopted the following approach:
(1) A pair of identical twins have been separated and reared apart in different environmental surroundings. The results of such experiments have sprung in favour of both heredity and environment as significant or non-significant differences have been found to exist in One or the other case.
(2) Identical twins have been compared to fraternal twins, siblings, cousins other relatives and individuals not having any blood relationship to ascertain whether or not the affinity in terms of blood relationship causes affinity in terms of physical and other characteristics.
(3) Families have been studied for generations past from the point of the unique presence or absence of some personality attributes. It has been found that family members and their descendants show a remarkable resemblance. For example, a family known to be rich and of repute may consistently display healthy signs of wealth and intelligence while a family of ill-repute may exhibit a record of the characterless, poor and defamed persons. Similarly many of the abnormalities and diseases have been found to perpetuate from generation to generation and consequently heredity has been made responsible for the subsequent development and behaviour of an individual.
However, from all types of experiments going on to support the role of heredity or environment, it may be easily concluded that the findings of these experiments can be interpreted either way. In the real sense, it is very difficult to” have proper experimentation for studying hereditary or environmental influences as shown as follows:
To study the impact of environment we have to take individuals with the same heredity and then study their differences by keeping them in different environments. Similarly for studying the impact of heredity, environmental factor needs to be made constant.
In actual experimentation it is impossible to get individuals having the same heredity (possessing exactly the same genes). However, if we take the case of identical twins (by assuming they are of similar hereditary stock), we cannot study the impact of environmental influences right from the time of their conception. Hence it ts difficult to make the heredity factor as constant.
On the other hand, it is also impossible to get the environmental factors as constant because it is very difficult to provide exactly the same environment for different individuals. Even a mother cannot show equal amount of love and affection to her own children.
What then is contributed by heredity and what by environment?
It is difficult to find an appropriate answer to the above question due to the following reasons:
(1) After the conception of a child we are unable to pin-point with accuracy whether a particular behaviour or trait emanates from our heredity or from our environment.
(2) With all the available resources at hand and experiments conducted we still cannot say with certainty what type of behaviour or trait is influenced most by heredity and what by environment.
In human beings, hereditary factors are predominantly accountable for the behaviour and characteristics as under:
Reflex and instinctive behaviour, characteristics like blood type, finger prints, eye colour, the colour and texture of the skin and _ hair, defective genes and chromosomal abnormalities, Schizophrenia, tuberculosis, cancer, hemophilia, etc.
Similarly, we can say that the environmental factors are predominantly accountable for the interests, attitudes, aptitudes, habits, temperaments, etiquettes and manners, social and culture norms, etc.
However, for most of the characteristics and traits including our somatic structure, and physical, mental, social and emotional makeup, it is the interaction between the individual’s genetically determined characteristics and its environment which is said to be more res~ ponsible for making the individual-what he is at a particular time. Speaking in a true sense, both heredity and environment are said to be jointly responsible for the acquisition of any type of behaviour and development of any personality characteristics in human beings.
The respective roles of heredity and environment become clear when we compare the individual’s growth and development with that of a tree. Whereas the maximum and minimum growth of a healthy treo is determined by its genes but exactly how tall it will grow within this range can only be determined by the environment soil, water, manure and sunlight it gets.
in a similar way our heredity endowments provide us the native capital to start the Journey of life. How successful we will be 1n life depends both on the potential value of our native capital and the opportunities and circumstances favourable or unfavourable we get from our environment for reaching the maximum out of our starting capital. The future outcome as a result of interaction with one’s environment are thus perfectly hidden m one’s inherited genetic character. Genetic factors, although influenced, directed and even surpassed in some cases by the environmental forces, play quite a substantial role in providing an approximate range for the minimum and maximum height reached in terms of the personality traits but how much height one will achieve along this range again depends upon the cooperation one receives from one’s environment.
Therefore, it is always advisable to take into account the sources like one’s heredity, his environment and the inseparable interaction between one’s heredity and environmental factors for determining the etiology of one’s behaviour or development of some specific personality traits.
SUMMARY
Species—specific characteristics, family resembiance and similarities as well as variations pertaining to the individuality of an orgi.nism can be explained in terms of the contributions of heredity and environment.
Heredity refers to a biological mechanism that is responsible for the transfer of the species—specific and ancestral characteristics from generation to generation with the help of immediate parents at the time of one’s conception in the mother’s womb.
Human hife starts from a single cell produced by the union of two germ cells, one from each parent and gradually develops into a complicated composition of trillions of body cells. Within each cell there are 46 chromosomes, arranged in 23 pairs, except for the reproductive cells which have only 23: chromosomes, in each. A human being receives 23 chromosomes from each parent. Within each chromosome are about 1000 genes. These genes contain two chemical substances, named DNA and RNA which are said to be responsible for carrying out the genetic code message from parent to offspring.
Transference of the traits was first scientifically studied by Gregor Mendel, an Austrian Monk, through his experiments on garden peas. His works Jed to the knowledge of dominant and recesSive genes in explaining the hereditary transmission of traits and the related facts about mutation inheritance.
Sex is determined by the X and Y sex chromosomes. All female eggs have only one type of sex chromosomes (i.e. X) but sperm cells of the male may contain both types X and Y. At the time of conception, therefore, the mother can contribute the same X chromosome
while the father can contribute either X or Y. Ifhe is transmitting X chromosome, then it results in a girl or if he transmits Y chromosomes, a boy is produced.
Environment consists of all those factors that influencé the growth and development of the individual from his conception onwards, These factors can be categorized as internal factors (operative in the womb of the mother from conception till birth) and external factors in the form of physical, social and cultural environment that surrounds the individual from his birth till death.
The role of heredity and environment in the development of personality and behaviour have been extensively searched in the form of twins and family studies (comparisons of genetically similar individuals) and experiments on selective breeding (copulating of males with particular traits to females with the same traits, in order to study the offspring).
The results of all such studies and experiments have failed to establish a clear cut role of either heredity or environment in explaining the presence of particular behaviour or trait in an individual. What behaviours are learned or what are inherited is a controversial question that can only be answered through a reasonable understanding that one’s behaviour or development of a specific personality trait is always a result of the interaction of the environmental forces on the genetically inherited characteristics.
References and Suggested Readings
Craig, G.J., Human Development, Englewood Cliffs, New Jersey: Prentice-Hail, 1976. Gordon, I.J., Human Development, Glenview, Ilinois: Scott & Co. 1965. Halacy, D.S. Jr., Genetic Revolution, New York: New American Library, 1974. Kallman, F.J., Heredity in Health and Mental Disorder, New York: Norton, 1953.
Kaplan, A.R., (Ed ); Human Behaviour Genetics, Springfield Hlinois: Thomas, 1976.
McClearn, G.E. & De Fries, J.C., Introduction to Behavioural Genetics, Sa® Francisco: W.H. Freeman & Co; 1973.
McGraw, M.B., Growth, New York: Appleton-Century, 1935,
Money. 3. & Ehshadt, A.. Man and Woman, Boy and Girl, Waltimore: Jobs Hopkins University Press, 1972.
Newman, H.H., Freeman, F.N. and Holzinger, K J., Twins: A study of HevedityY and Environment, Chicago University Press, 1937.
Stern c., Principles of Human Genetics, San Francisco: W.H. Freeman & Co. 197
Stockard, C.R., The Physical Basis of Personality, London: George Alicea & Unwin, 1931.
Woodworth, R.S. and Marquis, D.G., Psychology, (Sth Ed.) New York: Henry Holt & Co., 1948,
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CHAPTER 6
INSTINCTS AND EMOTIONS
What causes the organisms to behave in a specific way in a Specific situation. has been a subject of serious study for psychologists, From this point of view, the role of heredity and environment has also been fully explored. It has been found that there are certain specific innate and inborn modes of behaviour that may be exhibited by the organisms without any prior training or experience. Baby chicks, for example. do not have to learn to peck at seeds. A mother sparrow instinctively builds a nest, lays eggs, searches for food, and ceturns to the nest to feed her voung, the horses and buffaloes begin to swim just a few days after their birth, an infant cries for milk and sucks the nipple of the mother, an adulescent is attracted towards the members of the opposite sex usually without learning or experiencing such acts from his parents or environment. In psychology, behaviour of this type has been named as instinctive behaviour and the innate or inherited tendencies or the capacity and predisposition responsible for such behaviour patterns are known as instincts.
Understanding and defining instincts -
From time immemorial, the term instinct has been used for an innate disposition or characteristic that makes an organism to respond or to act in such a way that helps him in his adjustment:or adaptation including the survival of his species. Consequently instinctive behaviour has been understood as an unlearned species-specific behaviour patterns.
During the nineteenth century when Charles Darwin presented his theory that humans are linked to other species, it was also concluded that like their relatives, the behaviour of human beings is motivated by instincts. Inspired by the views of Charles Darwin in 1890, William James. a Harvard psychologist tried to provide a long list of the human instincts and defined the term instinct in the following Way:
‘Instinct is usually defined as the faculty of acting in such a way as to produce certain ends, without foresight of the ends, and without previous education in the performance.” (James, 1969, p. 392)
In 1906, the great American Socio-psychologist, William Mc Dougall noted that all behaviour is the result of instincts. He added five more instincts to the list of William James making the total as 14. He tried to define the term instinct as “an inherited or innate psycho-physical disposition which determines its possessor to perceive, and to pay aitention to objects of a certain class, to experience an emotional excitement of a particular quality upon perceiving such an object and to act in regard to it in a particular manner or at least, lo experience an impulse to such action” (McDougall, 1946, p. 25).
The definitions given by William James and McDougall may lead us to conclude that:
(i) Instincts are innate and inborn tendencies or psychological dispositions.
(ii) They do not require any sort of previous experience or training for their expression.
(iii) A particular instinct as an inborn tendency makes the organism:
(a) to notice or to perceive and to pay attention to certain specific kinds of things; (b) to arouse some feeling of excitement and specific interest after taking notice or perceiving such things; and (c) to act or have an impulse to action which finds expression in a specific mode of behaviour in relation to that specific thing.
From the above we may deduce that an instinct is found to possess three aspects—cognitive (perceiving or knowing), affective (feeling) and conative (doing or acting).
(i) Every instinct leads toward certain ends as it serves some specific purpose or purposes. For example, instinct of escape helps to escape danger, fight or combat to get rid of the enemies, instinct of sex to preserve the species and so on. In this way instinctive behaviour safeguards and ensures the welfare of the organism.
(ii) Although the instinctive behaviour, as pointed above leads to
an useful end, yet, it does not necessarily involve any foresight of that useful end. |
In the coming times, Sigmund Freud and his followers like Adler and Jung hypothesized that the instincts are the ultimate causes of all activities. They brought in the field some new instincts like Eros (the life instinct), the thanatos (the death instinct), the will to power, selfactualization and herd instinct.
With the adoption of the instinctive theory for explaining bdehaviour by more and more psychologists, the number of instincts gradually grew to more than thousands. It led to a great confusion in terms of the meaning and types of the instincts and with the advent of behaviourism in 1920, there emerged an anti-instinct revolt.
Opposition to the concept of instinct was based on two points. First, patterns of instinctive behaviour must be common to members
of species. Second, the behaviour must be complex and include activity of the entire organism, not just a single reflex behaviour like an eye blink or knee jerk.
In recent times there have been quite a lot of research for finding out the facts about the instinctive behaviour patterns of human beings. It has been found that contrary to the behaviour of lower organisms. it is very difficult to distinguish between learned behaviour patterns and instinctive ones in humans. There are no behaviours common to every member of the human species. Human infants cannot walk. feed themselves and perform other basic functions relatively independent of any prior learning or training. Sex behaviour, involves a natural urge in terms of attraction for the opposite sex and sex appetite is described as a quite complex behaviour pattern requiring a set of specific skills and learning experiences. In this way. human behaviour cannot be adjudged as purely instinctive or purely learned behaviour. Obviously, it is the result of the interaction between one’s individual environment and his biological structure and dispositions. The instincts alongwith the mechanism of instinctive behaviour may thus provide an essential capacity and predispositions (in terms of a specific level of maturity) to acquire specific behaviour patterns as a result of some adequate training and experiences.
Instincts and reflex actions
What are reflex actions? The action like the closing of the eyelid when something threatens the eye; the contraction of the pupils when there is bright light; the jerking of the hand when it touches something very hot or very cold etc., are known as reflex actions. Such reflex acts are almost automatic and mechanical in nature. They are innate or inborn as they can be carried out by the organism without any prior training or experience. As emphasized earlier in this article the four of this text while dealing with physiological basis of our behaviour, these reflex actions are directly operated by our spinal cord without bringing our brain into the picture. A sa result they always bring a prompt and immediate fixed response to a specific stimulus.
Similarities and differences with instinctive behaviour
The resemblance between instinct and reflex actions can be summarized as under: ,
(i) Both are innate and inborn,
(ii) Both involve fixed type of behaviour in a specified situation,
(iii) They are not individual traits but racial characteristics applicable to all living organisms.
(iv) Both are directed to the attainment of useful ends and safeguard as well as ensure the welfare of the organism.
On account of the above similarities, they are often confused with ach other. However, the following points of difference may help in drawing a line of demarcation between them.
Instinctive acts Reflex actions
1. An instinctive behavior involves all the cognitive, affective and canative aspect of the behavior 1. In a reflex action only conative aspect of the behavior is involved
2. An instinctive act to comparison with reflex act is very complex mode of reaction of a organism to stimulus receive from the environment 2. Reflex at represent quite simple automatic response of an organism
3. Instinctive acts are guided by the brain 3. Reflex action are directly operated by the spinal cord without consulting the brain
4. Instinctive behavior it's not so prompt and immediate ask reflex acts they may be prolonged 4. Reflex act s are most prompt and immediate they are not prolonged
5. Instinctive behavior can be improved or modified by experience and training 5. The reflex act s like sneezing blinking of eyes and so on remain the same.
Classification of instincts
Instincts have been classified in a variety of ways by different psychologists The list supplied by McDougall in terms of the 14 instincts still holds its ground. McDougall also insisted that an instinctive behaviour is associated with some emotional experience. Below, we reproduce this list alongwith the inherent meaning and the emotion accompanied with each of these instincts.
Instinct Meaning Emotions accompanying
1. Instinct of flight or escape Innate tendency to run away from danger or possibility of danger to a place of shelter and safety Emotional fear
2. Instinct of combat pugnacity Innate tendency to fight and struggle in order to secure what is an organism wants or to secure progress or success in any direction Emotions of anger
3. Instinct of repulsion Innate response to a distasteful we're a nasty object by going away from it or removing it from the field of one sensation on perception Motions of disgust
4. Instinct of curiosity Innate urge to know about new things and phenomena Emotions of Wonder
5. Parental instinct Innate urge in the organism to protect their young offspring to love them or to supply them with food Motions of love and caring
6. Instinct of appeal Innate urge and organism to protect itself but raising its voice for help from its fellow beings. Emotional of distress
7. Instinct of construction Innate urge we're natural tendency to construct something Emotions are creativity
8. And think of acquisition Innate urge to collect or hoard articles of once owned interest needs Emotions of ownership
9. Instinct of gregariousness Innate urge the compels human being to live in groups for society or club s and enjoy family and social life Emotions of loneliness
10 instinct of sex or copulating Innate urge to have a sex relationship with suitable partner. Emotion of lust
11. Instinct of self assertion Innate egoistic tendency and individual to show in one way or the other that he is better than others Emotion of elation or positive self feeling
12. Instinct of abasement or submission Innate urge compelling an individual to remain submissive and to follow others Emotion of feeling
13. Instinct of food seeking Innate urge compelling and organism to make attempt for getting food and to devour it Emotions of appetite
14. Instinct of laughter Innate urge found any human beings for maintaining their health and vigour by counteracting the evil influence of anger and similar other negative emotion Emotions of amusement
EMOTIONS
Defining Emotion
Etymologically the word emotion is derived from the Latin word ‘emovere’ which means ‘to stir up’, ‘to agitate’ or ‘to exite’ Accordingly, Woodworth clarifies that emotion is a ‘moved’ or stirred-up’ state of an organism. It is a stirred up state of feeling that is the way it appears to the indiv:dual himself. [t is a disturbed muscular and glandular activity that is the way it appears to an external observer (1945, p. 410).
Crow and Crow conveys that an emotion “‘is an affective experience that accompanies generalized inner adjustment and mental and physiological stirred-up states in the individual, and that shows itself in his overt behaviour.” (1973 p. 83).
McDougall (1949) considering instinct as an innate tendency maintains that an emotion is an affective experience that one undergoes during an instinctive excitement. For example when a child perceives a bull coming towards him (cognition) he experiences an
affective experience in the form-of the arousal of accompanied emotion of fear and consequently tries to run away (Conative aspect of one’s behaviour). McDougall discovered 14 basic instincts and concluded that each and every emotion, whatever it may be is, the product of some instinctive behaviour. The type of emotion experienced by the individual through a particular instinctive behaviour can be understood through provided earlier in this article
Taking an eclectic view of the nature of emotional experience Charles G. Morris defines emotion as ‘‘a complex affective experience that involves diffuse pkysiological changes and can be expressed overtly in characteristics behaviour patterns.” (1979 p. 386).
Thus, whatever, may be the terminology used by all these different writers and psychologists, their definitions tend to describe emotions as some sort of fezlings or affective experiences which are characterized by some physiological changes that generally lead them to perform some or the other types of behavioural acts.
Characteristics of emotions
Emotions have certain characteristics which can be described as under:
1. Emotions are universal — prevalent in every living organism at all stages of development from infancy to old age.
2. Emotions are personal and thus differ from individual to individual.
3. Same emotions can be aroused by a number of different stimuli —objects and situations.
4. Emotions rise abruptly but subside slowly. An emotion once aroused, tends to persist and leave behind emotional hang over.
5. Emotions have the quality of displacement. For example an angry reaction caused by a rebuke by the boss can find expression in the beating of the children at home.
6. An emotion can give birth to a number of other similar emotions.
7. There is a negative correlation between the upsurge of emotions and intelligence. Reasoning and sharp intellect restrain the sudden upsurge of emotions. On the other hand, emotional upsurge adversely affects the process of reasoning and thinking powers.
8. The emotional experiences are associated with one or the other instincts or biological drives.
9. The core of an emotion is feeling, which is aroused on account of the cognition of a perceived stimulus, giving birth to a sort of impulsive act or urge to do.
10. Every emotional experience involves many physical and physiological changes in the organism. Some of the changes which express themselves in overt behaviour are easily observable. Examples of such changes are the bulge of the eyes, the flush of the face, the flow of tears, the pulse rate, the beating of the heart, the choke in the voice,
increased perspiration, the butterflies in the stomach, the goose flesh sensations as the body’s. hair stand on end, the fleeing from the situation or the attack on the emotion arousing stimulus. In addition to these easily observable changes there are internal physiological changes. Examples of such changes are changes in Circulation of blood, the impact on digestive system and the changes in the functioning of some glands like adrenal glands etc.
Kinds of emotions
Emotions in general, can be categorized as positive emotions and negative emotions.
Unpleasant emotions like fear, anger, jealousy which are harmful to the well-being and development of an individual are termed as negative emotions while the pleasant emotions like amusement, love, curiosity, joy and happiness which are helpful and essential to the normal development are termed as positive emotions.
However, by their nature of positiveness or negativeness it should not be concluded that experiencing of positive emotions is always good and that of negative emotions is always bad. While weighing this impact we should also keep in mind the other factors like (i) the frequency and intensity of emotional experience and (i/) the situation. occasion and the nature of the stimulus which arouses the emotion. Excess of everything is bad. Emotions with too much intensity and frequency. whether positive or negative bring harmful effects. On the other hand the so called negative emotions may prove very essential for human welfare. For example, the emotion of fear prepares an individual to face the danger ahead. The child who has no emotion of fear is sure to get injured because he has not learnt to save himself against a possible danger.
The identification and measurement of emotions
There are a number of positive and negative emotions that may be exhibited by individuals from time to time. What type of specific emotion, at a particular moment is being exhibited by an individual and the nature or intensity of that emotion has been a subject of extensive research. Since the effects of emotion on behaviour can be measured, but emotion itself is not easy to analyse objectively, the proper identification and measurement of emotions has proved a tough and challenging task. However, some significant clues in this direction may be provided by the use of the following methods.
1. Introspective Reports: It is possible to identify and even quantify emotions according to an individual’s own introspective reports. He may be able to label the changes—internal or externalhe undergoes as joy, fear, sorrow, etc., and also describe what he was feeling. thinking or doing at the time of experiencing one or the other emotion. In search of some better device for the self-description of emotions, Wilhelm Wundt (1832-1920) developed a tri-dimensional model of introspective approach. He argued that emotions may vary along the three dimensions: pleasantness-unpleasantness, excitementdepression, and strain-relaxation and any given feeling could be located through introspection somewhere within the space defined by these three dimensions. However, this approach also suffered from serious problems as other psychologists did not agree on the dimensions defining feelings and criticised it on the basis of its dependence On introspection i.e., a highly unreliable and subjective approach. However whatever may be the validity of this approach, it carries a unique advantage. Since emotion is regarded as a highly subjective experience i.e.., emotional responses are often based on internal processes that can't be objectively studied, the self-reporting introspective reports can play a major role in the identification and measurement of emotions.
2. Observations of Facial Expressions: The non-verbal communication in the form of looks, gestures and bodily positions may provide a meaningful clue for identifying various emotional states. Face, to some extent, is Said to be the index of human behaviour and facial expressions in the real sense may provide readily observable identification signs of various.emotions. By looking at one’s facial expression, we can judge one’s intended emotion and level it as anger, laughter, fear, disgust, contempt, love, happiness or surprise. The basis for the correlation between facial expressions and emotions may be discovered both in one’s innate dispositions and socio-cultural environment. Where the way of expressing emotions may vary from culture to culture, 1t may also represent innate responses to particular situations like jumping at the time of hearing a sudden noise and baring teeth at the time of anger.
Behavioural expressions in the form of facial expressions and non-verbal communications, however, cannot be understood as sufficiently objective, reliable and valid instrument for the identification and measurement of one’s emotions. One can easily hide his feelings in the garb of an apparent mask of false facial expressions and other non-verbal communications and thus may make the task of identification quite difficult and most unreliable.
Measurement in terms of physiological change
Emotions, as we have already emphasized, are always accompanied with many physical and physiological changes in an organism. Some of these changes expressed in overt behaviour are easily observable while the others in terms of internal physiological changes require some special devices for their proper measurement. With the advancement of the knowledge and research in this area to day we have sophisticated instruments which can measure these physiological changes in terms of blood pressure, blood volume, respiration, pulse rate, muscle tension, skin temperature and sensitivity, brain waves as well as the pilometer reaction involving erection of body hair often associated with chilling of the skin.
Besides the common instruments available with the medical personnel, some more specialized instruments like galvanic skin reflex instrument, electroencephalograph (EEG) and syphygmomanometer and polygraph (lie detector) have been devised to detect and measure these physiological changes. Galvanic skin reflex instruments measure tbe skin's level of electrical conductivity (as it has been found that intense emotion can lead to sweating and increased conductivity), the EEG can record safely the electrical activity in the brain and with the help of Syphygmomanometer changes in blood pressure can be properly recorded.
The function of the machine called polygraph (lie detector) is to record autonomic nervous system changes brought on by emotion provoking stimuli. It is equipped with pens that automatically register Changes in respiration, blood pressure, heart rate and skin temperature On rolling graph paper. An individual is tested through this machine for ascertaining his telliog the truth or a lie on the assumption that even the thought of taking such a test can initiate marked physiological changes and thus yield responses that sharply differ from an individual's normal responses. To begin with, the guilty person may be asked for his name, father’s name, his age and his address, etc., the truth of which can be easily verified. The consequent readings on the graph paper for setting the base line of the normal physiological make-up of the individual are thus taken. In the next step, the person may be asked for the crime or guilty act. If he is truthful, then the machine will not show a significant shift from the earlier base line position. In case he lies, then he is liable to face a stressful emotional situation involving significant physiological changes that can be successfully interpreted through the polygraph.
However the results of these sophisticated instruments including lie detectors have been found wanting in determining and measuring the emotions. Individuals are found to show quite varied physiological responses while experiencing the same emotion. In case of pleasure and joy for example one person might be tense with expectation while another is relaxed and physically calm. Similarly in the lie detection case, a guilty person who is cool and calm can pass the test without any difficulty while the truthful person who is nervous may fall into trouble. Therefore, the measurement of physiological changes through the available sophisticated instruments need a very Cautious approach. There is a need for great expertise on the part of the experimenter. On the one hand he must have an adequate knowledge of the nature and potentials of the emotions of his clients, on the other hand the subjects are required to give him maximum cooperation for the detection and measurement of their emotions.
Physiology of Emotions
Physiological reactions and changes that are associated ‘vith emotions have their roots in our body chemistry. They are controlled by the endocrine glands, the autonomous nervous system and our rain.
As may be understood while going through Chapter four of this text, the endocrine glands affect the emotional behaviour of an individual by the undersecretion or over secretion of the respective hormones.
Our autonomic nervous system plays a significant role in controlling and regulating our emotional behaviour. It has two divisions, the sympathetic and para-sympathetic, that work in close cooperation at the time of an emotional experience. In fear and anger situations, for example, the sympathetic division stimulates the adrenal glands to secrete the hormones adrenaline and noradrenalin resulting in the increase of blood pressure and sugar level of the body. The sympathetic division also causes an enlargement of the pupils, a slowing of the salivary glands (leading to dry mouth) and a contraction of the digestive muscles. The para-sympathetic system, on the other hand, activates itself for the rescue operation. It lowers down the blood pressure and heart rate, starts up stomach and intestine mechanisms and finally helps the organism to return to its normal state of behaviour.
The sympathetic and para-sympathetic divisions of the autonomic nervous system are supposed to have centres’in the hypothalamus, an important constitute of our brain. While the stimulation of the posterior area of the hypothalamus increases sympathetic activities leading to excitement and tension etc., stimulation of the anterior area Causes increase in para-sympathetic activities leading to relaxation and depression etc.
The hypothalamus, in every way, tries to coordinate the activities of the internal organs associated with our emotiona! behaviour. Impulses that come from the hypothalamus increase both smooth muscle (involuntary) and skeletal muscle (voluntary) activities. Various experiments have been performed to study the results of the electrical stimulation of the different areas of hypothalamus result into different types of emotional behaviour e.g., while stimulation at one point produces aggressive behaviour the electrodes applied to another area lead to fear, pleasure or pain. Limbic system, the group of inter-related structures deep within the core of the brain (often called the ‘‘old brain’’) has also been found in union with emotional behaviour of an individual. Jose Delgado, a Spanish psychologist (1969) on the basis of his studies has concluded that stimulation of various areas of our limbic system may produce a variety of emotional reactions and it is easy to locate and identify fear, pain and killing sites in the limbic system, the stimulation of which will produce the concerned emotional reactions.
The connection between the emotional behaviour and stimulation of the various parts of the brain has brought the electric stimulation of the brain as a method for treating violent behaviour in human beings, particularly epileptics whose brain mal-function causes unusual aggressive behaviour. The method of electric stimulation has also been proved successful in relieving the Individuals from severe pain and stressful or depressed situations.
Theories of Emotions
For providing explanation about emotions, psychologists have propagated a number of theories. A few important one’s are described below:
1. The James-Lange Theory: One of the first psychologists to attempt a scientific explanation of emotion was a Harvard professor, William James. Incidentally a few years later in 1885, a Danish physiologist Carl Jang also arrived at the same conclusions as propagated by James and consequently the theory is jointly named as the James-Lange Theory.
2. The James-Lange theory advocates that emotions spring from physiological reactions. The perception of the stimulus causes our body to undergo certain physiological changes and we experience emotion.
This theory, however, reversed the old common sense notion about the sequence of the arousal of emotions. The previous sequence was we see a bear, we feel afraid, we run. According to the new theory. order was changed to we see a bear, we run, we feel afraid.
While commenting on his new theory James writes: ‘‘My theory, on the contrary, is that the bodily changes follow directly the perception of the exciting fact, and that our feeling of the same changes as they occur in the emotion. Common sense says, we loose our fortune, are sorry and weep; we meet a bear, are frightened and run: we are insulted by a rival. are angry and strike..... this order of sequence is incorrect and more rational statement is that we feel sorry because we cry, angry because we strike, afraid because we tremble’’. (1890, p. 450).
3. The Cannon-Bard Theory: In 1927 the American psychologist Walter Cannon unleashed an attack against the James-Lange theory. Later on reinforced by L.L. Bard’s work on the thalamus, he proposed that the lower brain centres, specifically the thalamus and bypothalamus, are responsible for inciting emotional reactions. After Perceiving a stimulus, the sensory impulses reach the thalamic-hypothalamic regions. From there they are carried simultaneously to the internal organs of the body and the cerebral cortex. The cerebral cortex, therefore, receives and experiences emotion at the same time that physical changes are occurring in the body.
In this way, Cannon-Bard theory tried to maintain that emotion and physiological responses occur simultaneously not one after another. For example, when we encounter a frightening stimulus like a bear, the sequence of the arousal of emotion takes the form: we perceive the bear, we run and are afraid, with neither reaction i.e..emotional response and emotional experience, preceding the Other.
5. Cognitive Theory: Round about 1970, the American psychologists Stanley Schachter and Jerome Singer, while adopting an eclectic approach to both the earlier theories of emotion, introduced a new theory named Cognitive theory of emotion. They suggested that our physical arousal together with our perception and judgment of situation (cognition) jointly determine which emotions we feel. In other words, Our emotional arousal depends on both physiological changes and the cognitive or mental interpretation of those changes. One cannot work without the other. However, the necessary detection and explanation for an emotional state always rests with the interpretation of a situation. Since this interpretation is purely a subject of cognitive functioning, the cognitive factors are said to be the potent determiners of our emotional states.
The views expressed by Schachter and Singer was also supported by Magda Arnold by stating that cognitive processes control how we interpret our feelings and how we act on them. She used the torm Cognitive Appraisal for the identification and interpretation of emotion provoking stimuli.
In this way, cognitive theory of emotion, tried to emphasize the role of the cognitive factors, a third element, in understanding the relationship between physical reactions and emotional experience aroused on account of the perception of an emotion provoking stimulus. Cognitive theory helped us to learn that the emotional experience and physiological changes through which we pass are determined by the way we interpret a situation through the cognitive functioning. In short, we can say that the dominant cognitive element of our behaviour in the form of our previous knowledge and our interpretation of the present situation directly affect our emotional experience.
Activation theory
The implications of the Cannon-Bard theory in suggesting that “emotions serve an emergency function by preparing the organism for appropriate action” led the way to the modern Activation theories of emotion. The term activation theory of emotion was actually coined in 1951 by Donald B. Lindsley. In_ general, Activation theory refers to the view that emotion represents a state of heightened arousal rather than a qualitatively unigue type of psychological, physiological or behavioural process. Arousal is considered to lie on a wide continuum ranging from a very low level such as deep sleep, to such extremely agitated states as rage or extreme anger.
According to Lindsley, (1951), emotion provoking stimuli activate the recticular activating system in the brain stem, which in turn sends impulses both upward toward the cortex and downward toward the musculature. For the occurrence of a significant emotional behaviour, the recticular formation must be properly activated. However, the activating system tries to serve only a general emerging function and the specific structures in the brain organise the input and determine the particular form of the expressed emotion.
Conclusion about Theories
All these four types of theories discussed above, have tried to provide explanation for the emotional behaviour in their own ways. The James-Lange theory states that our bodily responses stimulate our perception of emotion. The body first responds physiologically to a stimulus, and then the cerebral cortex determines the emotional experience. The Cannon-Bard theory states that impulses from the emotion provoking stimulus are sent simultaneously to the cerebral cortex and the internal organs of the body. Thus the emotional experience and the bodily responses occur simultaneously, but independently. Cognitive theory brings into the lime-light the dominant role played by cognitive factors stating that the emotion we experience and physiological responses we give are both determined by the cognitive functioning; the way in which our mind receives and interprets the stimuli. The Activation theory developed by Lindsley focusses on the role played by the recticular activating system for the arousing and display of emotions. If we try to evaluate the views proposed by these theories, we can come to the conclusicn that none of these existing theories can be termed as a comprehensive theory of emotional behaviour. However, to some extent it can be concluded that emotional behaviour is surely a product of the process of activation. The biological structure of an individual modulated by the environmental experiences, in one way or the other. naust activate the internal organs and the cerebral cortex for the various physiological responses and affective experiences that are experienced by an individual while going through an emotional behaviour.
SUMMARY
It has been found that there are certain specific, innate and inborn modes of behaviour that may be exhibited by the organisms without any prior training or experience. Behaviour of this type has been named as instinctive behaviour and the innate tendencies or predisposition responsible for such behaviour patterns are known as instincts.
The psychologists like William James, William McDougall, Sigmund Freud, Alfred Adler, Carl Jung, etc.. have supported the instinctive theory of behaviour by hypothesizing that the instincts are the ultimate cause of all activities. While James has given a list of 9 basic instincts, and McDougall a list of 14 instincts, the later psychologists Freud. Adler and Jung brought in the field some new instincts like the life instinct, death instinct, the will to power, selfactualization and herd instinct.
Nowadays the instinctive theory stands somewhat rejected for explaining human behaviour. Recent researches have concluded that contrary to the behaviour of lower organisms, it is very difficult to distinguish between learned behaviour patterns and instinctive ones jin human beings and therefore what behaviour one possesses, should be considered a consequence of the interaction between one’s individéal environment and his biological structures and disposition (both inherited and acquired).
Instincts should not be confused with reflex actions that are directly operated by our spinal cord without bringing our brain into the picture. Reflexes are more prompt, automatic and short lived. While instinctive behaviour can be modified or improved through experience or training, the reflex act like sneezing, blinking of eyes, etc., remain the same.
An Instinctive behaviour as McDougall demonstrated necessarily involves all the three aspects of our behaviour i.e., cognitive (perceiving or knowing), affective (feeling or emotion) and conative (doing or acting). In his list of 14 instincts, he also pointed out the names of specific emotions attached to each of the 14 instincts and termed emotions as the product of some instinctive behaviour. There exists a number of theories to explain emotions. The James-Lange theory advocates that emotions spring from physiological reactions. This theory reversed the notion about the sequence vf the arousal of emotions from we see a bear, we feel afraid, we run to, we see a bear, we run, we feel afraid.
The Cannon-Bard Theory tried to maintain that emotion and physiological responses occur simultaneously, not one after another. Therefore, the sequence of emotional arousal should be: We perceive the bear, we run and are afraid.
Cognitive theory tried to emphasize the role of the cognitive factors a third element, in understanding the relationship between physical reactions and emotional experiences aroused on account of the perception of an emotion-provoking stimulus.
Activation theories, the most modern in the line, in general refers to the view that emotion represents a state of heightened arousal. For the occurrence of a significant emotional behaviour, the recticular activating system located in our brain stem, must be properly activated to react in consultation with the higher structures of the brain.
Emotions, thus viewed, essentially represent strong feelings of affective experiences which are characterised by some definite internal and external bodily changes and they are accompanied with some of other types of behavioural acts. Emotions are generally categorized as positive and negative.
In positive emotions while we include the emotions of love curiosity, joy and happiness; the unpleasant emotions of fear, anger, jealousy are included in the category of nogative emotions.
The task of the identification and measurement of the nature and intensity of these positive and negative emotions—may be carried out through introspective reports, observation of facial expressions and Measurement in terms of internal physiological changes. The last mentioned method requires tho use of sophisticated instruments for measuring physiological changes in terms of blood pressure, respiration, pulse rate, skin temperature, sensitivity, brain waves etc. The most modern specialized instrument like EEG. Galvanic skin reflex instruments, syphygmomanometer and lie detector can also be put into use for the objective and reliable (to certain extent) measurement of the nature and intensity of emotions.
References and Suggested Readings
Arnold, M.B., Emotion and Persorality (2 Vols.}; New York: Columbia University Press, 1960.
Barnard, L.L.. Instincts: A Study in Social Psychology, London: George Allen, and Unwin, 1924.
Bimey, R.C. & Tee Van, R.L., Instincts, New York: Van Nostrand 1961].
Cannon, W.B., Bodily Changes in Pain, Hunger, Fear and Rage (2nd ed) New York: Appleton-Century-Crofts, 1929.
Crow, L.D. and Crow, A., Educational Psychology (3rd Indian reprint) New Delhi; Eurasia Publishing House, 1973.
Darwin, C., The Expression of the Emotions in Man and Animals (reprint) Chicago: Chicago University Press, 1965.
Delgado, J.M R., Physical Control of the Mind: Towards a Psycho-civilized Society, New York: Harper & Row, 1969.
Drever, J., Instinct in Man, Cambridge: Cambridge University Press, 1917.
James, William., The Principles of Psychology (Vol. land I), New York: Henry Holt & Co. 1980.
James, William., Psychology: Brief Course, London: Collier Macmillan Ltd., 1969.
Lindsley, D.B.. Emotion in S.S. Stevans (Ed.) Hand Book of Experimental Psychology, New York: John Wiley, 1951.
McDougall, William., An Introduction to Social Psychology (28th ed) London: Methuen, 1946.
McDougall, William G., An Outline of Psychology (13th ed.) London Methuen, 1949.
Morris, Charles G., Psychology (3rd ed.), Englewood Cliffs, New Jersey: Prentice Hall, 1979.
Schachter, S & Singer, J.E., Cognitive, Social and Physiological Determinants of Emotional State, *‘Psychological review’, 1962, 69 p. p. 369-399,
Schachter, S., Emotion Obesity and Crime, New York: Academic Press, 1971. Selye, H., The Stress of Life, New York: McGraw-Hill, 1956. Tinbergen N., The Study of Instinct, London: Oxford University Press, 1956.
Young, P.T.. Emotion in Men and Animal (2nd Ed.), Huntington: New York: Krieger, 1973.
Wood, J., How Do You Feel? Englewood Cliffs, New Jersey: Prentice Hall, 1974. Woodworth, R.S., Psychology, London: Methuen, 1945.
Chapter 7
SENSES AND SENSITIVITY
We do not live in vacuum. Our environment that surrounds us is fully charged with the existence and activities of the various living Organisms, inanimate objects and events. All that exists in our environment may be described in terms of various stimuli. These stimuli may lie both inside and outside of our body. Flowers present in the garden, birds flying in the air, hunger pangs in our stomach and pains somewhere in our body, all play a determined bid to call our attention for realizing their existence as well as awareness. This, in turn, makes us interact with these stimuli in terms of receiving, interpreting and responding to them. The exposure to the stimuli present in our environment is thus the primary source of the information. What we derive from our environment and the relevant response to this ts the origin of our behaviour.
How do we interact with the stimuli present in the environment? What is that which helps us in becoming aware of what Is going on both inside and outside of our body? The answer, lies in the existence and functioning of our body's sense organs. Let us try to know all about It.
Meaning and types of senses
Our senses are in fact the windows to the world—internal as_ well as external. These are the gateways of all information that our brain receives by interacting with the stimuli present inside and outside of our body. Our great ancient thinkers held that there were five human senses—vision, hearing, smell, taste and touch corresponding to the sense organs, eyes, ears, nose, tongue, and skin of our body. During the subsequent ages there has been an addition of some more senses to this list. These senses may be grouped into five categories as under:
Name of the category
1. The Visual Senses - Sense of vision.
2. The Auditory Senses - Sense of hearing.
3. The Chemical Senses - Sense of smell and sense of taste.
4. The Skin Senses - Sense of pressure, sense of temperature and sense of pain.
5. The Body Senses - Kinesthetic sense and Vestibular sense.
We would be discussing in detail each of these types somewhere in this chapter. Here first we will concentrate on some general features of these senses along with the mechanism of sensation.
Sensation and sensitivity
Each stimulus present outside and inside of our body emits a certain amount of physical energy that is ultimately responsible for producing some effect in one or the other sensory organs of our body. This page of the present book, for example, 1s working as a stimulus for producing some effects on our sense organs. It has a particular size and shape, colour and texture and itsletters reflect, a particular pattern. This effect produced on our sense organs for enabling us to become aware or conscious of the nature of a particular stimulus is known as sensation and the quality or tendency of a sense organ to help us in feeling some or the other type of sensation is known as Sensitivity.
We as human beings neither respond indiscriminately nor are we capable of becoming aware or conscious of each and every stimulus available in our environment. We do not have the same power of smelling as our dog has. We cannot see in the dark but our cat is capable of doing so. Similarly the light or sound waves that are beyond our sensation can be successfully caught by our television set. Not only in terms of detection but also in terms of discrimination (which sound frequency is higher, which object is bigger, etc.) we have our limitations. The degree to which we are capable of detecting a stimulus or discriminating between two or more stimuli for finding out the difference, we are. said to be sensitive or are attributed to possess sensitivity to that stimulus or that difference. -
The detection and discrimination of stimuli
The psychology of sensation, as we have seen above, is concerned with an organism's ability to become aware or conscious of some or the other stimuli present in our external or internal environment. This awareness or consciousness of the stimuli has two aspects. The first is concerned with the problem of detection; to find out whether a Stimulus is present or absent e.g. is there anv smell in toilet soap? The second is concerned with the problem of discriminating between stimuli e.g., judging which of two toilet soaps have a more pleasant odor. Let us have some thoughts over the questions of detection and discrimination of stimull.
Each: of our sense organs is specifically stimulated to produce a Particular kind of effect (Sensation) by the physical energy emitted by a particular kind of stimulus. For example the ears are stimulated by the sound stimuli to produce hearing sensation and eyes are stimulated by the light stimuli to produce vision sensation. It is not .essential that a stimulus should always result in some sensation for an Individual. One may or may not at all have heard a particular sound, smelt something or seen a light. The question arises how much sensory stimulation is needed to produce a given sensation or a noticeable difference in sensation? This question related with the problem of dotection and discrimination may be answered through two technical concepts, namely, absolute threshold and difference threshold.
Absolute threshold may be defined as the minimum intensity of physical energy of a stimulus that may produce any sensation at all in a person. It does not mean that below a certain intensity of physical enorgy, a Stimulus is not able to activate the receptor of a sense organ, The receptor of the sense organ is always activated or stimulated but the stimulation may not be strong enough to result ina sensation. In other words, an individual feels a sensation on account of the stimulation from a stimulus only when the condition of a required level of absolute threshold is fulfilled. The absolute thresho[p will, therefore, help in detecting sounds or odours, we may hear of smell from those we cannot.
How can absolute threshold be measured? In general the most common methods used for this purpose are (i) the method of limits, (ii) the method of constant stimuli and (iii) the method of forced choice. Let us illustrate the working of these methods in the case of auditory stimulation.
The method of limits: In the method of limits the work is carried out in two rounds. In the first round, the intensity of the sound is progressively raised from a quite low level until the subject says that he hears the sound. This value of the intensity of sound is recorded by the experimenter. Let it be say X1.
Second round begins with a quite high level of the intensity of the sound. This level is now successively lowered until the subject reports that he hears no sound. This value of the intensity of sound is then recorded by the experimenter. Let it be say Y1.
The experimenter in this way, tries to complete various rounds involving ascending and descending series of the intensity of sounds.
The average of the value x1 + Y1 / 2 , x2 + Y2 /2 + X3 + Y3 /2 etc, is designated as the absolute threshold.
The method of constant Stimuli: In this method the subject is exposed to a number of stimuli of varying intensity involving a wide range along a given dimension. The stimuli are presented to the subject in random order (not in ascending or descending order as in the method of limits) and each time he is asked to indicate whether or not he detects the stimulus. For example in the case of auditory stimulation, he may be asked to say whether or not he hears the sound. The responses of the subject are then recorded and a graph as shown opposite can be plotted to show which stimuli has been detected on which or not.
The method of forced choice: in this method the subject is exposed to a group of selected stimuli, e.g. he may listen to four sounds of varying intensity and may be asked to say ‘yes’ for any one of the four (showing detectability that he is able to hear it). This experiment may then be repeated with other groups of selected stimuli. The average value of the intensity of the stimulus derived from these sounds of the experiment, then, will give the absolute threshold.
Difference threshold and Weber’s Law
The question of discriminating between stimuli or finding difference in sensation, for example, first sound is louder than the second sound or vice versa, may be answered in terms of difference threshold and more clearly through Weber’s Law.
The difference threshold is the minimum difference in the intensity of two stimuli that a person is able to detect. In other words, it is the smallest change in stimulation that he is able to detect or the smallest difference in sensation he is able to discriminate. This is also named as just noticeable difference or j.n.d.
The difference threshold may be determined much in the same way as the absolute threshold by adopting any of the three methods described earlier. In any case its value represents the minimum intensity change that is detected by the subject on at least fit.y per Cent of the presentation.
The difference threshold like absolute threshold varies from Situation to situation and from individual to individual. One interesting feature of the difference threshold is that it varies with the strength or value of the stimulus. This relationship was first demon strated in 1834 by Ernst Weber by giving a law known as Weber's Law.
Weber’s Law: This law states that the difference threshold is proportional to the strength or value of the stimulus. It means that for creating a just noticeable difference we have to increase or reduce the intensity of the stimulus in the ratio of the strength of the stimulus. For example, if we have two fifty kilograms weights and during experiment it is found that we require a 100 gm. weight to be added or taken away for a just noticeable difference between these two weights, then it is implied that we will require 200 gm weight for discriminating between two hundred kilograms weights.
Various senses and their functioning
Let us now turn over to knowing in detail about the various types of senses. For this purpose, first we take our sense of vision.
Sense of vision
For human beings it is the most important sense as it supplies them with the greatest amount of information about the external world. The physical stimulus for the sense of vision is light. Light is an electromagnetic energy force that travels through space in the form of light waves at approximately 1,86,000 miles or 3,00,000 kilometers per second trom sources like, sun, electric bulbs, lamps etc. We as human beings are able to utilise but a very small portion of the light waves available in space, known as visible spectrum. Xrays, radar, television and radio waves are among those that cannot be received by the humin eye, the receptor of the light waves.
Rays of light enters the eye through the cornea, the transparent covering that protects our eyes. Approximately 3 percent of the light rays are reflected off the cornea surface and the remaining ones are passed through the liquid aqueous humor (the fluid behind the cornea) and the pupil of the eye. The pupil of the eye; a black circle Aies in the centre of the iris, the coloured part of the eye. The quantity of light that enters the eve is controlled by the size of the pupil which is controlled by the muscles that he in the inner boundary of the iris. In dim light the muscles of the iris relax, causing the pupil to open wider to let in more light. [n bright light the iris contracts, closing the pupil for cutting down the amount of light entering the eye.
Through the pupil, light enters the !ens. a transparent focussing mechanism which focusses it on a photosensitive surface called the retina lying well inside the wall of the eve ball. The common complaints of near-sightedness and far-sightcdness are caused by an error an cOmmunication between the lens and the retina.
The retina contains the receptor celis that respond to light. But before the light can reach the receptor cells, it must pass through a Jayer of nerve fibres and blood vessels existing within the retina. Near the middle of the retina, there lies a blind spot. There are no receptors in this blind spot. The receptor cells of the retina are classified into two groups—long thin rods and short squat cones. The retina is composed of millions of these two types of receptors. Cones are located at the centre of the retina, primarily in an area called the fovea. The cones enable us to see colour. They operate mainly in daylight and are responsible for visual acuity (Visual acuity is referred to keenness of vision, the ability to discriminate details and fine differences in the field of vision). The rods, that respond to low illumination, are situated on the outside, pheripheral areas. They are mainly responsible for night vision, the capability of seeing in the dark.
When the light falls at the rods and cones, it activates these light receptors and sets up neural impulses, messages in the form of electrochemical energy. This electrochemical energy from the rods and cones is then sent to bipolar cells and ganglion cells in the retina. In general, multiple rods and cones are connected to each bipolar cell and multiple bipolar cells coverge on each ganglion cell. The axons of ganglion cells make up the optic nerve. This optic nerve is responsible for sending the electrochemical messages to the visual area of the brain, where sensations of vision are indicated.
Adaptation: For the sake of our safety as well as our pleasure, receptors in our sense organs exhibit the property of adaption. This adaption is exhibited in two ways. Firstly, the receptors can receive sensory stimulation and operate effectively across quite a wide range. As a result our ears can work with the stimuli having miost intense sound to.the least audible sound; our eyes can function in the intense bright light as weil as in the dimlight and darkness. Secondly, as a result of continuing stimulation, the receptors in our sense organs get accustomed to that particular stimulation resulting in a greatly diminished sensitivity to that stimulus. For example the inhabitants of a slum area may get adapted to an extremely unpleasant odour of a stagnant pond or a chemical fertilizer.
Visual adaptation: The receptors in our visual system exhibit three types of adaptation:
(i) the retinal adaptation.
(ii) the dark adaptation and
(iii) the light adaptation.
In retinal adaptation, an individual in due course Of time perceives an image of a formless gray field of light if the rods and cones of his retina are exposed to constant stimulation. In order to do away with such adaptation which may make the light receptors as wholly insensitive, human eyes engage in minute involuntary movements. These movements keep the image moving across the retina and back and thus help the receptors to get rest and restore their chemical balance.
In case we happen to be shifted from sunlight abruptly into a dark surrounding, we feel a lot of difficulty in detecting objects in the darkness for a few minutes. Also we cannot identify any colour as there is not enough energy in the dim light to stimulate the cones to respond to colours. Then after a few minutes, the process of adaptation begins. The receptors of our eyes start adjusting to low light intensity by an enlarging of the pupil, a build-up of visual pigments in the receptors and a switch from colour (cone) vision to rod vision. As the rods can function effectively even when there is not enough light to stimulate the cones, we get adapted to the darkness and begin to identify the objects. But what we see is a black and white world of different brightness, completely deprived of the colours.
Afterwards when we come into brighter daylight again. our eyes feel difficulty in facing the light waves. It is because the continued exposure of the visual system to darkness makes our eyes so_ sensitive to light that bright intense light 1s nearly painful. Our immediate reaction is to squint and shield our eyes. Then the process of adaptation starts. The muscles of the eye squeeze the pupil smaller; build up of visual pigments (that occurred during darkness) gets reduced by decomposition and there is a shift from rod to cone vision. Gradually the eyes become less sensitive and its reception becomes light adapted.
Purkinje Effect: The Czech Psychologist Purkinje studied the visibility of the colour in terms of day and night vision and concluded that it depends upon their respective wave lengths. Red and yellow colours are usually taken asa brighter colour than blue and green. But, it has been observed that in dim lighting—for example in twilight —the red and yellow colours (having longer wave lengths) lose their brightness and in comparison, the blue and green colours (having shorter wave lengths) appear much brighter. As darkness of
the night increases, those colours that are the brightest by daylight will be lost and be replaced by gray; whereas green objects will continue to appear green for a longer time. This shift in visibility—from a longer wave length to the shorter—is called the Purkinje effect, named after a nineteenth century Czech physiologist Purkinje who was able to notice it first.
This effect occurs due to shift in the operation of receptor cells. The day or bright vision is effectively operated by cones whereas rods are responsible for dim light or night vision. The colours having longer wave length are intensely illuminated when they are activated through cones in dim light or at night, with the cones about to retreat and rods taking over the operation, the colours having shorter wave length get more illumination in comparison with the colours having longer wave length.
Colour Vision: We, human beings cannot respond to the whole world of light. We are limited to the visible spectrum of colours. The ability to see colours depends on the capacity of the receptor cells ia the retina for sending different messages to the brain in response to different wave lengths of the visible spectrum. The visible spectrum is divided into seven colours. It does not mean that we can detect only seven colours. Most of us can see between 125 and 130 separate colours irrespective of the fact that we have only a limited number of names for colours.
Colour Mixture: One of the important phenomena of colour vision is concerned with the mixing or combining of colours that are. usually available in the visible spectrum. There is usually two types of colour mixing — subtractive and additive.
Subtracting mixing takes place when we mix paints. In such colour mixture, each of the mixed paint tries to absorb (and thus subtracts) some wave length from the light falling on it. The remaining unabsorbed wave lengths are then reflected back to our eyes which makes us perceive the colour we see. For example, the mixture of yellow and blue paints is perceived as green. only because, our eye receives the green wave length which remain unabsorbed by either the yellow or blue.
Additive mixing takes place when we mix light waves of different colours. In such mixing none of the component wave lengths are absorbed (subtracted); rather all of them reach the eye and are then transmitted to the brain where they are somehow mixed to produce the colour that is visible by us. It has been experimentally observed that there are some primary colours the mixing of which can help in producing any colour in the spectrum. The primary colours of light (wave lengths) are red light, blue light and green light. [n case we try to project lights of any two or more primary colours on a screen and then try to combine them by their overlapping, the results will be as under:
In addition to this, every primary colour has a single complementary colour. Mixing of these two complementary colours results gray or if the two lights are bright enough, white.
Colour Blindness: The defects in colour vision which makes a person unable to see some or all colours is termed as colour blindness. The persons whose eyes see no colours at all are completely colour blind. This type of blindness is technically known as achromatism. It 1s on account of the genetically determined absence of cones m the retina. They can respond only to the shades of light and dark. Therefore, outside world of colours for these indrviduals is nothing but black, white and shades of gray. "
On the other hand, the persons whose eyes are unable to see some particular colours are termed as partially or mildly colour behind They suffer from various colour anomalities like red-green anomaly and yellow-blue anomaly. The person suffering from red-green anomaly are unable to see the red and green colours and their combrnations. They can see only variously saturated yellow, blue as well as gray. On the other hand, persons suffering from yellow-blue anomaly may see all of the reds and greens but perceives blues and yellows as eray or—if these colours are quite bright—as pure white.
Theories of colour vision
How we see colours has been a subject of extensive research. Two most popular theories, originated in the nineteenth century in this connection are known as Young-Helmholtz Trichomatic Theory and Hering’s Opponent Process Theory.
Young-Helmholtz Theory: It was first advocated by Thomas Young (1773-1829), an English physicist. Later on, it was elaborated by Hermann Von Helmholtz (1821-1894), a German physiologist. According to this theory, there are three types of cone cells in the retina which display three distinct types of sensitivity; one for each of the three primary colours—red, green and blue. Sensitivity to all other colours is caused by varving combinations and proportions of excitation of these three types of receptor cells in the same way as may be produced by mixing of the corresponding primary colours.
This theory, subsequently, faced criticism on various grounds, Firstly, it failed to explain red-green colour blindness. The absence of both red and green experiences in the red-green colour blind, according to this theory, may be explained on the basis of the presumed absence of red and green cones. However, it may further fail to explain the detection of yellow (a combination of red and green) .by a red-green blind.
The second weakness of the theory lies in its failure to explain the phenomena related to colour zones. In other words it could not answer why the red and green are seen only near the centre of the retina while blue and yellow are seen further out towards the peripheri.
Thirdly, it failed to explain the phenomena of after images and contrast (the alteration in the effect of one visual stimulus by another stimulus that occurs before, afterward. or at the same time).
In spite of all these weaknesses, Young-Helmholtz theory stll holds enough ground for providing explanations of colour vision on account of its belief in the association of three cone types with the three primary colours.
Hering’s opponent process theory
This theory was formulated by Edwald Hering (1834-1918). According to this theorv, the colour vision does not depend on the mixture of three primary colours as advocated by Helmholtz theory but depends on three different mechanisms or processes operating in the retina (containing three separate receptors) each producing two opposite qualities of sensation. These are (i) black-white mechanism, (ii) red-green mechanism and (iii) yellow-blue mechanism. While the black-white mechanism accounts for our perception of brightness, the other two account for colour.
In all these three mechanisms or processes, the colours in each pair Oppose each other i.e., sensation of black is opposed to white; sensation of red is opposed to the sensation of green and the sensation of yellow is opposed to the sensation of blue. This is why, we never see a reddish green or a bluish yellow, or a perception of white in the absence of light or a perception of black in the presence of visiblo light. The colour anomalies are the results of improper functioning of either the red-green or the yellow-blue mechanism. The Hering theory is called the opponent process theory because the two pro Cesses in each mechanism oppose each other.
In addition to the explanation of colour anomalies, Hering’s theory is also suitable for explaining our perception of complementary colours. It postulates that if two complementary colours—say red and green, simultaneously stimulate the red-green mechanism; they result in Opposing and counteracting each other. Moreover, this theory is also credited for providing explanation of the phenomena of colour zones, after effect and contrast.
The chief weakness of the Hering’s theory; as pointed out by Chaplin and Krawiec (1974, p. 109), lies in 1ts assumptions involving opponent processes in the retina. The assumptions are complex and involve the postulation of events for which there is no physiological evidence. The theory also suffers from the limitation of having to account for certain aspects of brightness phenomena in colour mixing in a highly complex manner. However, with all such minor limitations in the real sense, the Hering’s theory is continuing to enjoy wide recognition for its capability of explaining the truths about colour vision.
The sense of hearing
The sense of hearing gives us the pleasure of enjoying sound sensations. The physical stimuli for the sense of hearing are sound waves. These waves are molecules of air, travelling at approximately 750 miles per hour, compressing and expanding as they progress on their way. Such waves travel much like the ripples produced by a pebble thrown into a pond.
The Characteristics of Sound: Like light waves, sound waves vary jn frequency and amplitude. The frequency of the waves is measured gn cycles per second, expressed in a unit called Hertz (Hz). One wave cycle is that portion of a regularly recurring wave that is completed once. The human ear can detect frequencies of from 20 to 20,000 hert?
For their distinction and discrimination, sound-waves carry some more typical characteristics in the name of pitch, loudness, tone and timbre, etc,
When we have to see that a sound is low or high, it is said in terms of the pitch. Pitch of a sound is determined by the frequency of wave vibrations per second measured in hertz.
Loudness. of the sound involves its pitch as w: Il as its amplitude. It is measured in decibel units.
A tone is made up of regular wave vibrations. A pure tone consists of a single frequency However, we seldom hear the sounds resulting from pure tones. Most of the time it contains much of the overtones —consisting of a fundamental frequency and multiples of that frequency. A complex typical pattern of the over tones determines the timbre or texture of the sound.
The Structure and functioning of the ear
Our cars work as an auditory system for the sensation of hearing: The structure of the ear as shown in the figure below, can be roughly divided into three parts: outer ear, middle ear, and inner ear, Let us try to see, how the auditory system works.
The sound waves from the air are first collected by the pinna (the outer ear).
It channels them into the auditory canal to reach and bump up against the eardrum, the thin stretchable, vibrating membrane that separates the eardrum to vibrate. The quivering of the eardrum causes three tiny bones in the middle ear called the hammer, the anvil and the stirrup to hit each other in sequence and carry the vibrations to the inner ear. The last of these three bones, the stirrup is loosely connected to the oval window.
Just below the oval window, there is a membrane called the round window which tries to equalize the pressure in the inner ear when the Stirrup hits against the oval window.
The oval window is a membrane of the cochlea, the inner ear Mechanism. The cochlea is a pea-sized coiled tube, It is filled with
some fluid and contains the basilar membrane stretched throughout its lengths. Once transmitted across the oval window and into tie inner ear, the sound waves set up a disturbance in the fluids contain. ed in the cochlea. When the fluids in the cochlea begin to move, the basilar membrane vibrates. The basilar membrane then, transmits the sound vibration to the actual auditory receptors—hair cells located on the organ of Corti, a structure that is attached to the basilar membrane. As waves travel through the cochlea, the hair is moved and the hair cells are pulled by their movement. Stimulation. of the hair cells, in turn, excites the spiral ganglion cells, which send neural impulses (a coded message of the sound heard) through the auditory nerve to the brain.
Theories of hearing
When we speak something it is transmitted to the ears of other persons in the form of sound waves. How these sound waves are received by the receptors of the auditory system and travel all along the hair cells, has been discussed in the preceding pages. The questions which remain unanswered upto this stage are concerned with the process of auditory coding and discrimination of pitch. How are the many different sound wave patterns that reach our ears coded into neural impulses? How do the hair cells, the actual auditory receptors communicate with the brain about the loudness or pitch of the sound”? These questions have been a matter of great investigation resulting into theories of hearing. Let us discuss some major theories like Place theory, Frequency theory and Volley theory.
The Place theory: The place theory or resonance theory was formulated by Hermann Von Helmholtz, a German physiologist who is known to develop the trichomatic theory of colour vision. According to this theory, the basilar membrane, including the organ of corti with its hair cells, functions as a resonator. In other words, it vibrates in sympathy with the external sound waves coming into the ear by way of the auditory canal and oval window. These incoming sound waves vibrate the basilar membrane and those of different frequencies displace different parts of the membrane and stimulate different places of the organ of corti. The coding of physical frequency is determined by the place of stimulation on the organ of corti. In other words, the place theory asserts that the pitch of a sound is dependent on the place of stimulation on the organ of the corti. The analysis of the quality of the sound waves reaching the ear thus takes place in the cochlea through the identification of the places of stintulation,
The Frequency theory: The credit for the propagation of frequency theory goes to William Rutherfold (1839-1899). In essence a pure frequency theory holds that the cochlea responds to a sound wave entering the outer ear like a telephone transmitter by reproducing the waves frequencies, that is, it simply transmits neural impulses along ditory nerve at the same rate as incoming stimulus frequencies. The frequency theory, in this way, in contrast to place theory places
the entire burden of analysis of the quality of the sound wave (discrimination of intensity, pitch, etc.) on the auditory cortex of the brain.
The Volley theory: The frequency theories got into serious trouble on the ground as it was noted that nerve impulses cannot be fired as rapidly as the frequency of the highest pitched sound we are able to hear. This problem was solved by the evolution of the volley theory. This theory maintains that one nerve cannot fire rapidly enough to follow a high frequency and therefore, several nerves would have to alternate in transmitting volleys of impulses. In other words, nerve cells send impulses in sequence, not individually. For example, first one nerve cell fires, then a second and a third, and so on. By that time, the former ones take rest to recover and fire again.
None of the above theories alone may be said to give a full account of the auditory coding and discrimination of the sound in terms of pitch, intensity and timbre etc. However, their validity to explain these mechanisms somehow in their own way remains unaffected and this is why an electic approach incorporating the viewpoints of all the available theories is considered best to serve the required purposes.
The chemical sense
senses of smell and of taste are ealled chemical senses as both are said to be activated by chemical stimuli.
Sense of Smell: The receptors for the smell sensation are situated igh in each nasal cavity in a small cell packed area called the
olfactory epithelium. The olfactory epithelium is only about half the size of a postage stamp, but it is packed with nearly 600,000 receptor cells known as olfactory cells. These cells have a lot of olfactory hair, which is stimulated by molecules of substances that come in through the nose or rise up from the base of the mouth.
The axon of the receptors carry the smell sensations in the form of neural impulses directly to the olfactory bulbs in the brain and as a result we experience a particular odour. Although nothing has been definitely known about what kinds of molecules carry what kinds of odours, it has been concluded through some latest researches in this field that both the size and the shape of the aromatic molecules influence the particular odour they carry.
Sense of taste
The receptor cells for the sense of taste lie inside the taste buds, which may be located witbin small bumps of the tongue in the back of the mouth and in the throat. However, most of these taste buds numbering about !U,00U are concentrated on the tip, sides and back of the tongue. Each of the so-called taste buds contains about 20 taste cells, a cluster of taste receptors. These taste cells form an opening at the top of the bud known as the taste pore.
The chemical substances in the foods we eat when dissolved in saliva, are then passed through these taste pores to the cells responsible for taste detection and ultimately the taste sensations in the janguage of neural impulses are sent through axon of the taste cells and sensory nerves to the brain which tells us how we can experience the sense of taste. These taste experiences, established through various researches and experiments, are usually concerned with the temperature and consistency of the food, the smell of the food molecules, the four primary taste qualities—sweet, sour, salty and bitterand all other tastes results from a combination of these four qualities.
The skin sense
The group of skin senses includes three senses: the sense of touch or pressure, the sense of pain and the sense of temperature (warmth and cold).
The Receptors of the skin senses: The receptors in the skin for these three types of sensation fall into three general categories; free nerve endings, basket nerve endings and encapsulated end organs. All these different kinds of skin sense receptors send typical skin sensory messages to the brain through the spinal cord. The messages from the Jeft side of the body are transmitted to the right cerebral hemisphere and from the right side of the body to the left hemisphere. Let us now learn more about these receptors.
Free nerve endings receptors are found just below the surface of the skin. They‘ are involved in all the three types of skin sensations.
Basket nerve endings recoptors represent the nerve fibres that wrap around the base of the hair. They are more responsive to the stimuli carrying touch or pressure sensation.
Encapsulated end organs, the third type of skin sense receptors represent those nerve fibres that end inside some sort of capsule or shell. They are found to be sensitive to pressure and temperature.
Sense of touch or pressure. Sense of touch or pressure is helpful in feeling the sensation of touch or pressure on our body. The receptors concerning this sense are usually concentrated in the fingertips, Jips and other areas capable of spatial discrimination of pressure. Unlike the other senses, the receptors in the sense of touch respond only to changes in stimulation (increase or decrease in the amount of pressure) and consequently, they fail to detect continuous touch.
Sense of temperature: The sense of temperature helps us in feeling the sensation of warmth and cold as well as in detecting the difference between two temperatures. It has been established that there are no separate receptor cells for warmth and cold and as a receptor the free nerve endings are mostly responsible for the differences in sensitivity to temperature. The object at least 1or 2 degrees centigrade warmer than our body temperature are sensed by the receptor cells as warm and those at least 1 or 2 degrees centigrade colder than our body temperature are sensed as cold.
When we are touching something warm and something cool at the same time two types of paradoxical sensations may be felt. In the case of paradoxical cold, the high temperatures are felt almost like freezing cold at the first instant of stimulation. Similarly in the case of paradoxical heat, the brain may read the combined effect of warmth and cold sensations as a sensation of intense heat or burning.
Sense of pain: The sense of pain helps us in realising the sensation of pains. The receptors in the skin for pain lie mainly in the free nerve endings. However, the receptors for pain reside not only in the skin but in muscles and body organs as well, thus accounting for much of the distress that comes from cramps and intestinal disorders. In general, all such stimulation that produce tissue damage may cause pain.
An important theory concerning pain, known as the ‘gate control theory’, was propagated in 1965 by the psychologists Ronald Melzack and Patrick Wall. This theory maintains that there is a gatelike mechanism in our pain-signaling system. This gate may be opencd fully, partially, or not at all, depending on the levels of the activity of sensory fibres that run from the body's surface to the central nervous system. Some fibres when stimulated may ciose the gate ‘while some others when stimulated may open the gate. The opening of the gate increases pain while its closing diminishes the level of pain. [n addition to this, other brain mechanisms also play a part in feeling pain. For example, certain areas of the brain-stem can send out signals to fibres connected to the spinal cord, which can effectively block pam. Similarly the cerebral cortex may also affect the feeling of pain by inhibiting fibres that descend from the cortex. The gate way theory, in this way, may prove quite helpful in explaining the mechanisms of experiencing pain including the role of higher brain centres in blocking or desensitizing the feelings of pain.
However, the pain in all ways is quite a complex sensation both in its physiology and in the way that it is experienced by individuals. The sensation of pain to a particular degree may be felt in different ways by different persons or even by the same person at different times. Many patients have been found to be relieved of discomfort and agony through hypnosis or suggestion. It has led us to believe that the higher areas of the cerebral cortex (other than sensory areas) exert considerable influence on pain, modifying in some ways the reception and transmission of impulse.
The body senses
The body senses include the Kinesthetic and the Vestibular sense. These senses help us to maintain the balance of our body at the time when we stand, walk or stumble. With their help we are able to reach for objects accurately and manipulate them or even head for the right direction.
The kinesthetic sense
This sense plays a key role in relaying information about the position and movement of the parts of our body without actually observing or sensing them through our sense of vision. There is no one specific organ allotted to the Kinesthetic sense. The Kinesthetic receptors are scattered throughout the muscles and joints of our body. Nerve fibres from these receptors join together with the nerve fibres from the organs of the skin just before they enter the spinal cord for carrying Kinesthetic sense messages from one part of the body to the cerebral cortex almost in the same way as the skin receptors do.
The vestibular sense.
The vestibular sense related with equilibrium is concerned with the sensation of movement and changes in orientation of the head. It does more than just relaying information about body position. It helps us to run without falling, to walk on a high wirestrung stretched between two poles, to catch ourselves when we trip, to keep our balance on a bumpy air plane trip or a swaying bus, etc. The receptors for the vestibular sense lie in the inner ear. The vestibular system consists of three semicircular canals, arranged at right angles to one another and two sac-like chambers. The semicircular canals have enlarged ends containing receptor cells that respond to any movement or rotation of the head. The receptors in the utricle and Saccula respond to the changes in the position of the head with respect to the direction of gravity. The pattern of excitation of the receptor cells helps the brain to identify the position of the head with respect to gravity. When the vestibular sense receptors are stimulated harshly or abruptly—this occurs when we are in a boat on rough seas—it may cause dizziness and nausea. However, we can adapt to nearly any such outcomes, even the loss or damage of the vestibular system, on account of our ability to adjust and the assistance rendered by our visual and Kinesthetic systems.
SUMMARY
Human beings are found to possess at least nine senses: vision, hearing, smell, taste, pressure, temperature, pain, the vestibular and Kinesthetic sense. Each of these senses help us to become aware or conscious of the nature of a particular stimulus coming in contact with our senses. This awareness is termed as sensation and the quality of the sense organ like ear or eye which helps us in feeling one or other type of sensation is known as sensitivity.
Measurement of sensation or sensitivity (detection and discrimination of stimuli) is carried out through two different measures (i) the absolute threshold—the minimum intensity of physical energy of a stimulus that may produce any sensation at all in a person and (ii) the difference threshold—the smallest change in stimulation that a person can detect, also called the just noticeable difference (j.n d.)
Sense of vision is considered most important in humans as it supplies to them the greatest amount of information (about 80%) of the external world. The physical stimulus for the sense of vision is light which is received by the receptor cells (rods and cones) of the retina. When the light falls at the rods and cones it activates them and sets up neural impulses, a coded message that is sent to the visual area of the brain for inducing the sensation of vision.
Adaptation: is a unique property—exhibited by our sense organs. It comes into the picture when a receptor responds in a decreasing manner to continuing stimulation. The receptors in our visual system exhibit three types of adaptation, namely retinal adaptation, the dark adaptation and the light adaptation.
The rods are mainly responsible for night vision, the capacity of seeing in the dark; while the cones operate mainly in daylight and help us to see colour. The shift in the operations of reflector cells (rods to cones or vice versa) causes a peculiar light sensation effect known as Purkinje effect—shift in the visibility of the colour in terms of day and night vision depending upon their respective wave lengths. The visible spectrum of colours to which cones and rods can respond is called colour vision. In general, this spectrum, to most of us, is divided into seven colours. The phenomenon concerning mixing oF combining of colours available in our visible spectrum is called colour mixture. As a result we may perceive the combining effect of the colours i.e., green as the mixture of yellow and blue, The other important phenomenon belonging to colour vision is colour blindness the defects in colour vision which makes a person to see some or all colours.
How we see colours can be explained through the theories of vision. According to Young Helmholtz Trichomatic theory, the eye contains three different kinds of colour receptors that respond to red, green and blue light, respectively. By mixing these three basic colours, the eye can detect any colour in our visible spectrum.
The Opponent process theory accepts the notion of three separate kinds of receptors, but holds that each responds to either member of three basic colour pairs—red and green, yellow and blue, and black and white (producing two opposite qualities of sensation). The evaluation of these two theories may reveal that both theories may be correct at different stages of the visual process.
The physical stimuli for the sense of hearing are sound waves. Sound waves cause the eardrum to vibrate, which sets in motion the hammer, the anvil and the stirrup. The stirr up strikes the oval window, which transfers the vibration to the fluid in the cocklea. The basilar membrane then moves up and down, and the receptor cells in the Organ of Corti cause their adjacent bipolar neurons to fire and then send a coded message of the sound heard to the auditory centres in the brain.
The place theory of hearing asserts that the pitch of a sound is dependent on the place of stimulation on the organ of corti (where the bisic receptor cells of hearing hie). The Frequency theory holds that pi‘ch is determined on the basis of the frequency of firing of nerve cells, not by the receptor in organ of corti but by the brain self through its auditory centres. The Volley theory while supporting the frequency theory explain how the nerve inpulses fire as rapidly as the frequency of highest pitched sound. It maintains that instead of a single nerve, several nerves would have to alternate in transmitting Volleys of impulses. A combination of the viewpoints of these theories may prove more useful in explaining pitch discrimination.
The receptors for the smell sensations are situated high in each nasal cavity, in the area called the olfactory epithelium. The smell sensations are directly carried to the brain through the axon of these receptors.
The receptor for the sense of taste which lies in the taste buds on the tongue activate these receptors to send coded message of the taste to the brain which tells us how we can experience the sense of taste.
The receptors for Sense of pressure are concentrated in the finger tips, lips and various other areas of free nerve and basket nerve endings, capable of spatial discrimination of pressure. The receptors fur the sense of temperature (warmth and cold) and pain lie in the free nerve endings of our skin. While for the temperature receptors there is no other place to reside, the receptors for pain may reside in muscles and body organs as well. All these three kinds of skin senso (pressure, temperature and pain) receptors send typical skin sensory message to the brain through the spinal cord for the necessary interpretation. ‘
The Kinesthetic and vestibular senses are called body senses. The Kinesthetic sense plays a key role in relaying information about the position and movement of the parts of our body without actually observing or sensing them through our sense of vision. The receptors for these sense are scattered throughout the muscles and joints of our body. The Vestibular sense tells us what position we are in with respect to gravity. The receptors for this sense.are located in the Vestibular organ in the inner ear.
References and Suggested Readings
Chaplin. James P and Krawiec, T.S., Systems and Thearies of Psychology (3rd ed.), New York: Holt, Rinehart & Winson Inc, 1974.
Corso, J.F.. The Experimental Psychology of Sensory Behaviour, New York: Holt, Rinehart & Winston Inc. 1967.
Geldard F.A., The Human Seises (2nd ed.), New York: John Wiley, 1972. Gibson, J.J., Senses Considered as Perceprual Systems, Boston: Houghton Mifflin, 1966.
Gregory, R L., Eye and Brain: The Psychology of Seeing (2nd ed.}, New York: Mc Graw-Hill, 1973.
Harper, R., Human Senses in Action, New York: Longman, 1972,
Mueller C.G., Sensory Psychology, Englewood Cliffs, New Jersey: Prentice-Hall, 1965.
Teevan, R.E. & Birney, R.D. (ed.); Colour Vision, Princeton, New Jersey: Vaa Nostrand, 1961.
Warshofsky. F. and Stevens, SS; Sound and Hearing (Rev. ed.), New York: Time Life, 1969.