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How does auditory sensation take place?


Auditory sensation begins when sound enters ear and stimulates chief organs of hearing.

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What is meant by light and dark adaptation? How do they take place?


Light adaptation refers to the process of adjusting to bright light after exposure to dim light. This process takes nearly a minute or two. On the other hand, dark adaptation refers to the process of adjusting to a dimly illuminated environment after exposure to bright light. This may take half an hour or even longer depending on the previous level of exposure of the eye to light.

Light and dark adaptations occur due to certain photochemical processes. The rods have a photo-sensitive chemical substance, called rhodopsin or visual purple. By the action of light the molecules of this chemical substance get bleached or broken down. Under such conditions the light adaptation takes place in the eyes. On the other hand, the dark adaptation is achieved by the removal of light and thereby allowing for restorative processes to generate the pigment in the rods with the help of vitamin A. The regeneration of rhodopsin in rods is a time consuming process. That is why dark adaptation is a slower process than light adaptation.

It has been found that people who suffer from vitamin-A deficiency do not achieve dark adaptation at all, and find it really difficult to move in the dark. This condition is generally known as night blindness.

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What is colour vision and what are the dimensions of colour?


A person’s ability to distinguish different shades of colour is termed as colour vision. A person with normal colour vision can distinguish more than seven million different shades of colour.

There are three basic dimensions of colour-hue, saturation, and brightness. Hue is a property of chromatic colours. It refers to the name of the colour, e.g., red, blue, and green. Hue varies with wavelength, and each colour is identified with a specific wavelength. For example, blue has a wavelength of about 465 nm. and green of about 500 nm. Achromatic colours like black, white or grey are not characterised by hues.

Saturation is a psychological attribute that refers to the relative amount of hue of a surface or object. The light of single wavelength (monochromatic) appears to be highly saturated. As we mix different wavelengths, the saturation decreases. The colour grey is completely unsaturated.

Brightness is the perceived intensity of light. It varies across both chromatic and achromatic colours. White and black represent the top and bottom of the brightness dimension. White has the highest degree of brightness, whereas black has the lowest degree.

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Define attention. Explain its properties.


The process through which certain stimuli are selected from a group of others is generally referred to as attention.

Attention has different properties such as selection, alertness, concentration, and search.

(i) Selection: A large number of stimuli impinge upon our sense organs simultaneously but we do not notice all of them at the same time. Only a selected few of them are noticed. For example, when a student enters his classroom he encounters several things in it, such as doors, walls, windows, paintings on walls, tables, chairs, students, school bags, etc., but he selectively focus only on one or two of them at one time.

(ii) Alertness: It refers to an individual’s readiness to deal with stimuli that appear before him/her. For example while participating in a race in school, a student can see the participants on the starting line in an alert state waiting for the whistle to blow in order to run.

(iii) Concentration: It refers to focusing of awareness on certain specific objects while excluding others for the moment. For example in the classroom, a student concentrates on the teacher’s lecture and ignores all sorts of noise coming from different corners of the school.

(iv) Search: In search an observer looks for some specified subject or object among a set of objects. Example : When you go to fetch your younger sister and brother from the school, you just look for them among many boys and girls. All these activities require some kind of effort on the part of the people.

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Explain the functional limitations of sense organs.


Our sense organs provide us with first hand information about our external or internal world. Different sense organs deal with different forms of stimuli and serve different purposes. Each sense organ is highly specialised for dealing with a particular kind of information. However, all sense organs function with certain limitations. For example, our eyes cannot see things which are very dim or very bright. Similarly, our ears cannot hear very faint or very loud sounds. As human beings, we function within a limited range of stimulation. A stimulus, to be noticed by a sensory receptor, has to be of an optimal intensity or magnitude. In order to be noticed, a stimulus has to carry a minimum value or weight.

The minimum value of a stimulus required to activate a given sensory system is called absolute limen (AL). Absolute limen is not a fixed point, instead it varies considerably across individuals and situations depending on the people’s organic conditions and their motivational states. Hence, it is assessed on the basis of a number of trials. Further, it is not possible to differentiate between all stimuli. In order to notice two stimuli are different from each other. These has to be some minimum difference between the value of those stimuli. The smallest difference in the value of two stimuli that is necessary to notice them as different is termed as difference limen (DL). Thus, it is not possible to understand sensations without the AL and DL of different types of stimuli.

Besides the stimulus characteristics, sensory processes also depend on other characteristics. Sense organs and the neural pathways connecting them to various brain centres also play a vital role in this process. A sense organ receives the stimulus and encodes it as an electrical impulse. For being noticed this electrical impulse must reach the higher brain centres. Any structural or functional defect or damage in the receptor organs, its neural pathway, or the concerned brain area may lead to a partial or complete loss of sensation.

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