Man is blessed with a number of sense organs. These organs help him to see, hear, taste, touch, and smell. The sense organs receive impressions of the things found in the outer world. These impressions are known as ‘Sensations’. The organic structure of man functions through a network of sensory and motor nerves.
The sensory nerves help us in getting the very first impressions of the knowledge of the surrounding worlds We give the name sensations’ to these first impressions Thus, sensations are the most elementary processes that are necessary for cognition. They are the raw materials. of our knowledge of the external world. They are the simplest components of our consciousness. A sensation cannot be reduced to any simpler ingredients.
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Sensation Defined
The term.’ sensation has been defined variously.
(i) Essential act of sense-organ. A sensation in an act of the sense-organ which, when stimulated, sends nerve currents to the sensory centers of the brain, and the first response of the brain is sensation.”
(ii) A simple mental process. The sensation is a simple mental process caused by the stimulation or excitation of a particular series organs. Thus sensation is the reaction aroused in us by the stimulus.
(ii) Medium of contact with the external world. A sensation is our medium of contact with the external world. The sensation is aroused only after the stimulation is carried to the central nervous system. It is in this sense that sensation is regarded as the raw material of our knowledge
Pure sensation is-not possible
Pure sensation is not possible at all. An adult can never. it has a pure sensation. As soon as he gets a sensation, consciously or unconsciously, he tries to attach meaning to it which is derived from his past experience On the other hand, an infant may be said to have received a kind of elementary sensation as his experience is only fragmentary.
The Origin of Sensation
The origin of sensation is simple to understand. Our sense organs come into contact with the external environment of the world. They receive stimuli from the external world. The impression thus received of the things found in the outer world is called ‘sensation’. Accordingly, a sensation is defined as. a simple mental process caused by the stimulation or excitation of a particular sense organ
CHARACTERISTICS OF SENSATION
The following are the major characteristics of sensation :
(a)Quality
(b)Intensity
(c)Duration
(d)Extensity
1. Quality
This attribute distinguishes one sensation from another. It is this attribute that gives uniqueness to each sensation. The sensation of sound.is different from the sensation of sight. The difference is due to the ‘fact that the quality of the sensation of sight is not the same as the quality of the sensation of sound: In the same manner, we may distinguish red from blue, sweet from bitter, and hot from cold.
It may be pointed out here that quality does not mean the kind of sensation. For instance, red and blue belong to the same kind of sensation, that is both are sensations of sight, but they differ in
their qualities
2. Intensity
In simple words, intensity refers to quantity. Intensity means the strength of or the excess or less of a sensation, A loud noise may be distinguished from a faint noise; the excess of bitterness may be distinguished from mild bitterness; a strong smell may be distinguished from a weak one, an intense pain of a wound caused with a knife from the prick of a needle.
It may be remembered that the intensity of one kind of sensation cannot be compared with the intensity of another kind of sensation. That is to say, the intensity. of sound cannot be compared with that of taste.
3. Duration or Propensity
Every sensation has a duration. The duration may be one second, one minute or even more. Thus the duration of a sensation means the time for which the sensation endures. Every sensation must have some length or duration, however small it may be. It has been rightly said that A sensation which does not last an instant is inconceivable.” The difference between a sound that lasts for a second and that which lasts for a minute is one of duration or
propensity.
4. Extensity
Extensity is variously called volume, extensiveness, diffusion, massiveness or spreadoutness. If we immerse only one finger in hot water and then immerse our whole arm, the resulting experiences will be different. The second one is more diffused or extensive than the first one. Similarly, there is a difference between the sensations which arise when a few hairs of the head are pulled and when a big handful is pulled. Again, when we look at a thing from a certain distance, it looks smaller than when we approach it. The change is one of extensity in the visual sensation
KINDS OF SENSATION
Man is blessed with five important sense organs. Each of these organs produces a sensation,,, as shown below:
1. Visual Sensation:
The eye is the organ of our sensation of sight. It occupies the first place among the sense-organs and is called “the queen of senses”. The stimulus for the visual. the sensation is rays of light. They light-enter the eye through the cornea. After passing through the pupil and the lens they reach the retina: From the retina, the optic nerve carries the visual impulse to the brain, and we have the sensation of sight.
The visual sensation occupies the highest place among sensations. It is the most refined sensation. It is important to mark two stages in the. development, of sight sensation. These are Brightness sensations and Colour sensations. White, Black, and Grey are brightness sensations and belong to the most primitive and earliest sensations. The color sensations are those of blue; green, red, and yellow. They come at a later stage in the development of the eye.
2. Auditory Sensation
The ear is the organ of our-auditory sensations. The stimulus for sound sensation consists of the vibration or motion in the particles of air.
The ear consists of three parts :
(i) The external ear:
It collects the sound waves which are carried by the auditory canal to the central brain.
(ii) The middle ear:
It is a drum-shaped cavity from where certain bones oscillate and produce vibrations in the ear.
(iii) The inner ear:
It sends nerve impulses to the brain where the sensation arises.
We can mark two stages in the development of sound sensation These are:
(a) the sensation of noise
(b) the sensation of musical sounds. Noises are confused, mixed, and irregular. They are produced by irregular waves. Musical sounds are smooth, steady, and uniform. They are produced by rhythmical and periodic waves.
3. Olfactory (Smell) Sensation
The nose is the organ of smell. The appropriate stimuli for the sensation of smell are the gaseous substances included in the air. The factory nerve in the upper cavity of the nose. plays an active role in smell sensation. The olfactory nerve carries the odorous impulse to the brain where the sensation of smell takes place.
The important points to be noted about the smell sensation are:
(i) The sensation of smell is useful in to know the kind of surroundings we are placed in
(ii) The sensation of smell is connected with the sensation of taste. We can judge the taste of a thing by smelling its oders
4. Gastutory (Taste) Sensation
The tongue is the organ of taste. The sensation of taste can be stimulated only by fluids. Solid objects must first dissolve themselves before they can produce any taste sensation. At the back of the tongue, there are taste bulbs or ‘taste buds’ each of which contains several taste cells. When we put anything on the tongue, its particles come in contact with these cells, and the sensation is caused Thus, the ‘taste buds are the receptors of stimuli. There are only four basic tastes: sweet, bitter, sour, and saltish.
5. Tactual or Cutancous (Touch) Sensation
The skin is the sense organ. causes the sensation of touch.[more]
