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The sensitivity of the analyzer changes under the influence of sense organ adaptation to the operating irritant. This phenomenon is called adaptation. Adaptation can happen as in the direction of increase in sensitivity (when transition from strong irritants to weak is carried out), and in the direction of decrease it (when from weak irritants pass to strong irritants).

in the field of sense of smell process of adaptation proceeds differently to different smells. So, the smell of camphor ceases to be felt in 1 - 2 minutes that indicates strong falling of sensitivity. However to the smells including painful irritation (mustard, liquid ammonia), adaptation happens slowly, and with the sufficient force of an irritant does not happen at all, and the irritant causes intolerantly unpleasant feeling. Adaptation to smells, as well as adaptation to sounds, has selective character: at decrease in sensitivity to one smell the sensitivity to other smells can not decrease though adaptation and extends to group of similar smells.

Adaptation to painful irritations is expressed poorly. Very severe pains do not give adaptation at all. It is explained by a biological role of pain as signal of violation of the normal state of an organism.

The similar facts were observed in researches Kravkova, Kekcheeva, Schwartz and others. It is revealed, for example, that easy muscular work, rubdown of the person as cold water, weak sound collateral irritants increase sensitivity of sight (strong collateral irritants, on the contrary, owing to negative induction reduce it).

Not only the simultaneous irritation of other sense organ, but also simultaneous irritation of other parts of the same sense organ can have the sensibilizing effect. The sensitivity of some parts of a retina was kakpokazat, for example, by Teplov's experiences, raises if along with it to affect with moderate light other places of a retina of the same eye (the strong collateral irritation of the same sense organ causes and this time owing to negative induction decrease in sensitivity).

It is necessary to distinguish the sensitization phenomenon from adaptation. While adaptation represents increase in sensitivity (in some cases), and decrease it (in other cases) and at the same time is adaptation of body to the irritant operating on it, the sensitization is always increase in sensitivity and is caused by action of other reasons in comparison with adaptation. An essential role among them is played by interaction of analyzers. Under certain conditions it involves increase in sensitivity of one of sense organs under the influence of simultaneous functioning of another. This phenomenon well shows P.P. Lazarev's experiment conducted by it in wide audience. Indoors, where there were experiences, the silent tone of identical intensity sounded. At rhythmic inclusion and switching off of light the sound seemed vibrating, changing the intensity. Such change in feeling of a sound happened thanks to the fact that at effect of light the sensitivity of an organ of hearing increased and the sound was perceived by louder.

Adaptation is shown in all types of feelings. It is especially strong in the field of sight, sense of smell, skin feelings and taste; it is less expressed in the field of hearing. Adaptation of all sense organs proceeds on similar regularities and as adaptation of sight to darkness and to light is especially studied, consideration of visual adaptation can open the general laws of adaptation. can seem at first is hotter, but gradually thermal feeling weakens. However strong thermal and holodovy irritants do not give adaptation or it proceeds very slowly.