Habituation

In psychology, habituation is an example of non-associative learning in which there is a progressive diminution of behavioral response probability with repetition of a stimulus. It is another form of integration. An animal first responds to a stimulus, but if it is neither rewarding nor harmful the animal reduces subsequent responses. One example of this can be seen in small song birds - if a stuffed owl (or similar predator) is put into the cage, the birds initially react to it as though it were a real predator. Soon the birds react less, showing habituation. If another stuffed owl is introduced (or the same one removed and re-introduced), the birds react to it as though it were a predator, showing that it is only a very specific stimulus that is habituated to (namely, one particular unmoving owl in one place). Habituation has been shown in essentially every species of animal, including the large protozoan Stentor coeruleus.

Habituation need not be conscious - for example, a short time after we get dressed, the stimulus clothing creates disappears from our nervous systems and we become unaware of it. In this way, habituation is used to ignore any continual stimulus, presumably because changes in stimulus level are normally far more important than absolute levels of stimulation. This sort of habituation can occur through neural adaptation in sensory nerves themselves and through negative feedback from the brain to peripheral sensory organs.

The learning underlying habituation is a fundamental or basic process of biological systems and does not require conscious motivation or awareness to occur. Indeed, without habituation we would be unable to distinguish meaningful information from the background, unchanging information.

Habituation is stimulus specific. It does not cause a general decline in responsiveness. It functions like an average weighted history wavelet interference filter reducing the responsiveness of the organism to a particular stimulus. Frequently one can see opponent processes after the stimulus is removed.

Habituation is connected to associational reciprocal inhibition phenomena, opponent processes, motion aftereffects, color constancy, size constancy, and negative afterimages.

Habituation is frequently used in testing psychological phenomena. Both infants and adults look less and less at a particular stimulus the longer it is presented. The amount of time spent looking at a new stimulus after habituation to the initial stimulus indicates the effective similarity of the two stimuli. It is also used to discover the resolution of perceptual systems. For instance, by habituating someone to one stimulus, and then observing responses to similar ones, one can detect the smallest degree of difference that is detectable.

Dishabituation is when a second stimulus is used, which briefly increases habituated response, it has been shown that this is a different mechanism from sensitization.