Habituation

Habituation, a form of non-associative learning, is the psychological process in humans and other organisms in which there is a decrease in psychological and behavioral response to a stimulus after repeated exposure to that stimulus over a duration of time.

Background
Habituation is a type of non-associative learning leading to a decreased behavioral response to repeated stimuli. In other words, habituation is learning to ignore irrelevant stimuli. 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 has been shown in essentially every species of animal, as well as in the large protozoan Stentor coeruleus. . It is also essential to note that the decrease in responding is specific to the habituated stimulus (For example, if one was habituated to the taste of lemon, their responding would increase significantly when presented with the taste of lime) (Domjan, 2010). Also important to remember is that there are factors that influence whether or not habituation occurs; two of these factors are (Domjan, 2010):

1) Inter-stimulus Interval (Amount of time that passes between one presentation of the stimulus and the next)

"A longer interval between stimulus presentations results in slower rates of habituation."

2) Stimulus Duration (How long the stimulus lasts)

"A stimulus presented for 10 seconds will result in slower habituation than a stimulus presented for 30 seconds."

Neurobiology of Habituation
It is a neutral form of learning in which a neutral stimulus is repeated many times. The first time it is applied it is novel and evokes a reaction (the orienting reflex or "what is it?" response). However, it evokes less and less electrical response as it is repeated. Eventually the subject becomes habituated to the stimulus and ignores it. This is associated with decreased release of neurotransmitter from the presynaptic terminal because of decreased intracellular Ca++. The decrease in intracellular Ca++ is due to gradual inactivation of Ca++ channels.

Psychological significance in humans
Habituation need not be conscious—for example, a short time after a human dresses in clothing, 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.

Habituation is frequently used in testing psychological phenomena. Both adults and infants gaze less at a particular visual 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 presented in unison with a primary stimulus, and may briefly increase habituated response toward the primary stimulus until an organism distinguishes, or discriminates the differences between two different stimuli. Dishabituation has been demonstrated as being inherently different than psychological sensitization.