habituation

n. act of making one accustomed to, familiarization

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.
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Habituation /ha·bit·u·a·tion/ 1. the gradual adaptation to a stimulus or to the environment, with a decreasing response. 2. [more]Habituation - Community and Resources

Noun
1. being abnormally tolerant to and dependent on something that is psychologically or physically habit-forming (especially alcohol or narcotic drugs)
(synonym) addiction, dependence, dependency
(hypernym) physiological state, physiological condition
(hyponym) drug addiction, white plague
(derivation) habituate, accustom
(classification) narcotic
2. a general accommodation to unchanging environmental conditions
(hypernym) accommodation
(derivation) habituate, accustom

(n.)
The act of habituating, or accustoming; the state of being habituated.