dishabituation

Meaning: Habituation is a decrease in response to a repeated, harmless stimulus. Dishabituation is the return of that response when a new or different stimulus is introduced after habituation has occurred. It is a form of non-associative learning. It also shows that the earlier decline was not simple fatigue or sensory failure, because the organism still responds to something novel.

On the MCAT: The usual passage is an infant study. A baby sees the same picture repeatedly until looking time drops (habituation). A new picture is then shown. If looking time rises again, the baby has detected a difference, so dishabituation is used to test perception and discrimination in people who cannot speak. Animal examples also appear, such as gill withdrawal in Aplysia, where a strong stimulus elsewhere restores a response that had faded. The pattern to predict is a high response, a gradual fall, then a rise after the change. If the new stimulus is not noticed as different, the response stays low.

Common confusion: Students mix up dishabituation with sensitization. Sensitization is an increased response to stimuli after an intense or noxious stimulus, and it can occur without prior habituation. Dishabituation is specifically the restoration of a response that had been habituated. Some accounts describe dishabituation as sensitization acting on a habituated response, so the two are related. It is also not extinction, which involves conditioned responses.