Sensitization and dishabituation of infant visual fixation

Dishabituation is defined as the renewed response to a familiarized stimulus upon its retest after the introduction of a novel-stimulus. Two experiments tested an account of dishabituation of infant visual fixation based on the hypothesis that a general, state-dependent sensitization produced by the novel-stimulus energizes responding to any subsequent stimulus. However, this sensitization is thought to be time-dependent, so that increasing delays between the termination of the novel stimuli and the onset of the retest should lead to diminished dishabituation. In Experiment 1, the time between the end of familiarization and the start of the retest of the familiarized pattern was held constant and the temporal location in that inverval of 2 novel stimulus presentations was manipulated. Significant dishabituation was observed only when the novel stimuli occurred shortly before the retest. In Experiment 2, the number of novel-stimulus presentations was systematically manipulated and the magnitude of dishabituation was observed. Significant dishabituation occurred after 2 or 4, but not after 6, novel-stimulus presentations. These findings were consistent with the sensitization explanation of dishabituation, and cast doubt on an explanation of this form of dishabituation based on schema-change.