Electrophysiological Measures of Familiarity and Repetition Effects of Environmental Sounds and Naturalistic Scenes.

Abstract:
In daily life a constant stream of auditory and visual stimuli are encountered. Some are recognized immediately while others are encountered for the first time. How does the brain differentiate these events? In previous studies ERPs have been used to evaluate the effects of global familiarity (recognition) and local familiarity (repetition) of items in lists. However, the stimuli presented in these studies have frequently lacked ecological validity. In two related experiments we attempted to determine how familiarity and repetition affect processing of both naturalistic sounds and pictures. In one experiment undergraduate subjects listened to identifiable or non-identifiable environmental sounds; in another they viewed pictures of buildings from their campus mixed with those from other local campuses. In both experiments subjects indicated whether or not they could identify the items presented in two blocks of trials. Comparisons were made between familiar and unfamiliar items, and between first and second presentations. Preliminary results indicate that familiarity had little effect on the initial processing of either sounds or pictures. However, over repetitions familiar and unfamiliar sounds and pictures revealed differing effects with familiar items showing larger ERP differences between first presentations and repetitions than unfamiliar items. These differences may be due to recognition failures in the repetitions of novel stimuli.