Repetition effects elicited by objects and their contexts: an fMRI study.

Event-related fMRI responses were recorded during a recognition memory test for previously studied visual objects. Some studied objects were superimposed on the same context (landscape scenes) as at study, some were superimposed on a different studied context, and some were paired with new contexts. Unstudied objects were paired with either a studied or a new context. Relative to all other stimulus classes, test stimuli where both components were unstudied elicited enhanced responses in lateral and ventral extrastriate visual cortex. This effect, which is analogous to a previously described electrophysiological result obtained with the same experimental procedure, had the same magnitude regardless of whether a test item was composed of one or two studied components, or whether a single studied component was task relevant or task irrelevant. The findings point to the existence of repetition-sensitive neural mechanisms that operate in a non-linear manner. Copyright 2003 Wiley-Liss, Inc.