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Elissa Aminoff, Moshe Bar; Frequency of exposure modulates cortical activity in the contextual associations network. Journal of Vision 2010;10(7):744. doi: 10.1167/10.7.744.
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Objects are typically encountered embedded in a context with other objects, rather than appearing in isolation. The parahippocampal cortex (PHC) and the retrosplenial complex (RSC) are major components in a network that is more active for stimuli with such typical contextual associations compared with stimuli with weak contextual associations. Contextual processing provides a bridge between previous research that ascribed spatial functioning to the PHC and RSC and other research that demonstrated that these areas mediate episodic memory. Here we aimed to enrich this bridge by asking what is the effect of frequency of occurrence on activation in this network. The idea was that highly contextual objects that are encountered more often would elicit more associations than objects with weak contextual associations, and even compared with other highly contextual objects if these are not encountered as frequently. Participants viewed four types of objects in an fMRI scanning session: strongly contextual objects that are encountered frequently, strongly contextual objects that are encountered rarely, weakly contextual objects that are encountered frequently, and weakly contextual objects that are encountered rarely. Both strength of contextual associations and frequency of occurrence were determined using surveys. First, as has been shown before, activation in the context network demonstrated a strong main effect of context, whereby activation increased significantly for strong context compared with weak context. More importantly, both the RSC and the PHC were more active for frequent objects than to rare objects, supporting our context-related hypothesis. We will discuss the difference between the exposure effect on RSC and on PHC, and will also tie exposure to the potential role of the prefrontal cortex in the interaction between context, number of associations and frequency of occurrence.
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