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Kestas Kveraga, Avniel Ghuman, Karim Kassam, Elissa Aminoff, Matti Hamalainen, Maximilien Chaumon, Moshe Bar; Early activation of contextual associations during object recognition. Journal of Vision 2010;10(7):1192. doi: 10.1167/10.7.1192.
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© ARVO (1962-2015); The Authors (2016-present)
Our visual system relies on stored memory associations to achieve recognition. Objects in natural scenes tend to be grouped by a particular semantic context and these contextual associations are employed during object recognition. Behavioral research has demonstrated that stimuli congruent with the scene context are recognized more easily than incongruent stimuli (e.g., Palmer, 1975; Biederman et al., 1982; Davenport and Potter, 2004). Investigations of context-related activity using fMRI (e.g. Bar and Aminoff, 2003; Aminoff et al., 2008, Peters et al., 2009) revealed a network of regions that are consistently engaged by contextual associations of objects and scenes. This network comprises the parahippocampal cortex (PHC), retrosplenial complex (RSC), and medial prefrontal cortex (MPFC). To understand how this context network is recruited and activated to facilitate recognition, one needs to first reveal its temporal and connectivity properties. Therefore, we investigated the spatiotemporal dynamics of contextual association processing here with a combination of fMRI and magnetoencephalography (MEG). We contrasted the neural response to objects with strong contextual associations (SCA) with the response elicited by weak contextual associations (WCA). Both fMRI and MEG responses revealed stronger activations in the context network for the SCA vs. WCA comparison. To explore the spatiotemporal dynamics of this process, we analyzed the phase synchrony, a measure of neural coupling, in the MEG data. The results show stronger overall phase synchrony for SCA objects than for WCA objects within the context network. Furthermore, we found an early, enhanced phase synchrony between the visual cortex and PHC, followed by PHC-RSC, and then by somewhat later RSC-MPFC coupling, occurring mainly in the beta band between 150-450 ms. Our findings reveal for the first time the spatiotemporal and connectivity properties of context processing. Implications of these findings to our understanding of how contextual information is used during recognition will be discussed.
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