The object-based P2d effect in the current experiment was found over the contralateral hemisphere and localized to the contralateral LOC. This is consistent with studies demonstrating spatial selectivity in the LOC (Aggelopoulos & Rolls,
2005; DiCarlo & Maunsell,
2003; Larsson & Heeger,
2006; MacEvoy & Epstein,
2011; Martínez et al.,
2006; Martínez, Ramanathan, et al.,
2007; Martínez, Teder-Sälejärvi, & Hillyard,
2007; McKyton & Zohary,
2007; Niemeier, Goltz, Kuchinad, Tweed, & Vilis,
2005; Strother et al.,
2011; Yoshor, Bosking, Ghose, & Maunsell,
2007), and points to the close interaction between the “space” and “object” systems in the brain (e.g., Faillenot, Decety, & Jeannerod,
1999; Kravitz & Behrmann,
2011; Merigan & Maunsell,
1993). The fact that the object-based P2d enhancement localized to the LOC adds to the growing body of literature that implicates this critical region in object perception, both in functional magnetic resonance imaging (fMRI; e.g., Grill-Spector et al.,
1999,
2001; Grill-Spector & Sayres,
2008; Malach et al.,
1995) and EEG/ERP (e.g., Martínez et al.,
2007) experiments. Indeed, recent fMRI experiments using the ambiguous diamond display found that activity in the LOC increased and activity in V1 decreased during object perception versus fragment perception (Fang et al.,
2008; Murray & Kersten,
2002). The results from the current experiment support and extend those findings, suggesting that increased activity in the LOC during object perception also results in additional processing of visual elements associated with the object (i.e., occurring within its boundaries). This may reflect a figural enhancement process that integrates the new elements with the existing object percept, as has been demonstrated for figure-selective neurons in early visual areas V1 and V2 (e.g., Hung et al.,
2007; Lamme,
1995; Lamme et al.,
1998; Qui et al.,
2007; Zhang & von der Heydt,
2010; Zipser et al.,
1996). In a more recent fMRI study, Caclin and colleagues (
2012) manipulated contrast, motion, and shape separately in the ambiguous diamond display and compared bistable and unambiguous (i.e., externally changing) percepts of the object versus fragments. For both bistable and unambiguous displays, they found increased activity in ventral and occipital regions during perception of the bound object, and greater activity in motion-related dorsal areas during fragment perception. Further, they found that the different feature manipulations preferentially modulated regions sensitive to those features, with enhanced activity in dorsal areas (i.e., hMT+) than ventral and occipital areas for the motion display and
vice versa for the shape and contrast displays. In the present study we attempted to remove stimulus-related activity from that related to the probe by subtracting activity in the no-probe trials from activity in the probe trials. Specifically, we used this subtraction method to remove motion-related activity in order to focus on perceptual processing of the probes as a function of perceptual state (see
Supplementary Figure 2 for data without this subtraction method). As such, we did not design our study to examine motion processing or form-motion binding
per se. An interesting avenue for future research could investigate if the integration of different features (e.g., motion, color) differentially modulates the P2d.