Perceptual specificity in visual object priming: functional magnetic resonance imaging evidence for a laterality difference in fusiform cortex

Seeing an object on one occasion may facilitate or prime processing of the same object if it is later again encountered. Such priming may also be foun d - but at a reduced level - for different but perceptually similar objects that are alternative exemplars or 'tokens' of the initially presented obje ct. We explored the neural correlates of this perceptual specificity using event-related functional magnetic resonance imaging (fMRI) procedures, cont rasting neural activity when participants made object classification decisi ons (size judgments) regarding previously presented objects (repeated same) , alternative exemplars of previously presented objects (repeated different ), or entirely new objects (novel). Many frontal regions (including bilater al frontal operculum, bilateral posterior inferior frontal/precentral, left anterior inferior frontal, and superior frontal cortices) and multiple lat e visual and posterior regions (including middle occipital, fusiform, fusif orm-parahippocampal, precuneus, and posterior cingulate, all bilaterally), demonstrated reduced neural activity for repeated compared to novel objects . Greater repetition-induced reductions were observed for same than for dif ferent exemplars in several of these regions (bilateral posterior inferior frontal, right precuneus, bilateral middle occipital, bilateral fusiform, b ilateral parahippocampal and bilateral superior parietal). Additionally, ri ght fusiform (occipitotemporal) cortex showed significantly less priming fo r different versus same exemplars than did left fusiform. These findings co nverge with behavioral evidence from divided visual field studies and with neuropsychological evidence underscoring the key role of right occipitotemp oral cortex in processing specific visual form information; possible differ ences in the representational-functional role of left fusiform are discusse d. (C) 2000 Elsevier Science Ltd. All rights reserved.