Object-sensitive activity reflects earlier perceptual and later cognitive processing of visual objects between 95 and 500ms.
Object-sensitive areas have been defined using functional magnetic resonance imaging (fMRI), but the time course of this cortical activation is largely unknown. In a high-density, event-related brain potential (ERP) version of a prior fMRI study of object-sensitive areas, people categorized intact grayscale pictures of known objects and discriminated them from scrambled versions created by randomizing the phases of the spatial frequency spectrum; no object or parts can be discerned in scrambled versions. Both indirect functional and direct anatomical approaches were taken to integrate ERP and fMRI results. The two-state interactive account of visual object cognition predicts object-sensitivity (intact vs. scrambled) both before and after 200ms during early and later ERPs that index processes in posterior cortex critical to visual object perception and cognition. As predicted, findings from 57 participants revealed early object-sensitive activation during the P100 (95-140ms) and VPP/N170 (145-175ms), reflecting figure-ground segregation. After 200ms, activity was object-sensitive during the frontocentral N3 complex (200-500ms) implicated in cognitive decisions about visual objects, as well as a right occipitotemporal P200 (200-300ms) implicated in perceptual grouping. All effects localized to extrastriate occipitotemporal cortex. Altogether, the findings demonstrate the time course of object-sensitive activity, which is in cortical regions defined using fMRI, and indicate that processes of figure-ground segregation (95-175ms or longer), perceptual grouping (200-300ms), and object model selection for a cognitive decision (200-530ms) are achieved more for intact known objects than uncategorizable, phase scrambled versions.
Schendan
Haline E
HE
Psychology Department, Tufts University, 490 Boston Avenue, Medford, MA 02155, USA. Haline_E.Schendan@tufts.edu
Lucia
Lisa C
LC
D000293:Adolescent; D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D002540:Cerebral Cortex / Q000502:physiology; D003071:Cognition / Q000502:physiology*; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009483:Neuropsychological Tests; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult