Recent reports of a high response to bodies in the fusiform face area (FFA) challenge the idea that the FFA is exclusively selective for face stimuli. We examined this claim by conducting a functional magnetic resonance imaging experiment at both standard (3.125 x 3.125 x 4.0 mm) and high resolution (1.4 x 1.4 x 2.0 mm). In both experiments, regions of interest (ROIs) were defined using data from blocked localizer runs. Within each ROI, we measured the mean peak response to a variety of stimulus types in independent data from a subsequent event-related experiment. Our localizer scans identified a fusiform body area (FBA), a body-selective region reported recently by Peelen and Downing (2005) that is anatomically distinct from the extrastriate body area. The FBA overlapped with and was adjacent to the FFA in all but two participants. Selectivity of the FFA to faces and FBA to bodies was stronger for the high-resolution scans, as expected from the reduction in partial volume effects. When new ROIs were constructed for the high-resolution experiment by omitting the voxels showing overlapping selectivity for both bodies and faces in the localizer scans, the resulting FFA* ROI showed no response above control objects for body stimuli, and the FBA* ROI showed no response above control objects for face stimuli. These results demonstrate strong selectivities in distinct but adjacent regions in the fusiform gyrus for only faces in one region (the FFA*) and only bodies in the other (the FBA*).

Separate face and body selectivity on the fusiform gyrus

Recent evidence suggests that blindness enables visual circuits to contribute to language processing. We examined whether this dramatic functional plasticity has a sensitive period. BOLD fMRI signal was measured in congenitally blind, late blind (blindness onset 9-years-old or later) and sighted participants while they performed a sentence comprehension task. In a control condition, participants listened to backwards speech and made match/non-match to sample judgments. In both congenitally and late blind participants BOLD signal increased in bilateral foveal-pericalcarine cortex during response preparation, irrespective of whether the stimulus was a sentence or backwards speech. However, left occipital areas (pericalcarine, extrastriate, fusiform and lateral) responded more to sentences than backwards speech only in congenitally blind people. We conclude that age of blindness onset constrains the non-visual functions of occipital cortex: while plasticity is present in both congenitally and late blind individuals, recruitment of visual circuits for language depends on blindness during childhood.

A sensitive period for language in the visual cortex: Distinct patterns of plasticity in congenitally versus late blind adults

Selective attention may be flexibly directed toward particular locations in the visual field (spatial attention) or to entire object configurations (object-based attention). A key question is whether spatial attention plays a direct role in the selection of objects, perhaps by spreading its facilitatory influence throughout the boundaries of an object. We studied the relationship between spatial and object-based attention in a design in which subjects attended to brief offsets of one corner of a real or illusory square form. Object-selective attention was indexed by differences in event-related potential (ERP) amplitudes and blood oxygen level-dependent (BOLD) activations to unattended corner offsets in conditions in which the objects were intact versus fragmented or absent. This design ensured that object-based attention effects were not an artifact of attention being guided by simple directional cues such as parallel lines, which may have occurred in previous studies. Both space-based and object-based attention were associated with enhanced negative ERPs (N1 component at 140 - 180 ms) that were colocalized with BOLD activations in lateral occipital cortex (LOC). These results provide physiological evidence that directing spatial attention to one part of an object (whether real or illusory) facilitates the processing of the entire object at the level of the LOC and thus contributes directly to object-based selective attention.

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The role of spatial attention in the selection of real and illusory objects - eScholarship

Angular Gyrus Involvement at Encoding and Retrieval Is Associated with Durable But Less Specific Memories

Does the brain's ventral visual pathway compute object shape?

Thestages ofintegration leading fromlocal feature analysis toobject recognition wereexplored inhuman visual cortex byusing thetechnique offunctional magnetic resonance imaging. Herewereport evidence forobject-related activation. Suchactivation waslocated atthelateral-posterior aspect oftheoccipital lobe, just abutting theposterior aspect ofthemotion-sensitive areaMT/V5,inaregion termed the lateral occipital complex (LO). LOshowedpreferential acti- vation toimages ofobjects, compared toawiderangeof texture patterns. Thisactivation wasnotcaused byaglobal difference intheFourier spatial frequency content ofobjects versus texture images, since object images produced enhanced LOactivation compared totextures matched inpowerspectra butrandomized inphase. Thepreferential activation toob- jects alsocould notbeexplained bydifferent patterns ofeye movements: similar levels ofactivation wereobserved when subjects fixated ontheobjects andwhentheyscanned the objects withtheir eyes. Additional manipulations suchas spatial frequency filtering anda4-fold change invisual size didnotaffect LO activation. Theseresults' suggest thatthe enhanced responses toobjects werenotamanifestation of low-level visual processing. A striking demonstration that activity inLOisuniquely correlated toobject detectability was produced bythe"Lincoln" illusion, inwhichblurring of objects digitized intolarge blocks paradoxically increases their recognizability. Suchblurring ledtosignificant en- hancement ofLOactivation. Despite thepreferential activa- tion toobjects, LO didnotseemtobeinvolved inthefinal, "semantic," stages oftherecognition process. Thus,objects varying widely intheir recognizability (e.g., famous faces, commonobjects, andunfamiliar three-dimensional abstract sculptures) activated ittoasimilar degree. Theseresults are thusevidence foranintermediate linkinthechainofpro- cessing stages leading toobject recognition inhumanvisual cortex.

/pdf/object-related-activity-revealed-byfunctional-magnetic-1a8vllt6eu.pdf

R. R. Benson

Papers

Object-related activity revealed byfunctional magnetic resonance imaging inhumanoccipital cortex