[Abstract Title]. - Society for Neuroscience

human object selective cortex, little is known about how multiple, simultaneous objects are
encoded. Here we examined whether the neural representations of multiple simultaneouslyviewed
objects reflect the patterns evoked by each component object, or whether they reflect
entirely novel patterns of activity. We applied multivariate analyses to fMRI data collected while
subjects viewed objects belonging to four categories (brushes, chairs, shoes, and cars), presented
either singly or in pairs. Subjects performed a one-back task that required them to attend to all
items on the screen (i.e. either a single item, or both items in a pair.) We found that information
about the identities of object pairs in activity patterns of the lateral occipital complex (LOC) was
finely grained, permitting pattern classification techniques to reliably discriminate among all
pairs. To understand the rules governing the representation of object pairs, we performed a
voxel-by-voxel analysis of the relationship between responses evoked by each pair and responses
evoked by its component objects. Within individual voxels, variations in response strength across
object pairs were well-predicted by the mean of responses to the corresponding component
objects. We assessed the generality of this rule by measuring the ability of the classifier to
identify object pairs after training with synthetic “pair” responses derived from the voxelwise
means of the responses to component single items. Pair classification accuracy after training with
synthetic pair input was comparable to accuracy after training with actual pair input. These
results suggest that the representation of multiple objects in LOC is governed by response
normalization mechanisms similar to those reported in single neuron studies of macaque
extrastriate and inferotemporal cortices.
Disclosures: S.P. MacEvoy, None; R.A. Epstein, None.
Poster
260. Objects and Faces in Humans II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 260.17/BB29
Topic: D.04.j. Processing of objects and faces
Title: TMS evidence for category-selectivity in lateral occipital cortex: Triple dissociation
between faces, objects, and bodies
Authors: *D. J. PITCHER 1 , L. CHARLES 2 , J. DEVLIN 1 , V. WALSH 1 , B. DUCHAINE 1 ;
1 Univ. Col. London, Instit of Cog Neurosciene, London, United Kingdom; 2 École Normale
Supérieure, Paris, France
Abstract: Does object recognition depend on representations distributed across high-level visual
cortex or on representations in specialized modules? Functional magnetic resonance imaging
(fMRI) studies have identified category-selective areas, but these areas also carry information