Abstract
Haxby et al. Science 293 (2001) 2425 recently argued that category-related
responses in the ventral temporal (VT) lobe during visual object
identification were overlapping and distributed in topography. This
observation contrasts with prevailing views that object codes are
focal and localized to specific areas such as the fusiform and parahippocampal
gyri. We provide a critical test of Haxby's hypothesis using a neural
network (NN) classifier that can detect more general topographic
representations and achieves 83\% correct generalization performance
on patterns of voxel responses in out-of-sample tests. Using voxel-wise
sensitivity analysis we show that substantially the same VT lobe
voxels contribute to the classification of all object categories,
suggesting the code is combinatorial. Moreover, we found no evidence
for local single category representations. The neural network representations
of the voxel codes were sensitive to both category and superordinate
level features that were only available implicitly in the object
categories.
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