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J Neurosci. 2014 Jun 18;34(25):8570-84. doi: 10.1523/JNEUROSCI.1375-14.2014.

The role of visual area V4 in the discrimination of partially occluded shapes.

Author information

  • 1Department of Biological Structure, Washington National Primate Research Center, University of Washington, Seattle, Washington 98195.
  • 2Department of Biological Structure, Washington National Primate Research Center, University of Washington, Seattle, Washington 98195 pasupat@uw.edu.

Abstract

The primate brain successfully recognizes objects, even when they are partially occluded. To begin to elucidate the neural substrates of this perceptual capacity, we measured the responses of shape-selective neurons in visual area V4 while monkeys discriminated pairs of shapes under varying degrees of occlusion. We found that neuronal shape selectivity always decreased with increasing occlusion level, with some neurons being notably more robust to occlusion than others. The responses of neurons that maintained their selectivity across a wider range of occlusion levels were often sufficiently sensitive to support behavioral performance. Many of these same neurons were distinctively selective for the curvature of local boundary features and their shape tuning was well fit by a model of boundary curvature (curvature-tuned neurons). A significant subset of V4 neurons also signaled the animal's upcoming behavioral choices; these decision signals had short onset latencies that emerged progressively later for higher occlusion levels. The time course of the decision signals in V4 paralleled that of shape selectivity in curvature-tuned neurons: shape selectivity in curvature-tuned neurons, but not others, emerged earlier than the decision signals. These findings provide evidence for the involvement of contour-based mechanisms in the segmentation and recognition of partially occluded objects, consistent with psychophysical theory. Furthermore, they suggest that area V4 participates in the representation of the relevant sensory signals and the generation of decision signals underlying discrimination.

KEYWORDS:

curvature; macaque monkey; object recognition; shape processing; ventral visual pathway; visual encoding

PMID:
24948811
PMCID:
PMC4061394
DOI:
10.1523/JNEUROSCI.1375-14.2014
[PubMed - indexed for MEDLINE]
Free PMC Article
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