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Population coding of shape in area V4

Abstract

Shape is represented in the visual system by patterns of activity across populations of neurons. We studied the population code for shape in area V4 of macaque monkeys, which is part of the ventral (object-related) pathway in primate visual cortex. We have previously found that many macaque V4 neurons are tuned for the curvature and object-centered position of boundary fragments (such as 'concavity on the right'). Here we tested the hypothesis that populations of such cells represent complete shapes as aggregates of boundary fragments. To estimate the population representation of a given shape, we scaled each cell's tuning peak by its response to that shape, summed across cells and smoothed. The resulting population response surface contained 3–8 peaks that represented major boundary features and could be used to reconstruct (approximately) the original shape. This exemplifies how a multi-peaked neural population response can represent a complex stimulus in terms of its constituent elements.

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Figure 1: Single neuron shape-tuning example.
Figure 2: Population response to an example shape.
Figure 3: Population responses to the 49 basic shapes, each at one orientation.
Figure 4: Population coding accuracy.

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Acknowledgements

Technical assistance was provided by W. Nash and B. Sorenson. A.J. Bastian, K.O. Johnson, T. Poggio and M. Riesenhuber made helpful comments on previous versions of the manuscript. This work was supported by the National Eye Institute and by the Pew Scholars Program in the Biomedical Sciences.

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Correspondence to Charles E. Connor.

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Pasupathy, A., Connor, C. Population coding of shape in area V4. Nat Neurosci 5, 1332–1338 (2002). https://doi.org/10.1038/972

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