Spectral Receptive Fields Do Not Explain Tuning for Boundary
نویسندگان
چکیده
23 24 The mid-level visual cortical area V4 in the primate is thought to be critical for the neural 25 representation of visual shape. Several studies agree that V4 neurons respond to 26 contour features, e.g., convexities and concavities along a shape boundary, that are 27 more complex than the oriented segments encoded by neurons in the primary visual 28 cortex. Here we compare two distinct approaches to modeling V4 shape selectivity: one 29 based on a spectral receptive field (SRF) map in the orientation and spatial frequency 30 domain and the other based on a map in an object-centered angular-position and 31 contour curvature space. We test the ability of these two characterizations to account 32 for the responses of V4 neurons to a set of parametrically designed two-dimensional 33 shapes recorded previously in the awake macaque. We report two lines of evidence 34 suggesting that the SRF model does not capture the contour sensitivity of V4 neurons. 35 First, the SRF model discards spatial phase information, which is inconsistent with the 36 neuronal data. Second, the amount of variance explained by the SRF model was 37 significantly less than that explained by the contour curvature model. Notably, cells best 38 fit by the curvature model were poorly fit by the SRF model, the latter being appropriate 39 for a subset of V4 neurons that appear to be orientation tuned. These limitations of the 40 SRF model suggest that a full understanding of mid-level shape representation requires 41 more complicated models that preserve phase information and perhaps deal with object 42 segmentation. 43
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