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Jeffrey Yau, Anitha Pasupathy, Scott Brincat, Charles Connor; Dynamic synthesis of curvature in area V4. Journal of Vision 2010;10(7):911. doi: 10.1167/10.7.911.
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© ARVO (1962-2015); The Authors (2016-present)
Object perception depends on integration of small, simple image fragments (represented in early visual cortex) into larger, more complex shape constructs (represented in intermediate and higher-level ventral pathway visual cortex). We have previously described a dynamic process for shape integration in macaque monkey posterior inferotemporal cortex (PIT) (Brincat & Connor, 2006, Neuron; VSS 2008; VSS 2009). In PIT, linear tuning for individual curved contour fragments evolves into nonlinear selectivity for more complex multi-fragment configurations over a time course of approximately 60 ms. Here, we describe the antecedent stage of shape integration in area V4, which provides feedforward inputs to PIT. In V4, early responses reflect linear tuning for individual contour orientation values, comparable to orientation tuning in early visual cortex (V1, V2). These signals evolve into nonlinear tuning for curvature (change in orientation along contours) over a time course of approximately 50 ms. The emergence of V4 curvature responses matches the time course of V4-like curvature signals in PIT, implying that this dynamic process in V4 provides critical input signals to PIT. These results suggest a comprehensive model of sequential shape synthesis in the ventral pathway. Orientation signals emerge first, and are dynamically synthesized into curvature signals in V4. V4-like curvature signals appear with nearly the same time course in PIT, and are subsequently synthesized into larger, more complex shape constructs. The time course of this transformation complements an extensive body of human psychophysical and neurophysiological research showing that object perception develops over a span of several hundred milliseconds from very crude distinctions to finer categorization and identification.
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