Color Constancy of V1 Double Opponent Cells to Natural Images

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Event Abstract Back to Event Color Constancy of V1 Double Opponent Cells to Natural Images The human visual system perceives colors of objects as largely independent of the lighting conditions even though the spectral composition of the incident light, and thus of the light reflected off objects and reaching the eye, can be very different under different types of lighting (such as midday sun, sunset, fluorescent or incandescent light). The ability to maintain constant perception of object color is called color constancy, and its neural basis remains unknown. Neurons in the retina and lateral geniculate nucleus (LGN) do not show response properties consistent with color constancy, indicating that this computation is performed at a subsequent stage of neural processing. The critical computation underlying color constancy is a comparison of the relative cone activations across visual space. Recent studies have confirmed the existence of double-opponent cells in V1 that, in principle, have the appropriate receptive field structure to contribute to color constancy: they are sensitive not to absolute cone responses but rather to differences in cone responses both across cone types (cone opponency) and across space (spatial opponency). To test the hypothesis that double-opponent cells contribute to color constancy we compare the color constancy of experimentally characterized V1 neurons to that of model LGN neurons and model V1 neurons constructed on the basis of physiological measurements. We use experimentally measured receptive fields of V1 double-opponent cells in alert macaque monkeys (Conway, 2001; Conway and Livingstone, 2006). To model the responses of a neuron population tiling a portion of the visual field, each measured receptive field was spatially convolved with natural images both before and after a simulated change in lighting conditions (modeled by a von Kries transformation). Natural images were taken from Olmos and Kingdom (2004). We show that, due to their double-opponent structure, both the physiologically characterized and model V1 cells show stronger color constancy in response to natural images than the model LGN neurons. We quantify the improvement across a range of different recorded cells and natural images. We further quantify the effects of receptive-field shape and cone-type balance upon the color constancy of V1 double-opponent cells by comparing the recorded V1 cells to model V1 cells with different surround shapes and balances of L, M, and S cone contributions. Finally, we consider the effect of contrast normalization by the responses of neighboring neurons and generate experimental predictions for the influence of contrast normalization on color constancy. Acknowledgments: This work was supported by the Whitehall Foundation (BC); and the Sloan Foundation, UC Davis, and a UC Davis Ophthalmology Research to Prevent Blindness grant (MG,DF).