For the past few years we have sought to clarify the manner in which the brain computes and represents the surface properties of objects such as their brightness and color. From a neurobiological perspective this is a challenge because, in the absence of contrast, brightness and color are not effective stimuli for activating most neurons. Our past physiological and psychophysical experiments suggest that these surface properties are computed through neural interactions over a range greatly exceeding the size of receptive fields in the retina and striate cortex. Our ongoing research is aimed at clarifying the nature of these neural interactions and their locations in the brain, with the ultimate goal of understanding the neural basis of perception. Neural correlates of brightness in the responses of neurons in the retina, LGN, and primary visual cortex.
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The representation of brightness in primary visual cortex. Filling-in percepts produced by luminance modulation. Temporal limits of brightness induction and mechanisms of brightness perception. Feature-specific effects of selective visual attention. If there is steady illumination of the receptive field, modulation of light outside the receptive field causes the central gray area to perceptually appear to vary between light and dark.