Vision is by far the most dominant human sense, one to which at least half of the cerebral cortex is devoted. My students and I study the visual system using psychophysical methods. One of our primary interests is in the role of color in a variety of visual tasks. For example, we have examined the extent to which fine spatial discriminations can be accurately made when the only available information is based upon color differences in the stimulus. We find that spatial vision using only color information is surprisingly good. We have also looked at the ways in which color and luminance variations interact when both are present, as is normally the case. Under some conditions we find that color is profoundly dominant, greatly decreasing the usefulness of luminance cues.
One of our major current interests is in the visual analysis of motion, particularly motion defined by color changes. We have devised new methods that allow us to compare motion sensitivity based upon color to that based upon luminance in very direct and instructive ways. Our current results suggest that the visual system analyzes chromatic motion as though it were a second-order stimulus--that is, it makes explicit positional comparisons over time. Luminance motion, however, is generally analyzed by first-order mechanisms that respond directly to the Fourier motion energy in a moving pattern. We are now examining several possible explanations for the failure of the first-order motion system in color.
A third interest is in the way the visual system codes information about spatial position and object characteristics. Our studies suggest that position does not just reflect the direct, low-level retinotopicity of the visual projection, but rather that it is encoded in a more explicit and more complex manner that takes into account the characteristics of the object that is being localized. The local position of object features both affects and is affected by other perceived object characteristics, as well as by the subject's state of attention.
De Valois, R. L. & De Valois, K. K. (1988). Spatial vision. New York: Oxford University Press.
De Valois, K. K., Lakshminarayanan, V., Nygaard, R., Schlussel, S., & Sladky, J. (1990). Discrimination of relative spatial position. Vision Research, 30, 1649-1660.
De Valois, K. K. & Kooi, F. L. (1991). Functional classification of parallel visual pathways. In A. Valberg & B. B. Lee (Eds.), From pigments to perception. New York: Plenum.
Kooi, F. L. & De Valois, K. K. (1992). The role of color in the motion system. Vision Research, 32, 657-668.