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Critical problems in spatial vision.

In recent years the study of spatial vision seems to have come almost full circle. Localized stimuli (such as lines, bars, and edges) were abandoned in favor of textured patterns (such as sinusoidal gratings), a trend that was accelerated by the discovery that gratings of sufficiently different spatial frequencies or orientations (stimuli localized in the Fourier domain) were detected independently. This led to various attempts to model form vision in terms of spatial frequency analysis. More recently there has been a shift toward models that include, once again, the local aspects of spatial processing; this trend is more consistent with both retinal and cortical physiology. (Still surviving is the notion of a complete set of orthonormal basis functions, but not sinusoidal ones.) Other important developments include attempts to model spatiotemporal interaction, and the discovery that spatial processing takes on an entirely different character in the absence of any temporal variation (i.e., when the retinal image is stabilized). We attempt to trace these developments in terms of a selected group of representative studies, which we examine in some depth.