Research into visual perception is currently dominated by three types of investigation: neurophysiology, psychophysics and computational studies. A complete understanding of a visual task requires a synthesis of all three. At present, our conception of the mechanisms of early vision is mainly derived from psychophysics and neurophysiology, and from these has emerged in recent years a fairly robust theory of the initial stages of vision. It is now widely accepted that early visual processes are served by multiple, independent, band-pass filters, each acting approximately linearly. The theory explains many phenomena in the vision of low-contrast repetitive patterns, but little progress has been made in understanding its implications in the more “natural” case of high-contrast, non-repetitive patterns. We have good reason to believe that the same mechanisms operate. Neurophysiological studies have shown that the single neural units which are assumed to underlie the psychophysically determined channels do not greatly change their properties in high-contrast conditions . Furthermore, some aspects of high-contrast vision, such as the spatial frequency shift , and the frequency specific disruption of contrast matching after adaptation , make it likely that the band-pass channels at work in low-contrast conditions also serve high-contrast vision.
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