The Charles F. Prentice Award Lecture 1990: specific tests and specific blindnesses: keys, locks, and parallel processing.

Classical color vision theory incorporates the concepts of hard-wired parallel independent processing and of hard-wired opponent-processing. These two powerful concepts can be applied more generally in visual psychophysics. The concept of parallel independent processing can help to understand two extremes of visual performance: disordered vision in patients and the extraordinary visual abilities of athletes and aviators. Three illustrations of this thesis are discussed. First, evidence for dissociations of spatial vision for low-contrast and high-contrast objects. Second, evidence that a binocular system for motion in depth runs in parallel with the classical disparity-driven binocular system for relative position in depth. Third, evidence that a visual system for motion-defined form parallels the well known system for contrast-defined form. However, in principle these two concepts have limited value because they do not incorporate the possibility that the functional organization of the visual pathway could be modified by descending task-dependent signals.