Dynamic contour perception.

Contour in visual perception has not received an amount of attention deserved by the fundamental role it plays in all visual activities. One investigator has indicated his view of the importance of contour by writing, " . . . the matter of contour formation is one of the central phenomena of sensory psychology and nerve physiology" (1, p. 334). If visual acuity, form perception, visual contrast, and stereopsis depend primarily upon the ability of the visual system to "construct" an edge from varying patterns of energy that strike retinal receptors, then it is clear that contour must be systematically investigated if we seek to understand any visual activity. Contour is usually defined as an abrupt gradient of stimulation of adjacent areas on the retina, and this gradient is dependent upon intensity differentials in the objective field (2, 11). Ordinarily this definition is adequate but phenomena of "subjective contour," certain contrast effects, and the perception of edges of apparently moving stimuli are instances which require an extension of the definition. Perceived contour does not always depend upon an abrupt gradient in stimulation even though this is the usual stimulus correlate (5, 6). Time is required to form visual contours. The exact magnitudes for various conditions of observation, however, have not been studied systematically. Werner, neverthe-