DETERMINANTS OF STABILITY IN THE PERCEPTION OF SUBJECTIVE CONTOURS

The Present study constituted an initial experimental effort to examin e the fragmentation characteristics of subjective contours within the photopic and upper scotopic ranges of illumination. Four stimulus fact ors known to influence the visibility of subjective contours-target lu minance, inducing area size and contrast, and contour orientation-were examined. Results indicated that subjective contours are indeed unsta ble perceptual phenomena. On the average, fragmentation or fading occu rred after only 15 sec of observation, and some form of stimulus outag e was present for 28% of the viewing time of each stimulus. Fragmentat ion latency was significantly shorter and total time in fragmentation longer for diamond than for square contours, and total time in fragmen tation varied inversely with inducing-area size. Fragmentation tended to occur in whole units rather than in isolated elements, a result rem iniscent of the fading of real contours under impoverished viewing con ditions.