Subjective Contours, Visual Acuity, and Line Contrast

Overall brightness decrease observed in the Ehrenstein illusion induced for both contrast polarities

“…Spillmann (1985) reviewed the peculiarities of the Ehrenstein illusion and related phenomena as clarified by phenomenological, psychophysical, and neurophysiological approaches. Up to now, the amount of assimilation occurring in the background of an Ehrenstein pattern has been described only qualitatively (Ehrenstein, 1941;Day & Jory, 1978;it has not yet been investigated quantitatively. The present study investigated the following quesThis research was supported by Grants-in-Aid for Scientific Research (59710073,60510066) …”

The effects of perceptual set on the shape and apparent depth of subjective contours

“…The first attributes their existence to physiological mechanisms. Most subjective-contour figures show systematic brightness effects; therefore, the same mechanisms that account for brightness contrast have been used to explain the emergence of these figures (Brigner & Gallagher, 1974;Coren & Theodor, 1977;Day & Jory, 1978Frisby & Clatsworthy, 1975;Jory & Day, 1979). Other investigators have suggested that subjective contours arise from the interactions among the receptive fields of orientation-specific cortical cells (Jung;1973;Jung & Spillman, 1970;Kennedy, 1979;Smith & Over, 1975, 1979 or that they are due to Fourier analysis processes in the visual system (Becker & Knopp, 1978;Ginsburg, 1975).…”

Illusory figures: Individual differences apparent depth and lightness

“…Altenatively, given the regular spacing of the repeated bar elements in the present pattern, assimilation ofdarkness between the bars (cf. Day & Jory, 1978) would seem to be a likely candidate for the illusory lightness effect seen here.…”