[Quantitative studies on discrimination of simple geometric patterns and related visual illusions]

Using quantitative psychophysical measurements, the abilities in discriminating some simple geometric patterns and the related visual illusions (Zoellner, Muller-Lyer, Ponzo and Delboeuf illusions) were investigated under luminance contrast (LC) and isoluminance color contrast (ICC). The results showed that the subjects possessed identical abilities in discriminating parallelity, length and area, and illusory distortion perceived for these geometric properties were of the same strength, no matter the figures were displayed by LC or ICC. The contour- and border illusions, however, vanished at ICC. The minimum contrast inducing contour and border illusions (1.8% and 5.3%, respectively) was considerably lower than that inducing parallelity illusion (15%). These imply that simple geometric properties and contours (or borders) of visual images may be separately transmitted by different visual pathways.