The effect of viewing slant and distance on some visual illusions

Abstract
This study is concerned with the effect of (a) viewing slant and (b) viewing distance on the perception of 9 illusions which involve straight parallel lines or squares embedded in geometrical patterns. 32 Ss, all of them University students, took part in the experiment. The results show (a) that at a reduced viewing slant the illusory effect disappears with all 9 stimulus figures, the required viewing slant being greater for squares than for parallel lines, (b) that the illusory effects disappear as a function of distance of observation with all 9 stimulus figures, the distance varying from one figure to another. The disappearance of such effects is considered to be a function of fixations on the illusory patterns.

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