Effect of size on visual slant.

2 experiments were conducted to determine the generality of the finding by Stavrianos (1945) that judged slant of plane rectangular figures varies directly with size. In Experiment I, equal-slant contours were obtained from 54 undergraduate Ss for 14 rectangles whose lengths varied in equal log steps from 1.0 to 42.2 cm. with a reference stimulus of 7.5 cm. In Experiment II, 72 Ss were tested on 9 rectangles varying linearly in 4-cm. steps from 8 to 40 cm., with a 24-cm. reference. Observation was monocular and under complete reduction conditions from a distance of 135 cm. The effect of size on judged slant was only partly reliable in Experiment I, but highly significant in Experiment II. The "size effect" was attributed to the "perspective" cue to slant which was shown to vary with physical size as well as slant, and was probably more discriminable in the stimuli in Experiment II than in Experiment I.