Judging spatial properties of simple figures

Discrimination was measured for height, area, and aspect ratio of ovals and rectangles. Random jittering of the orthogonal property (width, aspect ratio, and area) was used to control the observers' criterion. Weber fractions for aspect ratio were consistently lower than those for area, and about the same as those for height. Performance with ovals and rectangles did not differ significantly. Two different methods were employed to assess the side effects of jittering. It was found that jittering reduces the discriminability of each property, though less for aspect ratio than for height or area. The hypothesis that judgements of both area and aspect ratio are linear combination of noisy estimates of height and width predicts Weber fractions for aspect ratio and for area to be 2(1/2) times higher than those for height. Results from unjittered trials clearly reject the hypothesis with respect to aspect ratio but not for area.