Shape and slant judgments of rotated or frontoparallel ellipses were elicited from three groups of 10 subjects. A masking stimulus was introduced to control processing time. Backward masking trials were presented with interstimulus intervals of 0, 25, and 50 msec, Reduction of processing time altered shape judgments in the direction of projective shape and slant judgments in the direction of frontoparallelness. This finding is consistent with the shapeslant invariance hypothesis. In order to

more »

... dy the effects of processing load, one group of subjects was given prior knowledge of the kind of judgment to be made on each trial, one group had no prior knowledge, and a third group made both judgments on each trial. The effects of the processing load manipulation were interpreted in terms of the role of attention in perceptual encoding. Consistent with previous findings, allocation of attention did not affect perceptual encoding. Leibowitz and Bourne (1956) found that exposure duration affected the shape judgment of a circle rotated in depth. Reduction of exposure duration was accompanied by deviations from shape constancy, shape matches that were in closer agreement with projective shape than with objective shape. For exposure durations of 100 msec and less, the matches conformed perfectly to projective shape, that is, the subject selected as a match an elliptical shape equal to the frontoparallel projection of the rotated circle. The effect of exposure duration is analogous to the effect of reduction of depth information in a variety of perceptual constancy experiments (