document: The limits of shape constancy : point-to-point mapping of perspective projections of flat figures The present experiments investigate point-to-point mapping of perspective transformations of 2D outline figures under diverse viewing conditions : binocular free viewing , monocular perspective with 2D cues masked by an optic tunnel , and stereoptic viewing through an optic tunnel . The first experiment involved upright figures , and served to determine baseline point-to-point mapping accuracy , which was found to be very good . Three shapes were used : square , circle and irregularly round . The main experiment , with slanted figures , involved only two shapes-square and irregularly shaped-showed at several slant degrees . Despite the accumulated evidence for shape constancy when the outline of perspective projections is considered , metric perception of the inner structure of such projections was quite limited . Systematic distortions were found , especially with more extreme slants , and attributed to the joint effect of several factors : anchors , 3D information , and slant underestimation . Contradictory flatness cues did not detract from performance , while stereoptic information improved it
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