Abstract

Parallel projections of rigidly rotating stimuli were studied in a kinetic depth paradigm. Five subjects viewed four types of eight-vertex object: (1) line drawings of polyhedra with randomly placed vertices: (2) line drawings of polygons with randomly placed vertices where the initial orientation was constrained to appear as a Necker cube; (3) vertex-only drawings with randomly placed vertices; and (4) vertex-only drawings with randomly placed vertices and the Necker cube constraint. Some rigidly rotating objects take on a nonrigid quality (e.g., Green,¹ Sparrow and Stine²). A five-point rating scale (1 = rigid, 5 = nonrigid) was used to indicate the perceived rigidity in all four conditions. Most of the stimuli received ratings of 1. However, the line drawings with the Necker cube constraint elicited the highest number of deformation ratings. Stimuli from the remaining three conditions received rating distributions that were not discriminable from one another. This study was replicated using a larger group of observers (N = 28). A second group (N = 27) judged the perceived direction of rotation to test Green’s² reversibility hypothesis. Finally, the observer’s ability to discriminate rigidly rotating stimuli from nonrigidly rotating stimuli was measured using TSD.

© 1988 Optical Society of America