Viewing angle and the perceived orientation of pictorial elements: geometric or representational effects?

The role of geometric shape properties in determining the perceived orientation (heading) change of picture elements was investigated in four experiments. In experiment 1 the systematic change in perceived heading of each of a depicted team of horses which projected irregular geometric shapes was measured. In experiment 2, involving silhouettes, the perceptual axes of these same horse shapes, together with those of a pair of enantiomorphic deltoid shapes, were derived. These derived shape axes were used in experiment 3, along with single oblique contours, to determine the degree of heading shift as a function of the complexity and orientation of the shape. The degree of heading shift was remarkably similar for both silhouette shapes and the single contours when the axes were oblique but, whereas vertical orientation was predicted to abolish heading shift, this was only true for the deltoid shapes. In experiment 4 a possible explanation of the nonpredicted heading shift for the vertically oriented horse silhouettes was investigated. Subjects' individual estimates of the axes of the horse shapes, rather than a group mean value, were used to set the horse shapes to the vertical. When viewing was from two positions no significant heading change with view was found. Taken as a whole the data suggest that the geometric properties of patterns, rather than their representative nature, determine the very obvious heading shift when pictures are viewed from different angles.