Recognizing depth-rotated objects: Evidence and conditions for three-dimensional viewpoint invariance.

Five experiments on the effects of changes of depth orientation on (a) priming the naming of briefly flashed familiar objects, (b) matching individual sample volumes (geons), and (c) classifying unfamiliar objects (that could readily be decomposed into an arrangement of distinctive geons) all revealed immediate (i.e.. not requiring practice) depth invariance. The results can be understood in terms of 3 conditions derived from a model of object recognition (I. Biederman, 1987; J. E. Hummel & I. Biederman, 1992) that have to be satisfied for immediate depth invariance: (a) that the stimuli be capable of activating viewpoint-invariant (e.g., geon) structural descriptions (GSDs), (b) that the GSDs be distinctive (different) for each stimulus, and (c) that the same GSD be activated in original and tested views. The stimuli used in several recent experiments documenting extraordinary viewpoint dependence violated these conditions. Consider Figure 1. The viewer readily appreciates that it shows two different views of the same object, despite myriad differences in the two silhouettes and in the local image features (namely, vertices, lines, and length and curvature of these lines). In general, people typically evidence little difficulty in recognizing a familiar object when they view that object from a different perspective in depth.