Orientation Invariance and Geometric Primitives in Shape Recognition

Although it is generally assumed thot vision is orientation invariant, that is, that shapes can be recognized regardless of viewing angle, there is little evidence that speaks directly to this issue, ond what evidence there is fails to support orientation invariance. We propose an explanation for the previous results in terms of the kinds of shape primitives used by the visual system in achieving orientation invariance: Whereas contours are used at stages of vision thot are not orientation invariant, surfaces and/or volumes are used at stages of vision that are orientotion invariant. The stimuli in previously reported studies were wire forms, which con represented only in terms of contour. In four experiments, testing both short-term and long-term memory for shape, we replicated the previous failures of orientation invariance using wire forms, but found relatively good or perfect orientation invariance with equivalently shaped surfaces.