ORIENTATION INVARIANCE AND GEOMETRIC PRIMITIVES IN SHAPE-RECOGNITION

Although it is generally assumed that vision is orientation invariant, that is, that shapes con be recognized regardless of viewing angle, t here is little evidence that speaks directly to this issue, and what e vidence there is fails to support orientation invariance. We propose a n explanation for the previous results in terms of the kinds of shape primitives used by the visual system in achieving orientation invarian ce: Whereas contours are used at stages of vision that are not orienta tion invariant, surfaces and/or volumes are used at stages of vision t hat are orientation invariant. The stimuli in previously reported stud ies were wire forms, which can represented only in terms of contour. I n four experiments, testing both short-term and long-term memory for s hape, we replicated the previous failures of orientation invariance us ing wire forms, but found relatively good or perfect orientation invar iance with equivalently shaped surfaces.