The Computational Mechanism of Perception
Steven M. Lehar · Psychology Press eBooks · 2003
The basic function of visual perception can be described as the transformation from a two dimensional retinal image, or a pair of images in the binocular case, to a solid three dimensional percept. Figure 4.1 A depicts a two-dimensional stimulus that produces a three-dimensional percept of a solid cube complete in three dimensions. For simplicity, a simple line drawing is depicted in the figure, but the argument applies more appropriately to a view of a real cube observed in the world. Every point on every visible surface of the percept is experienced at a specific location in depth, and each of those surfaces is experienced as a planar continuum, with a specific three-dimensional slope in depth. The information in this perceptual experience can therefore be expressed as a three dimensional model, as suggested in Fig. 4. IB, constructed on the basis of the input image in Fig. 4.1 A. The percept also includes an amodal representation of the hidden rear face of the cube, which appears to be similar to the visible front face, that is, with equal sides and orthogonal angles. The transformation from a two-dimensional image space to a three dimensional perceptual space is known as the inverse optics problem, because the intent is to reverse the optical projection in the eye, in which three-dimensional information from the world is collapsed by the optics of the eye into a two-dimensional image. However, the inverse optics problem is underconstrained, for there are an infinite number of possible three-dimensional configurations that can give rise to the same two-dimensional projection. How does the visual system select from this infinite range of possible percepts to produce the single perceptual interpretation observed phenomenally?