Component processes in the perception of bilaterally symmetric dot textures

Abstract

If a random-dot texture is reflected about a given axis, the resulting bilateral symmetry is immediately detected. In order to account for this ability, it has been suggested that the visual system detects reflection in these dot textures because of the existence of a symmetric neural organization, centered about the fovea, which performs a point-by-point analysis. As yet, there is no evidence of such an organization in the human visual system. An alternative description of a bilaterally symmetric texture, that of a two-dimensional distribution of uniformly oriented point-pair elements, of nonuniform size and with collinear midpoints, is more consistent with known mammalian visual-system neurophysiology. Experiments were conducted in order to determine whether the human visual system is sensitive to the orientational uniformity of otherwise nonuniform point-pair elements and to their midpoint collinearity. The results indicate that there are three processes involved in the perception of bilaterally symmetric dot textures: the detection of orientational uniformity of the different sized point-pair elements; the fusion of salient element point-pairs into a salient feature; the detection of the symmetry of the resulting feature. This component-process hypothesis eliminates the necessity to postulate the existence of a symmetrical neural organization centered about the fovea.