[Processing of asymmetrical noise in two- and three-dimensional global symmetry]

We investigated how the visual system processes asymmetrical noise in globally symmetrical patterns, and how much noise the visual system needs to discriminate between the perfectly symmetrical and imperfectly symmetrical patterns. Two experiments were carried out in which subjects were required to discriminate between the above patterns. This task was equivalent to a kind of the visual search task because subjects had to search for some targets asymmetrical dot pairs in two-dimensional (Experiment 1) or in three-dimensional mirror symmetry of dot patterns (Experiment 2). The results showed that the visual system processes noise largely in parallel in the two-dimensional symmetry, but largely in serial in the three-dimensional symmetry. In addition, analyses of the percent correct data suggested that the mechanism involved in detecting both the two- and three-dimensional symmetries in activated even by the patterns with a small amount of noise.