BILATERAL SYMMETRY EMBEDDED IN NOISE IS DETECTED ACCURATELY ONLY AT FIXATION

Bilateral or mirror symmetry is a ubiquitous feature of biological for ms that the visual system could exploit for segmenting an object from a cluttered background. If this is so, the visual system may be prepar ed to detect symmetry at all retinal locations in parallel. Indeed, a biologically plausible model that responds optimally at axes of symmet ry is quite easy to construct. Our data show, however, that if such a mechanism exists, it works with high efficiency only at the fovea. The detection of vertical bilateral symmetry embedded in random noise is very poor unless the axis of symmetry is very close to the point of fi xation. This leads to the conclusion that symmetry does not play an im portant role in image segmentation and that it is important to the vis ual system only after it is fixated. (C) 1998 Elsevier Science Ltd. Al l rights reserved.