The symmetry magnification function varies with detection task.
Detection of the presence of bilateral symmetry was investigated at various retinal eccentricities for static and dynamic noise reflected around a vertical axis. At a low detection criterion (60% correct), peak duration sensitivities were high and varied little (<0.2 log units) from 0 masculine eccentricity to 10 masculine eccentricity for either static or dynamic targets. Duration thresholds for symmetry in dynamic noise fields were significantly higher (about 100 ms) than those for static symmetry detection (about 40 ms), despite the fact that the information was refreshed many times during the threshold presentation period. The spatial summation width for symmetry processing was evaluated with randomization around the axis of symmetry. The estimated summation width for static symmetry detection was approximately constant with eccentricity for short duration stimuli. For long duration stimuli, the summation width was substantially greater in central vision but decreased with eccentricity, the first known visual function to exhibit such reverse magnification behavior (Tyler, 1999). These findings suggest that static and dynamic symmetry detection are supported by different neural mechanisms and that these mechanisms are relatively invariant across the retina, unlike known mechanisms of spatial processing.
Tyler
C W
CW
Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA. cwt@ski.org
D001288:Attention / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological; D017603:Signal Detection, Psychological / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*