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Lynn A. Olzak, Patrick J. Hibbeler; Center-surround masks operate over a narrower range of orientations and spatial frequencies than overlaid masks. Journal of Vision 2010;10(15):75. doi: 10.1167/10.15.75.
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© ARVO (1962-2015); The Authors (2016-present)
We measured the range of spatial frequencies and orientations over which masking occurs when masks are presented as annuli surrounding a center target disk. In one experiment, observers made hyperacuity-level orientation discriminations on the center disk, which contained a near-vertical, 4 cpd grating (10% contrast). In different blocks of trials, the orientation of the 4 cpd (10% contrast) mask was systematically changed away from vertical. In a second experiment, the observers made spatial frequency judgments on the center disc, and the spatial frequency of the mask was systematically changed away from 4 cpd. In the first experiment, masking disappeared between tilts of ±20-30 degrees off vertical, a much narrower range than overlaid masks, which continue to operate up to about ±80 degrees. In the second experiment, masking occurred up to about ±1 octave difference on spatial frequency. When masks are overlaid, masking occurs over a much wider range, up to ±2 octaves. These results suggest that to the extent that these types of masking reflects pooled gain control processes, the processes are in some way different between the two stimulus configurations. They may be entirely separate processes, or the processes may be the same, but a more limited pool of neurons in recruited in the center-surround configuration. Another possibility is that as the percept of the illusory contour separating center from surround becomes more salient with increasing orientation or spatial frequency differences, it acts in some way to restrict the masking/gain control process.
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