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Joseph S Lappin, Duje Tadin, Anup Panduranga; Center-surround antagonism affects visual motion coherence. Journal of Vision 2003;3(9):272. doi: 10.1167/3.9.272.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Motion responses of many cells in the macaque area MT exhibit center-surround antagonism. Recently, we discovered a surprising psychophysical correlate of this physiological effect: Duration thresholds for discriminating directions of brief moving Gabors increase substantially when spatial area and contrast exceed critical values (e.g., Tadin & Lappin, VSS 02). The present study extended this finding to partially correlated random-dot kinematograms (RDKs). We asked two questions: (1) Does increasing the size of a moving pattern reduce its visual signal/noise ratio? (2) Is the signal/noise of a central pattern enhanced by an oppositely moving surround?
Methods: RDKs appeared in Gaussian spatial and temporal windows. A Quest procedure adjusted the percentage of pixels maintaining the same value (black or white) between adjacent frames (120 Hz), with the remaining pixels independently regenerated. One experiment measured correlation thresholds for discriminating directions of brief (2s = 16–64 ms) patterns of varied spatial area (15–300 arcmin diameter). Another experiment evaluated correlation thresholds for discriminating correlated from uncorrelated central patterns surrounded seamlessly by RDKs moving the same or opposite direction.
Results: With increasing size, spatial summation initially produced lower correlation thresholds at small sizes, but further size increases produced spatial suppression. The largest patterns had the highest thresholds. Correlation thresholds were also higher when the surrounding pattern moved the same direction than when it moved the opposite direction.
Conclusion: Signal/noise ratios of visual motion signals are context-sensitive, apparently involving early spatial differentiation.
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