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Bei Xiao, Alex. R. Wade; Surround suppression between S-cone and luminance signals measured with psychophysics and source-imaged EEG. Journal of Vision 2009;9(14):49. doi: 10.1167/9.14.49.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To characterize the interaction of S-cone driven signals and luminance signals in the early visual pathways and in perception, we used psychophysics and source-imaged EEG to measure surround suppression (SS) of S-cone signals, luminance signals and the interactions between them.
Psychophysics: Observers were asked to match the contrast level of a test stimulus to that of a target. The target was a Gabor patch presented in isolation and the test was a similar Gabor patch presented either in isolation or within an annular surround. The probe and surround were defined by either S-cone or luminance contrast. The probe flashed at 6Hz and the surround drifted at 5cpd. The relative orientation of the probe and the surround were either co-linear or orthogonal to each other. For collinear conditions, the results showed that S-cone surrounds suppressed the apparent contrast of S-cone probes by 40% and luminance surrounds also suppressed luminance probes by 40%. For orthogonal conditions, SS for both within-channel stimuli were reduced to 30%. In addition, we found that both slow drifting (1cpd) and fast-drifting (10cpd) S-cone surrounds suppressed the S-cone probes with significantly more suppression from the slow surrounds. The initial data showed no significant cross-channel surround suppression.
Source-imaged EEG: We used high-density source-imaged EEG to measure surround suppression of neural responses. Stimuli were presented peripherally and consisted of 6 Gabor patches with annular surrounds. The probes and the surrounds were matched in almost all respects (chromaticity, relative orientation, contrast level and temporal and spatial frequency) to those used in the psychophysical experiments. We measured the amplitude of the frequency tagged responses due to the probe in V1. The results were similar to the psychophysics except that the effect of orientation on within-channel SS was not significant. S-cone driven surrounds suppressed the responses amplitude of S-cone probes by 50%; luminance surrounds suppressed luminance probes by 40%. For both orientations, luminance surrounds weakly suppressed S-cone probes by 20% and S-cone surrounds did not suppress luminance probes. We also found that within S-cone signals the slow surrounds suppressed the probes much more than the fast surrounds, which was similar as the psychophysics results.
Conclusion: Our psychophysical and source-imaged EEG measurements suggest that luminance and S-cone pathways are relatively independent at the site where surround suppression is implemented.
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