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Bei Xiao, Alex Wade; Interaction Between S-cone and Luminance Signals in Surround Suppression. Journal of Vision 2010;10(7):383. doi: 10.1167/10.7.383.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Neural signals driven by achromatic and S-cone isolating stimuli are processed in relatively independent early visual pathways. Although some interactions between these two types of stimuli are observed when they are presented in the same spatial location, the degree of long-range interaction is less well understood. To examine this, we measured surround suppression in spatially-separated luminance-driven and S-cone-driven signals using both behavioral psychophysics and source-imaged EEG. Methods and Results: Appearance matching: We used a psychophysical asymmetric appearance-matching task to measure perceived contrast of a central Gabor patch with a spatially-separated annular surround. We found strong suppression measured in this manner when the surround and the probe were driven by stimuli having the same chromaticities (within-channel). Suppression was absent when signals had different chromaticities (across-channel), suggesting little long-range interaction between luminance and S-cone signals for this task. Within-channel surround suppression was tuned for relative orientation and temporal frequency. Source-imaged EEG: We measured surround suppression in retinotopically-defined V1 using high-density source-imaged EEG. The neural data showed orientation tuned within-channel surround suppression. However, in contrast to the psychophysical results, we also observed weak but significant cross-channel suppression for S-cone driven centers with achromatic luminance surrounds. We hypothesized that the cross-channel interaction in the EEG might be due to indiscriminate pooling of neural responses that included neurons weakly tuned for chromaticity. Contrast modulation detection: To test this, we measured surround suppression using similar stimuli but a different psychophysical task (contrast modulation detection) that isolated a different subset of the neural population. With this task we found cross-channel interactions similar to those in the EEG. Conclusion: Luminance signal and S-cone signals are processed relatively independently in early visual system. Some neural populations experience more long-range cross-channel interactions than others and the degree of independence measured psychophysically depends on the task of choice.
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