title: Measurements of long-range suppression in human opponent S-cone and achromatic luminance channels.
abstract: Cortical responses to spatially discrete patches of achromatic luminance contrast can be altered by the presence of high-contrast, spatially remote "surrounds" and this achromatic "surround suppression" has been the subject of much recent research. However, the nature of long-range contrast normalization in chromatic signals has been less studied. Here we use a combination of neuroimaging data from source-imaged EEG and two different psychophysical measures of surround suppression to study contrast normalization in stimuli containing achromatic luminance and S-cone-isolating contrast. In an appearance matching task, we find strong within-channel but little between-channel suppression. However, using a contrast increment detection task, we do find evidence for weak but significant between-channel effects. Our neural measurements agree with the appearance matching data, showing significant within-channel suppression and no significant interactions between signals initiated in different pre-cortical pathways. We hypothesize that appearance judgments and V1 population responses are dominated by neurons with chromatically matched classical and extra-classical surrounds while contrast increment detection tasks rely on a subpopulation of neurons that have extra-classical surrounds sensitive to both chromatic and achromatic contrasts. Our psychophysical and source-imaged EEG results are consistent with a hypothesis based on natural scene statistics that long-range contrast normalization in early visual system is largely driven by signals within the same chromatic channel.
authors.affiliation: Smith-Kettlewell Eye Research Institute, Brain Imaging Center, CA, USA.
authors.forename: Bei
authors.initials: B
authors.lastname: Xiao
authors.forename: Alex R
authors.initials: AR
authors.lastname: Wade
mesh_terms: D000328:Adult; D003118:Color Perception / Q000502:physiology*; D055253:Color Vision / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics / Q000379:methods*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology