Attention modulates S-cone and luminance signals differently in human V1

摘要

INTRODUCTION: Attention modulates the steady-state EEG response to luminance and (L-M)-cone gratings by altering the response amplitude and phase (DiRusso et al, 2001). However, little is known about attention modulation in short-wave (Sa??cone) pathways. We used a combination of steady stage, source-imaged EEG and fMRI to extract luminance and S-cone contrast response functions (CRFs) in retinotopic human V1. We then evaluated how attention affected these CRFs as well as the temporal phase of each component. METHODS: 12 subjects viewed a series of on/off flickering Gabor patches (2cpd, 6Hz, duration 10s) defined by either luminance or S-cone contrast. The contrast and color of each patch were chosen at random. S-cone stimuli were presented at 10, 20, 40 or 80% contrast and luminance stimuli at 5, 10, 20 or 40%. Subjects performed one of two attentional tasks. 1: Detecting near-threshold contrast decrements. 2: Detecting target letters among distracters. Performance was around 75% correct on both tasks. Each combination of contrast, attentional condition and chromaticity was presented 10 times while we collected high-density EEG data. We computed the steady-state, visual evoked current density timecourses in retinotopically-defined V1 using a minimum norm inverse and boundary element models of individual heads. Finally, we extracted the phase and amplitude of the stimulus-driven responses. RESULTS: Luminance and S-cone stimuli generated qualitatively different responses. The amplitude, but not the phase of luminance responses changed with increasing stimulus contrast while S-cone-driven responses showed systematic phase changes in addition to amplitude changes. Attending to the contrast of the Gabor changed the amplitude but not the phase of the luminance responses, consistent with a contrast gain change. Attention changed the phase, rather than the amplitude of S-cone-driven responses. CONCLUSION: Attention affects S-cone and Luminance pathways differentially. This may reflect their segregation in the early visual system.