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Peng Zhang, Stephen Engel, Cristina Rios, Bin He, Sheng He; Binocular rivalry requires visual attention: Evidence from EEG. Journal of Vision 2009;9(8):291. doi: 10.1167/9.8.291.
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It remains an open question whether incompatible dichoptic patterns rival when attention is directed away from them. We used frequency-tagging in a steady state visual evoked potential (VEP) paradigm to track alternations in dominance of each eye's signal with and without attention. Two checkerboard patterns, flickering at different temporal frequencies (6.6 Hz and 7.5 Hz), were presented in the parafoveal visual field. An adaptive filter was used to extract the VEP amplitude of corresponding frequencies in the EEG signals with surface Laplacian spatial filtering. In a dichoptic condition, the two checkerboard stimuli were simultaneously each presented to one eye. Four subjects either attended to the checkerboards (and reported their perceptual dominance), or attended a continuously deforming ellipsoid shape that changed color at fixation (and performed a demanding shape-color conjunction detection task). VEP amplitudes to each monocular stimulus showed strong negative correlations, an indication of alternation in dominance, when subjects attended to the dichoptic checkerboards (r = −0.49). The signals also correlated well with subjects' reports of perceptual dominance. However, no reliable correlation was observed when subjects attended the dynamic ellipsoid at the fixation (r = −0.08). In a monocular “replay” condition, perceptual dominances were simulated by alternatively presenting monocular stimuli. Here VEP amplitudes showed strong negative correlations both while subjects attended to the checkerboards (r = −0.60) and while they attended to the ellipsoid at the fixation (r = −0.43). This control shows that the low correlation in the unattended dichoptic condition was not due to reduced monocular signal; signal-to-noise ratios were comparable between the unattended dichoptic and unattended replay conditions. Our results suggest that dichoptically presented incompatible stimuli only engage in binocular rivalry when attention is directed towards them.
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