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Janine Mendola, Athena Buckthought, Jeremy Fesi; Special role of parietal cortex in binocular rivalry demonstrated by fMRI comparison with stimulus rivalry. Journal of Vision 2014;14(10):1242. doi: 10.1167/14.10.1242.
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Binocular rivalry results in perceptual alternations with conflicting images in each eye. Stimulus rivalry allows a similar percept despite repeated swapping of the images in each eye (Logothetis et al, 1996, Blake, 2001). Recent studies have further characterized the parameters required for rivalry, and proposed an integrated framework that may suggest a similar mechanism for both types of rivalry (Van Boxtel et al, 2008). However, a direct comparison of binocular and stimulus rivalry with fMRI has not been reported. We tested subjects with matched stimuli in both rivalry conditions. The stimuli were 1.4 cpd sinusoidal gratings (left & right oblique orientations) at 3.8 deg. Luminance contrast was 100%. For binocular rivalry, dynamic images were presented dichoptically (with polarizers) for 90msec periods with a periodic short blank ISI of 60 msec. For stimulus rivalry, the stimuli were identical except that the images shown to each eye were swapped at 6.67 Hz. We employed active scans where subjects indicated alternations with key press, as well as scans with passive viewing only. Overall, cortical activation for binocular rivalry was consistently greater than for stimulus rivalry. In whole brain statistical maps, this was pronounced in the intraparietal sulcus. Follow-up analysis with retinotopic regions of interest showed also that binocular rivalry exceeded stimulus rivalry in V1, V2, V3, and V3A. Based on comparisons between active and passive conditions, we interpret parietal activity to reflect a relatively automatic process that is triggered by object individuation/attentional tracking. In contrast, regions of ventral temporal cortex might reflect active categorization demands. These results suggest that despite a global network similar to binocular rivalry, the increased interocular masking in stimulus rivalry results in lower BOLD signals as early as V1, consistent with a lower effective contrast and slower alternations. These physiological observations are relevant to competing models of rivalry.
Meeting abstract presented at VSS 2014
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