Abstract
Correlates of visual fusion were studied independent from binocular rivalry by fMRI at various eccentricities in visual cortical areas V1 to V4 and MT+. Stimuli to elicit visual fusion (BF), binocular rivalry (BR), and simultaneous fusion and rivalry (BFR) were designed by superimposing fusable and non-fusable lattices. Responses to these were acquired in a group of ten subjects together with meridian-, eccentricity- and motion mapping in the same session. Retinotopic maximum probability maps on an average flat map for the group were calculated for dorsal and ventral visual areas V1 to V4 at five eccentricity intervals and motion area MT+, resulting in 41 ROIs for each hemisphere. To isolate either fusion- or rivalry-related activity within each ROI, 2×2 ANOVAs with factors eye and condition were performed where, for fusion, the condition levels were BFR and BR, and for rivalry BFR and BF, respectively. Resulting F values are reported as measure of activity. Visual fusion showed the highest activity within V3 and V4 at ROIs with increasing eccentricity, and further within Area MT+. Binocular rivalry, in contrast, mainly showed highest activities within V1 and V2, preferring lower eccentricities. In conclusion, fusion seems to be predominantly processed in the peripheral visual field representations in areas V3 and V4 as well as in MT+, playing a lower role within earlier visual areas.