Abstract
During binocular rivalry, the alternation of the two eyes' percept correlates with the fluctuation of neural activities throughout the visual pathway, from as early as LGN and V1 to high-level occipital temporal visual cortices. However, it is not clear how feedforward and feedback processes interact to resolve the rivalrous inputs, and in particular, whether the observed neural fluctuations reflect feedforward, local or feedback modulations of resolved rivalry competition. To answer this question, we used ultra-high field fMRI at 7T with submillimeter resolution to measure rivalry-related signals from different layers of the human primary visual cortex, with the assumption that the middle layer is dominated by feedforward signals while feedback signals modulate the superficial and deep layers. BOLD signals in early visual cortex were acquired with T2*-weighted gradient echo EPI or T2-weighted balanced-SSFP pulse sequences. In the rivalry condition, a pair of orthogonal red and green gratings were dichoptically presented, and subjects reported their percept with button presses (red, green or mixed). In the replay condition, the same red/green gratings were monocularly presented in physical alternations to simulate the rivalry percept. The ocular dominance bias of V1 voxels was determined in separate scans using monocular checkerboard stimulus. Results show that in the replay condition, eye-specific modulation of BOLD signal was strongest in the middle (input) layer of V1; while in the rivalry condition, the rivalrous modulation of BOLD signal was strongest in the superficial layer. A transient signal was also observed, mainly from the superficial layer of V1, at the time points of perceptual transitions in the rivalry but not in the replay condition. These layer-specific fMRI findings support the idea that rivalry-related activity fluctuation in human primary visual cortex reflects feedback modulation from higher cortical areas.
Meeting abstract presented at VSS 2018