Merriam EP, Gardner JL, Movshon JA, Heeger DJ, Modulation of visual responses by gaze direction in human visual cortex, Journal of Neuroscience, 33:9879-9889, 2013.
Abstract: To locate visual objects, the brain combines information about retinal location and direction of gaze. Studies in monkeys have demonstrated that eye position modulates the gain of visual signals with "gain fields", so that single neurons represent both retinotopic location and eye position. We wished to know whether eye position and retinotopic stimulus location are both represented in human visual cortex. Using functional magnetic resonance imaging, we measured cortical responses to stimuli that varied periodically in retinal locus, separately for each of several different gaze positions. Visually-evoked responses were periodic, following the periodic retinotopic stimulation. Only the response amplitudes depended on eye position; response phases were indistinguishable across eye positions. We used multi-voxel pattern analysis to decode eye position from the spatial pattern of response amplitudes. The decoder reliably discriminated eye position in five of the early visual cortical areas by taking advantage of a spatially heterogeneous eye-position dependent modulation of cortical activity. We conclude that responses in retinotopically-organized visual cortical areas are modulated by gain fields qualitatively similar to those previously observed neurophysiologically.