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Tomas Knapen, Jascha Swisher, Benjamin Wolfe, Frank Tong, Patrick Cavanagh; Phase-encoded fmri investigation of retinotopic remapping responses. Journal of Vision 2010;10(7):510. doi: 10.1167/10.7.510.
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In order to maintain visual stability in the face of continuous saccadic eye movements, the brain has to incorporate the motor commands for upcoming saccades into visual processing. The process by which saccadic motor commands impinge on visual processing is called remapping. In remapping, neurons with receptive fields sensitive to the post-saccadic retinotopic location of the stimulus pre-activate before the saccade, and thus, before they receive visual input. Using single-cell physiology in monkeys and fmri in humans, evidence for remapping has been found in areas ranging from parietal lobe to lower levels of visual cortex.
We devised a novel method to investigate the topographic properties of remapping activity in the human brain. Subjects made saccades back-and-forth between two lateral fixation marks every second. An expanding ring stimulus was shown alternately at either fixation position. In separate runs, the ring appeared either at the current gaze position (shifting position in sync with gaze, foveal stimulation condition), or at the position opposite the current gaze location (shifting position out of sync with gaze, remapping condition). In the first condition, the intermittent presentation of the expanding ring stimulus caused a traveling wave of activity, allowing us to employ classic phase-encoded retinotopic mapping techniques. In the second, remapping condition, subjects always made a saccade to the location where a stimulus had just disappeared. Remapping responses of this stimulus presentation should therefore produce responses with phases equivalent to the first condition. Furthermore, phases in the remapping condition should be uncorrelated with a control condition that has identical retinal stimulation but no saccades.
We use this novel technique to extend previous results regarding remapping responses in human visual cortex.
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