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Julie Golomb, James Mazer, Marvin Chun; Attentional updating across saccades in retinotopic visual cortex. Journal of Vision 2009;9(8):258. doi: https://doi.org/10.1167/9.8.258.
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A fundamental property of the visual system is the ability to update visual representations across saccades. While representations of transient visual stimuli may update before a saccade is completed, representations of endogenous sustained spatial attention appear to update more slowly. Previous psychophysical work has demonstrated that attention remains in retinotopic (eye-centered) coordinates for 100–200ms after a saccade during a spatiotopic (world-centered) task where attention to retinotopic locations confers no behavioral advantage (Golomb, Chun, and Mazer, 2008, J. Neurosci.). To explore attentional updating in retinotopically-organized visual areas, we conducted an fMRI study in humans using a similar task. Subjects covertly attended to a consistent spatiotopic location (“target” location) for the duration of the experiment. Trials began with a fixation dot appearing in one of four locations surrounding the target location, such that the target location occupied a different visual quadrant for each fixation. After a variable delay, an array of randomly oriented masked Gabors was briefly flashed on the screen. Subjects indicated the orientation of the stimulus appearing at the target location with a button press. On half of the trials, the fixation dot moved and a saccade was executed before the stimuli appeared. Stimuli were arranged to provide equivalent visual stimulation in all four visual quadrants - corresponding to the spatiotopic target, retinotopic non-target, and two control non-targets. In retinotopically-mapped regions representing human V4, BOLD responses were enhanced for retinotopic non-targets appearing 50ms after the saccade, consistent with residual behavioral facilitation. When stimuli appeared 1550ms after the saccade, only spatiotopic targets were facilitated. This novel finding demonstrates that when top-down signals redirect spatial attention to a new retinotopic location, residual facilitation transiently remains in cortical areas representing the previously relevant retinotopic location. These results provide further evidence that the native coordinate system of visual attention is retinotopic.
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