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Pankhuri Malik, Joost Dessing, Douglas Crawford; rTMS OVER HUMAN EARLY VISUAL CORTEX DEGRADES LOW LEVEL VISUAL FEATURE MEMORY IN THE REMAPPED, NOT PERCEIVED, VISUAL FIELD DURING A TRANSSACCADIC INTEGRATION TASK. Journal of Vision 2014;14(10):1227. doi: 10.1167/14.10.1227.
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Early visual cortex (EVC) is involved in short term visual memory (Harrison and Tong Nat Neurosci. 2009) and remapping of visual targets during saccades (Merriam et al. J. Neurophys. 2007). We proposed that EVC is also involved in transsaccadic integration (TSI) of visual features (Prime et al. Exp Brain Res 2006; J. Neurosci. 2008). Here, we tested this hypothesis with the use of a combined fMRI-rTMS protocol. Participants (n = 8) were required to discriminate orientation change in a Gabor patch across a memory interval during fixation or across saccade that either maintained the stimulus within the same visual field (VF) or changed location to opposite VF. Difficulty levels were set to 75-85% performance for each subject based on a preliminary test. Bifield alternating checkerboard localizer was used to identify peak voxel responses within the left and right EVC corresponding to bottom-left and bottom-right VF. rTMS (10Hz; starting 100 msec after onset of second fixation point) was applied over either of these two locations during the fixation task and saccade task, and effects were compared to behavioral controls and relative to TMS over the opposite VF. Consistent with previous experiments with one object (van de Ven et al. J. Neurosci. 2012), TMS during the fixation task (and for saccades within the same field) had no rTMS effects. rTMS over EVC corresponding to the viewed location of the initial stimulus never yielded an effect in any condition. However, when the saccade caused the remembered stimulus to reverse VF, TMS over the 'incoming' field (i.e. the EVC target site for any putative remapping) revealed a suppressive effect, which increased with saccade size (and/or the eccentricity of remapping into the stimulated hemifield). These results causally implicate human EVC (and/or its network connections) in the gaze centered remapping TSI visual feature information across saccades.
Meeting abstract presented at VSS 2014
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