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André D Gouws, Ivan Alvarez, David Watson, Maiko Uesaki, Jess Rodgers, Antony B Morland; The role of cortical and subcortical suppression in spatial attention.. Journal of Vision 2014;14(10):618. doi: https://doi.org/10.1167/14.10.618.
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© ARVO (1962-2015); The Authors (2016-present)
The allocation of spatial attention results in enhanced perception at attended locations at the cost of perception at unattended locations. While functional MRI (fMRI) studies have shown that cortical representations of unattended visual locations can display negative BOLD responses, this â€˜suppressionâ€™ remains poorly understood. We sought to characterise the suppression expressed in retinotopic representations of unattended locations asking the following questions. At what stages of the visual hierarchy is suppression expressed? What is the task- and stimulus contrast- dependence of suppression? Participants viewed a lateralised 120° sector of an annulus (inner radius 4°, outer 18°), equally divided by the horizontal meridian. Upper and lower halves of the stimulus were luminance contrast gratings (6%, 12%, 25% or 100%) drifting in opposite directions and reversing unpredictably. Each fMRI run comprised eight, 16s, grating blocks alternating with a 16s uniform field equiluminant to the grating. High resolution (1.5x1.5x2.4mm3) fMRI data we acquired (128 volumes, TR=2s, 8 cycles, 4 scans per contrast/task combination), while participants fixated a dynamic central target and counted either the number of grating reversals (stimulus-related task) or the number of targets at fixation (central task). Separate functional and anatomical acquisitions were used to define V1, V5 and LGN regions of interest contralateral and ipsilateral to the stimulus in each participant. Repeated measures linear modelling analysis of positive BOLD responses revealed expected increasing attention-dependence but decreasing contrast-dependence moving up the visual hierarchy from the LGN to V5. In the representations of unattended locations of the LGN and V1, however, we observed suppression, which was highly task dependent but largely independent of the attended stimulus contrast. Whole brain analysis revealed that these suppressive effects were also found in the pulvinar, which has been frequently associated with attention. Suppression therefore, most notably in subcortical structures, plays an important role in spatial attention.
Meeting abstract presented at VSS 2014
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