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Ramakrishna Chakravarthi, Patrick Cavanagh; Hemifield independence in visual crowding. Journal of Vision 2006;6(6):1104. doi: https://doi.org/10.1167/6.6.1104.
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We presented a set of three T's arranged in a line along a radius from fixation and subjects reported the orientation of the central T (eccentricity 7.5 degrees). This radial array was placed along one of the four obliques centered in each quadrant of the visual field. We determined the target-distracter separation at which the identification of target orientation was 85%. The average of this threshold distance for 7 subjects was 3.5 degrees. Keeping the target-distracter separation fixed at their individually determined value for each subject, we then presented two crowding arrays simultaneously in adjacent quadrants situated either both on the same side of the vertical meridian (unilateral presentation) or one on each side (bilateral presentation). When the two arrays were presented, subjects had to report only one of the targets indicated by a cue that followed the offset of the arrays. Adding the second array did not significantly affect performance when presented in opposite hemifields (80% mean accuracy vs. 85% with one array). However, when the two arrays were presented within one hemifield, performance dropped significantly (to 73%, t(6) = 2.67, p<0.05). This bilateral versus unilateral difference was not found for identification of uncrowded letters at the same eccentricity. A similar unilateral disadvantage has been reported for multiple tracking tasks when presented within the same hemifield (Alvarez and Cavanagh, 2005). Our results suggest that crowding might also be bound by hemifield limits on attentional resources.
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