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Derick Valadao, Marc Hurwitz, James Danckert; Decreasing fidelity of peripheral visual information modulates performance on the manual line bisection task. Journal of Vision 2011;11(11):250. doi: 10.1167/11.11.250.
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The line bisection task-commonly used as a clinical measure of unilateral neglect-requires participants to place a mark on a horizontal line to indicate where they think center is. Previous research suggests that the allocation of attention mediates performance on this task. Interestingly, previous eye tracking research has shown that participants rarely explore the endpoints of lines. As a result, any conceptualization of line bisection behavior must take into account this lack of visual exploration. We endeavored to show how participants could arrive at an accurate judgment of center while minimizing ocular exploration. We hypothesized that accurate line bisection depends on the fidelity of visual information in the periphery. Lines were presented to participants either as black lines or as lines that contained either symmetrical or asymmetrical ‘noise’ (i.e., monochromatic static). Participants were asked to judge center by placing their finger on a touch screen where they believed center to be. Consistent with the literature, we found that bisections erred slightly to the left in the no noise condition (i.e., pseudoneglect) in addition to an increased leftward bias for lines presented in left space. Contrary to our expectations, symmetrical noise produced an increased leftward bias relative to the control condition. Additionally, asymmetrical noise shifted bisections towards the end of the line that contained the most noise. Finally, the degree of bias was largest in all conditions for lines presented in left space. These results indicate that the fidelity of peripheral visual information mediates bisection behavior. Furthermore, these results suggest that attention serves to remove the influence of distracting information rather than for sensory enhancement. Finally, the pattern of results for lines presented in left versus right space supports the converging line of evidence implicating right parietal cortex in governing the allocation of attention towards objects in space.
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