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Parampal S. Grewal, Jayalakshmi Viswanathan, Jason J. S. Barton; The role of attentional gradients in line bisection performance of hemineglect. Journal of Vision 2011;11(11):146. doi: 10.1167/11.11.146.
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Background: Subjects with hemineglect fail to attend to stimuli on the contralateral side of space. A common finding in hemineglect is an ipsilesional bias in line bisection, a task in which subjects indicate the perceived mid-point of a horizontal line. However, others suggest that patients with parietal lesions may have abnormal spatial representations for contralateral space that account for the ipsilesional bias.
Objective: Our goal was to determine if an attentional shift in healthy subjects was sufficient to create an ipsilesional bias in line bisection.
Method: We created a dual task paradigm, in which subjects had to bisect a line while simultaneously attending to the right side of the display for highly salient moving and flashing coloured targets in an attentionally demanding conjunction search task. We measured ocular fixation distributions as well as bisection judgments.
Results: First, using flashed probes at various locations in space we confirmed in a detection task that our conjunction search task did generate an attentional gradient favouring the right hemispace. When subjects were engaged in a manual line bisection task concurrent to the right-sided conjunction search task, this created right-biased patterns of ocular fixation similar to those in hemineglect, but did not generate a significant rightward bias in bisection judgments. Accuracy rates for the conjunction task were similar in the probe condition and the dual-task paradigm, indicating that the lack of bisection bias was not due to failure to engage in the conjunction task.
Conclusion: A rightward shift of attention can reproduce neglect-like ocular motor behaviour but not bias in a manual bisection task. This may indicate either that healthy subjects can shift rapidly between task-based spatial attentional sets or that bisection bias in hemineglect patients is generated by additional spatial factors besides an attentional gradient, such as altered representations of space.
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