title: Line bisection under an attentional gradient induced by simulated neglect in healthy subjects.
abstract: Whether an attentional gradient favouring the ipsilesional side is responsible for the line bisection errors in visual neglect is uncertain. We explored this by using a conjunction-search task on the right side of a computer screen to bias attention while healthy subjects performed line bisection. The first experiment used a probe detection task to confirm that the conjunction-search task created a rightward attentional gradient, as manifest in response times, detection rates, and fixation patterns. In the second experiment subjects performed line bisection with or without a simultaneous conjunction-search task. Fixation patterns in the latter condition were biased rightwards as in visual neglect, and bisection also showed a rightward bias, though modest. A third experiment using the probe detection task again showed that the attentional gradient induced by the conjunction-search task was reduced when subjects also performed line bisection, perhaps explaining the modest effects on bisection bias. Finally, an experiment with briefly viewed pre-bisected lines produced similar results, showing that the small size of the bisection bias was not due to an unlimited view allowing deployment of attentional resources to counteract the conjunction-search task's attentional gradient. These results show that an attentional gradient induced in healthy subjects can produce visual neglect-like visual scanning and a rightward shift of perceived line midpoint, but the modest size of this shift points to limitations of this physiological model in simulating the pathologic effects of visual neglect.
authors: Human Vision and Eye Movement Laboratory, Department of Ophthalmology and Visual Science, University of British Columbia, Vancouver, BC, Canada.
authors: Parampal
authors: P
authors: Grewal
authors: Jayalakshmi
authors: J
authors: Viswanathan
authors: Jason J S
authors: JJ
authors: Barton
authors: Linda J
authors: LJ
authors: Lanyon
mesh_terms: D000293:Adolescent; D000328:Adult; D001288:Attention; D005260:Female; D005403:Fixation, Ocular; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008954:Models, Biological; D010468:Perceptual Disorders / Q000503:physiopathology*; D010775:Photic Stimulation / Q000379:methods; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D014794:Visual Fields; D014796:Visual Perception / Q000502:physiology*