The effects of unilateral visuospatial neglect on perception of Müller-Lyer illusory figures.
Left visuospatial neglect after right hemisphere damage is a lateralised disorder of spatial perception and cognition. A study is reported of the extent to which patients with left visuospatial neglect are susceptible to the illusory effects normally elicited by Müller-Lyer figures, in which inducing fins are located on one end or on both ends of a horizontal line. Seven patients with left visuospatial neglect and seven normal controls were tested on a task of horizontal-line bisection in which stimuli consisted of plain lines of three lengths (100, 150, and 200 mm), randomly interleaved with lines with unilateral or bilateral fins. As a group, normals made accurate bisection judgments in the baseline (no-fins) condition, and exhibited significant illusory effects in both the unilateral-fin and the bilateral-fin conditions. In contrast, patients made substantial rightward errors in the baseline condition, consistent with their neglect of the left end of the line. However, as a group, patients still exhibited significant illusory effects with left-sided outward-projecting fins on 100 mm lines and with left-sided inward-projecting fins on 150 mm lines. Moreover, at least one patient exhibited consistent illusory effects both for inward-projecting and for outward-projecting left-sided fins at all line lengths. Normal illusory effects in patients were also obtained with stimuli containing unilateral right-sided and bilateral fins. The existence of such effects with inducing elements on the contralesional extremity of horizontal line stimuli suggests preservation of low-level, perhaps preattentive, perceptual mechanisms responsible for coding elementary visual features. The results may be relevant for an understanding of the influence of attentional factors on illusory perception.
Mattingley
J B
JB
Department of Psychology, Monash University, Clayton, Victoria, Australia.
Bradshaw
J L
JL
Bradshaw
J A
JA
D000328:Adult; D000368:Aged; D001288:Attention; D001925:Brain Damage, Chronic / Q000523:psychology*; D002544:Cerebral Infarction / Q000523:psychology; D004292:Dominance, Cerebral; D005260:Female; D006423:Hemianopsia / Q000523:psychology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009903:Optical Illusions; D010364:Pattern Recognition, Visual; D011597:Psychomotor Performance; D011601:Psychophysics