title: An investigation of the relationship between free-viewing perceptual asymmetries for vertical and horizontal stimuli.
abstract: Two experiments examine the relationship between free-viewing vertical and horizontal perceptual biases. In Experiment 1, normal participants (n=24) made forced-choice luminance judgments on two mirror-reversed luminance gradients (the 'grayscales' task). The stimuli were presented in vertical, horizontal and oblique (+/-45 degrees ) orientations. Leftward and upward biases were observed in the horizontal and vertical conditions, respectively. In the oblique conditions, leftward and upward biases combined to produce a strong shift of attention away from the lower/right space toward the upper/left. Regression analyses revealed that the oblique biases were the combined product of the vertical and horizontal biases. A lack of correlation between the vertical and horizontal biases, however, suggests they reflect the operation of independent cognitive/neural mechanisms. In Experiment 2, the same stimuli were given to right-hemisphere-lesioned patients with spatial neglect (n=4). Rightward and upward biases were observed for horizontal and vertical stimuli, respectively. The biases combined to produce a strong shift of attention away from the lower/left space toward the upper/right. While our research demonstrates that vertical and horizontal attentional biases are additive, it also appears that they reflect the operation of independent cognitive/neural mechanisms. Potential applications of these findings to the remediation of spatial neglect are discussed.
authors.affiliation: Department of Psychology, University of Melbourne, Swanston St., Parkville, VIC 3010, Australia. m.nicholls@psych.unimelb.edu.au
authors.forename: Michael E R
authors.initials: ME
authors.lastname: Nicholls
authors.forename: Jason B
authors.initials: JB
authors.lastname: Mattingley
authors.forename: Nadja
authors.initials: N
authors.lastname: Berberovic
authors.forename: Amanda
authors.initials: A
authors.lastname: Smith
authors.forename: John L
authors.initials: JL
authors.lastname: Bradshaw
mesh_terms: D000293:Adolescent; D000368:Aged; D000704:Analysis of Variance; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010468:Perceptual Disorders / Q000503:physiopathology; D010775:Photic Stimulation / Q000379:methods*; D011930:Reaction Time / Q000502:physiology; D012044:Regression Analysis; D014796:Visual Perception / Q000502:physiology*