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A Normal Bias Toward a Pictorially Defined Top in Line Bisection

Published online by Cambridge University Press:  18 September 2015

Cory Toth  and
Andrew Kirk
Cory Toth*
Affiliation:
Division of Neurology, Department of Medicine, University of Saskatchewan, Saskatoon
Andrew Kirk*
Affiliation:
Division of Neurology, Department of Medicine, University of Saskatchewan, Saskatoon
*
Department of Medicine, Royal University Hospital, 103 Hospital Drive, Saskatoon. Saskatchewan, Canada S7N 0W8
Department of Medicine, Royal University Hospital, 103 Hospital Drive, Saskatoon. Saskatchewan, Canada S7N 0W8
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Abstract:

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Background: We set out to determine whether separable visual and representational components underlie normal subjects’ upward and distal biases in bisecting vertical and radial lines under visual guidance. Methods: Thirty-four normal subjects were asked to bisect lines oriented horizontally, vertically, and radially. Human silhouette figures were placed at either end of each line. These figures were presented upright or upside down in order to pictorially define a “top” to each line independent of the actual top of the visual field. Results: Although subjects erred toward the top of the visual field, they also demonstrated a significant bias toward the heads of the figures for lines in all spatial orientations. Conclusions: This result supports the existence of two biases: one toward the upper visual field, and another toward an internally represented “top” as suggested pictorially. These findings provide further support for the hypothesis that normal subjects’ upward and distal biases on bisection of vertical and radial lines under visual guidance have both representational and visual-based components.

Type
Original Articles
Information
Canadian Journal of Neurological Sciences , Volume 23 , Issue 2 , February 1996 , pp. 110 - 113
Copyright
Copyright © Canadian Neurological Sciences Federation 1996

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