Why we move to the right? The dominant hand motor-spatial bias.

Abstract

Our motor behavior and interactions with the external world are mediated by many spatial systems. This study investigated the absence of visual control of performance in the manual line bisection task, with the goal of teasing apart the role of the motor component of the visuomotor spatial system. Results show a rightward bias when right-handed individuals bisect lines using their right hand. This effect is traced back to a motor-spatial representation of space centered on the dominant hand. This finding was replicated and further explored in 4 experiments, with the same "open loop" bisection procedure. The mechanism underlying the rightward bias does not interact with the visuo-perceptual processing involved in visual illusions of extension. Besides, this bias no longer appears when perceptual judgments of prebisected lines are required, and is substantially reduced when the influence of visual feedback is minimized by a ballistic movement. The emergence of a leftward shift in left-handed individuals, when using their left hand, confirms the hypothesis of a dominant-hand-centered motor-spatial bias. Finally, when the lines to be bisected are placed to the left or to the right of the midsagittal plane of the participants' trunk, the error shifts overall toward the side of displacement of the stimulus, both in left- and right-handers, independent of the bisection bias, which does not appear related to the egocentric position of the stimulus. We reexamined the spatial biases occurring both in healthy (i.e., pseudoneglect) and neurological (i.e., neglect) populations, by emphasizing the integration mechanism of different spatial coordinate systems. (PsycINFO Database Record (c) 2018 APA, all rights reserved).