Ecological Psychology, 23:247–266, 2011 Copyright © Taylor & Francis Group, LLC ISSN: 1040-7413 print/1532-6969 online DOI: 10.1080/10407413.2011.617215 Postural Sway and the Amplitude of Horizontal Eye Movements M. Russell Giveans and Ken Yoshida School of Kinesiology University of Minnesota Benoît Bardy EuroMov University of Montpellier-1 Michael Riley Department of Psychology University of Cincinnati Thomas A. Stoffregen Affordance Perception-Action Laboratory University of Minnesota In 2 experiments, we evaluated relations between postural activity and the ampli- tude of visually guided eye movements. Participants shifted their gaze to follow horizontal oscillation of a visible target. The target moved with amplitude 9 ı or 24 ı . In different experiments, the frequency of target oscillation was 0.5 Hz or 1.1 Hz. In both experiments, the variability of head and torso motion was reduced (in the anterior-posterior axis) when participants viewed moving targets, relative to sway during viewing of stationary targets. Sway variability was not influenced by the amplitude of target motion. The results are compatible with the hypothesis that postural activity was modulated relative to the demands of suprapostural visual tasks. Correspondence should be addressed to Thomas A. Stoffregen, Affordance Perception-Action Laboratory, School of Kinesiology, University of Minnesota, 1900 University Avenue SE, Min- neapolis, MN 55455. E-mail: tas@umn.edu 247 Downloaded by [University of Minnesota Libraries, Twin Cities] at 09:28 07 November 2011