Differential effects of a visual illusion on online visual guidance in a stable environment and online adjustments to perturbations Simone R. Caljouw a,⇑ , John van der Kamp b,c , Moniek Lijster d , Geert J.P. Savelsbergh b,e a Center for Human Movement Sciences, Medical Center Groningen, University of Groningen, Groningen, The Netherlands b Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, Amsterdam, The Netherlands c Institute of Human Performance, University of Hong Kong, Hong Kong SAR, China d Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, The Netherlands e Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, UK article info Article history: Received 7 September 2010 Available online xxxx Keywords: Illusion Allocentric information Online control Goal-directed hitting Perturbation abstract In the reported, experiment participants hit a ball to aim at the vertex of a Müller–Lyer configuration. This configuration either remained stable, changed its shaft length or the orientation of the tails during movement execution. A significant illusion bias was observed in all perturbation conditions, but not in the stationary condition. The illusion bias emerged for perturbations shortly after movement onset and for perturbations during execution, the latter of which allowed only a minimum of time for making adjustments (i.e., approx.170 ms). These findings indicate that allocentric information is exploited for online control when people make rapid adjustments in response to a sudden change in the environment and not when people guide their limb movements to interact with a sta- ble environment. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction People make goal-directed actions, such as hitting, catching or reaching to bring about changes in their environment. Of- ten this environment is relatively stable and predictable while the action is performed. In these situations performers can evaluate the task requirements in advance and execute the movements without the need for further visual control of the spatio-temporal unfolding of the movements (Plamondon, 1995; Schmidt, Zelaznik, Hawkins, Frank, & Quinn, 1979). Yet, for more than a century, researchers have tried to establish that even during execution, movements are under instantaneous or online visual guidance (Woodworth, 1899). Indeed, many studies have shown that visual information about the target, hand, and eye position is used online both in relatively stable environments and in more dynamic environments. Online vi- sual control ensures the required accuracy of a movement outcome especially when adjustments in the ongoing movements are needed in response to perturbations in the environment (Caljouw, van der Kamp, & Savelsbergh, 2006; Pelisson, Prablanc, Goodale, & Jeannerod, 1986; Pisella et al., 2000; Prablanc & Martin, 1992; Prablanc, Pelisson, & Goodale, 1986; Saunders & Knill, 2003). Rapid online adjustments of goal-directed movement to sudden displacement of a target object are thought to be controlled ‘automatically’ by an ancient visuomotor system (Milner & Goodale, 1995, 2008). From an evolutionary per- spective, one early function for vision was online movement control (i.e., action). For example, catching prey requires the fast pick up of instantaneous information about the motion of the prey in relation to the predator’s own displacements. 1053-8100/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.concog.2011.03.002 ⇑ Corresponding author. Address: Center for Human Movement Sciences, Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands. E-mail address: s.r.caljouw@med.umcg.nl (S.R. Caljouw). Consciousness and Cognition xxx (2011) xxx–xxx Contents lists available at ScienceDirect Consciousness and Cognition journal homepage: www.elsevier.com/locate/concog Please cite this article in press as: Caljouw, S. R., et al. Differential effects of a visual illusion on online visual guidance in a stable environ- ment and online adjustments to perturbations. Consciousness and Cognition (2011), doi:10.1016/j.concog.2011.03.002