Brain and Cognition 59 (2005) 71–81 www.elsevier.com/locate/b&c 0278-2626/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bandc.2005.05.003 The eVects of local and global processing demands on perception and action Laura E. Hughes a,¤ , Timothy C. Bates a , Anne M. Aimola Davies a,b a Macquarie Centre for Cognitive Science, Macquarie University, Sydney, Australia b School of Psychology, The Australian National University, Canberra ACT 0200, Australia Accepted 16 May 2005 Available online 12 July 2005 Abstract The line-bisection task, adapted to utilise a wooden rod as the bisection stimulus, has revealed that patients with visuo-spatial neglect may be more accurate at bisection when asked to pick up the rod, compared to pointing to its centre. We recently reported that neurologically intact participants show a similar dissociation on this task—demonstrating a rightward bias when pointing to the centre, which was not present when grasping the rod by the centre. The current paper examined how pointing and grasping responses were aVected by adapted rod-bisection tasks that emphasised local or global processing. In Experiment 1, 26 participants completed four rod-bisection tasks. The rods were compound stimuli and the participants directed to focus on either the local or global level. The results demonstrated that when participants focused on the global level, the previous dissociations found for pointing and grasp- ing conditions were evident. However, the perception of centre did change when participants focused on the local level: both the pointing and grasping responses were rightward biased. In Experiment 2, 42 participants completed three bisection tasks which again emphasised either the local or global level, but in diVerent sets of stimuli. The results of this task further support the Wndings in Experiment 1: the rightward bias in the local-bisection task was again evident and in addition, the global-bisection task resulted in no bias and no diVerence between the pointing and grasping bisections. These results demonstrate how task demands can similarly aVect the pointing and grasping responses, and indicate that local and global processing may be involved in perception/action dissociations on rod bisection.  2005 Elsevier Inc. All rights reserved. Keywords: Perception; Action; Local and global processing; Pseudoneglect 1. Introduction A number of neuropsychological studies have reported that perceptual judgements and visually guided actions can be aVected diVerentially after brain injury. Patients have been reported who have diYculty describ- ing or estimating the dimensions of objects, but, never- theless, are able to accurately direct their actions towards the objects to manipulate them (e.g., Goodale et al., 1994; Milner et al., 1991). Patients with visuo-spatial neglect show a similar dissociation: when asked to bisect a rod they often nominate a point to the right of centre demonstrating a lack of awareness of the left extent, however, when asked to pick the same rod up by its cen- tre, they do not show such a bias (Edwards & Humph- reys, 1999; Robertson, Nico, & Hood, 1995). Dissociations between perception and action have also been observed in neurologically intact participants (e.g., Aglioti, DeSouza, & Goodale, 1995; Ellis, Flana- gan, & Lederman, 1999; HaVenden & Goodale, 1998). These studies report that actions directed towards per- ceptual illusions, such as the Ebbinghaus, Muller-Lyer or Judd illusion, were not as inXuenced by the illusory * Corresponding author. Fax: +61 2 9850 6059. E-mail address: lhughes@maccs.mq.edu.au (L.E. Hughes).