title: How obstructing is an obstacle? The influence of starting posture on obstacle avoidance.
abstract: The introduction of non-target objects into a workspace leads to temporal and spatial adjustments of reaching trajectories towards a target. Currently, there are two different explanations for this phenomenon: the non-target objects are considered as either physical obstacles to which we maintain a preferred distance (see Tresilian, 1998) or as distractors that interfere with movement planning (see Tipper, Howard, & Jackson, 1997). These components are difficult to disentangle, however. Our aim was to determine the unique contribution of the avoidance of a physical obstacle to the adjustments of reaching trajectories. In this study, we manipulate the degree of physical obstruction by non-target objects while keeping the a priori visual layout of the workspace more or less constant. This is achieved by placing participants in different starting postures with respect to the orientation of their limb segments. Participants reach towards and grasp target objects with non-targets present in the workspace in a frontal and a lateral starting posture. In the frontal conditions participants showed larger movements away from the non-target on the ipsilateral side of the workspace than in the lateral conditions. The results provide evidence for the interpretation that non-targets influence the movement trajectory partly because they are 'obstructing'.
authors: Experimental Psychology, Helmholtz Institute, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands. r.menger@uu.nl
authors: Rudmer
authors: R
authors: Menger
authors: Stefan
authors: S
authors: Van der Stigchel
authors: H Chris
authors: HC
authors: Dijkerman
mesh_terms: D000328:Adult; D001288:Attention; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement; D009949:Orientation; D011187:Posture; D011597:Psychomotor Performance; D013028:Space Perception; D014796:Visual Perception