POSTURAL DYNAMICS AND THE PREFERRED CRITICAL BOUNDARY FOR VISUALLY GUIDED REACHING

How do people choose an action to satisfy a goal from among the action s that are afforded by the environment? In 3 experiments the action mo des used by actors to reach for a block placed at various distances fr om them were observed. In each experiment, when actors were not restri cted in how they could reach for the object, the transition from their reaching using only arm extension to a mode of reaching in which they used the upper torso to lean forward occurred al closer distances tha n each actor's absolute critical boundary, beyond which the former act ion was no longer afforded. In Experiments 2 and 3 actors' seated post ure was varied so that the effect of postural dynamics on the distance at which actors actually chose to make the transition between action modes, the preferred critical boundary, could be examined. The results are consistent with the proposal that the preferred critical boundary reflects the relative comfort of available modes of reaching.