Toward naturalistic reaching: Intermediate reaches under uncertainty generalize to walking, but are not obligatory

Abstract

Highly-constrained laboratory-based experiments have provided important insights into movement planning. When people reach toward one of several stimuli before knowing which to target, their hand trajectories are situated intermediate to direct reaches to each stimulus. Real-world reaching, however, involves a greater decision landscape than typical laboratory tasks. We extended the go-before-you-know paradigm to a walk-to-reach task resembling unconstrained natural behavior. Participants walked three steps toward a touchscreen before reaching for one of two stimuli, marked as the target either at walk onset or after reach onset. Under uncertainty, intermediate reaches occurred, but only for some stimulus layouts and participants. Individual reaches varied considerably; many directly targeted one stimulus and corrected late. Body position at reach onset was anchored to the screen more than the stimuli and was partly intermediate. Thus, intermediate movements generalize beyond the laboratory, but as one flexible strategy among several, not as obligatory motor plan averaging.