The Effect of Planning and Hand Position on Hand Choice When Reaching

Abstract

<p>A fundamental decision when interacting with objects in our environment involves hand selection. Two major factors that influence this choice include handedness (the proficiency of one hand over the other) and the spatial relationships perceived between the object and both effectors (Gabbard & Rabb, 2000). Previous studies have altered the location of an object in space and the complexity of a task as it relates to hand choice decisions (Bryden et al., 2003; Gabbard et al., 2003; Mamalo et al., 2006). This thesis investigates the idea of reaching toward a series of predictable target locations and its effect on the frequency of hand use when compared to unpredictable reaches. Predictable reaches allow participants to assign hand use prior to movement initiation. Participants reached to a series of 3-target sequences in one of two groups: unpredictable reaches, selecting a hand to reach each target as it appeared; and predictable reaches, where the target sequence was presented prior to initiating a reach. Unpredictable reaches at different hand positions in space demonstrate that object proximity often mediates hand choice by promoting use of the effector that affords the shortest reaching amplitude. Further, predictive reaches demonstrate a preference to complete larger reaching amplitudes earlier in the sequence in order to place both hands in a position where object proximity mediates hand choice later in the sequence. Overall, predictable reaches seem to resemble the end-state comfort effect (Rosenbaum, 1992), where participants change their approach to executing reaches when they know the sequence of targets that follows.</p>