Handedness, limb selection, and reach control: a test of the dynamic dominance hypothesis

This study examined the generalization of the Dynamic Dominance Hypothesis (DDH) in regard to limb dominance, limb selection, and limb action. This study was inspired by the finding that limb selection changes from dominant-arm to nondominant-arm occur around an object position of 80? for right-handers and 100? for left-handers after passing the body midline (90?) into contralateral hemispace. For Study 1 and Study 2, 10 right-handed and 10 left-handed adults participated and reaching with the right and left arms of right- and left-handers was made to each of nine targets using free-choice and forced-choice paradigms. The purpose of Study 1 was to determine the relationship between limb selection and the DDH among both handedness groups. Thus, Study 1 addressed the following questions: Can the DDH explain why people select their nondominant hand for reaching into their contalateral hemispace? Do predictions of the DDH hold for right- and left-handers? Our results suggest that control efficiency with regard to a reduction in degrees of freedom in reaching movements seems to be a more fundamental cause for the limb selection phenomenon rather than the DDH. Also, our data reveal that kinematic differences between right- and left-handers with regard to utilization of joints for reaching explain limb selection differences between both handedness groups. The aim of Study 2 was to extend generalization of the DDH using a wide range of movement speed. Thus, Study 2 addressed the following question: Do propositions of the DDH hold for a wide range of speeds? Our data indicate the DDH does not hold for either slow or fast speed in reaching movements. Rather, a change in kinematics with regard to utilization of joints in reaching movements is associated with movement speed. Considered together, our data indicate that the DDH is an inadequate explanation of differences in limb selection, limb dominance (handedness), and limb action (speed). Rather, our findings with regard to control efficiency seem to be more fundamental and justified explanations for limb differences in the control of reaching based on the context of our task.