title: Effort, success, and nonuse determine arm choice.
abstract: How do humans choose one arm or the other to reach single targets in front of the body? Current theories of reward-driven decisionmaking predict that choice results from a comparison of "action values," which are the expected rewards for possible actions in a given state. In addition, current theories of motor control predict that in planning arm movements, humans minimize an expected motor cost that balances motor effort and endpoint accuracy. Here, we test the hypotheses that arm choice is determined by comparison of action values comprising expected effort and expected task success for each arm, as well as a handedness bias. Right-handed subjects, in either a large or small target condition, were first instructed to use each hand in turn to shoot through an array of targets and then to choose either hand to shoot through the same targets. Effort was estimated via inverse kinematics and dynamics. A mixed-effects logistic-regression analysis showed that, as predicted, both expected effort and expected success predicted choice, as did arm use in the preceding trial. Finally, individual parameter estimation showed that the handedness bias correlated with mean difference between right- and left-arm success, leading to overall lower use of the left arm. We discuss our results in light of arm nonuse in individuals' poststroke.
authors.affiliation: Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California; schweigh@usc.edu.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Schweighofer
authors.affiliation: Neuroscience Graduate Program, University of Southern California, Los Angeles, California; and.
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California;
authors.forename: Sujin
authors.initials: S
authors.lastname: Kim
authors.affiliation: Advanced Telecommunications Research Institute, Computational Neuroscience Laboratories, Kyoto, Japan.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Yoshioka
authors.affiliation: Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California;
authors.forename: James
authors.initials: J
authors.lastname: Gordon
authors.affiliation: Advanced Telecommunications Research Institute, Computational Neuroscience Laboratories, Kyoto, Japan.
authors.forename: Rieko
authors.initials: R
authors.lastname: Osu
mesh_terms: D001132:Arm / Q000502:physiology; D001696:Biomechanical Phenomena; D002755:Choice Behavior; D005260:Female; D007839:Functional Laterality; D006801:Humans; D016015:Logistic Models; D008297:Male; D008954:Models, Biological; D011597:Psychomotor Performance / Q000502:physiology; D011601:Psychophysics; D055815:Young Adult
keywords: decisionmaking; motor control; motor cost; motor effort; reaching