Differential impacts of energetic reward and penalty on arm choice

Arm choice can be altered by introducing energy imbalance between two arms by asymmetrically changing visual feedback of their movements. Theoretically, the choice of an arm can be promoted by virtually increasing its range of motion (ROM) (energetic reward), or by decreasing ROM of the other arm (energetic penalty), but it remains unclear whether they would result in similar adaptation patterns. Fourteen neurologically-intact subjects participated in an experiment where they reached towards visual targets in a virtual-reality environment. Their nondominant arm choice was encouraged by either amplifying its ROM (energetic reward), or by reducing the ROM of their dominant arm (energetic penalty). The impact of energetic penalty was found greater, as the change in the nondominant arm choice induced by imposing energetic penalty on dominant arm was significantly larger than the change created by energetic reward on nondominant arm (p < 0.01). Kinematic changes were found mostly in the promoted arm under both conditions (energetic reward/penalty), as the energetic reward on the nondominant arm increased its movement vigor (peak velocity), while energetic penalty on the dominant arm reduced reaction time of the nondominant arm. Individual differences in adaptation (i.e., arm choice change) were also explained by the change in the kinematics of the encouraged arm, particularly reaction time. These results suggest that avoidance learning via energetic penalty has a greater impact on arm choice, and the changes in arm choice were indicated by the changes in the kinematics of the encouraged arm, regardless of how the energetic imbalance was created.