Dominant limb selection frequency increases under restricted movement planning time

We previously showed that limb selection in targeted reaching task when given choice is associated with model of motor lateralization, which attributes dominant left hemisphere specialization to efficient coordination of limb and task dynamics. For example, we found that this motor behavior of hand selection can be modified instantaneously by occluding visual feedback during movement, as well as through a long-term unimanual athletic training such as fencing. Our findings suggested that limb selection might be driven by kinetic costs, which should place heavy demands on the planning process. We now ask if restricting the time available for movement planning would affect the pattern of limb selection behavior. One group of right-handed participants was given the choice of limb selection and two other groups were forced to move with either right or left arm to each of 32 randomly presented targets covering frontal space. Whereas in previous studies we gave the subject unlimited time, here we gave an imperative ‘go’ signal, upon which the subject was required to move to the target. We found that restricting time for movement planning led to significantly increased frequency of the dominant limb selection for targeted reaching, in particular to contralateral hemispace. These findings suggest that in this task the limb selection does not vary with kinetic costs, thus it is not associated with interlimb differences in sensorimotor performance identified in the model of motor lateralization. Furthermore, we found that the reaction time of the dominant limb did not vary between choice and forced condition, but intriguingly, there was substantial increase in choice condition for the nondominant limb, which in forced condition had actually shorter reaction time than the dominant limb