End-State Comfort in Bimanual Object Manipulation

The present experiment investigated the sensitivity for end-state comfort in a bimanual object manipulation task. Participants were required to simultaneously reach for two bars and to place the objects' ends into two targets on the table. The design of the experiment allowed to dissociate the relative roles of initial means (e.g., the selection of grips) and final postures (e.g., the anticipation of end-states). The question of interest was whether affording different grip patterns for the two hands would introduce a bias away from reaching end-state comfort. Results revealed a strong sensitivity for end-state comfort, independent of the required grip patterns. In particular, end-state comfort was preferred even if this meant selecting different initial means (i.e., different grips) for the two hands. Hence, end-state oriented action planning appears to dominate interaction costs that may result from motor-related, intermanual interference. We infer that movement planning is constrained by action goals (e.g., a comfortable end-posture for both hands), but largely unaffected by the type of motor actions necessary to achieve these goals.