Problems in planning bimanually incongruent grasp postures relate to simultaneous response specification processes

•We examined problems associated with bimanually incongruent grasp planning.•Grasp planning improved when the stimuli were separated by more than 1000 ms.•Reach-to-grasp kinematics were not influenced by stimulus onset asynchrony.•Results indicate that cross-talk arises from constraints active at multiple levels.

The purpose of the current experiments was to examine whether the problems associated with grasp posture planning during bimanually incongruent movements are due to crosstalk at the motor programming level. Participants performed a grasping and placing task in which they grasped two objects from a table and placed them onto a board to targets that required identical (congruent) or non-identical degrees of rotation (incongruent). The interval between the presentation of the first stimulus and the second stimulus (stimulus onset asynchrony: SOA) was manipulated. Results demonstrate that the problems associated with bimanually incongruent grasp posture planning are reduced at SOA durations longer than 1000 ms, indicating that the costs associated with bimanual incongruent movements arise from crosstalk at the motor programming level. In addition, reach-to-grasp times were shorter, and interlimb limb coupling was higher, for congruent, compared to incongruent, object end-orientation conditions in both Experiment 1 and 2. The bimanual interference observed during reach-to-grasp execution is postulated to arise from limitations in the visual motor system or from conceptual language representations. The present results emphasize that bimanual interference arises from constraints active at multiple levels of the neurobiological–cognitive system.