Crossmodal interference in bimanual movements: effects of abrupt visuo-motor perturbation of one hand on the other.

Studies on bimanual control inevitably deal with questions about interactions between the two effectors, mostly under conditions of sensory feedback of the same modality-usually vision-for both hands. This study used a novel paradigm in which one hand performed target-directed movements under visual control, while the other hand operated under predominantly kinesthetic control, without visual feedback. By introducing an abrupt visual feedback perturbation in the 'visible' hand, resulting in an update of its visuo-motor map, the robustness of the kinesthetic-motor map of the 'invisible' hand against interference from the visually controlled hand could be tested. Results show that the visuo-motor adaptation resulted in asymmetric directional interference: when the 'visible' right hand adapted to the perturbation, it interfered substantially more with the 'invisible' left hand (group 1) than when the left hand was under visual control and the right hand under kinesthetic control (group 2). The results support recent theories of functional lateralization postulating dominance of the right hand for trajectory control and demonstrate that on the level of arm kinematics, this interference crosses modality boundaries. Interestingly, while in most participants interference manifested itself in isodirectional deviations of the kinesthetically guided hand, the deviations in a small subsample of participants mirrored those of the visually guided hand. The results are discussed in the context of potential neural crosstalk.