Haptic information differentially interferes with visual analysis in reaching-grasping control and in perceptual processes

We used an interference paradigm in order to study integration between haptic and visual information in motor control and in perceptual analysis. Subjects either reached and grasped a visually presented sphere or matched its size with their left hand while manipulating with their right hand another sphere whose size could be smaller or greater. In four experiments haptic analysis of the manipulated sphere could be either automatically incorporated with or explicitly dissociated from visual analysis. In a fifth experiment reaching-grasping and matching were executed with the right hand, whereas manipulation was executed with the left hand. Manipulation with the right hand influenced finger shaping during grasping with the left hand when the sizes of the two objects were different. Interference was observed mainly in those experiments in which haptic analysis could be automatically integrated with visual analysis. In the matching task, no effect was observed. Finally, manipulation with the left hand did not produce any interference effect on reaching-grasping and matching executed by the right hand. The results of the present study suggest that somesthetic information is integrated with visual information only in sensorimotor transformations. In addition, they support the notion that the left hemisphere together with the right hemisphere is involved in the control of left hand reaching- grasping movements.