Integration of proprioceptive and visual position-information: An experimentally supported model

To localize one's hand, i.e., to find out its position with respect to the body, humans may use proprioceptive information or visual information or bo th. It is still not known how the CNS combines simultaneous proprioceptive and visual information. In this study, we investigate in what position in a horizontal plane a hand is localized on the basis of simultaneous proprioc eptive and visual information and compare this to the positions in which it is localized on the basis of proprioception only and vision only. Seated a t a table, subjects matched target positions on the table top with their un seen left hand under the table. The experiment consisted of three series. I n each of these series, the target positions were presented in three condit ions: by vision only, by proprioception only, or by both vision and proprio ception. In one of the three series, the visual information was veridical. In the other two, it was modified by prisms that displaced the visual field to the left and to the right, respectively. The results show that the mean of the positions indicated in the condition with both vision and proprioce ption generally lies off the straight line through the means of the other t wo conditions. In most cases the mean lies on the side predicted by a model describing the integration of multisensory information. According to this model, the visual information and the proprioceptive information are weight ed with direction-dependent weights, the weights being related to the direc tion-dependent precision of the information in such a way that the availabl e information is used very efficiently. Because the proposed model also can explain the unexpectedly small sizes of the variable errors in the localiz ation of a seen hand that were reported earlier, there is strong evidence t o support this model. The results imply that the CNS has knowledge about th e direction-dependent precision of the proprioceptive and visual informatio n.