| Estimating a hand's position for the purpose of reaching to it with the other hand is an important computation for humans. When both visual and proprioceptive information about the target hand's position are available, the brain weights and combines these sources to form a single estimate, often modeled by minimum variance integration. Sensory information can change rapidly (e.g., entering a dimly-lit room), but the type of information causing the brain to change weights (reweight) is unknown. Through a series of virtual reality reaching experiments, we found that subjects could reweight strongly by conscious effort and changing target salience, but visual error history was not a robust cue.;If visual and proprioceptive estimates are in disagreement (e.g., wearing prism goggles), it may be advantageous for the nervous system to bring them back into register by realigning one or both. The minimum variance model predicts that the lower-weighted modality will realign more toward the higher-weighted estimate. However, the dependence of realignment on weights has never been directly tested, and in theory the two phenomena could operate independently. Here we imposed a misalignment between visual and proprioceptive estimates of target hand position in a reaching task designed to allow simultaneous, independent measurement of weights and realignment. We found that while weighting and realignment operate in conjunction in certain circumstances, they are biologically independent processes that give humans behavioral flexibility in compensating for sensory perturbations.;The neural substrates involved in sensory realignment and weighting are prisms is unknown, but it is recognized that the motor adaptation elicited by laterally-displacing cerebellum-dependent. To determine if the cerebellum is also involved in sensory realignment or weighting, we compared the performance of cerebellar patients on reaching tasks that elicit sensory and/or motor adaptation with their performance in a prism task that is known to elicit cerebellum-dependent motor adaptation. The data suggest that unlike motor adaptation, sensory realignment and weighting are not cerebellum-dependent. These results have implications for our understanding of sensorimotor processing as well as the capacity for adaptation of individuals with cerebellar damage. |
