Different sensory information is used for state estimation when stationary or moving

Abstract

Accurate estimation of limb state is necessary for both movement planning and execution. It requires both feedforward and feedback information. Prior literature has shown that feedback-based estimates of static limb position are improved by integrating visual and proprioceptive information. However, differences in visual and proprioceptive feedback delays suggest that multisensory integration could be disadvantageous when the limb is moving. To investigate multisensory integration in different movement contexts, we compared the degree of interference created by discrepant visual or proprioceptive feedback on limb position estimates in two tasks: a static task in which estimates were made at the end of a passive movement, and a dynamic task in which estimates were made at movement midpoint. Participants were asked to ignore either the visual or proprioceptive information and report only the location or motion cued by the other sensory modality. In the static context, bimodal trials showed a pattern of idiosyncratic interference: only discrepant proprioceptive feedback significantly interfered with reports of the visual target location, leading to a bias of the reported position toward the proprioceptive cue. In the dynamic context, no interference was seen: participants could ignore sensory feedback from one modality and accurately reproduce the motion indicated by the other modality. We modeled feedback-based state estimation by updating the longstanding maximum likelihood estimation model of multisensory integration to account for sensory delays. Consistent with our behavioral results, the model showed that the benefit of multisensory integration is largely lost when the limb is moving. Together, these findings suggest that the sensory feedback used to compute a state estimate differs depending on whether the limb is stationary or moving. While the former may tend toward multimodal integration, the latter is more likely to be based on feedback from a single sensory modality.