No abstract

Significance Tactile sensations on a moving hand are perceived weaker than when presented on the same but stationary hand. There is an ongoing debate about whether this weaker perception is based on sensorimotor predictions or is due to a blanket reduction in sensitivity. Here, we show greater suppression of sensations matching predicted sensory feedback. This reinforces the idea of precise estimations of future body sensory states suppressing the predicted sensory feedback. Our results shine light on the mechanisms of human sensorimotor control and are relevant for understanding clinical phenomena related to predictive processes.

The perception of tactile stimuli presented on a moving hand is systematically suppressed. Such suppression has been attributed to the limited capacity of the brain to process task-irrelevant sensory information. Here, we examined whether humans do not only suppress movement-irrelevant but also enhance in parallel movement-relevant tactile signals when performing a goal-directed reaching movement. Participants reached to either a visual (LED) or somatosensory target (thumb or index finger of their unseen static hand) and discriminated 2 simultaneously presented tactile stimuli: a reference stimulus on the little finger of their static hand and a comparison stimulus on the index finger of their moving hand. Thus, during somatosensory reaching the location of the reference stimulus was task-relevant. Tactile suppression, as reflected by the increased points-of-subjective-equality (PSE) and just-noticeable-differences (JND), was stronger during reaching to somatosensory than visual targets. In Experiment 2, we presented the reference stimulus at a task-irrelevant location (sternum) and found similar suppression for somatosensory and visual reaching. This suggests that participants enhanced the sensation of the reference stimulus at the target hand during somatosensory reaching in Experiment 1. This suggestion was confirmed in Experiment 3 using a detection task in which we found lower detection thresholds on the target hand during somatosensory but not during visual reaching. We postulate that humans can flexibly modulate their tactile sensitivity by suppressing movement-irrelevant and enhancing movement-relevant signals in parallel when executing a reaching movement. (PsycINFO Database Record

Sensorimotor control of human action integrates feedforward policies that predict future body states with online sensory feedback. These predictions lead to a suppression of the associated feedback signals. Here, we examine whether somatosensory processing throughout a goal-directed movement is constantly suppressed or dynamically tuned so that online feedback processing is enhanced at critical moments of the movement. Participants reached towards their other hand in the absence of visual input and detected a probing tactile stimulus on their moving or static hand. Somatosensory processing on the moving hand was dynamically tuned over the time course of reaching, being hampered in early and late stages of the movement, but, interestingly, recovering around the time of maximal speed. This novel finding of temporal somatosensory tuning was further corroborated in a second experiment, in which larger movement amplitudes shifted the absolute time of maximal speed later in the movement. We further show that the release from suppression on the moving limb was temporally coupled with enhanced somatosensory processing on the target hand. We discuss these results in the context of optimal feedforward control and suggest that somatosensory processing is dynamically tuned during the time course of reaching by enhancing sensory processing at critical moments of the movement.

Tactile stimuli on moving limbs are typically attenuated during reach planning and execution. This phenomenon has been related to internal forward models that predict the sensory consequences of a movement. Tactile suppression is considered to occur due to a match between the actual and predicted sensory consequences of a movement, which might free capacities to process novel or task-relevant sensory signals. Here, we examined whether and how tactile suppression depends on the relevance of somatosensory information for reaching. Participants reached with their left or right index finger to the unseen index finger of their other hand (body target) or an unseen pad on a screen (external target). In the body target condition, somatosensory signals from the static hand were available for localizing the reach target. Vibrotactile stimuli were presented on the moving index finger before or during reaching or in a separate no-movement baseline block, and participants indicated whether they detected a stimulus. As expected, detection thresholds before or during reaching were higher compared with baseline. Tactile suppression was also stronger for reaches to body targets than external targets, as reflected by higher detection thresholds and lower precision of detectability. Moreover, detection thresholds were higher when reaching with the left than with the right hand. Our results suggest that tactile suppression is modulated by position signals from the target limb that are required to reach successfully to the own body. Moreover, limb dominance seems to affect tactile suppression, presumably due to disparate uncertainty of feedback signals from the moving limb. Tactile suppression on a moving limb has been suggested to release computational resources for processing other relevant sensory events. In the current study, we show that tactile sensitivity on the moving limb decreases more when reaching to body targets than external targets. This indicates that tactile perception can be modulated by allocating processing capacities to movement-relevant somatosensory information at the target location. Our results contribute to understanding tactile processing and predictive mechanisms in the brain.