Abstract
Somatosensory perception is hampered on a limb that is performing visually-guided goal-directed movements. This suppression has been attributed to a forward model that predicts future sensorimotor states based on the established motor command. Here we examine whether and how this suppression is modulated by the predictability of object features important for controlling a visually-guided grasping movement. Participants reached to grasp an object with a precision grip and then lifted it as straight as possible. Objects with symmetric or asymmetric mass distributions were presented either in a blocked or random manner, i.e. their mass distribution was predictable or not. At the moment of object contact, a brief vibrotactile stimulus was presented on the moving index finger and participants had to respond whether they detected it or not. Grasping control benefited when participants could predict the relevant object features: When the object’s mass distribution was predictable, the chosen contact points resulted in minimized object roll during lifting. When the distribution was unpredictable, participants chose a ‘default’ grasping configuration that resulted in greater object roll for objects with asymmetric distributions. Participants also took longer to start lifting the object, presumably to allow enough time for processing afferent signals related to the object’s mass distribution and for building up appropriate digit forces for lifting. Somatosensory perception was hampered during grasping compared to a baseline (no-movement) block. Importantly, suppression was stronger when participants could predict the object’s mass distribution. We suggest that not only grasping characteristics but also the strength of somatosensory suppression depend on the predictability of movement-relevant object features.