Investigating tactile suppression during goal-directed movement
When we move our ability to detect tactile events on the moving limb is reduced. This process, known as movement-related tactile suppression, prevents unimportant sensory information from bombarding our central nervous system. This thesis aimed to extend the tenets of movement-related suppression during goal-directed reaching and explore any modulation of this suppression according to task-relevance. In three experiments participants performed volitional self-driven (Experiment 1, 3) and
... nt 1, 3) and motor-driven (Experiment 1, 2) reaching and grasping movements. Over the course of the movement, weak electrical stimulation was presented at task-relevant (i.e., index finger and thumb) and task-irrelevant sites on the moving limb. In Experiment 1, participants displayed reduced detectability during movement of a readily detectable tactile stimulus (90% resting detection). This was true for all locations on the moving limb irrespective of task-relevance and during both self and motor-driven movements. In Experiment 2 and 3 a range of stimulus amplitudes was presented to one task relevant location during both self and motor-driven movements (Experiment 2) and to a task relevant and irrelevant site during self-driven movements (Experiment 3). This slight change in methodology allowed us to get a direct estimate of perceptual thresholds and asses the magnitude of movement-related tactile suppression. During both self and motor-driven movement participants exhibited an increased perceptual threshold at the index finger (Experiment 2). The magnitude of suppression however, was greater at the forearm than at the index finger (Experiment 3). Collectively these experiments suggest that tactile suppression is a general consequence of movement. Although evident at all locations on the moving limb, we suggest that tactile suppression can be modulated in a relevance-dependent manner.