Visual area V5/hMT+ contributes to perception of tactile motion direction: a TMS study

Human imaging studies have reported activations associated with tactile motion perception in visual motion area V5/hMT+, primary somatosensory cortex (SI) and posterior parietal cortex (PPC; Brodmann areas 7/40). However, such studies cannot establish whether these areas are causally involved in tactile motion perception. We delivered double-pulse transcranial magnetic stimulation (TMS) while moving a single tactile point across the fingertip, and used signal detection theory to quantify perceptual sensitivity to motion direction. TMS over both SI and V5/hMT+, but not the PPC site, significantly reduced tactile direction discrimination. Our results show that V5/hMT+ plays a causal role in tactile direction processing, and strengthen the case for V5/hMT+ serving multimodal motion perception. Further, our findings are consistent with a serial model of cortical tactile processing, in which higher-order perceptual processing depends upon information received from SI. By contrast, our results do not provide clear evidence that the PPC site we targeted (Brodmann areas 7/40) contributes to tactile direction perception

Adaptation to motion presented with a tactile array

We investigated the effects of adaptation to 2 min of tactile apparent motion along the proximo-distal axis of the finger pad, produced with a vibrotactile array (Optacon), and developed a novel method to reveal the tactile motion aftereffect. Participants continuously reported perceived direction during adaptation to motion in the distal or proximal direction. The clarity of the direction percept weakened over time. Following this adaptation phase, participants judged the direction of a dynamic test stimulus composed of simultaneous motion in both directions. A tactile motion aftereffect (tMAE) resulted - the test stimulus was felt to move in the direction opposite to the adapting motion. The tMAE was robust to changes in the stimulus including speed and spatial features of the moving pattern, but there was a general bias to perceive distal motion. The implication for tactile devices is that motion signals should be brief and varied to avoid adaptation artifacts