Re-examining overlap between tactile and visual motion responses within hMTÂ + and STS

Here, we examine overlap between tactile and visual motion BOLD responses within the human MT + complex. Although several studies have reported tactile responses overlapping with hMT +, many used group average analyses, leaving it unclear whether these responses were restricted to subregions of hMT +. Moreover, previous studies either employed a tactile task or passive stimulation, leaving it unclear whether or not tactile responses in hMT + are simply the consequence of visual imagery. Here, we carried out a replication of one of the classic papers finding tactile responses in hMT +. We mapped MT and MST in individual subjects using visual field localizers. We then examined responses to tactile motion on the arm, either presented passively or in the presence of a visual task performed at fixation designed to minimize visualization of the concurrent tactile stimulation. To our surprise, without a visual task, we found only weak tactile motion responses in MT (6% of voxels showing tactile responses) and MST (2% of voxels). With an unrelated visual task designed to withdraw attention from the tactile modality, responses in MST were reduced to almost nothing (< 1% regions). Consistent with previous results, we did observe tactile responses in STS regions superior and anterior to hMT +. Despite the lack of individual overlap, group-averaged responses produced strong spurious overlap between tactile and visual motion responses within hMT + that resembled those observed in previous studies. The weak nature of tactile responses in hMT + (and their abolition by withdrawal of attention) suggests that hMT + may not serve as a supramodal motion processing module.