Adverse effects of viewing the hand on tactile-spatial selection between fingers depend on finger posture

Primary somatosensory cortex (S1) is known to rapidly adapt to task demands and to intermodal information (e.g. from vision). Here, we show that also intramodal information (i.e. posture) can affect tactile attentional selection processes and the intermodal effects of vision on those processes at S1 stages of processing. We manipulated the spatial separation between adjacent fingers, that is, thumb and index finger where close, far apart, or touching. Participants directed their attention to either the index finger or thumb to detect infrequent tactile targets at that location while either they saw their fingers or these were covered from view. In line with the previous results, we found that attentional selection affected early somatosensory processing (P45, N80) when fingers were near and this attention effect was abolished when fingers were viewed. When fingers were far or touching, attentional modulations appeared reliably only from the P100, and furthermore, enhanced tactile-spatial selection was found when touching fingers were viewed. Taken together, these results show for the first time a profound effect of finger posture on attentional selection between fingers and its modulations by vision at early cortical stages of processing. They suggest that the adverse effects of vision on tactile attention are not driven by a conflict between the selected information in vision (two fingers) and touch (one finger) and imply that external spatial information (i.e. finger posture) rapidly affects the organisation of primary somatosensory finger representations and that this further affects vision and tactile-spatial selection effects on S1.