Multiple spatial representations determine touch localization on the fingers.

Abstract

Touch location can be specified in different anatomical and external reference frames. Temporal order judgments (TOJs) in touch are known to be sensitive to conflict between reference frames. To establish which coordinates are involved in localizing touch to a finger, participants performed TOJ on tactile stimuli to 2 out of 4 possible fingers. We induced conflict between hand- and finger-related reference frames, as well as between anatomical and external spatial coding, by selectively crossing 2 fingers. TOJ performance was impaired when both stimuli were applied to crossed fingers, indicating conflict between anatomical and external finger coordinates. In addition, TOJs were impaired when stimuli were mapped to the same hand based on either anatomical or external spatial codes. Accordingly, we observed a benefit rather than impairment with finger crossing when both stimuli were applied to 1 hand. Complementary, participants systematically mislocalized touch to nonstimulated fingers of the targeted hand. The results indicate that touch localization for the fingers involves integration of several sources of spatial information: the anatomical location of the touched finger, its position in external space, the stimulated hand, and the hand to which the touch is (re)mapped in external space.