Integration of somatotopic and spatiotopic reference frames in tactile localization


Accurate processing of tactile stimuli requires our brain to both localize the stimuli on the body surface and integrate the spatial location and orientation of the stimulated area. Processing initially occurs within a somatotopic reference frame and is subsequently remapped to incorporate the spatiotopic reference frame. When body parts are dissociated from their hemispace, such as when the hands are crossed, the spatiotopic representation of the crossed posture must be integrated with the somatotopic representation to achieve accurate localization. For the hands, this remapping has been shown to occur within 300 ms (Yamamoto & Kitazawa, 2001). With more unusual postures, such as crossing the middle finger over the index, there appears to be a deficiency in remapping and consequently poor integration of the crossed posture (de Haan et al., 2012). We investigated whether postural familiarity influences spatiotopic integration of different finger postures. Participants were asked to make both temporal order (which finger was stimulated first/second) and directional judgments (spatial direction of stimuli) of tactile stimuli applied successively to their left index and middle fingers which were held in different flexed postures. Stimuli were delivered at 7 SOAs and 2 orders. In both judgment tasks, participants consistently made accurate judgments at longer SOAs, suggesting that they were able to incorporate different, but familiar, finger postures given sufficient time. Response times were also shorter at longer SOAs. Findings suggest that postural familiarity can influence the integration of somatotopic and spatiotopic information and facilitate the accurate localization of tactile stimuli.

Acknowledgments: Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).