Visual and vestibular impacts on tactile remapping: an exploration of reference frames and response demands.

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Perceiving the location of a touched object seems like a simple task that comes automatically with the tactile sensation; yet, integration of multiple sources of information is required. The sensation at the end of your finger must be integrated with the posture of your arm, the position of your body, and the information from your eyes. Transforming the tactile sense from the skin's surface to provide a location in space external to the body is termed tactile remapping. In the present project we use the tactile temporal order judgment (TOJ) task to explore the remapping processes. When the hands are placed across the body midline a profound deficit is observed—changes in the size of deficit are informative about how the brain remaps internal representations of tactile stimuli to an external representation. ****The goal of the present proposal is to examine the contribution of vestibular signals to this remapping process. The vestibular organs send signals to the brain about orientation of the head relative to gravity. Previous research on remapping had assumed, either implicitly or explicitly, that vision dominated. Recent work from our lab demonstrates a profound contribution from vestibular inputs. We explore these contributions through four converging projects. First, we change the response demands on participants to bias them to a body-based or space-based representation—this manipulation affects the size of the deficit. Second, we use the Tumbling Room at York University to place participants at various angles relative to gravity and independently manipulate the relative angle of the visual world. This allows a determination of the relative contributions from the two sensory sources. Third, we electrically stimulate the vestibular system to introduce noise, which masks its contribution to our sense of upright—this will provide a measure of how this system contributes to the remapping process. Finally, we tap the neural processes underlying remapping use Electroencephalography (EEG). The four projects converge on the understanding of how our representation of external space is constructed, and how tactile stimuli are remapped into that representation. ****For scientists focused on basic research, these data will help integrate findings from multiple research domains, both related to multisensory integration, and for modality-specific domains. In application, these findings will support development of higher fidelity human-computer interfaces, which will, in turn, support the development of augmented perception tools. Augmented perception can help restore function for people who have lost a sense, or provide additional information for those who have not. Finally, these findings will support research into how humans can function in outer space. All of these impacts will support research in Canada, and, in application, its citizens. **