| Abstract
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This dissertation examines the reference frames used in the representation of location of tactile stimuli, using data from neurologically intact participants in experiments that use a spatial interference effect, and from brain-damaged individuals with tactile perception deficits. Previous research indicates that neurologically intact individuals respond more slowly in a non-spatial task when the stimulus and response are on different sides of space (the Simon effect, Simon & Small, 1969). The work presented in this dissertation includes a novel application of the Simon effect paradigm to examine tactile reference frames. The results revealed that---when a participant's arms are uncrossed---tactile stimulus codes are generated based on a representation that encodes location relative to the position of another stimulus (a relative position reference frame). However, when participants performed the task with their arms crossed, the data indicate that tactile stimulus codes are generated based on a somatotopic reference frame in which, for example, the left hand is always encoded as left regardless of hand position. The second part of this dissertation examines the performance of two brain-damaged individuals. RSB and DLE, with left-hemisphere lesions. Each participant exhibits (a) tactile synchiria, a deficit in which stimulation on the ipsilesional side of the body is perceived as stimulation on both sides of the body, and (b) tactile extinction, in which bilateral stimulation is perceived only on the ipsilesional side. First, the investigation revealed that DLE 'accurately' localizes the 'phantom' synchiric percept at a location contralateral to the ipsilesional stimulation. This result is consistent with the claim that there is cross-hemispheric somatosensory connectivity, and that removal of inhibition of this cross-hemispheric connection subsequent to lesion allows for contralateral synchiric sensations. Second, further testing demonstrated that DLE and RSB exhibited a pattern of increased synchiria and decreased extinction as their hands moved from ipsilesional to contralesional space in both trunk- and head-centered reference frames. These and other results demonstrate that cross-hemispheric connections are inhibited by multiple representations that operate in trunk-centered, head-centered, and relative position reference frames. Overall, the results of this dissertation provide evidence for the involvement of various reference frames in representing the location of tactile stimuli.
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