Intact tactile detection yet biased tactile localization in a hand-centered frame of reference: A case study

We examined the performance of an individual with subcortical damage, but an intact somatosensory thalamocortical pathway, to examine the functional architecture of tactile detection and tactile localization processes. Consistent with the intact somatosensory thalamocortical pathway, tactile detection on the contralesional hand was well within the normal range. Despite intact detection, the individual demonstrated substantial localization biases. Across all experiments, he consistently localized tactile stimuli to the left side in space relative to the long axis of his hand. This was observed when the contralesional hand was palm up, palm down, rotated 90° relative to the long axis of the trunk, and when making verbal responses. Furthermore, control experiments demonstrated that this response pattern was unlikely a motor response error. Overall these findings provide strong evidence that tactile detection and localization are completely dissociable processes, and tactile localization on the body is influenced by proprioceptive information specifically in a hand-centered frame of reference. We discuss implications of these findings on models of tactile processing.