Evidence for a unimodal somatosensory attention system

Extinction is generally viewed as a disorder of selective attention for spatial locations. Recent physiologic, behavioral and lesion studies view spatial locations as a complex construct in which multiple modalities and motor systems are integrated. Accordingly, cross-modal and sensory-motor conditions often modify extinction. In a patient with tactile extinction, we tested the hypothesis that attentional deficits can also be confined to a specific sensory modality. Using objectively and subjectively balanced tactile stimuli and signal detection analysis, we found that our patient's contralesional tactile discrimination was not modulated by proprioceptive or visual input or by movement. By contrast, increasing the salience of the contralesional tactile stimuli did improve her contralesional tactile discrimination, consistent with our hypothesis that she suffered from a modality-specific attentional deficit. Additionally, she did not have any evidence of visual extinction, again bolstering our claim that her extinction was confined to touch. These data suggest that in addition to polymodal and sensory-motor attentional systems, spatial attention also operates on specific sensations. We also advocate the use of signal detection analysis, a method that has been surprisingly neglected in extinction research.