TACTILE AGNOSIA - UNDERLYING IMPAIRMENT AND IMPLICATIONS FOR NORMAL TACTILE OBJECT RECOGNITION

In a series of experimental investigations of a subject with a unilate ral impairment of tactile object recognition without impaired tactile sensation, several issues were addressed. First, is tactile agnosia se condary to a general impairment of spatial cognition? On tests of spat ial ability, including those directed at the same spatial integration process assumed to be taxed by tactile object recognition, the subject performed well, implying a more specific impairment of high level, mo dality specific tactile perception. Secondly, within the realm of high level tactile perception, is there a distinction between the ability to derive shape ('what') and spatial ('where') information? Our testin g showed an impairment confined to shape perception. Thirdly, what asp ects of shape perception are impaired in tactile agnosia? Our results indicate that despite accurate encoding of metric length and normal ma nual exploration strategies, the ability tactually to perceive objects with the impaired hand, deteriorated as the complexity of shape incre ased. In addition, asymmetrical performance was not found for other bo dy surfaces (e.g. her feet). Our results suggest that tactile shape pe rception can be disrupted independent of general spatial ability, tact ile spatial ability, manual shape exploration, or even the precise per ception of metric length in the tactile modality.