Covert processing of information in hemianesthesia: a case report.

A 69-year-old patient with a cortical lesion of the primary sensory area showed a surprising sensorimotor control of the anesthetized arm. This observation suggested the existence of residual capacities of somesthetic information processing. This hypothesis was tested using a forced choice procedure on four tasks involving discrimination between different characteristics of the tactual-kinaesthetic stimulus. Whereas the patient was unable to identify the direction of movement or to discriminate between different letters, she could detect the occurrence of the stimulation or its dynamic quality significantly well. These results are discussed in reference to an anatomo-functional organization analogous to the one underlying the processing of visual information.