Action-perception dissociation: preserved reactive grip force despite tactile extinction due to cortical stroke

Sensory extinction following stroke, manifests as a bias in spatial attention towards ipsilesional spatial locations, which arises when stimuli from other locations compete for pathologically limited attentional resources. In the tactile domain, extinction results in a failure to verbally report tactile stimuli applied to a contralesional body part when they are timed to coincide with ipsilesional tactile contact. While it is typical for research in this area to focus on the verbal report of sensory stimuli as a measure of conscious awareness, work in visual extinction has shown that when contralesional stimuli fail to reach conscious awareness, they may still contribute to the control of actions. We describe the case of a woman with tactile extinction who failed to verbally report contralesional tactile input associated with perturbations to bimanual grasp. Despite this, the same stimulus was sufficient to drive reflexive grip force responses.