Impaired Haptic Size Perception Following Cortical Stroke: A Case Study

Accurate encoding of object size is important for the control of grasp aperture and object manipulation. When an object is grasped between index finger and thumb, size perception may be based on kinaesthetic input, indicating digit separation, and tactile input from the digit pads, signalling the moment of contact with the object. We present a case study of stroke patient JB with tactile extinction who underestimated the size of contralesional objects in simultaneous bimanual grasping and, with the passage of time, when objects were held in a contralesional unimanual grasp. We propose that extinction of tactile input from the contralesional finger pads signalling the moment of contact with grasped objects resulted in the contralesional digits being perceived to be closer together than those of the ipsilesional hand. In contrast, when objects were held in a contralesional unimanual grasp, fading tactile afferent input from the finger pads, in combination with a stable motor output and sense of effort resulted in fading perception of object size.