The reach to grasp movement of blind subjects.

The importance of vision for the processing and coordination of the transport and manipulation components of a reach to grasp movement was assessed. Four blind volunteers (two men, two women; aged 25-40) were compared with matched control groups: (1) blindfolded and (2) full vision. Subjects reached 20 or 30 cm for a large or small diameter (6 cm or 0.7 cm, respectively) cylinder. For condition 1 trials they were given no instruction as to the type of grasp to adopt; for condition 2 they were instructed to consistently use a precision grip; while for condition 3 they were required to use whole had prehension. Blind subjects demonstrated a double grip pattern and either a low-velocity phase (20 cm) or a double transport movement (30 cm). However, their pattern of prehension with respect to intrinsic (size) and extrinsic (distance) cylinder properties was similar to that of the control groups. Grip aperture was appropriately scaled and, when greater precision was required, deceleration time was prolonged. Temporal coupling was evident between the two components. It was concluded that experience of vision is not necessary for the coordination or patterning of the basic reach to grasp movement. It does allow, however, for a movement consisting of only one opening and closing of the hand.