Blind humans rely on muscle sense more than normally sighted humans for guiding goal-directed movement

The purpose of this study was to investigate whether totally blind humans rely on muscle sense for guiding goal-directed movement more than do blindfolded normally sighted humans. Twelve totally blind humans and 12 blindfolded normally sighted humans performed goal-directed movement. The subjects rapidly extended the elbow to a target angle in response to an auditory start cue while a vibration was applied to the antagonist muscle. Verbal feedback, concerning whether the movement was terminated near the target angle, was given immediately after each trial. Through these trials, the subjects acquired a movement terminating near the target angle. Immediately after these trials, the same movement was performed 20 times without the vibration and the verbal feedback. In the trials without the vibration and verbal feedback, the terminal angle of the movement was overshot as a reference to the last 5 trials where there was the vibration and verbal feedback. The amount of overshooting in the blind humans was significantly larger than that in blindfolded normally sighted humans. These findings indicate that for guiding goal-directed movement blind humans rely on their muscle sense more than do normally sighted humans.