Some sensory and motor factors influencing the control and appreciation of eye and limb position

Summary

Some aspects of the manner in which the central nervous system uses sensory information for the guidance of eye and arm movements were investigated. When subjects experience apparent motion of their restrained forearm, induced by vibration of their biceps muscle in the dark, they are able to pursue with their eyes at least part of this “motion” and to point with their nonvibrated limb to the apparent location of the vibrated arm. The presence of a small target light on the vibrated hand limits the extent of illusory change in limb position and results in illusory motion of the target light in the same direction as the arm motion. When asked to indicate the spatial position of the light or hand, subjects still point with their nonvibrated arm to the apparent locations. Although visual pursuit of the illusory motion of the forearm can still be elicited in the presence of the target light on the hand, the subjects' eyes remain steadily fixating the stationary target light when they are instructed to track its illusory motion. These findings demonstrate that sensory and motor factors affecting the perception of visual direction and the guidance of arm and eye movements can be differentially employed at several levels of central nervous control.