THE EFFECTS OF ALTERED SENSORY INPUT ON A SKILLED MOTOR TASK

The purpose of this study was to characterize the manner in which altered visual input modifies the voluntary motor behavior seen during stair walking.;Subjects walked down three steps while a surface electrode placed over the gastrocnemius-soleus complex of the swinging limb recorded muscle activity, a potentiometer measured sagittal plane ankle motion, switches registered bilateral foot-ground contact and release, an accelerometer recorded vertical acceleration and a transducer in the second step measured the force with which it was hit. The EMG signal was integrated within 10 ms bins over the entire first swing interval (toe off to toe strike) and ease of landing was described by the angular velocity which occurred at the ankle and the rate at which load was applied at the time of contact with the second step.;Control performance was compared to that recorded under the following conditions: blindfolded with audition masked and unaware of stair height; aware of stair height and wearing a collar which masked stair height during descent; aware of stair height and wearing a collar while the room moved.;Precontact muscle activity was diminished and landing was altered for each of the experimental conditions. These results imply that there is adequate time for a sensory perturbation which occurs during the swing phase to alter the subsequent landing.;Fourteen healthy human subjects walked down three steps whose height was randomly varied to be 20.3, 30.5, or 40.6 cm. The steps were surrounded by a room 2.77 m high and 0.7 m wide which was connected through a servo system to the vertical position of the subject. Circuitry was developed to allow the room to remain still, move up, or move down as the subject stepped from the first to the second step.;Conclusions from this study are as follows: (1)Vision is necessary for optimal stair walking performance. (2)The subject's pre-task execution expectation can alter subsequent motor performance. (3)The relationship between precontact gastrocnemius-soleus muscle activity and the subsequent landing is related to landing strategy. (4)Visual information predominates when there is a conflict between visual and other sensory information. (5)Specific visual information is necessary for the input from the visual system to override the other sensory systems.