An empirical note on attaining a spatial target after distorting the initial conditions of movement via muscle...

Can one's limb be accurately positioned to a spatial location without a veridical estimate of the initial conditions of movement? The experiment reported here examined this question by distorting perception of a limb's starting position via muscle vibration. Subjects executed rapid flexion movements under no-vibration, contralateral arm vibration, and ipsilateral arm vibration conditions. Vibration was applied to the biceps for 10 sec prior to the start of a reproduction movement. The results showed that vibration on the ipsilateral arm caused a significant increase in reproduction error, relative to the no-vibration and contralateral-vibration conditions. This finding provides additional evidence that accurate knowledge about the initial conditions of movement is a necessary component in positioning a limb.