INFLUENCE OF AFFERENT FEEDBACK ON ISOMETRIC FINE FORCE RESOLUTION IN HUMANS

The influence of afferent feedback on isometric fine force resolution was studied in humans. Subjects performed the smallest possible isomet ric flexion force increments with the index finger while visual, cutan eous, and muscle spindle feedback conditions were varied. In the contr ol conditions with visual feedback, isometric force resolution was fin est and independent of cutaneous or muscle spindle feedback. In the ab sence of visual cues, force resolution was significantly coarser. When agonist muscle spindles were vibrated (100 Hz and 150 Hz), fine force resolution capabilities declined further. Diminution of cutaneous fee dback per se did not affect fine force resolution. However, the effect of agonist vibration was attenuated when full cutaneous feedback was available. We conclude that in voluntary isometric contractions the de gree of fine force resolution depends on the type of afferent feedback available for calibrating central motor commands. Visual feedback is more powerful than spindle feedback, which is more efficient than cuta neous feedback. The extent to which the central motor command itself c ontributes to the sensation of force is indirectly implied by reproduc ible, yet coarser force resolution levels when peripheral information is minimized.