Limb segment information transmission capacity.

Movement time for finger, wrist, and whole arm motions were investigated in relation to Fitts' Index of Difficulty (ID = log2 2A/W) over movement distances of 0.25 to 30.5 cm. Results supported Fitts' original theory that various limb segments may show different maximum information processing rates. Short-distance finger and wrist motions showed much higher rates than longer distance arm motions. Examination of motion trajectories qualitatively supported a descriptive model whereby a visually mediated discrete correction control process is used. However, evidence of severe nonlinearities in the measured humam movement responses did not support the use of linear control models in explaining the empirical validity of Fitts' law in predicting human motor performance.