Micro-movements of varying difficulties: wrist and arm movements

An experiment was designed to determine the degree to which reducing movement amplitude (16A degrees, 8A degrees, to 4A degrees) while keeping the relative accuracy requirements (IDs 1.5, 3, 4.5, and 6) and visual feedback display constant by increasing the display gain proportional to the decrease in amplitude (1x, 2x, 4x) influences reciprocal aiming movements of the wrist and arm. Research on smaller amplitude movements is limited and inconclusive, but these types of movement conditions are becoming increasingly more important as microsurgery and micro-mechanical applications increase. Participants were asked to flex/extend their limb/lever in the horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. The targets and current position of the limb were projected on the screen in front of the participant. Target width was manipulated with amplitude constant (16A degrees, 8A degrees or 4A degrees). Results indicated that the linear relationship between MT and ID, typically observed for Fitts' tasks, was observed. There were moderate decreases in MT as amplitude was decreased but only for high ID movements. ID 6 movements at 4A degrees amplitude, for example, were produced more quickly than at amplitude 16A degrees without sacrificing end-point accuracy. The decrease in movement time was, however, related to increased dwell time and very low peak velocities.