Moving the Arm at Different Rates: Slow Movements are Avoided

Abstract

Qualitative and quantitative changes characterize locomotion and rhythmic interlimb coordination at different speeds. Legs and hands do not just move more or less quickly; they also adopt different relative coordination patterns. Here we asked whether similar transitions occur for unimanual hand movements when speed is slowed below the preferred speed. Participants moved a hand-held dowel back and forth between two large circular targets in time with a metronome at periods between 370 ms and 1667 ms. We analyzed the kinematics of participants’ movements at each period and found that proportional dwell time and number of peaks in the velocity profile increased as driving periods increased. Path lengths and peak velocities remained relatively constant for driving periods exceeding 800 ms. Participants made only gradual changes to their movement parameters, such that they went from a continuous mode to a more discrete mode of behavior for longer driving periods. Thus, unlike for rhythmic bimanual movements or locomotory patterns, there are quantitative but no clear qualitative changes for unimanual movements. The results suggest that participants tried to move close to their preferred tempo at different rates, and that they avoided moving slowly.