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 move more or less quickly; they also adopt different relative coordination patterns. In the present article, the authors asked whether similar transitions occur for unimanual hand movements when speed is slowed below the preferred speed. Participants moved a handheld dowel back and forth between 2 large circular targets in time with a metronome at periods between 370 ms and 1667 ms. The authors 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, so 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.

Keywords:

• aiming
• coordination patterns
• dwell time
• preferred speed movement
• rate control

ACKNOWLEDGMENT

The authors thank Rajal Cohen, Jeffrey Eder, Bruno Repp, and Joe Santamaria for helpful comments. The authors also thank Christine Schiller and Matthew Walsh for their help with data collection. This research was supported by grant SBR-94-96290 from the National Science Foundation, grants KO2-MH0097701A1 and R15 NS41887-01 from the National Institute of Mental Health, and grants from the Social Science Research Institute and the College of Liberal Arts Office of Research and Graduate Studies at Pennsylvania State University. Dagmar Sternad was supported by grants from the National Science Foundation, BCS-0450218, the National Institutes of Health, R01 HD045639, and the Office of Naval Research, N00014-05-1-0844.