Characteristics of unintentional movements by a multijoint effector

Tao Zhou, Lei Zhang, Mark L. Latash

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


The authors explored the phenomenon of unintentional changes in the equilibrium state of a multijoint effector produced by transient changes in the external force. The subjects performed a position-holding task against a constant force produced by a robot and were instructed not to intervene voluntarily with movements produced by changes in the robot force. The robot produced a smooth force increase leading to a hand movement, followed by a dwell time. Then, the force dropped to its initial value leading to hand movement toward the initial position, but the hand stopped short of the initial position. The undershoot magnitude increased linearly with the peak hand displacement and exponentially with dwell time (time constant of about 1 s). For long dwell times, the hand stopped at about half the total distance to the initial position. The authors interpret the results as consequences of a drift of the referent hand coordinate. Our results provide support for back-coupling between the referent and actual body configurations during multijoint actions and produce the first quantitative analysis of this phenomenon. This mechanism can also explain the phenomena of slacking and force drop after turning visual feedback off during accurate force production task.

Original languageEnglish (US)
Pages (from-to)352-361
Number of pages10
JournalJournal of motor behavior
Issue number4
StatePublished - Jul 4 2015

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Orthopedics and Sports Medicine
  • Experimental and Cognitive Psychology
  • Cognitive Neuroscience


Dive into the research topics of 'Characteristics of unintentional movements by a multijoint effector'. Together they form a unique fingerprint.

Cite this