Intermittency in human manual tracking tasks

R. Christopher Miall, D. J. Weir, J. F. Stein

Research output: Contribution to journalArticlepeer-review

171 Citations (Scopus)


We confirm Craik's (1947) observation that the human manually tracking a visual target behaves like an intermittent servo-controller. Such tracking responses are indicative of “sampled” negative-feedback control but could be the result of other, continuous, mechanisms. Tracking performance therefore was recorded in a task in which visual feedback of the position of the hand-held joystick could be eliminated. Depriving the subjects of visual feedback led to smoother tracking and greatly reduced the signal power of their responses between 0.5-1.8 Hz. Their responses remained intermittent when they used feedback of their own position but not of the target to track a remembered (virtual) target. Hence, intermittency in tracking behavior is not exclusively a signature of visual feedback control but also may be a sign of feedback to memorized waveforms. Craik's (1947) suggestion that the intermittency is due to a refractory period following each movement was also tested. The errors measured at the start of each intermittent response, during tracking of slow waveforms, showed evidence of a small error deadzone (measuring 0.7 cm on the VDU screen or 0.8° at the eye). At higher target speeds, however, the mean size of starting errors increased, and the upper boundary of the distribution of starting errors was close to that expected of a refractory delay of approximately 170 ms between responses. We consider a model of the control system that can fit these results by incorporating an error deadzone within a feedback control loop. We therefore propose that the initiation of intermittent tracking responses may be limited by a positional error deadzone and that evidence for a refractory period between successive corrective movements can be satisfied without evoking an explicit timing or sampling mechanism.

Original languageEnglish
Pages (from-to)53-63
Number of pages11
JournalJournal of motor behavior
Issue number1
Publication statusPublished - 1 Jan 1993

ASJC Scopus subject areas

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


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