A voluntary movement can be made rapidly or slowly, and it appears to the person making a movement that it can be made about equally accurately at any intermediate speed. However, if the mechanism responsible for timing the movement has one or more characteristic frequencies of oscillation, the actual speed of movement would be expected to depart from the intended value in the direction of one of these frequencies. That is, each intended speed would be subject to its own degree and direction of bias. Collyer, Broadbent, and Church have recently demonstrated a pattern of biases across a wide range of movement speeds which confirms the existence of characteristic frequencies in motor timing and allows them to be measured. This finding shows that motor timing is categorical rather than continuously adjustable, and this is an important step toward an adequate theory of the timing of voluntary acts. However, much remains to be learned about this categorical timing mechanism. This research is designed to examine some basic properties of this type of motor timing. The basic task involves repetitive manual tapping at target rates set by a series of computer- generated sounds. It will involve three types of experiments: (1) Manipulation of the relative contribution of external and internal bases for motor timing, with the expectation that the biases introduced by characteristic frequencies will be greatest when internal (cognitive) factors predominate; (2) Study of the role of the characteristic frequencies in controlling fast and slow speeds of movement and transitions between speeds; and (3) Examination of correlations between characteristic frequencies and other behavior such as preferred rates of movement and perceived durations of signals. The research will advance our understanding of normal motor timing processes and provide information about a potentially important link between time perception and time production.
