Date of Award

2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Psychology

Department

Psychology

First Advisor

Charles Collyer

Abstract

It is well known that people can produce regular rhythms, such as clapping or finger tapping-what is not well known is how such rhythms are maintained over time. One of the simplest activities to measure human rhythms is "continuation finger tapping," in which subjects are first asked to copy an audible rhythm by tapping along with their finger, and then attempt to maintain that tapping rate after the pacer tones stop.

The purpose of this study was to learn more about how tempo is regulated in continuation finger-tapping. In this context, "regulated" refers to the rules, both empirical and hypothetical, that govern the maintenance of a uniform tapping rate. The method used in this study was to determine whether there was evidence of two strategies for regulating rhythms: 1) Subrange/tapping style, and 2) Targeted drift-and-correction. Both archival and new data were analyzed for this research.

The first phase of the study was to determine whether at least two distinct subranges of tapping behaviors exist, and whether subjects used different tapping strategies for each subrange as reported in Vaughan, Matson, & Rosenbaum (1998). Two different variables were analyzed for the subrange/tapping style phase of the study: Duty Cycle (normalized time-on-target) and Velocity (force upon target).

The second phase of the study was to determine whether the subjects used a "target-sweeping" strategy to maintain a steady rhythm for their tap intervals (IRIs). In such a process, they would introduce continual, small negative biases ("drift") which would then be countered by occasional, larger positive corrections. If this regulatory method were used to maintain an average rhythm, there would be evidence of bimodal symmetry in the distributions of the IRI First Differences.

The first main finding is that Duty Cycle and Velocity change continuously as a function of ISL This finding stands in marked contrast to two hypotheses that were plausible prior to this research. The first hypothesis was that duty cycle might have been constant, which would suggest that the hand motion for finger-tapping is a very simple process, in which all elements are "scaled" up or down proportionately to match a particular tempo. The data suggest rather that the pattern changes with the rate, but the change is very orderly, resembling a smooth quadratic function. The second hypothesis that was plausible before this study was that of discontinuous change. Discontinuous change had been suggested by Vaughan's terms "elastic" and "intermittent", which were two hypothesized regulatory styles for fast and slow tapping respectively. The data suggest that a sharp distinction between these two styles is not useful, because as ISI changes there is a gradual rather than an abrupt transition.

The second main finding is that distributions of IRI First-Differences do not conform to the prediction of a simple drift-and-correction theory of tempo regulation. Instead of a bimodal distribution, with one component representing numerous little "drifts" and the other representing a few bigger "corrections", we see a variety of distributional shapes, most of which are unimodal.

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