Preferred tempo of motor performance.

The magnitude of individual differences in within-subject variability in performance of repetitive movements at a self-paced tempo was investigated. Subjects (N = 150) performed an accuracy task involving consecutive arm swings at an individually chosen tempo. Odd-even and serial half reliability coefficients for within-subject variances (r =.72, .66) were significant at the .01 level. Also, statistically significant correlation coefficients ranging from .70 to .76 were found between subjects' mean response times and within-subject variances. With the effect of mean response times partialled out, the reliability coefficients for within-subject variances were reduced (r = .41, .30) but were still statistically significant (p<.01). The findings indicated that individual differences in within-subject variance were present to a moderate degree.