The authors investigated performance in 2 rhythm tasks in young (M = 23.8 y
ears) and older (M = 71.4 years) amateur pianists to test whether slowing o
f a central clock can explain age-related changes in timing variability. Su
ccessive keystrokes in the rhythm tasks were separated by either identical
(isochronous) time intervals or varying (anisochronous) intervals. Variabil
ity was comparable for young and older adults in the isochronous task; pron
ounced age effects were found for the anisochronous rhythm. Analyses of cov
ariances between intervals rule out slowing of a central clock as an explan
ation of the findings, which instead support the distinction between target
specification, timekeeper execution, and motor implementation proposed by
the rhythm program hypothesis (D. Vorberg & A. M. Wing, 1996). Age stabilit
y was found at the level of motor implementation, but there were a.-c-relat
ed deficits for processes related to target-duration specification.