Late onset of age-related difference in unpaced tapping with no age-related difference in phase-shift error detection and correction.

An age-related difference in accuracy and variability of unpaced timing tasks suggests that the internal clock for the processing of intervals of hundreds of milliseconds slows down with age. However, we recently found that sensorimotor synchronization (SMS) error detection and correction abilities are preserved into the ninth and tenth decades, although fastest tapping rate decreases (Turgeon, Wing, & Taylor, 2011). Further testing with the same sample of participants in the present study provides evidence for slowing of the internal clock with age. We report an age-related decrease in spontaneous motor tempo (SMT), an age-related increase in produced period when estimating target durations of 500 ms and 1000 ms, and an age-related increase in "clock variance" in continuing tapping intervals ranging from 300 ms to 900 ms. The profile of age-related difference across the 2 studies suggests a late onset, starting in the ninth decade, of clock slowing without age-related difference in timing error monitoring. The finding that unpaced timing is affected by age, whereas paced timing involved in SMS is not, suggests separate underlying mechanisms for internally generated intervals and monitoring of external timing errors.