State space analysis of human timing: Timing accuracy limit is 9 ms

Understanding timing accuracy in humans is critical as it presents an important constraint on skilled motor performance. The limits intrinsic to the central nervous system, however, remain highly disputed and reported values range from 1ms to 9ms. Using a virtual throwing task that allowed precise control and measurement of task performance, this study explored the bounds of human timing accuracy in a long-term learning experiment. Eleven naive subjects practiced 240 throws per day for 11 days. We hypothesized that subjects (1) cannot control timing more accurately than 9 ms, and (2) shape their hand trajectory to become less sensitive to timing inaccuracy. A state space analysis of timing developed by [1] was used to quantify change in timing accuracy and sensitivity of the hand trajectory with practice. Consistent with our hypothesis, results revealed that subjects reached a limit in their timing accuracy at approximately 9.5 ms. Subjects also showed a monotonic increase of time insensitivity of the hand trajectory. These results support the prior finding of [1] that timing accuracy is a limiting factor in skilled performance, and that humans shape their movements to compensate for this intrinsic limitation.