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Abstract In typing, when the fingers executing two successive movements are on the same hand, the time between keystrokes is longer than when the fingers are on different hands. Biomechanical limitations of the hands are thought to account for this difference. The generality of this finding was explored by investigating skilled pianists' performance of two successive notes. Experiment 1 failed to find comparable differences in timing as a function of the hands involved. Experiment 2, employing both a piano production and a typing task, replicated the previous piano performance results, and revealed that the timing differences in typing were limited to letter sequences requiring fore-aft and lateral finger movements. Experiment 3 extended this finding to piano performance. Together, these findings clarify the nature of biomechanical constraints on skilled manual performance. The ability of adults to coordinate hand and finger movements during skilled manual tasks is impressive, especially in the two prominent exemplars of such skill: typing and piano performance. Typically, a skilled typist produces between 60-80 words per minute, or approximately 5-7 keystrokes per second, with typing speed reaching up to about 200 words per minute (Genther, 1983; Rumelhart & Norman, 1982). Piano performance can be even more rapid. Lashley (1951) noted that piano performance has the potential for 15 movements per second; others suggest that pianists routinely play up to 30 sequential notes per second over extended passages (Rumelhart & Norman, 1982). Accordingly, the study of piano performance and typing can provide insight into processes of skilled manual motor control. By and large, the majority of such work has examined transcription typing, in which typists type short passages of prose. Analyses of the timing of typing, and of errors made during typing, provide a window onto the cognitive and motoric processes involved in this behaviour. One focal point in typing research involves the production of "digraphs," which are sequences of two different letters, identified with reference to the hands and fingers involved in their production. Two common classes of digraphs are two-hand (2H) and two-finger (2F) digraphs, which account for roughly 50% and 34% of English digraphs, respectively (computed using data in Solso, Barbuto, & Juel, 1979). A 2H digraph consists of two keystrokes typed by fingers from different hands; examples of 2H digraphs...