Differences between fingers and hands in tapping ability: dissociation between speed and regularity.

The mean inter-tap interval (ITI) and the coefficient of variation of the ITI (ITIVAR) were measured in all five fingers of the preferred and non-preferred hand in two experiments. Subjects were right- or left-handed, males or females in experiments I and right-handed female typists, pianists, or controls in experiment II. Lack of consistent difference between right- and left-handers, and between those with and without special manual skills, suggested that hand differences in tapping are not a consequence of differential practise between hands. ITI showed differences both between fingers and between hands, whereas ITIVAR only showed differences between fingers. Separate mechanisms are inferred, and it is suggested that differences between fingers are a function of differential peripheral motor control, whereas differences between hands are a consequence of cerebral dominance of control mechanisms, and a model is presented.