Force Modulation as a Source of Hand Differences in Rapid Finger Tapping

The purpose of this study was to examine the factors contributing to hand differences in rapid single finger tapping. To this end, task-defined temporal variables and motor outflow, as reflected by the magnitude and duration of force, were simultaneously measured. Thirty-one right-handed college age subjects performed a rapid finger-tapping task with the index finger of the right and left hands. The order of hand use was counterbalanced across subjects. Significant differences favoring the right hand were found in the rate of tapping as indicated by the inter-tap interval, dwell (duration of key closure), the interval between force peaks and the variance of the force peak intervals. Additionally, relative to the left hand, the right hand used significantly smaller amounts of force and exhibited less variation in force. These data are conceptually consistent with Kimura’s (1979) contention that the left hemisphere is uniquely specialized to control sequences of action such as postural transitions. However, Kimura argues that this unique ability is manifest in multiple-finger sequences but not rapid single finger tapping. The present data indicate such a mechanism may be observed in rapid single finger tapping if the appropriate dependent measures are obtained.