THE DEPENDENCE OF DISCRETE MOVEMENTS ON RHYTHMIC MOVEMENTS - SIMPLE RT DURING OSCILLATORY TRACKING

Four experiments examined the time taken to initiate a discrete movement of the fingers while performing rhythmical tracking movements with an arm. Simple reaction time (RT - finger flexion to a tone) was measured at various phases of oscillations of the forearm as it tracked a visual stimulus either in phase or antiphase. In Experiments 1 and 2, discrete responses were made by the oscillating hand, either parallel or orthogonal to the plane of motion of the oscillation. In both experiments, RT differed as a function of phase of the response cycle rather than phase of the stimulus cycle. Experiment 3, which tested RTs at different locations of a stationary hand, demonstrated that these differences are not attributable to the locations at which responses were solicited. Experiment 4 measured RT in a stationary right hand while the left hand oscillated; again dependence on response phase was observed. Tracking condition effects and frequency effects were interpreted in terms of the coupling of the arm as oscillator to the visual oscillator; phase effects were interpreted in terms of the phase relation between the rhythmic action and the discrete action.