The effect of entrainment on the timing of periodic eye movements.

We performed an experiment in which eight healthy individuals made periodic eye movements at five pacing interval conditions (500 ms, 750 ms, 1000 ms, 1250 ms, and 1500 ms). Three methods of entrainment were used in the synchronization phase: saccade, continuous pursuit and discontinuous pursuit. The stimulus train was extinguished and in the continuation phase, subjects made saccadic eye movements at the entrained movement frequencies between two static targets. Using the Wing-Kristofferson model, clock and motor variance were extracted from the time series of continuation trials for all three entrainment conditions. Our results revealed a main effect of time interval on total variance clock variance (as predicted by Weber's law) and on motor variance. We also report that the pursuit entrainment conditions resulted in and mean duration and variance to the saccade entrainment. These results suggest that the neural networks recruited to support a periodic motor timing task depend on the method used to establish the temporal reference.