Abstract
Magnetoencephalography (MEG) was recorded under attend and ignore conditions to detect auditory steady-state responses (ASSR) to stimuli regularly repeated 40 times/s for 2 s, and synchronization of its 40-Hz component was measured using phase coherence. The major finding of the experiment was that the increased ASSR obtained by averaging in the attend condition was due to the increased degree of synchronization as the result of stimulation during the 40-Hz activity rather than the increase in power. We made a simple differential equation model for phase dynamics and compared the change of phase coherence calculated from the model with that obtained from the measurement. The model predicted the behavior of experimental phase coherence quite well, and the estimated value of one of the two parameters in the model representing the effect of stimulus on the phase was significantly larger for the attend condition than for the ignore condition, suggesting the validity of the model.
