Abstract
The dual process model (Yoshida, 1990) was applied to visual evoked potentials to photic stimulus trains (train-VEPs). A small light disk subtending 2 or 5 degrees in visual angle was presented at different contrast levels of 1.0, 2.2, and 3.4. A pulse-light with a duration of 10ms was repeated, as a stimulus train, at the intervals of 50,100, and 200ms for the period of 1 s. Typical train-VEPs from the midline occiput (Oz) were analyzed. The model hypothesized that the train-VEPs were composed of the on and off basic dual (excitatory and inhibitory) processes and the small after rhythmic waves whose latencies were shorten by light adaptation. Thirteen parameters of the model were determined by the Fletcher-Powell method and the multiple regression method. The synthesized model waves fitted the raw train-VEPs well, and were able to express their early suppression and later enhancement of amplitudes. Contrast potentials of train-VEPs had close relationships with the steady-state VEPs and psychological correlates.
