On the cerebral evoked response in man as a function of the intensity of flicker stimulation

Abstract

1. 1. The average evoked potentials (cross-correlograms of the flash stimulus and EEG potentials) in six areas of the scalp of normal adults (parieto-occipital on both sides), elicited by flicker at 8–12/sec were observed in relation to the stimulation intensity and location. 2. 2. In spite of individual variations, the response was predominant on the occipital and parieto-occipital regions and its size increased and its phase changed by increasing the stimulating intensity. 3. 3. In many instances, a sinusoidal response was induced using weak or intermediate intensity monocular stimulation, whereas the response configuration changed to a one to two correspondence with the stimulus with binocular or intense monocular stimulations. Typically, the maximal amplitude in the response and superimposed peak height in the frequency spectrum of the response had approximately linear relationships to the logarithmic amount of the relative strength of the mono- and binocular stimulations. Augmentative and depressive binocular interactions were revealed respectively by weak and intense stimulations. 4. 4. Peak latencies of the response components tended to be decreased by strengthening the stimulation. The fast response of 20–30 msec peak latency showed little fluctuation, whereas the fluctuation in the later responses was considerable. 5. 5. The spatio-temporal contour of the evoked response were observed in relation to the stimulation intensity. 6. 6. It was postulated that the evoked potential in the parieto-occipital human scalp elicited by flicker at a frequency of about 10 f/sec is a mixture of primary and secondary responses.