Auditory P50 obtained with a repetitive stimulus paradigm shows suppression to high-intensity tones

We manipulated stimulus intensity and number of frequency bands in auditory stimuli in order to investigate the nature of P50 in human auditory evoked potentials. Pure-tone and mixed-tone conditions were examined. For each co ndition, four stimulus intensities were used: 55, 70, 85 and 100 dB sound p ressure level (SPL). The P50s were obtained at Cz using a repetitive stimul us paradigm. P50 amplitudes increased as stimulus intensities increased up to 85 dB; with 100 dB stimulation amplitudes decreased. The number of frequ ency bands in the stimulus did not affect P50 amplitude. Considered in term s of P50 suppression under a conditioning/testing paradigm, the results sug gest that the P50 wave reflects activity of the sensory gating mechanism in humans.