The period evoked potential: objective response detection and 500 Hz thresholds in normally hearing adults

In this study an investigation of the period evoked potential (PEP) (a variant of the frequency following response) recorded from 27 ears in 15 normally hearing adults was performed. Response waveforms were averaged over 5008 cycles (acquisition time = 10.016 s) and 50080 cycles (100.16 s) of 500 Hz pure tone stimuli, at intensities ranging between 15 and 75 dB SPL. Responses were assessed using both subjective visual coherence and objective measures based on RMS voltage, magnitude squared coherence and phase coherence. Thresholds derived from subjective and objective measures ranged from 25 dB SPL to >75 dB SPL, with RMS voltage giving significantly the poorest performance. Subjective visual coherence estimates of threshold were not significantly different from objective coherence estimates, but the latter were preferred since they eliminate tester bias. The best inter-ear average threshold was 35 dB SL and was obtained using magnitude squared coherence calculated from waveforms averaged over 50080 cycles of the stimulus.