Spectral Analysis of Auditory Evoked Potentials with Pseudorandom Noise Excitation

Pseudorandom noise (PRN) of various bandwidths was used in testing both normal and hearing impaired subjects by means of auditory-evoked potentials (AEP´s). The AEP´s were studied in the frequency domain via spectral analysis rather than in the time domain as is often done. Spectral analysis provides such system features as power spectral densities (PSD´s) and transfer and coherence functions. The results show that these AEP´s are similar to the frequency following responses obtained with pure tones. The PSD´s of the evoked responses tend to correlate slightly with those of the PRN simuli, as verified by the presence of coherence between the stimulus and the response. The average coherence over the bandwidth of the stimulus decreases with increased sensory-neural hearing loss and also as the stimulus bandwidth is increased. No unique transfer functions, with respect to the subjects or the intensities of stimuli, could be obtained. However, an attempt has been made to correlate subjects´ audiograms with the spectral analysis results.