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Application of phase spectral analysis for brain stem auditory evoked potential detection in normal subjects and patients with posterior fossa tumors.

A statistical test of the brain stem auditory-evoked potential (BAEP) detection is presented. The data were collected by averaging groups of 200 sweeps in order to obtain a set of group averages. The synchrony measure (SM), which represents the degree of reproducibility for group averages, is used as a statistical measure and is calculated from the phase variance for selected Fourier components of the group averages. The sensitivity of the test was demonstrated on 375 normal BAEPs with different stimulus intensities (45, 60, 75 dB SL) from both the ipsilateral and contralateral recordings, and on 82 BAEP recordings in the absence of stimulus. In all 375 cases of normal BAEPs the SM exceeds the threshold level while in the absence of stimulation the SM was below the threshold level. The clinical usefulness of the test was demonstrated on 22 patients with tumors of the posterior fossa. The absence of the BAEP was detected in 21 patients. In 12 out of 13 patients with lateralized tumors (acoustic neuromas), absence of the BAEP was noted for stimulation of the affected ear.