Effects of Phase Difference on the Latency of Compound Action Potential (CAP) in the Harmonic Stimulation

Lim, Duk Hwan

Abstract

BACKGROUND AND OBJECTIVE: Comprehensive auditory evaluation often requires complex sounds in addition to pure tones. The sum of pure tones (harmonic stack) is a useful complex stimulus in examining auditory response interactions. In a harmonic stimulus, the phase relationship between pure tones may affect the results of auditory evaluation. The aim of this study was to investigate the effects of relative phases between harmonic frequencies on the latency of compound action potentials (CAP).
MATERIALS AND METHODS
Relative phases between two frequencies of a harmonic were varied systematically and compound action potentials (CAP) were, then, recorded in guinea pigs in response to these stimuli. These latencies were compared with the latency to the harmonic complex with the relative phase of zero.
RESULTS
The latency of the CAP was shifted within a restricted range to the stimuli with systematically varied phases. These relative phases between the two frequencies directly affected the temporal waveform of the harmonic stimulus although all of these stimuli exhibited the same frequency spectrum. Some phase spectra appeared to contribute more to the latency difference of the CAP.
CONCLUSIONS
Findings indicated that the phase relationship in a tonal complex is important to the latency of the CAP, and the phase should be controlled carefully in the objective auditory evaluation with tonal complex stimuli.