MULTICOMPONENT ACOUSTIC DISTORTION-PRODUCT OTOACOUSTIC EMISSION PHASEIN HUMANS .1. GENERAL-CHARACTERISTICS

Phase characteristics and latency of 2f1 - f2, 3f1 - 2f2, and 2f2 - f1 acoustic distortion product otoacoustic emissions (DPOAEs) have been analyzed in 12 adults with normal hearing. Phase-versus-frequency func tions (PFF) have been recorded at each of ten pairs of primary frequen cies, by two methods, depending on which one of the primary frequencie s fl or f2 was swept in frequency. Whichever sweep method was used, lo cal phase irregularities were found in the PFF and were shown to be in dependent of the phase variability due to the measured noise, to be re producible and frequency specific. Phase irregularities were significa ntly greater in subjects exhibiting spontaneous otoacoustic emissions. The latency calculation was unaffected by phase irregularities provid ed that a suitably large range of f2/f1 ratio was used. The DPOAE late ncies that were obtained at low ratios of primaries were significantly longer than those obtained at higher ratios. For all DPOAE components and sweep methods used, the latency decreased as frequency increased from 750 Hz to 6 kHz. Substantial intersubject differences were found. They might be due to two main factors: differences in middle ear acou stic properties and in cochlea mechanical characteristics. The influen ce of pressure in the outer ear canal increased the DPOAE latencies re corded with both the fl and f2 sweep methods at low frequencies. Men s howed significantly longer 2f2 - f1 DPOAE latencies than women, especi ally at low frequencies, which can be attributed to the difference in length of the cochlea according to gender. Lastly, the latencies measu red using the f2 sweep were consistently longer than the latencies obt ained using an f1 sweep for lower sideband DPOAEs, but no difference w as observed for upper sideband DPOAEs. (C) 1996 Acoustical Society of America.