MULTICOMPONENT ACOUSTIC DISTORTION-PRODUCT OTOACOUSTIC EMISSION PHASEIN HUMANS .2. IMPLICATIONS FOR DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS GENERATION

Phase characteristics and latency of 2f1 - f2, 3f1 - 2f2, and 2f2 - f1 acoustic distortion product otoacoustic emissions (DPOAEs) recorded i n normally hearing adults have been described in a companion paper [Mo ulin and Kemp, ''Multicomponent acoustic distortion product otoacousti c emission phase in humans. I. General characteristics,'' J. Acoust. S ec. Am. 100, 1617-1639 (1996)]. Phase-versus-frequency functions (PFF) have been recorded using two methods, depending whether fl or f2 was swept in frequency, defining, respectively, an ''f1 sweep'' and an ''f 2 sweep'' method. The present study compares 2f1 - f2, 3f1 - 2f2, 4f1 - 3f2, and 2f2 - f1 DPOAEs phase characteristics, and latencies obtain ed by these two methods. For lower sideband DPOAEs, the f2 sweep gave consistently longer latencies than the fl sweep method, whereas no dif ference was obtained for the 2f2 - f1 DPOAE. This suggests that the lo wer sideband DPOAEs and the 2f2 - f1 DPOAE do not come from the same a spect of the traveling wave. The longer delay obtained with an f2 swee p is suggested to be due to an additional delay added by the proximity of the peak of the f2 traveling wave. The place-fixed and the wave-fi xed models of DPOAE generation are discussed, and an ''intermediate'' model of DPOAE generation is introduced to explain such additional del ay and the existence of phase irregularities which were observed in th e PFF. The ratio of the latencies obtained by the two sweep methods is frequency dependent and a relation to cochlear frequency selectivity is suggested. Finally, analysis of the differences in latency of the d ifferent lower sideband DPOAE components allowed an estimation of the return latency of DPOAEs. (C) 1996 Acoustical Society of America.