Locus of generation for the 2f1-f2 vs 2f2-f1 distortion-product otoacoustic emissions in normal-hearing humans revealed by suppression tuning, onset latencies, and amplitude correlations.
The present study used distortion-product otoacoustic emission (DPOAE) suppression tuning curves (STCs), DPOAE onset latencies (OLs), and DPOAE amplitude correlations to investigate the locus of generation of the 2f1-f2 DPOAE versus the 2f2-f1 DPOAE in humans. The results of the tuning study revealed that, for the 2f1-f2 DPOAE, the tips of the STCs tuned consistently below the geometric-mean (GM) frequency of the primary tones. In contrast, for the 2f2-f1 DPOAE, STCs tuned above the GM of the primaries, with 50% of the tip frequencies at, or above, the 2f2-f1 frequency place. When the average ratio of the 2f2-f1 to the 2f1-f2 tip frequencies was computed, a factor of 1.44 provided an estimate of the frequency shift needed to align the two DPOAE generation sites. Other results showed that OLs for the 2f2-f1 DPOAE were uniformly shorter than those for the 2f1-f2, with differences at the low frequencies amounting to as much as 6-7 ms. Further, for both DPOAEs, curves describing latency decreases as a function of increasing GM frequencies were best fit by power functions. Shifting the GM frequency producing the 2f2-f1 DPOAE by a factor of 1.6 caused the latency distributions for both DPOAEs to overlap thus resulting in a single function that described cochlear delay as a function of GM frequency. Finally, for each GM frequency in the DP-gram, sliding correlations from 108 normal ears were performed on both DPOAEs by holding the primaries producing the 2f1-f2 DPOAE constant, while all 2f2-f1 DPOAE amplitudes were successively correlated with the 2f1-f2 amplitudes. This procedure demonstrated that, for a given GM frequency producing the 2f1-f2, the correlations between the two DPOAEs peaked when the primaries of the 2f2-f1 were at a GM frequency that positioned the 2f2-f1 frequency place near the GM of the primaries that produced the 2f1-f2 DPOAE. As a whole, the above findings strongly suggest that the 2f2-f1 DPOAE in humans is generated basal to the primary-tone place on the basilar membrane.
Martin
G K
GK
Department of Otolaryngology, University of Miami School of Medicine, Florida, USA.
Jassir
D
D
Stagner
B B
BB
Whitehead
M L
ML
Lonsbury-Martin
B L
BL
D000161:Acoustic Stimulation; D000328:Adult; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold; D001489:Basilar Membrane / Q000502:physiology; D003051:Cochlea / Q000502:physiology*; D005260:Female; D006309:Hearing / Q000502:physiology*; D006801:Humans; D008297:Male; D013997:Time Factors