Locus of generation for the 2 f1−f2 vs 2 f2−f1 distortion-product otoacoustic emissions in normal-hearing humans revealed by suppression tuning, onset latencies, and amplitude correlations

Abstract

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.

Comparing Distortion Product Otoacoustic Emissions to Intracochlear Distortion Products Inferred from a Noninvasive Assay

“…It is interesting to note that group delays calculated along equal f 2 lines on the L/P maps that are noted as thin white diagonal lines in Figure FIG. 3A-L closely agree with actual time-domain onset latencies, thus indicating that 2f 1 -f 2 DPOAEs have longer latencies than their 2f 2 -f 1 counterparts (Whitehead et al 1996;Martin et al 1998;Stagner et al 2007).…”

“…This interaction causes the phase to be constant for a given DP frequency on the map and presents as vertical banding. This concept is also helpful in explaining the large body of varied evidence in both animals and humans, indicating that 2f 2 -f 1 DPOAE components at wide f 2 /f 1 ratios are limited to more basal regions than their 2f 1 -f 2 counterparts that are generated by the same set of primary tones (Martin et al 1998). It is interesting to note that group delays calculated along equal f 2 lines on the L/P maps that are noted as thin white diagonal lines in Figure FIG.…”

A modified adenovirus can transfect cochlear hair cells in vivo without compromising cochlear function

“…Stimulus generation and response acquisition were computer-controlled using an on-board digital signal processor, along with customized software controlling stimulus presentation and response analysis. 22 DPOAEs were obtained in the form of level/frequency functions, or DP-grams (see example in Figure 1b) for geometric-mean (GM) frequencies (ie (f 1 × f 2 ) 0.5 ) in 0.1-octave steps, from 1.4-17.8 kHz (f 2 = 1.8-19 kHz). Primary tone-levels ranged from 45-75 dB SPL, in systematic 5-dB steps, with f 2 /f 1 = 1.2.…”

Growth of suppression in humans based on distortion-product otoacoustic emission measurements

“…Suppression based on DPOAE measurements has been described in several studies involving both humans and lower animals (e.g., Abdala, 1998Abdala, , 2001Abdala, , 2004Abdala, , 2005Brown and Kemp, 1984;Gorga et al, 2002Gorga et al, , 2008Martin et al, 1987Martin et al, , 1998aMartin et al, , 1998bMills, 1998;Pienkowski and Kunov, 2001). In these and other DPOAE suppression experiments, DPOAEs are elicited by a pair of primary tones (f 2 , f 1 ; f 2 =f 1 % 1.2), whose levels are held constant while a third, suppressor tone (f 3 ) is presented.…”