Search

Previous studies have shown a high within-subject correspondence between distortion product otoacoustic emission (DPOAE) input/output (I/O) curves and behaviorally inferred basilar membrane (BM) I/O curves for frequencies above approximately 2 kHz. For lower frequencies, DPOAE I/O curves contained notches and plateaus that did not have a counterpart in corresponding behavioral curves. It was hypothesized that this might improve by using individualized optimal DPOAE primary levels. Here, data from previous studies are re-analyzed to test this hypothesis by comparing behaviorally inferred BM I/O curves and DPOAE I/O curves measured with well-established group-average primary levels and two individualized primary level rules: one optimized to maximize DPOAE levels and one intended for primaries to evoke comparable BM responses at the f(2) cochlear region. Test frequencies were 0.5, 1, and 4 kHz. Behavioral I/O curves were obtained from temporal (forward) masking curves. Results showed high within-subject correspondence between behavioral and DPOAE I/O curves at 4 kHz only, regardless of the primary level rule. Plateaus and notches were equally common in low-frequency DPOAE I/O curves for individualized and group-average DPOAE primary levels at 0.5 and 1 kHz. Results are discussed in terms of the adequacy of DPOAE I/O curves for inferring individual cochlear nonlinearity characteristics.

The fine frequency structure of the 2f1-f2 acoustic distortion product (ADP fine structure) was examined in ten human subjects with normal hearing. Primary frequencies (f1 and f2) were incremented in steps of 1/32 octave with an f2/f1 ratio of 1.2. The primary levels were kept equal to each other and varied from 45 to 65 dB SPL in 2.5-dB steps. The results show that the ADP fine structure is characterized by a series of peaks and valleys across frequency, with a peak-to-peak frequency spacing of about 3/32 octave and a peak-to-valley amplitude ratio of up to 20 dB. At frequencies below 4000 Hz, as primary level increases, the sharpness of the ADP fine structure is not significantly reduced and the pattern gradually shifts to lower frequencies. At frequencies above 4000 Hz, a flattening of the pattern is sometimes observed at high levels. A consequence of the underlying process responsible for the fine structure is that ADP input/output (I/O) functions can be highly variable in shape. Dramatic shape changes can occur for ADP I/O functions obtained with primary frequency changes of as little as 1/32nd of an octave. The outward cause of I/O function variability is the behavior of the ADP fine structure with level; i.e., it remains robust at high levels and systematically shifts to lower frequencies with level. As a result, ADP peaks can shift to valleys with increasing level and vice versa. Thus, small shifts in primary frequency can result in significant changes in the shape of the ADP I/O function in humans.

The combined influence of primary-level differences (L1-L2) and primary-frequency ratio (f2/f1) on distortion product otoacoustic emission (DPOAE) level was investigated in 20 normal-hearing subjects. DPOAEs were recorded with continuously varying stimulus levels [Neely et al. J. Acoust. Soc. Am. 117, 1248-1259 (2005)] for the following stimulus conditions: f2= 1, 2, 4, and 8 kHz and f2/f1=1.05 to 1.4; various L1-L2, including one individually optimized to produce the largest DPOAE. For broadly spaced primary frequencies at low L2 levels, the largest DPOAEs were recorded when L1 was much higher than L2, with L1 remaining relatively constant as L2 increased. As f2/fl decreased, the largest DPOAEs were observed when L1 was closer to L2 and increased as L2 increased. Optimal values for L1-L2 and f2 f1 were derived from these data. In general, average DPOAE levels for the new L1-L2 and f2/f1 were equivalent to or larger than those observed for other stimulus combinations, including the L1-L2 described by Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)] and those defined by Neely et al. in which L1-L2 was evaluated, but f2/f1 was fixed at 1.2.

The standard procedure for measuring distortion‐product otoacoustic emission (DPOAEs) input/output (I/O) curves involves using primaries whose levels conform to the rule of Kummer [Kummer et al., J. Acoust. Soc. Am. 103, 3431‐44 (1998)]. The assumption is that the DP originates at the F2 cochlear site and primaries that conform to this rule produce equal excitation at that site, which maximizes the DP amplitude. These ideas were tested psychophysically by measuring temporal masking curves (TMCs) for masker frequencies equal to the primary frequencies. A TMC‐based level rule was obtained by plotting the levels of the F1 masker against those for the F2 one for corresponding masker‐probe intervals. DPOAE I/O curves were then measured using the Kummer rule, the TMC‐based rule, and primary levels optimized individually to maximize DP amplitude. DPOAEs for the TMC‐based and the Kummer rule had statistically similar amplitudes, but they were both lower than those measured with individually‐optimized levels. This undermines the assumption that maximum DP responses occur for primaries that produce equal excitation at the F2 cochlear site. Individually‐optimized levels showed that L1 should be higher than prescribed by the Kummer rule. [Work supported by IMSERSO‐131/06, PROFIT‐CIT‐390000‐2005‐4, and MEC‐BFU‐2006‐07536, and The Oticon Foundation.]

Noise was assesed in a primary school in Mexico City (six to twelve year old kids), known as having significant noise inside classrooms. Several sources were identified, among them, traffic noise and noise from the sports and recreational areas, which were in the center of the school with the classrooms surrounding them. Reverberation was an issue, but not very significant. But in some cases the most annoying sound (noise), was the one made by the students within the classroom, inducing a number of reactions in the lecturers. These reactions ranged from shouting to give the lecture, through trying to control the students, to ignore them and let it go. Lecturer’s voice levels were also measured, finding out a wide spread in normal speech voice level, and some of their experiences and comments were analyzed. Results are sumarized in this presentation.

To better understand the nature of nonmonotonic notches in input/output (I/O) functions of 2f1–f2 acoustic distortion products (ADP), I/O functions were examined in 10 young, normal‐hearing human subjects in conjunction with measurements of the ADP fine frequency structure [Gaskill and Brown, J. Acoust. Soc. Am. 88, 821–839 (1990)]. Primary frequencies were incremented in 1/32‐oct. steps, the f2/f1 ratio was 1.2, and the primary levels were equal. ADP fine structure was measured over a 1/6 to 1/3 octave surrounding either 2000 or 4000 Hz with primary levels between 45 to 65 dB SPL in 2.5‐dB steps. As primary level increased, a downward frequency shift of the peaks and valleys of the ADP fine structure was observed. This shift is responsible for the nonmonotonic notch and the wide variety of shapes of the I/O functions. As a result, even small changes in the frequency or level ratio of the primaries can drastically alter the shape of the I/O function. [Work supported by NIH‐NIDCD P50‐DC00422.]

Stimulus-like properties of the 2f1-f2 cubic difference tone (CDT) were examined by determining whether a binaural masking-level difference (BMLD) could be obtained for a 500-Hz physical tone to one ear and a CDT of the same frequency to the other ear. Masked thresholds for the physical tone (signal) were obtained as the phase of this tone varied through 360 degrees relative to harmonically related primaries (f1 = 625 Hz, f2 = 750 Hz). A continuous low-pass (2000 Hz) diotic noise comprised the masking stimulus. The level of this noise was varied to establish thresholds in a two-interval same-different adaptive procedure with the primaries occurring in both observation intervals. In keeping with other stimulus-like properties of the CDT, the results show BMLDs of 10-13 dB. Additional BMLDs were obtained with a method of adjustment to derive phase and level estimates of the CDT as a function of primary level. These estimates are compared to cancellation estimates obtained from the same subjects. Both BMLD and cancellation estimates of CDT level show a 10-dB growth in the CDT with each of 10-dB increase in primary level. However, cancellation-level estimates are consistently above corresponding BMLD-level estimates, greater by an average of 4-14 dB, depending on the subject. BMLD and cancellation estimates of CDT phase show a near-identical dependence on primary level, decreasing by an average of 5 degrees/dB. The agreement between the two procedures argues against the notion that the phase dependence is the result of confounding peripheral interactions between the cancellation tone and the primaries in the cancellation procedure.

The levels of the difference bands, fh − fl and 2(fh − fl), generated by a pure tone and a narrow band of noise, have been estimated in a manner reported in previous papers (Greenwood, 1971a, 1972a, 1972b). Results and conclusions follow: (a) Combination bands of the form fh − fl and 2(fh − fl) vary in level as functions of stimulus parameters in ways very similar to the variation in level of the difference tone, fh − fl, produced by tonal primaries, as measured by cancellation techniques. Difference band levels are rather insensitive to increases of primary frequency ratio in the ranges explored (about 1.35–1.85). Difference band level obeys different functions of primary intensity depending on whether one or two, and whether the upper or the lower, primaries are varied. When the lower primary level is varied alone, square‐law behavior is observed, in agreement with Goldstein (1967) and with Zwicker (1955); when the upper primary or both primaries vary, curves depart from square‐law behavior in near agre...

The present study examined the dependence of difference tone level [L(f2-f1)] on the following parameters of the two-tone input: f1, f2/f1 (f2 greater than f1), L1, L2, and L1 = L2. Difference tone levels were estimated in four normal hearers using a 2AFC adaptive temporal gap-masking paradigm. The key finding in this study is the apparent interaction of each factor with the other. For example, primary level (L1 = L2) was found to affect the dependence of L(f2-f1) on f1 and on f2/f1. In addition, the frequency separation of the primaries (f2/f1) was also seen to exert an influence on the dependence of difference tone level on L1, L2, and L1 = L2.

The level of the simple difference tone [L(f2−f1] arising from a two‐tone input (frequencies: f1 and f2, f2 > f1; levels: L1 and L2) was estimated in four normal‐hearing listeners using a nonsimultaneous gap masking technique. Parameters studied include: f1 (800 and 1550 Hz). f2/f1 (1.08 to 1.61), and primary level (L1 varied, L2 fixed; L1 fixed, L2 varied; L1 = L2 varied). The growth of L(f2 − f1 as a function of primary level was found to be affected by f2/f1. For L1 = L2, for instance, L(f2 − f1) growth rates of approximately 1.0 dB/dB were obtained for small f2/f1 values (f1/f1 ⩽ 1.16), whereas growth rates of roughly 2.0 dB/dB were observed for larger f2/f1 values (f2/f1 ⩾ 1.41). For L1 or L2 varied separately, L(f2 − f1) grew at a rate of 1.0 dB/dB throughout the range studied (L2/L1 or L1/L2 = −15 to + 15 dB) for large f2/f1 (f2/f1 = 1.41). For small f2/f1 = 1.08 or 1.16), however, L(f2 − f1) grew at a rate of 1.0 dB/dB for L1 < L2 or L2 < L1 and at a rate of less than 1.0 dB/dB (0.4 to −0.4 dB/dB)...