Amplitude of distortion product otoacoustic emissions in the guinea pig in f(1)- and f(2)-sweep paradigms

The amplitude versus frequency relations of distortion product otoacoustic emissions (DPOAEs) were studied in the guinea pig, using both the f(1)- and the f(2)-sweep paradigms to vary the primary frequency separation. The amplitude of the DPOAEs 2f(1)-f(2), 3f(1)-2f(2), 4f(1)-3f(2), and 2f(2)-f(1), plotted as a function of DP frequency, exhibited a bandpass structure. The separation of the primaries for which the DPOAE level is maximum is referred to as the optimum ratio f(2)/f(1). For the lower sideband DPOAEs (f(dp)相似文献   

Sensitivity of transient evoked and distortion product otoacoustic emissions to the direct effects of noise on the human cochlea

Measurement of otoacoustic emissions (OAEs) has been proposed as a sensitive test to reliably assess the effects of noise exposure. The present study in humans was designed to evaluate the sensitivity and applicability of transient evoked OAEs (TEOAEs) and 2f1-f2 distortion product OAEs (DPOAEs) as quantitative indices of the functional integrity of the outer hair cells (OHC) during growth of and recovery from temporary threshold shift (TTS). This was examined in two different groups of volunteers by measuring the per- and post-stimulatory effects of a one hour BBN and an on-site five hour exposure to loud music from a discotheque. The results of both experiments show consistent growth and recovery patterns for both DPOAEs and TEOAEs. For TEOAEs, both the reproducibility scores and signal to noise ratio values for the 4 kHz frequency band exhibited the greatest sensitivity. The DPOAEs, on the other hand, showed the greatest sensitivity between 2 and 5.5 kHz. Thus, both the TEOAEs and DPOAEs have a great potential in the detection of TTS after noise exposure.     

Generation of DPOAEs in the guinea pig

In humans, distortion product otoacoustic emissions (DPOAEs) at frequencies lower than the f(2) stimulus frequency are a composite of two separate sources, these two sources involving two distinctly different mechanisms for their production: non-linear distortion and linear coherent reflection [Talmadge et al., J. Acoust. Soc. Am. 104 (1998) 1517-1543; Talmadge et al., J. Acoust. Soc. Am. 105 (1999) 275-292; Shera and Guinan, J. Acoust. Soc. Am. 105 (1999) 332-348; Kalluri and Shera, J. Acoust. Soc. Am. 109 (2001) 662-637]. In rodents, DPOAEs are larger, consistent with broader filters; however the evidence for two separate mechanisms of DPOAE production as seen in humans is limited. In this study, we report DPOAE amplitude and phase fine structure from the guinea pig with f(2)/f(1) held constant at 1.2 and f(2) swept over a range of frequencies. Inverse Fast Fourier Transform analysis and time-domain windowing were used to separate the two components. Both the 2f(1)-f(2) DPOAE and the 2f(2)-f(1) DPOAE were examined. It was found that, commensurate with human data, the guinea pig DPOAE is a composite of two components arising from different mechanisms. It would appear that the 2f(1)-f(2) emission measured in the ear canal is usually dominated by non-linear distortion, at least for a stimulus frequency ratio of 1.2. The 2f(2)-f(1) DPOAE exhibits amplitude fine structure that, for the animals examined, is predominantly due to the variation in amplitude of the place-fixed component. Cochlear delay times appear consistent with a linear coherent reflection mechanism from the distortion product place for both the 2f(1)-f(2) and 2f(2)-f(1) place-fixed components.     

Distortion-product otoacoustic emissions in the common marmoset (Callithrix jacchus): parameter optimization

Distortion-product otoacoustic emissions (DPOAEs) were measured in a New World primate, the common marmoset (Callithrix jacchus). We determined the optimal primary-tone frequency ratio (f(2)/f(1)) to generate DPOAEs of maximal amplitude between 3 and 24kHz. The optimal f(2)/f(1), determined by varying f(2)/f(1) from 1.02 to 1.40 using equilevel primary tones, decreased with increasing f(2) frequency between 3 and 17kHz, and increased at 24kHz. The optimal f(2)/f(1) ratio increased with increasing primary-tone levels from 50 to 74dB SPL. When all stimulus parameters were considered, the mean optimal f(2)/f(1) was 1.224-1.226. Additionally, we determined the effect of reducing L(2) below L(1). Decreasing L(2) below L(1) by 0, 5, and 10dB (f(2)/f(1)=1.21) minimally affected DPOAE strength. DPOAE levels were stronger in females than males and stronger in the right ear than the left, just as in humans. This study is the first to measure OAEs in the marmoset, and the results indicate that the effect of varying the frequency ratio and primary-tone level difference on marmoset DPOAEs is similar to the reported effects in humans and Old World primates.     

Suppression of the 2f1-f2 otoacoustic emission in humans.

Suppression of the 2f1-f2 distortion-product otoacoustic emission (DPOAE), stimulated with primaries, f1 and f2, in the frequency regions of 1, 2, and 4 kHz was measured in one ear of 14 human subjects with normal hearing. Suppression rate functions were generated with a suppressor at either 1, 2, or 4 kHz increasing in level from 30 to 76 dB SPL for the corresponding f1 and f2 combinations. Stimulus levels for DPOAEs were L1 = 70 dB SPL and L2 adjusted to produce the highest amplitude DPOAE for each ear (range, 0 to 6 dB below L1). Results indicated that DPOAEs were reduced 3 dB in amplitude for a mean suppressor level of 61 dB SPL. Maximum amplitude reduction occurred at a mean suppressor level of 69 dB SPL. These levels varied little for the three stimulus frequency regions. Mean slopes of the rate functions decreased as stimulus frequency region increased. Suppression tuning curves (STCs) were generated in the same three frequency regions and with L1 at either 70 or 55 dB SPL and L2 adjusted individually for each ear. The tips of the STCs were at frequencies associated with f1 and f2. The tip regions of the STCs for the 4-kHz stimulus condition were more complex in that they contained more multiple minima than did those for the 1- and 2-kHz regions. Results confirm that optimal suppression of the 2f1-f2 DPOAE occurs for frequencies in the vicinity of f1 and f2 rather than at 2f1-f2.     

Aging and middle ear function in rhesus monkeys (Macaca mulatta).

This study provided tympanometric data on rhesus monkeys (Macaca mulatta) and more support for this monkey as a good model for human peripheral auditory function. There have been few published reports concerning middle ear function in rhesus monkeys, and these experiments addressed that need. In the first experiment, peak acoustic admittance (Ytm) and ear-canal volume (Vea) were measured in 17 older adult monkeys and 16 younger adult monkeys. In the second experiment, middle ear resonance frequency was measured in eight younger adult monkeys and four older adult monkeys. Overall, peak Ytm, Vea, and resonance frequency were similar for monkeys and humans. Specifically, peak mean Ytm and mean Vea in monkeys were comparable to those values in human children. There was a trend for older monkeys to have decreased peak Ytm and Vea, but these trends did not reach statistical significance. There was a significant sex effect similar to what has been reported in humans. Male monkeys had larger peak Ytm values and larger Vea values compared with female monkeys regardless of age. Finally, there were no significant age or sex effects on resonance frequency.     

Alternative distortion product otoacoustic emissions and hearing loss in a clinical population

Parameters of the alternative distortion product otoacoustic emissions (DPOAEs) 4f1-3f2, 3f1-2f2, 2f2-f1, 3f2-2f1 and 4f2-3f1 as well as the cubic distortion product 2f1-f2 were extracted from the ILO 92 binary files of patients reported on earlier (Lind, 1998). The DPOAEs were recorded at 18 stimulus levels between 19 and 70 dB SPL. The prevalence of at least one valid DPOAE data-point varied from 74% at 4f1-3f2 to 100% at 2f2-f1. The mean number of valid points was six for 2f2-f1, but generally below four for the others. The mean maximum amplitude for the alternative DPOAEs was 6-12 dB below that of the 2f1-f2. The mean maximum signal-to-noise-ratio (SNR) was between 2.5 and 3.5 dB SPL for the four most peripheral emissions and increased to 6.7 dB SPL for the 2f2-f1. As reported earlier, the 2f1-f2 distortion was fairly well correlated with hearing threshold at 2 kHz. The 2f2-f1 shows some correlation with hearing loss at frequencies above f2, but the other DPOAEs were not correlated with hearing loss at any frequency, which may suggest different generating mechanisms and/or sites. The inf1uence of age on maximum amplitude was small but significant for all DPOAEs.     

Two-tone distortion at different longitudinal locations on the basilar membrane

When listening to two tones at frequency f1 and f2 (f2>f1), one can hear pitches not only at f1 and f2 but also at distortion frequencies f2-f1, (n+1)f1-nf2, and (n+1)f2-nf1 (n=1,2,3...). Such two-tone distortion products (DPs) also can be measured in the ear canal using a sensitive microphone. These ear-generated sounds are called otoacoustic emissions (OAEs). In spite of the common applications of OAEs, the mechanisms by which these emissions travel out of the cochlea remain unclear. In a recent study, the basilar membrane (BM) vibration at 2f1-f2 was measured as a function of the longitudinal location, using a scanning laser interferometer. The data indicated a forward traveling wave and no measurable backward wave. However, this study had a relatively high noise floor and high stimulus intensity. In the current study, the noise floor of the BM measurement was significantly decreased by using reflective beads on the BM, and the vibration was measured at relatively low intensities at more than one longitudinal location. The results show that the DP phase at a basal location leads the phase at an apical location. The data indicate that the emission travels along the BM from base to apex as a forward traveling wave, and no backward traveling wave was detected under the current experimental conditions.     

Development of 2f1-f2 otoacoustic emissions in the rat

2f1-f2 otoacoustic emissions have been recorded from the rat cochlea during its development. Acoustic responses were recorded at 3, 5 and 7 kHz using a fixed value of the f2/f1 ratio (= 1.17). The first 2f1-f2 acoustic responses were obtained at 12 days after birth for 2f1-f2 = 7 and 5 kHz, and 2 days later for 2f1-f2 = 3 kHz. Adult-like patterns of the acoustic responses were achieved by day 18 for 2f1-f2 = 3 kHz, by day 20 for 2f1-f2 = 5 kHz and by day 28 for 2f1-f2 = 7 kHz. These results are discussed in relation to the available anatomical and functional data on the cochlear development of the rat. The delayed appearance of the 3 kHz acoustic responses might be related to the basal-to-apical gradient of morphological cochlear maturation. The fact that the 2f1-f2 otoacoustic emissions reached adult characteristics from the low to high frequencies is consistent with the development of the tuning properties of the basilar membrane. The long development of the 2f1-f2 acoustic responses at 7 kHz suggests that the organ of Corti undergoes subtle changes well after the end of its apparent maturation.     

Effect of acute inner ear pressure changes on low-level distortion product otoacoustic emissions in the guinea pig

OBJECTIVE: To determine a relation between acute inner ear pressure changes and cochlear function as measured by low-level 2f(1)-f(2) distortion product otoacoustic emissions (DPOAEs). MATERIAL AND METHODS: During and after a change in inner ear pressure induced by injection or aspiration of perilymph, the 2f(1)-f(2) DPOAE at 4.5 kHz generated by low-level primaries was recorded in the guinea pig. RESULTS: Large changes in overall inner ear pressure produced only small changes in the 2f(1)-f(2) amplitude and phase. During injection of 0.5 microl of artificial perilymph into the scala tympani over a 10-s period, the mean inner ear pressure increased by approximately 500 Pa, with an accompanying mean increase in the 2f(1)-f(2) amplitude of 0.7 dB. During aspiration of 0.5 microl of perilymph over a 10-s period, the mean inner ear pressure decreased by approximately 700 Pa, with an accompanying mean decrease in the 2f(1)-f(2) amplitude of 0.9 dB. Changes in DPOAE amplitude followed inner ear pressure changes with a delay of 1-2 s. The magnitude and sign of the amplitude changes can (partly) be explained by a change in oval window stiffness. No explanation was found for the measured delay. CONCLUSION: Clinically, these experiments can be of value in gaining insight into the pathophysiological mechanisms of pathological pressure changes as seen in Meniere's disease and perilymphatic fistulae.     

A comparison of OAEs arising from different generation mechanisms in guinea pig

Otoacoustic emissions provide unambiguous evidence that the cochlea supports energy propagation both towards, and away from, the stapes. The standard wave model for energy transport and cochlear mechanical amplification provides for compressional and inertial waves to transport this energy, the compressional wave through the fluids and the inertial wave along the basilar membrane via fluid coupling. It is generally accepted that energy propagation away from the stapes is dominated by a traveling wave mechanism along the basilar membrane. The mechanism by which energy is predominantly transported back to the stapes remains controversial. Here, we compared signal onset delay measurements and rise/steady-state/fall times for SFOAEs and 2f1-f2 OAEs (f2/f1=1.2) obtained using a pulsed-tone paradigm in guinea pig. Comparison of 2f1-f2 OAE signal onset delay for the OAE arising from the f2 region with SFOAE signal onset delay (matched to the f2 stimulus frequency) based on signal onset occurring at 10% of the peak signal amplitude was suggestive of a bi-directional traveling wave mechanism. However, significant variability in signal onset delay and signal rise, steady-state duration, and fall times for both the 2f1-f2 OAE and SFOAE was found, qualifying this interpretation. Such variability requires explanation, awaiting further studies.     

短时纯音暴露对畸变产物耳声发射的影响

畸变产物耳声发射（ＤＰＯＡＥ）测试所采用的参数可以对测试结果有明显影响，为研究改变ＤＰＯＡＥ测试参数对反映耳蜗功能变化是否有影响，使１０只大白兔（１６耳）接触短时（３分钟）、中等强度（８２ｄＢ ＳＰＬ）的纯音暴露后发现，以等强原始音（Ｌ１＝Ｌ２）诱发的ＤＰＯＡＥ的幅度变化小于以差强原始音（Ｌ２＝Ｌ１－１２ｄＢ）诱发的ＤＰＯＡＥ（相差１０．１１ｄＢ），而其恢复过程也短于后者（相差１００．７１秒）。这     

The 2f1-f2 DPOAE amplitudes and latencies in the groups of older people with presbyacusis and young people with normal hearing

Otoacoustic emissions have been shown to be useful as indicators of the cochlear function. One of the most valuable techniques is distortion product otoacoustic emission recording (DPOAE), mostly 2f1-f2 distortion, which is described as being present regularly and indicating the strongest connection with hearing level. DPOAE amplitudes are analysed as relating to the frequency (DP-gram) or to the signal levels (input-output function). Another feature of DPOAE providing many details with regard to cochlear mechanics seems to be the assessment of 2f1-f2 DPOAE latencies. In the present study 2f1-f2 DPOAE amplitudes and latencies were analysed and compared in two groups: the elderly with presbyacousis and the young with normal hearing level. All measurements were taken using Otodynamics ILO 92 system. DPOAE latencies were recorded by phase gradient method with fixed-f1 and swept-f2 signal. The following signal parameters were used: f2 ranging from 732 to 6396 Hz, signal levels L1 = L2 = 70 dB SPL, f2/f1 ratio ranging from 1.18 to 1.25. According to the mathematical formula y = 1.412 + exp(7.685-0.7698*ln(f2)) 2f1-f2 DPOAE latencies were calculated in the group of young people at f2 = 1.0 kHz; 2.0 kHz; 3.0 kHz; 4.0 kHz; 5.0 kHz; 6.0 kHz as follows: 12.08 ms; 7.67 ms; 5.99 ms; 5.08 ms; 4.50 ms; 4.10 ms. The analogous analysis revealed the following results in the group of the elderly: y = 2.402 + exp(9.293-1.019*ln(f2)) and calculated latencies--11.9 ms; 7.09 ms; 5.50 ms; 4.71 ms; 4.24 ms; 3.93 ms. The greater differentiation of the latencies measured in low frequency band was observed in the elderly while in the young subjects in mid and high frequency bands. The 2f1-f2 DPOAE amplitudes recorded for the whole frequency band were significantly higher in the young people than in the elderly. No correlation was observed between latencies and amplitudes in both investigated groups.     

The effect of systematic change in middle ear pressure on transitorily evoked otoacoustic emissions--a pressure chamber study]

Otoacoustic emission power spectrum and amplitude are influenced by the middle ear transmission mechanism. In this study, the influence of progressive increase in atmospheric pressure on the frequency and amplitude of transiently evoked otoacoustic emissions (TEOAEs) was determined in normally hearing humans. For testing, subjects were seated in a pressure chamber. Transiently evoked otoacoustic emissions were tested in 20 ears of 20 subjects using of 80 microseconds unfiltered click and tone bursts duration at 0.5, 1, 2, 3, and 4 kHz presented at 40 dBnHL. Ambient air pressure was increased from 0 kPa up to 8 kPa in 2-kPa steps. In spite of large interindividual differences, the results demonstrate that the changes that occur in TEOAEs with variations in ambient air pressure are frequency specific. Amplitude and reproducibility of high-frequency TEOAEs are less influenced by middle ear pressure changes than are the amplitude and reproducibility of low- and middle-frequency TEOAEs. Results have implications for clinical and research applications of TEOAE measurements in that middle-ear and inner-ear effects on OAEs can be differentiated.     

Human efferent adaptation of DPOAEs in the L1,L2 space

The adaptive properties of distortion product otoacoustic emissions (DPOAEs) at 2f(1)-f2 were investigated in 12 ears of normally hearing adults aged 18-30 years using long-lasting 1-s primary-tone on-times. In this manner, DPOAE adaptation at a single f2 of 1.55 kHz (f2/f1=1.21) was evaluated as a function of the levels of the primary tones in a matrix of L1, L2 settings, which varied from 45 to 80 dB SPL, in 5-dB steps. DPOAEs were elicited under both monaural and binaural stimulus-presentation conditions. Adaptation was defined as the difference in DPOAE levels between the initial 92-ms baseline measure using a standard protocol and one obtained during the final 92 ms of the prolonged 1-s primary-tones. These differences were averaged across subjects to create contour plots of mean adaptation in the L1,L2 space. The 2f(1)-f2 DPOAE revealed consistent regions of suppression (-0.5 dB difference) or enhancement (+0.5 dB difference) with respect to baseline measures within the L(1),L(2) matrix for both acoustic-stimulation conditions. Specifically, 2f(1)-f2 DPOAE suppressions of 1-2 dB occurred for both monaural and binaural presentations, typically at level combinations in which L1>L2. In contrast, larger 2f(1)-f2 DPOAE enhancements of 3-4 dB occurred for only the binaural condition, at primary-tone level combinations where L1相似文献   

Head-related transfer functions of the Rhesus monkey

Head-related transfer functions (HRTFs) are direction-specific acoustic filters formed by the head, the pinnae and the ear canals. They can be used to assess acoustical cues available for sound localization and to construct virtual auditory environments. We measured the HRTFs of three anesthetized Rhesus monkeys (Macaca mulatta) from 591 locations in the frontal hemisphere ranging from -90 degrees (left) to 90 degrees (right) in azimuth and -60 degrees (down) to 90 degrees (up) in elevation for frequencies between 0.5 and 15 kHz. Acoustic validation of the HRTFs shows good agreement between free field and virtual sound sources. Monaural spectra exhibit deep notches at frequencies above 9 kHz, providing putative cues for elevation discrimination. Interaural level differences (ILDs) and interaural time differences (ITDs) generally vary monotonically with azimuth between 0.5 and 8 kHz, suggesting that these two cues can be used to discriminate azimuthal position. Comparison with published subsets of HRTFs from squirrel monkeys (Saimiri sciureus) shows good agreement. Comparison with published human HRTFs from the frontal hemisphere demonstrates overall similarity in the patterns of ILD and ITD, suggesting that the Rhesus monkey is a good acoustic model for these two sound localization cues in humans. Finally, the measured ITDs in the horizontal plane agree well between -40 degrees and 40 degrees in azimuth with those calculated from a spherical head model with a radius of 52 mm, one-half the interaural distance of the monkey.     

Aging and Middle Ear Function in Rhesus Monkeys (Macaca mulatta): Envejecimiento y funcion del oido medio en monos Rhesus [Macaca mulatta)

This study provided tympanometric data on rhesus monkeys (Macaca mulatta) and more support for this monkey as a good model for human peripheral auditory function. There have been few published reports concerning middle ear function in rhesus monkeys, and these experiments addressed that need. In the first experiment, peak acoustic admittance (Y_tm) and ear-canal volume (V_ea) were measured in 17 older adult monkeys and 16 younger adult monkeys. In the second experiment, middle ear resonance frequency was measured in eight younger adult monkeys and four older adult monkeys. Overall, peak Y_tm, V_ea and resonance frequency were similar for monkeys and humans. Specifically, peak mean Y_tm and mean V_ea in monkeys were comparable to those values in human children. There was a trend for older monkeys to have decreased peak Y_tm and V_ea, but these trends did not reach statistical significance. There was a significant sex effect similar to what has been reported in humans. Male monkeys had larger peak Y_tm values and larger V_ea values compared with female monkeys regardless of age. Finally, there were no significant age or sex effects on resonance frequency.

Sumario

En este estudio se obtuvieron datos timpanométricos de monos rhesus (Macaca mulatta) y más evidencias de que este mono es un buen modelo para estudiar la audición periférica del humano. Hay pocas publica-ciones acerca de la función del oído medio de los monos rhesus y aquí demostramos la necesidad de tales estudios. En el primer experimento se midió la admitancia acústica pico (Ytm) y el volumen del conducto auditivo (Vea) en 17 monos adultos may-ores y 16 monos adultos jóvenes. En el segundo experimento se midió la frecuencia de resonancia del oído medio en 8 adultos jóvenes y 4 adultos mayores. Las tres mediciones resultaron similares a las del humano. Específicamente las cifras pico promedio de Ytm y promedio de Vea en monos fueron compara-bles a las del nino. Hay cierta tendencia a tener cifras menores de Ytm y Vea en los monos mayores, pero esta tendencia no es estadísticamente significa-tiva. Sí existe una diferencia significativa en cuanto a genero, tal como se ha reportado en el humano. Los monos humanos tienen valores mayores de Ytm y de Vea en comparacion con los monos hembras, sin importar la edad. Finalmente, no hubo diferencia significativa en la frecuencia de resonancia entre los grupos etáreos o de género.     

The maximum permissible ambient noise and frequency-specific averaging time on the measurement of distortion product otoacoustic emissions

The effects of ambient noise and averaging time on distortion product otoacoustic emission (DPOAE) measurements were systematically examined in 20 normally hearing adults. For each frequency from 0.7 to 6 kHz, 2f1-f2 DPOAEs were measured at nine intensity levels of ambient noise for each of four different averaging times. The dependent variable of interest was the DPOAE:noise ratio (D:N)--the relationship between DPOAE amplitude and noise level at 2f1-f2. Findings indicated that, relative to the baseline condition (25 dBA), ambient noise levels of 40 dBA or greater affected the D:N considerably in the lower frequencies. However, noise levels of 55-65 dBA did not affect the D:N in the higher frequencies. Results also indicated that, to achieve detectable DPOAEs, longer averaging times were required as ambient noise increased and as frequency decreased. Based on the results, the maximum permissible ambient noise levels (MPANLs) were estimated in relation to averaging time.     

Suppression and enhancement of distortion-product otoacoustic emissions by interference tones above f(2). II. Findings in humans

Distortion-product otoacoustic emission (DPOAE) suppression tuning curves (STCs) can be obtained in a variety of laboratory animals and humans by sweeping the frequencies and levels of a third tone (f(3)) around a set of f(1) and f(2) primaries. In small laboratory animals, it was previously observed that, when the suppressor tone (f(3)) is above f(2), substantial suppression and or enhancement (suppression/enhancement) could be obtained. In the present study, it was of interest to determine if similar suppression/enhancement phenomena could be observed in humans and to what extent this might influence the interpretation of STC results reported in the literature. To this end, STCs were measured for DPOAEs at 2f(1)-f(2) and 2f(2)-f(1) in human subjects at geometric-mean frequencies (GM) of 1, 2, 3, and 4 kHz, and primary-tone equilevels of 80/80 and 75/75 dB SPL and unequal levels of 65/55 dB SPL. Overall, STC parameters were found to be comparable to those reported in the literature. For the 2f(1)-f(2) DPOAE, STC tip frequencies tuned to the region of the primaries, and tip frequencies were slightly influenced by primary-tone level. STC tip thresholds were typically within 10 dB of the level of L(2), and Q(10dB) values ranged from 1.0 to 2.5, which was consistent with the higher-level primaries employed. The 2f(1)-f(2) DPOAE showed consistent regions of suppression that were approximately an octave above the GM for the 1-kHz, 65/55-dB SPL condition. The 2f(2)-f(1) DPOAE tuned to its characteristic place above f(2) and showed reliable enhancement above the STC tip region for the 1-kHz, 75/75-dB SPL primaries. Overall, the results clearly revealed that human ears also display suppression/enhancement phenomena when f(3) reaches frequencies considerably above f(2). If suppression/enhancement phenomena reflect secondary DPOAE sources, then these sources are present in the ear-canal signal from humans as well as small laboratory animals.     

Frequency and intensity discrimination in Mongolian gerbils, African monkeys and humans.

Frequency (delta F) and intensity (delta I) difference limens were directly compared in Mongolian gerbils (Meriones unguiculatus), Old World African Monkeys (Cercopithecus mitis, Cercocebus albigena), and humans. Methods employed a repeating background AX discrimination procedure, and positive (food) reinforcement for animals. For delta I, there were small quantitative differences between the species. At 1 kHz, 70 dB SPL, DLs averaged 2.82 dB for gerbils, 2.29 dB for monkeys, and 0.75 dB for humans. For delta F, there were larger differences between the species. At 1 kHz, 60 dB SPL, frequency DLs were highest for gerbils, averaging 108 Hz. DLs were lower for monkeys, averaging 32.6 Hz, similar to recently reported DLs for other Old World monkeys (Prosen et al., 1990). Human DLs, averaging 2.27 Hz, were markedly lower than those of either monkeys or gerbils. These results suggest that animals provide better models of human delta I than delta F.