The effects of maturation and stimulus parameters on the optimal f(2)/f(1) ratio of the 2f(1)-f(2) distortion product otoacoustic emission in neonates(1).

Distortion product otoacoustic emission (DPOAE) measurements are becoming popular in the clinical realm because they have been shown to reflect cochlear function. The primary tones used to evoke the DPOAE are important in determining the amplitude of the emission recorded in the ear canal. This study examined the ratio of the primaries necessary to determine the maximum amplitude emission as a function of development, stimulus level and frequency. Optimum f(2)/f(1) ratios were measured utilizing the f(1)-sweep technique from 105 neonates between 30-42 weeks conceptional age (CA) and 40 adults. No significant difference for optimum ratio was shown between the neonatal and the adult groups. Primary tone frequency had a significant effect on optimum ratio for both neonates and adults. Low f(2) frequencies (<4 kHz) were associated with higher optimum ratios than high f(2) frequencies (>4 kHz). The adult group was used to investigate the effect of stimulus level on the optimum f(2)/f(1) ratio for f(2) frequencies from 1.7 to 10 kHz. Regression analysis showed significant differences across levels of the primaries at all frequencies except for f(2)=3.4 and 7.0 kHz. These differences in f(2)/f(1) ratio across stimulus frequency and level may be attributed to the change in the shape of the excitation profiles along the basilar membrane.

An examination of gender differences in DPOAE phase delay measurements in normal-hearing human adults.

This study examined gender differences in f(1)- and f(2)-sweep distortion product otoacoustic emission (DPOAE) phase delay measures in 60 normal-hearing human adults. Phase delay measures were obtained at six different f(2) frequencies ranging from 1.1 to 6.0 kHz (f(2)/f(1) ratios were 1.1-1.3). Primary levels for f(2) were 45 and 50 dB SPL (f(1)f(2)). Gender differences have been observed in normal-hearing human adults in both auditory brainstem response (ABR) and f(1)-sweep DPOAE studies. Gender differences in delay have been attributed to differences in the average length of the cochlea, where female cochleas are 13% shorter than male cochleas. Previously, the authors have proposed that the f(1)-sweep phase delay estimate is predominantly composed of a level-independent transport time to the site of DPOAE generation and a small proportion of the level and frequency-dependent filter build-up time. The f(2)-sweep delay also contains the transport time, however, it is predominantly composed of the filter build-up time. Therefore, delay differences between stimulation paradigms are equal to a proportion of the filter build-up time. In this study, mean f(1)- and f(2)-sweep delays were significantly longer in male ears than female ears at 1.1 kHz (45 and 50 dB). At 50 dB, f(1)-sweep phase delay measures were 18% longer in male ears (6.5 ms) than female ears (5.5 ms). Mean f(2)-sweep delays were 23% longer in male ears (10.0 ms) than female ears (8.1 ms). This gender difference was not observed when the isolated filter build-up time was calculated from the DPOAE phase delay difference. These observations may therefore be attributed to a gender-related anatomical difference in cochlear length.

Applications of distortion-product emissions to an otological practice.

OBJECTIVES: The multiple clinical applications of distortion-product emissions (DPEs) to an otological practice are reviewed. Through an examination of studies involving thousands of infants, as well as adult ears, the relationships between measurements of DPEs and PTTs (PTTs) are examined. The cochlear physiology underlying generation of DPEs and the interpretation of these measurements are described in some detail. We study the contribution of phase measurements of DPEs to calculation of delay in cochlear traveling waves. The clinical applications of these measurements are described. The objective of this work is to demonstrate the clinical utility of DPEs through an examination of the correlation of the features of DPEs with PTTs in patients varying in age from newborn to the elderly. METHODS: Experimental design and methodology involved careful prospective selection of large numbers of subjects in each age group, novel techniques for recording DPEs, and multivariate statistical analysis of the data. Three separate experiments encompass issues surrounding the age groups of adults, neonates, and elderly individuals. RESULTS: The results show that current techniques allow a 90% correct prediction of auditory PTTs for frequencies varying from 1,000 to 6,000 Hz, for patients of all ages. CONCLUSION: Techniques for measurement of DPEs currently represent an integral diagnostic component for an otological practice. The potential future application of measures of DPEs to diagnosis of tinnitus is described. With an extension of the technique for measuring DPEs to the phenomenon of reflectance, there may be promise of application to novel approaches to the treatment of tinnitus and the design of hearing aids.

Flexible approach to tympanomastoidectomy.

This article identifies pathologic obstructive sites within the temporal bone germane to the pathogenesis of chronic otitis media. Surgical approaches to the middle ear and mastoid are thoroughly discussed in the context of middle ear and mastoid pathology. Specifically, canal treatment techniques including canalplasty and meatoplasty are detailed in conjunction with middle ear reconstruction in the effort to obtain and maintain a disease free state. Mastoidectomy approaches and techniques, and their relationship to external and middle ear treatment are demonstrated in this article.

Estimating cochlear filter response properties from distortion product otoacoustic emission (DPOAE) phase delay measurements in normal hearing human adults.

This study examined cochlear filter response properties derived from f1- and f2-sweep phase delay difference measures in 60 normal hearing human adults. Seven different f2 frequencies ranging from 1.1 to 9.2 kHz were presented (f2/f1 ratios of 1.1-1.3). F2 intensity level was varied in 5 dB steps from 30 to 50 dB SPL (the level of f1 was 15 dB above the level of f2). DPOAE delay estimates in a f2-sweep paradigm are longer than in a f1-sweep paradigm at the same frequency and intensity. This indicates that the f2-sweep DPOAE phase delay is composed of a greater proportion of the filter response time at the site of DPOAE generation than the f1-sweep delay. This proportion was isolated by subtracting f1-sweep DPOAE delays from f2-sweep delays at similar f2 frequencies and intensities. Under the assumption of linearity and minimum phase the impulse response of the filter at each f2 stimulus level was calculated from the mean phase delay difference. Frequency response properties were calculated by Fourier transformation of the impulse response at each f2 frequency and intensity. High frequency low intensity impulse responses had longer response times and narrower frequency bandwidths than low frequency high intensity responses. The Q10dB values of DPOAE derived tuning curves ranged from 2.4 (1.5 kHz) to 7.3 (8.5 kHz).

The effect of sound intensity on f1-sweep and f2-sweep distortion product otoacoustic emissions phase delay estimates in human adults.

Phase measurements of distortion product otoacoustic emissions (DPOAE) provide an estimate of round-trip travel times in the cochlea. This study examined differences in f1- and f2-sweep round-trip delays estimated from DPOAE phase responses in 20 normal-hearing adult human subjects as a function of f2 frequency and sound intensity. Eight different f2 frequencies ranging from 1.1-13 kHz were presented. For both the f1- and the f2-sweep stimulation conditions the f2/f1 ratios were between 1.1 and 1.3. Primary intensity levels for f2 were varied in 5-dB steps from 30-50 dB SPL (where f1 was 15 dB > f2). Delays in the f2-sweep condition were equal to or longer than travel times in the f1-sweep condition. Round-trip delays showed a significant intensity dependence in both the f1- and f2-sweep conditions (p < or = 0.01). In both conditions, the delay increased as stimulus intensity decreased. Delay estimates in the f2-sweep condition were more strongly intensity dependent than estimates in the f1-sweep condition at f2 frequencies above 1.6 kHz. The mean difference in f2- and f1-sweep delays at low intensities ranged from 15.9 periods at the 9.2 kHz f2 place, to 2.5 periods at the 1.6 kHz f2 place. The intensity dependence of round-trip delay estimates in both conditions may be attributed to intensity-dependent changes in the cochlear filter response time related to the sharpness of tuning of DPOAE responses. The steeper intensity dependence and longer delays observed in the f2-sweep condition may similarly be attributed to a greater proportion of the f2-sweep response being composed of the filter response time.

Comparison of distortion product otoacoustic emission (DPOAE) and auditory brain stem response (ABR) traveling wave delay measurements suggests frequency-specific synapse maturation.

OBJECTIVE: To determine whether the source of age-dependent latency changes for ABR wave I results from cochlear mechanics or the haircell-neuron synapse. DESIGN: Cochlear traveling wave delays were estimated on the basis of derived ABR response latencies and DPOAE phase delays. The difference in travel time between adjacent one octave-separated frequencies was calculated for four age groups: 30 to 33 wk old, 34 to 37 wk old, 38 to 42 wk old (term), and young adults. RESULTS: We found that there were essentially no travel time differences between newborns in the 34 to 37 and the 38 to 42 wk conceptional age (CA) groups as estimated from DPOAE phase delays. For the 30- to 33-wk-olds, DPOAE travel times were increased at all frequencies, likely due to mild (about 10 to 15 dB) conductive hearing losses. Differences in travel times between adjacent bands, however, were not different from the other neonatal groups. Estimates on basis of wave I latency showed delays for the high-frequency region, 6 to 11 kHz, that were still immature at term. CONCLUSIONS: A comparison of frequency-dependent travel times calculated for wave I and DPOAE data in comparable age groups suggests mature cochlear functioning at 35 wk CA and a delayed maturation for the haircell-auditory nerve synapses relative to the preneural components for the basal turn with center frequencies above 6 kHz.

Distortion product emission features and the prediction of pure tone thresholds.

Distortion product emission (DPE) growth functions, demographic data, and pure tone thresholds (PTTs) were recorded in 229 normal-hearing and hearing-impaired ears. Half of the data set (115 ears) was used by a discriminant analysis routine to classify DPE and demographic features into either a normal PTT group or an impaired PTT group (PTT greater than 30 dB SPL [sound pressure level]) at six frequencies in the audiometric range. The six discriminant functions developed from this classification process were then used to predict PTT group membership in the remaining 114-ear data set. Frequency-specific prediction accuracy was approximately 85% overall. Of the 45 DPE and demographic variables evaluated, the DPE amplitude associated with an f2 (a primary tone of frequency) of moderate level (50 dB SPL) and a frequency corresponding to PTT was generally most predictive. DPE features associated with frequencies immediately adjacent to the PTT frequency also appear to be useful. DPE level was found to be weakly correlated with subject age; perhaps for this reason, age was frequently included in discriminant functions. This study describes the DPE measures that can most reliably categorize PTTs as normal or impaired in large populations with varied cochlear hearing status.

A neural network approach to the prediction of pure tone thresholds with distortion product emissions.

Distortion Product Emission (DPE) growth functions, demographic data, and pure tone thresholds were recorded in 229 normal-hearing and hearing-impaired ears. Half of the data set (115 ears) was used to train a set of neural networks to map DPE and demographic features to pure tone thresholds at six frequencies in the audiometric range. The six networks developed from this training process were then used to predict pure tone thresholds in the remaining 114-ear data set. When normal pure tone threshold was defined as a threshold less than 20 dB HL, frequency-specific prediction accuracy varied from 57% (correct classification of hearing impairment at 1025 Hz) to 100% (correct classification of hearing impairment at 2050 Hz). Overall prediction accuracy was 90% for impaired pure tone thresholds and 80% for normal pure tone thresholds. This neural network approach was found to be more accurate than discriminant analysis in the prediction of pure tone thresholds. It is concluded that a general strategy exists whereby DPE measures can accurately categorize pure tone thresholds as normal or impaired in large populations of ears with purely cochlear hearing dysfunction.

Predicting pure tone thresholds in normal and hearing-impaired ears with distortion product emission and age.

Distortion product emission (DPE) growth functions, demographic data, and pure tone thresholds were recorded in 229 normal-hearing and hearing-impaired ears. Half of the data set (115 ears) was used by a discriminant analysis routine to classify DPE and demographic features into either a normal pure tone threshold (PTT) group or an impaired PTT group (PTT greater than 30 dB SPL) at six frequencies in the audiometric range. The six discriminant functions developed from this classification process were then used to predict pure tone threshold group membership in the remaining 114-ear data set. Frequency-specific prediction accuracy varied from 71% (correct classification of hearing impairment at 1025 Hz) to 92% (correct classification of normal hearing at 2050 Hz). Of the 45 DPE and demographic variables evaluated, the DPE amplitude associated with an f2 of moderate level (50 dB SPL) and a frequency corresponding to pure tone threshold was generally most predictive. DPE level was found to be weakly correlated with subject age and perhaps for this reason age was frequently included in discriminant functions. For our data, discriminant functions with one variable, two variables, or 5-10 variables showed no differences in predictive performance. This research suggests that DPE measures can reliably categorize pure tone thresholds as normal or impaired in large populations with varied cochlear hearing status.

Bilateral digital hearing aids for binaural hearing.

The rehabilitation of binaural hearing performance in hearing impaired listeners has received relatively little attention to date. Both localization ability and speech-understanding-in noise are affected in the impaired listener. When localization performance is tested in impaired ears with conventional hearing aid fittings it is found to be worse than the unaided condition. Advances in electronic design now permit speculation about the implementation of complex digital filters within the confines of an in-the-ear hearing aid. We have begun exploring strategies to enhance the localization performance of impaired listeners with bilateral digital signal processing. We are examining three strategies in bilateral hearing aid design to improve localization performance in hearing impaired listeners, namely 1) more accurate fitting of individual ear losses, 2) equalization of the effect of the hearing aid itself on the acoustics within the ear canal, and 3) binaural fitting strategies which in effect modify individual ear fittings to enhance localization performance. The results of early psychophysical testing suggests that localization performance can be improved with these strategies.

Measuring human cochlear traveling wave delay using distortion product emission phase responses.

A method is presented here in which cochlear traveling wave delays are estimated through the measurement of distortion product emission phase (DPE) responses. This method assumes that the site of generation of DPEs is at the f2 place. Eighteen adult female and 18 adult male human ears, all with normal hearing, underwent DPE testing. For each ear, DPE phase responses were computed for eight values of f2 varying from 10 to 0.78 kHz. Linear DPE phase versus DPE frequency relationships were found. Estimates of traveling wave delay from the ear canal to the f2 place varied from about 1 ms for the 10-kHz place to 3.5 ms for the 0.78-kHz place. These estimates agree well with previous traveling wave delay estimates using electrocochleography. Test-retest comparisons of delay estimates were generally within 0.25 ms. In addition, within-subject interaural delay differences were smaller than between-subject interaural differences. Within-subject interaural delay differences were generally less than 0.5 ms. Male ears, when grouped together, had significantly longer delays (8%) to the 0.78-kHz place in comparison to female ears. The effect of DPE stimulus level on delay is presented for stimulus levels between 15 and 60 dB SPL. These data support the use of DPE phase responses as estimates of cochlear traveling wave delay. In comparison with electrophysiological and psychophysical techniques this method is purely cochlear-based and has the advantage of being rapid and noninvasive.

Temporal bone histopathology in chronically infected ears with intact and perforated tympanic membranes.

Chronic suppurative otitis media has been clinically defined as a chronic discharge from the middle ear in the presence of a perforation of the tympanic membrane. However, irreversible tissue pathology in the middle ear or mastoid can occur behind an intact tympanic membrane. One hundred forty-four human temporal bones with chronic otitis media were divided into two groups: those with perforated (28) and those with nonperforated (116) tympanic membranes. The histopathological findings of their middle ears were compared. Granulation tissue in various degrees was the most prominent pathological feature. It was observed in 96% of temporal bones with perforation of the tympanic membrane, and in 97% of those without perforation. Also found were ossicular bony changes (96% with perforation; 90.5% without), middle ear effusion (93% with perforation; 89% without), cholesterol granuloma (21% with perforation; 12% without), cholesteatoma (36% with perforation; 4% without), and tympanosclerosis (43% with perforation; 20% without). This study shows that the histopathological changes of the middle ear are similar in temporal bones with and without perforation of the tympanic membrane. The clinician should, therefore, be aware that an intact tympanic membrane does not necessarily preclude the presence of gross pathological changes of the middle ear cleft.

Distortion-product emissions and auditory sensitivity in human ears with normal hearing and cochlear hearing loss.

Distortion product emissions (DPEs) at 2f1-f2 frequencies were measured in 53 human ears; 21 of them exhibited cochlear hearing loss. DPEs were obtained as a function of stimulus level (DPE growth curves) at seven frequency regions between 707 Hz and 5656 Hz. Several distinctly different shapes or patterns of DPE growth curves were observed. These included single-segment monotonic growth curves with and without saturation at moderate and high stimulus levels, diphasic growth curves with nulls at moderate stimulus levels, and non-monotonic growth curves with negative slopes at high stimulus levels. Low-level, irregularly shaped segments were more frequent in normal-hearing ears, suggestive of normal low-level active nonlinearities from the outer-hair-cell subsystem. High-level, steeply sloped segments were frequent in hearing-impaired ears, suggestive of residual nonlinearities from a cochlear partition without functional outer hair cells. The stimulus level at which the DPE could just be distinguished from the noise floor, the DPE detection threshold, demonstrated moderate positive correlations (r's from 0.50 to 0.81) with auditory thresholds when all ears, both normal and impaired, were considered together. Those correlations were not strong enough to quantitatively predict auditory thresholds with any great accuracy. However, DPE thresholds were able to predict abnormal auditory sensitivity with some precision. DPE thresholds correctly predicted abnormal auditory sensitivity 79% of the time in the present study, and up to 96% of the time in previous studies. These results suggest that DPE thresholds may prove useful for hearing screening in cases where cooperation from the subject is limited or where corroboration of cochlear hearing loss is required. Different patterns of DPE growth curves suggest underlying micro-mechanical differences between ears, but the differential diagnostic value of those patterns remains to be determined.

The concept of silent otitis media. Its importance and implications.

This article defines silent otitis media and describes its continuum of signs and symptoms and its sequelae. Chronic silent otitis media and silent otitis media in children are also examined, and treatment principles are provided.

Pathogenesis of Menière's disease.

While endolymphatic hydrops is a characteristic pathologic feature of Menière's disease, there are exceptions to this rule. There is evidence that hydrops develops as a result of malabsorption of endolymph. This implies dysfunction of the endolymphatic sac and duct, which normally absorb endolymph. In approximately 20% of cases of Menière's disease, a specific pathologic condition in the temporal bone can be associated as a cause of endolymphatic hydrops. Syphilis, fractures of the temporal bone, otosclerosis, and preceding chronic otitis media are some of the more commonly encountered pathologic conditions so associated. Hypoplasia of the mastoid air-cell system and of periaqueductal air cells, and especially displacement medially but also anteriorly of the sigmoid (lateral) sinus are commonly observed in patients with Menière's disease. Evidence is available to substantiate the etiologic bases of Menière's disease as including multifactorial inheritance (1). The clinical symptoms and findings result from both chemical and physical mechanisms. Pathogenesis appears to be due to malabsorption of endolymph in the environment of the endolymphatic sac, primarily affecting longitudinal flow. The possible role of such processes as autoimmune reactions and viral inflammation, especially in the endolymphatic sac, should be further investigated in the future.

Distortion product emissions and sensorineural hearing loss.

Distortion product emissions (DPEs) are intimately linked to normal outer hair cell function. Outer hair cell function is itself intimately linked with normal auditory thresholds. We sought to correlate frequency-specific DPE measurements with auditory thresholds, in seven frequency regions from 700 Hz to 6 kHz, in each of 21 ears. Eleven of these ears had thresholds below 25 dB SPL at every test frequency, whereas 10 ears demonstrated some degree of purely sensorineural hearing loss. An analysis of the correlation between DPE measurements and sensory thresholds suggests that DPE measures can predict frequency-specific auditory thresholds to within 10 dB over a range of sensory thresholds from 0 dB SPL to 60 dB SPL. Distortion product emissions promise to provide an objective, non-invasive measure of sensory thresholds. The clinical value of DPE measurement is enhanced by that fact that it is brief and requires minimal subject participation. A clinical test based on the DPE measurement will not displace conventional audiometry or auditory brain stem response measurement. It promises to provide new information about cochlear function to both the clinician and auditory physiologist.

Temporal overshoot in simultaneous-masked psychophysical tuning curves from normal and hearing-impaired listeners.

Simultaneous-masked psychophysical tuning curves (PTCs) were obtained from normal-hearing and sensorineural hearing-impaired listeners. The 20-ms signal was presented at the onset or at the temporal center of the 400-ms masker. For the normal-hearing listeners, as shown previously [S. P. Bacon and B. C. J. Moore, J. Acoust. Soc. Am. 80, 1638-1645 (1986)], the PTCs were sharper on the high-frequency side for a signal in the temporal center of the masker. For the hearing-impaired listeners, however, the shape of the PTC was virtually independent of the temporal position of the signal. These data suggest that the mechanisms responsible for sharpening the PTC with time in normal-hearing listeners are ineffective in listeners with moderate-to-severe sensorineural hearing loss.

Cochlear implant hearing performance at the University of Minnesota.

The hearing performance of six post-lingually deaf adults implanted with the Nucleus 22-channel device are presented. All patients achieved measurable open set speech recognition with implant alone. The best hearing performance was achieved with a combination of lipreading and cochlear implant. For this condition our group achieved an average open set speech discrimination score of 85% (CID sentences) and an average speech tracking rate of 70 words per minute. We attribute the success of our group to careful pre-operative selection, including attention to candidate motivation toward hearing rehabilitation.