Auditory Status Research Articles

Distortion product otoacoustic emission test performance when both 2f1-f2 and 2f2-f1 are used to predict auditory status.

The objective of this study was to determine whether distortion product otoacoustic emission (DPOAE) test performance, defined as its ability to distinguish normal-hearing ears from those with hearing loss, can be improved by examining response and noise amplitudes at 2 f1-f2 and 2f2-f1 simultaneously. In addition, there was interest in knowing whether measurements at both DPs and for several primary frequency pairs can be used in a multivariate analysis to further optimize test performance. DPOAE and noise amplitudes were measured at 2f1-f2 and 2 f2-f1 for 12 primary levels (L2 from 10 to 65 dB SPL in 5-dB steps) and 9 pairs of primary frequencies (0.5 to 8 kHz in 1/2-octave steps). All data were collected in a sound-treated room from 70 subjects with normal hearing and 80 subjects with hearing loss. Subjects had normal middle-ear function at the time of the DPOAE test, based on standard tympanometric measurements. Measurement-based stopping rules were used such that the test terminated when the noise floor around the 2 f1-f2 DP was < or = -30 dB SPL or after 32 s of artifact-free averaging, whichever occurred first. Data were analyzed using clinical decision theory in which relative operating characteristics (ROC) curves were constructed and areas under the ROC curves were estimated. In addition, test performance was assessed by selecting the criterion value that resulted in a sensitivity of 90% and determining the specificity at that criterion value. Data were analyzed using traditional univariate comparisons, in which predictions about auditory status were based only on data obtained when f2 = audiometric frequency. In addition, multivariate analysis techniques were used to determine whether test performance can be optimized by using many variables to predict auditory status. As expected, DPOAEs were larger for 2f1-f2 compared to 2 f2-f1 in subjects with normal hearing. However, noise amplitudes were smaller for 2f2-f1, but this effect was restricted to the lowest f2 frequencies. A comparison of signal-to-noise ratios (SNR) within normal-hearing ears showed that the 2f1-f2 DP was more frequently characterized by larger SNRs compared to 2f2-f1. However, there were several subjects in whom 2f2-f1 produced a larger SNR. ROC curve areas and specificities for a fixed sensitivity increased only slightly when data from both DPs were used to predict auditory status. Multivariate analyses, in which the inputs included both DPs for several primary frequency pairs surrounding each audiometric frequency, produced the highest areas and specificities. Thus, DPOAE test performance was improved slightly by examining data at two DP frequencies simultaneously. This improvement was achieved at no additional cost in terms of test time. When measurements at both DPs were combined with data obtained for several primary frequency pairs and then analyzed in a multivariate context, the best test performance was achieved. Excellent test performance (ROC) curve areas >0.95% and specificities >92% at all frequencies, including 500 Hz, were achieved for these conditions. Although the results described should be validated on an independent set of data, they suggest that the accuracy with which DPOAE measurements identify auditory status can be improved with multivariate analyses and measurements at multiple DPs.

Distortion product otoacoustic emission test performance for a priori criteria and for multifrequency audiometric standards.

1) To describe distortion product otoacoustic emission (DPOAE) test performance when a priori response criteria are applied to a large set of DPOAE data. 2) To describe DPOAE test performance when multifrequency definitions of auditory function are used. 3) To determine DPOAE test performance when a single decision regarding auditory status is made for an ear, based on DPOAE data from several frequencies. 4) To compare univariate and multivariate test performance when multifrequency gold standard definitions and response criteria are applied to DPOAE data. DPOAE and audiometric data were analyzed from 1267 ears of 806 subjects. These data were evaluated for three different frequency combinations (2, 3, 4 kHz; 2, 3, 4, 6 kHz; 1.5, 2, 3, 4, 6 kHz). DPOAE data were collected for each of the f2 frequencies listed above, using primary levels (L1/L2) of 65/55 dB SPL and a primary ratio (f2/f1) of 1.22. Sensitivity and specificity were evaluated for signal to noise ratios (SNRs) of 3, 6, and 9 dB, which are in common clinical use. In addition, test performance was evaluated using clinical decision theory, following the convention we have used in previous reports on otoacoustic emission test performance. Both univariate and multivariate analyses techniques were applied to the data. In addition to evaluating DPOAE test performance for the case when audiometric and f2 frequency were equal, multifrequency gold standards and multifrequency criterion responses were evaluated. Three new gold standards were used to assess test performance: average pure-tone thresholds, extrema thresholds that took into account both the magnitude of the loss and the number of frequencies at which hearing loss existed, and a combination of the two. These new gold standards were applied to each of the three frequency groups described above. As expected, SNR criteria of 3, 6, and 9 dB never resulted in perfect DPOAE test performance. Even the most stringent of these criteria (9 dB SNR) did not result in a sensitivity of 100%. This result suggests that caution should be exercised in the interpretation of DPOAE test results when these a priori criteria are used clinically. Excellent test performance was achieved when auditory status was classified on the basis of the new gold standards and when either SNR or the output of multivariate logistic regressions (LRs) were used as criterion measures. Invariably, the LR resulted in superior test performance compared with what was achieved by the SNR. For SNR criteria of 3, 6, and 9 dB and (by definition) for the LR, specificity, in general, exceeded 80% and often was greater than 90%. Sensitivity, however, depended on the magnitude of hearing loss. Diagnostic errors, when they occurred, were more common for patients with mild hearing losses (21 to 40 dB HL); sensitivity approached 100% once the hearing loss exceeded 40 dB HL. The largest differences between test performance based on SNR or LR occurred for the ears with mild hearing loss, where the LR resulted in more accurate diagnoses. It should not be assumed that the use of a priori response criteria, such as SNRs of 3, 6, or 9 dB, will identify all ears with hearing loss. Test performance when multifrequency gold standards are used to define an ear as normal or impaired and when data from multiple f2 frequencies are used to make a diagnosis, resulted in excellent test performance, especially when the LR was used. When predicting auditory status with multifrequency gold standards, the LR resulted in relative operating characteristic curve areas of 0.95 or 0.96. An output from the LR can be selected that results in a specificity of 90% or better. When the loss exceeded 40 dB HL, the same output from the LR resulted in test sensitivity of nearly 100%. These were the best test results that were achieved. (ABSTRACT TRUNCATED)

One-Year Audiologic Monitoring of Individuals Exposed to the 1995 Oklahoma City Bombing

This longitudinal study evaluated subjective, behavioral, and objective auditory function in 83 explosion survivors. Subjects were evaluated quarterly for 1 year with conventional pure-tone and extended high-frequencies audiometry, otoscopic inspections, immittance and speech audiometry, and questionnaires. There was no obvious relationship between subject location and symptoms or test results. Tinnitus, distorted hearing, loudness sensitivity, and otalgia were common symptoms. On average, 76 percent of subjects had predominantly sensorineural hearing loss at one or more frequencies. Twenty-four percent of subjects required amplification. Extended high frequencies showed evidence of acoustic trauma even when conventional frequencies fell within the normal range. Males had significantly poorer responses than females across frequencies. Auditory status of the group was significantly compromised and unchanged at the end of 1-year postblast.

Predicting audiometric status from distortion product otoacoustic emissions using multivariate analyses.

1) To determine whether multivariate statistical approaches improve the classification of normal and impaired ears based on distortion product otoacoustic emission (DPOAE) measurements, in comparison with the results obtained with more traditional single-variable applications of clinical decision theory. 2) To determine how well the multivariate predictors, derived from analysis on a training group, generalized to a validation group. 3) To provide a way to apply the multivariate approaches clinically. Areas under the relative operating characteristic (ROC) curve and cumulative distributions derived from DPOAE, DPOAE/Noise, discriminant function (DF) scores and logit function (LF) scores were used to compare univariate and multivariate predictors of audiometric status. DPOAE and Noise amplitudes for 8 f2 frequencies were input to a discriminant analysis and to a logistic regression. These analyses generated a DF and LF, respectively, composed of a linear combination of selected variables. The DF and LF scores were the input variables to the decision theory analyses. For comparison purposes, DPOAE test performance was also evaluated using only one variable (DPOAE or DPOAE/Noise when f2 = audiometric frequency). Analyses were based on data from over 1200 ears of 806 subjects, ranging in age from 1.3 to 96 yr, with thresholds ranging from -5 to >120 dB HL. For statistical purposes, normal hearing was defined as thresholds of 20 dB HL or better. For the multivariate analyses, the database was randomly divided into two groups of equal size. One group served as the "training" set, which was used to generate the DFs and LFs. The other group served as a "validation" set to determine the robustness of the DF and LF solutions. For all test frequencies, multivariate analyses yielded greater areas under the ROC curve than univariate analyses, and greater specificities at fixed sensitivities. Within the multivariate techniques, discriminant analysis and logistic regression yielded similar results and both yielded robust solutions that generalized well to the validation groups. The improvement in test performance with multivariate analyses was greatest for conditions in which the single predictor variable resulted in the poorest performance. A more accurate determination of auditory status at a specific frequency can be obtained by combining multiple predictor variables. Although the DF and LF multivariate approaches resulted in the greatest separation between normal and impaired distributions, overlap still exists, which suggests that there would be value in continued efforts to improve DPOAE test performance.

Clinical interpretations of transient otoacoustic emissions

Purpose: The purpose of this study was to characterize the relation of different ordinal patterns of transient otoacoustic emissions (TEOAES) with respect to underlying otologic disorders and auditory status. Patients and Methods: The results of TEOAEs in 225 patients with various auditory disorders were investigated and compared with normative data established from 90 subjects of various ages. TEOAEs were categorized according to four patterns: (1) normal (general response level within 90% of normative data, (2) reduced amplitude (general response level was ≥2 dB peak sound pressure level (pSPL), but less than the mean −1.64 SD of the normative data), (3) abnormal morphology of frequency spectrum (general response level was within normal limits, but reduced at ≥2 individual octave frequencies between 1,000 and 5,000 Hz), and (4) total absence (response level <2 dB pSPL). Results: This study showed that the normal pattern of TEOAEs, in terms of response amplitude, varied with age. Our results further indicated that a reduced amplitude pattern of TEOAEs was noted in patients with a mild sensorineural hearing loss (SNHL), negative tympanometric pressure, a pressure-equalization tube, and Meniere's disease. TEOAEs provided good frequency-specific information for patients with a noise-induced hearing loss. All patients with ossicular chain abnormalities, more than moderate SNHL, and a middle ear mass or effusion had total absence of TEOAEs. Patients with acoustic neuroma and brainstem lesions presented a complex profile of TEOAEs. In the follow-up of auditory function in patients undergoing otologic surgery, different patterns of TEOAEs between the preoperative and postoperative recordings were evident, which correlated with the hearing thresholds and middle ear status. The abnormal findings of TEOAEs due to specific auditory diseases were discussed. Conclusion: The interpretation of TEOAEs can be facilitated through an analysis of specific patterns and in combination with other audiologic tests.

From laboratory to clinic: a large scale study of distortion product otoacoustic emissions in ears with normal hearing and ears with hearing loss.

1) To describe distortion product otoacoustic emission (DPOAE) measurements in large groups of subjects with normal hearing and with hearing loss, and to use these data to provide comprehensive descriptions of DPOAE test performance. 2) To describe the effects of primary frequency and audiometric threshold on the extent to which DPOAE measurements accurately identify auditory status. 3) To develop an approach that describes the probability that any measured response is coming from either a normal or an impaired ear. 4) To develop an approach for representing DPOAE data clinically. 5) To explore the relation between magnitude of hearing loss and DPOAE measurements. DPOAE measurements were made in 1267 ears of 806 subjects, using stimulus conditions that previously had been demonstrated to result in the greatest separation between normal and impaired ears (i.e., primary levels of 65/55 dB SPL for f1/f2; Stover et al., 1996). Subjects were recruited from local clinical populations and through local advertisements. All data were analyzed using clinical decision theory, including relative operating characteristic (ROC) curves and estimates of areas under these curves (Az). In addition, cumulative distributions were constructed of response properties from both normal and hearing-impaired ears. These cumulative distributions were used to select specific probabilities that measured responses were coming from either the normal or impaired distributions, and to develop an approach for describing clinical DPOAE data. For no conditions were the distributions of DPOAE responses from normal and impaired ears completely separated, meaning that optimal criterion values would still result in errors in identification of auditory status. Test performance, defined by Az, was best for mid and high frequencies and poorest for lower frequencies and for the highest frequency tested (8000 Hz). Performance was best when normal hearing was defined as audiometric thresholds between 20 and 30 dB HL, with poorer performance for more stringent or lax audiometric criteria. Within the limits related to the effects of primary frequency and audiometric criterion, it appears that DPOAE measurements can be used to accurately identify auditory status. An approach is described, using the present data set, that allows one to assign to any measured DPOAE value (DPOAE amplitudes, DPOAE/noise) the probability that the response is coming either from the distribution of normal or impaired responses. In addition, DPOAE/noise systematically decreases as hearing loss increases over the range of hearing losses from 0 to about 40 to 60 dB HL (depending on frequency), thus potentially enabling one to differentiate hearing losses over this range. For hearing losses greater than 50 to 60 dB HL, ears do not produce measurable DPOAEs and thus, no predictive relationship exists.

Spontaneous otoacoustic emission prevalence patterns in humans

In humans the prevalence of spontaneous otoacoustic emissions (SOAEs) depends on gender, pigmentation (race), and auditory status. Potential sources for variations in SOAE prevalence may include outer/middle ear characteristics and trauma to the auditory system. To explore these variables, auditory system structure, status, and history was obtained for each subject from whom SOAE recordings were obtained. Outer ear characteristics were determined from resonance peaks in a spectrum of white noise measured in the ear canal. Middle ear characteristics were obtained with multifrequency tympanometry. Auditory system trauma was determined by assessing hearing thresholds and from reports of noise exposure, medication history, and otologic surgery/illnesses. The results will be discussed in terms of their implications for clinical applications and models of the auditory system. [Work supported by the Showalter Foundation.]

Auditory brain stem responses to air- and bone-conducted clicks in the audiological assessment of at-risk infants.

Auditory brain stem responses (ABRs) to air- and bone-conducted clicks were used to assess the auditory status of 170 at-risk neonates. During the perinatal period, 20.6% (35/170 cases) of the at-risk infants failed ABRs to air-conducted clicks at 30 dB nHL in at least one ear. Ear-specific results indicated an initial failure rate of 15.0% (51/340 ears). Approximately two-thirds (32/51 ears) of these initial failures showed purely conductive deficits, whereas the remaining one-third (19/51 ears) involved suspected sensorineural components. Follow-up audiological evaluations were performed for 87.1% (148 cases) of these at-risk infants at 4 mo and/or 1 yr corrected age. Based on the initial tests and follow-up assessments, the tentative operating characteristics of ABRs to both air- and bone-conducted clicks for identification of sensorineural deficits in at-risk neonates were calculated. It was found that the ABR to bone-conducted clicks yielded better specificity, predictive value of positive results, and overall efficiency. It is suggested that the ABR to bone-conducted stimuli should be viewed as a valuable addition in the assessment of cochlear reserve in infants who fail a newborn auditory screening to air-conducted stimuli.

Audiological evaluation of very low birthweight infants.

A population of consecutively surviving very low birthweight (VLBW) infants comprising 41 infants (24 female) birthweight less than 1000 g and 108 infants (63 female) birthweight 1000-1500 g received detailed audiological evaluation. The audiological test battery comprised auditory brainstem evoked response (ABR) prior to hospital discharge, behavioural audiometry and tympanometry at 8-12 months and monitoring as necessary. The ABR results were interpreted with reference to a normative group of 36 full-term infants (birthweight 2.4-4.5 kg). Of the 142 VLBW infants completing audiological evaluation, one (0.7%) had evidence of moderate-severe high frequency sensorineural hearing loss, 83 (58.5%) evidence of conductive dysfunction (18 severe, 42 moderate and 23 mild) and only 58 (40.8%) normal hearing. The 19 infants with severe auditory impairment were more likely to have suffered moderate-severe apnoea, greater than or equal to two courses of mechanical ventilation, prolonged oxygen therapy and recurrent upper respiratory tract infections in the first year of life than infants without severe impairment (P less than 0.05). Because of the incidence of conductive pathology, difficulties occurred when attempting to compare ABR status at 36-42 weeks postmenstrual age with peripheral hearing status at 8-12 months as assessed by visual reinforcement orientation audiometry (VROA) and impedance audiometry. The most useful ABR test parameters as screening measures of peripheral auditory status were Wave I-III-V morphology, wave V threshold levels and wave V absolute latency values when used in combination as a test battery.(ABSTRACT TRUNCATED AT 250 WORDS)

Hearing Disorders in Sickle Cell Disease

The auditory system was assessed in 34 adult subjects with sickle cell disease using standard audiometric test techniques. The study results indicate that patients with sickle cell disease are at risk for retro-cochlear as well as cochlear dysfunction of the auditory system. However, there is no consistent audiometric pattern that is pathognomonic of sickle cell disease. The test results indicate that auditory status should be carefully monitored in all adult patients with sickle cell disease.

Speech understanding in the elderly.

Both auditory and cognitive status were determined in 130 elderly persons, in the age range from 51 to 91 years. Data were analyzed from the standpoint of the congruence of auditory and cognitive deficits. The prevalence of central auditory processing disorder was 50%, and the prevalence of cognitive deficit was 41%. Findings in the two areas were congruent, however, in only 63% of the total sample. Central auditory status was abnormal in the presence of normal cognitive function in 23% of subjects. Central auditory status was normal in the presence of cognitive deficit in 14% of subjects. In general, results did not support the hypothesis that decline in speech understanding in the elderly can be explained as the consequence of concomitant cognitive decline.

Toy weapons and firecrackers: a source of hearing loss.

Although acoustic injury as a result of exposure to noisy toys and firecrackers has been reported previously, most of these studies have been conducted on adults. The purpose of this prospective study, conducted at the time of Deepawali, an Indian festival of fireworks, was two-fold: 1. to measure the acoustic output of representative samples of toy weapons and firecrackers and the intensity level at critical spectator points from the site of emission; and 2. to determine the auditory status of a cross section of the target population, involving 600 participants from various age groups, before and after exposure to firecracker noise at Deepawali. The average sound level at a distance of 3 m was 150 dB, thus exceeding the damage risk criterion for adults (i.e., 130 dB peak level). An average 30 dB persistent sensorineural hearing loss was found in 2.5% of the target population as a result of toy weapon/firecracker noise during Deepawali. The 9- to 15-year-old age group was most affected. A judicious approach in the manufacture and use of toy weapons and firecrackers, in addition to legal restraints, is advocated.

Intraoperative variability of auditory brain-stem responses during cranial nerve microvascular decompression

The auditory brain-stem response (ABR) recordings of 40 patients who underwent microvascular decompression of cranial nerves V and VII were analyzed. The latencies of waves I, V, and the I-V interpeak interval were examined as a function of subject age, subject gender, operative site, and operative stage. The results indicated that: (1) subject age was not a significant factor in intraoperative ABR variability; (2) significant male-female latency differences were present only in the earlier operative stages; (3) greater latency changes were produced during decompression of the facial nerve than during trigeminal nerve decompression; and (4) greater response variability was present during the later operative stages. The patients' postoperative auditory status was studied to determine the predictive efficiency of three currently used criteria for significant intraoperative latency change.

Perceived Benefits of Amplification as a Function of Central Auditory Status in the Elderly

A measure of perceived hearing aid benefit was obtained from 24 older hearing-impaired adults who had received their hearing aids a minimum of 6 months prior to this study. Subjects were also administered a battery of tests, including comparisons of maximum scores for phonetically balanced words and the Synthetic Sentence Identification Test to identify central auditory disorder. There appears to be no relationship between perceived hearing aid benefit and central auditory function as measured in this study. Several explanations for these somewhat surprising findings are offered, as well as clinical implications regarding the use of hearing aids by older adults.

Hearing impairment and cognitive decline in senile dementia of the Alzheimer's type.

Hearing impairment has been hypothesized as contributing to symptoms of dementia. Data from a longitudinal study were analyzed to determine if auditory status predicted cognitive functional decline in senile dementia of the Alzheimer's type (SDAT). As part of a larger study, 156 consecutive SDAT outpatients had received a comprehensive medical evaluation including baseline screening for hearing impairment with the finger friction test and serial assessment of cognitive function with the Mini-Mental State examination. Age and cognitive function at entry to the study were greater among individuals with impaired hearing (N = 36) than with normal hearing (N = 120). The demographic profiles of the impaired and normal hearing groups were otherwise similar, as was the prevalence of depression. Intervening mortality rates were nearly identical. Decline in cognitive function one year later, however, was nearly twice as great in the impaired hearing group, a statistically significant difference (P less than .05, by one-tailed t test) even when controlled for age and initial cognitive function. These results, which need to be verified with sophisticated audiometric techniques, suggest that hearing impairment may be a prognostic indicator for subsequent cognitive dysfunction in SDAT. They are consistent with the hypothesized relationship between hearing impairment and dementia in SDAT as well as alternative hypotheses discussed in the text.

Pediatric applications of serial auditory brainstem and middle-latency evoked response recordings

Serial auditory brainstem (ABR) and middle-latency (AMR) response recordings were made for 12 children (8 male, 4 female) ranging in age from 2 weeks to 10 years. A total of 40 ABR and 32 AMR assessments were carried out at bedside in varied hospital environments, including a pediatric intensive care unit (ICU), a neonatal ICU and an operating room. Clinical entities were distributed as follows: acute, severe head injury (5), hydrocephalus (2), meningomyelocele (2), hyperbilirubinemia (1), ototoxic drug overdose (1), severe developmental delay (1). Auditory evoked responses were applied in monitoring peripheral and central auditory system status, and contributed to medical, surgical and audiologic management. Abnormalities of the ABR were reversed in some children, such as those with hydrocephalus, with medical or surgical therapy. In other cases, such as a hyperbilirubinemic child, a marked ABR abnormality apparently reversed spontaneously. We present five cases to illustrate diverse applications of serial auditory evoked response measures in children.

Audiologic Evaluation in Infancy and Childhood

The identification and measurement of hearing loss in infants and young children is necessary to implement appropriate medical treatment, to diagnose other conditions that may have hearing loss as an associated sign, and to implement habilitative measures that should prevent the delay of speech and language acquisition, psychosocial developmental problems and educational handicaps. Testing hearing in the 0 to 5-year-old age group is difficult but not impossible. Technological advances of the past 15 years have made reliable hearing test results rather common even with very young infants. The pediatrician is the first line of defense against the potentially serious effects of hearing loss. While the actual testing that can be done in the pediatrician's office is quite limited with the very young age group, suspicion of hearing loss is most frequently created through history and observational data. When suspicion exists, diagnostic facilities are available that can provide the instrumentation and techniques to determine the patient's auditory status.

Assessment of a Primary School Educational Program

Historically, governmental reaction to perceived educational deficit has been to establish new programs, as did the Florida legislature (the Primary Education Program) (3) to implement in Grades K-3 appropriate instructional strategies for prereading readiness, precomputational skills, auditory discrimination, visual perception, and kinetic and motor skills. Evaluation of the program was completed in an east central Florida school district. Over the past five years the district has administered a test of motor, visual, auditory, and language status to kindergarten children, The Yellow Brick Road (4). In Grade 2 each pupil was given the Comprehensive Test of Basic Skills (1) with specific subscales of reading, language, and mathematics (2). Transition to the program created a unique quasi-experimental, time-lagged situation so students in and out of the program could be compared on academic achievement. Since the program had not begun, the 1979 group served as controls. A second pool of similar pupils in the new program in 1980 were designated the experimental group. Samples involved about 37 schools. 500 teachers, and 12,000 children. Groups, compared on age, gender, and racial composition, were equivalent. Randomly selected samples (programs = 227 and nonprograms = 223) were drawn from each population and differences in scores on the Yellow Brick Road and Comprehensive Test of Basic Skills compared by multivariate analyses of variance. Also, univariate P ratios were computed for each score. The multivariate test for scores on the Yellow Brick Road was nonsignificant (P,,M = 2.28, p < .06), which established the groups' equivalence on these scores. Means, standard deviations, and P ratios for scores on the Comprehensive Test of Basic Skills in the table show a significant over-all difference between the two groups (P3,rro = 5.19, ? < .01). Each univariate P ratio indexed a significant difference favoring children In the program on reading. language, and mathematics. These such programs designed for early intervention with young children may improve their academic functioning, but the differences observed here were small and might well be related to uncontrolled factors.

Selection of Patients

The Vienna Group uses two types of cochlear prosthesis, a unichannel extracochlear and a four-channel endocochlear device with unichannel stimulation. The limitations in patient selection are the same for both, except for the auditory status. My answer to the first two questions therefore involves a definition of what we call deafness and residual hearing. The endocochlear four-channel prosthesis is limited to patients who have bilateral deafness with pure-tone thresholds above 95 dB, with or without hearing of words, absence of noise discrimination, and no visual unaided word or sentence comprehension even with the use of bilateral hearing aids. The extracochlear unichannel prosthesis is limited to patients who have pure-tone thresholds of 85 dB and above, hearing of words but no visual unaided word or sentence comprehension even with the use of hearing aids. The main difference here is that the patients of this group are able to understand some numbers and to discriminate environmental sounds. This very important function must be preserved. This is only possible with an extracochlear device. Regarding the question of pre- or post-lingual deafness, I should like to state that the majority of our 35 patients were post-lingually deaf. Only recently we accepted a small number of pre-lingual deaf patients, though one should realize that the rehabilitation of speech comprehension in these patients takes much longer than in the post-lingual deaf and that the results achieved after a reasonable rehabilitation period can only be compared within the same group of pre-lingual deaf patients, because it will probably never be as good as in the post-lingual deaf group. To questions number 4 and 5, concerning age limitation, I should like to comment that it seems very reasonable to me to decrease the age below 13-15 years which is now our present age limitation. There are nevertheless also a few valid arguments against this. In most patients below 10 years it is very difficult to obtain reliable data with preoperative electrical stimulation-a subjective test which has to be performed under local anaesthesia. The second argument concerns the post-operative rehabilitation. From my experience it seems to be very difficult to effect a consistent rehabilitation procedure because of various psychological and environmental circumstances. These objections are probably not justified with the age group of 24 years because their rehabilitation coincides with the physiological development of speech and hearing. I believe that this age group should be our future goal when it becomes possible to test the electrical sensitivity of nerve fibres objectively, for example, with the registration of electrical evoked BSP under general anaesthesia; only extracochlear stimulation would be warranted in small children. Besides the audiometric criteria mentioned, we have the following restrictions to cochlear implants.

Normal neonatal brainstem auditory evoked potentials.

Brainstem auditory evoked potentials present a unique opportunity to assess the neuronal and auditory status of the newborn. To date, sample data have been few in number, thereby limiting their interpretive value. The present study was undertaken in an effort to accrue data generated from a large sample size. One hundred fifty-five normal neonates were tested within the first 36 hours of life. No subjects qualified for inclusion in the High Risk Register for Hearing Loss established by the American Academy of Pediatrics. Each ear was tested independently, using click stimuli at a rate of 30.1 per second at 65 dB HTL. Test runs were replicated for purposes of reliability. A run consisted of 2,000 sweeps of data, each being 10 ms in length. Identification of wave forms were assessed by two or more observers. Total agreement was required from all observers for inclusion of wave peaks for analysis. Latencies of onset of stimulus to peak were obtained. Descriptive as well as inferential statistics were computed. Results provide standardized data for comparison.