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PubMed2005

Maturation of outcomes of behavioral and electrophysiologic tests of central auditory function.

UNLABELLED: The human peripheral auditory system is fully developed at birth; however, myelination continues for several years in the higher auditory pathways. The aim of the present study was to assess the maturation course of the frequency and duration pattern tests and the middle latency response (MLR). One hundred and fifty normal participants ranging from 7 to 16 years of age were tested using conventional protocols. Results showed increased performance with increased age on both the behavioral tests up to age 12. However, there was no significance change across this age range for either latency or amplitude measures on the MLR. The MLR showed less variability for older children. High variability was a likely factor for the statistical outcome of the MLR. The data obtained on the frequency and duration pattern tests were applied to the development of age related norms. LEARNING OUTCOMES: As a result of this experience, the reader will obtain information about (a) the normal development of the auditory system; (b) performance of children on several standard tests of auditory function; and (c) the characteristics of MLRs in the same group of children.

Adolescent↗
PubMed1994

Temporal coding of 200% amplitude modulated signals in the ventral cochlear nucleus of cat.

The quasiperiodicity in the acoustic waveform in speech and music is a pervasive feature in our acoustic environment. The use of 200% amplitude modulated (AM) signals allows the study of rate and temporal envelope coding using three equal amplitude components, a situation that is frequently approximated in natural vocalizations. The recordings reported here were made in the ventral cochlear nucleus of the cat, a site of auditory signal feature enhancement and the origin of several ascending auditory pathways. The discharge rate vs modulation frequency relation was nearly always all-pass in shape for all unit types indicating that discharge rate is not a code for modulation frequency. Onset cells, especially onset-choppers and onset-I units, exhibited remarkable phase locking to the signal envelope, nearly to the exclusion of phase locking to the AM components. They exhibited lowpass temporal modulation transfer functions (tMTF) that occasionally had corner frequencies greater than 1 kHz. Primary-like, primary-like with notch, and onset-L units all exhibited considerable variability in their coding properties with tMTFs that varied from lowpass to bandpass in shape. The bandpass shape became more frequent with increasing stimulus levels. A common feature in cochlear nucleus units was less sensitivity to the level of the AM stimulus than is present in the auditory nerve. Phase locking to the envelope persisted over a wider range of stimulus levels than rate changes in a subset of the units studied. The tMTFs for a 100% sinusoidally modulated, spectrally-flat noise was similar in amplitude and bandwidth to those obtained for AM stimuli. The tMTF was relatively insensitive to carrier frequencies different than the unit characteristic frequency. AM synchrony vs level curves exhibited systematic shifts that equaled or exceeded dynamic rate shifts that occur with increasing levels of a noise masker. Phase locking to the envelope was robust under a wide variety of signal conditions in all unit types. The ordering of response types based on the maximum of the tMTF is onset-I = onset-chop > choppers = primarylike-with-notch = onset-L > primarylike.

Acoustic Stimulation↗
PubMed1993

Postnatal development of the auditory brainstem response (ABR) in beagles.

Postnatal development of the auditory brainstem response (ABR) in beagles was studied by repeated ABR recordings from birth to 16 weeks of age. In ABR recording, waves I, II and III appeared at the same time 13 to 17 days of age, while wave IV during 13 to 20 days of age and wave V during 20 to 35 days of age, respectively. The latencies of waves II, III and IV became close to the control level at 6 weeks of age, whereas wave I had a similar latency to the control at 3 weeks of age. The latency of wave V became close to the control level at 8 weeks of age. I-III interpeak latency stabilized at 4 weeks of age, however, I-V and III-V interpeak latencies stabilized during 8 to 10 weeks of age. There was a marked individual difference in amplitude of ABR components in beagles. Wave I amplitude reached the plateau level at 3 weeks of age, and wave II, III and IV at 6 weeks of age. No further development in ABR was observed on and after 10 weeks of age. It may be concluded, from electrophysiological point of view, that the peripheral auditory pathway matures at 3 weeks of age and the auditory rely system in brainstem at 10 weeks of age in beagles.

Age Factors↗
PubMed2000

Time evolution of acoustic 'information' processing in the mesencephalon of Wistar rats.

A traditional analysis of intra-encephalic auditory evoked potentials does not highlight the dynamical evolution of the auditory 'information' processing in neither time nor space. This work presents a method for tracing such signal evolution throughout the primary auditory pathway in the mesencephalon of adult anesthetized Wistar rats, using a unilateral 3 kHz tone burst stimulus. The results of the acoustic evoked potentials mapping are presented as conventional 20 ms recordings and re-analyzed in intervals of 1 ms-time windows. The parameter used, as an 'activity' correlate, was the maximum/minimum voltage difference obtained from each time window. The methodology used clearly indicates sequential signal propagation from the dorsal and ventral nuclei of the lateral lemniscus up to the inferior colliculus.

Acoustic Stimulation↗
PubMed1992

A comparison of the interaural time sensitivity of neurons in the inferior colliculus and thalamus of the unanesthetized rabbit.

The localization of low-frequency sounds (less than 3 kHz) along the azimuth involves comparing the ongoing difference in the time of arrival of a sound at the two ears. Information about interaural time differences (ITDs) is derived from an initial comparison performed in the superior olivary complex. However, little is known about which aspects of this information are transformed as it ascends the brainstem. To address this issue, we compared the ITD sensitivity of neurons in the inferior colliculus (IC) and auditory thalamus, successive stations in the auditory pathway. We found ITD sensitivity in the IC and thalamus to be similar in several respects. At both levels, the large majority of neurons responded maximally to ITDs within the range that a rabbit would normally encounter (+/- 300 microseconds) and preferred ipsilateral delays, delays that would be created by sounds in the contralateral sound field. The range of frequencies over which ITD sensitivity was expressed was also similar in the midbrain and thalamus. Several differences were also apparent. In comparison to IC neurons, neurons in the thalamus responded over more restricted ranges of ITD, responded at lower rates, and, in response to monaural stimulation, showed an increased influence of inhibition. Finally, a greater proportion of thalamic units had characteristic delays corresponding to intermediate discharge rates. The preservation of a bias for ipsilateral delays from IC to thalamus suggests that a representation of contralateral azimuths is present at both levels. Similarities between the two levels suggest that information about ITDs is faithfully transmitted from midbrain to thalamus. Differences in ITD sensitivity, such as the sharper tuning for ITDs, suggest that the thalamus is not a simple relay. Enhanced sensitivity to ITDs should translate to better-defined azimuthal receptive fields, and therefore may be a step toward achieving an optimal representation of azimuth within the auditory pathway.

Acoustic Stimulation↗
PubMed2001

The development of the middle ear in neonatal chinchillas II. Two weeks to adulthood.

Studies of auditory function in the human neonate indicate adult-like hearing sensitivity, mature cochlear function and well-developed responses in the auditory pathway. Paradoxically, measurements of middle ear function are characterized by responses that would be interpreted as abnormal in older subjects. Consequently, there is not an accepted clinical test for middle ear disease in the newborn population. Like human neonates, chinchillas have normal hearing sensitivity at birth, but middle ear function tested by multifrequency tympanometry is abnormal compared to the adult. A previous study from our laboratory indicated that the newborn chinchilla middle ear is free of mesenchyme and other debris. Over the first 2 weeks of life there were no significant changes in tympanic membrane thickness and diameter, tympanic membrane to promontory distance and stapes footplate length. There were small changes in mastoid bulla area and perimeter and in mastoid bulla bone thickness. The most striking difference between the newborn and adult temporal bone was in bone composition, the newborn bone having a less dense, spongy appearance. Impedance characteristics of the newborn chinchilla ear, measured by multifrequency tympanometry, were abnormal relative to adult animals and did not change over the first 2 weeks of life. This investigation is an extension of the previous study, designed to better understand the relationship between middle ear function, hearing sensitivity and the structural changes of the newborn chinchilla middle ear. Twenty animals, aged 2-8 weeks, were studied. Additional adult animals were used as controls. Middle ear function was assessed by a wideband reflectance impedance system. Hearing sensitivity was measured by auditory brainstem response in 2- and 8-week-old animals. Structural characteristics of the temporal bone were analyzed using histopathologic preparations. There was an orderly progression in middle ear impedance and reflectance characteristics as the chinchilla ear matured from 2 to 8 weeks of age. At 8 weeks of age, impedance and reflectance patterns approached, but did not match, those of the adult animal. Hearing sensitivity was unchanged throughout this maturational period. Finally, histological analysis demonstrated no age-related changes in distance from the tympanic membrane (TM) to the promontory and in stapes footplate length. There was a small significant decrease in the TM thickness from 2 weeks to adulthood. The most significant developmental changes were a reduction in mastoid bone thickness and concomitant increases in the perimeters and areas of the middle ear and posterior bulla.

Acoustic Impedance Tests↗
PubMed1993

The Munich screening programme in neonates.

For development, it is necessary to stimulate the auditory pathway during the first weeks of life. This knowledge and improved techniques for the treatment of young children with hearing loss make early detection even more important, otherwise developmental disabilities inevitably occur. The method of transient-evoked otoacoustic emissions is the most useful test for neonatal screening and has the following advantages: emissions are quickly measured (i.e. within a few minutes), the measurements can be performed in the hospital nursery by trained volunteer examiners, the test produces the same results in awake, anaesthetized, sedated, and sleeping patients, and the existence of TEOAEs excludes with very high probability a peripheral hearing loss which may influence the development of speech. A prerequisite of a successful evaluation with crying and moving neonates is an apparatus with two specific rejection thresholds; one for time, the second for amplitude. Additionally, the probe has to be robust, but also small both to minimize its weight and to fit comfortably within the diameter of the neonatal ear canal.

Acoustic Impedance Tests↗
PubMed1979

Brain stem evoked response audiometry in a clinical practice.

Brain stem evoked response audiometry (BERA) is an effective method of evaluating the auditory pathway from the peripheral endorgan through the brain stem. The authors have found this test to be a valuable adjunct to the neurotologic evaluation and have applied the study to over 500 patients (639 ears) in a 22 month time span. BERA has an excellent success rate (98%) in determining the presence of cerebellopontine angle lesions and is helpful in establishing whether a hearing loss is of cochlear or retrocochlear type. The authors have found BERA of use in the diagnosis of multiple sclerosis as well as other neurologic diseases affecting the brain stem. It is a valid method of dealing with suspected malingerers and those who cannot respond to standard audiometric techniques. BERA has been helpful in determining the threshold of hearing in these patients. The authors conclude that BERA is a clinical study of practical significance and that more otolaryngologists should consider adding it to their diagnostic protocol.

Adolescent↗
PubMed2001

Tinnitus suppression by electrical promontory stimulation (EPS) in patients with sensorineural hearing loss.

OBJECTIVE: Almost 10-15% of the population suffer from chronic tinnitus. There are clinical indications that a 'pathological sound' may be induced by any level of the auditory pathways. Theraupeutical difficulties and many hypotheses about tinnitus and places from which they originate might indicate various methods of treatment. Electrostimulation tinnitus suppression was achieved by many authors from 22 (Graham, Hazell) to 87% (Portman). The aim of our study was to define the usefulness of electrostimulation in treatment of persistent noise induced cochlear lesion tinnitus (group I - 43 men) and compare the results with the non noise induced tinnitus group II (68 patients). METHODS: Otolaryngological and audiological examination of the patients was made before and after electrostimulation, and at 90 days. The stimulation system consisted of a prototype tinnitus suppressor, the active platino-iridium needle electrode and silver surface electrode located on the forehead. Transtympanal electrical stimulation was performed using positive polarity direct current. Parameters of electrical impulse were individually different and depended on tinnitus parameters and patients sensation. The current levels ranged from 20 to 600 microA and frequency ranged from 60 to 10000 Hz. Average time of EPS was 60 s. RESULTS: The control examination 90 days after stimulation in group I showed subjective improvement in 18 (41.9%) patients, 22 (51.2%) did not notice any change and tinnitus deteriorated in 3 (6.9%) of the patients. In the comparative group II improvement was occurred in 34 (50%) persons including 2 (17.6%) in whom tinnitus was abolished, in 30 (44.1%) tinnitus was unchanged and 4 (0.6%) became worse. In both groups our method did not have a destructive influence on hearing. Electrical stimulation to relieve tinnitus has been used for nearly 200 years, but it is unclear how electrical stimulation works to suppress tinnitus. CONCLUSION: In our opinion electrical stimulation by using positive DC changes the spontaneous activity of cochlear nerve fibres. According to our results it is suggested that the mechanism of beneficial effects is due to increased microcirculation in part of the auditory pathways. Poorer results in patients with noise induced tinnitus could be explained by greater damage of the cochlea outer hair cells. In our opinion EPS could be a method of treatment for persistent tinnitus in cases which fail to respond to other methods.

Adolescent↗
PubMed2005

The inhibitory effect of intravenous lidocaine infusion on tinnitus after translabyrinthine removal of vestibular schwannoma: a double-blind, placebo-controlled, crossover study.

OBJECTIVE: Intravenous infusion of lidocaine has previously been demonstrated to have a transient inhibitory effect on tinnitus in 60% of individuals. The site of action has variously been proposed as the cochlea, the cochlea nerve, and the central auditory pathways. To determine whether a central site of action exists, this study investigated the effect of intravenous infusion of lidocaine in individuals with tinnitus who had previously undergone translabyrinthine excision of a vestibular schwannoma, which involves division of the cochlear nerve. STUDY DESIGN: Double-blind, placebo-controlled, crossover study. SETTING: University hospital. PATIENTS: Patients who had undergone translabyrinthine removal of a unilateral, sporadic, and histologically proven vestibular schwannoma in the last decade and who had reported postoperative tinnitus at follow-up were identified from a departmental database. Sixteen patients participated (12 men and 4 women). The mean age (+/- standard deviation) of the patients was 58 +/- 8.6 years, and the meantime since operation was 24.3 +/- 7.3 months. INTERVENTION: Solutions of 2% lidocaine hydrochloride and sodium chloride 0.9% were prepared in identical randomized vials. The volume required for 1.5 ml/kg body weight lidocaine was calculated, and this volume was given over 5 minutes for either vial. Blood pressure, pulse oximetry, and cardiac monitoring were set up and performed throughout the infusions. All investigators were blinded. OUTCOME MEASURES: Patient-completed visual analogue scale measures of tinnitus intensity, pitch, and distress, performed before infusion, 5 minutes after infusion onset, and 20 minutes after infusion onset. RESULTS: A significant difference (Wilcoxon signed-rank test, p < 0.05) between placebo and lidocaine infusion conditions was demonstrated for change in visual analogue scale estimates (preinfusion versus 5 min postinfusion) of tinnitus loudness (p = 0.036), pitch (p = 0.026), and distress (p = 0.04). No significant difference between placebo and lidocaine infusion conditions was demonstrated for change in visual analogue scale estimates (preinfusion versus 20 min postinfusion) of tinnitus loudness (p = 0.066), pitch (p = 0.173), and distress (p = 0.058). The indication is of a short-lasting inhibitory effect on tinnitus of lidocaine infusion compared with saline placebo in patients who have undergone translabyrinthine excision of a vestibular schwannoma. CONCLUSION: Intravenous infusion of lidocaine has a statistically significant inhibitory effect on tinnitus in patients who have previously undergone translabyrinthine removal of a vestibular schwannoma. The site of action of lidocaine in this instance must be in the central auditory pathway, as the cochlear and vestibular nerves are sectioned during surgery, and this finding has important implications for the task of identifying other agents that will have a similar tinnitus-inhibiting effect.

Adult↗
PubMed2001

Physiological correlates of comodulation masking release in the mammalian ventral cochlear nucleus.

Comodulation masking release (CMR) enhances the detection of signals embedded in wideband, amplitude-modulated maskers. At least part of the CMR is attributable to across-frequency processing, however, the relative contribution of different stages in the auditory system to across-frequency processing is unknown. We have measured the responses of single units from one of the earliest stages in the ascending auditory pathway, the ventral cochlear nucleus, where across frequency processing may take place. A sinusoidally amplitude-modulated tone at the best frequency of each unit was used as a masker. A pure tone signal was added in the dips of the masker modulation (reference condition). Flanking components (FCs) were then added at frequencies remote from the unit best frequency. The FCs were pure tones amplitude modulated either in phase (comodulated) or out of phase (codeviant) with the on-frequency component. Psychophysically, this CMR paradigm reduces within-channel cues while producing an advantage of approximately 10 dB for the comodulated condition in comparison with the reference condition. Some of the recorded units showed responses consistent with perceptual CMR. The addition of the comodulated FCs produced a strong reduction in the response to the masker modulation, making the signal more salient in the poststimulus time histograms. A decision statistic based on d' showed that threshold was reached at lower signal levels for the comodulated condition than for reference or codeviant conditions. The neurons that exhibited such a behavior were mainly transient chopper or primary-like units. The results obtained from a subpopulation of transient chopper units are consistent with a possible circuit in the cochlear nucleus consisting of a wideband inhibitor contacting a narrowband cell. A computational model was used to confirm the feasibility of such a circuit.

Acoustic Stimulation↗
PubMed2002

The coding of spatial location by single units in the lateral superior olive of the cat. II. The determinants of spatial receptive fields in azimuth.

The lateral superior olive (LSO) is one of the most peripheral nuclei in the auditory pathway to receive inputs from both ears, and its cells are sensitive to interaural level disparities (ILDs) when stimulated by sounds presented over earphones. It has, accordingly, long been hypothesized that the functional role of the LSO is to encode a correlate of ILDs, one of the acoustical cues to the spatial location of sound. In the companion paper, we used the virtual space (VS) technique to present over earphones stimuli containing all the acoustical cues to the location of broadband stimuli and measured the spatial receptive fields (SRFs) in azimuth of single LSO cells. The shapes of the SRFs were generally consistent with the ILD sensitivity of the cells (Tollin and Yin, 2002), but because the only variable under our control was azimuth, and not ILD directly, the precise cues responsible for the SRFs could not be unambiguously determined. Here, we test more directly the hypothesis that ILDs are the primary determinants of the SRFs in azimuth of LSO cells by digitally manipulating the head-related transfer functions used to create the VS stimuli by independently varying (or holding constant) in azimuth each of the primary localization cues in isolation while holding constant (or varying) the others. Our results support the classical view of the LSO that the form of the SRFs of the cells in azimuth is determined primarily by the ILDs in a small band of frequencies around the characteristic frequencies of the cells.

Acoustic Stimulation↗
PubMed2000

Neural measurement of sound duration: control by excitatory-inhibitory interactions in the inferior colliculus.

In the inferior colliculus (IC) of the big brown bat, a subpopulation of cells ( approximately 35%) are tuned to a narrow range of sound durations. Band-pass tuning for sound duration has not been seen at lower levels of the auditory pathway. Previous work suggests that it arises at the IC through the interaction of sound-evoked, temporally offset, excitatory and inhibitory inputs. To test this hypothesis, we recorded from duration-tuned neurons in the IC and examined duration tuning before and after iontophoretic infusion of antagonists to gamma-aminobutyric acid-A (GABA(A)) (bicuculline) or glycine (strychnine). The criterion for duration tuning was that the neuron's spike count as a function of duration had a peak value at one duration or a range of durations that was >/=2 times the lowest nonzero value at longer durations. Out of 21 units tested with bicuculline, duration tuning was eliminated in 15, broadened in two, and unaltered in four. Out of 10 units tested with strychnine, duration tuning was eliminated in four, broadened in one, and unaltered in five. For units tested with both bicuculline and strychnine, bicuculline had a greater effect on reducing or abolishing duration tuning than did strychnine. Bicuculline and strychnine both produced changes in discharge pattern. There was nearly always a shift from an offset response to an onset response, indicating that in the predrug condition, inhibition arrived simultaneously with excitation or preceded it. There was often an increase in the length of the spike train, indicating that in the predrug condition, inhibition also coincided with later parts of excitation. These findings support two hypotheses. First, duration tuning is created in the IC. Second, although the construction of duration tuning varies in some details among IC neurons, it follows three rules: 1) an excitatory and an inhibitory event are temporally linked to the onset of sound but temporally offset from one another; 2) the duration of some inhibitory event must be linked to the duration of the sound; 3) an excitatory event must be linked to the offset of sound.

Acoustic Stimulation↗
PubMed1993

Effects of occupational exposure to mercury and lead on brainstem auditory evoked potentials.

A study was performed to examine the effects of industrial exposures to lead and mercury on the brainstem auditory pathway by recording brainstem auditory evoked potentials (BAEPs). BAEPs were recorded from 22 workers exposed to lead, from eight exposed to mercury and from two control groups of age- and sex-matched subjects never exposed to neurotoxic substances. The time between BAEP peaks I and V were evaluated. The mean durations of exposure were 9.3 and 11.7 years for lead and mercury, respectively. Blood lead concentration (PbBc) on the morning of the test day was 47.5 micrograms/dl, whereas urinary mercury content at the end of the previous work day was 325 micrograms/g creatinine. Both mercury and lead exposed workers showed a significant prolongation of wave I-V time. In addition, the interwave time was longer in a lead subgroup with the greatest mean level of lead in blood. These results are consistent with other studies and show that BAEPs may provide a sensitive tool for detecting subclinical central neurotoxicity caused by lead and mercury.

Acoustic Stimulation↗
PubMedDate not supplied

Chromosome 10p deletion in a patient with hypoparathyroidism, severe mental retardation, autism and basal ganglia calcifications.

Chromosome 10p terminal deletions have been associated with a DiGeorge like phenotype. Haploinsufficiency of the region 10p14-pter, results in hypoparathyroidism, sensorineural deafness, renal anomaly, that is the triad that features the HDR syndrome. Van Esch (2000) identified in a HDR patient, within a 200 kb critical region, the GATA3 gene, a transcription factor involved in the embryonic development of the parathyroids, auditory system and kidneys. We describe a new male patient, 33-year-old, with 10p partial deletion affected by hypocalcemia, basal ganglia calcifications and a severe autistic syndrome associated with mental retardation. Neurologically he presented severe impairment of language, hypotonia, clumsiness and a postural dystonic attitude. A peripheral involvement of auditory pathways was documented by auditory evoked potentials alterations. CT scan documented basal ganglia calcifications. Hyperintensity of the lentiform nuclei was evident at the MRI examination. Renal ultrasound scan was normal. Haploinsufficiency for GATA3 gene was documented with FISH analysis using cosmid clone 1.2. Phenotypic spectrum observed in del (10p) is more severe than the classical DGS spectrum. GATA3 has been found to regulate the development of serotoninergic neurons. A serotoninergic dysfunction may be linked with autism in this patient.

Abnormalities, Multiple↗
PubMed2000

Cochleotopic fos immunoreactivity in cochlea and cochlear nuclei evoked by bipolar cochlear electrical stimulation.

Fos-like immunoreactivity evoked by basal, second or apical turn bipolar intracochlear electrical stimulation was evaluated in the spiral ganglion and cochlear nuclei. At stimulation levels of six times the electrically evoked auditory brain stem response thresholds, immunoreactive neurons were observed at appropriate discrete cochleotopic regions relative to stimulation site. The number of neurons increased with stimulus level and closely correlated to wave I amplitude. At 10 times thresholds, some spread in fos-like immunoreactivity to adjacent cochlear turns was found. However, fos-like immunoreactivity at this high level of stimulation still clearly showed a differential distribution in density of expression. These results indicated that the restricted topographic distribution of activity evoked by high levels of electrical stimulation is initiated at first order primary neurons of the system. For the profoundly deaf with cochlear implants, this indicates that place (channel) information can be maintained in the spiral ganglion and central nervous system even at very high levels of electrical stimulation. Together with our previous studies, these results indicate that fos provides a marker which can be used for evaluation of extent and pattern of cellular activation throughout the central auditory pathways, including activation of auditory nerve cells.

Animals↗
PubMed1997

Musical auditory hallucinosis from Listeria rhombencephalitis.

BACKGROUND: Complex auditory hallucinations have rarely been reported in cases of brainstem stroke or tumor. METHOD: Case study. RESULTS: A patient with acute Listeria rhombencephalitis complained of formed musical auditory hallucinations on the side of recent sensorineural deafness. MRI revealed an abscess in the middle cerebellar peduncule with extensive surrounding edema. CONCLUSIONS: Disruption of brainstem auditory pathways may cause complex auditory hallucinations. Potential pathogenetic mechanisms are discussed and a diagnostic approach is proposed.

Adult↗
PubMed2004

Central effects of residual hearing: implications for choice of ear for cochlear implantation.

OBJECTIVES/HYPOTHESIS: The study tested the hypothesis that among patients with similar levels of residual hearing in the nonimplanted ear, speech perception outcome is the same whether or not the implanted ear has profound or severe levels of hearing loss. STUDY DESIGN: Retrospective. METHODS: Levels of hearing loss in postlingually deafened adults who had cochlear implantation at Johns Hopkins University (Baltimore, MD) between 1991 and 2002 were classified according to pure-tone averages as bilateral severe (n = 20), severe-profound (severe in one ear and profound in the other) (n = 23), and bilateral profound (n = 43). There was no significant difference in the age at onset and duration of deafness among the three patient groups. Individuals in the bilateral severe and severe-profound groups had comparable levels of severe hearing loss in their nonimplanted ears, whereas those in severe-profound and bilateral profound groups had comparable levels of profound hearing loss in their implanted ears. Speech perception performance was evaluated using words from the Consonant Nucleus Consonant word list, Hearing in Noise Test sentences in quiet, and Central Institute for the Deaf sentences through recorded presentation at 70 dB sound pressure level (SPL). RESULTS: Despite the profound hearing loss of the implanted ear in the asymmetrical group, there was no significant difference in mean speech perception scores compared with the bilateral severe group within the first year after implant surgery. By comparison, the bilateral profound group had lower speech perception results compared with patients with residual hearing in one or both ears. CONCLUSION: The study results suggest that implantation of the profoundly deafened ear does not diminish the functional advantage conferred by residual hearing in a patient with asymmetrical hearing loss. Therefore, the central auditory pathway may be the site at which persistent auditory function has its most beneficial effects.

Adult↗