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PubMed2002

Acoustic neuroma management: an evidence-based medicine approach.

BACKGROUND: Partisan claims supporting the use of microsurgical resection, radiologic surveillance, and radiosurgery in acoustic neuroma management appear widely in the published literature. However, the strength of the evidence supporting these claims has not been assessed, and the management of acoustic tumors continues to be controversial. METHODS: The English-language medical literature for the past 23 years was searched for articles dealing with outcomes after acoustic neuroma management. The quality of evidence in each article was classified according to the categories of evidence as defined by a standard appraisal instrument for clinical guidelines. RESULTS: The search produced 111 articles reporting outcomes after acoustic neuroma management. From the 111 studies, 78 (70.3%) concerned surgery, 20 (18%) concerned radiosurgery, 9 (8.1%) concerned radiologic surveillance, and 4 (3.6%) compared different methods of management. From these studies, 95 (85.6%) represented Type III evidence, 6 (5.4%) represented Type IV evidence, and in 10 (9%) a clear-cut definition between Type III and Type IV could not be made. No study was supported by Type I or Type II evidence. CONCLUSIONS: The evidence supporting the various methods of acoustic neuroma management is of low quality (Type III or Type IV evidence). Well-designed comparisons between treatment methods do not exist, and therefore claims by clinicians favoring a particular treatment are unfounded. Better quality of evidence from large, well-designed, randomized clinical trials should now be undertaken at the points of clinical equipoise to address the true merits of each modality of acoustic neuroma management.

Evidence-Based Medicine↗
PubMed2002

Facial motion analysis with a video and computer system after treatment of acoustic neuroma.

OBJECTIVE: To objectively evaluate facial function with a computer and video system in a group of normal adults and a group of adults who have been treated for acoustic neuroma. STUDY DESIGN: A prospective descriptive study was performed in which the experimenter performing the objective facial motion analysis was blinded to the subjective rating of facial function. PATIENTS: The normal subjects comprised 18 women and 16 men. The subjects who had been treated for acoustic neuroma included 12 patients (seven women and five men) who underwent treatment for acoustic neuroma. METHODS: Light-reflective markers were placed at selected facial sites. A video and computer-assisted system was used to measure displacement that was unconfounded by head motion at these sites during two expressions. Proximal and remote displacement were measured for the x and y coordinates. Percentage of asymmetry relative to the total displacement was determined. RESULTS: Significant asymmetry in displacement for the y coordinate during the eyes-closed expression occurred in 100% of the subjects who had been treated for acoustic neuroma with apparent facial dysfunction and 0% of the subjects who had been treated for acoustic neuroma with no apparent facial dysfunction. Synkinesis was severe (>0.2 cm) in 17%, moderate (0.1-0.2 cm) in 25%, mild (>95th percentile for normal subjects but <0.1 cm) in 42%, and absent in 16% of the subjects who had been treated for acoustic neuroma. CONCLUSION: This method of objective assessment of facial function is useful in the evaluation of the asymmetry in facial motion and in the detection and quantification of synkinesis. The findings suggest that those subjective rating systems of facial function that compare the abnormal to the normal side may be confounded by compensatory motion on the presumed normal side.

Adult↗
PubMed2004

Acoustic startle reactivity during acute alcohol withdrawal in rats that differ in genetic predisposition toward alcohol drinking: effect of stimulus characteristics.

BACKGROUND: We have previously reported an association between greater alcohol withdrawal magnitude after a single alcohol exposure and a genetic predisposition toward low alcohol drinking in rats selectively bred for differences in alcohol intake when acoustic startle reactivity to a tone stimulus was used to index acute alcohol withdrawal. The purpose of this study was to examine whether the quality of the acoustic startle stimulus (noise versus tone) is important for detecting a genetic relationship between alcohol withdrawal magnitude and alcohol drinking behavior. METHODS: Alcohol-naive male rats selectively bred for high alcohol intake [alcohol-preferring (P), high-alcohol-drinking (HAD)1, and HAD2] or low alcohol intake [alcohol-nonpreferring (NP), low-alcohol-drinking (LAD)1, and LAD2] received a single intragastric infusion of water or alcohol (4.0 g/20.3 ml/kg; 25% v/v), and acoustic startle test sessions were given at 14, 16, 18, 20, and 24 hr after infusion. Each test session consisted of a 5-min acclimation period followed by random presentation of various white noise stimuli (90, 100, 110, and 120 dB.) RESULTS: Line differences in acoustic startle magnitude under control conditions were present in all three pairs of selectively bred lines; P rats showed a greater startle magnitude relative to NP rats, whereas both LAD lines showed a greater startle magnitude relative to both HAD lines. During alcohol withdrawal, the P, HAD1, and HAD2 lines showed enhanced startle magnitude compared with their water-treated controls. No change in startle magnitude during alcohol withdrawal was found in the NP, LAD1, or LAD2 lines. CONCLUSIONS: In contrast to our prior findings, these results showed a genetic association between high alcohol drinking and a greater startle response magnitude to a noise stimulus during alcohol withdrawal. It seems that the genetic association between alcohol drinking and alcohol withdrawal, as assessed by the acoustic startle response, depends on the quality of the acoustic startle stimulus.

Acoustic Stimulation↗
PubMed2003

Acoustic characteristics of the speech of young cochlear implant users: a comparison with normal-hearing age-mates.

OBJECTIVE: The primary objective of this study was to compare select acoustic characteristics of the speech of deaf children who use cochlear implants (young cochlear implant users) with those of children with normal hearing. A secondary objective of this study was to examine the effect, if any, of the deaf child's education (oral versus total communication) on the similarity of these acoustic characteristics to those of normal-hearing age-mates. DESIGN: Speech was recorded from 181 young cochlear implant users and from 24 children with normal hearing. All speech was produced by imitation, and consisted of complete sentences. Acoustic measures included voice onset time (/t/, /d/), second formant frequency (/i/, /[U0254]/), spectral moments (mean, skew and kurtosis of /s/ and /[U0283]/), a nasal manner metric, and durations (of vowels, words, and sentences). RESULTS AND DISCUSSION: A large percentage (46 to 97%) of the young cochlear implant users produced acoustic characteristics with values within the range found for children with normal hearing. Exceptions were sentence duration and vowel duration in sentence-initial words, for which only 23 and 25%, respectively, of the COCHLEAR IMPLANT users had values within the normal range. Additionally, for most of the acoustic measures, significantly more COCHLEAR IMPLANT users from oral than from total communication settings had values within the normal range. CONCLUSIONS: Compared with deaf children with hearing aids (from previous studies by others), deaf children who use cochlear implants have improved speech production skills, as reflected in the acoustic measures of this study. Placement in an oral communication educational setting is also associated with more speech production improvement than placement in a total communication setting.

Child↗
PubMed2006

Digital spectral analysis of the drill-bone acoustic interface during temporal bone dissection: a qualitative cadaveric pilot study.

HYPOTHESIS: To qualitatively assess the different acoustic signatures of an otologic drill burr-bone interface during temporal bone dissection on full thickness calvarial and thin tegmen bone. BACKGROUND: An appreciable change in the sound generated by drilling occurs with progressive thinning of the bone during temporal bone dissection. To date, descriptions of this phenomenon are limited to a handful of subjective characterizations. Using digital power spectral analysis, interpretation of complex functions of time such as acoustic signals can be interpreted. METHODS: Acoustic data recorded from five cadaveric temporal bone dissections were studied using digital spectral analysis. RESULTS: The energy bandwidth concentration was between 5.0 and 7.9 kHz for full thickness bone using the cutting burr. Thin tegmen bone bandwidth concentration was lower, between 3.7 and 7.4 kHz and 3.9 and 6.0 kHz, using cutting and diamond burrs, respectively. Harmonic frequencies for thin tegmen bone-burr signals were 630 Hz. CONCLUSION: There is a consistent, reproducible qualitative difference in the spectral domain of the acoustic signature from the drill burr-bone interface between thick calvarial bone and thin tegmen bone caused by a higher harmonic peak interval and lower energy bandwidth concentration in the thinned tegmen bone-burr interface signal thus concentrating the acoustic signal within a more optimal frequency range for human perception. These results allow for a better understanding of the perceived change in sound with progressive thinning of bone with drilling. In addition, these data may allow the development of more realistic acoustic interfaces in virtual reality temporal bone dissection simulators.

Acoustics↗
PubMed2006

Comparison of growth patterns of acoustic neuromas with and without radiosurgery.

OBJECTIVE: To compare the natural history of acoustic neuroma growth to the reported growth rate of acoustic neuromas after radiosurgical therapy, a retrospective review and meta-analysis of the literature was performed. The retrospective review was of one hundred eleven patients (average age, 71 yr) who chose to have their acoustic neuromas managed conservatively in our institution. These patients underwent serial magnetic resonance imaging for assessment of tumor growth for an average period of 38 months. Growth patterns if these untreated tumors were compared to that of radiosurgically treated acoustic neuromas reported in the literature. DATA SOURCES: The English-language literature on the topic was searched systematically by Medline and Pubmed using the following key words: acoustic neuroma, vestibular schwannoma, conservative management, conservative treatment, nonsurgical, age, elderly, growth, observation, untreated, radio-surgery, gamma knife, 13 Gy and 12 Gy. There were no limits to the year of publication. STUDY SELECTION: Articles that fulfilled inclusion criteria (methods) were studied in detail. DATA EXTRACTION: All the articles described in the study selection were used in the review. CONCLUSION: The average growth rate of the untreated tumors was 0.7 +/- 1.4 mm/yr. Eighty-two percent grew less than 1 mm/yr, whereas 18% grew equal to or more than 1 mm/yr. Thirteen percent grew more than 2 mm/yr, with growth being noted at an average of 2.2 years after diagnosis. This represents an 87% control rate if tumor control rate is defined as less than 2-mm growth/yr. Meta-analysis indicates that tumor control rates range in the radiosurgical literature from 86% to 100%. The mean follow-up periods in the radiosurgical literature are generally not reported. Tumor control is not uniformly defined. Based on the results of this study, there is no discernable significant difference between growth patterns of untreated acoustic neuromas and those treated radiosurgically. To establish a significant difference, longer-term follow-up studies with larger sample sizes and tumor control rates are needed. Tumor control should be defined as zero growth.

Adult↗
PubMed2005

Acoustic neuromas after failed radiation therapy: challenges of surgical salvage.

OBJECTIVES: As stereotactic radiation has emerged as a treatment option for acoustic neuromas, cases that require surgical salvage after unsuccessful radiation have emerged. We present a comparison of the technical challenges faced by the surgeons in the treatment of irradiated versus nonirradiated acoustic neuromas. STUDY DESIGN: Matched case-control series. METHODS: We identified nine patients with acoustic neuromas that required surgical resection after radiation therapy. Cases were performed with suboccipital and translabyrinthine approaches. Nine nonirradiated case-control subjects matched for age, sex, tumor size, and surgical approach were identified for purposes of general comparison. Operative findings and outcomes were compared for the two groups. RESULTS: Surgical removal was found to be significantly more difficult after radiation therapy because of increased fibrosis and adhesion to adjacent nervous structures, particularly at the porus acousticus. Excessive scarring hindered identification of the facial nerve and added uncertainty as to the completeness of tumor removal. Decompression of the internal auditory canal (IAC) dura and resection of neoplasm in the IAC before cerebellopontine angle dissection was required for facial nerve identification. Operative time was significantly longer for irradiated cases, and facial nerve outcomes tended to be poorer, particularly when facial nerve dysfunction prompted the salvage procedure. CONCLUSIONS: Surgical salvage of acoustic neuromas after radiation therapy is feasible, but it presents technical challenges beyond that associated with primary surgical therapy. Poorer outcomes of postoperative cranial nerve status were caused primarily by anatomic changes at the nerve/tumor interface. As surgical experience with the irradiated acoustic neuroma grows, operative observations should be incorporated into the counsel provided to patients with acoustic neuromas as they weigh different management options.

Adult↗
PubMed2006

Acoustic rhinometry: should we be using it?

PURPOSE OF THE REVIEW: The purpose of this review is to examine the role of acoustic rhinometry in clinical practice. Although acoustic rhinometry was first described for clinical use in 1989, it is not in common use today. Should we be using it? Yes. I think we should be using it more often. This review provides an update of the new standard for interpretation and expanded clinical uses. RECENT FINDINGS: The most significant advances in the past year in this area have been the publication of standards for its clinical use. In addition, the repertoire of clinical problems that can be analyzed objectively with acoustic rhinometry has expanded to include turbinoplasty, sleep disorders, more types of cosmetic/reconstructive procedures, sinus surgery, vasomotor rhinitis, maxillofacial expansion procedures, and aspirin and methacholine challenge. (Its ability for pediatric disorders, such as adenoidectomy, has been reaffirmed.) Some case examples are included to demonstrate the utility of acoustic rhinometry for 'mixed' pathology. SUMMARY: Acoustic rhinometry is a rapid, objective, painless, noninvasive technique for assessing nasal airway obstruction. Recently, standards have been developed that aid its expansion for clinical use. Expanded clinical applications include sleep disorders, cosmetic/reconstructive and maxillofacial disorders, sinus and turbinate procedures, and pediatrics. Acoustic rhinometry should be utilized to improve our ability to practice evidence-based medicine in rhinology.

Adult↗
PubMed1994

Acoustic rhinometry compared with posterior rhinomanometry in the measurement of histamine- and bradykinin-induced changes in nasal airway patency.

1. Acoustic rhinometry is a relatively new method for objectively assessing nasal airway patency. In this paper we compare acoustic rhinometry with active posterior rhinomanometry. 2. Twenty normal healthy volunteers underwent nasal challenge with either histamine or bradykinin, 100 micrograms to 1000 micrograms, and responses were assessed by acoustic rhinometry. A further 20 subjects received identical nasal challenges and responses were assessed by active posterior rhinomanometry. 3. On a subsequent occasion, the subjects challenged previously with histamine, were given the selective H1-receptor antagonist, cetirizine, 10 mg orally, 3 h before repeat nasal challenge with histamine, 100-1000 micrograms. Again, responses were assessed by active posterior rhinomanometry and acoustic rhinometry. 4. The acoustic reflection measurements and the nasal airway resistance measurements showed comparable, significant dose-related changes in nasal patency to both histamine and bradykinin. Pretreatment with cetirizine blocked the histamine-induced change in nasal patency as measured by both methods. 5. We conclude that acoustic rhinometry has a number of advantages over posterior rhinomanometry. It is quick to perform, requires minimal subject co-operation and gives a reliable objective, measurement of dose-related changes in nasal airway patency before and after pharmacological treatment.

Acoustics↗
PubMed2004

In vivo intracellular responses of the medial geniculate neurones to acoustic stimuli in anaesthetized guinea pigs.

In the present study, we investigated the auditory response features of the medial geniculate neurones, using in vivo intracellular recordings in anaesthetized guinea pigs. Of the 76 neurones examined, 9 showed 'off' or 'on-off' responses to an acoustic stimulus and thus were defined as 'off' or 'on-off' neurones. Among the remaining 67 neurones, 42 showed an excitatory postsynaptic potential (EPSP) to acoustic stimuli and 25 showed either a pure inhibitory postsynaptic potential (IPSP, 7 neurones), or an IPSP preceded by an EPSP (EPSP-IPSP type, 18 neurones). The EPSP responses exhibited a mean latency of 15.7 +/- 6.1 ms, which was significantly shorter than that of the IPSP responses (21.3 +/- 8.6 ms, P < 0.01). The IPSP responses also showed a significantly greater duration than the EPSP responses (208.5 +/- 128.2 ms versus 122.4 +/- 84.8 ms, P < 0.05), while there were no significant differences between the amplitudes of IPSP and EPSP (8.3 +/- 3.2 mV versus 8.7 +/- 5.3 mV). Of the 11 neurones that showed EPSP responses to acoustic stimuli and were histologically labelled, 7 were located in the lemniscal medial geniculate body (MGB) and 4 in the non-lemniscal MGB. Another 6 labelled neurones that showed IPSP responses to acoustic stimuli were located in the non-lemniscal MGB. With a membrane potential of above -72 mV, the neurones showed greater EPSP or IPSP to an acoustic stimulus when their membrane potential was depolarized. However, upon hyperpolarization to below -74 mV, the neurones shifted to low-threshold calcium spikes (LTS)/LTS bursts. In response to auditory stimuli of different durations, 'off' neurones that responded to the offset of the acoustic stimulus and were located in the non-lemniscal MGB showed different response latencies or deviations of latencies in addition to exhibiting different numbers of spikes, suggesting that the timing of the spikes could be another component utilized by thalamic neurones to encode information on the stimulus. Given that some non-lemniscal neurones are multisensory and project to the entire auditory cortex, the selective corticofugal inhibition in the non-lemniscal MGB would enable the ascending pathway to prepare the auditory cortex to receive subsequent auditory information, avoiding the interference of other sensory inputs.

Acoustic Stimulation↗
PubMed2000

Turboprop and rotary-wing aircraft flight parameter estimation using both narrow-band and broadband passive acoustic signal-processing methods.

Flight parameter estimation methods for an airborne acoustic source can be divided into two categories, depending on whether the narrow-band lines or the broadband component of the received signal spectrum is processed to estimate the flight parameters. This paper provides a common framework for the formulation and test of two flight parameter estimation methods: one narrow band, the other broadband. The performances of the two methods are evaluated by applying them to the same acoustic data set, which is recorded by a planar array of passive acoustic sensors during multiple transits of a turboprop fixed-wing aircraft and two types of rotary-wing aircraft. The narrow-band method, which is based on a kinematic model that assumes the source travels in a straight line at constant speed and altitude, requires time-frequency analysis of the acoustic signal received by a single sensor during each aircraft transit. The broadband method is based on the same kinematic model, but requires observing the temporal variation of the differential time of arrival of the acoustic signal at each pair of sensors that comprises the planar array. Generalized cross correlation of each pair of sensor outputs using a cross-spectral phase transform prefilter provides instantaneous estimates of the differential times of arrival of the signal as the acoustic wavefront traverses the array.

Acoustics↗
PubMed2002

Acoustic streaming induced by ultrasonic flexural vibrations and associated enhancement of convective heat transfer.

Acoustic streaming induced by ultrasonic flexural vibrations and the associated convection enhancement are investigated. Acoustic streaming pattern, streaming velocity, and associated heat transfer characteristics are experimentally observed. Moreover, analytical analysis based on Nyborg's formulation is performed along with computational fluid dynamics (CFD) simulation using a numerical solver CFX 4.3. Two distinctive acoustic streaming patterns in half-wavelength of the flexural vibrations are observed, which agree well with the theory. However, acoustic streaming velocities obtained from CFD simulation, based on the incompressible flow assumption, exceed the theoretically estimated velocity by a factor ranging from 10 to 100, depending upon the location along the beam. Both CFD simulation and analytical analysis reveal that the acoustic streaming velocity is proportional to the square of the vibration amplitude and the wavelength of the vibrating beam that decreases with the excitation frequency. It is observed that the streaming velocity decreases with the excitation frequency. Also, with an open-ended channel, a substantial increase in streaming velocity is observed from CFD simulations. Using acoustic streaming, a temperature drop of 40 degrees C with a vibration amplitude of 25 microm at 28.4 kHz is experimentally achieved.

Acoustics↗
PubMed2002

Acoustic propagation through anisotropic internal wave fields: transmission loss, cross-range coherence, and horizontal refraction.

Results of a computer simulation study are presented for acoustic propagation in a shallow water, anisotropic ocean environment. The water column is characterized by random volume fluctuations in the sound speed field that are induced by internal gravity waves, and this variability is superimposed on a dominant summer thermocline. Both the internal wave field and resulting sound speed perturbations are represented in three-dimensional (3D) space and evolve in time. The isopycnal displacements consist of two components: a spatially diffuse, horizontally isotropic component and a spatially localized contribution from an undular bore (i.e., a solitary wave packet or solibore) that exhibits horizontal (azimuthal) anisotropy. An acoustic field is propagated through this waveguide using a 3D parabolic equation code based on differential operators representing wide-angle coverage in elevation and narrow-angle coverage in azimuth. Transmission loss is evaluated both for fixed time snapshots of the environment and as a function of time over an ordered set of snapshots which represent the time-evolving sound speed distribution. Horizontal acoustic coherence, also known as transverse or cross-range coherence, is estimated for horizontally separated points in the direction normal to the source-receiver orientation. Both transmission loss and spatial coherence are computed at acoustic frequencies 200 and 400 Hz for ranges extending to 10 km, a cross-range of 1 km, and a water depth of 68 m. Azimuthal filtering of the propagated field occurs for this environment, with the strongest variations appearing when propagation is parallel to the solitary wave depressions of the thermocline. A large anisotropic degradation in horizontal coherence occurs under the same conditions. Horizontal refraction of the acoustic wave front is responsible for the degradation, as demonstrated by an energy gradient analysis of in-plane and out-of-plane energy transfer. The solitary wave packet is interpreted as a nonstationary oceanographic waveguide within the water column, preferentially funneling acoustic energy between the thermocline depressions.

Acoustics↗
PubMed2002

Ultrasound-induced lung hemorrhage: role of acoustic boundary conditions at the pleural surface.

In a previous study [J. Acoust. Soc. Am. 108, 1290 (2000)] the acoustic impedance difference between intercostal tissue and lung was evaluated as a possible explanation for the enhanced lung damage with increased hydrostatic pressure, but the hydrostatic-pressure-dependent impedance difference alone could not explain the enhanced occurrence of hemorrhage. In that study, it was hypothesized that the animal's breathing pattern might be altered as a function of hydrostatic pressure, which in turn might affect the volume of air inspired and expired. The acoustic impedance difference between intercostal tissue and lung would be affected with altered lung inflation, thus altering the acoustic boundary conditions. In this study, 12 rats were exposed to 3 volumes of lung inflation (inflated: approximately tidal volume; half-deflated: half-tidal volume; deflated: lung volume at functional residual capacity), 6 rats at 8.6-MPa in situ peak rarefactional pressure (MI of 3.1) and 6 rats at 16-MPa in situ peak rarefactional pressure (MI of 5.8). Respiration was chemically inhibited and a ventilator was used to control lung volume and respiratory frequency. Superthreshold ultrasound exposures of the lungs were used (3.1-MHz, 1000-Hz PRF, 1.3-micros pulse duration, 10-s exposure duration) to produce lesions. Deflated lungs were more easily damaged than half-deflated lungs, and half-deflated lungs were more easily damaged than inflated lungs. In fact, there were no lesions observed in inflated lungs in any of the rats. The acoustic impedance difference between intercostal tissue and lung is much less for the deflated lung condition, suggesting that the extent of lung damage is related to the amount of acoustic energy that is propagated across the pleural surface boundary.

Acoustics↗
PubMed2002

Acoustic intensity, impedance and reflection coefficient in the human ear canal.

The sound power per unit cross-sectional area was determined in human ear canals using a new method based on measuring the pressure distribution (P) along the length of variable cross-section acoustic waveguides. The technique provides the pressure/power reflection coefficients (R/R) as well as the acoustic intensity of the nonplanar incident wave (I+, the acoustic input to the ear) and the nonplanar outgoing wave (I-, the acoustic output of the ear). Results were compared to the classical acoustic impedance (Z) and associated plane-wave power reflection coefficient (R(Z)). Performance of the method was investigated theoretically using horn equation simulations and evaluated experimentally using pressure data recorded in nonuniform waveguides. The method was applied in normal-hearing young adults to determine ear-canal position- and frequency-dependence of I(+/-), R, and R(Z) using random phase broadband stimuli (1-15 kHz; approximately 75 dB SPL). Reflection coefficient (R) measurements at two different locations within individual human ear canals exhibited a position dependence averaging deltaR approximately 0.1 (over 6 mm distance)--a difference consistent with predictions of inviscid acoustics in nonuniform waveguides. Since this position dependence was relatively small, an "optimized" position-independent reflection coefficient was defined to facilitate practical application and intersubject comparisons.

Acoustic Impedance Tests↗
PubMed2005

Modal analysis and intensity of acoustic radiation of the kettledrum.

The acoustical features of kettledrums have been analyzed by means of modal analysis and acoustic radiation (p/v ratio) measurements. Modal analysis of two different kettledrums was undertaken, exciting the system both by a hammer and a shaker. Up to 15 vibrational modes were clearly identified. Acoustic radiation was studied using two ways. Based on previous experiments of other researchers, a new parameter, called intensity of acoustic radiation (IAR), has been defined and measured. Results show a strict relationship between IAR and the frequency response function (FRF, which is the v/F ratio), and IAR also strongly relates the modal pattern to acoustic radiation. Finally, IAR is proposed for vibro-acoustical characterization of kettledrums and other musical instruments such as strings, pianos, and harpsichords.

Acoustics↗
PubMed2005

Speech and melody recognition in binaurally combined acoustic and electric hearing.

Speech recognition in noise and music perception is especially challenging for current cochlear implant users. The present study utilizes the residual acoustic hearing in the nonimplanted ear in five cochlear implant users to elucidate the role of temporal fine structure at low frequencies in auditory perception and to test the hypothesis that combined acoustic and electric hearing produces better performance than either mode alone. The first experiment measured speech recognition in the presence of competing noise. It was found that, although the residual low-frequency (<1000 Hz) acoustic hearing produced essentially no recognition for speech recognition in noise, it significantly enhanced performance when combined with the electric hearing. The second experiment measured melody recognition in the same group of subjects and found that, contrary to the speech recognition result, the low-frequency acoustic hearing produced significantly better performance than the electric hearing. It is hypothesized that listeners with combined acoustic and electric hearing might use the correlation between the salient pitch in low-frequency acoustic hearing and the weak pitch in the envelope to enhance segregation between signal and noise. The present study suggests the importance and urgency of accurately encoding the fine-structure cue in cochlear implants.

Acoustic Stimulation↗
PubMed2006

Electromotile hearing: acoustic tones mask psychophysical response to high-frequency electrical stimulation of intact guinea pig cochleae.

When sinusoidal electric stimulation is applied to the intact cochlea, a frequency-specific acoustic emission can be recorded in the ear canal. Acoustic emissions are produced by basilar membrane motion, and have been used to suggest a corresponding acoustic sensation termed "electromotile hearing." Electromotile hearing has been specifically attributed to electric stimulation of outer hair cells in the intact organ of Corti. To determine the nature of the auditory perception produced by electric stimulation of a cochlea with intact outer hair cells, guinea pigs were tested in a psychophysical task. First, subjects were trained to report detection of sinusoidal acoustic stimuli and dynamic range was assessed using response latency. Subjects were then implanted with a ball electrode placed into scala tympani. Following the surgical implant procedure, subjects were transferred to a task in which acoustic signals were replaced by sinusoidal electric stimulation, and dynamic range was assessed again. Finally, the ability of acoustic pure-tone stimuli to mask the detection of the electric signals was assessed. Based on the masking effects, it is concluded that sinusoidal electric stimulation of the intact cochlea results in perception of a tonal (rather than a broadband or noisy) sound at a frequency of 8 kHz or above.

Acoustics↗