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PubMed2004

Voice changes after androgen therapy for hypogonadotrophic hypogonadism.

OBJECTIVES/HYPOTHESIS: Males with isolated hypogonadotropic hypogonadism (IHH) fail to undergo normal sexual development, including the lack of masculinization of the larynx. The objective of this study was to measure the mean vocal fundamental frequency (MF0) in IHH patients and determine the impact of androgen treatment. An additional aim was to compare the MF0 between IHH patients and controls. STUDY DESIGN: Prospective observational study. METHODS: Twenty-four patients with IHH were identified along with 30 normal males and females. Voice recordings were obtained on all subjects. Androgen therapy was administered to the IHH patients. The MF0 and serum sex hormone levels were measured before treatment and at intervals during therapy. These results were compared with the pretreatment data within the IHH group. Voice parameters were also compared between the pre- and posttreatment IHH patients and the normal males and females. RESULTS: The MF0 in untreated IHH patients was 229 +/- 41 Hz. This was intermediate between the normal male (150 +/- 22 Hz, P < .001) and normal female patients (256 +/- 29 Hz, P < .01). After treatment, the MF0 in the IHH group decreased to 173 +/- 30 Hz (P < .0001); indeed, their posttreatment MF0 approached that of normal males (P < .08). Serum hormone levels responded to the injected testosterone, but these levels did not directly correlate with MF0. CONCLUSIONS: MF0 in IHH patients is intermediate between normal male and female levels. After treatment with testosterone, these values approach the range of normal males. This prospective study details the impact of androgens on the larynx and vocal function in patients with IHH.

Adult↗
PubMed2004

Viscoelastic properties of three vocal-fold injectable biomaterials at low audio frequencies.

OBJECTIVES: Previous measurements of viscoelastic properties of Zyderm were to be extended to low audio frequencies, and properties of two other biomaterials not previously measured, thiolated hyaluronic acid (HA-DTPH) and Cymetra, were obtained. STUDY DESIGN: Rheologic investigation. METHODS: Oscillatory shear stress was applied to each sample using a controlled stress rheometer at frequencies between 0.01 and 100 Hz with a parallel plate apparatus. Versuscoelastic moduli were recorded at each frequency. The calculated resonance frequency of the machine and sample were then used to determine the maximum frequency at which reliable data existed. Extrapolation functions were fit to viscoelastic parameters, which predicted the properties up to 1,000 Hz. RESULTS: Frequency trends of Zyderm were similar to those previously reported, whereas magnitudes were different. The elastic moduli logarithmically increased with frequency, whereas dynamic viscosity demonstrated shear thinning, a condition of primary importance for humans to vocalize over a broad frequency range. Previous measurements were extended from 15 Hz up to 74 Hz. Differences in magnitude between a previous study and the present study were attributed to particulate orientation during testing. Cymetra was found to have nearly identical viscoelastic properties to those of bovine collagen, both in magnitude and frequency trend, with reliable measures extending up to 81 Hz. Rheologic properties of the hyaluronic acid gel were the closest match to cadaveric vocal fold mucosa in magnitude and frequency trend. CONCLUSIONS: Viscoelastic properties of Cymetra and Zyderm are nearly the same and are significantly greater than those of vocal fold mucosa. HA-DTPH possesses a good viscoelastic match to vocal fold mucosa and may be useful in future lamina propria repair.

Collagen↗
PubMed2000

Hearing and ultrasound-assisted liposuction: the effect on surgeon and patient.

Ultrasound-assisted liposuction has become an important tool in body-contouring surgery. Although ultrasound frequency is by definition outside the range of normal human hearing, an audible sound is heard during ultrasound-assisted liposuction. This study measured sound intensity during ultrasound-assisted liposuction performed with two commercially available systems. Sound intensity was measured at the surgeon's ear, surgical site, and patient's glabella. All measurements obtained with both machines fell within acceptable standards as defined by the Occupational Safety and Health Administration. Use of ultrasound-assisted liposuction does not pose a risk to the patient, the surgeon, or operating room personnel.

Equipment Design↗
PubMed1997

Laryngeal manifestations of gastroesophageal reflux before and after treatment with omeprazole.

BACKGROUND: Laryngeal manifestations of gastroesophageal reflux disease are thought to be prevalent in our society. In general, diagnosis has been primarily based on symptoms. Historically, additional testing has included laryngoscopy, barium swallow, manometry, and single and double probe pH monitoring. METHODS: We assessed 96 patients who had symptoms suggestive of reflux laryngitis. We administered surveys grading their symptoms. All patients had standardized videolaryngostroboscopic evaluation and computerized acoustic analysis. Patients then received a uniform regimen of dietary restrictions and omeprazole (a proton pump inhibitor) for 12 weeks, after which they were retested. RESULTS: Using the new laryngoscopic grading system, we found that this regimen produced statistically significant improvement in all symptoms except granulomas. In patients with the pretherapy complaint of hoarseness, acoustic measurements of jitter, shimmer, habitual frequency, and frequency range all showed significant improvement. CONCLUSIONS: We conclude that in patients with symptomatic reflux laryngitis, standardized videolaryngoscopy and, if the patient is hoarse, acoustic analysis are useful techniques to aid diagnosis and monitor therapy. Antireflux therapy with omeprazole is effective, and improvement can be objectively shown with the techniques described.

Adult↗
PubMed2002

Impact of long-term erythrocytapheresis on splenic function in patients with sickle cell disease.

Fifteen children with sickle cell disease undergoing long-term erythrocytapheresis were assessed for splenic regeneration using abdominal ultrasound and radionuclide spleen scans. Despite a significant level of reduction of hemoglobin S (HbS), none of the 15 patients showed evidence of splenic regeneration. Comparing our results with other published reports on hypertransfusion therapy in patients with sickle cell disease, it appears that the process of splenic regeneration in these patients is minimal and may depend partly on the intensity of transfusion therapy and the length of time that HbS has been maintained below 20%.

Adolescent↗
PubMed2002

Photoacoustic effects of carbon dioxide lasers in stapes surgery: quantification in a temporal bone model.

HYPOTHESIS: The use of the CO2 laser in stapes surgery creates sound waves that could damage hearing. BACKGROUND The application of a laser to any medium has absorption, reflection, and thermal effects. To date, the majority of research on the safety of CO2 laser stapedotomy has focused on the thermal effects of the laser alone. Because of the properties of the CO2 laser, its absorption also presents some risk to the inner ear. This absorbed energy can be converted to photoacoustic or photochemical effects. The goal of this paper is to measure these photoacoustic effects (sounds) produced by the CO2 laser. METHODS: Using a variety of settings, a Sharplan 150 XJ Laser and a Contour model Erbium:YAG laser were applied to the oval window of human temporal bones. Perilymph was simulated by fixing the temporal bone in a normal saline bath. Photoacoustic waves were measured by a hydrophone 2 mm beneath the oval window. Measurements were made with and without a simulated tissue seal over the window. RESULTS: No detectable sounds were created below 4 watts (continuous mode) or 60 mJ (superpulse mode). Above those settings, intensities of 90 dB sound pressure level and higher were detected when the laser was applied directly to the perilymph. With the tissue seal in place, no detectable sounds were identified. The accuracy of this model was confirmed by comparing these results with previously published results using the Erbium:YAG laser. CONCLUSIONS: Below 4 watts in continuous wave mode and below 60 mJ in superpulse mode, any sound generated by the laser is small. Above these thresholds, however, impact sounds are produced that could result in threshold shifts with repeated applications.

Humans↗
PubMed2003

In vivo characterization of piezoelectric transducers for implantable hearing AIDS.

BACKGROUND: Piezoelectric bimorph transducers may be used at the input stage of implantable hearing aids to convert ossicle vibrations into electrical waveforms, and at the output stage to convert electrical signals into mechanical motion that drives the ossicles. This study assessed transducer performance in anesthetized, acutely implanted cats using computer-averaged, laser-Doppler vibrometer measures and cochlear potentials. METHODS: Measures of output linearity and distortion for a transducer placed on the umbo were obtained from averaged laser-Doppler vibrometer outputs. Frequency response and equivalent sound pressure level for transducers placed against the stapes were estimated by comparing compound action potentials and cochlear microphonics elicited preoperatively by acoustic signals with responses elicited postoperatively by signals presented through transducers. RESULTS: The transducer placed on the umbo exhibited an effective bandwidth that exceeded 8 kHz, linear response behavior for driving voltages up to 2 Vrms, and harmonic distortion of -40 dB or better at all frequencies greater than 250 Hz. Except for a shorter latency, transducer-elicited cochlear potentials were indistinguishable from acoustically elicited responses. Frequency response varied widely across transducers, ranging from reasonably flat to possessing a bandpass characteristic with a peak at 2 to 4 kHz; 1-Vrms signals applied to transducers with various geometries yielded equivalent intensities of 62 to 108 dB sound pressure level at 4 kHz, 51 to 98 dB sound pressure level at 2 kHz, and 55 to 80 dB sound pressure level at 1 kHz. Differences in frequency response and equivalent sound pressure level stemmed from different resonance frequencies in transducers with dissimilar lengths and, more importantly, from variation in transducer-stapes contact force. CONCLUSIONS: Appropriately designed piezoelectric transducers can provide the cochlea with high-fidelity, wide-bandwidth signals. However, using them in implantable hearing aids requires that geometry and contact force be optimized to reduce variability in output level. Recording cochlear potentials is a cost-effective means of assessing transducer performance intraoperatively, but care must be exercised to take into account any temporary, drill-induced sensitivity loss.

Action Potentials↗
PubMed2005

Underwater hearing and sound localization with and without an air interface.

HYPOTHESIS: Underwater hearing acuity and sound localization are improved by the presence of an air interface around the pinnae and inside the external ear canals. BACKGROUND: Hearing threshold and the ability to localize sound sources are reduced underwater. The resonance frequency of the external ear is lowered when the external ear canal is filled with water, and the impedance-matching ability of the middle ear is significantly reduced due to elevation of the ambient pressure, the water-mass load on the tympanic membrane, and the addition of a fluid-air interface during submersion. Sound lateralization on land is largely explained by the mechanisms of interaural intensity differences and interaural temporal or phase differences. During submersion, these differences are largely lost due to the increase in underwater sound velocity and cancellation of the head's acoustic shadow effect because of the similarity between the impedance of the skull and the surrounding water. METHODS: Ten scuba divers wearing a regular opaque face mask or an opaque ProEar 2000 (Safe Dive, Ltd., Hofit, Israel) mask that enables the presence of air at ambient pressure in and around the ear made a dive to a depth of 3 m in the open sea. Four underwater speakers arranged on the horizontal plane at 90-degree intervals and at a distance of 5 m from the diver were used for testing pure-tone hearing thresholds (PTHT), the reception threshold for the recorded sound of a rubber-boat engine, and sound localization. For sound localization, the sound of the rubber boat's engine was randomly delivered by one speaker at a time at 40 dB HL above the recorded sound of a rubber-boat engine, and the diver was asked to point to the sound source. The azimuth was measured by the diver's companion using a navigation board. RESULTS: Underwater PTHT with both masks were significantly higher for frequencies of 250 to 6000 Hz when compared with the thresholds on land (p <0.0001). No differences were found in the PTHT or the reception threshold for the recorded sound of a rubber-boat engine for dry or wet ear conditions. There was no difference in the sound localization error between the regular mask and the ProEar 2000 mask. CONCLUSIONS: The presence of air around the pinna and inside the external ear canal did not improve underwater hearing sensitivity or sound localization. These results support the argument that bone conduction plays the main role in underwater hearing.

Acoustic Impedance Tests↗
PubMed2003

Efficient stimuli for evoking auditory steady-state responses.

OBJECTIVE: To compare the magnitudes of the steady-state responses evoked by several types of stimuli, and the times required to recognize these responses as significant. DESIGN: In the first two experiments, we examined auditory steady-state responses to pure tones, broadband noise and band-limited noise. The stimuli were amplitude modulated in the 75 to 100 Hz range with sinusoidal or exponential envelopes. A third experiment investigated the effects of exponential envelopes on the responses to broadband noise. The final experiment examined auditory steady-state responses evoked by rapidly presented transient stimuli, such as clicks, brief tones and brief noise-bursts. All stimuli were presented dichotically at intensities 30 to 50 dB above behavioral thresholds. The subjects were adults, who drowsed or slept during the recording sessions. RESULTS: The responses to the noise were larger than the responses to the tones. At an intensity of 32 dB nHL, the average amount of time needed to obtain significant responses for the amplitude-modulated noise was 43 sec and the maximum time was 2 minutes. The average time for pure tone stimuli was approximately 2 minutes but 25% of the responses remained undetected after 5 minutes. Combining the responses to all the frequency-specific stimuli showed results similar to using noise stimuli. Using exponential envelopes did not increase response amplitudes for noise stimuli. At 45 dB nHL, the steady-state responses to clicks and other transient stimuli were larger than responses to the broadband noise. The average time to detect steady-state responses to transient stimuli was approximately 20 sec, which was a little faster than for amplitude modulated noise. CONCLUSIONS: Auditory steady-state potentials evoked by amplitude modulated noise or transient stimuli might be useful in providing rapid and objective tests of hearing during screening procedures. Another approach might be to record responses to multiple frequency-specific stimuli and to evaluate the combined responses for a rapid indication that some hearing is present.

Acoustic Stimulation↗
PubMed2004

Sensitivity to interaural level and envelope time differences of two bilateral cochlear implant listeners using clinical sound processors.

OBJECTIVES: To assess the sensitivity of two bilateral cochlear implant users to interaural level and time differences (ILDs and ITDs) for various signals presented through the auxiliary inputs of clinical sound processors that discard fine timing information and only preserve envelope cues. DESIGN: In a lateralization discrimination experiment, the just noticeable difference (JND) for ILDs and envelope ITDs was measured by means of an adaptive 2-AFC method. Different stimuli were used, including click trains at varying repetition rates, a speech fragment, and noise bursts. For one cochlear implant listener and one stimulus, the sensitivity to envelope ITDs was also determined with the method of constant stimuli. The dependency of ILD-JNDs on the interaural place difference was studied with stimulation at single electrode pairs by using sinusoidal input signals in combination with appropriate single-channel processor fittings. In a lateralization position experiment, subjects were required to use a visual pointer on a computer screen to indicate in-the-head positions for blocks of stimuli containing either ILD or ITD cues. All stimuli were loudness balanced (before applying ILD) and fed directly into the auxiliary inputs of the BTE processors (TEMPO+, Med-El Corp.). The automatic gain control and the processors' microphones were deactivated. RESULTS: Both cochlear implant listeners were highly sensitive to ILDs in all broadband stimuli used; JNDs approached those of normal-hearing listeners. Pitch-matched single electrode pairs showed significantly lower ILD-JNDs than pitch-mismatched electrode pairs. Envelope ITD-JNDs of cochlear implant listeners obtained with the adaptive method were substantially higher and showed a higher test-retest variability than waveform ITD-JNDs of normal-hearing control listeners and envelope ITD-JNDs of normal-hearing listeners reported in the literature for comparable signals. The envelope ITD-JNDs for the click trains were significantly lower than for the speech token or the noise bursts. The best envelope ITD-JND measured was ca. 250 mus for the click train at 100 cycles per sec. Direct measurement of the psychometric function for envelope ITD by the method of constant stimuli showed discrimination above chance level down to 150 micros. The lateralization position experiment showed that both ILDs and envelope ITDs can lead to monotonic changes in lateral percept. CONCLUSIONS: The two cochlear implant users tested showed strong effects of ILDs in various broadband stimuli with respect to JNDs as well as lateralization position. The high dependency of ILD-JNDs on the interaural pitch difference suggests the potential importance of pitch-matched assignment of electrodes in the two ears by the speech processors. Envelope ITDs appear to be more ambiguous cues than ILDs, as reflected by the higher and more variable JNDs compared with normal-hearing listeners. The envelope ITD-JNDs of cochlear implant listeners depended on the stimulus.

Acoustic Stimulation↗
PubMed2004

Recording auditory steady-state responses in young infants.

OBJECTIVES: This study examined the auditory steady-state responses evoked by amplitude-modulated (AM), mixed-modulated (MM), exponentially-modulated (AM2), and frequency-modulated (FM) tones in 50 newborn infants (within 3 days of birth) and in 20 older infants (within 3-15 wk of birth). Our hypothesis was that MM and AM2 tonal stimuli would evoke larger responses than either the AM or FM tones, and that this increased size would make the responses more readily detectable. DESIGN: Multiple auditory steady-state responses were recorded to four tonal stimuli presented simultaneously to each ear at 50 dB SPL. The carrier frequencies of the stimuli were 500, 1000, 2000, and 4000 Hz and the modulation rates were between 78 and 95 Hz. Recordings lasting 12 minutes were obtained for each of the three types of modulation: 100% AM, MM (100% AM and 20% FM) and AM2. In six infants, responses to 20% FM were also recorded. RESULTS: In newborn infants, MM and AM2 stimuli produced responses that were on average 15% larger than AM stimuli. For AM, MM, and AM2 stimuli, the percentage of significant responses was 67%, 73%, 76%, respectively. Responses to FM stimuli were clearly evident in newborn infants and were about half the amplitude of the AM responses. Responses recorded in the older infants were 17% larger when evoked by MM and AM2 stimuli, rather than AM stimuli. Responses in the older infants were, on average, 32% larger and showed a higher incidence of significant responses than for infants in the first 3 days of life. For AM, MM, and AM2 stimuli, the percentage of significant responses was 82%, 82%, 84%, respectively. In both newborn and older infants, the overall percentage of significant responses was decreased by the 500 Hz results, which showed lower amplitudes and were less frequently detected than responses evoked by other frequencies. CONCLUSIONS: The responses to MM and AM2 tones were larger than those evoked by AM tones. Using these stimuli will increase the reliability and efficiency of evoked potential audiometry in infancy. Responses at 50 dB SPL are more easily detected at 3-15 wk of age than in the first few days after birth. Comprehensive frequency-specific testing of hearing using steady-state responses will likely be more accurate if postponed until after the immediate neonatal period.

Auditory Perception↗
PubMed2005

Brain stem response to speech: a biological marker of auditory processing.

The auditory brain stem response to speech mimics the acoustic characteristics of the speech signal with remarkable fidelity. This makes it possible to derive from it considerable theoretical and clinically applicable information relevant to auditory processing of complex stimuli. Years of research have led to the current characterization of these neural events with respect to the underlying acoustic information they reflect. The majority of data reviewed here originates from studies using a /da/ syllable to elicit the brain stem response, which consists of transient and periodic (frequency following) neural activity. We describe how the human auditory brain stem response separately encodes source and filter characteristics of the acoustic signal, which reflects paralinguistic and linguistic information simultaneously conveyed in speech. In normal-hearing individuals, these two classes of response components (source and filter) are highly correlated within a class but not between classes. This response dissociation becomes pronounced when stimuli are presented in background noise or with faster stimulus rates. In addition, some learning-impaired children show a selective deficiency in the neural encoding of acoustic features associated with the filter characteristics of speech. These children show no deficits in the encoding of source components, further supporting the notion of separate neural mechanisms. Overall, the auditory brain stem response to speech provides a way to access subcortical auditory processing mechanisms and may be used as a biological marker of deficient sound encoding associated with learning and auditory processing disorders.

Acoustic Stimulation↗
PubMed2005

Rapid word-learning in normal-hearing and hearing-impaired children: effects of age, receptive vocabulary, and high-frequency amplification.

OBJECTIVE: This study examined rapid word-learning in 5- to 14-year-old children with normal and impaired hearing. The effects of age and receptive vocabulary were examined as well as those of high-frequency amplification. Novel words were low-pass filtered at 4 kHz (typical of current amplification devices) and at 9 kHz. It was hypothesized that (1) the children with normal hearing would learn more words than the children with hearing loss, (2) word-learning would increase with age and receptive vocabulary for both groups, and (3) both groups would benefit from a broader frequency bandwidth. DESIGN: Sixty children with normal hearing and 37 children with moderate sensorineural hearing losses participated in this study. Each child viewed a 4-minute animated slideshow containing 8 nonsense words created using the 24 English consonant phonemes (3 consonants per word). Each word was repeated 3 times. Half of the 8 words were low-pass filtered at 4 kHz and half were filtered at 9 kHz. After viewing the story twice, each child was asked to identify the words from among pictures in the slide show. Before testing, a measure of current receptive vocabulary was obtained using the Peabody Picture Vocabulary Test (PPVT-III). RESULTS: The PPVT-III scores of the hearing-impaired children were consistently poorer than those of the normal-hearing children across the age range tested. A similar pattern of results was observed for word-learning in that the performance of the hearing-impaired children was significantly poorer than that of the normal-hearing children. Further analysis of the PPVT and word-learning scores suggested that although word-learning was reduced in the hearing-impaired children, their performance was consistent with their receptive vocabularies. Additionally, no correlation was found between overall performance and the age of identification, age of amplification, or years of amplification in the children with hearing loss. Results also revealed a small increase in performance for both groups in the extended bandwidth condition but the difference was not significant at the traditional p = 0.05 level. CONCLUSIONS: The ability to learn words rapidly appears to be poorer in children with hearing loss over a wide range of ages. These results coincide with the consistently poorer receptive vocabularies for these children. Neither the word-learning or receptive-vocabulary measures were related to the amplification histories of these children. Finally, providing an extended high-frequency bandwidth did not significantly improve rapid word-learning for either group with these stimuli.

Adolescent↗
PubMed2006

Optimizing the stimuli to evoke the amplitude modulation following response (AMFR) in neonates.

OBJECTIVE: The goal was to identify stimulus features that enhance the detection of the amplitude modulation following response (AMFR) in neonates. The features explored were (1) envelope type, sinusoidal versus a half-wave rectified sinusoid (transposed); (2) best modulation frequency; and (3) spectral content, i.e., tone versus band-pass noise. DESIGN: Results are based on recordings from 149 babies (80 babies in the neonatal intensive care unit and 69 newborn infants). All had passed hearing screening based on the click-evoked ABR. Babies were not sedated. We used carrier frequencies of approximately 500, 1000, 2000, and 4000 Hz and modulation frequencies between approximately 25 and 98 Hz. For the noise stimuli, we used band-pass noise at center frequencies of 500, 1000, 2000, and 4000 Hz. All stimuli were presented through insert earphones delivered simultaneously to both ears, at intensities ranging from 20 to 70 dB SPL. Magnitude squared coherence, phase coherence, and spectral criteria were used to detect criterion AMFRs. We analyzed four measures: (1) percent of satisfied runs; (2) the amplitude of criterion AMFR; (3) time to detect a criterion AMFR; and (4) response strength (e.g., the value of the magnitude squared coherence when it reached criterion minus the critical value it had to exceed for that number of averages all divided by the critical value). RESULTS: (1) The AMFRs evoked by transposed tones were larger and detected faster than those to sinusoidal amplitude modulated tones. Consequently, remaining protocols all used the transposed envelopes. (2) The range of effective modulation frequencies was broad (41 to 88 Hz) across carrier frequencies. (3) The AMFRs evoked by transposed noise were faster and more efficient than those to transposed tones. CONCLUSIONS: In neonates, transposed tones are more effective than sinusoidal amplitude modulated tones in evoking the AMFR, modulation frequencies between 41 to 88 Hz are almost equally effective in evoking the AMFR, and band-pass noises are more effective in evoking the AMFR than tones. These three stimulus factors all add incrementally to the efficiency of evoking the AMFR. The short detection times indicate that the AMFR could be an effective tool for hearing screening.

Acoustic Stimulation↗
PubMed2006

Neural representation of amplified speech sounds.

OBJECTIVE: To determine if (1) evoked potentials elicited by amplified speech sounds (/si/ and /[symbol: see text]/) can be recorded reliably in individuals, (2) amplification alters neural response patterns, and (3) different amplified speech sounds evoke different neural patterns. DESIGN: Cortical evoked potentials were recorded in sound field from seven normal-hearing young adults in response to naturally produced speech tokens /si/ and /[symbol: see text]/ from the Nonsense Syllable Test. With the use of a repeated-measures design, subjects were tested and then retested within an 8-day period in both aided and unaided conditions. RESULTS: (1) Speech-evoked cortical potentials can be recorded reliably in individuals in both aided and unaided conditions. (2) Hearing aids that provide a mild high-frequency gain only subtly enhance peak amplitudes relative to unaided cortical recordings. (3) If the consonant-vowel boundary is preserved by the hearing aid, it can also be detected neurally, resulting in different neural response patterns for /si/ and /[symbol: see text]/. CONCLUSIONS: Speech-evoked cortical potentials can be recorded reliably in individuals during hearing aid use. A better understanding of how amplification (and device settings) affects neural response patterns is still needed.

Acoustic Stimulation↗
PubMed2006

Determination of the potential benefit of time-frequency gain manipulation.

OBJECTIVE: The purpose of this study was to determine the maximum benefit provided by a time-frequency gain-manipulation algorithm for noise-reduction (NR) based on an ideal detector of speech energy. The amount of detected energy necessary to show benefit using this type of NR algorithm was examined, as well as the necessary speed and frequency resolution of the gain manipulation. DESIGN: NR was performed using time-frequency gain manipulation, wherein the gains of individual frequency bands depended on the absence or presence of speech energy within each band. Three different experiments were performed: (1) NR using ideal detectors, (2) NR with nonideal detectors, and (3) NR with ideal detectors and different processing speeds and frequency resolutions. All experiments were performed using the Hearing-in-Noise test (HINT). A total of 6 listeners with normal hearing and 14 listeners with hearing loss were tested. RESULTS: HINT thresholds improved for all listeners with NR based on the ideal detectors used in Experiment I. The nonideal detectors of Experiment II required detection of at least 90% of the speech energy before an improvement was seen in HINT thresholds. The results of Experiment III demonstrated that relatively high temporal resolution (<100 msec) was required by the NR algorithm to improve HINT thresholds. CONCLUSIONS: The results indicated that a single-microphone NR system based on time-frequency gain manipulation improved the HINT thresholds of listeners. However, to obtain benefit in speech intelligibility, the detectors used in such a strategy were required to detect an unrealistically high percentage of the speech energy and to perform the gain manipulations on a fast temporal basis.

Acoustic Stimulation↗