Martin S. Robinette

Effect of temperature elevation on rabbit cochlear function as measured by distortion-product otoacoustic emissions

Low-intensity laser stapedotomy has been shown to produce temperature elevations of 3 degrees to 4 degrees C within the cochlea. This study investigates the effect of temperature elevations in this range on cochlear outer hair cell function by use of distortion-product otoacoustic emissions in rabbits. Using esophageal temperature monitoring, we compared 2f1-f2 distortion-product otoacoustic emissions over a range of frequencies (1806 to 8691 Hz) at rabbit normothermia, normothermia plus 3 degrees C, and normothermia after passive cooling. Cochlear temperature was found to exceed changes in esophageal temperature by as much as 1.2 degrees C. We found that a maximum of 3 degrees C elevation in esophageal temperature did not permanently impair outer hair cell function in the rabbit cochlea. Results of this study suggest that moderate changes in cochlear temperature, such as those produced by low-intensity CO2 and holmium-yttrium aluminum garnet lasers, may not produce irreversible thermal damage to the cochlear outer hair cells.

Application of the LMS adaptive filter to improve speech communication in the presence of noise

A major complaint of individuals with normal hearing and hearing impairment is a reduced ability to understand speech in a noisy environment. An adaptive LMS filter was employed to process speech in signal-to-noise ratios (S/N) varying from -8 to +12 dB. The filter configuration is commonly called noise cancellation. Intelligibility measures were obtained on normal and hearing impaired individuals using CID-W22 word lists. For the normal subjects mean intelligibility scores unprocessed were near zero for the S/N ratios -8, -4, and 0 dB and increased from 30 to 50% for the same S/N ratios when processed. For S/N ratios of +4 through +12, mean intelligibility scores prior to filtering ranged from 24 to 46%; after filtering, the scores improved from 67 to 75% i.e., within 7% of the nolse-free sound-field recordings. Preliminary data for the hearing impaired showed the same pattern with their improvement also approaching the scores obtained with no noise present in the sound field.

Influence of Dietary Magnesium on the Amplitude of Wave V of the Auditory Brainstem Response

Thirty-six weanling guinea pigs were fed either a low (600 ppm) or normal (3000 ppm) diet of magnesium for 8 weeks. One half of each diet group received intramuscular injections of magnesium-depleting drugs, furosemide and gentamicin. The other half were controls and received equal intramuscular injections of saline. Auditory brainstem responses were obtained from all animals before and after 8 weeks of treatment of diet and drugs to examine the effects of treatment upon hearing and auditory brainstem function. A three-way analysis of variance of dietary magnesium, by drug and by sex, showed no significant differences in auditory brainstem wave V thresholds, wave V latencies, or interpeak wave I-V latencies between the control and experimental groups. The low magnesium diet group, which received drugs, had significantly greater wave V auditory brainstem response amplitudes. Results can be explained on the basis of magnesium influencing the uptake of calcium into both the hair cells and associated brainstem pathways.

Electronic sound transmission hearing protectors and horizontal localization: Training/adaptation effects

Auditory situation awareness is known to be affected by some hearing protectors, even advanced electronic devices. A horizontal localization task was employed to determine how use/training with electronic sound transmission hearing protectors affected auditory localization ability, as compared to open-ear. Twelve normal-hearing participants performed baseline localization testing in a hemi-anechoic field in three listening conditions: open-ear, in-the-ear (ITE) device (Etymotic EB-15), and over-the-ear (OTE) device (Peltor ComTac II). Participants then wore either the ITE or OTE protector for 12, almost daily, one-hour training sessions. Post-training, participants again underwent localization testing with all three conditions. A computerized custom software-hardware interface presented localization sounds and collected accuracy and timing measures. ANOVA and post hoc statistical tests revealed that pre-training localization performance with either the ITE or OTE protector was significantly worse (p<0.05)...

Effects of N‐acetylcysteine on noise‐induced temporary threshold shift and temporary emission shift

Animal research has shown that antioxidants can provide significant protection to the cochlea from traumatic noise exposure with some benefit when given after the exposure. Similar results in humans would have a significant impact on both prevention and treatment of noise‐induced hearing loss. The current study evaluates the effectiveness of N‐acetylcysteine (NAC) on temporary threshold shift (TTS) by using both behavioral and physiological measures. Sixteen healthy, normal‐hearing subjects were given NAC or a placebo prior to exposure to a 10‐min, 102‐dB narrow‐band noise, centered at 2 kHz. This exposure was designed to induce a 10–15‐dB TTS. Following the noise exposure, pure‐tone thresholds (Bekesy) and transient‐evoked otoacoustic emissions (TEOAE) were measured for 60 min to monitor the effects of NAC on TTS recovery. Postexposure measures were compared to baseline data. [Work supported by American BioHealth Group.]

Aural signal processing in the context of a digital hearing model

A nonlinear model of the human aural system is proposed. Utilizing a homomorphic transformation, the model is implemented in a digital computer and accounts for the Fletcher critical bands in hearing, the nonlinear relationship between input sound intensity and perceived loudness known as recruitment, as well as the thresholds of audibility and the maximum tolerance threshold. The transformed or output signal domain is identified as a perceptual space. It is shown that the model can be used to reproduce the Fletcher Munson equal loudness contours for normal hearing populations. Modification of easily measured parameters results in the generation of equal loudness contours for hearing impaired individuals. Through a combination of the forward homomorphic transformation for normal hearing to the perceptual domain and the inverse mapping utilizing parameters of a hearing impaired individual, it is shown that hearing intelligibility is dramatically improved. It is postulated that signal processing performed i...

The effects of microphone placement and azimuth on peak sound pressure level of type A impulses

Single, repeatable type A impulses were generated by colliding steel spheres in an acoustically reverberant room, and measured as A‐weighted sound levels by a sound level meter having four exponential time averaging modes with time constants ranging from 2 μs to 1 s. Measurements using peak hold (2‐μs time constant) were then obtained on KEMAR at four azimuths and four microphone placements at each azimuth. Comparative measurements showed peak hold to give the most accurate estimation of A‐weighted sound level, as verified electrically. The remaining three underestimated this value. Maximum underestimation of 34.8 dB was demonstrated using the slow time constant. KEMAR measurements demonstrated peak A‐weighted sound levels to be sensitive to both microphone placement and azimuth. Measurements made in the reference field and at external microphone placements tended to underestimate peak A‐weighted sound level at the tympanic membrane (TM). Two conclusions were reached. Time constant of the exponential time...

Real-ear Masking Calibration for Portable Pure-Tone Audiometers

A transformer mixing network is described which allows the calibration of broad-band masking for portable audiometers that lack a built-in mixing network. For many instruments the transformer netwo...

Effect of alcohol on acoustic reflex relaxation

The Reflex Relaxation Index (RRI) was introduced by Norris et al. [Arch. Otolaryngol. 99, 194–97 (1974)] as an objective test for sensorineural hearing loss. The test consists of measuring the acoustic reflex response to pulsed pure tone stimuli. Sensorineural loss subjects show a different response pattern due in part to an increased reflex relaxation latency. Brey and Robinette [J. Acoust. Soc. Am. Suppl. 1 63, S53 (1978)] noted that post stimullus reflex latencies were increased for normal hearing subjects following the ingestion of alcohol. In the present study eleven normal hearing subjects were given the RRI test under two alcohol conditions: blood alcohol levels of 0.00 and 0.10%. Results showed six of the eleven subjects changed from a diagnosis criteria of normal cochlear function to that of sensorineural loss following alcohol consumption. Data suggests a simple positive or negative interpretation of the RRI test is not always appropriate.

Differential effect of at rest eye closure and orbicularis oculi contraction (squinting) on acoustic reflex

Previous eye closure studies have suggested muscle tension is responsible for acoustic reflex (AR) enhancement during light eye closure (A. L. Corcoran, M.Sc. dissertation, University of South‐hampton, England, 1976). AR threshold and magnitude were determined for nine normal hearing adults under counterbalanced conditions: (1) eyes open, (2) lightly closed, and (3) tightly closed (contraction of orbicularis oculi). For a 1‐kHz stimulus a 1.1 dB difference was noted between thresholds for eyes open or lightly closed. Squinting however, resulted in a significant 3.6‐ and 4.7‐dB enhancement over the eyes open and closed conditions, respectively. Broadband noise stimuli resulted in a marked enhancement of 9.8 dB while squinting. All conditions differed significantly for the noise stimuli. AR magnitude, however, did not differ across eye closure conditions for either stimuli. Results are compared with previous data on the effects of visual, tactile, olfactory, and mental tasks [Robinette et al., J. Acoust. So...