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PubMed1991

What is the cochlear place code for pitch?

The advent of cochlear implants has increased the clinical interest in the cochlear code for pitch. It is widely believed that pitch is determined by the location of the excitation maximum in the cochlea. However, direct recordings from cochlear hair cells indicate that, for a given sound frequency, the location changes appreciably with sound intensity, whereas the corresponding pitch remains approximately constant. Correlated with this constancy is a surprising constancy of the location of the high-frequency cutoff of cochlear excitation.

Acoustics↗
PubMed1993

Identification of rat brainstem sites with neuronal Fos protein induced by acoustic stimulation with pure tones.

Induction of Fos, a proto-oncogene c-fos protein product, was immunohistochemically examined in the rat brainstem by using pure tone stimuli (0.25 kHz, 4kHz and 8 kHz) at 60 and 80 dB sound pressure levels for 30 min. In comparison with non-stimulated control rats, the brainstem of sound-stimulated rats exhibited distinct Fos-labeled neuronal cell nuclei in i) the ascending auditory nuclei, ii) the brainstem sites which receive afferents from the auditory nuclei, i.e. the pretectum and rostroventrolateral reticular nucleus, iii) the parvocellular part of the ventral lateral geniculate nucleus, lateral reticular nucleus, ventral border region of the spinal trigeminal nucleus, and the medial vestibular and spinal vestibular nuclei, all of which lack established auditory projections, and iv) the brainstem sites where some Fos-labeled neurons were present in controls. Sound stimulation at 80 dB led to widespread Fos-labeling in all these sites. Sound stimulation at 60 dB caused a decrease in number of positive cells in the brainstem sites and yielded a tone-dependent subregional distribution pattern in the dorsal cochlear nucleus and central nucleus of the inferior colliculus.

Animals↗
PubMedDate not supplied

Post-operative stapedius reflex tests with simultaneous loudness scaling in patients supplied with cochlear implants.

The estimation of the maximum comfort loudness levels (MCL) by measurements of the electrically elicited stapedius reflex was examined in six experienced cochlear implant users supplied with the COMBI 40 implant system. The stapedius reflex was tested and loudness scaling was performed simultaneously using an up/down stimulation protocol close to the reflex threshold with automated recording of both test procedures. The electrical stapedius reflex threshold (ESRT) and loudness scaling were evaluated separately. Scaling at the reflex threshold ranged between normal and loud. The range of stimulus intensities corresponding to ESRT is much smaller than that at a particular loudness category. The overall correlation between ESRT and MCL was high (r=0.92), with a similar dependence of ESRT and MCL on the channel stimulated. Thus, when the stapedius reflex can be detected post-operatively, the ESRT can be applied successfully for the fitting procedure of the speech processor. Simultaneous loudness scaling during the entire reflex test showed that overstimulation via the implant can be avoided effectively.

Adult↗
PubMedDate not supplied

Cross-modal matching of loudness and brightness as a recruitment test for hearing-impaired children.

Normal 5-year-olds have been reported to be able, in a simple game situation, to match brightness to loudness in the same way as a control group of adults. This study investigated supplanting the normal ear in an alternate binaural loudness balance test (ABLB) with the visual modality, as a recruitment test designed especially for bilaterally hearing-impaired children. The results of normal 10-year-olds, with simulated hearing losses, suggest that category scaling was adopted naturally as a simplifying strategy in preference to ratio scaling (absolute judgements). No proportional increase in the matching function slope was evident, despite the amount of recruitment measured with an ABLB. The instructions needed to combat this strategy render the test unfeasible with hearing-impaired children.

Acoustic Stimulation↗
PubMed1980

Just audible pitch and loudness modulations with cochlear impairment.

Just noticeable combined modulations in amplitude and frequency were determined for an observer (DP) with a bowl-shaped sensorineural hearing loss of about 40 dB between 1 and 2 kHz. In all stimulus conditions, interactions were found between the detection of amplitude modulations and frequency modulations. These interactions appear to correlate quantitatively with the effect of frequency on loudness (as given by the slope of the equal-loudness contour). When this effect of frequency on loudness if taken into account, the data support the hypothesis of independent detection of pitch and loudness modulations. The experimental data are also discussed in relation to the single-mechanism hypothesis for the detection of changes in amplitude and frequency (Zwicker, Maiwald). This model could not provide a satisfactory explanation of interactions between amplitude and frequency.

Adult↗
PubMed1980

Loudness summation across frequency under masking and in sensorineural hearing loss.

The loudness summation across frequency was measured in unmasked and masked normally hearing subects, using noise bands centered at 1 kHz. Homolateral masking reduced the loudness summation of supracritical noise bands to a degree roughly proportional to the degree of threshold shift produced by the masking. Between thresholds and moderate sensation levels, the loudness summation increased at an invariable rate in the unmasked and the masked condition, reflected in an invariable supracritical growth of loudness with increasing stimulus bandwidth at identical sensation levels. At high intensities, the loudness summation decreased to roughly similar values in both conditions. Similar results were obtained by pooling the data from patients with sensorineural hearing losses and comparable threshold elevation. The critical bands appeared to be identical in unmasked and masked normally hearing subjects and in patients with sensorineural hearing losses. Contralateral, 35 dB effective masking produced a slight but consistent central masking effect; compared to the unmasked condition, the loudness summation of supracritical noise bands was reduced between threshold and medium stimulus levels, while it was increased at high levels.

Adolescent↗
PubMed1981

Test-retest stability and effects of psychophysical methods on the speech loudness discomfort level.

It is generally agreed that the saturation sound pressure level of a hearing aid should not exceed the patient's loudness discomfort level (LDL) for speech. This study investigated (1) the stability of the test and retest LDLs when obtained on different days using McCandless's and Berger's instructional sets and (2) the effects of a psychophysical method (adjustment versus limits) on the speech LDL using McCandless's instructions. Good reliability was observed since one-half of the listeners had test-retest differences of 2 dB or less and nearly all subjects obtained LDLs within 8 dB. The mean LDLs for the respective methods of adjustment and limits were 86.8 and 92.9 dB SPL, and statistically significant. Additionally, a significant interaction between the two methods was observed. The LDL measurement is also discussed in relation to other tests used to evaluate hearing aid performance.

Adolescent↗
PubMed1981

Heterophonic auditory adaptation to critical and noncritical bandwidths.

Auditory adaptation effects were measured for narrow bands of noise both within and outside of the critical band for 1 000 Hz. In keeping with previous research, a pure-tone condition resulted in more adaptation than any of the noise band conditions. However, as the noise bands were increased in width, a significant decrease in adaptation was observed, which is not in agreement with earlier findings. Adaptation results converted to theoretical auditory units show a trend which conforms to the Hood-Weiler model for loudness coding.

Acoustic Stimulation↗
PubMed1981

Discrimination of level differences by hearing-impaired patients.

A technique for measuring the discrimination of level differences with pulsed tones is proposed. Alternating tone bursts, each of 500 ms duration but of different sound pressure levels, are separated by 200-ms pauses. The advantages of this method in comparison with traditional methods (SISI test, Lüscher-Zwislocki test) which use modulated tones are that level discrimination is independent of frequency and that it shows very little dependence on sensation level. With this technique, the level discrimination of patients with conductive hearing loss, 'toxic' hearing impairment, noise-induced hearing loss, sudden deafness, presbyacusis, Meniere's disease, and retrocochlear impairment was determined and compared to the results obtained in normal ears. Using the level discrimination test proposed, retrocochlear disorders can be diagnosed with great reliability.

Adult↗
PubMed1982

Amplification bandwidth and speech intelligibility for two listeners with sensorineural hearing loss.

The intelligibility of speech as a function of its bandwidth was measured for two listeners with similar, moderately severe sensorineural hearing losses. The shape of the speech spectrum was adjusted to approximate the individual listener's contour of most comfortable listening levels (MCLs) and the overall level was set so that the levels in each band were below (-7 dB), near to (+3 dB), or above (+13 or +18 dB) the MCLs. At each level, nine pairings of three low-frequency and three high-frequency cutoffs (266, 375 and 530 Hz; 3,000, 4,242 and 6,000 Hz) were used. These conditions were achieved by passing the speech through a Limiting Master Hearing Aid (LMHA) which allows independent control of gain and maximum output in each of nine, half-octave bands. It was found that the wider the bandwidth, the higher the score, and the greater the amount of speech energy above threshold, the higher the score. Listeners' ability to understand the test material, after adjustment for listener differences, was correlated (0.7 and 0.8) with the articulation index.

Adult↗
PubMed1982

Sensitivity of auditory lateralization and temporal order tests to benzodiazepines.

The responses to tests of auditory lateralization and temporal order to the administration of desmethyldiazepam (DMDZ) and of chlorodesmethyldiazepam (Cl-DMDZ) have been investigated. Therapeutic doses of these two benzodiazepines were used. We have tested four groups of 10 healthy normally hearing subjects. It was demonstrated that both DMDZ and Cl-DMDZ cause a temporary disturbance in the lateralization tests: delta i but especially delta t. The temporal order test is not altered after drug administration. The physiopathological and topodiagnostic value of these tests and the site of action of the benzodiazepines are discussed.

Adult↗
PubMed1983

Amplification bandwidth and intelligibility of speech in quiet and noise for listeners with sensorineural hearing loss.

The intelligibility of speech mixed with noise (+6 dB S/N) and in quiet was measured as a function of its audible bandwidth for 7 listeners with moderate sensorineural hearing losses. Words were presented at three levels in the field (50, 60 and 70 dB SPL) and amplified with a Limiting Master Hearing Aid (LMHA) which allows independent control of gain and maximum power output in each of nine, half-octave channels. The frequency gain characteristics were chosen so the speech spectrum (60 dB SPL) at the input was shaped to approximate the individual listener's contour of most comfortable listening levels at the output. At each level and for the words in noise as well as quiet, the LMHA was set for four bandwidths (266-6 000, 375-4 242, 530-3 000 and 750-2 121 Hz). For these conditions, the listeners all obtained the highest mean score with the LMHA set for the widest bandwidth. The listener's ability to understand the words, after adjustment for individual differences, was well correlated (0.77-0.91) with the articulation index. Preliminary observations on the acceptability of amplified sounds, that is, loud speech, impact noise, an air-horn blast, and a party ratchet, are included.

Adult↗
PubMed1983

Monaural and binaural intensity discrimination in normal and cochlear-impaired listeners.

Monaural and binaural intensity difference limens for 75-dB SPL pure tones were determined for 6 normal subjects and for 6 subjects with cochlear hearing loss. The magnitude of binaural masking level difference (BMLD) was also determined. Both normal and hearing-impaired subjects showed a 0.45-dB binaural advantage for intensity discrimination. In contrast, the BMLD was appreciably reduced with hearing impairment. Results are discussed in terms of specific effects of hearing loss on binaural hearing.

Adult↗
PubMed1983

Effects of intensity variations on auditory processing in aphasia. I. Equal intensities at each ear.

Clinical observations have led several authors to suggest that talking louder improves auditory comprehension for the aphasic patient, while others suggest that it does nothing to help comprehension. To clarify these observations under experimental conditions, four measures of auditory processing (cortical-evoked responses, nonverbal intensity sequencing, phoneme in word discrimination and sequencing, and a semantic-syntactic measure of comprehension) were used in diotic presentation of stimuli to 10 aphasic subjects with left temporal lobe damage. The stimuli were presented at 70, 85, and 100 dB SPL. Results suggest that a simple diotic (true binaural) increase of stimulus intensity is not a potent variable for influencing auditory processing in patients with aphasia. Although a few subjects improved their performances on selected levels when stimulus intensity was increased, the performances of others decreased. Auditory-evoked response (AER) latencies and amplitudes generally were not significantly different between the damaged and intact hemispheres. The time-intensity trading function was demonstrated with the AER, particularly for the N2 component. The ear with the greatest advantage on dichotic listening was contralateral to the lesion and was contralateral to the hemisphere that had the shorter P1 latencies, longer N2 latencies, and smaller AER amplitudes.

Adult↗
PubMed1983

Effects of intensity variations on auditory processing in aphasia. II. Different intensities at each ear.

A neurologic extinction model was applied to the auditory-processing disorders evidenced by 10 persons with aphasia. This model suggests that messages travel faster to the intact hemisphere, where they are more differentiated and articulated, than to the affected hemisphere. This leads to extinction and interference of the message. To overcome this extinction, the stimulus intensity was raised by 15 or 30 dB to one ear at a time. The stimuli were a cortical auditory-evoked response (AER) measure, a nonverbal intensity sequencing test (NVIST), a minimally varied phoneme-in-word discrimination and sequencing test (MVPT). and a semantic-syntactic level test (RTT). The results suggest that intensity can be traded for time in quantities large enough to overcome the extinction interference of auditory stimuli. Although some statistically significant results and meaningful trends toward improved performance were evident on the NVIST and the MVPT, a unilateral increase of stimulus intensity did not prove to be a potent mechanism for improving auditory comprehension. Sentence length material was not affected in either direction by selective amplification. The role of the left ear/right hemisphere as a facilitator of processing for linguistic and nonlinguistic material was suggested by the results of this study.

Adult↗
PubMed1984

Release from first-formant masking in presbyacusis.

Using synthetic vowels, the effects of first-formant masking on discrimination of the presence of a transition in the second formant were measured under conditions of first-formant attenuation and dichotic presentation. The subjects were 26 listeners between the ages of 61 and 91 with borderline to moderate sensorineural hearing losses. Results indicated: (1) dichotic presentation was significantly superior to monotic presentation; (2) attenuation of the first formant did not result in significant improvement of second-formant transition discrimination. Improved performance in the dichotic conditions may be related to the fact that subjects selected lower most comfortable listening levels than for monotic conditions. Results are compared to those of another study using natural speech stimuli.

Aged↗
PubMed1985

Simple and induced loudness adaptation.

Simple loudness adaptation is the decrease in loudness that takes place when a continuous sound is presented alone for a period of time. Simple adaptation normally occurs only when a sound is soft to begin with, no more than 30 dB above threshold; except for some persons with a retrocochlear lesion, sounds above 30 dB SL do not diminish in loudness over time. However, adaptation can be induced in at least two ways: (1) A steady sound to one ear, presented together with an intermittent sound to the contralateral ear, decreases in loudness by 50-60% within 3 min. (2) An otherwise steady sound that is intermittently increased in level by at least 5 dB becomes softer during its weaker periods. When, for example, a 40-dB tone is increased every 20 s to 60 dB for 15 s, its loudness decreases by about 50% within 3 min. We report measurements of both simple and induced adaptation on 10 persons listening to a 1 000-Hz tone via earphones or from a loudspeaker. The results provide an overview of both types of adaptation. They also permitted a correlational analysis that reveals some of the similarities and differences between the two kinds of adaptation.

Adaptation, Physiological↗
PubMed1988

High-frequency audiometry: comparison of electric bone-conduction and air-conduction thresholds.

Thresholds have been measured with two commercially available high-frequency (HF) audiometers providing respectively air-conduction (AC) and electric bone-conduction (EBC) stimulation. Normative values for the latter have been obtained, and the reduction of HF sensitivity with both stimulus modes documented in two groups aged 50-59 and 70-79 years. EBC reproducibility is of the same order of magnitude as the AC signal through 14 kHz, while the dynamic range is limited to 50 dB. Lateralization of the EBC signal occurs up to at least 17 kHz. The logarithmic conversion factor of Tonndorf and Kurman [Ann. Otol. Rhinol. Lar. 93: 576-582, 1984] does not result in equivalent AC and EBC thresholds at all frequencies, but does provide similar loudness sensation increases. The 40 log (i) re 1 mA conversion factor must be adjusted with a frequency-dependent additive correction.

Adult↗