Audiology : official organ of the International Society of Audiology最新文献

The auditory brainstem response (ABR) was recorded from 20-month-old Long Evans hooded female rats to determine if latency reductions occur from estrogen replacement. The ABR in these post-breeding age rats was also examined for reductions in response latencies as a function of adult age. Tone pip stimuli (8 and 40 kHz) were presented at 21, 51, or 81 s(-1). Aging control and ovariectomized animals showed slower response latencies for waves Ib-VI than young adults for 8 and 40 kHz stimulation at 21 s(-1). Increased stimulus rate resulted in longer latencies for all waves at 20 months. In contrast to hormone treatment effects in young adults, ABR latencies in post-breeding age estrogen-treated animals were not reduced, consistent with a general decrease in CNS responsiveness to estrogen steroids associated with age. The results also suggest that sensorineural modifications in the auditory system which prolong ABR latencies can occur early in the aging process of adult female subjects.

The speech recognition threshold (SRT) is believed to be related primarily to the pure-tone average (PTA) and the steepness of the hearing loss. However, there are indications that it may also be influenced by perceptual or cognitive-linguistic factors, or both, such as meaningfulness of the speech stimuli. The purpose of the present study was to ascertain the correspondence between SRT and PTA in noise-exposed workers with various degrees of speech recognition threshold shift in noise. To this end, a total of 807 SRTs and PTAs collected from fluent speakers of Quebec French noise-exposed workers were compared. Measurements of context effects on speech recognition were taken based on a general hypothesis that they should be facilitating phoneme or word restoration in conditions of high stimulus uncertainty as present in SRT assessment, thus acting to confound the SRT PTA relationship. Using principal components analysis, we found a significant effect not only of low-frequency hearing sensitivity but language context effects on SRT. After a correction was introduced to partial out these linguistic context effects, correlations between SRT and PTA increased but they were lower than predicted. In a related treatment analysis, we found a large number of observations (230 out of 807) where SRTs were more sensitive than PTAs by a factor of 8 to 16 dB. This was the case even though correlations between the two measurements were within the range commonly advocated in the field of clinical audiology (0.85-0.95). This was interpreted as a sign of phonological and lexical context effects on the speech recognition task actually used by individual subjects to facilitate speech understanding, to the point perhaps of making it as simple as the detection of pure tones.

Measurement of otoacoustic emissions (OAEs) has been proposed as a sensitive test to reliably assess the effects of noise exposure. The present study in humans was designed to evaluate the sensitivity and applicability of transient evoked OAEs (TEOAEs) and 2f1-f2 distortion product OAEs (DPOAEs) as quantitative indices of the functional integrity of the outer hair cells (OHC) during growth of and recovery from temporary threshold shift (TTS). This was examined in two different groups of volunteers by measuring the per- and post-stimulatory effects of a one hour BBN and an on-site five hour exposure to loud music from a discotheque. The results of both experiments show consistent growth and recovery patterns for both DPOAEs and TEOAEs. For TEOAEs, both the reproducibility scores and signal to noise ratio values for the 4 kHz frequency band exhibited the greatest sensitivity. The DPOAEs, on the other hand, showed the greatest sensitivity between 2 and 5.5 kHz. Thus, both the TEOAEs and DPOAEs have a great potential in the detection of TTS after noise exposure.

The cerebral perfusion of a 55-year-old female patient with chronic tinnitus was investigated quantitatively by single photon emission computed tomography (SPECT) with the xenon133 inhalation method. The first investigation was performed under standard conditions, the second during suppression of tinnitus with intravenous injection of lidocaine. As a reference a healthy volunteer was included under the same conditions. The global cortical perfusion was identical on both sides except for increased perfusion in the auditory cortex, especially on the right side when tinnitus lasted during the first measurement. The second investigation under treatment with lidocaine and during the tinnitus-free interval showed a decrease of the global cortical perfusion with a slightly higher value at the temporal cortex bilaterally. In comparison to the first investigation, a difference between right and left auditory cortex could no longer be demonstrated, and also the difference between regional and global perfusion decreased. A cerebral effect under treatment of tinnitus with lidocaine was shown by the quantitative measurement of brain perfusion. It is debatable whether this effect on cerebral activity results from the medication or as a reaction to the tinnitus-free interval.

Auditory brainstem responses (ABRs) to click stimuli have been compared in young (21-day-old), adult (6-month-old), and old (18-month-old) rats fed a normal (Arachid-Colza) or an alpha-linolenic acid deficient (Arachid only) diet. Wave I amplitude and latency did not show any significant change with either age or diet. However, wave III showed a progressive decrease in amplitude and latency from young to adult and from adult to old rats having a normal diet. With alpha-linolenic acid deficiency, wave III amplitude and latency values decreased faster than in the normal diet control groups. Although final values in the old groups with the two diets were similar, with alpha-linolenic acid deficiency values for wave III decreased to this final level in the adult group. These data indicate that the central auditory nervous system ages faster, or earlier, with a fatty acid deficiency.

Auditory alone, visual alone and audiovisual recognition of consonant-vowel consonant syllables were measured in 32 severely hearing-impaired children with hearing loss (PTA) in a narrow range around 90 dB HL when using their hearing aids. Multidimensional scaling analysis (INDSCAL) and information transmission analysis (ITA), applied to the confusion matrices obtained from the responses in each presentation mode and for each phoneme category, revealed perceptual dimensions and percentages of transmitted feature information (PTI). These were studied in relation to PTA, the auditory alone score and in relation to the efficiency of the audiovisual interaction (enhancement) over the probalistic summation of the auditory alone and visual alone score. INDSCAL analysis shows that auditory alone recognition of vowels is based on the perceptual dimensions F2 and F1 and that of consonants on the dimensions 'frication' and 'voicing'. In the auditory mode the interpretation of the INDSCAL dimensions in the stimulus spaces is in reasonable agreement with the ITA results. PTI decreases gradually with decreasing auditory alone phoneme score. Audiovisual recognition of vowels is based on a combination of the auditory dimension 'open/closed' (F1), and the visual dimensions 'lip rounding' and 'vertical lip opening'. Audiovisual recognition of initial consonants is based on a combination of the visual dimension 'front/back' and the auditory dimension 'continuance'. Recognition of final consonants is based on a combination of the visual dimension 'front/back' and an uninterpretable dimension. The perceptual dimensions are independent of both the level of the auditory alone phoneme score and audiovisual enhancement. Audiovisual enhancement is mainly a property of an individual and independent of both auditory alone and visual alone scores. ITA analysis, based on a phonological classification of the features, supports the results of the INDSCAL analysis in the auditory alone mode. It is not useful in the description of the audiovisual interaction, probably due to the phonological basis of the feature classification.

Some cochlear implant patients achieve better speech recognition with pulsatile electrical stimulation presented at high rates. The present study aimed to explore, in an animal model of cochlear implants, how the excitability of the cochlear nerve is affected by pulsatile electrical stimulation delivered at high rates, of up to 1,000-2,000 pulses per second (pps). Adult rats (n=23) were implanted with two or three stimulating electrodes in the left cochlea. In four of these rats, the left cochlea was deafened by local perfusion with 1 per cent or 4 per cent neomycin solutions prior to implantation. Pulsatile stimuli consisted of 20 micros electrical pulses, delivered in trains of 200 ms duration, separated by a pause of 200 ms. The pulse rates ranged from 100 to 2,000 pps (intra-train pulse rate). Electrically evoked compound action potentials (ECAPs) of the cochlear nerve were recorded either intracochlearly or from epidural electrodes (extra-cochlearly). With increasing pulse rates, the average ECAP amplitude decreased, whereas the average ECAP latency and its variability (SD) increased. For rates above 300 pps, the amplitude of the ECAP to the individual successive pulses delivered in the train progressively decreased during the initial part of the train, corresponding to a short-term adaptation of the cochlear nerve. This effect progressively increased for pulse rates ranging from 300 to 2,000 pps. In addition, there was a phenomenon of long-term adaptation, as indicated by a decrease in the amplitude of the ECAP to the first pulse of the train, indicating that the pause of 200 ms between each train was not long enough for full recovery of the cochlear nerve. This long-term adaptation was progressively more pronounced for increasing pulse rates. To characterize further the recovery in excitability of the cochlear nerve, forward masking experiments were conducted, showing a decrease of the ECAP amplitude when the interval between the first pulse (masker) and the second pulse (probe) was shorter than 2 ms. This ECAP decrease was slow for intervals between 2 and 1 ms and then abrupt for shorter intervals. The observations described above were similar for extra- and intra-cochlear recordings and were little, if at all, affected by treatment of the cochlea with neomycin.

Preliminary investigations have been made in normally hearing alert adults to establish whether the 40 Hz modulation-following response (MFR) can be used to predict 400 Hz uncomfortable loudness levels (ULLs). The MFR stimulus was a 400 Hz carrier, amplitude- and frequency-modulated by a 40 Hz sine function. Subjective ULLs were obtained using standard procedures. Objective ULLs were obtained from MFR parameter intensity functions using rms amplitude, phase angle and magnitude-squared coherence (40 Hz components). The best predictions of the subjective ULL were made using objective ULLs calculated from the gradients of linear best-fit lines for individual phase-intensity functions (80 per cent predicted within 10 dB of the subjective ULL; maximum deviation=16 dB). Poorest predictions were based on inter-subject average rms amplitude-intensity functions, where as few as 14 per cent were within 10 dB of the subjective value. The best predictions were considered sufficiently accurate to warrant further investigation using a variety of modulation and carrier frequencies in different age groups and with varying degrees of hearing loss.

As part of a continuing quality improvement program, this project was undertaken to define the frequency of hearing loss in patients admitted to a surgical intensive care unit in order to identify patients at risk for impaired communication. The study evaluated 168 consecutive admissions over a ten week period to a ten bed adult surgical intensive care unit in a university hospital. Patients were screened as close to admission to the ICU as possible with otoscopy, tympanometry, and distortion product otoacoustic emissions. A total of 113 patients (226 ears, mean age 58.0+/-15.8 years) were screened within 1.5+/-1.4 days of ICU admission; 55 of the 168 admissions could not be screened (48 out of 55 due to short ICU stays). Of the 226 ears evaluated, 6.6 per cent had abnormal otoscopy and 43.2 per cent abnormal tympanograms. OAE failure occurred in 58.4 per cent of ears while OAE results were uninterpretable due to high ambient noise in 2.7 per cent of ears, and technical difficulty in 3.5 per cent of ears. Mean time for screening was 9.3 minutes. OAEs provide an efficient screening modality for hearing impairment in critically ill adults. The results suggest a significant prevalence of hearing impairment in the population studied. More definitive testing should be considered when clinically indicated in patients who fail OAE screening.

In patients with some residual hearing and minor benefit from conventional hearing aids, the benefits of cochlear implantation have to be weighed carefully against eventual adverse effects. In this study, pre- and post-operative thresholds as well as functional results after cochlear implantation are reported; 17 of 44 implanted adults had residual hearing pre-operatively (mean threshold(250 to 4000 Hz): 106 dB HL) in the implanted ear. Residual hearing in the implanted ear could not, in general, be preserved post-operatively. Seventeen of 44 implanted children had some amount of residual hearing in the implanted ear pre-operatively (implanted ear: 114 dB HL; contralateral ear: 109.9 dB HL; mean thresholds(250 to 4000 Hz))). Contrary to the results in adults, residual hearing in the implanted ear remained statistically unchanged. Hearing in the contralateral ear increased significantly from 109.9 to 101.9 dB HL post-operatively. This increase was mainly attributed to maturation of the central auditory pathway. In adults with residual hearing, the monosyllable word recognition scores increased significantly from 9 per cent pre-operatively to 42 per cent post-operatively. Children with residual hearing tended to perform better on speech-related test material compared to children without prior auditory experience. Cochlear implantation is indicated in adults and children with residual hearing and minor benefit from conventional amplification. The contralateral ear in children should be considered for additional acoustical stimulation.