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The neural representation of consonant-vowel transitions in adults who wear hearing AIDS.

Hearing aids help compensate for disorders of the ear by amplifying sound; however, their effectiveness also depends on the central auditory system's ability to represent and integrate spectral and temporal information delivered by the hearing aid. The authors report that the neural detection of time-varying acoustic cues contained in speech can be recorded in adult hearing aid users using the acoustic change complex (ACC). Seven adults (50-76 years) with mild to severe sensorineural hearing participated in the study. When presented with 2 identifiable consonant-vowel (CV) syllables ("shee" and "see"), the neural detection of CV transitions (as indicated by the presence of a P1-N1-P2 response) was different for each speech sound. More specifically, the latency of the evoked neural response coincided in time with the onset of the vowel, similar to the latency patterns the authors previously reported in normal-hearing listeners.

Aged↗

Factors to consider when in-the-canal hearing instruments are used in aural rehabilitation.

The purpose of this investigation was to determine what subjective factors may influence the success of fitting in-the-canal hearing instruments (ITCs). Four different types of ITC were fitted to four matched groups of 20 experienced ITC users. In addition to the subjective experiences of the users, the results were checked using insertion gain (IG) measurements. The results indicate that too sharp sound quality from paper rustle, from running water and from use of kitchen utensils is a common problem that it is important to be aware of. The possibility of maximal venting is of special importance in order to avoid autophony. Feedback may be a problem, especially when maximal venting is necessary. However, for several models of ITC, feedback is, in reality, a minor problem. High cost of batteries may be a problem for persons with ITC using 10/230 batteries. IG measurements indicated that a gain of approximately 0.3 in relation to the hearing losses was preferred. It may be advantageous to choose a model of ITC that has extensive flexibility.

Adult↗

The detection of anisochrony in monaural and interaural sound sequences.

Nakao and Axelrod (1976) and van Noorden (1975) showed that the threshold for discriminating an anisochronous duple rhythm (a series of clicks with a temporal offset on every other one) from an isochronous rhythm (no offset) is poorer when the clicks are presented alternately to the two ears than when they are presented to the same ears. Van Noorden reported that the difference between the thresholds in the alternating and nonalternating conditions varied with the tempo of the sequence. Nakao and Axelrod found invariance of this threshold difference with sequence speed. According to our quantification of temporal processing of interaural sequences, the latter result should be expected. We carried out five psychophysical experiments to establish interaural and monaural discrimination between isochronous and anisochronous rhythms. Across experiments, base time intervals of 60-720 msec were spanned. The main result was that we replicated the poorer discrimination for interaural sequences. This deterioration in discrimination was the same for all sequence speeds. It was also the case that the thresholds were almost constant up to a sound repetition rate of about 3 per second, but increased linearly with slower rates. This result supports evidence in the literature that temporal processing of sequences faster than about 3-4 sounds per second differs from temporal processing of slower sequences.

Attention↗

Audiologic evaluation of patients with localized intracranial lesions.

A battery of audiological tests for retrocochlear disorders was performed of 79 cases with localized intracranial lesions confirmed surgically or neurologically. The Type III trace of Békésy audiometry was found to originate from pathologies in the brainstem and the Type IV from abnormalities in the first neuron of the VIIIth nerve or in the brainstem. It was suggested that an unusually large amplitude peak in the Békésy tracing indicates a lesion in the temporal lobe. Large values of differential limen for short increment (DLSI) were found in patients with brainstem lesions. A good speech discrimination with a poor filtered speech discrimination apparently indicated supratentorial lesions. The binaural separation test using dichotically presented digit sounds was found to be helpful for differential diagnosis between the supratentorial and subtentorial lesions.

Adult↗

Functional MR of the primary auditory cortex: an analysis of pure tone activation and tone discrimination.

PURPOSE: To use functional MR imaging to measure the effect of frequency (pitch), intensity (loudness), and complexity of auditory stimuli on activation in the primary and secondary auditory cortexes. METHODS: Multiplanar echo-planar images were acquired in healthy subjects with normal hearing to whom auditory stimuli were presented intermittently. Functional images were processed from the echo-planar images with conventional postprocessing methods. The stimuli included pure tones with a single frequency and intensity, pure tones with the frequency stepped between 1,000, 2,000, 3,000, or 4,000 Hz, and spoken text. The pixels activated by each task in the transverse temporal gyrus (TTG) and the auditory association areas were tabulated. RESULTS: The pure tone task activated the TTG. The 1,000-Hz tone activated significantly more pixels in the TTG than did the 4,000-Hz tone. The 4,000-Hz tone activated pixels primarily in the medial TTG, whereas the 1,000-Hz tone activated more pixels in the lateral TTG. Higher intensity tones activated significantly more pixels than did lower intensity tones at the same frequency. The stepped tones activated more pixels than the pure tones, but the difference was not significant. The text task produced significantly more activation than did the pure tones in the TTG and in the auditory association areas. The more complex tasks (stepped tones and listening to text) tended to activate more pixels in the left hemisphere than in the right, whereas the simpler tasks activated similar numbers of pixels in each hemisphere. CONCLUSION: Auditory stimuli activate the TTG and the association areas. Activation in the primary auditory cortex depends on frequency, intensity, and complexity of the auditory stimulus. Activation of the auditory association areas requires more complex auditory stimuli, such as the stepped tone task or text reading.

Acoustic Stimulation↗

Auditory influences on visual temporal rate perception.

Visual stimuli are known to influence the perception of auditory stimuli in spatial tasks, giving rise to the ventriloquism effect. These influences can persist in the absence of visual input following a period of exposure to spatially disparate auditory and visual stimuli, a phenomenon termed the ventriloquism aftereffect. It has been speculated that the visual dominance over audition in spatial tasks is due to the superior spatial acuity of vision compared with audition. If that is the case, then the auditory system should dominate visual perception in a manner analogous to the ventriloquism effect and aftereffect if one uses a task in which the auditory system has superior acuity. To test this prediction, the interactions of visual and auditory stimuli were measured in a temporally based task in normal human subjects. The results show that the auditory system has a pronounced influence on visual temporal rate perception. This influence was independent of the spatial location, spectral bandwidth, and intensity of the auditory stimulus. The influence was, however, strongly dependent on the disparity in temporal rate between the two stimulus modalities. Further, aftereffects were observed following approximately 20 min of exposure to temporally disparate auditory and visual stimuli. These results show that the auditory system can strongly influence visual perception and are consistent with the idea that bimodal sensory conflicts are dominated by the sensory system with the greater acuity for the stimulus parameter being discriminated.

Acoustic Stimulation↗

Response properties of auditory activated cells in the occipital cortex of the blind mole rat: an electrophysiological study.

Previous studies have demonstrated that despite its blindness, the subterranean blind mole rat (Spalax ehrenbergi) possesses a noticeable lateral geniculate nucleus and a typical cyto-architectural occipital cortex that are reciprocally connected. These two areas, as revealed by the metabolic tracer 2-deoxyglucose, are activated by auditory stimuli. Using single unit recordings, we show that about 57% of 325 cells located within the occipital cortex of anesthetized mole rats responded to at least one of the following auditory stimuli--white noise, pure tones, clicks, and amplitude modulated tones--with the latter two being the most effective. About 85% of cells driven by either contralateral or ipsilateral stimulation also responded to binaural stimulation; about 13% responded only to binaural stimulation; and 2% were driven exclusively by contralateral stimulation. Comparing responsiveness and response strength to these three modes of stimulation revealed a contralateral predominance. Mean latency (+/-SD) of ipsilateral and contralateral responses were 48.5+/-32.6 ms and 33.5+/-9.4 ms, respectively. Characteristic frequencies could be divided into two distinct subgroups ranging between 80 and 125 Hz and between 2,500 and 4,400 Hz, corresponding to the most intensive spectral components of the vibratory intraspecific communication signals and airborne vocalizations.

Acoustic Stimulation↗

Behavioral and neural measures of auditory temporal acuity in aging humans and mice.

Three experiments compared auditory temporal acuity in humans and in the behavior and single cells in the inferior colliculus (IC) of mice, to establish the comparability of aging effects on temporal acuity across species, and to suggest a neural foundation. The thresholds for silent gaps placed in white noise (MGTs) were similar in young mice and young humans, and increased in some but not all old humans and old mice. Neural MGT in the most sensitive cells of both young and old mice was comparable to behavioral MGT in the young of both species, but older mice had more cells with very high MGT. Human listeners were selected to have minimal absolute hearing loss. Older mice had significant hearing loss that was correlated with MGT in behavioral, but not in neural, measures. Some old mice and some old IC cells, however, had low MGTs coupled with elevated absolute hearing thresholds. Age-related changes in temporal acuity appear comparable in humans and mice. The data suggest a common deficit in neural mechanisms.

Acoustic Stimulation↗

A problem with auditory processing?

Recent studies have found associations between auditory processing deficits and language disorders such as dyslexia; but whether the former cause the latter, or simply co-occur with them, is still an open question.

Adult↗

Duration discrimination in listeners with cochlear hearing loss: effects of stimulus type and frequency.

This study examined the effects of cochlear hearing loss on the ability to discriminate increments in the duration of a stimulus under conditions where the frequency and/or amplitude of the stimulus change dynamically. Three stimulus types were used: pure tones, frequency-modulated tones, and narrow bands of noise. The carrier/center frequency of each 250-ms stimulus either remained constant at 1035 Hz or varied randomly from presentation to presentation across the frequency range 432-2804 Hz. Two groups of listeners participated: 9 with bilateral cochlear hearing loss and 7 with normal hearing sensitivity. The results showed no differences in performance between the 2 groups. However, both groups showed poorer duration discrimination for the conditions where the carrier/center frequency changed randomly than for the conditions where the carrier/center frequency remained constant. In addition, performance was poorer for the narrowband noise stimuli than for the tonal stimuli. This pattern of results suggests that across-frequency temporal judgments are more difficult than isofrequency temporal judgments, but that cochlear hearing loss does not exacerbate this difficulty per se.

Acoustic Stimulation↗

Music and the brain: disorders of musical listening.

The study of the brain bases for normal musical listening has advanced greatly in the last 30 years. The evidence from basic and clinical neuroscience suggests that listening to music involves many cognitive components with distinct brain substrates. Using patient cases reported in the literature, we develop an approach for understanding disordered musical listening that is based on the systematic assessment of the perceptual and cognitive analysis of music and its emotional effect. This approach can be applied both to acquired and congenital deficits of musical listening, and to aberrant listening in patients with musical hallucinations. Both the bases for normal musical listening and the clinical assessment of disorders now have a solid grounding in systems neuroscience.

Auditory Perception↗

A case study of pure word deafness: modularity in auditory processing?

AL, a woman with an acquired disturbance of auditory processing beginning in the second decade, was originally diagnosed as having pure word deafness. Recent analysis with a wide range of stimuli suggests that her comprehension deficit also extends to a subset of musical and non-verbal environmental sounds. The perceptual demands of the different auditory stimuli appear to account for part of the apparent material specificity. Additionally, over the years, the presumed temporal lobe cortical pathology has been supplemented by a mild to moderate, peripheral low-frequency hearing loss and evidence of dysfunction in lower level auditory processing pathways. The current peripheral dysfunction closely resembles cases recently labeled as auditory neuropathy. The diagnosis of pure word deafness should not be based on a limited set of auditory stimuli; additionally, a careful assessment using modern audiological techniques should be performed to evaluate peripheral auditory functions.

Achievement↗

Psychophysical evidence for a general temporal processing deficit in children with dyslexia.

The hypothesis of a general (i.e. cross-modal) temporal processing deficit in dyslexia was tested by examining rapid processing in both the auditory and the visual system in the same children with dyslexia. Participants were 10- to 12-year-old dyslexic readers and age-matched normal reading controls. Psychophysical thresholds were estimated for auditory gap and visual double flash detection, using a two-interval, two-alternative forced-choice paradigm. Significant group differences were found for the auditory and the visual test. Furthermore, temporal processing measures were significantly related to word and pseudo-word reading skills. As 70% of the dyslexic readers had significantly higher thresholds than controls for both auditory and visual temporal processing, the evidence tends to support the hypothesis of a general temporal processing deficit in children with dyslexia.

Auditory Perception↗

Audiological results in children with a cochlear implant.

Audiological data collected through June 1984 were analyzed for 126 children with the cochlear implant. Preimplant hearing aid results were compared to cochlear implant results at 6-month follow-up test intervals. Auditory thresholds to warble tones and speech stimuli, and auditory discrimination test scores were significantly better with the cochlear implant at all test intervals than preoperatively with a hearing aid. Electrical measurements were also monitored. Mean thresholds remained consistent over time. Electrical comfort levels increased slightly over time, indicating a widening of the electrical dynamic range. Results have been extremely encouraging. Some trends are beginning to develop, but more long-term data are needed to define the potential benefit of the implant in children.

Adolescent↗

Auditory performance of children with unilateral sensorineural hearing loss.

Horizontal sound localization and syllable recognition skills were examined in a group of children with unilateral sensorineural hearing loss and a matched group of normal hearers. The results showed that the unilaterally hearing-impaired children performed more poorly than the normal counterparts in both localization and speech recognition of nonsense syllables. The unilaterally hearing-impaired children had considerable difficulty understanding in a background of noise. The clinical implications of these findings are discussed.

Achievement↗

Estimates of basilar-membrane nonlinearity effects on masking of tones and speech.

OBJECTIVE: The aim of this experiment was to assess the contribution of cochlear nonlinearities to speech recognition in noise for individuals with normal hearing and a range of quiet thresholds. For signals close to the characteristic frequency (CF) of a place on the basilar membrane, the normal growth of response of the basilar membrane is linear at lower signal levels and compressed at medium to higher signal levels. In contrast, at moderate to high CFs, the basilar membrane responds more linearly to stimuli at frequencies well below the CF regardless of input level. Thus, for moderate-level speech and a lower frequency masker, the response to the masker grows linearly whereas the response to the speech is compressed, which may result in changes in the effectiveness of the masker on speech recognition with increases in masker level. To test this hypothesis, observed speech-recognition scores were compared with scores predicted using an audibility-based model, which did not include nonlinear effects that may influence masker effectiveness. DESIGN: Growth of simultaneous masking was measured for moderate-level bandpass-filtered nonsense syllables and for 350-msec pure tones at frequencies within the speech passband. Masker frequencies were within (on-frequency) or below (off-frequency) the speech passband. Estimates of basilar-membrane nonlinearities were derived from growth-of-masking functions for 10-msec, 2.0- and 4.0-kHz tones in narrowband, off-frequency maskers presented simultaneously. Subjects were 26 adults with normal hearing with approximately a 20-dB range of average quiet thresholds. RESULTS: Breakpoints (i.e., the levels corresponding to the transitions from linear to nonlinear responses) were strongly associated with quiet thresholds but slopes measured above the breakpoints were independent of quiet thresholds. Individual differences were substantially larger for off-frequency masking of pure tones and speech than for on-frequency masking of pure tones and speech. Using an audibility-based predictive model, the change in speech audibility resulting from the compressed response to speech with increasing off-frequency masker level (and the resulting decline in scores) was well predicted from nonlinear growth of masking for pure tones measured in the same off-frequency masker. However, absolute speech-recognition predictions were generally inaccurate and were a function of how well pure-tone signal levels at masked threshold estimated masker effectiveness for speech. That is, subjects with lower off-frequency masked thresholds had less accurate predictions of speech recognition in off-frequency maskers. CONCLUSIONS: Large individual differences in off-frequency masking of pure tones and speech are consistent with the assumption that small changes in the shape of the basilar-membrane input-output function result in large changes in the amount of off-frequency masking but small (if any) changes in on-frequency masking where the signal and masker are subject to a similar compression. Growth of off-frequency masking of pure tones and speech were correlated with each other, consistent with the underlying basilar-membrane response, and consistent with changes in breakpoints for subjects with normal hearing and a range of quiet thresholds. These results provide support for a role of nonlinear effects in the understanding of speech in noise.

Adult↗

Effects of simultaneous exercise and loud music on hearing acuity and auditory function.

Hearing acuity can be reduced temporarily after exposure to loud noise, and the physiological responses that occur with exercise may enhance this effect. Currently, it is not known whether short-term reductions in hearing acuity after noise exposure and exercise are a result of temporary changes in auditory function. Therefore, the purpose of this investigation was to determine the acute effects of simultaneous exercise and loud music on hearing acuity and auditory function in young, healthy women. Nine women (age = 22 +/- 5 years, body mass index = 23.9 +/- 2.2, Vo(2)peak = 30.6 +/- 6.0 ml x kg(-1) x min(-1)) with normal hearing thresholds (<20 dB hearing level) underwent each of 3 conditions in a randomized counterbalanced design: (a) loud music exposure of 90 to 95 dB sound pressure level for 20 minutes, (b) exercise at 60% Vo(2)peak on a cycle ergometer for 20 minutes, and (c) simultaneous exercise and music exposure for 20 minutes. Hearing acuity and auditory function were assessed via pure-tone hearing thresholds and distortion product otoacoustic emission amplitudes, respectively, at frequencies of 2, 3, 4, 6, and 8 kHz presented in random order before and after each condition. Results indicate that hearing acuity and auditory function remained unaltered after exposure to each condition (p > 0.05). These findings provide evidence that hearing acuity and auditory function in young women do not change after short-term exposure to moderate-intensity exercise and loud music. Thus, listening to loud music with earphones during moderate-intensity exercise does not pose acute hearing health concerns for young physically fit adults with normal hearing.

Adolescent↗