Young Normal-hearing Subjects Research Articles

Short-Term Test-Retest Reliability of Contralateral Suppression of Click-Evoked Otoacoustic Emissions in Normal-Hearing Subjects.

Purpose The objective of the current study was to investigate the short-term test-retest reliability of contralateral suppression (CS) of click-evoked otoacoustic emissions (CEOAEs) using commercially available otoacoustic emission equipment. Method Twenty-three young normal-hearing subjects were tested. An otoscopic evaluation, admittance measures, pure-tone audiometry, measurements of CEOAEs without and with contralateral acoustic stimulation (CAS) to determine CS were performed at baseline (n = 23), an immediate retest without and with refitting of the probe (only CS of CEOAEs; n = 11), and a retest after 1 week (n = 23) were performed. Test-retest reliability parameters were determined on CEOAE response amplitudes without and with CAS, and on raw and normalized CS indices between baseline and the other test moments. Results Repeated-measures analysis of variance indicated no random or systematic changes in CEOAE response amplitudes without and with CAS, and in raw and normalized CS indices between the test moments. Moderate-to-high intraclass correlation coefficients with mostly high significant between-subjects variability between baseline and each consecutive test moment were found for CEOAE response amplitude without and with CAS, and for the raw and normalized CS indices. Other reliability parameters deteriorated between CEOAE response amplitudes with CAS as compared to without CAS, between baseline and retest with probe refitting, and after 1 week, as well as for frequency-specific raw and normalized CS indices as compared to global CS indices. Conclusions There was considerable variability in raw and normalized CS indices as measured using CEOAEs with CAS using commercially available otoacoustic emission equipment. More research is needed to optimize the measurement of CS of CEOAEs and to reduce influencing factors, as well as to make generalization of test-retest reliability data possible.

Effects of Age and Hearing Loss on the Discrimination of Amplitude and Frequency Modulation for 2- and 10-Hz Rates.

Detection of frequency modulation (FM) with rate = 10 Hz may depend on conversion of FM to amplitude modulation (AM) in the cochlea, while detection of 2-Hz FM may depend on the use of temporal fine structure (TFS) information. TFS processing may worsen with greater age and hearing loss while AM processing probably does not. A two-stage experiment was conducted to test these ideas while controlling for the effects of detection efficiency. Stage 1 measured psychometric functions for the detection of AM alone and FM alone imposed on a 1-kHz carrier, using 2- and 10-Hz rates. Stage 2 assessed the discrimination of AM from FM at the same modulation rate when the detectability of the AM alone and FM alone was equated. Discrimination was better for the 2-Hz than for the 10-Hz rate for all young normal-hearing subjects and for some older subjects with normal hearing at 1 kHz. Other older subjects with normal hearing showed no clear difference in AM-FM discrimination for the 2- and 10-Hz rates, as was the case for most older hearing-impaired subjects. The results suggest that the ability to use TFS cues is reduced for some older people and most hearing-impaired people.

Influence of visual cues on head and eye movements during listening tasks in multi-talker audiovisual environments with animated characters

Recent studies of hearing aid benefits indicate that head movement behavior influences performance. To systematically assess these effects, movement behavior must be measured in realistic communication conditions. For this, the use of virtual audiovisual environments with animated characters as visual stimuli has been proposed. It is unclear, however, how these animations influence the head- and eye-movement behavior of subjects. Here, two listening tasks were carried out with a group of 14 young normal hearing subjects to investigate the influence of visual cues on head- and eye-movement behavior; on combined localization and speech intelligibility task performance; as well as on perceived speech intelligibility, perceived listening effort and the general impression of the audiovisual environments. Animated characters with different lip-syncing and gaze patterns were compared to an audio-only condition and to a video of real persons. Results show that movement behavior, task performance, and perception were all influenced by visual cues. The movement behavior of young normal hearing listeners in animation conditions with lip-syncing was similar to that in the video condition. These results in young normal hearing listeners are a first step towards using the animated characters to assess the influence of head movement behavior on hearing aid performance.

Effects of age on the discrimination of modulation type for 2- and 10-Hz rates

Frequency modulation (FM) at a rate of 10 Hz may be detected via conversion of FM to amplitude modulation (AM) in the cochlea, while 2-Hz FM may be detected partly using temporal fine structure (TFS) information. Greater age may impair the processing of TFS information while sparing the processing of AM information. To test these ideas, while controlling for the effects of detection efficiency, a two-stage experiment was conducted. In stage 1, psychometric functions were measured for the detection of AM alone and FM alone imposed on a 1000-Hz carrier, using 2- and 10-Hz rates. In stage two, the task was to discriminate AM from FM at the same modulation rate when the detectability of the AM alone and FM alone was equated. For young normal-hearing subjects, discrimination was markedly better for the 2-Hz than for the 10-Hz rate, consistent with the idea that FM is coded in a different way from AM at 2 Hz. For older subjects with normal hearing at 1000 Hz, a similar pattern was obtained, but discrimination of AM from FM at 2 Hz was somewhat poorer than for the young normal-hearing subjects, consistent with an age-related reduction in ability to use TFS cues.

Auditory brainstem, middle and late latency responses to short gaps in noise at different presentation rates

Objective: The effects of rate on auditory-evoked potentials (AEP) to short noise gaps (12 ms) recorded at high sampling rates using wide-band filters were investigated. Design: Auditory brainstem (ABR), middle latency (MLR), late latency (LLR) and steady-state (ASSR) responses were simultaneously recorded in adult subjects at four gap rates (0.5, 1, 5 and 40 Hz). Major components (V, Na, Pa, Nb, Pb, N1 and P2) were identified at each rate and analysed for latency/amplitude characteristics. Gap responses at 40 Hz were recovered from Quasi-ASSRs (QASSR) using the CLAD deconvolution method. Study Sample: Fourteen right ears of young normal hearing subjects were tested. Results: All major components were present in all subjects at 1 Hz. P1 (P50) appeared as a low-pass filtered component of Pa and Pb waves. At higher rates, N1 and P2 disappeared completely while major ABR-MLR components were identified. Peak latencies were mostly determined by noise onsets slightly delayed by offset responses. Conclusions: Major AEP components can be recorded to short gaps at 1 Hz using high sampling rates and wide-band filters. At higher rates, only ABR and MLRs can be recorded. Such simultaneous recordings may provide a complete assessment of temporal resolution and processing at different levels of auditory pathways.

On the Cost of Introducing Speech-Like Properties to a Stimulus for Auditory Steady-State Response Measurements.

Validating hearing-aid fittings in prelingual infants is challenging because typical measures (aided audiometry, etc.) are impossible with infants. One objective alternative uses an aided auditory steady-state response (ASSR) measurement. To make an appropriate measurement, the hearing aid’s signal-processing features must be activated (or deactivated) as if the ASSR stimulus was real speech. Rather than manipulating the hearing-aid settings to achieve this, an ASSR stimulus with speech-like properties was developed. This promotes clinical simplicity and face validity of the validation. The stimulus consists of narrow-band CE-Chirps®, modified to mimic the International Speech Test Signal (ISTS). This study examines the cost of introducing the speech-like features into the ASSR stimulus. Thus, 90 to 100 Hz ASSRs were recorded to the ISTS-modified stimulus as well as an equivalent stimulus without the ISTS modification, presented through insert phones to 10 young normal-hearing subjects. Noise-corrected ASSR magnitudes and clinically relevant detection times were estimated and analyzed with mixed-model analyses of variance. As a supplement, the observed changes to the ASSR magnitudes were compared with an objective characterization of the stimuli based on modulation power. The main findings were a reduction in ASSR magnitude of 4 dB and an increase in detection time by a factor of 1.5 for the ISTS-modified stimulus compared with the standard. Detection rates were unaffected given sufficient recording time. For clinical use of the hearing-aid validation procedure, the key metric is the detection time. While this varied considerably across subjects, the observed 50% mean increase corresponds to less than 1 min of additional recording time.

Hearing Loss and Speech Recognition in the Elderly

Elderly people often complain about poor speech understanding in noisy environments. In clinical practice, speech tests under noise conditions are used to examine hearing ability. The HÖRSTAT study, conducted on a population-based random sample consisting of 1903 adults, used the Goettingen Sentence Test (GÖSA) under noise conditions along with pure-tone audiometry. Hearing impairment was defined as pure-tone average at 0.5, 1, 2 and 4 kHz (PTA-4) greater than 25 dB HL in the better ear (WHO criterion). As expected, pure-tone thresholds and speech recognition thresholds (SRT) in GÖSA worsened steadily with age. For a comparison of PTA-4, SRTGÖSA and self-reported hearing, analysis was limited to 553 adults aged 60-85 years with PTA-4 below 50 dB HL and SRTs measured with a constant 65 dB SPL noise level. The percentage of hearing-impaired increased from 13 % in the 60-65 year-old people to 60 % in those aged 80-85 years. Overall, 68 % of the 60-85 years adults showed normal hearing in terms of unimpaired hearing according to the WHO criterion. The SRTGÖSA of 66 % of the elderly adults with normal hearing, however, did not lie within the reference range established with young normal hearing subjects in the HÖRSTAT study (4.8 ± 1.8 dB SNR, mean±2 * standard deviation). Among the 553 elderly, only 24 % reached this reference range. PTA-4 and SRTGÖSA results showed moderate to good correlations (Pearson r = 0.562, within 5-years bands: 0.372-0.514). From PTA-4 ≥ 30 dB HL and SRTGÖSA ≥- 2 dB SNR, respectively, more than half of the subjects reported hearing difficulties. Despite the continuous decline of PTA-4 and SRTGÖSA with age, the proportion of self-reported hearing difficulties as well as the self-rated hearing ability score stagnated. From the age of 70 years onwards, the elderly in the HÖRSTAT sample tend to overestimate their hearing abilities and to underestimate their difficulties.

The Gap Detection Test: Can It Be Used to Diagnose Tinnitus?

Objectives:Animals with induced tinnitus showed difficulties in detecting silent gaps in sounds, suggesting that the tinnitus percept may be filling the gap. The main purpose of this study was to evaluate the applicability of this approach to detect tinnitus in human patients. The authors first hypothesized that gap detection would be impaired in patients with tinnitus, and second, that gap detection would be more impaired at frequencies close to the tinnitus frequency of the patient.Design:Twenty-two adults with bilateral tinnitus, 20 age-matched and hearing loss–matched subjects without tinnitus, and 10 young normal-hearing subjects participated in the study. To determine the characteristics of the tinnitus, subjects matched an external sound to their perceived tinnitus in pitch and loudness. To determine the minimum detectable gap, the gap threshold, an adaptive psychoacoustic test was performed three times by each subject. In this gap detection test, four different stimuli, with various frequencies and bandwidths, were presented at three intensity levels each.Results:Similar to previous reports of gap detection, increasing sensation level yielded shorter gap thresholds for all stimuli in all groups. Interestingly, the tinnitus group did not display elevated gap thresholds in any of the four stimuli. Moreover, visual inspection of the data revealed no relation between gap detection performance and perceived tinnitus pitch.Conclusions:These findings show that tinnitus in humans has no effect on the ability to detect gaps in auditory stimuli. Thus, the testing procedure in its present form is not suitable for clinical detection of tinnitus in humans.

Analysis of subtle auditory dysfunctions in young normal-hearing subjects affected by Williams syndrome

ObjectiveTo assess if young subjects affected by Williams syndrome (WS) with normal middle ear functionality and normal hearing thresholds might have subtle auditory dysfunctions that could be detected by using clinically available measurements. MethodsOtoscopy, acoustic reflexes, tympanometry, pure-tone audiometry, and distortion product otoacoustic emissions (DPOAEs) were measured in a group of 13 WS subjects and in 13 age-matched, typically developing control subjects. Participants were required to have normal otoscopy, A-type tympanogram, normal acoustic reflex thresholds, and pure-tone thresholds ≤15dB HL at 0.5, 1, and 2kHz bilaterally. To limit the possible influence of middle ear status on DPOAE recordings, we analyzed only data from ears with pure-tone thresholds ≤15dB HL across all octave frequencies in the range 0.25–8kHz, middle ear pressure (MEP)>−50daPa, static compliance (SC) in the range 0.3–1.2cm3, and ear canal volume (ECV) in the range 0.2–2ml, and we performed analysis of covariance to remove the possible effects of middle ear variables on DPOAEs. ResultsNo differences in mean hearing thresholds, SC, ECV, and gradient were observed between the two groups, whereas significantly lower MEP values were found in WS subjects as well as significantly decreased DPOAEs up to 3.2kHz after adjusting for differences in middle ear status. ConclusionsResults revealed that WS subjects with normal hearing thresholds (≤15dB HL) and normal middle ear functionality (MEP>−50daPa, SC in the range 0.3–1.2cm3, ECV in the range 0.2–2ml) might have subtle auditory dysfunctions that can be detected by using clinically available methods. Overall, this study points out the importance of using otoacoustic emissions as a complement to routine audiological examinations in individuals with WS to detect, before the onset of hearing loss, possible subtle auditory dysfunctions so that patients can be early identified, better monitored, and promptly treated.

SŁUCHOWE ODPOWIEDZI BEHAWIORALNE I ELEKTROFIZJOLOGICZNE U DOROSŁYCH: OCENA OŚRODKOWEGO PRZETWARZANIA SŁUCHOWEGO

BackgroundIn addition to well known declines in the peripheral auditory system successful perception of speech is dependent on behavioural factors, as well as sound processing at subcortical and cortical levels. We hypothesized that cause and hence localization of impairment in the brain may be diverse in young and elderly people with hearing impairment, accordingly not always related with aging. The aim of the study is to determine the hallmarks of auditory behaviour and auditory cortical evoked responses that could be used in audiology clinics to help explain deficits in speech recognition in young and elderly listeners and recognize the most indicative effects of cortical auditory evoked potentials associated with difficulties of speech intelligibility.Material and MethodsThree groups of adults participated: young normal hearing, young and elderly subjects with difficulty to understand speech especially in complex listening environments despite normal pure tone thresholds. We supposed that differences could be found between young and elderly subjects. Procedure involved behavioural hearing tests, dichotic word tests and sentence recognition test in quiet and noise, and electrophysiological measures as cortical auditory evoked potential components P1, N1, P2, P3 in quiet and noise.ResultsSignificant correlation was found between hearing behavioural tests and auditory cortical evoked potentials. This dichotic study demonstrated differences in cortical processing in people with good hearing, young and elderly listeners with speech recognition difficulties. Results provide information about central tests showing significant decrease of perception in young and elderly participants with hearing impairment and it is most strongly associated with event related potential response P3. Sensitivity to signal intensity level significantly changes in the group of young and elderly subjects with hearing impairment for responses P1, N1, P2(p<0.5).ConclusionsDespite of resembling results from behaviour tests outcomes of auditory evoked potentials mark less influence of signal intensity level latencies in young then in older subject group. They could be useful in audiology practice for clinical diagnostics and evaluation of hearing rehabilitation.

Neural plasticity expressed in central auditory structures with and without tinnitus

Sensory training therapies for tinnitus are based on the assumption that, notwithstanding neural changes related to tinnitus, auditory training can alter the response properties of neurons in auditory pathways. To assess this assumption, we investigated whether brain changes induced by sensory training in tinnitus sufferers and measured by electroencephalography (EEG) are similar to those induced in age and hearing loss matched individuals without tinnitus trained on the same auditory task. Auditory training was given using a 5 kHz 40-Hz amplitude-modulated (AM) sound that was in the tinnitus frequency region of the tinnitus subjects and enabled extraction of the 40-Hz auditory steady-state response (ASSR) and P2 transient response known to localize to primary and non-primary auditory cortex, respectively. P2 amplitude increased over training sessions equally in participants with tinnitus and in control subjects, suggesting normal remodeling of non-primary auditory regions in tinnitus. However, training-induced changes in the ASSR differed between the tinnitus and control groups. In controls the phase delay between the 40-Hz response and stimulus waveforms reduced by about 10° over training, in agreement with previous results obtained in young normal hearing individuals. However, ASSR phase did not change significantly with training in the tinnitus group, although some participants showed phase shifts resembling controls. On the other hand, ASSR amplitude increased with training in the tinnitus group, whereas in controls this response (which is difficult to remodel in young normal hearing subjects) did not change with training. These results suggest that neural changes related to tinnitus altered how neural plasticity was expressed in the region of primary but not non-primary auditory cortex. Auditory training did not reduce tinnitus loudness although a small effect on the tinnitus spectrum was detected.

Temporal Processing in Low-Frequency Channels: Effects of Age and Hearing Loss in Middle-Aged Listeners

Hearing loss and age interfere with the auditory system's ability to process temporal changes in the acoustic signal. A key unresolved question is whether high-frequency sensorineural hearing loss (HFSNHL) affects temporal processing in the low-frequency region where hearing loss is minimal or nonexistent. A second unresolved question is whether changes in hearing occur in middle-aged subjects in the absence of HFSNHL. The purpose of this study was twofold: (1) to examine the influence of HFSNHL and aging on the auditory temporal processing abilities of low-frequency auditory channels with normal hearing sensitivity and (2) to examine the relations among gap detection measures, self-assessment reports of understanding speech, and functional measures of speech perception in middle-aged individuals with and without HFSNHL. The subject groups were matched for either age (middle age) or pure-tone sensitivity (with or without hearing loss) to study the effects of age and HFSNHL on behavioral and functional measures of temporal processing and word recognition performance. These effects were analyzed by individual repeated-measures analyses of variance. Post hoc analyses were performed for each significant main effect and interaction. The relationships among the measures were analyzed with Pearson correlations. Eleven normal-hearing young adults (YNH), eight normal-hearing middle-aged adults (MANH), and nine middle-aged adults with HFSNHL were recruited for this study. Normal hearing sensitivity was defined as pure-tone thresholds ≤25 dB HL for octave frequencies from 250 to 8000 Hz. HFSNHL was defined as pure-tone thresholds ≤25 dB HL from 250 to 2000 Hz and ≥35 dB HL from 3000 to 8000 Hz. Gap detection thresholds (GDTs) were measured under within-channel and between-channel conditions with the stimulus spectrum limited to regions of normal hearing sensitivity for the HFSNHL group (i.e., <2000 Hz). Self-perceived hearing problems were measured by a questionnaire (Abbreviated Profile of Hearing Aid Benefit), and word recognition performance was assessed under four conditions: quiet and babble, with and without low-pass filtering (cutoff frequency = 2000 Hz). The effects of HFSNHL and age were found for gap detection, self-perceived hearing problems, and word recognition in noise. The presence of HFSNHL significantly increased GDTs for stimuli presented in regions of normal pure-tone sensitivity. In addition, middle-aged subjects with normal hearing sensitivity reported significantly more problems hearing in background noise than the young normal-hearing subjects. Significant relationships between self-report measures of hearing ability in background noise and word recognition in babble were found. The conclusions from the present study are twofold: (1) HFSNHL may have an off-channel impact on auditory temporal processing, and (2) presenescent changes in the auditory system of MANH subjects increased self-perceived problems hearing in background noise and decreased functional performance in background noise compared with YNH subjects.

Cochlear active mechanisms in young normal-hearing subjects affected by Williams syndrome: Time–frequency analysis of otoacoustic emissions

The aim of this study was to investigate the functionality of cochlear active mechanisms in normal-hearing subjects affected by Williams syndrome (WS). Transient evoked otoacoustic emissions (TEOAEs) were recorded in a group of young WS subjects and a group of typically developing control subjects, all having normal-hearing thresholds and normal middle-ear functionality. We also analysed the narrow-band frequency components of TEOAEs, extracted from the broad-band TEOAE recordings by using a time–frequency analysis algorithm based on the Wavelet transform. We observed that TEOAEs and the frequency components extracted from TEOAEs measured in WS subjects had significantly lower energy compared to the controls. Also, the narrow-band frequency components of TEOAEs measured in WS subjects had slightly increased latency compared to the controls. Overall, results would suggest a subtle (i.e., sub-clinical) dysfunction of the cochlear active mechanisms in WS subjects with otherwise normal hearing. Also, results point out the relevance of using otoacoustic emissions in the audiological evaluation and monitoring of WS subjects to early identify possible subtle auditory dysfunctions, before the onset of mild or moderate hearing loss that could exacerbate language or cognitive impairments associated with WS.

Central Auditory Processing Disorders: Effects of Age and Hearing Loss to Electrophysiological and Behavioral Responses

Central Auditory Processing Disorders: Effects of Age and Hearing Loss to Electrophysiological and Behavioral Responses Introduction. Central auditory processing involve normal sound perception, speech recognition, ability of cognition and memory. Accordingly speech recognition difficulties may manifest due to changes at any segment of auditory processing. Cortical auditory evoked potentials (CAEPs) and behavioral measures provide insight into the neural mechanisms underlying speech recognition. These disorders are observed both in young and elderly population. Aim of the study. To evaluate central auditory processing for subjects of different age and hearing level through the presentation of noise using CAEPs and behavioral measures of speech discrimination. However due to complicated connectivity in auditory pathway it is difficult to identify the central auditory processing damage. Behavioral tests in conjunction with electrophysiological examination will reveal more complicated information for differenciation between peripheral and central auditory processing disorders. Materials and methods. Three groups of subjects participated: young normal hearing, young hearing-impaired and elderly hearing-impaired subjects. To minimaze subject variables, the CAEPs (wave peaks P1, N1, P2, N2, P3, N3 in miliseconds) was investigated using passive listening paradigme. The CAEPs were elicited by 1,1s change in frequency 1000 Hz and 2000 Hz in pure tones presented at 65, 70 and 75 dB SPL. Sentence recognition tests in quite and noise, Digit Pairs (DP) and Word Pairs (WP) were developed in Latvian language prior to investigation. They were presented to all subjects. Results. The most prominent finding was the increased latency of P3, N3 in elderly and also in younger hearing impaired adults groups and highly differed within groups. More prolonged latencies were find of N1, P2 in elderly hearing impaired group than in younger hearing impaired group adults. Conclusions. During this investigation the CAEPs are performed for the first time in our clinic therefore the main standarts are determined for our laboratory. The speech recognition tests (Sentence recognition test, DD, DW) are developed in Latvian. The present findings suggest patterns of CAEP are variable within individuals however shows that auditory perception and cognitive function is not only a result of aging and must be associated with a general slowing of neuronal processing or decreased neuronal synchrony within the central auditory nervous system. Determination of central auditory processing capacity level is of crucial significance to prognose and evaluate the hearing result after hearing prosthetics and to appraise indications for hearing prosthetics, cochlear and middle ear implantation including.

Psychoacoustic Tests for Central Auditory Processing: Normative Data

The comprehension of spoken language is based on the analysis of complex acoustic signals by the central auditory system, Direct relationships between gradual, spectrotemporal modifications of speech sounds and the impairment of the comprehension of such altered sounds have been found in many psychophysical studies. Thus, it is reasonable to assume that deficits in the understanding of speech seen in patients with acquired brain lesions may, to a certain degree, result from impaired central processing of acoustic signals. We report normative data collected from 94 young normal-hearing subjects on a battery of psychoacoustic tests designed to evaluate signal processing at different levels of the central auditory system. Monaural pure tone thresholds were used to evaluate the performance of peripheral hearing. The integrity of auditory brainstem processing was evaluated by quantifying masking level difference (MLD) values and gap detection (GD) thresholds. Three monaural speech tests (time-compressed speech [CS], filtered speech [FS] and speech in noise [SIN]) were conducted to evaluate the processing of distorted speech materials by cortical auditory processing mechanisms. Evaluating performance of naïve, young normal-hearing subjects, as we did here, is indispensable for (a) evaluating the effectiveness of potential tests, (b) evaluating their suitability for the examination of patients, and (c) the revision and further development of central auditory tests.

Effect of amplitude modulation of background noise on auditory-evoked magnetic fields

Although it is known that amplitude modulation of a background masker improves signal detection, its effects on supra-threshold sounds are still unclear. In this study, the effects of amplitude modulation of a background masker on supra-threshold sounds were evaluated using a whole-head magnetoencephalography system. We compared the auditory-evoked magnetic fields recorded with a 500-Hz tone-burst of supra-threshold level with either random speech-spectrum noise (Unmodulated noise) or amplitude-modulated noise (Modulated noise) in 10 young normal-hearing subjects. The sounds were presented binauraly. The strengths of the N100m in the two noise conditions were examined. The masking effect of Modulated noise on supra-threshold sound was stronger than that of Unmodulated noise, a finding opposite to that on peri-threshold sound. The growth rate of the N100m strengths in the Modulated noise condition was less than that in the Unmodulated noise condition in the left hemisphere, whereas they were not different in the right hemisphere, suggesting that the left hemisphere was more susceptible to the envelope fluctuation.

The psychoacoustics of noise vocoded speech: A physiological means to a perceptual end

Noise vocoded speech tokens produce temporal patterns in the ensemble response of the auditory nerve similar to those of their naturally produced counterparts [Loebach, J.L., Wickesberg, R.E., 2006. The representation of noise vocoded speech in the auditory nerve of the chinchilla: Physiological correlates for the perception of spectrally reduced speech. Hear. Res. 213 (1–2), 130–144]. Moreover, the degree of pattern similarity increased as more noise bands were used to synthesize the vocoded stimuli, suggesting a relationship between the patterns that these stimuli evoke in the auditory nerve and their recognition by human subjects. In order to make a direct comparison between the psychoacoustic and physiological domains, the present study obtained the perceptual identification scores for these stimuli. A set of 120 stimuli containing the 16 tokens of interest was presented to 30 young normal hearing subjects, who identified the tokens in a closed set task. Overall, the perceptual identification of the tokens increased in accuracy with the addition of noise bands. The neural pattern similarity was quantified using dynamic time warping, and correlated with the perceptual identification scores for the target stimuli of interest. A significant linear relationship between the pattern similarity and perceptual identification scores was found, such that as neural pattern similarity increased, the accuracy of stimulus identification also increased. These findings suggest a possible physiological substrate for the recognition of noise vocoded consonants.

Racial and gender effects on pure-tone thresholds and distortion-product otoacoustic emissions (DPOAEs) in normal-hearing young adults

This study examined racial and gender effects on behavioral thresholds and distortion-product otoacoustic emissions (DPOAEs) in the same subjects. Pure-tone behavioral thresholds and DPOAEs were measured in 60 young normal-hearing adult subjects (20 Caucasian, 20 Asian, 20 African-American, with ten females and ten males in each group). Behavioral thresholds were measured from 1000 through 16 000 Hz using Békèsy tracking. A DPOAE frequency sweep was measured with primary stimulus levels of L1/L2=60/45 dB SPL, and an f2/f1 of 1.2 at discrete f2 frequencies between 2000 through 12 000 Hz for each subject. Significant racial and gender differences in behavioral thresholds were found at 14 000 and 16 000 Hz, with the African Americans and females having the best hearing sensitivity. Based on the current results, similar findings for DPOAE frequency sweeps can be expected amongst different racial groups given that no significant differences were identified between the groups. To further define the effects of race and gender on auditory measures, future studies should include larger numbers of subjects, measurement of body size and middle ear reflectance, and examine emission generators.

Auditory measures of selective and divided attention in young and older adults using single-talker competition

In this study, two experiments were conducted on auditory selective and divided attention in which the listening task involved the identification of words in sentences spoken by one talker while a second talker produced a very similar competing sentence. Ten young normal-hearing (YNH) and 13 elderly hearing-impaired (EHI) listeners participated in each experiment. The type of attention cue used was the main difference between experiments. Across both experiments, several consistent trends were observed. First, in eight of the nine divided-attention tasks across both experiments, the EHI subjects performed significantly worse than the YNH subjects. By comparison, significant differences in performance between age groups were only observed on three of the nine selective-attention tasks. Finally, there were consistent individual differences in performance across both experiments. Correlational analyses performed on the data from the 13 older adults suggested that the individual differences in performance were associated with individual differences in memory (digit span). Among the elderly, differences in age or differences in hearing loss did not contribute to the individual differences observed in either experiment.

Contribution of consonant versus vowel information to sentence intelligibility by normal and hearing-impaired listeners

The purpose of this study was to examine the contribution of information provided by vowels versus consonants to sentence intelligibility in young normal-hearing (YNH) and elderly hearing-impaired (EHI) listeners. Sentences were presented in three conditions, with either the vowels or the consonants replaced with speech shaped noise, or unaltered. Sentences from male and female talkers in the TIMIT database were selected. EHI subjects listened at 95 dB SPL, and YNH subjects at both 95 and 70 dB SPL. Subjects listened to each sentence twice and were asked to repeat the entire sentence after each presentation. Words were scored correct if identified exactly. Average performance for unaltered sentences was greater than 94%. Vowel-present conditions were always significantly more intelligible than consonant-present conditions, similar to data reported by Cole and colleagues [Proceedings of ICASSP, 1996]. Across groups, performance in the vowel-present conditions exceeded that in the consonant-present conditions by 14% to 40%, although EHI subjects performed more poorly than YNH subjects. In contrast to written English, vowels in spoken language carry more information about sentences than consonants for both normal and hearing-impaired listeners. [Work supported by NIDCD-02229.]