Young Normal-hearing Listeners Research Articles

Perceptual weighting of the envelope and fine structure across frequency bands for sentence intelligibility: effect of interruption at the syllabic-rate and periodic-rate of speech.

Listeners often only have fragments of speech available to understand the intended message due to competing background noise. In order to maximize successful speech recognition, listeners must allocate their perceptual resources to the most informative acoustic properties. The speech signal contains temporally-varying acoustics in the envelope and fine structure that are present across the frequency spectrum. Understanding how listeners perceptually weigh these acoustic properties in different frequency regions during interrupted speech is essential for the design of assistive listening devices. This study measured the perceptual weighting of young normal-hearing listeners for the envelope and fine structure in each of three frequency bands for interrupted sentence materials. Perceptual weights were obtained during interruption at the syllabic rate (i.e., 4 Hz) and the periodic rate (i.e., 128 Hz) of speech. Potential interruption interactions with fundamental frequency information were investigated by shifting the natural pitch contour higher relative to the interruption rate. The availability of each acoustic property was varied independently by adding noise at different levels. Perceptual weights were determined by correlating a listener's performance with the availability of each acoustic property on a trial-by-trial basis. Results demonstrated similar relative weights across the interruption conditions, with emphasis on the envelope in high-frequencies.

The adaptive pattern of the auditory N1 peak revealed by standardized low-resolution brain electromagnetic tomography

The N1 peak in the late auditory evoked potential (LAEP) decreases in amplitude following stimulus repetition, displaying an adaptive pattern. The present study explored the functional neural substrates that may underlie the N1 adaptive pattern using standardized Low Resolution Electromagnetic Tomography (sLORETA). Fourteen young normal hearing (NH) listeners participated in the study. Tone bursts (80 dB SPL) were binaurally presented via insert earphones in trains of 10; the inter-stimulus interval was 0.7 s and the inter-train interval was 15 s. Current source density analysis was performed for the N1 evoked by the 1st, 2nd and 10th stimuli (S 1, S 2 and S 10) at 3 different timeframes that corresponded to the latency ranges of the N1 waveform subcomponents (70–100, 100–130 and 130–160 ms). The data showed that S 1 activated broad regions in different cortical lobes and the activation was much smaller for S 2 and S 10. Response differences in the LAEP waveform and sLORETA were observed between S 1 and S 2, but not between the S 2 and S 10. The sLORETA comparison map between S 1 and S 2 responses showed that the activation was located in the parietal lobe for the 70–100 ms timeframe, the frontal and limbic lobes for the 100–130 ms timeframe, and the frontal lobe for the 130–160 ms timeframe. These sLORETA comparison results suggest a parieto-frontal network that might help to sensitize the brain to novel stimuli by filtering out repetitive and irrelevant stimuli. This study demonstrates that sLORETA may be useful for identifying generators of scalp-recorded event related potentials and for examining the physiological features of these generators. This technique could be especially useful for cortical source localization in individuals who cannot be examined with functional magnetic resonance imaging or magnetoencephalography (e.g., cochlear implant users).

Speech perception in steady and amplitude modulated band-pass noise.

The purpose of the current study was to examine the effects of temporal and spectral interferences on sentence recognition for cochlear (CI) implant listeners. Nie and Nelson (2010) investigated vocoded speech perception in amplitude-modulated band-pass noises in order to assess young normal-hearing (NH) listeners’ speech understanding through cochlear implant simulations. They reported that while the spectra of the noise bands affected vocoder speech perception, there was no significant effect of the noise AM rate on performance, indicating spectral but not temporal interference. As a follow-up, young CI listeners with various devices and processing strategies participated in the current study. IEEE sentences and white noise were divided into 16 bands, and band-pass noise maskers were formed from varying combinations of 4–6 adjacent bands. The spectra of the maskers relative to the spectra of speech were set to be one of the following: completely overlapping, partially overlapping or completely separate from the speech. Noise was sinusoidally modulated at three rates: 4, 16, and 32 Hz. It is hypothesized that sentence recognition scores for CI listeners are affected by both spectral and temporal characteristics of the noise, which is different from the performance for NH listeners reported previously.

Perceptual weighting of individual and concurrent cues for sentence intelligibility: frequency, envelope, and fine structure.

The speech signal may be divided into frequency bands, each containing temporal properties of the envelope and fine structure. For maximal speech understanding, listeners must allocate their perceptual resources to the most informative acoustic properties. Understanding this perceptual weighting is essential for the design of assistive listening devices that need to preserve these important speech cues. This study measured the perceptual weighting of young normal-hearing listeners for the envelope and fine structure in each of three frequency bands for sentence materials. Perceptual weights were obtained under two listening contexts: (1) when each acoustic property was presented individually and (2) when multiple acoustic properties were available concurrently. The processing method was designed to vary the availability of each acoustic property independently by adding noise at different levels. Perceptual weights were determined by correlating a listener's performance with the availability of each acoustic property on a trial-by-trial basis. Results demonstrated that weights were (1) equal when acoustic properties were presented individually and (2) biased toward envelope and mid-frequency information when multiple properties were available. Results suggest a complex interaction between the available acoustic properties and the listening context in determining how best to allocate perceptual resources when listening to speech in noise.

Content and Procedural Learning in Repeated Sentence Tests of Speech Perception

Repeated testing of speech perception is unavoidable in evaluating the benefits of hearing aids and auditory rehabilitation, but procedural and content learning due to repeated test administration can masquerade as a general improvement in speech perception. A previous study of the speech reception threshold (SRT) in quiet reported procedural learning that was sufficiently large to call into question the use of repeated sentence testing in evaluating the effects of auditory rehabilitation. The objective of the first experiment was to measure the effects of content and procedural learning in noise using the Hearing in Noise Test (HINT) when some sentences were repeated and others were not. The objective of the second experiment was to estimate the effects of procedural learning in a larger group of listeners using both the HINT and the Quick Speech in Noise test (QuickSIN) without sentence repetition across test sessions. The objective of the third experiment was to evaluate content learning in the HINT and the QuickSIN when sentence tests were repeated at intervals of several months. In experiment 1, eight normal-hearing listeners completed five 1-hr test sessions on separate days. All sessions included sets of HINT sentences that were presented twice per session to evaluate content learning. Sessions 1 and 5 also included sets of unique sentences to measure procedural learning. In experiment 2, 23 young normal-hearing listeners completed three sessions over a 10-day period with unique HINT and QuickSIN sentence lists presented in each session. In experiment 3, 11 older, normal-hearing listeners completed three sessions of unique HINT and QuickSIN sentence lists, as in experiment 2. After an interval corresponding to a course of auditory rehabilitation training or hearing-aid acclimatization, the listeners were tested with the same sentence lists. In experiment 1, the SRT for repeated sentences improved by an average of 2.7 dB, whereas that for unique sentences showed an insignificant 0.3 dB change. These results demonstrate that HINT SRTs can be affected by content learning for repeated sentences, but are minimally affected by procedural learning for unique sentence material. Significant procedural learning was found only in the first session. In experiment 2, HINT SRTs improved by 0.2 dB per session whereas improvements on the QuickSIN (0.1 dB per session) failed to reach statistical significance. In experiment 3, both tests showed significant improvements; HINT SRTs improved by 0.5 dB and QuickSIN SRTs by 0.4 dB. Both the HINT and the QuickSIN provide stable and sensitive measures of speech perception across repeated test sessions provided that sentences are not repeated. Practice with at least two sentence lists is needed to eliminate the initial effect of procedural learning in the first session. The results with the HINT and QuickSIN at moderate noise levels differ from previous results of sentence testing in quiet, whereas SRTs improved 6 to 9 dB over five sessions for both repeated and unique sentences. Differences between testing at moderate noise levels and in quiet seem to account for the difference in the stability of these sentence-test measurements.

Vowel identification by younger and older listeners: Relative effectiveness of vowel edges and vowel centers

Young normal-hearing (YNH) and older normal-hearing (ONH) listeners identified vowels in naturally produced /bVb/ syllables and in modified syllables that consisted of variable portions of the vowel edges (silent-center [SC] stimuli) or vowel center (center-only [CO] stimuli). Listeners achieved high levels of performance for all but the shortest stimuli, indicating that they were able to access vowel cues throughout the syllable. ONH listeners performed similarly to YNH listeners for most stimuli, but performed more poorly for the shortest CO stimuli. SC and CO stimuli were equally effective in supporting vowel identification except when acoustic information was limited to 20 ms.

Perception of speech in reverberant conditions using AM–FM cochlear implant simulation

This study assessed the effects of speech misidentification and cognitive processing errors in normal-hearing adults listening to degraded auditory input signals simulating cochlear implants in reverberation conditions. Three variables were controlled: number of vocoder channels (six and twelve), instantaneous frequency change rate (none, 50, 400 Hz), and enclosures (different reverberation conditions). The analyses were made on the basis of: (a) nonsense word recognition scores for eight young normal-hearing listeners, (b) ‘ease of listening’ based on the time of response, and (c) the subjective measure of difficulty. The maximum score of speech intelligibility in cochlear implant simulation was 70% for non-reverberant conditions with a 12-channel vocoder and changes of instantaneous frequency limited to 400 Hz. In the presence of reflections, word misidentification was about 10–20 percentage points higher. There was little difference between the 50 and 400 Hz frequency modulation cut-off for the 12-channel vocoder; however, in the case of six channels this difference was more significant. The results of the experiment suggest that the information other than F0, that is carried by FM, can be sufficient to improve speech intelligibility in the real-world conditions.

Recognition of accented English in quiet by younger normal-hearing listeners and older listeners with normal-hearing and hearing loss

This investigation examined the effects of listener age and hearing loss on recognition of accented speech. Speech materials were isolated English words and sentences that featured phonemes that are often mispronounced by non-native speakers of English whose first language is Spanish. These stimuli were recorded by a native speaker of English and two non-native speakers of English: one with a mild accent and one with a moderate accent. The stimuli were presented in quiet to younger and older adults with normal-hearing and older adults with hearing loss. Analysis of percent correct recognition scores showed that all listeners performed more poorly with increasing accent, and older listeners with hearing loss performed more poorly than the younger and older normal-hearing listeners in all accent conditions. Context and age effects were minimal. Consonant confusion patterns in the moderate accent condition showed that error patterns of all listeners reflected temporal alterations with accented speech, with major errors of word-final consonant voicing in stops and fricatives, and word-initial fricatives.

Effects of Talker Variability on Speech Recognition of Normal-Hearing Listeners for Korean Speech Audiometry

The purpose of this study was to examine effects of talker variability manipulated by the number of target talkers (two- versus multitalker) on the speech recognition results of Korean Speech Audiometry. Korean Speech Audiometry (KSA, www.kops.co.kr) included three types of the speech test materials (one-, two-syllable words, and sentences), and was recorded digitally in CDs by either a male or female talker. Given that some researchers have reported a significant effect of talker variability on speech recognition accuracy, we recorded all the speech materials in CDs by 20 talkers (10 male and 10 female). The effect of talker variability was then determined by comparing speech recognition performances of 5 young normal-hearing listeners by two-talker (in KSA CD) versus 20-talker conditions from -5 to 40 dB HL in 5 dB steps. The results showed that speech recognition accuracy of young normal-hearing listeners did not significantly differ in conditions for each of the three speech materials at each presentation level. This indicated important clinical implications of CD materials in KSA for the speech audiometric tests. KEY WORDS：Korean speech audiometry·Speech recognition·Talker variability.

Acoustic correlates of clear speech vowel intelligibility for elderly hearing-impaired listeners.

Earlier work on vowels in clear and conversational speech produced by a single talker suggested that the acoustic cues that underlie the superior intelligibility of clear speech for older adults with hearing loss may differ from the cues that young normal-hearing listeners find beneficial. In the present study, clear and conversational vowel stimuli produced by all 41 talkers from the Ferguson Clear Speech Database were presented in a background of 12-talker babble to 40 older adults with mild-to-moderately severe sloping sensorineural hearing loss. Acoustic analyses (vowel duration, steady-state formant frequencies, and measures of dynamic formant movement) were also performed for all stimuli. Vowel intelligibility scores for each talker in each speaking style as well as the magnitude of the clear speech vowel intelligibility effect for each talker will be compared to those obtained from young listeners with normal hearing in a previous study. Regression and other statistical analyses of intelligibility and acoustic data will also be performed to determine the acoustic correlates associated with improved clear speech vowel intelligibility for each listener group. [Work supported by NIHDCD-008886.]

Speech recognition and working memory capacity in young-elderly listeners: Effects of hearing sensitivity.

Young normal-hearing listeners and young-elderly listeners between 55 and 65 years of age, ranging from near-normal hearing to moderate hearing loss, were compared using different speech recognition tasks (consonant recognition in quiet and in noise, and time-compressed sentences) and working memory tasks (serial word recall and digit ordering). The results showed that the group of young-elderly listeners performed worse on both the speech recognition and working memory tasks than the young listeners. However, when pure-tone audiometric thresholds were used as a covariate variable, the significant differences between groups disappeared. These results support the hypothesis that sensory decline in young-elderly listeners seems to be an important factor in explaining the decrease in speech processing and working memory capacity observed at these ages.

The Benefits of Hearing Aids and Closed Captioning for Television Viewing by Older Adults with Hearing Loss

Although watching television is a common leisure activity of older adults, the ability to understand televised speech may be compromised by age-related hearing loss. Two potential assistive devices for improving television viewing are hearing aids (HAs) and closed captioning (CC), but their use and benefit by older adults with hearing loss are unknown. The primary purpose of this initial investigation was to determine if older hearing-impaired adults show improvements in understanding televised speech with the use of these two assistive devices (HAs and CC) compared with conditions without these devices. A secondary purpose was to examine the frequency of HA and CC use among a sample of older HA wearers. The investigation entailed a randomized, repeated-measures design of 15 older adults (59 to 82 yr) with bilateral sensorineural hearing losses who wore HAs. Participants viewed three types of televised programs (news, drama, and game show) that were each edited into lists of speech segments and provided an identification response. Each participant was tested in four conditions: baseline (no HA or CC), HA only, CC only, and HA + CC. Also, pilot testing with young normal-hearing listeners was conducted to establish list equivalence and stimulus intelligibility with a control group. All testing was conducted in a quiet room to simulate a living room, using a 20 in flat screen television. Questionnaires were also administered to participants to determine the frequency of HA and CC use while watching television. A significant effect of viewing condition was observed for all programs. Participants exhibited significantly better speech recognition scores in conditions with CC than those without CC (p < 0.01). Use of personal HAs did not significantly improve recognition of televised speech compared with the unaided condition. The condition effect was similar across the three different programs. Most of the participants (73%) regularly wore their HAs while watching television; very few of them (13%) had ever used CC. On average, use of CC while watching television dramatically improved speech understanding by a sample of older hearing-impaired adults compared with conditions without CC, including when HAs were worn.

Recovery Function of the Late Auditory Evoked Potential in Cochlear Implant Users and Normal-Hearing Listeners

It has been theorized that neural recovery is related to temporal coding of speech sounds. The recovery function of cortically generated auditory evoked potentials has not been investigated in cochlear implant (CI) users. This study characterized the recovery function of the late auditory evoked potential (LAEP) using a masker-probe paradigm in postlingually deafened adult CI users and young normal-hearing (NH) listeners. A case-control study of the late auditory evoked potentials using electrophysiological technique was performed. The LAEP was evoked by 1 kHz tone bursts presented in pairs, with the first stimuli as the maskers and the second stimuli as the probes. The masker-probe intervals (MPIs) were varied at 0.7, 1, 2, 4, and 8 sec, with an interpair interval of 12 sec. Nine CI users and nine NH listeners participated in this study. The normalized amplitude from the probe response relative to the masker response was plotted as a function of the MPI to form a recovery function. The latency shift for the probe response relative to the masker response was calculated. The recovery function was approximately linear in log scale of the MPI in NH listeners, while it showed somewhat different recovery patterns with a large intersubject variability in CI users. Specifically, although the probe response was approximately 60 percent of the masker response for the MPI of 0.7 sec in both groups, the recovery function of CI users displayed a nonlinear pattern, with a steeper slope than that of NH listeners. The probe response completely recovered at the MPI of 4 sec in NH listeners and at the MPI of 2 sec in CI users. N1 and P2 latencies from probe responses were shorter than those from masker responses in NH listeners, while no latency difference was found between probe responses and masker responses in CI users. Our interpretation of these findings is that the faster recovery of the LAEP in CI users is related to abnormal adaptation mechanisms and a less prominent role of the components with longer latencies in the LAEP of CI users. Other mechanisms such as the compromised inhibitory regulation in the auditory system and the aging effect in CI users might also play a role. More research needs to be done to determine whether the slope of the LAEP recovery function is correlated with speech-perception performance.

Perceptual Consequences of Changes in Vocoded Speech Parameters in Various Reverberation Conditions

To study the perceptual consequences of changes in parameters of vocoded speech in various reverberation conditions. The 3 controlled variables were number of vocoder bands, instantaneous frequency change rate, and reverberation conditions. The effects were quantified in terms of (a) nonsense words' recognition scores for young normal-hearing listeners, (b) ease of listening based on the time of response (response delay), and (c) the subjective measure of difficulty (10-degree scale). It has been shown that the fine structure of a signal is a relevant cue in speech perception in reverberation conditions. The results obtained for different number of bands, frequency-modulation cutoff frequencies, and reverberation conditions have shown that all these parameters are important for speech perception in reverberation. Only slow variations in the instantaneous frequency (<50 Hz) seem to play a critical role in speech intelligibility in anechoic conditions. In reverberant enclosures, however, fast fluctuations of instantaneous frequency are also significant.

The incongruency advantage in elderly versus young normal‐hearing listeners.

Previous research [Gygi & Shafiro (2007); Leech et al. (2007)] reported that environmental sounds heard in contextually incongruous naturalistic auditory scenes are better identified than sounds contextually congruous with the scene (e.g., rooster crowing in a farm ambience versus rooster in an office ambience). This incongruency advantage (IA) averages about four‐to‐five percentage points in p(c) and has been observed in both well‐trained and naive young normal hearing listeners [Gygi and Shafiro (2008)] and in children [Leech et al. (2007)]. One aspect of the IA is that it appears to be level‐dependent, in that the effect is not present for lower sound/scene ratios (So/Sc). For experienced young listeners, the IA appears at a So/Sc of −15 dB. However, for naive young listeners, it is not manifest until −7.5 dB. A group of elderly normal‐hearing listeners were tested and exhibited an IA only at So/Sc of −9 dB and above. The results show that the incongruency advantage are complex effects resulting from a...

The role of temporal cues in word identification by younger and older adults: Effects of sentence context

Prior investigations, using isolated words as stimuli, have shown that older listeners tend to require longer temporal cues than younger listeners to switch their percept from one word to its phonetically contrasting counterpart. The extent to which this age effect occurs in sentence contexts is investigated in the present study. The hypothesis was that perception of temporal cues differs for words presented in isolation and a sentence context and that this effect may vary between younger and older listeners. Younger and older listeners with normal-hearing and older listeners with hearing loss identified phonetically contrasting word pairs in natural speech continua that varied by a single temporal cue: voice-onset time, vowel duration, transition duration, and silent interval duration. The words were presented in isolation and in sentences. A context effect was shown for most continua, in which listeners required longer temporal cues in sentences than in isolated words. Additionally, older listeners required longer cues at the crossover points than younger listeners for most but not all continua. In general, the findings support the conclusion that older listeners tend to require longer target temporal cues than younger normal-hearing listeners in identifying phonetically contrasting word pairs in isolation and sentence contexts.

Temporal order discrimination of tonal sequences by younger and older adults: The role of duration and rate

The effect of tone duration and presentation rate on the discrimination of the temporal order of the middle two tones of a four-tone sequence was investigated in young normal-hearing (YNH) and older hearing-impaired (OHI) listeners. The frequencies and presentation level of the tone sequences were selected to minimize the effect of hearing loss on the performance of the OHI listeners. Tone durations varied from 20 to 400 ms and presentation rates from 2.5 to 25 toness. Two experiments were conducted with anisochronous (nonuniform duration and rate across entire sequence) and isochronous (uniform rate and duration) sequences, respectively. For the YNH listeners, performance for both isochronous and anisochronous sequences was determined primarily by presentation rate such that performance decreased at rates faster than 5 toness. For anisochronous tone sequences alone, the effects of rate were more pronounced at short tone durations. For the OHI listeners, both presentation rate and tone duration had an impact on performance for both isochronous and anisochronous sequences such that performance decreased as rate increased above 5 toness or duration decreased below 40 ms. Temporal masking was offered as an explanation for the interaction of short durations and fast rates on temporal order discrimination for the anisochronous sequences.

Categorical dependence of vowel detection in long-term speech-shaped noise

The goal of this study was to measure detection thresholds for 12 isolated American English vowels naturally spoken by three male and three female talkers for young normal-hearing listeners in the presence of a long-term speech-shaped (LTSS) noise, which was presented at 70 dB sound pressure level. The vowel duration was equalized to 170 ms and the spectrum of the LTSS noise was identical to the long-term average spectrum of 12-talker babble. Given the same duration, detection thresholds for vowels differed by 19 dB across the 72 vowels. Thresholds for vowel detection showed a roughly U-shaped pattern as a function of the vowel category across talkers with lowest thresholds at /i/ and /ae/ vowels and highest thresholds at /u/ vowel in general. Both vowel category and talker had a significant effect on vowel detectability. Detection thresholds predicted from three excitation pattern metrics by using a simulation model were well matched with thresholds obtained from human listeners, suggesting that listeners could use a constant metric in the excitation pattern of the vowel to detect the signal in noise independent of the vowel category and talker. Application of the simulation model to predict thresholds of vowel detection in noise was also discussed.

Improvement of speech recognition thresholds by spectral modulation enhancement

Our previous studies have shown that vowel identification in noise was significantly improved by spectral enhancement resulting from modifications in the spectral modulation domain. The present study investigates whether spectral enhancement results in improved speech recognition in background competition. Speech recognition thresholds (SRT) were measured in a long-term speech shaped (LTSS) noise and in multi-talker babble using NU-6 words with and without spectral enhancement for young normal-hearing listeners. Results indicated that SRTs were significantly reduced, by 2.2 dB, in LTSS noise and in babble when speech sounds were spectrally enhanced between 2.0 and 2.5 cycles/octave, while no significant changes in SRTs occurred for enhancement between 1.5 and 2 cycles/octave or between 1.5 and 2.5 cycles/octave. Spectral modulation transfer functions were also measured for each listener. Linear regression analyses showed that SRT improvement was moderately correlated with modulation detection thresholds at a spectral modulation frequency of 0.5 cycles/octave. Thus, it appears that better modulation detection at low spectral modulation frequencies is associated with greater improvement in word recognition in background competition.

Factors affecting vowel formant discrimination by hearing-impaired listeners

The goal of this study was to measure the ability of adult hearing-impaired listeners to discriminate formant frequency for vowels in isolation, syllables, and sentences. Vowel formant discrimination for F1 and F2 for the vowels /I epsilon ae / was measured. Four experimental factors were manipulated including linguistic context (isolated vowels, syllables, and sentences), signal level (70 and 95 dB SPL), formant frequency, and cognitive load. A complex identification task was added to the formant discrimination task only for sentences to assess effects of cognitive load. Results showed significant elevation in formant thresholds as formant frequency and linguistic context increased. Higher signal level also elevated formant thresholds primarily for F2. However, no effect of the additional identification task on the formant discrimination was observed. In comparable conditions, these hearing-impaired listeners had elevated thresholds for formant discrimination compared to young normal-hearing listeners primarily for F2. Altogether, poorer performance for formant discrimination for these adult hearing-impaired listeners was mainly caused by hearing loss rather than cognitive difficulty for tasks implemented in this study.