Young Normal-hearing Listeners Research Articles

Advantages of binaural amplification to acceptable noise level of directional hearing aid users.

ObjectivesThe goal of the present study was to examine whether Acceptable Noise Levels (ANLs) would be lower (greater acceptance of noise) in binaural listening than in monaural listening condition and also whether meaningfulness of background speech noise would affect ANLs for directional microphone hearing aid users. In addition, any relationships between the individual binaural benefits on ANLs and the individuals' demographic information were investigated.MethodsFourteen hearing aid users (mean age, 64 years) participated for experimental testing. For the ANL calculation, listeners' most comfortable listening levels and background noise level were measured. Using Korean ANL material, ANLs of all participants were evaluated under monaural and binaural amplification with a counterbalanced order. The ANLs were also compared across five types of competing speech noises, consisting of 1- through 8-talker background speech maskers. Seven young normal-hearing listeners (mean age, 27 years) participated for the same measurements as a pilot testing.ResultsThe results demonstrated that directional hearing aid users accepted more noise (lower ANLs) with binaural amplification than with monaural amplification, regardless of the type of competing speech. When the background speech noise became more meaningful, hearing-impaired listeners accepted less amount of noise (higher ANLs), revealing that ANL is dependent on the intelligibility of the competing speech. The individuals' binaural advantages in ANLs were significantly greater for the listeners with longer experience of hearing aids, yet not related to their age or hearing thresholds.ConclusionBinaural directional microphone processing allowed hearing aid users to accept a greater amount of background noise, which may in turn improve listeners' hearing aid success. Informational masking substantially influenced background noise acceptance. Given a significant association between ANLs and duration of hearing aid usage, ANL measurement can be useful for clinical counseling of binaural hearing aid candidates or unsuccessful users.

Effects of vowel duration and increasing dynamic spectral information on identification of center-only and edges-only syllables by cochlear-implant users and young normal-hearing listeners

In a previous study, cochlear implant (CI) users’ vowel-identification performance was compared to that of young normal-hearing (YNH) listeners. Stimuli included full syllables and two duration-neutralized conditions: center-only and edges-only (silent-center). CI users performed more poorly than YNH listeners overall and showed proportionately larger decrements in performance for partial syllables. Error analyses suggested that at least some CI users rely more heavily on vowel-duration cues than YNH listeners. The present study was designed to test this hypothesis and to determine whether increasing duration of dynamic cues in the edges-only conditions would improve performance, particularly among poorer-performing CI users. Ten YNH listeners and ten adult CI users heard /dVd/ syllables recorded from three talkers. Full syllables were edited to create center-only and edges-only stimuli in which vowel duration cues were or were not preserved, plus edges-only stimuli with different durations of dynamic information. Performance of both groups improved in the duration-preserved condition for center-only, but not edges-only, stimuli. The center-only duration benefit was larger for the CI than for the YNH group. Increasing the duration of dynamic information in the silent-center stimuli improved vowel-identification performance for both groups. Individual differences among CI users and implications for listener-training programs will be discussed.

Vowel identification by cochlear implant users: Contributions of static and dynamic spectral cues

Previous research has shown that normal hearing listeners can identify vowels in syllables on the basis of either quasi-static or dynamic spectral cues; however, it is not known how well cochlear implant (CI) users with current-generation devices can make use of these cues. The present study assessed vowel identification in adult CI users and a comparison group of young normal hearing (YNH) listeners. Stimuli were naturally spoken /dVd/ syllables and modified syllables that retained only quasi-static spectral cues from an 80-ms segment of the vowel center ("C80" stimuli) or dynamic spectral cues from two 20-ms segments of the vowel edges ("E20" stimuli). YNH listeners exhibited near-perfect performance for the unmodified (99.8%) and C80 (92.9%) stimuli and maintained good performance for the E20 stimuli (70.2%). CI users exhibited poorer average performance than YNH listeners for the Full stimuli (72.3%) and proportionally larger reductions in performance for the C80 stimuli (41.8%) and E20 stimuli (29.0%). Findings suggest that CI users have difficulty identifying vowels on the basis of spectral cues in the absence of duration cues, and have limited access to brief dynamic spectral cues. Error analyses suggest that CI users may rely strongly on vowel duration cues when those cues are available.

Auditory and Cognitive Effects of Aging on Perception of Environmental Sounds in Natural Auditory Scenes

Previously, Gygi and Shafiro (2011) found that when environmental sounds are semantically incongruent with the background scene (e.g., horse galloping in a restaurant), they can be identified more accurately by young normal-hearing listeners (YNH) than sounds congruent with the scene (e.g., horse galloping at a racetrack). This study investigated how age and high-frequency audibility affect this Incongruency Advantage (IA) effect. In Experiments 1a and 1b, elderly listeners ( N = 18 for 1a; N = 10 for 1b) with age-appropriate hearing (EAH) were tested on target sounds and auditory scenes in 5 sound-to-scene ratios (So/Sc) between -3 and -18 dB. Experiment 2 tested 11 YNH on the same sound-scene pairings lowpass-filtered at 4 kHz (YNH-4k). The EAH and YNH-4k groups exhibited an almost identical pattern of significant IA effects, but both were at approximately 3.9 dB higher So/Sc than the previously tested YNH listeners. However, the psychometric functions revealed a shallower slope for EAH listeners compared with YNH listeners for the congruent stimuli only, suggesting a greater difficulty for the EAH listeners in attending to sounds expected to occur in a scene. These findings indicate that semantic relationships between environmental sounds in soundscapes are mediated by both audibility and cognitive factors and suggest a method for dissociating these factors.

Sound localization in noise and sensitivity to spectral shape

Individual differences exist in sound localization performance even for normal-hearing listeners. Some of these differences might be related to acoustical differences in localization cues carried by the head related transfer functions (HRTF). Recent data suggest that individual differences in sound localization performance could also have a perceptual origin. The localization of an auditory target in the up/down and front/back dimensions requires the analysis of the spectral shape of the stimulus. In the present study, we investigated the role of an acoustic factor, the prominence of the spectral shape (“spectral strength”) and the role of a perceptual factor, the listener's sensitivity to spectral shape, in individual differences observed in sound localization performance. Spectral strength was computed as the spectral distance between the magnitude spectrum of the HRTFs and a flat spectrum. Sensitivity to spectral shape was evaluated using spectral-modulation thresholds measured with a broadband (0.2–12.8 kHz) or high-frequency (4–16 kHz) carrier and for different spectral modulation frequencies (below 1 cycle/octave, between 1 and 2 cycles/octave, above 2 cycles/octave). Data obtained from 19 young normal-hearing listeners showed that low thresholds for spectral modulation frequency below 1 cycle/octave with a high-frequency carrier were associated with better sound localization performance. No correlation was found between sound localization performance and the spectral strength of the HRTFs. These results suggest that differences in perceptual ability, rather than acoustical differences, contribute to individual differences in sound localization performance in noise.

Preliminary comparison of second-formant discrimination thresholds in cochlear implant users and young normal-hearing listeners

Formant discrimination thresholds (FDTs) may provide insights regarding factors limiting vowel perception by cochlear implant (CI) users, but have not been systematically studied in this population. In the present study, estimates of second-formant (F2) FDTs obtained in three CI users were compared to FDTs obtained from three young normal-hearing (YNH) listeners. Procedures and stimuli were modeled after Kewley-Port and Watson [J. Acoust. Soc. Am. 95, 485–496 (1994)] but employed fewer trials and an expanded F2 frequency range. Stimuli were formant-synthesized versions of three target vowels. FDTs were estimated using an adaptive 3AFC task with feedback and based on six consecutive 80-trial stimulus blocks. FDTs for the three YNH listeners were comparable to previously reported FDTs (2.4% of reference frequency versus 1.5% in Kewley-Port and Watson). FDTs for two of the CI users were about 70% larger than the average for the YNH listeners. FDTs for the third CI user approached YNH average values in one frequency region but were enlarged in another region. Data for this CI user could not be explained by place-pitch thresholds (obtained in a previous study) and suggest that CI users’ spectral acuity for complex stimuli may not be directly predictable from measures of spectral acuity for simple stimuli.

Importance of sentence-level and phoneme-level envelope modulations during vowels in interrupted speech

Speech interrupted by noise has been used as a simplified case for listening to speech in the presence of a fluctuating masker. The present study investigated the importance of overall vowel amplitude and intrinsic vowel amplitude modulation to sentence intelligibility. Eight young normal-hearing listeners participated in the experiment. Sentences were processed according to three conditions that replaced vowel segments with noise matched to the long-term average speech spectrum. Vowels were replaced with (1) low-level noise that distorted the overall sentence envelope, (2) segment-level noise that restored the overall syllabic amplitude modulation of the sentence, and (3) segment-modulated noise that further restored faster temporal envelope modulations during the vowel. Results demonstrated incremental benefit with increasing resolution of the temporal envelope. An additional seven listeners participated in a separate experiment that replaced vowels with a vowel masker instead of noise. The vowel masker was modified to have a flattened fundamental frequency at the mean of the replaced segment. The vowel masker either had a standard temporal envelope or was modulated by the envelope of the replaced vowel. Listeners who heard vowel maskers performed more poorly than those who heard noise maskers. No benefit of segment modulation was observed with the vowel masker.

Acoustic correlates of vowel intelligibility in clear and conversational speech for young normal-hearing and elderly hearing-impaired listeners

Previous reports on the relationship between clear speech acoustic changes and the clear speech intelligibility benefit for vowels have used an “extreme groups” design, comparing talkers who produced a large clear speech benefit to talkers who produced little or no clear speech benefit. In Ferguson and Kewley-Port (2007), 12 talkers from the Ferguson Clear Speech Database (Ferguson, 2004) were assigned to groups based on the vowel identification performance of young normal-hearing listeners, while Ferguson (2010) chose 20 talkers based on the performance of elderly hearing-impaired listeners. The present investigation is employing mixed-effects models to examine relationships among acoustic and perceptual data obtained for vowels produced by all 41 talkers of the Ferguson database. Acoustic data for the 1640 vowel tokens (41 talkers X 10 vowels X 2 tokens X two speaking styles) include vowel duration, vowel space, and several different measures of dynamic formant movement. Perceptual data consist of vowel intelligibility in noise as reflected by the performance of young normal-hearing and elderly hearing-impaired listeners. Analyses will explore the relative importance of the various clear speech acoustic changes to the clear speech vowel intelligibility effect as well as the degree to which this relationship varies between the two listener groups.

Bone-Conduction Sensitivity along with Static Force, Location, and Stimulus

This study sought to estimate bone-conducted hearing sensitivity as static force levels of the oscillator as well as identify the most sensitive bone-conducted location on the human head when stimulated by tone and speech stimuli. In Experiment I, 24 young normal hearing listeners responded to bone-conducted thresholds ranging from 250 to 8,000 Hz in three placement locations: the forehead and the left and right mastoids. At each location and across all participants, the static force applied to various forces related to the individual’s head size (i.e., Hooke’s raw). The results of this experiment indicated that increased static force would not significantly cause more sensitive (or lower) thresholds. Thresholds of the forehead placement were less sensitive than both mastoids. Experiment II involved 24 young normal hearing listeners to determine the bone-conducted hearing thresholds at five placements (i.e., condyle, jaw angle, mastoid, temple, vertex) of the head, using tones ranging from 500 to 6,000 Hz and spondee words. The results indicated that the condyle and vertex are the most and least sensitive placements, respectively, regardless of tone and speech stimuli. Such information may be extended to future series of studies related to develop effective bone-conduction communication devices under harmful noisy conditions as well as contribute to the development of a computational model of bone-conducted sound transmission pathways in the human skull.

Effect of Speech Degradation on Top-Down Repair: Phonemic Restoration with Simulations of Cochlear Implants and Combined Electric–Acoustic Stimulation

The brain, using expectations, linguistic knowledge, and context, can perceptually restore inaudible portions of speech. Such top-down repair is thought to enhance speech intelligibility in noisy environments. Hearing-impaired listeners with cochlear implants commonly complain about not understanding speech in noise. We hypothesized that the degradations in the bottom-up speech signals due to the implant signal processing may have a negative effect on the top-down repair mechanisms, which could partially be responsible for this complaint. To test the hypothesis, phonemic restoration of interrupted sentences was measured with young normal-hearing listeners using a noise-band vocoder simulation of implant processing. Decreasing the spectral resolution (by reducing the number of vocoder processing channels from 32 to 4) systematically degraded the speech stimuli. Supporting the hypothesis, the size of the restoration benefit varied as a function of spectral resolution. A significant benefit was observed only at the highest spectral resolution of 32 channels. With eight channels, which resembles the resolution available to most implant users, there was no significant restoration effect. Combined electric–acoustic hearing has been previously shown to provide better intelligibility of speech in adverse listening environments. In a second configuration, combined electric–acoustic hearing was simulated by adding low-pass-filtered acoustic speech to the vocoder processing. There was a slight improvement in phonemic restoration compared to the first configuration; the restoration benefit was observed at spectral resolutions of both 16 and 32 channels. However, the restoration was not observed at lower spectral resolutions (four or eight channels). Overall, the findings imply that the degradations in the bottom-up signals alone (such as occurs in cochlear implants) may reduce the top-down restoration of speech.

Effect of Speech Material on the Benefit of Temporal Fine Structure Information in Speech for Young Normal-Hearing and Older Hearing-Impaired Participants

The purpose of this study was to investigate the influence of the type of speech material on the benefit obtained from temporal fine structure (TFS) information in speech for young normal-hearing (YNH) and older hearing-impaired (OHI) participants. The design was based on the work of . They measured the speech reception thresholds for a target talker in a background talker as a function of the frequency range over which TFS information was available. The signal was split into 32 channels, each with a bandwidth equal to the equivalent rectangular bandwidth of the "normal" auditory filter at the same center frequency. Above a cutoff (CO) channel, channels were vocoded and contained only temporal envelope information. Channels up to and including CO were not processed. Hopkins et al. found that, as CO was increased, speech reception thresholds decreased more for normal-hearing participants than for participants with cochlear hearing loss, suggesting that the latter were less able to use TFS information. We used the same design, but compared results when the target speech materials were open-set sentences, as used by Hopkins et al., and when they were more predictable sentences with a closed word set (Danish Dantale 2). With the open-set material, YNH listeners benefited more from TFS information than OHI listeners, replicating . For the YNH participants, the benefit of adding TFS was greater for the open-set material than for the closed-set material, while no difference in TFS benefit across speech materials was found for the OHI participants. The choice of speech material is important when assessing the benefit of TFS. Several factors may facilitate recognition in the absence of TFS cues, including small set size, predictable temporal structure of the target speech, and contextual effects. We speculate that TFS information is useful for reducing informational masking, by providing cues for the perceptual segregation of the target and background. When the target speech is highly predictable, informational masking may be minimal, rendering TFS cues unnecessary.

The role of context in the perception of environmental sounds

Past work has shown involvement of context in the perception of sequences of meaningful speech sounds. The present study extended investigation to meaningful environmental sounds, evaluating the accuracy in identifying individual sources in sequences of five environmental sounds that were either likely or not to have occurred together in place and time. Rating of sequence coherence confirmed the subjective distinction between sequence types. In the main task, young normal-hearing listeners were instructed to identify and order each sound they heard by selecting from among 20 randomly selected labels. Listeners were significantly more accurate in reporting both the names and order of the sounds of the coherent sequences in which sounds were more likely to have occurred together. If not scored in terms of source order, a smaller but still significant difference was obtained between coherent and incoherent sequences. For both sequence types, there was a trend for best performance for the initial and final sources of the sequences. Overall, results are consistent with speech findings and demonstrate a positive effect of context in the perceptual processing of environmental sounds. [Work supported by NIH/NIDCD.]

The usefulness of the modified nonsense syllable test as a measure of speech identification

The NST is a standardized speech-identification test involving closed-set identification of nonsense syllables. Its organization permits speech-identification testing with a variety of consonants and vowel contexts, but its usefulness is limited by the long time it takes to administer and the limited confusion matrices that can be generated. A modified version of the NST (MNST) was developed by Gelfand et al. (1992). They reported data on young normal-hearing listeners at presentation levels ranging from 20 dB to 52 dB SPL in quiet and in noise. A previous study extended the work of Gelfand et al. (1992) to higher presentation levels more suited for older and/or hearing impaired listeners. This work indicated that the MNST is a potentially useful measure of nonsense syllable identification. A significant advantage of the MNST is that it allows detailed analyses of consonant confusions among all the test consonants while reducing the test time greatly. The present work describes the confusion matrices of the two subsets of the MNST for a group of young normal-hearing listeners. This work further validates the MNST and its usefulness as a tool for measuring speech-identification scores and generating detailed consonant confusion matrices in a relatively short amount of time. The above work was supported in part by NIH NIDCD 5R03DC10266-2 awarded to the first author.

Effects of age and hearing loss on the recognition of interrupted words in isolation and in sentences

The ability to recognize spoken words interrupted by silence was investigated with young normal-hearing listeners and older listeners with and without hearing impairment. Target words from the revised SPIN test by Bilger et al. [J. Speech Hear. Res. 27(1), 32-48 (1984)] were presented in isolation and in the original sentence context using a range of interruption patterns in which portions of speech were replaced with silence. The number of auditory "glimpses" of speech and the glimpse proportion (total duration glimpsed/word duration) were varied using a subset of the SPIN target words that ranged in duration from 300 to 600 ms. The words were presented in isolation, in the context of low-predictability (LP) sentences, and in high-predictability (HP) sentences. The glimpse proportion was found to have a strong influence on word recognition, with relatively little influence of the number of glimpses, glimpse duration, or glimpse rate. Although older listeners tended to recognize fewer interrupted words, there was considerable overlap in recognition scores across listener groups in all conditions, and all groups were affected by interruption parameters and context in much the same way.

Effects of low-pass filtering on intelligibility of periodically interrupted speech

The combined effect of low-pass filtering (cut-off frequencies between 500 and 3000 Hz) and periodic interruptions (1.5 and 10 Hz) on speech intelligibility was investigated. When combined, intelligibility was lower than each manipulation alone, even in some conditions where there was no effect from a single manipulation (such as the fast interruption rate of 10 Hz). By using young normal-hearing listeners, potential suprathreshold deficits and aging effects that may occur due to hearing impairment were eliminated. Thus, the results imply that reduced audibility of high-frequency speech components may partially explain the reduced intelligibility of interrupted speech in hearing impaired persons.

Slow Cortical Potentials and Amplification—Part I: N1-P2 Measures

Slow cortical potentials (SCPs) are currently of great interest in the hearing aid fitting process for infants; however, there is conflicting evidence in the literature concerning the use of SCPs for this purpose. The current study investigated SCP amplitudes and latencies in young normal-hearing listeners in response to a 60 ms duration tonal stimulus (1000 Hz) presented at three intensities (30, 50, and 70 dB SPL) in aided and unaided conditions using three hearing aids (Analog, DigitalA, and DigitalB) with two gain settings (20 and 40 dB). Results showed that SCP amplitudes were smaller for the digital hearing aids compared with the analog hearing aid, and none of the hearing aids resulted in a reliable increase in response amplitude relative to the unaided across conditions. SCP latencies in analog conditions were not significantly different from latencies in the unaided conditions; however, both digital hearing aids resulted in significantly delayed SCP latencies. The results of the current study (as well as several previous studies) indicate that the SCP may not accurately reflect the amplified stimulus expected from the prescribed hearing aids. Thus, “aided-SCP” results must be interpreted with caution, and more research is required concerning possible clinical use of this technique.

Effects of talker gender and spatial location on sentence recognition for young and old listeners with normal hearing

This study aimed to determine the effect of gender and spatial difference between two talkers on the sentence recognition of young and old listeners with normal hearing. Gender difference was manipulated using gender-matched (i.e., male-male or female-female) or gender-mismatched (i.e., male-female or female-male) sentence pairs. Four spatial separation conditions (-45/45°, -90/90°, -135/135°, 180° azimuth) were presented through eight directional speakers. The ability of sentence recognition was identified by key word scoring. Overall, young normal-hearing (YNH) listeners performed better than old normal-hearing listeners (ONH) in all conditions. The gender mismatch between two talkers was beneficial to recognize closed-set sentences by creating the release from informational masking, more for the ONH group compared to the YNH group. The effect of spatial separation was not significant in both groups. Year of education for ONH listeners significantly affected their two-talker speech recognition. Results of individual differences in ONH listeners suggest that the ability to use acoustic cues given by gender and spatial difference between two competing talkers appears to be related to their cognitive ability.

Contributions of static and dynamic spectral cues to vowel identification by cochlear implant users

Relatively little is known about cochlear implant (CI) users' ability to make use of static versus dynamic spectral cues in vowel perception tasks. The present study measured vowel identification in CI users and young normal hearing (YNH) listeners using naturally produced /dVd/ stimuli (deed, did, Dade, dead, dad, dud, and Dodd). Vowel identifcation was tested for (1) the unmodified syllables, (2) syllables modified to retain only 60 or 80 ms of the vowel center (center-only conditions), and (3) syllables modified to retain only 30 or 40 ms of the initial and final vowel transitions, with vowel duration neutralized (edges-only conditions). YNH listeners achieved high levels of performance for the unmodified stimuli (avg. 99.8%) and for the center-only stimuli (90.8%); their performance dropped to more moderate levels (68.1%) for the edges-only stimuli. CI users demonstrated moderate performance for the unmodified stimuli (avg. 72.0%) but demonstrated substantially poorer performance for both the center-only (41.1%) and edges-only stimuli (27.8%). Findings suggest that CI users (1) have difficulty identifying vowels in syllables when one or more cues are absent and (2) rely more strongly on quasi-static cues from the vowel center as compared to dynamic cues at the syllable edges.

Envelope and temporal fine structure perceptual weights for sentences: Effect of age, hearing loss, and amplification

The speech signal may be divided into spectral frequency bands, each band containing temporal properties of the envelope and fine structure. This study measured the perceptual weighting strategies for the envelope and fine structure in each of three frequency bands for sentence materials in young normal-hearing listeners, older normal-hearing listeners, aided older hearing-impaired listeners, and noise-matched young normal-hearing listeners. A novel processing method was designed to vary the availability of each acoustic property independently through noisy signal extraction. Thus, the full speech stimulus was presented with noise used to mask the different auditory channels. Perceptual weights were determined by correlating a listener's performance with the signal-to-noise ratio of each acoustic property on a trial-by-trial basis. Preliminary results demonstrate that fine structure perceptual weights remain stable across the four listener groups. However, a different weighting typography was observed between the listener groups for envelope cues. Preliminary results suggest that spectral shaping used to preserve the audibility of the speech stimulus may alter the allocation of perceptual resources. The relative perceptual weighting of envelope cues may also change with age. These effects were largely limited to envelope weights. [Work supported by NIA R01 AG008293.]

Some normative data on lip-reading skills (L)

The ability to obtain reliable phonetic information from a talker's face during speech perception is an important skill. However, lip-reading abilities vary considerably across individuals. There is currently a lack of normative data on lip-reading abilities in young normal-hearing listeners. This letter describes results obtained from a visual-only sentence recognition experiment using CUNY sentences and provides the mean number of words correct and the standard deviation for different sentence lengths. Additionally, the method for calculating T-scores is provided to facilitate the conversion between raw and standardized scores. This metric can be utilized by clinicians and researchers in lip-reading studies. This statistic provides a useful benchmark for determining whether an individual's lip-reading score falls within the normal range, or whether it is above or below this range.