Presence Of Multi-talker Babble Research Articles

Are there binaural consequences of speech envelope enhancement?

Fluctuations in the amplitude envelope play a critical role in the spatial perception of sounds. For example, listeners place increased perceptual weight on binaural cues occurring at onsets, and the steepness of onset slopes can influence binaural sensitivity. For speech stimuli, we recently showed that the temporal weighting of binaural cues is non-uniform and depends in part on the detailed behavior or the envelope. Here, we examined the potential binaural consequences of two monaural speech enhancement strategies that operate by altering the speech envelope: consonant enhancement (CE) and envelope expansion (EE). While CE and EE improve speech intelligibility under certain conditions, their effect on binaural perception has not been considered. We measured sensitivity to interaural time differences (ITDs) carried by single-word stimuli that were either unprocessed or processed with CE/EE. Thresholds were measured in quiet, in the presence of multi-talker babble, or for a vocoded condition designed to limit the availability of fine-structure ITDs. For ten listeners with normal hearing, while sensitivity depended on the specific word token, there were no systematic effects of speech enhancement on ITD sensitivity. Ongoing work is considering supra-threshold binaural tasks and listeners with hearing loss who have reduced spatial sensitivity. [Work supported by NIDCD.]

Recognition of vocoded words and sentences in quiet and multi-talker babble with children and adults

A vocoder is used to simulate cochlear-implant sound processing in normal-hearing listeners. Typically, there is rapid improvement in vocoded speech recognition, but it is unclear if the improvement rate differs across age groups and speech materials. Children (8–10 years) and young adults (18–26 years) were trained and tested over 2 days (4 hours) on recognition of eight-channel noise-vocoded words and sentences, in quiet and in the presence of multi-talker babble at signal-to-noise ratios of 0, +5, and +10 dB. Children achieved poorer performance than adults in all conditions, for both word and sentence recognition. With training, vocoded speech recognition improvement rates were not significantly different between children and adults, suggesting that improvement in learning how to process speech cues degraded via vocoding is absent of developmental differences across these age groups and types of speech materials. Furthermore, this result confirms that the acutely measured age difference in vocoded speech recognition persists after extended training.

Tinnitus impairs segregation of competing speech in normal-hearing listeners

Many tinnitus patients report difficulties understanding speech in noise or competing talkers, despite having “normal” hearing in terms of audiometric thresholds. The interference caused by tinnitus is more likely central in origin. Release from informational masking (more central in origin) produced by competing speech may further illuminate central interference due to tinnitus. In the present study, masked speech understanding was measured in normal hearing listeners with or without tinnitus. Speech recognition thresholds were measured for target speech in the presence of multi-talker babble or competing speech. For competing speech, speech recognition thresholds were measured for different cue conditions (i.e., with and without target-masker sex differences and/or with and without spatial cues). The present data suggest that tinnitus negatively affected masked speech recognition even in individuals with no measurable hearing loss. Tinnitus severity appeared to especially limit listeners’ ability to segregate competing speech using talker sex differences. The data suggest that increased informational masking via lexical interference may tax tinnitus patients’ central auditory processing resources.

Effect of exceeding compliance voltage on speech perception in cochlear implants

ObjectivesIn cochlear implants, the maximum current I (Amperes) that can be delivered on a cochlear implant electrode is determined by V = I * R, where V = compliance voltage (Volts) and R = electrode impedance (Ohms). Generally, electrode impedances are measured during each clinical visit and are used to set electrical stimulation parameters in cochlear implants. However, electrode impedances can rise during the course of cochlear implant use and lead to electrical stimulation voltage requirements exceeding the maximum compliance voltage of the medical device. Electric stimulation requirements that exceed the compliance voltage lead to clipping of the biphasic electrical pulse (current going into the cochlea) and are known to adversely affect cochlear implant outcomes. DesignThirteen (11 unilateral and 2 bilateral) Advanced Bionics cochlear implant patients with a HiRes 90k™ cochlear implant participated in this study. Speech perception scores were measured using the patient's baseline clinical program with the most comfortable loudness levels (M-levels) and the following four test programs: (1) stimulation clipped at 15% below clinical M-levels (15%C) (2) stimulation clipped at 30% below clinical M-levels (30%C) (3) M-levels decreased by 15% (15%M) and (4) M-levels decreased by 30% (30%C). Speech perception scores were measured using AzBio sentences presented at 60 dB SPL in quiet and in the presence of multi-talker babble (+10 dB SNR). ResultsRelative to the clinical baseline program, speech perception scores with the four test programs decreased in both quiet and noisy listening conditions. In quiet, speech perception scores measured with the 30%M and 30%C programs were significantly (p < 0.001) poorer than the baseline program. No significant differences in speech perception scores were measured between the baseline and the 15%C or 15%M programs. In the noisy listening condition, speech perception scores were significantly poorer than the baseline program for the 15%C (p = 0.008), 30%C (p < 0.001), and 30%M (p < 0.001) programs. No significant differences in speech perception scores were obtained between the baseline and the 15%M program in the noisy listening condition. Speech perception scores measured with the 30%C program were significantly (p < 0.001) poorer than those with the 30%M program, suggesting that clipping was more detrimental than reducing electrical stimulation levels. ConclusionSmall amounts (15%) of clipping can significantly decrease speech perception in the presence of background noise. Large amounts (30%) of both clipping and M-level reduction may lead to significantly poorer speech perception in quiet and in background noise. The decrease in speech perception scores can most likely be attributed to reduced volume and poorer spectro-temporal representation. Therefore, it is important to establish comfortably loud electrical stimulation levels without exceeding the compliance voltage to maximize cochlear implant outcomes.

Variability of Electrolaryngeal Speech Intelligibility in Multitalker Babble.

Purpose The purpose of this study was to report the variability of electrolarynx (EL) users' speech intelligibility in quiet and in multitalker babble. Method Ten EL users (five Servox® Digital, five TruTone™) who were at least 2 years postlaryngectomy provided recordings of five sentences from the 1965 Revised List of Phonetically Balanced Sentences. Recordings were judged by two groups of naïve listeners in quiet and in the presence of multitalker babble. Fifteen listeners orthographically transcribed a total of 750 sentences containing 3,750 key words in quiet, and another 15 listeners orthographically transcribed the same sentences mixed with multitalker babble. Results Significant differences in speech intelligibility were observed between listening conditions; 17.9% more key words were correctly identified in quiet compared to multitalker babble. Significant differences in fundamental frequency (F0) standard deviation and range but not speech intelligibility were observed between EL device types. A positive correlation of moderate significance was observed between F0 standard deviation and intelligibility for TruTone users in multitalker babble. Conclusions Findings suggest that listeners are able to identify a significantly higher percentage of EL users' speech in quiet compared to multitalker babble, but a large variability in EL users' speech intelligibility exists. Continued investigation involving a larger number of EL users is necessary to confirm this study's findings. Future research should explore the relationships among F0 measures, speaker characteristics (e.g., rate of speech, articulatory precision), and speech intelligibility, in addition to improving alaryngeal rehabilitation training protocols for EL users.

Working Memory and Speech Comprehension in Older Adults With Hearing Impairment.

This study examined the relationship between working memory (WM) and speech comprehension in older adults with hearing impairment (HI). It was hypothesized that WM would explain significant variance in speech comprehension measured in multitalker babble (MTB). Twenty-four older (59-73 years) adults with sensorineural HI participated. WM capacity (WMC) was measured using 3 complex span tasks. Speech comprehension was assessed using multiple passages, and speech identification ability was measured using recall of sentence final-word and key words. Speech measures were performed in quiet and in the presence of MTB at + 5 dB signal-to-noise ratio. Results suggested that participants' speech identification was poorer in MTB, but their ability to comprehend discourse in MTB was at least as good as in quiet. WMC did not explain significant variance in speech comprehension before and after controlling for age and audibility. However, WMC explained significant variance in low-context sentence key words identification in MTB. These results suggest that WMC plays an important role in identifying low-context sentences in MTB, but not when comprehending semantically rich discourse passages. In general, data did not support individual variability in WMC as a factor that predicts speech comprehension ability in older adults with HI.

Temporal fine structure mediated recognition of speech in the presence of multitalker babble.

This experiment investigated the mechanisms of temporal fine structure (TFS) mediated speech recognition in multi-talker babble. The signal-to-noise ratio 50 (SNR-50) for naive-listeners was measured when the TFS was retained in its original form (ORIG-TFS), the TFS was time reversed (REV-TFS), and the TFS was replaced by noise (NO-TFS). The original envelope was unchanged. In the REV-TFS condition, periodicity cues for stream segregation were preserved, but envelope recovery was compromised. Both the mechanisms were compromised in the NO-TFS condition. The SNR-50 was lowest for ORIG-TFS followed by REV-TFS, which was lower than NO-TFS. Results suggest both stream segregation and envelope recovery aided TFS mediated speech recognition.

Release From Perceptual Masking for Children and Adults

The purpose of this study was to test the hypothesis that a carrier phrase can improve word recognition performance for both children and adults by providing an auditory grouping cue. It was hypothesized that the carrier phrase would benefit listeners under conditions in which they have difficulty in perceptually separating the target word from the competing background. To test this hypothesis, word recognition was examined for maskers that were believed to vary in their ability to create perceptual masking. In addition to determining the conditions under which a carrier-phrase benefit is obtained, age-related differences in both susceptibility to masking and carrier-phrase benefit were examined. Two experiments were conducted to characterize developmental effects in the ability to benefit from a carrier phrase (i.e., "say the word") before the target word. Using an open-set task, word recognition performance was measured for three listener age groups: 5- to 7-year-old children, 8- to 10-year-old children, and adults (18-30 years). For all experiments, target words were presented in each of two carrier-phrase conditions: (1) carrier-present and (2) carrier-absent. Across experiments, word recognition performance was assessed in the presence of multi-talker babble (Experiment 1), two-talker speech (Experiment 2), or speech-shaped noise (Experiment 2). Children's word recognition performance was generally poorer than that of adults for all three masker conditions. Differences between the two age groups of children were seen for both speech-shaped noise and multi-talker babble, with 5- to 7-year-olds performing more poorly than 8- to 10-year-olds. However, 5- to 7-year-olds and 8- to 10-year-olds performed similarly for the two-talker masker. Despite developmental effects in susceptibility to masking, both groups of children and adults showed a carrier-phrase benefit in multi-talker babble (Experiment 1) and in the two-talker masker (Experiment 2). The magnitude of the carrier-phrase benefit was similar for a given masker type across age groups, but the carrier-phrase benefit was greater in the presence of the two-talker masker than in multi-talker babble. Specifically, the children's average carrier-phrase benefit was 7.1% for multi-talker and 16.8% for the two-talker masker condition. No carrier-phrase benefit was observed for any age group in the presence of speech-shaped noise. Effects of auditory masking on word recognition performance were greater for children than for adults. The time course of development for susceptibility to masking seems to be more prolonged for a two-talker speech masker than for multi-talker babble or speech-shaped noise. Unique to the present study, this work suggests that a carrier phrase can provide an effective auditory grouping cue for both children and adults under conditions expected to produce substantial perceptual masking.

Lexical Neighborhood Density Effects on Spoken Word Recognition and Production in Healthy Aging

We examined the effects of lexical competition and word frequency on spoken word recognition and production in healthy aging. Older (n = 16) and younger adults (n = 21) heard and repeated meaningful English sentences presented in the presence of multitalker babble at two signal-to-noise ratios, +10 and -3 dB. Each sentence contained three keywords of high or low word frequency and phonological neighborhood density (ND). Both participant groups responded less accurately to high- than low-ND stimuli; response latencies (from stimulus offset to response onset) were longer for high- than low-ND sentences, whereas response durations-time from response onset to response offset-were longer for low- than high-ND stimuli. ND effects were strongest for older adults in the most difficult conditions, and ND effects in accuracy were related to inhibitory function. The results suggest that the sentence repetition task described here taps the effects of lexical competition in both perception and production and that these effects are similar across the life span, but that accuracy in the lexical discrimination process is affected by declining inhibitory function in older adults.

Effect of Release Time on Preferred Gain and Speech Acoustics

Eighteen experienced hearing aid users with mild to moderate sensorineural hearing loss were fit with a digital hearing instrument. An adaptive procedure was used to determine their preferred gain setting for continuous speech under six conditions. Release time (RT) was set to 40, 160, or 640 msec. A prerecorded speech stimulus was presented in quiet or in the presence of multitalker babble (10 dB signal-to-babble ratio); all other compression variables were fixed. Real-ear data obtained with settings for each condition suggest that RT did not affect gain preference; however, subjects preferred higher gain in the presence of the multitalker babble. The RMS amplitudes of 30 phonemic units were calculated using ear canal recordings of the speech stimulus for each subject in each condition. Altering RT resulted primarily in decreased amplitude with increased RT, but this effect was not predictable across listeners or conditions.

Recognition of speech produced in noise.

A two-part study examined recognition of speech produced in quiet and in noise by normal hearing adults. In Part I 5 women produced 50 sentences consisting of an ambiguous carrier phrase followed by a unique target word. These sentences were spoken in three environments: quiet, wide band noise (WBN), and meaningful multi-talker babble (MMB). The WBN and MMB competitors were presented through insert earphones at 80 dB SPL. For each talker, the mean vocal level, long-term average speech spectra, and mean word duration were calculated for the 50 target words produced in each speaking environment. Compared to quiet, the vocal levels produced in WBN and MMB increased an average of 14.5 dB. The increase in vocal level was characterized by increased spectral energy in the high frequencies. Word duration also increased an average of 77 ms in WBN and MMB relative to the quiet condition. In Part II, the sentences produced by one of the 5 talkers were presented to 30 adults in the presence of multi-talker babble under two conditions. Recognition was evaluated for each condition. In the first condition, the sentences produced in quiet and in noise were presented at equal signal-to-noise ratios (SNR(E)). This served to remove the vocal level differences between the speech samples. In the second condition, the vocal level differences were preserved (SNR(P)). For the SNR(E) condition, recognition of the speech produced in WBN and MMB was on average 15% higher than that for the speech produced in quiet. For the SNR(P) condition, recognition increased an average of 69% for these same speech samples relative to speech produced in quiet. In general, correlational analyses failed to show a direct relation between the acoustic properties measured in Part I and the recognition measures in Part II.