Concurrent Vowels Research Articles

Contribution of Temporal Fine Structure Cues to Concurrent Vowel Identification and Perception of Zebra Speech.

Introduction The limited access to temporal fine structure (TFS) cues is a reason for reduced speech-in-noise recognition in cochlear implant (CI) users. The CI signal processing schemes like electroacoustic stimulation (EAS) and fine structure processing (FSP) encode TFS in the low frequency whereas theoretical strategies such as frequency amplitude modulation encoder (FAME) encode TFS in all the bands. Objective The present study compared the effect of simulated CI signal processing schemes that either encode no TFS, TFS information in all bands, or TFS only in low-frequency bands on concurrent vowel identification (CVI) and Zebra speech perception (ZSP). Methods Temporal fine structure information was systematically manipulated using a 30-band sine-wave (SV) vocoder. The TFS was either absent (SV) or presented in all the bands as frequency modulations simulating the FAME algorithm or only in bands below 525 Hz to simulate EAS. Concurrent vowel identification and ZSP were measured under each condition in 15 adults with normal hearing. Results The CVI scores did not differ between the 3 schemes (F (2, 28) = 0.62, p = 0.55, η 2 p = 0.04). The effect of encoding TFS was observed for ZSP (F (2, 28) = 5.73, p = 0.008, η 2 p = 0.29). Perception of Zebra speech was significantly better with EAS and FAME than with SV. There was no significant difference in ZSP scores obtained with EAS and FAME ( p = 1.00) Conclusion For ZSP, the TFS cues from FAME and EAS resulted in equivalent improvements in performance compared to the SV scheme. The presence or absence of TFS did not affect the CVI scores.

Predicting Level-Dependent Changes in Concurrent Vowel Scores Using the 2D-CNN Models

Differences in fundamental frequencies (F0s) are an important cue for segregating multiple speakers. However, the ability to avail this cue for identification varies with sound levels. For different-and same-F0 conditions, the identification scores of both vowels increased from low- to mid-levels and then reduced at higher levels for younger adults with normal hearing (YNH). These subjects benefited from the F0 difference; however, this benefit varied across the levels. The current study aims to develop a deep-neural-network (DNN) model that can predict the level-dependent changes in concurrent-vowel scores for YNH subjects. This DNN-model includes two-dimensional convolutional neural networks (2D-CNNs) in parallel, with the same architecture, to predict the concurrent-vowel scores. The input layer was neural responses of the auditory-nerve model to concurrent vowels. The 2D-CNN models were trained and validated using the subsets of the concurrent vowels from 50, 65, and 75 dB SPL for both F0 conditions, using the batch gradient descent algorithm. The trained model was then fine-tuned with a single epoch. The 2D-CNN models were evaluated against vowel levels (25 to 85 dB SPL) and F0 conditions. Compared with previous models, the current model accurately predicts the level-dependent changes in concurrent vowel scores for different-and same-F0 conditions.

Level differences impact the fusion of concurrent vowels dissimilarly within versus across ears.

This study investigated how level differences affect the fusion and identification of dichotically and monaurally presented concurrent vowel pairs where the vowels differed in level by 0, 4, 8, or 12 dB. With dichotic presentation, there was minimal variation in fusion and identification-vowels were nearly always fused and were identified consistently across level differences. Conversely, with monaural presentation, fusion and identification varied systematically across level differences-with the more intense vowel dominating fused percepts. The dissimilar effect of level difference for dichotic versus monaural presentation may arise from differences in energetic masking and/or divergent mechanisms underlying sound segregation and integration.

Dominance patterns in concurrent vowel recognition

When hearers encounter multiple people speaking at the same, they can often pick out the speech of one person from the others, but the mechanisms which they use in their acoustic discrimination process are not fully understood. To look into vowel discrimination processes, this project entailed combining sound files of minimal pairs generated by synthetic speakers. As a point of departure from many similar experiments, these files were standardized for pitch and intensity. Participants were asked to select the word they heard from a list of four potential words that shared the same beginning and ending consonants, differing only in the vowel. Participants were significantly more likely to select a word if its vowel had a higher F1 than the F1 of the other vowel of the combined audio file. Higher F2 and F3 frequencies and greater movement of F1 also contributed to increased selection rates, although not as much as the F1 ratio. Participants were also asked to describe a subset of the combined sound files. That task showed similar dominance patterns, such that participants were often unaware of the presence of one of the concurrent vowels.

Comparing the Recognition of Stop Consonants in Persian Between Adults Aged 30-39 and 40-49 Years

Background and Objectives Due to the improvement of living conditions in recent decades, there is an important issue called quality of life (QoL). One of the important factors that affect the QoL is the ability to communicate with others. Everyday communication is usually interfered by noise. Consonants play an important role in understanding the meaning of words. Since stop consonants are dependent on the following vowels, they are more vulnerable to the masking effects of noise. The present study aims to evaluate the effect of age, signal-to-noise ratio (SNR), and concurrent vowels on the recognition of stop consonants in Persian. Subjects and Methods The present cross-sectional study was conducted on 60 adults with normal hearing in two age groups of 30-39 and 40-49 years. After the auditory and speech assessments, the recognition of stop consonants in the form of consonant-vowel-consonant syllables and in the presence of babble noise at three SNRs was compared between two age groups. Results The difference in the recognition score of stop consonants was significant between two age groups at the SNRs of 0, -5, and -10. There was also a significant difference between the two age groups regarding the recognition of stop consonants in the presence of some vowels at three SNRs. Conclusion With increasing age, the recognition ability of stop consonants in the presence of babble noises decreases. Increasing noise also reduces the recognition of stop consonants, especially those with some vowels.

Modeling Concurrent Vowel Scores Using the Time Delay Neural Network and Multitask Learning

The difference in fundamental frequency (F0) between vowels is a segregation cue for identifying concurrent vowels. Younger listeners with normal hearing (YNH) showed that the percent identification score of both vowels improved with increasing F0 difference and asymptoted at higher F0 difference. The current study developed a deep-neural-network model consisting of a time-delay neural network and multitask learning (TDNN-MTL) to predict the concurrent vowel scores. The input to the TDNN-MTL were temporal responses of concurrent vowels obtained using the auditory-nerve model. The TDNN-MTL was trained at a 3-Hz F0 difference until the score (80%) became closer to the YNH score (85%). The TDNN-MTL learned the formant coding and aided in the segregation of concurrent vowels into dominant and recessive vowels. The total weighted loss was tailored to mimic the dominant-recessive relationship of the YNH scores. The TDNN-MTL was tested against the other five F0 differences. The TDNN-MTL model scores of both vowels were successful in predicting the YNH scores. The chi-square tests revealed that the TDNN-MTL model scores correlated well with the YNH scores compared with other F0-segregation and multi-layer perceptron models. The TDNN-MTL also correctly predicted the one vowel identification scores and F0 benefit. These findings suggest that the trained TDNN-MTL accurately predicts the formant coding of the concurrent vowels across F0 differences, which aided in capturing the YNH scores. The TDNN-MTL can be extended to validate the behavioral studies on concurrent vowels obtained across acoustic (e.g., vowel duration and level) and auditory changes (e.g., aging and hearing loss).

Comparison of temporal fine structure sensitivity and concurrent vowel perception between children with and without reading disability

Background: Children with reading disabilities (RD) exhibit difficulty in perceiving speech in background noise due to poor auditory stream segregation. There is a dearth of literature on measures of temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities to assess auditory stream segregation in children with reading disabilities. Hence the present study compared temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities between children with and without reading deficits. Method: The present research consisted of a total number of 30 participants, 15 children with reading disabilities (RD) and fifteen typically developing (TD) children within the age range of 7-14 years and were designated as Group 1 and Group 2 respectively. Both groups were matched for age, grade, and classroom curricular instructions. The groups were evaluated for TFS and concurrent vowel perception abilities and the performance was compared using independent ‘t’ test and repeated measure ANOVA respectively. Results: Results revealed that the children with RD performed significantly (p < 0.001) poorer than TD children on both TFS and concurrent vowel identification task. On concurrent vowel identification tasks, there was no significant interaction found between reading ability and F0 difference suggesting that the trend was similar in both the groups. Conclusion: The study concludes that the children with RD show poor temporal fine structure sensitivity and concurrent vowel identification scores compared to age and grade matched TD children owing to poor auditory stream segregation in children with RD.

Comparison of temporal fine structure sensitivity and concurrent vowel perception between children with and without reading disability

Background: Children with reading disabilities (RD) exhibit difficulty in perceiving speech in background noise due to poor auditory stream segregation. There is a dearth of literature on measures of temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities to assess auditory stream segregation in children with reading disabilities. Hence the present study compared temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities between children with and without reading deficits. Method: The present research consisted of a total number of 30 participants, 15 children with reading disabilities (RD) and fifteen typically developing (TD) children within the age range of 7-14 years and were designated as Group 1 and Group 2 respectively. Both groups were matched for age, grade, and classroom curricular instructions. The groups were evaluated for TFS and concurrent vowel perception abilities and the performance was compared using independent ‘t’ test and repeated measure ANOVA respectively. Results: Results revealed that the children with RD performed significantly (p < 0.001) poorer than TD children on both TFS and concurrent vowel identification task. On concurrent vowel identification tasks, there was no significant interaction found between reading ability and F0 difference suggesting that the trend was similar in both the groups. Conclusion: The study concludes that the children with RD show poor temporal fine structure sensitivity and concurrent vowel identification scores compared to age and grade matched TD children owing to poor auditory stream segregation in children with RD.

Modeling the effects of age and hearing loss on concurrent vowel scores.

A difference in fundamental frequency (F0) between two vowels is an important segregation cue prior to identifying concurrent vowels. To understand the effects of this cue on identification due to age and hearing loss, Chintanpalli, Ahlstrom, and Dubno [(2016). J. Acoust. Soc. Am. 140, 4142-4153] collected concurrent vowel scores across F0 differences for younger adults with normal hearing (YNH), older adults with normal hearing (ONH), and older adults with hearing loss (OHI). The current modeling study predicts these concurrent vowel scores to understand age and hearing loss effects. The YNH model cascaded the temporal responses of an auditory-nerve model from Bruce, Efrani, and Zilany [(2018). Hear. Res. 360, 40-45] with a modified F0-guided segregation algorithm from Meddis and Hewitt [(1992). J. Acoust. Soc. Am. 91, 233-245] to predict concurrent vowel scores. The ONH model included endocochlear-potential loss, while the OHI model also included hair cell damage; however, both models incorporated cochlear synaptopathy, with a larger effect for OHI. Compared with the YNH model, concurrent vowel scores were reduced across F0 differences for ONH and OHI models, with the lowest scores for OHI. These patterns successfully captured the age and hearing loss effects in the concurrent-vowel data. The predictions suggest that the inability to utilize an F0-guided segregation cue, resulting from peripheral changes, may reduce scores for ONH and OHI listeners.

Comparison of temporal fine structure sensitivity and concurrent vowel perception between children with and without reading disability.

Background: Children with reading deficits (RD) exhibit difficulty in perceiving speech in background noise due to poor auditory stream segregation. There is a dearth of literature on measures of temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities to assess auditory stream segregation in children with reading deficits. Hence the present study compared temporal fine structure sensitivity (TFS) and concurrent vowel perception abilities between children with and without reading deficits. Method: The present research consisted of a total number of 30 participants, 15 children with reading deficits (RD) and fifteen typically developing (TD) children within the age range of 7-14 years and were designated as Group 1 and Group 2 respectively. Both groups were matched for age, grade, and classroom curricular instructions. The groups were evaluated for TFS and concurrent vowel perception abilities and the performance was compared using independent 't' test and repeated measure ANOVA respectively. Results: Results revealed that the children with RD performed significantly (p < 0.001) poorer than TD children on both TFS and concurrent vowel identification task. On concurrent vowel identification tasks, there was no significant interaction found between reading ability and F0 difference suggesting that the trend was similar in both the groups. Conclusion: The study concludes that the children with RD show poor temporal fine structure sensitivity and concurrent vowel identification scores compared to age and grade matched TD children owing to poor auditory stream segregation in children with RD.

Modeling concurrent vowel identification for shorter durations

Behavioral studies on concurrent vowels with shorter duration (50 ms) show that overall identification scores across fundamental frequency (F0) differences are reduced when compared to longer duration (200 ms). In this current study, we investigated the effect of shorter durations on concurrent vowel scores using the temporal responses of an auditory-nerve model (Zilany et al., 2014) with a modified version of the Meddis and Hewitt (1992) F0-guided vowel segregation algorithm. The F0 representations of 50 ms vowel pairs were reduced but could not fully account for reduced identification, suggesting a limited ability to avail an F0-guided vowel segregation cue. Thus, by limiting only this cue in the segregation algorithm for 200 ms, the model was qualitatively successful in capturing lower scores across F0 differences for 50 ms. This differential ability to utilize an F0-guided segregation cue might contribute to a variable F0 benefit across normal-hearing listeners. The model also predicted an improvement in identification scores of the second vowel of the pair, when the duration was increased from 50 ms to 200 ms. These model predictions suggest that the inability to utilize an F0-guided segregation cue at shorter durations can account for reduced concurrent vowel identification scores across F0 differences.

Infants' use of isolated and combined temporal cues in speech sound segregation.

This paper investigates infants' and adults' use of envelope cues and combined onset asynchrony and envelope cues in the segregation of concurrent vowels. Listeners heard superimposed vowel pairs consisting of two different vowels spoken by a male and a female talker and were trained to respond to one specific target vowel, either the male /u:/ or male /i:/. Vowel detection was measured in three conditions. In the baseline condition the two superimposed vowels had similar amplitude envelopes and synchronous onset. In the envelope cue condition, the amplitude envelopes of the two vowels differed. In the combined cue condition, both the onset time and amplitude envelopes of the two vowels differed. Seven-month-old infants' concurrent vowel segregation improved both with envelope and with combined onset asynchrony and envelope cues to the same extent as adults'. A preliminary investigation with 3-month-old infants suggested that neither envelope cues nor combined asynchrony and envelope cues improved their ability to detect the target vowel. Taken together, these results suggest that envelope and combined onset-asynchrony cues are available to infants as they attempt to process competing speech sounds, at least after 7 months of age.

Infants use onset asynchrony cues in auditory scene analysis.

This experiment investigated the effect of onset asynchrony on the segregation of concurrent vowels in infants and adults. Two vowels, randomly chosen from seven American-English vowels, were superimposed. Each vowel pair contained one vowel by a male and one by a female talker. A train of such vowel pairs was presented to listeners, who were trained to respond to the male target vowel /i:/ or /u:/. The ability to identify the target vowel was compared among three conditions: synchronous onset, 100-, and 200-ms onset asynchrony. Experiment 1 measured performance, in d', in 7-month-old infants and adults. Infants and adults performed better with asynchronous than synchronous vowel onset, regardless of asynchrony duration. Experiment 2 compared the proportion of 3-month-old infants achieving an 80% correct criterion with and without onset asynchrony. Significantly more infants reached criterion with asynchronous than with synchronous vowel onset. Asynchrony duration did not influence performance. These experiments show that infants, as young as 3 months old, benefit from onset asynchrony.

Revisiting Models of Concurrent Vowel Identification: The Critical Case of No Pitch Differences.

When presented with two vowels simultaneously, humans are often able to identify the constituent vowels. Computational models exist that simulate this ability, however they predict listener confusions poorly, particularly in the case where the two vowels have the same fundamental frequency. Presented here is a model that is uniquely able to predict the combined representation of concurrent vowels. The given model is able to predict listener's systematic perceptual decisions to a high degree of accuracy.

Infants' use of amplitude modulation cues in the segregation of concurrent vowels

Infants have difficulties separating speech from competing sounds. One explanation is that infants do not use acoustic cues to sound source segregation as adults do. This study investigated 3- and 7-month-old infants’ and adults’ ability to use AM cues in concurrent vowel segregation. Seven American-English vowels were produced by a male and by a female talker. One male and one female vowel were randomly chosen and superimposed. A train of such vowel pairs was presented to listeners, who were trained to respond to the male target vowel /i:/ or /u:/. Target-to-nontarget ratios were chosen to equate performance across age groups. In the baseline condition, all vowels had flat envelopes. In the cue condition, male vowels were modulated with three envelopes from infant-directed vowels. The proportion of 3-month-old infants achieving an 80% correct criterion at a ratio of + 15dB was higher in the cue than in the baseline condition. For 7-month olds and adults d' could be estimated based on 15 target and 15 nontarget trials in each condition. Preliminary results indicate that both 7-month-old infants and adults have a higher d' in the cue than in the baseline condition. Thus, infants appear to use AM to segregate concurrent vowels.

Effect of below-damage-risk criteria environmental noise on auditory perception and working memory

Background: The current research finding is the first in reporting impaired auditory and cognitive abilities consequent to chronic exposure to below-damage-risk criteria (DRC) environmental noise in humans. Objective: The objective of this study is to assess the chronic effects of occupational noise below DRC on auditory and cognitive abilities. Methods: A static-group comparison design was used, with three groups with varying levels of noise exposure below DRC. Shopkeepers working in busy areas exposed daily to environmental noise below DRC and shopkeepers working in quiet residential areas and college students in quiet environments. Speech perception in noise, acceptable noise levels, and concurrent vowel identification were used to assess auditory abilities, while Operation SPAN and Backward Digit Span were used to assess cognitive abilities. The data were analyzed using multivariate analysis of variance, Pearson's product-moment correlation, discriminant function analysis, and mediation analysis. Results: The results showed significantly poor auditory stream segregation abilities and working memory abilities in the shopkeepers exposed to environmental noise below DRC when compared to the other two groups with very low levels of occupational noise. The findings of the study are discussed in light of the deleterious effect of the supposedly safe (below DRC) levels of environmental noise on auditory and cognitive abilities. Conclusions: The novel results of affected auditory and cognitive abilities resulting from below-DRC occupational noise exposure as observed in the current study will have a great impact on the applicability to the general populace and also open up new avenues of research in ecological acoustics.

Noise and pitch interact during the cortical segregation of concurrent speech

Behavioral studies reveal listeners exploit intrinsic differences in voice fundamental frequency (F0) to segregate concurrent speech sounds—the so-called “F0-benefit.” More favorable signal-to-noise ratio (SNR) in the environment, an extrinsic acoustic factor, similarly benefits the parsing of simultaneous speech. Here, we examined the neurobiological substrates of these two cues in the perceptual segregation of concurrent speech mixtures. We recorded event-related brain potentials (ERPs) while listeners performed a speeded double-vowel identification task. Listeners heard two concurrent vowels whose F0 differed by zero or four semitones presented in either clean (no noise) or noise-degraded (+5 dB SNR) conditions. Behaviorally, listeners were more accurate in correctly identifying both vowels for larger F0 separations but F0-benefit was more pronounced at more favorable SNRs (i.e., pitch × SNR interaction). Analysis of the ERPs revealed that only the P2 wave (∼200 ms) showed a similar F0 x SNR interaction as behavior and was correlated with listeners' perceptual F0-benefit. Neural classifiers applied to the ERPs further suggested that speech sounds are segregated neurally within 200 ms based on SNR whereas segregation based on pitch occurs later in time (400–700 ms). The earlier timing of extrinsic SNR compared to intrinsic F0-based segregation implies that the cortical extraction of speech from noise is more efficient than differentiating speech based on pitch cues alone, which may recruit additional cortical processes. Findings indicate that noise and pitch differences interact relatively early in cerebral cortex and that the brain arrives at the identities of concurrent speech mixtures as early as ∼200 ms.

Infants' use of onset asynchrony in the segregation of concurrent vowels

Separating speech from competing speech is a difficult task for infants even though their ability to encode sounds appears to be mature. One possible explanation is that infants have greater difficulties extracting speech from the complex sound mixture arriving at their ears. Adults use acoustic cues such as differences in onset or harmonicity to group components that belong to the same sound source and separate those that do not. The sparse evidence on how infants segregate sounds indicates that they use some of these acoustic cues. However, temporal cues, which are strong cues for adults, have not been investigated in infants. This study examined infants’ ability to use onset asynchrony cues to separate simultaneous vowels using a single-interval observer-based procedure. Three- and seven-month-old infants and young adults were trained to identify one target vowel in a modified double-vowel paradigm. Listeners were tested in a simultaneous onset condition and either a 100 or 200 ms asynchrony condition. Cue benefit was defined as the improvement in sensitivity resulting from the addition of the asynchrony cue. Pilot data indicates that an onset asynchrony of 100ms improves performance for all age groups and that the cue benefit increases with age.

Effects of age and hearing loss on concurrent vowel identification.

Differences in formant frequencies and fundamental frequencies (F0) are important cues for segregating and identifying two simultaneous vowels. This study assessed age- and hearing-loss-related changes in the use of these cues for recognition of one or both vowels in a pair and determined differences related to vowel identity and specific vowel pairings. Younger adults with normal hearing, older adults with normal hearing, and older adults with hearing loss listened to different-vowel and identical-vowel pairs that varied in F0 differences. Identification of both vowels as a function of F0 difference revealed that increased age affects the use of F0 and formant difference cues for different-vowel pairs. Hearing loss further reduced the use of these cues, which was not attributable to lower vowel sensation levels. High scores for one vowel in the pair and no effect of F0 differences suggested that F0 cues are important only for identifying both vowels. In contrast to mean scores, widely varying differences in effects of F0 cues, age, and hearing loss were observed for particular vowels and vowel pairings. These variations in identification of vowel pairs were not explained by acoustical models based on the location and level of formants within the two vowels.

Neural Representation of Concurrent Vowels in Macaque Primary Auditory Cortex.

Successful speech perception in real-world environments requires that the auditory system segregate competing voices that overlap in frequency and time into separate streams. Vowels are major constituents of speech and are comprised of frequencies (harmonics) that are integer multiples of a common fundamental frequency (F0). The pitch and identity of a vowel are determined by its F0 and spectral envelope (formant structure), respectively. When two spectrally overlapping vowels differing in F0 are presented concurrently, they can be readily perceived as two separate “auditory objects” with pitches at their respective F0s. A difference in pitch between two simultaneous vowels provides a powerful cue for their segregation, which in turn, facilitates their individual identification. The neural mechanisms underlying the segregation of concurrent vowels based on pitch differences are poorly understood. Here, we examine neural population responses in macaque primary auditory cortex (A1) to single and double concurrent vowels (/a/ and /i/) that differ in F0 such that they are heard as two separate auditory objects with distinct pitches. We find that neural population responses in A1 can resolve, via a rate-place code, lower harmonics of both single and double concurrent vowels. Furthermore, we show that the formant structures, and hence the identities, of single vowels can be reliably recovered from the neural representation of double concurrent vowels. We conclude that A1 contains sufficient spectral information to enable concurrent vowel segregation and identification by downstream cortical areas.