Neural correlates of lexical-tone and vowel-quality processing in 6- and 9-month-old German-learning infants and adults.

We examined the neurophysiological underpinnings of lexical-tone and vowel-quality perception in learners of a non-tonal language. We tested 25 6- and 25 9-month-old German-learning infants, as well as 24 German adults and expected developmental differences for the two linguistic properties, as they are both carried by vowels, but have a different status in German. In adults, both lexical-tone and vowel-quality contrasts elicited mismatch negativities, with a stronger response to the vowel-quality contrast. Six-month-olds showed positive mismatch responses for lexical-tone and vowel-quality contrasts, with an emerging negative mismatch response for vowel-quality only. The negative mismatch responses became more pronounced for the vowel-quality contrast at 9 months, while the lexical-tone contrast elicited mainly positive mismatch responses. Our data reveal differential developmental changes in the processing of vowel properties that differ in their lexical relevance in the ambient language.

Asymmetries in Infants' Vowel Perception: Changes in Vowel Discrimination in German Learning 6- and 9-Month-Old Infants.

Infants' speech perception is characterized by substantial changes during the first year of life that attune the processing mechanisms to the specific properties of the ambient language. This paper focuses on these developmental changes in vowel perception. More specifically, the emergence and potential cause of perceptual asymmetries in vowel perception are investigated by an experimental study on German 6- and 9-month-olds' discrimination of a vowel contrast that is not phonemic in German. Results show discrimination without any asymmetry in the 6-month-olds but an asymmetrical pattern with better performance when the vowel changes from the less focal to the more focal vowel than vice versa by the 9-month-olds. The results concerning the asymmetries are compatible with the Natural Referent Framework as well as with the Native Language Magnet model. Our results foster two main conclusions. First, bi-directional testing must be mandatory when testing vowel perception. Second, when testing non-native vowel perception, the relation of the stimuli to the native language vowel system has to be considered very carefully as this system impacts the perception of non-native vowels.

English Vowel Discrimination and Perceptual Assimilation by Japanese Listeners.

This study examined whether the discrimination accuracy of nonnative vowels could be predicted by how listeners assimilate nonnative phones into their L1. The results demonstrated that Japanese listeners discriminated between English /æ/ and /ʌ/ better than they did between /ɑ/ and /ʌ/, although they categorized all those stimuli as the Japanese /a/. Given that the acoustic distance between stimuli was controlled to be identical, this result was attributed not to the acoustic difference but to the category-goodness difference. The goodness-of-fit to the Japanese /a/ phoneme differed between the English /æ/ and /ʌ/ but not between the English /ɑ/ and /ʌ/, suggesting that it is more difficult to discriminate between vowels when the category-goodness difference between two nonnative stimuli is smaller. In addition, this study examined the relationship between perceptual assimilation and the focalization effect. Focalization affects directional asymmetry in a manner that renders detecting a sound change from a more-focal to a less-focal vowel more difficult than detecting a change in the opposite direction. The results demonstrated that this directional asymmetry is only observed when listeners assimilate two nonnative phones into a single L1 phonemic category, with no category-goodness difference between the two nonnative phones.

Vowel-internal cues to vowel quality and prominence in speech perception.

This study examines how variation in F0 and intensity impacts the perception of American English vowels. Both properties vary intrinsically as a function of vowel features in the speech production literature, raising the question of the perceptual impact of each. In addition to considering listeners' interpretation of either cue as an intrinsic property of the vowel, the possible prominence-marking function of each is considered. Two patterns of prominence strengthening in vowels, sonority expansion and hyperarticulation, are tested in light of recent findings that contextual prominence impacts vowel perception in line with these effects (i.e. a prominent vowel is expected by listeners to be realized as if it had undergone prominence strengthening). Across four vowel contrasts with different height and frontness features, listeners categorized phonetic continua with variation in formants, F0 and intensity. Results show that variation in level F0 height is interpreted as an intrinsic cue by listeners. Higher F0 cues a higher vowel, following intrinsic F0 effects in the production literature. In comparison, intensity is interpreted as a prominence-lending cue, for which effect directionality is dependent on vowel height. Higher intensity high vowels undergo perceptual re-calibration in line with (acoustic) hyperarticulation, whereas higher intensity non-high vowels undergo perceptual re-calibration in line with sonority expansion.

Individual differences in attention control and the processing of phonological contrasts in a second language.

This study investigated attention control in L2 phonological processing from a cognitive individual differences perspective, to determine its role in predicting phonological acquisition in adult L2 learning. Participants were 21 L1-Spanish learners of English, and 19 L1-English learners of Spanish. Attention control was measured through a novel speech-based attention-switching task. Phonological processing was assessed through a speeded ABX categorization task (perception) and a delayed sentence repetition task (production). Correlational analyses indicated that learners with more efficient attention switching skill and faster speed in correctly identifying the target phonetic features in the speech dimension under focus could perceptually discriminate L2 vowels at higher processing speed, but not at higher accuracy rates. Thus, attentional flexibility provided a processing advantage for difficult L2 contrasts but did not predict the extent to which precise representations for the target L2 vowels had been established. However, attention control was related to L2 learners' ability to distinguish the contrasting L2 vowels in production. In addition, L2 learners' accuracy in perceptually distinguishing between two contrasting vowels was significantly related to how much of a quality distinction between them they could make in production.

Neurophysiological Correlates of Asymmetries in Vowel Perception: An English-French Cross-Linguistic Event-Related Potential Study.

Behavioral studies examining vowel perception in infancy indicate that, for many vowel contrasts, the ease of discrimination changes depending on the order of stimulus presentation, regardless of the language from which the contrast is drawn and the ambient language that infants have experienced. By adulthood, linguistic experience has altered vowel perception; analogous asymmetries are observed for non-native contrasts but are mitigated for native contrasts. Although these directional effects are well documented behaviorally, the brain mechanisms underlying them are poorly understood. In the present study we begin to address this gap. We first review recent behavioral work which shows that vowel perception asymmetries derive from phonetic encoding strategies, rather than general auditory processes. Two existing theoretical models-the Natural Referent Vowel framework and the Native Language Magnet model-are invoked as a means of interpreting these findings. Then we present the results of a neurophysiological study which builds on this prior work. Using event-related brain potentials, we first measured and assessed the mismatch negativity response (MMN, a passive neurophysiological index of auditory change detection) in English and French native-speaking adults to synthetic vowels that either spanned two different phonetic categories (/y/vs./u/) or fell within the same category (/u/). Stimulus presentation was organized such that each vowel was presented as standard and as deviant in different blocks. The vowels were presented with a long (1,600-ms) inter-stimulus interval to restrict access to short-term memory traces and tap into a "phonetic mode" of processing. MMN analyses revealed weak asymmetry effects regardless of the (i) vowel contrast, (ii) language group, and (iii) MMN time window. Then, we conducted time-frequency analyses of the standard epochs for each vowel. In contrast to the MMN analysis, time-frequency analysis revealed significant differences in brain oscillations in the theta band (4-8 Hz), which have been linked to attention and processing efficiency. Collectively, these findings suggest that early-latency (pre-attentive) mismatch responses may not be a strong neurophysiological correlate of asymmetric behavioral vowel discrimination. Rather, asymmetries may reflect differences in neural processing efficiency for vowels with certain inherent acoustic-phonetic properties, as revealed by theta oscillatory activity.

Bilateral age-related atrophy in the planum temporale is associated with vowel discrimination difficulty in healthy older adults.

In this study we investigated the association between age-related brain atrophy and behavioural as well as electrophysiological markers of vowel perception in a sample of healthy younger and older adults with normal pure-tone hearing. Twenty-three older adults and 27 younger controls discriminated a set of vowels with altered second formants embedded in consonant-vowel syllables. Additionally, mismatch negativity (MMN) responses were recorded in a separate oddball paradigm with the same set of stimuli. A structural magnet resonance scan was obtained for each participant to determine cortical architecture of the left and right planum temporale (PT). The PT was chosen for its function as a major processor of auditory cues and speech. Results suggested that older adults performed worse in vowel discrimination despite normal-for-age pure-tone hearing. In the older group, we found evidence that those with greater age-related cortical atrophy (i.e., lower cortical surface area and cortical volume) in the left and right PT also showed weaker vowel discrimination. In comparison, we found a lateralized correlation in the younger group suggesting that those with greater cortical thickness in only the left PT performed weaker in the vowel discrimination task. We did not find any associations between macroanatomical traits of the PT and MMN responses. We conclude that deficient vowel processing is not only caused by pure-tone hearing loss but is also influenced by atrophy-related changes in the ageing auditory-related cortices. Furthermore, our results suggest that auditory processing might become more bilateral across the lifespan.

Cross-Linguistic Perceptual Categorization of the Three Corner Vowels: Effects of Listener Language and Talker Age.

The present study examined the center and size of naïve adult listeners' vowel perceptual space (VPS) in relation to listener language (LL) and talker age (TA). Adult listeners of three different first languages, American English, Greek, and Korean, categorized and rated the goodness of different vowels produced by 2-year-olds and 5-year-olds and adult speakers of those languages, and speakers of Cantonese and Japanese. The center (i.e., mean first and second formant frequencies (F1 and F2)) and size (i.e., area in the F1/F2 space) of VPSs that were categorized either into /a/, /i/, or /u/ were calculated for each LL and TA group. All center and size calculations were weighted by the goodness rating of each stimulus. The F1 and F2 values of the vowel category (VC) centers differed significantly by LL and TA. These effects were qualitatively different for the three vowel categories: English listeners had different /a/ and /u/ centers than Greek and Korean listeners. The size of VPSs did not differ significantly by LL, but did differ by TA and VCs: Greek and Korean listeners had larger vowel spaces when perceiving vowels produced by 2-year-olds than by 5-year-olds or adults, and English listeners had larger vowel spaces for /a/ than /i/ or /u/. Findings indicate that vowel perceptual categories of listeners varied by the nature of their native vowel system, and were sensitive to TA.

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.

Dogs perceive and spontaneously normalize formant-related speaker and vowel differences in human speech sounds.

Domesticated animals have been shown to recognize basic phonemic information from human speech sounds and to recognize familiar speakers from their voices. However, whether animals can spontaneously identify words across unfamiliar speakers (speaker normalization) or spontaneously discriminate between unfamiliar speakers across words remains to be investigated. Here, we assessed these abilities in domestic dogs using the habituation-dishabituation paradigm. We found that while dogs habituated to the presentation of a series of different short words from the same unfamiliar speaker, they significantly dishabituated to the presentation of a novel word from a new speaker of the same gender. This suggests that dogs spontaneously categorized the initial speaker across different words. Conversely, dogs who habituated to the same short word produced by different speakers of the same gender significantly dishabituated to a novel word, suggesting that they had spontaneously categorized the word across different speakers. Our results indicate that the ability to spontaneously recognize both the same phonemes across different speakers, and cues to identity across speech utterances from unfamiliar speakers, is present in domestic dogs and thus not a uniquely human trait.

[The development of vowel perception in pediatric cochlear implants of 1-3 years old].

Objective:To explore the early vowel perception development of pediatric cochlear implant（CI） of 1-3 years old. Method:A total of 123 children who had accepted cochlear implantation under 3 years old were analyzed retrospectively. According to the age of implantation, all participants were divided into two groups as 1 year old group（1-<2） and 2 years old group（2-<3）. The vowel perception of mandarin early speech perception（MESP） test scores at 12, 24, 36 momths after implantation as well as the trends in vowel perception between group 1 and normal hearing pediatrics of the same age were analyzed to research the development of vowel perception in pediatric cochlear implants and the effect of implanted age as well as physiological age. Result:The scores improved notably in two groups with the increase of physiological age（P<0.01）; The vowel perception of group 1 was significantly better than that of group 2（P<0.01）, However, there were great difference between group 1 and normal hearing pediatrics of the same age. Conclusion:With the increase of physiological age, the vowel perception would be improved correspondingly within 3 years of pediatric cochlear implants under the age of 3; However, the earlier the age of implant, the better the vowel perception is.

Perception of American-English Vowels by Early and Late Spanish-English Bilinguals.

Increasing numbers of Hispanic immigrants are entering the US and learning American-English (AE) as a second language (L2). Previous studies investigating the relationship between AE and Spanish vowels have revealed an advantage for early L2 learners for their accuracy of L2 vowel perception. Replicating and extending such previous research, this study examined the patterns with which early and late Spanish-English bilingual adults assimilated naturally-produced AE vowels to their native vowel inventory and the accuracy with which they discriminated the vowels. Twelve early Spanish-English bilingual, 12 late Spanish-English bilingual, and 10 monolingual listeners performed perceptual-assimilation and categorical-discrimination tasks involving AE /i,ɪ,ɛ,ʌ,æ,ɑ,o/. Early bilinguals demonstrated similar assimilation patterns to late bilinguals. Late bilinguals' discrimination was less accurate than early bilinguals' and AE monolinguals'. Certain contrasts, such as /æ-ɑ/, /ʌ-ɑ/, and /ʌ-æ/, were particularly difficult to discriminate for both bilingual groups. Consistent with previous research, findings suggest that early L2 learning heightens Spanish-English bilinguals' ability to perceive cross-language phonetic differences. However, even early bilinguals' native-vowel system continues to influence their L2 perception.

Perception of American English vowels by sequential Spanish-English bilinguals.

Research on American-English (AE) vowel perception by Spanish-English bilinguals has focused on the vowels /i/-/ɪ/ (e.g., in sheep/ship). Other AE vowel contrasts may present perceptual challenges for this population, especially those requiring both spectral and durational discrimination. We used Event-Related Potentials (ERPs), MMN (Mismatch Negativity) and P300, to index discrimination of AE vowels /ɑ/-/ʌ/ by sequential adult Spanish-English bilingual listeners compared to AE monolinguals. Listening tasks were non-attended and attended, and vowels were presented with natural and neutralized durations. Regardless of vowel duration, bilingual listeners showed no MMN to unattended sounds, and P300 responses were elicited to /ɑ/ but not /ʌ/ in the attended condition. Monolingual listeners showed pre-attentive discrimination (MMN) for /ɑ/ only; while both vowels elicited P300 responses when attended. Findings suggest that Spanish-English bilinguals recruit attentional and cognitive resources enabling native-like use of both spectral and durational cues to discriminate between AE vowels /ɑ/ and /ʌ/.

F2 slope as a Perceptual Cue for the Front-Back Contrast in Standard Southern British English.

Acoustic studies of several languages indicate that second-formant (F2) slopes in high vowels have opposing directions (independent of consonantal context): front [iː]-like vowels are produced with a rising F2 slope, whereas back [uː]-like vowels are produced with a falling F2 slope. The present study first reports acoustic measurements that confirm this pattern for the English variety of Standard Southern British English (SSBE), where /uː/ has shifted from the back to the front area of the vowel space and is now realized with higher midpoint F2 values than several decades ago. Subsequently, we test whether the direction of F2 slope also serves as a reliable cue to the /iː/-/uː/ contrast in perception. The findings show that F2 slope direction is used as a cue (additional to midpoint formant values) to distinguish /iː/ from /uː/ by both young and older Standard Southern British English listeners: an otherwise ambiguous token is identified as /iː/ if it has a rising F2 slope and as /uː/ if it has a falling F2 slope. Furthermore, our results indicate that listeners generalize their reliance on F2 slope to other contrasts, namely /ɛ/-/ɒ/ and /æ/-/ɒ/, even though F2 slope is not employed to differentiate these vowels in production. This suggests that in Standard Southern British English, a rising F2 seems to be perceptually associated with an abstract feature such as [+front], whereas a falling F2 with an abstract feature such as [-front].

Acoustic Properties Predict Perception of Unfamiliar Dutch Vowels by Adult Australian English and Peruvian Spanish Listeners.

Research suggests that the size of the second language (L2) vowel inventory relative to the native (L1) inventory may affect the discrimination and acquisition of L2 vowels. Models of non-native and L2 vowel perception stipulate that naïve listeners' non-native and L2 perceptual patterns may be predicted by the relationship in vowel inventory size between the L1 and the L2. Specifically, having a smaller L1 vowel inventory than the L2 impedes L2 vowel perception, while having a larger one often facilitates it. However, the Second Language Linguistic Perception (L2LP) model specifies that it is the L1-L2 acoustic relationships that predict non-native and L2 vowel perception, regardless of L1 vowel inventory. To test the effects of vowel inventory size vs. acoustic properties on non-native vowel perception, we compared XAB discrimination and categorization of five Dutch vowel contrasts between monolinguals whose L1 contains more (Australian English) or fewer (Peruvian Spanish) vowels than Dutch. No effect of language background was found, suggesting that L1 inventory size alone did not account for performance. Instead, participants in both language groups were more accurate in discriminating contrasts that were predicted to be perceptually easy based on L1-L2 acoustic relationships, and were less accurate for contrasts likewise predicted to be difficult. Further, cross-language discriminant analyses predicted listeners' categorization patterns which in turn predicted listeners' discrimination difficulty. Our results show that listeners with larger vowel inventories appear to activate multiple native categories as reflected in lower accuracy scores for some Dutch vowels, while listeners with a smaller vowel inventory seem to have higher accuracy scores for those same vowels. In line with the L2LP model, these findings demonstrate that L1-L2 acoustic relationships better predict non-native and L2 perceptual performance and that inventory size alone is not a good predictor for cross-language perceptual difficulties.

Categorization of Natural Whistled Vowels by Naïve Listeners of Different Language Background.

Whistled speech in a non-tonal language consists of the natural emulation of vocalic and consonantal qualities in a simple modulated whistled signal. This special speech register represents a natural telecommunication system that enables high levels of sentence intelligibility by trained speakers and is not directly intelligible to naïve listeners. Yet, it is easily learned by speakers of the language that is being whistled, as attested by the current efforts of the revitalization of whistled Spanish in the Canary Islands. To better understand the relation between whistled and spoken speech perception, we look herein at how Spanish, French, and Standard Chinese native speakers, knowing nothing about whistled speech, categorized four Spanish whistled vowels. The results show that the listeners categorized differently depending on their native language. The Standard Chinese speakers demonstrated the worst performance on this task but were still able to associate a tonal whistle to vowel categories. Spanish speakers were the most accurate, and both Spanish and French participants were able to categorize the four vowels, although not as accurately as an expert whistler. These results attest that whistled speech can be used as a natural laboratory to test the perceptual processes of language.

Auditory event-related responses to diphthongs in different attention conditions.

The modulation of auditory event-related potentials (ERP) by attention generally results in larger amplitudes when stimuli are attended. We measured the P1-N1-P2 acoustic change complex elicited with synthetic overt (second formant, F2Δ=1000Hz) and subtle (F2Δ=100Hz) diphthongs, while subjects (i) attended to the auditory stimuli, (ii) ignored the auditory stimuli and watched a film, and (iii) diverted their attention to a visual discrimination task. Responses elicited by diphthongs where F2 values rose and fell were found to be different and this precluded their combined analysis. Multivariate analysis of ERP components from the rising F2 changes showed main effects of attention on P2 amplitude and latency, and N1-P2 amplitude. P2 amplitude decreased by 40% between the attend and ignore conditions, and by 60% between the attend and divert conditions. The effect of diphthong magnitude was significant for components from a broader temporal window which included P1 latency and N1 amplitude. N1 latency did not vary between attention conditions, a finding that may be related to stimulation with a continuous vowel. These data show that a discernible P1-N1-P2 response can be observed to subtle vowel quality transitions, even when the attention of a subject is diverted to an unrelated visual task.

Effects of an Open Jaw Posture on Vowel Perception in the Aging Voice.

PURPOSE: This study aimed to verify through an auditory-perceptual approach, whether an "open jaw" posture would result in improved speech quality for older adults. METHODS: Forty normal-hearing listeners (20 males; 20 females) aged between 18 and 47 listened to vowel segments and performed two separate tasks: identifying vowels and comparing vowel clarity. Stimuli included vowels segmented from a sentence ("We saw two cars.") produced using a normal and an open jaw posture by 40 individuals aged between 30s and 80s. Three types of stimuli were presented: variable length and intensity, fixed length and variable intensity, and fixed length and normalized intensity. Mixed model analyses of variance were used to determine whether there was a jaw posture effect on the percentage of correct vowel identification. Chi-square tests were used to determine whether vowels produced with an open jaw posture were more likely to be identified as being "clearer." RESULTS: Open jaw posture resulted in higher rates of correct vowel identification, and vowels from contrast pairs were consistently judged as being "clearer" than vowels produced in normal jaw posture. Investigations on the effect of stimulus type revealed that the jaw-related improvement in speech quality was not solely due to an increase in intensity or length induced by an open jaw posture. CONCLUSIONS: Listeners assessing vowel identification and clarity in the aging voice were able to better differentiate among vowels spoken using an open jaw posture, and a greater number of vowels produced in an open jaw posture were perceived as sounding clearer.

Information theoretic evaluation of a noiseband-based cochlear implant simulator.

Noise-band vocoders are often used to simulate the signal processing algorithms used in cochlear implants (CIs), producing acoustic stimuli that may be presented to normal hearing (NH) subjects. Such evaluations may obviate the heterogeneity of CI user populations, achieving greater experimental control than when testing on CI subjects. However, it remains an open question whether advancements in algorithms developed on NH subjects using a simulator will necessarily improve performance in CI users. This study assessed the similarity in vowel identification of CI subjects and NH subjects using an 8-channel noise-band vocoder simulator configured to match input and output frequencies or to mimic output after a basalward shift of input frequencies. Under each stimulus condition, NH subjects performed the task both with and without feedback/training. Similarity of NH subjects to CI users was evaluated using correct identification rates and information theoretic approaches. Feedback/training produced higher rates of correct identification, as expected, but also resulted in error patterns that were closer to those of the CI users. Further evaluation remains necessary to determine how patterns of confusion at the token level are affected by the various parameters in CI simulators, providing insight into how a true CI simulation may be developed to facilitate more rapid prototyping and testing of novel CI signal processing and electrical stimulation strategies.