Phonetic enhancement of sibilants in infant-directed speech

The hypothesis that vocalic categories are enhanced in infant-directed speech (IDS) has received a great deal of attention and support. In contrast, work focusing on the acoustic implementation of consonantal categories has been scarce, and positive, negative, and null results have been reported. However, interpreting this mixed evidence is complicated by the facts that the definition of phonetic enhancement varies across articles, that small and heterogeneous groups have been studied across experiments, and further that the categories chosen are likely affected by other characteristics of IDS. Here, an analysis of the English sibilants /s/ and /ʃ/ in a large corpus of caregivers’ speech to another adult and to their infant suggests that consonantal categories are indeed enhanced, even after controlling for typical IDS prosodic characteristics

Neural mechanisms of foreign language phoneme acquisition in early adulthood : MEG study

Tämän tutkimuksen tavoitteena on selvittää omaan äidinkieleen kuulumattomien foneemikontrastien oppimisen mekanismeja nuorilla aikuisilla neurofysiologisten ja behavioraalisten menetelmien avulla. Perinteisesti kielen foneettisen avaruuden omaksumisen on ajateltu tapahtuvan ensisijaisesti varhaislapsuuden kielellisten herkkyyskausien aikana, jonka jälkeen uusien foneemien oppiminen on haastavaa. Myöhemmät tutkimukset ovat kuitenkin osoittaneet, että vieraiden foneemien omaksuminen on mahdollista myös aikuisiällä. Uusien foneemikategorioiden muodostuminen vaatii aivoissa solutason plastisia muutoksia. Aivojen kykyä erotella läheisesti toisiaan muistuttavia foneemikategorioita kielenprosessoinnin varhaisella tasolla on tutkittu neurofysiologisin menetelmin esimerkiksi tapahtumasidonnaisen poikkeavuusnegatiivisuusvasteen (eng. mismatch negativity, MMN) avulla. MMN-vaste, tai sen magneettinen vastine MMNm, syntyy seurauksena muutoksiin sensorisessa havaintoympäristössä. Tutkimuksissa lyhyenkin auditiivisen harjoittelujakson on havaittu vahvistavan aivojen kykyä erotella läheisesti toisiaan muistuttavia vieraita foneemeja ja voimistavan MMN- ja MMNm-vasteita. Tässä tutkimuksessa vieraan kielen foneettisen oppimisen neuraalista perustaa ja oppimisen aiheuttamia plastisia muutoksia aivoissa tutkittiin magnetoenkefalografialla (MEG) neuromagneettisten tapahtumasidonnaisten vasteiden (erityisesti MMNm) avulla. Tutkimuksessa mitattiin 20 suomalaista koehenkilöä, joiden tehtävänä oli oppia erottelemaan akustisesti toisiaan läheisesti muistuttavia venäjän kielen frikatiiveja Ш /ʂ/ ja Щ /ɕ(ː)/. Erottelukykyä mitattiin ensin behavioraalisella tehtävällä, jossa koehenkilöille toistettiin nauhoitettuja venäjänkielisiä epäsanaminimipareja, jossa sanan ensimmäistä foneemia varioitiin. Koehenkilöiden tehtävänä oli vastata, kuulivatko he sanoissa eroa. Samoja kuuloärsykkeitä toistettiin koehenkilöille sen jälkeen passiivisessa MEG-tehtävässä, jossa testattiin aivojen kykyä havaita ero ärsykkeissä ilman, että niihin kiinnitetään huomiota (koehenkilöt katselivat samalla äänetöntä elokuvaa). Mittauksen jälkeen koehenkilöt harjoittelivat foneemien erottelua kotona noin viikon ajan tietokoneavusteisen oppimispelin avulla, jonka jälkeen heidät mitattiin uudelleen. MEG-signaalien lähdemallinnusta varten koehenkilöiden aivoista otettiin myös rakenteelliset magneettikuvat. Tutkittavien foneemien behavioraalinen erottelukyky oli selvästi tuttuja kontrollifoneemeita heikompaa. Erottelukyky vaikutti paranevan harjoittelun seurauksena hieman, mutta ero ei ollut tilastollisesti merkitsevä. Hypoteesien vastaisesti tilastollisesti merkitseviä MMNm-vasteita ei löydetty ennen eikä jälkeen harjoittelun, eikä muissakaan auditorisissa MEG-vasteissa tai niiden neuraalisten lähdevirtojen voimakkuuksissa tai jakaumassa ollut tilastollisesti merkitsevää eroa mittauskertojen välillä. Yksilölliset erot oppimisessa olivat kuitenkin suuria. Koehenkilöillä, joilla behavioraalinen erottelukyky parani harjoittelun myötä, oli silmämääräisesti havaittavissa hypoteesien mukaista vahvistumista auditorisissa vasteissa. Vaikka efekti oli erittäin pieni eikä tilastollisesti merkitsevä, vastaavaa ei havaittu epäoppijoilla eikä kontrollitilanteessa. Tässä tutkimuksessa ei kyetty replikoimaan aiempien tutkimusten tuloksia foneemien omaksumisesta aikuisiällä. Vaikka on todennäköistä, että tietyt metodologiset heikkoudet (mm. vähäinen ärsykkeiden määrä MEG-tehtävässä, haastavat ärsykkeet) vaikuttivat tulosten merkitsevyyteen, voidaan tämän tutkimuksen valossa aiempien tutkimustulosten yleistettävyyttä kyseenalaistaa.The aim of this study is to examine the learning mechanisms and acquisition of non-native phoneme contrasts in young adults using neurophysiological and behavioral methods. According to the traditional view, acquiring novel phonemes after the sensitive periods in the early childhood is very difficult. However, later findings have shown that foreign phoneme contrasts can be learned at a later age, too. Acquiring new phonemic categories requires neuroplastic changes in the brain. Neurophysiological studies have examined the brain’s ability to differentiate between closely related phonemic categories at the early stage of spoken language processing by measuring, for example, event-related mismatch negativity responses (MMN). MMN, or its magnetic equivalent MMNm, is elicited when the brain registers a difference in a repetitive sensory stimulus. Studies have shown that even a moderate amount of auditory training with closely related foreign phonemes improves the brain’s ability to discriminate between them resulting in enhanced MMN or MMNm responses. In this experiment the neural mechanisms of foreign language phoneme acquisition and the learning-related neuroplastic changes were studied using magnetoencephalography (MEG) and neuromagnetic evoked responses (MMNm in particular). 20 Finnish subjects were measured in the experiment. Their task was to learn to differentiate between acoustically closely related Russian fricatives Ш /ʂ/ and Щ /ɕ(ː)/. The subjects’ differentiation skills were first tested in a behavioral task where Russian pseudoword minimal pairs were presented to them auditorily. The first phoneme in the word pairs was varied and the subjects had to report whether they heard a difference between the words or not. The same stimuli were then presented in a passive MEG task where the brain’s change detection responses were tested in an unattended situation as the subjects were watching a silent film. After the measurement the subjects practiced the phonemes at home for approximately one week by playing a learning game by computer. After training they were measured again. Structural magnetic resonance images of the subjects’ brain were also measured for MEG source localization purposes. Behavioral discrimination ability of the experimental phonemes was considerably worse than with familiar control phonemes. The discrimination skills seemed to improve by training, but the difference was not statistically significant. Contrary to the hypotheses, statistically significant MMNm responses were not found before or after training. No significant differences were found in other auditory MEG responses or their neural source current distributions between the measurements either. However, individual differences in learning were sizeable. For the subjects who improved their performance in the behavioral task a modest training-related boost in the auditory responses supporting the hypotheses could be observed. Although very small and statistically insignificant, the effect was opposite for control stimuli and did not exist in the non-learner group suggesting some sort of change in neural processing in the learner group. This study was not able to replicate the findings from various previous studies on phoneme acquisition in adulthood. Although it is likely that certain methodological limitations (e.g. small number of stimulus repetitions, challenging stimuli) affected the significance of the results, based on this study the generalizability of some of the previous findings can be called into question

Perception of voicing in English fricatives by Spanish listeners

Los contrastes fonémicos que no son funcionalmente distintivos en la lengua materna son difíciles de diferenciar para oyentes no nativos. En el presente trabajo se exponen los resultados del segundo experimento de la investigación enfocada a analizar la percepción de contrastes no nativos por parte de 26 oyentes hispanohablantes, que se utilizaron como informantes. Un grupo de hablantes ingleses sirvió como el grupo de control. Los oyentes fueron expuestos al contraste inglés /s/ vs /z/, que no es fonémico en español, en dos palabras sintentizadas, Sue y zoo. Los resultados mostraron que parte de los oyentes habían adquirido el contraste; además, se apreciaron diferencias en el uso de ciertos índices acústicos que señalaban el contraste, posiblemente causadas por la influencia de la L1.Asimismo, los resultados no tuvieron correlación ni con la edad ni el tiempo de aprendizaje de la L2, ni la edad del participante. Las conclusiones finales recogen los resultados obtenidos en el presente trabajo así como las del trabajo sobre las diferencias basadas en el lugar de articulación.Speech contrasts which are not functionally distinctive in the mother tongue are difficult to differentiate perceptually for non-native listeners. A two-fold experiment was carried out in order to investigate the L2 perception by 26 Spanish listeners of English, with an English group used as a control. In the present paper, listeners were exposed to the English contrast /s/ vs. /z/, which is not phonemic in Spanish, in two synthesized words, Sue and zoo. The results showed that there were listeners who had already acquired the contrast with some language-specific differences in the use of some of the acoustic cues that signalled this contrast. Furthermore there was no correlation between the results obtained and the variables age of L2 learning, length of L2 learning, or listener’s age. Final conclusions will be drawn from this research and the previous work devoted to place of articulation differences

Effects of Phonological Contrast on Within-Category Phonetic Variation

This dissertation investigates an often assumed hypothesis in phonetics and phonology: that there should be relatively less within-category phonetic variation in production in languages which have relatively more phonological contrasts (Lindblom, 1986, on vowels). Although this hypothesis is intuitive, there is little existing evidence to support the claim and it is difficult to generalize outside of vowels. In this dissertation, I argue that this hypothesis is not trivially true and needs additional specification. I propose an extension of this hypothesis, Contrast-Dependent Variation, which predicts relative differences in extent of within-category variation between languages and individual speakers. Contrast-Dependent Variation can make predictions across multiple phonetic spaces as it considers individual phonetic dimensions to be the relevant units of comparison, rather than phonological inventory subsets (stops, vowels, etc.). Relative differences in extent of within-category variation are predicted by differences in cue weight, rather than differences in number of phonemes. The dissertation tests this hypothesis by examining two between-language case studies: stops in Hindi and English and sibilants in French and Polish. I also consider a within-language case study: individual differences in extent of within-category variation in Mandarin sibilants. The results here show that differences in extent of phonetic variability between languages and speakers are systematic; they are structured according to the system of phonological contrasts

Perceptual distinctiveness between dental and palatal sibilants in different vowel contexts and its implications for phonological contrasts

Mandarin Chinese has dental, palatal, and retroflex sibilants, but their contrasts before [_i] are avoided: The palatals appear before [i] while the dentals and retroflexes appear before homorganic syllabic approximants (a.k.a. apical vowels). An enhancement view regards the apical vowels as a way to avoid the weak contrast /si-ɕi-ȿi/. We focus on the dental vs. palatal contrast in this study and test the enhancement-based hypothesis that the dental and palatal sibilants are perceptually less distinct in the [_i] context than in other vowel contexts. This hypothesis is supported by a typological survey of 155 Chinese dialects, which showed that contrastive [si, tsi, tsʰi] and [ɕi, tɕi, tɕʰi] tend to be avoided even when there are no retroflexes in the sound system. We also conducted a speeded-AX discrimination experiment with 20 English listeners and 10 Chinese listeners to examine the effect of vowels ([_i], [_a], [_ou]) on the perceived distinctiveness of sibilant contrasts ([s-ɕ], [ts-tɕ], [tsʰ-tɕʰ]). The results showed that the [_i] context introduced a longer response time, thus reduced distinctiveness, than other vowels, confirming our hypothesis. Moreover, the general lack of difference between the two groups of listeners indicates that the vowel effect is language-independent

Cross-language Differences in Fricative Processing and Their Influence on Non-native Fricative Categorisation

Studies have shown that native speakers of Mandarin Chinese and Hong Kong Cantonese tend to have difficulty perceiving the English fricative /θ/. However, although both languages have /f/ and /s/ categories, Mandarin speakers tend to assimilate it to their /s/ category whilst Cantonese speakers would assimilate it to their /f/ category. Over three studies, this thesis investigated various factors that may lead to this difference, while enhancing our understanding of the acoustics and the perception of the fricatives of these languages. Study 1 explored acoustic properties of target fricatives of the three languages (Mandarin, Cantonese, English) using audio recordings from native speakers, and conducted comparisons of the fricatives within and across languages. The results showed that the phonemes /f s/, even though shared by the three languages, were produced differently in the different languages, likely due to the effects of the different fricative inventories. Moreover, different acoustic cues were more or less effective in distinguishing between the different fricatives in each language, indicating that native speakers of these languages likely rely on these cues differently. Study 2 examined how transition cues may affect the identification of /f/ and /s/ by native speakers of the respective languages by combining a phoneme monitoring task and EEG measures. Target fricatives were spliced with vowels to create stimuli with congruent or incongruent transitions. In contrast to previous studies (e.g., Wagner, Ernestus & Cutler, 2006), the results revealed that all groups attended to formant transitions when processing fricatives, despite their differing native fricative inventory sizes. Study 3 investigated cross-language differences in categorisation boundaries of target fricative pairs using a behavioural identification task. The study interpolated pairs of stimuli to create a frication continuum and a vowel continuum, forming a 2-dimensional stimuli grid. The results indicated that frication was the primary cue for fricative identification for the native English, Cantonese, and Mandarin speakers, but also revealed cross-language differences in fricative boundaries. Overall, the results of these studies demonstrate that the processing of fricatives was largely driven by the frication section, and the differential assimilation of /θ/ was likely due to the different acoustics of the same fricative category across languages. The results also motivate a reconsideration of the role of coarticulatory cues in fricative perception

Learning of second language sound contrasts: Effects of training on the perception and production of second language vowel and consonant duration

Listen-and-repeat training has been shown to be an effective tool for the learning of non-native phoneme contrasts. The aim of this thesis was to examine the learning of non-native duration contrasts using short-term listen-and-repeat training with adult learners. Learning results were examined with event-related potentials, behavioral discrimination and identification tasks, and production tasks. In addition, the learning of non-native vowel duration in a classroom setting was investigated. Study I focused on listen-and-repeat training with articulation instructions in the learning of a non-native vowel quality contrast. The results showed that the participants were able to adjust their production of the contrast after only one training session. In Studies II and III, participants underwent two days of training with a nonnative vowel duration contrast, and their performance was measured on trained, untrained and non-linguistic duration contrasts. Study II used behavioral discrimination and production tasks, and Study III additionally used the electric event-related potentials MMN and N1. Study II showed tentative training-related improvements in the discrimination and production of the trained contrast. Study III found increased MMN amplitudes, decreased N1 latencies and improved behavioral discrimination performance for the trained stimuli. Changes to general detection of acoustic duration contrasts were also seen in the elicitation of an N1 response for the untrained contrast. No training-related changes in production were observed. Study IV used a two-day training paradigm on stop and sibilant duration contrasts, measuring learning results with MMN, behavioral discrimination and a production task. No training-related improvement was observed, but a clear difference emerged between the consonant types, with sibilants proving less difficult for the participants than stops. Study V examined the learning of non-native vowel duration contrasts on an intensive language course. Similarly to the listen-and-repeat studies, perceptual identification performance improved, but no improvement was observed in production. Overall, these results suggested that perception of non-native vowel duration contrasts can be improved fairly quickly, and they are learned more easily than production. More research is needed regarding the learning of consonant duration.Vieraan kielen äänne-erojen oppiminen: Harjoittelun vaikutus vieraan kielen vokaali- ja konsonanttikestoerojen havaitsemiseen ja tuottoon Kuuntele ja toista –harjoittelun on osoitettu olevan tehokasta vieraan kielen äänneerojen oppimisessa. Tämän opinnäytetyön tavoitteena oli tutkia vieraan kielen kestoerojen oppimista aikuisilla oppijoilla lyhyen kuuntele ja toista –harjoittelun avulla. Oppimistuloksia mitattiin herätevasteilla, behavioraalisilla erottelu- ja identifikaatiokokeilla, sekä tuottokokeilla. Lisäksi tutkittiin vieraan kielen vokaalikestoerojen oppimista luokkahuoneessa. Osatutkimus I tutki artikulaatio-ohjeilla tuettua kuuntele ja toista –harjoittelua vieraan kielen vokaalilaatueron oppimisessa. Tulokset osoittivat, että osallistujat pystyivät muokkaamaan tuottoaan jo yhden harjoituskerran jälkeen. Osatutkimuksissa II ja III käytettiin kahden päivän kuuntele ja toista –harjoitusta vieraan kielen vokaalikeston oppimiseen. Oppimista mitattiin harjoitellulla, harjoittelemattomalla ja ei-kielellisellä kestoerolla. Osatutkimuksessa II käytettiin behavioraalista erottelua ja tuottokoetta, ja osatutkimuksessa III lisäksi MMN- ja N1-herätevasteita. Osatutkimuksessa II todettiin alustavia parannuksia harjoitellun eron havaitsemisessa ja tuotossa. Osatutkimuksessa III havaittiin harjoitellulla erolla kasvanut MMN-amplitudi, laskenut N1-vasteen latenssi sekä parantunut behavioraalinen erottelukyky. N1-vasteen elisitoituminen harjoittelemattomalle erolle viittasi myös yleisen akustisen erottelukyvyn paranemiseen. Tuoton suhteen muutoksia ei havaittu. Osatutkimuksessa IV käytettiin kaksipäiväistä harjoittelua vieraan kielen klusiili- ja sibilanttikestoerojen harjoitteluun. Oppimista mitattiin MMN:n, erottelukokeen sekä tuottokokeen avulla. Harjoittelu ei parantanut konsonanttien havaitsemista eikä tuottoa, mutta konsonanttien välillä havaittiin selkeä ero, jonka perusteella sibilantit olivat koehenkilöille helpompia kuin klusiilit. Osatutkimus V tarkasteli vieraan kielen vokaalikestoerojen oppimista intensiivisellä kielikurssilla. Kuten aiemmissa osatutkimuksissa, behavioraalinen havaitseminen kehittyi, mutta tuotossa ei havaittu parannusta. Kokonaisuudessaan tutkimukset viittasivat siihen, että vieraan kielen vokaalikestoerojen havaitsemista voidaan parantaa suhteellisen nopeasti harjoittelulla, ja se kehittyy helpommin kuin kestoerojen tuotto. Konsonanttien keston oppimisen suhteen tarvitaan jatkotutkimusta

The relationship between maternal speech clarity and infant language outcomes

Mothers' use of infant-directed speech (IDS) may assist infants in decoding language input. IDS is characterized by exaggerated prosodic features (Fernald, 1989), shorter mean length of utterance (Cooper, 1997; Bernstein Ratner, 1996), repetition (Bernstein Ratner, 1996), and more highly clarified acoustic qualities (Bernstein Ratner, 1984; Malsheen, 1980) in comparison to speech directed to adults. However, it is not yet known to what extent such measures of maternal input have long-term impacts on language development. This thesis seeks to test the overarching hypothesis that children who receive more clarified speech input during the prelinguistic stage may be expected to have better language skills at an earlier age than children who receive poorer quality input

Formant transitions in fricative identification: The role of native fricative inventory

The distribution of energy across the noise spectrum provides the primary cues for the identification of a fricative. Formant transitions have been reported to play a role in identification of some fricatives, but the combined results so far are conflicting. We report five experiments testing the hypothesis that listeners differ in their use of formant transitions as a function of the presence of spectrally similar fricatives in their native language. Dutch, English, German, Polish, and Spanish native listeners performed phoneme monitoring experiments with pseudowords containing either coherent or misleading formant transitions for the fricatives / s / and / f /. Listeners of German and Dutch, both languages without spectrally similar fricatives, were not affected by the misleading formant transitions. Listeners of the remaining languages were misled by incorrect formant transitions. In an untimed labeling experiment both Dutch and Spanish listeners provided goodness ratings that revealed sensitivity to the acoustic manipulation. We conclude that all listeners may be sensitive to mismatching information at a low auditory level, but that they do not necessarily take full advantage of all available systematic acoustic variation when identifying phonemes. Formant transitions may be most useful for listeners of languages with spectrally similar fricatives