Native Talkers Research Articles

The Interlanguage Speech Intelligibility Benefit for Korean Learners of English: Perception of English Front Vowels

ABSTRACTThe present work is a follow-up study to that of Han, Choi, Lim and Lee (2011), where an asymmetry in the source segments eliciting the interlanguage speech intelligibility benefit (ISIB) was found such that the vowels which did not match any vowel of the Korean language were likely to elicit more ISIB than matched vowels. In order to identify the source of the stronger ISIB in non-matched vowels, acoustic analyses of the stimuli were performed. Two pairs of English front vowels [i] vs. [ɪ], and [ɛ] vs. [ae] were recorded by English native talkers and two groups of Korean learners according to their English proficiency, and then their vowel duration and the frequencies of the first two formants (F1, F2) were measured. The results demonstrated that the non-matched vowels such as [ɪ], and [ae] produced by Korean talkers seemed to show more deviated acoustic characteristics from those of the natives, with longer duration and with closer formant values to the matched vowels, [i] and [ɛ], than those of the English natives. Combining the results of acoustic measurements in the present study and those of word identification in Han et al. (2011), we suggest that relatively better performance in word identification by Korean talkers/listeners than the native English talkers/listeners is associated with the shared interlanguage of Korean talkers and listeners. Key words: the interlanguage speech intelligibility benefit (ISIB), Korean front vowels

Honoring Native American Code Talkers

Honoring Native American Code Talkers

A Comparison of Long-Term Average Speech Spectrum (LTASS) among Korean Monosllyabic Words, Sentences, and English Sentences

The purpose of this study was to compare long-term average speech spectrum (LTASS) of Korean monosyllabic words, sentences, and English sentences. For Korean speech material, 200 monosyllabic words and 80 sentences were recorded by 20 native talkers of Korean (10 males, 10 females). As English speech material, 100 IEEE Harvard Psychoacoustic Sentences spoken by 20 native talkers of English (10 males, 10 females) were used. The LTASS was analyzed via one-third octave band filters from 150 Hz to 5,000 Hz. The following results were obtained. 1) LTASS of 10 male talkers showed larger differences at higher frequencies, regardless of speech material whereas LTASS of 10 females had the largest difference at 125 Hz. 2) The male LTASS of three speech materials did not significantly differ at one-third octave scales from 150 Hz to 5,000 Hz, except four frequencies (125 Hz, 160 Hz, 500 Hz, and 4,000 Hz). 3) The female LTASS was also similar at all frequencies from 150 Hz to 5,000 Hz, regardless of speech material. 4) The LTASS averaged across three materials showed a significant difference depending on the target-talker gender, especially the largest difference at 125 Hz. 5) The LTASS of Korean monosyllabic words, sentences, and English sentences did not significantly differ except three frequencies (160, 500, 630 Hz). Those results support previous finding of the universal characteristics of LTASS (Byrne et al., 1994), regardless of language. KEY WORD：Long-term average speech spectrum (LTASS) of Korean and English speech materials.

Development of the non‐native English sentence test for speech recognition.

Though the US population is becoming more diverse, there are no normalized sentence recognition tests for non‐native English listeners. It is, therefore, difficult to examine sources of perceptual problems in speech recognition tasks by non‐native listeners in laboratory and audiology clinics. The goal of this project is to develop test materials appropriate for assessing non‐native listeners’ speech recognition and hearing abilities. In order to limit linguistic biases, we recorded naturally elicited conversations with 100 non‐native talkers from 28 nations and with 15 different native languages on 20 topics. The recordings were transcribed and a lexicon of over 5000 unique words was compiled. The most frequent words across speakers of varying proficiency levels and language backgrounds were used to create test sentences with an equal number of keywords and with the syntactic structure appropriate for non‐native listeners. The sentences will be recorded by four native talkers of English and evaluated for...

The Wildcat Corpus of native- and foreign-accented English: communicative efficiency across conversational dyads with varying language alignment profiles.

This paper describes the development of the Wildcat Corpus of native- and foreign-accented English,a corpus containing scripted and spontaneous speech recordings from 24 native speakers of American English and 52 non-native speakers of English.The core element of this corpus is a set of spontaneous speech recordings, for which a new method of eliciting dialogue-based, laboratory-quality speech recordings was developed (the Diapix task). Dialogues between two native speakers of English, between two non-native speakers of English (with either shared or different LIs), and between one native and one non-native speaker of English are included and analyzed in terms of general measures of communicative efficiency.The overall finding was that pairs of native talkers were most efficient, followed by mixed native/non-native pairs and non-native pairs with shared LI. Non-native pairs with different LIs were least efficient.These results support the hypothesis that successful speech communication depends both on the alignment of talkers to the target language and on the alignment of talkers to one another in terms of native language background.

Perceptual adaptation to foreign-accented English.

Foreign-accented speech presents an interesting challenge for native listeners due to its deviations from native accented speech along multiple acoustic-phonetic dimensions. Nevertheless, since these deviations arise primarily from interactions of the native (L1) and target (L2) language sound systems, they are highly systematic both within individuals and across talkers from the same L1. Moreover, since numerous features of English are typologically rare (e.g., coda clusters and large vowel inventory), various foreign-accents of English frequently converge on similar specific deviations (e.g., cluster reduction and vowel category conflation). Thus, despite a high degree of deviation from native talker norms, the systematicity of foreign-accented speech should facilitate listener adaptation. We examined adaptation at the level of the individual (talker-dependent), the L1 (talker-independent), and the population (accent-independent). First, we showed variation in the speed and extent of talker-dependent adaptation depending on the talker’s baseline English speech intelligibility. Second, we demonstrated that talker-independent adaptation required exposure to multiple talkers of the accent. Finally, we demonstrated that exposure to multiple accents (e.g., Korean-, Hindi-, Mandarin-, and Romanian-accented English) can facilitate accent-independent adaptation, i.e., adaptation to both a trained accented (Mandarin-accented English) and an untrained accent(Slovakian-accented English). This work builds a strong case for highly flexible speech perception mechanisms.

Influence of visual speech information on the identification of foreign accented speech.

Seeing a native talker’s face improves speech intelligibility in noise for native perceivers. The intelligibility of foreign accented speech (English spoken by native talkers of Mandarin) is more susceptible to the effects of noise than the speech of native talkers. [Rogers et al., Lang Speech 47(2), 139–154 (2004)]. The current experiment investigated the influence of seeing the non‐native talker’s face on the intelligibility of speech presented in noise. Ten talkers (nine non‐native and one native) were recorded producing 155 sentences each. Talker‐specific speech shaped noise was mixed with the audio of the sentences. Eighty‐one native perceivers of English (nine per non‐native talker) responded to 20 sentences spoken by the native talker and 28 by the non‐native talker in each condition (audio‐alone, visual‐alone, audiovisual). Open set identification responses were scored as percent words correct for each condition and talker. Preliminary analyses demonstrate that although seeing the non‐native talke...

Native and non-native clear speech production.

Previous work established that both native and non-native clear speech increase intelligibility for native and proficient non-native listeners. However, non-native clear speech enhanced intelligibility less than native clear speech. In this study, we examine native and non-native conversational and clear speech productions with an eye on the differences in hyperarticulation strategies that may underlie a smaller clear speech intelligibility benefit. Results revealed a slower conversational speaking rate for non-native talkers compared with native talkers. Clear speaking rate was similar for both groups suggesting a limit in the speaking rate decrease in intelligibility enhancing clear speech. The durational distinction between tense and lax vowels was increased less in non-native speech due to the smaller speaking rate decrease in clear speech. Analyses of the stop voice onset time (VOT) showed that non-native talkers lengthened the voiced category in the negative VOT direction, while the voiceless category was lengthened less in clear speech. Finally, examination of vowel space expansion in clear speech revealed differences between the two talker groups reflecting non-native talkers’ inexperience in producing some of the vowel targets. Combined, these results suggest that a complex interaction of articulatory difficulty, proficiency, and native language background determines levels of non-native clear speech intelligibility.

The role of linguistic experience in lexical recognition.

Lexical recognition is typically slower in L2 than in L1. Part of the difficulty comes from a not precise enough processing of L2 phonemes. Consequently, L2 listeners fail to eliminate candidate words that L1 listeners can exclude from competing for recognition. For instance, the inability to distinguish /r/ from /l/ in rocket and locker makes for Japanese listeners both words possible candidates when hearing their onset (e.g., Cutler, Weber, and Otake, 2006). The L2 disadvantage can, however, be dispelled: For L2 listeners, but not L1 listeners, L2 speech from a non‐native talker with the same language background is known to be as intelligible as L2 speech from a native talker (e.g., Bent and Bradlow, 2003). A reason for this may be that L2 listeners have ample experience with segmental deviations that are characteristic for their own accent. On this account, only phonemic deviations that are typical for the listeners’ own accent will cause spurious lexical activation in L2 listening (e.g., English magic pronounced as megic for Dutch listeners). In this talk, I will present evidence from cross‐modal priming studies with a variety of L2 listener groups, showing how the processing of phonemic deviations is accent‐specific but withstands fine phonetic differences.

Sound structure and function of English as a global language

Many English conversations across the globe today involve non-native speakers. To understand the sound structure of English in a global context, we asked native and non-native listeners to rate the similarity of various languages (n=17) to English. In general, the native and non-native listeners' distance-from-English ratings were positively correlated; but, the non-natives tended to rank languages as more distant from English than the natives. Native and non-native listeners then rated the accents of native and non-native speakers. Again, the native and non-native listener ratings were positively correlated, but the non-native listeners generally rated both native and non-native speakers as more foreign-accented than did the native listeners. Together, these data suggest that both native and non-native English generally sound less “marked” to native listeners than to non-native listeners. As a means of understanding how English functions as a global language, we examined communicative efficiency in task-oriented dialogues between various combinations of natives and non-natives. All pairs successfully completed the task; yet, when one or more non-native talkers were involved, the task took about twice as long to complete as when both were native talkers. Together, these studies help characterize the structure and function of English as a twenty-first century lingua franca.

Perceptual adaptation to non-native speech

This study investigated talker-dependent and talker-independent perceptual adaptation to foreign-accent English. Experiment 1 investigated talker-dependent adaptation by comparing native English listeners’ recognition accuracy for Chinese-accented English across single and multiple talker presentation conditions. Results showed that the native listeners adapted to the foreign-accented speech over the course of the single talker presentation condition with some variation in the rate and extent of this adaptation depending on the baseline sentence intelligibility of the foreign-accented talker. Experiment 2 investigated talker-independent perceptual adaptation to Chinese-accented English by exposing native English listeners to Chinese-accented English and then testing their perception of English produced by a novel Chinese-accented talker. Results showed that, if exposed to multiple talkers of Chinese-accented English during training, native English listeners could achieve talker-independent adaptation to Chinese-accented English. Taken together, these findings provide evidence for highly flexible speech perception processes that can adapt to speech that deviates substantially from the pronunciation norms in the native talker community along multiple acoustic-phonetic dimensions.

Relationships between the intelligibility and acoustic properties of native English and Mandarin-accented English

Studies examining effects of talkers’ and listeners’ linguistic backgrounds on speech intelligibility have produced mixed results, and relatively little is known about which acoustic-phonetic features of native and non-native speech are responsible for many findings. These issues are addressed here via investigation of how acoustic properties of final consonant voicing contrasts influence word intelligibility. Native English and native Mandarin talkers’ productions of English words were presented in isolation to native English and native Mandarin listeners in an identification task. Intelligibility findings were related to preceding vowel duration, stop consonant duration, burst duration, and proportion of voicing during stop closure. As expected, native English listeners were more accurate identifying words spoken by native than non-native talkers. In contrast to previous findings of an interlanguage speech intelligibility benefit (ISIB) for sentences, non-native listeners found native speech more intelligible than non-native speech. However, non-native listeners found non-native speech more intelligible than did native listeners. For native talkers, all four acoustic measures contributed significantly to correct identification of voicing contrasts by both native and non-native listeners (with closure voicing most salient). In contrast, for non-native talkers, listeners tended to rely primarily on closure voicing and burst duration. Ramifications for ISIB will be discussed.

Evidence against the mismatched interlanguage speech intelligibility benefit hypothesis

In a follow-up study to that of Bent and Bradlow (2003), carrier sentences containing familiar keywords were read aloud by five talkers (Korean high proficiency; Korean low proficiency; Saudi Arabian high proficiency; Saudi Arabian low proficiency; native English). The intelligibility of these keywords to 50 listeners in four first language groups (Korean, n = 10; Saudi Arabian, n = 10; native English, n = 10; other mixed first languages, n = 20) was measured in a word recognition test. In each case, the non-native listeners found the non-native low-proficiency talkers who did not share the same first language as the listeners the least intelligible, at statistically significant levels, while not finding the low-proficiency talker who shared their own first language similarly unintelligible. These findings indicate a mismatched interlanguage speech intelligibility detriment for low-proficiency non-native speakers and a potential intelligibility problem between mismatched first language low-proficiency speakers unfamiliar with each others' accents in English. There was no strong evidence to support either an intelligibility benefit for the high-proficiency non-native talkers to the listeners from a different first language background or to indicate that the native talkers were more intelligible than the high-proficiency non-native talkers to any of the listeners.

Understanding foreign-accented speech

Why is foreign-accented speech hard to understand? In one view, foreign-accented speech intelligibility is poor due to its marked deviation from the native talker norm. An alternative view claims that if the talkers and listeners shared knowledge systems are sufficiently aligned with each other, foreign-accented speech intelligibility can be good despite its deviation from the native talker norm. Results from two studies in support of this latter alternative will be presented. Study 1 investigated whether intelligibility of Chinese-accented English could be improved for native English listeners through perceptual training. This study showed that if given exposure to multiple talkers of Chinese-accented English during training, native English listeners could achieve talker-independent adaptation to Chinese-accented English. Study 2 compared intelligibility of foreign-accented and native-accented English for non-native and native listeners. Results showed that native listeners found native-accented English more intelligible than foreign-accented English, but non-native listeners found foreign-accented English as intelligible as native-accented English. Interestingly, this pattern was obtained even for non-native listeners and talkers from different language backgrounds. Taken together, these findings demonstrate that intelligibility of foreign-accented speech varies depending on the degree of talker–listener attunement rather than on the extent of its deviation from a native talker norm per se.

Production and perception of a temporal contrast by native and non-native speakers

In previous work, we found that both native and Chinese-accented talkers of English varied considerably in the extent to which they realized the duration contrast for vowels before voiced versus before voiceless consonants. The current study explored the perceptual consequences of this individual variability in production. Twenty native and 35 non-native listeners participated in a minimal pair identification task using stimuli from two native and two non-native talkers who differed substantially in the extent to which they realized the temporal contrast. Stimuli were consonant-vowel-consonant words that differed only in the voicing of the final consonant. Both native and non-native listeners exhibited sensitivity to variation in the production of this temporal contrast: greater identification accuracy was observed for relatively large duration differences. There was also a talker-listener interaction such that non-native listeners identified words produced by the non-native talkers more accurately than those produced by the native talkers. In a follow-up experiment, we investigated the perception-production relationship for this temporal contrast in the non-native listeners. Generally, non-native listeners who were more sensitive to this duration contrast in native-accented English showed a greater duration contrast in English production than non-native listeners who were less sensitive to this contrast. [Work supported by NIH-NIDCD.]

Quantifying the intelligibility of speech in noise for non-native talkers.

The intelligibility of speech pronounced by non-native talkers is generally lower than speech pronounced by native talkers, especially under adverse conditions, such as high levels of background noise. The effect of foreign accent on speech intelligibility was investigated quantitatively through a series of experiments involving voices of 15 talkers, differing in language background, age of second-language (L2) acquisition and experience with the target language (Dutch). Overall speech intelligibility of L2 talkers in noise is predicted with a reasonable accuracy from accent ratings by native listeners, as well as from the self-ratings for proficiency of L2 talkers. For non-native speech, unlike native speech, the intelligibility of short messages (sentences) cannot be fully predicted by phoneme-based intelligibility tests. Although incorrect recognition of specific phonemes certainly occurs as a result of foreign accent, the effect of reduced phoneme recognition on the intelligibility of sentences may range from severe to virtually absent, depending on (for instance) the speech-to-noise ratio. Objective acoustic-phonetic analyses of accented speech were also carried out, but satisfactory overall predictions of speech intelligibility could not be obtained with relatively simple acoustic-phonetic measures.

Temporal characteristics of Chinese-accented English: Preliminary findings

This study investigated several temporal features of English to determine the extent of their occurrence in the speech of talkers of Chinese-accented English who had relatively limited experience with spoken English. Specifically, the extent to which these speakers produced the following temporal contrasts was examined: (1) tense versus lax vowel duration, (2) vowel duration before voiced versus voiceless consonants, and (3) vowel and consonant duration in sentence-final versus nonfinal position. Preliminary data from sentences produced by eight non-native and eight native talkers indicates that the native English speakers and the Chinese-accented talkers did not differ in the extent to which they realized the inherent duration difference between tense and lax vowels. However, the native English subjects tended to show substantially greater vowel lengthening before voiced versus before voiceless consonants than the Chinese-accented talkers. In addition, while the two groups did not differ significantly in the extent to which they lengthened sentence-final consonants relative to nonfinal consonants, the native English talkers showed greater sentence-final vowel lengthening than the Chinese-accented talkers. When group differences for a given temporal parameter were found, 1 or 2 of the non-native subjects typically fell within the range of performance shown by the native speakers.

Effects of training on learning non-native speech contrasts

An animal psychoacoustic procedure was used to train human listeners to categorize two non-native phonemic distinctions. In Exp 1, Japanese perception of the English liquid contrast /r-l/ was examined. In Exp 2, American-English perception of the Hindi dental-retroflex contrast /d-D/was examined. The training methods were identical in the two studies. The stimuli consisted of 64 CVs produced by four different native talkers (two male, two female) using four different vowels. The procedure involved manually moving a lever to make either a ‘‘go-left’’ or ‘‘go-right’’ response to categorize the stimuli. Feedback was given for correct and incorrect responses after each trial. After 32 training sessions, lasting about 8 weeks, performance was analyzed using both percent correct and response time as measures. Results showed that the Japanese listeners, as a group, were statistically similar to a group of native listeners in categorizing the liquid contrast. In contrast, the Amercan-English listeners were not nativelike in categorizing the dental-retroflex contrast. Hypotheses for the different results in the two experiments are discussed, including possible subject-related variables. In addition, the use of an animal model is proposed to objectively ‘‘calibrate’’ the psychoacoustic salience of various phoneme contrasts used in human speech.

Interlanguage intelligibility benefit as a function of talker and listener language background and L2 proficiency

For non-native listeners, intelligibility of non-native speakers (NNS) can surpass intelligibility of native speakers [T. Bent, J. Acoust. Soc. Am. 109, 2472 (2001)]. The present study further investigated how language background and L2 proficiency of talker and listener affect L2 intelligibility. Two Chinese NNS, two Korean NNS, and one English monolingual were recorded reading simple English sentences. Listeners were English monolinguals, Chinese NNS, Korean NNS, and NNS with other L1s. For native English listeners, the native English talker was most intelligible. For non-native listeners, intelligibility of non-native talkers with high degrees of L2 proficiency was better than or equal to native talker intelligibility. This pattern held regardless of whether non-native talkers and listeners matched in L1. Additionally, the interlanguage benefit (i.e., the intelligibility difference between non-native and native talkers) decreased as the listeners’ proficiency in English increased. This interlanguage benefit can be accounted for by a combination of a shared systematic interlanguage (when talker and listener match in L1) and the influence of interlanguage universals (when talker and listener do not match in L1). However, both of these factors become less influential as listeners L2 proficiency develops causing a decrease in the interlanguage benefit. [Work supported by NIH-NIDCD Grant DC 03762.]

The effect of a non-native accent in Dutch on speech intelligibility

It is well known that second-language talkers are usually less intelligible than native talkers, especially under adverse listening conditions. Background noise tends to influence the intelligibility of foreign accented speech more profoundly than unaccented speech. In order to quantify this effect, speech reception threshold (SRT) experiments were carried out using Dutch speech by American, German, Polish, Chinese and (native) Dutch talkers (15 speakers, 3 talkers per language background). The experience with the Dutch language varied between talkers from 3 months to 28 years. Ten Dutch university students participated as listeners. In order to obtain 50% sentence intelligibility, non-native talkers were found to require a 0–3-dB better speech-to-noise ratio than native talkers do. A significant correlation between self-reported proficiency and SRT-score was observed (R=0.78). Also, an objective estimate of the degree of foreign accent of the individual speakers was obtained by means of a pairwise comparison experiment, in which 19 native Dutch listeners participated. The accent ratings which were obtained (after Thurstone normalization) were also significantly correlated with the SRT-scores (R=0.85). The conclusion may be drawn that the effect of noise on the intelligibility of foreign accented speech can be predicted quantitatively from easily obtained measures of perceived foreign accent.