Accent Intelligibility Differences in Noise Across Native and Nonnative Accents: Effects of Talker-Listener Pairing at Acoustic-Phonetic and Lexical Levels

Intelligibility of Natively and Nonnatively Produced English Speech Presented in Noise to a Large Cohort of United States Service Members

PURPOSE

A corpus of English matrix sentences produced by 60 native and nonnative speakers of English was developed as part of a multinational coalition task group. This corpus was tested on a large cohort of U.S. Service members in order to examine the effects of talker nativeness, listener nativeness, masker type, and hearing sensitivity on speech recognition performance in this population.

METHOD

A total of 1,939 U.S. Service members (ages 18-68 years) completed this closed-set listening task, including 430 women and 110 nonnative English speakers. Stimuli were produced by native and nonnative speakers of English and were presented in speech-shaped noise and multitalker babble. Keyword recognition accuracy and response times were analyzed.

RESULTS

General(ized) linear mixed-effects regression models found that, on the whole, speech recognition performance was lower for listeners who identified as nonnative speakers of English and when listening to speech produced by nonnative speakers of English. Talker and listener effects were more pronounced when listening in a babble masker than in a speech-shaped noise masker. Response times varied as a function of recognition score, with longest response times found for intermediate levels of performance.

CONCLUSIONS

This study found additive effects of talker and listener nonnativeness when listening to speech in background noise. These effects were present in both accuracy and response time measures. No multiplicative effects of talker and listener language background were found. There was little evidence of a negative interaction between talker nonnativeness and hearing impairment, suggesting that these factors may have redundant effects on speech recognition.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.26060191.

The Korean Speech Recognition Sentences: A Large Corpus for Evaluating Semantic Context and Language Experience in Speech Perception

PURPOSE

The aim of this study was to develop and validate a large Korean sentence set with varying degrees of semantic predictability that can be used for testing speech recognition and lexical processing.

METHOD

Sentences differing in the degree of final-word predictability (predictable, neutral, and anomalous) were created with words selected to be suitable for both native and nonnative speakers of Korean. Semantic predictability was evaluated through a series of cloze tests in which native (n = 56) and nonnative (n = 19) speakers of Korean participated. This study also used a computer language model to evaluate final-word predictabilities; this is a novel approach that the current study adopted to reduce human effort in validating a large number of sentences, which produced results comparable to those of the cloze tests. In a speech recognition task, the sentences were presented to native (n = 23) and nonnative (n = 21) speakers of Korean in speech-shaped noise at two levels of noise.

RESULTS

The results of the speech-in-noise experiment demonstrated that the intelligibility of the sentences was similar to that of related English corpora. That is, intelligibility was significantly different depending on the semantic condition, and the sentences had the right degree of difficulty for assessing intelligibility differences depending on noise levels and language experience.

CONCLUSIONS

This corpus (1,021 sentences in total) adds to the target languages available in speech research and will allow researchers to investigate a range of issues in speech perception in Korean.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24045582.

How sociolinguistic factors shape children's subjective impressions of teacher quality

When university students are asked to rate their instructors, their evaluations are often influenced by the demographic characteristics of the instructor-such as the instructor's race, gender, or language background. These influences can manifest in unfair systematic biases against particular groups of teachers and hamper movements to promote diversity in higher education. When and how do these biases develop? Here, we begin to address these questions by examining children's sociolinguistic biases against teachers who speak with different accents. To do this, we presented 5-year-old Canadian English-speaking children with pairs of adult talkers. Children were asked to select "who they'd like to be their teacher" then they rated "how good of a teacher" they thought each talker would be on a 5-point scale. In each trial, one talker spoke in the locally dominant variety of Canadian English, and the other spoke in a different accent. Children strongly preferred Canadian-accented teachers over teachers who spoke with non-native (i.e., French or Dutch) accents, but also demonstrated a preference for Canadian teachers over teachers who spoke with non-local regional accents (i.e., Australian or British). In line with the binary choice data, children rated the Canadian talkers more favourably. The relationship between the gender of the teacher and the gender of the child also impacted ratings. This work demonstrates that even at the onset of formal education, children may already exhibit signs of accent-based biases. We discuss these findings in relation to the growing literature on implicit bias in higher education.

How pronunciation distance impacts word recognition in children and adults

Although unfamiliar accents can pose word identification challenges for children and adults, few studies have directly compared perception of multiple nonnative and regional accents or quantified how the extent of deviation from the ambient accent impacts word identification accuracy across development. To address these gaps, 5- to 7-year-old children's and adults' word identification accuracy with native (Midland American, British, Scottish), nonnative (German-, Mandarin-, Japanese-accented English) and bilingual (Hindi-English) varieties (one talker per accent) was tested in quiet and noise. Talkers' pronunciation distance from the ambient dialect was quantified at the phoneme level using a Levenshtein algorithm adaptation. Whereas performance was worse on all non-ambient dialects than the ambient one, there were only interactions between talker and age (child vs adult or across age for the children) for a subset of talkers, which did not fall along the native/nonnative divide. Levenshtein distances significantly predicted word recognition accuracy for adults and children in both listening environments with similar impacts in quiet. In noise, children had more difficulty overcoming pronunciations that substantially deviated from ambient dialect norms than adults. Future work should continue investigating how pronunciation distance impacts word recognition accuracy by incorporating distance metrics at other levels of analysis (e.g., phonetic, suprasegmental).

Replicability of neural responses to speech accent is driven by study design and analytical parameters

Recent studies have reported evidence that listeners' brains process meaning differently in speech with an in-group as compared to an out-group accent. However, among studies that have used electroencephalography (EEG) to examine neural correlates of semantic processing of speech in different accents, the details of findings are often in conflict, potentially reflecting critical variations in experimental design and/or data analysis parameters. To determine which of these factors might be driving inconsistencies in results across studies, we systematically investigate how analysis parameter sets from several of these studies impact results obtained from our own EEG data set. Data were collected from forty-nine monolingual North American English listeners in an event-related potential (ERP) paradigm as they listened to semantically congruent and incongruent sentences spoken in an American accent and an Indian accent. Several key effects of in-group as compared to out-group accent were robust across the range of parameters found in the literature, including more negative scalp-wide responses to incongruence in the N400 range, more positive posterior responses to congruence in the N400 range, and more positive posterior responses to incongruence in the P600 range. These findings, however, are not fully consistent with the reported observations of the studies whose parameters we used, indicating variation in experimental design may be at play. Other reported effects only emerged under a subset of the analytical parameters tested, suggesting that analytical parameters also drive differences. We hope this spurs discussion of analytical parameters and investigation of the contributions of individual study design variables in this growing field.

Non-native speech recognition sentences: A new materials set for non-native speech perception research

Research into non-native (L2) speech perception has increased the need for specialized experimental materials. The Non-Native Speech Recognition (NNSR) sentences are a new large-scale set of speech recognition materials for research with L2 speakers of English at CEFR level B1 (North, Ortega, & Sheehan, 2010) and above. The set comprises 439 triplets of sentences in three related conditions: semantically predictable, neutral, and anomalous. The sentences were created by combining a strongly or weakly contextually constrained sentence frame with a congruent or anomalous final keyword, and they were matched on a number of factors during development, to maintain consistency across conditions. This article describes the development process of the NNSR sentences, along with results of speech-in-noise intelligibility testing for L2 and native English speakers. Suggestions for the sentences’ application in a range of investigations and experimental designs are also discussed.

Auditory neural tracking and lexical processing of speech in noise: Masker type, spatial location, and language experience

The present study investigated how single-talker and babble maskers affect auditory and lexical processing during native (L1) and non-native (L2) speech recognition. Electroencephalogram (EEG) recordings were made while L1 and L2 (Korean) English speakers listened to sentences in the presence of single-talker and babble maskers that were colocated or spatially separated from the target. The predictability of the sentences was manipulated to measure lexical-semantic processing (N400), and selective auditory processing of the target was assessed using neural tracking measures. The results demonstrate that intelligible single-talker maskers cause listeners to attend more to the semantic content of the targets (i.e., greater context-related N400 changes) than when targets are in babble, and that listeners track the acoustics of the target less accurately with single-talker maskers. L1 and L2 listeners both modulated their processing in this way, although L2 listeners had more difficulty with the materials overall (i.e., lower behavioral accuracy, less context-related N400 variation, more listening effort). The results demonstrate that auditory and lexical processing can be simultaneously assessed within a naturalistic speech listening task, and listeners can adjust lexical processing to more strongly track the meaning of a sentence in order to help ignore competing lexical content.