Non-native speech perception in adverse conditions: A review <s> Introduction <s> This research provides a multidisciplinary perspective on the factors influencing the process of integrating auditory and visual information in speech perception, and the nature of the mental representations to which speech input is matched for identification. Most previous studies of L2 speech perception had focused on only one source of input—the auditory modality. In this study, however, the occurrence of the McGurk effect (the influence of visual or lip-read information on speech perception) pointed to the power of visible speech in face-to-face communication for L2 learners as well as native speakers. Participants were advanced ESL learners of 4 L1s (Japanese, Korean, Spanish, and Malay) and native speakers of English. In this experimental design, six CV syllables with /p, f, w, r, t, k/ were combined on videotape to create concordant and discordant conditions (i.e., where audiovisual cues were matched and mismatched). This design permits the tagging of input according to its source in order to evaluate the relative contributions of each modality to the perceptual outcome. Results indicated that the learners' L1s influenced the relative information value of the auditory and visual cues, and thus their contribution to a single percept. The Japanese and Korean learners' identification accuracy of /f/ and /r/ increased with matched visual cues. It was evident that learners attended to visual cues to identify speech sounds even though they had not received any explicit training. ::: ::: ::: ::: By drawing from the literature on L2 phonology, speechreading, speech perception, attention, similarity, and categorization, this work demonstrates the need for a model of L2 speech acquisition within a cognitive framework to account for bimodal input in the broader context of spoken language processing. Findings also point to the need to incorporate into perceptual training for L2 learners the enhancement of the information value of visual cues as a second channel of input. <s> BIB001 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> To determine how age of acquisition influences perception of second-language speech, the Speech Perception in Noise (SPIN) test was administered to native Mexican-Spanish-speaking listeners who lea... <s> BIB002 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> A review of the effects of ambient noise and reverberation on speech intelligibility in classrooms has been completed because of the long-standing lack of agreement on preferred acoustical criteria for unconstrained speech accessibility and communication in educational facilities. An overwhelming body of evidence has been collected to suggest that noise levels in particular are usually far in excess of any reasonable prescription for optimal conditions for understanding speech in classrooms. Quite surprisingly, poor classroom acoustics seem to be the prevailing condition for both normally-hearing and hearing-impaired students with reported A-weighted ambient noise levels 4-37 dB above values currently agreed upon to provide optimal understanding. Revision of currently proposed room acoustic performance criteria to ensure speech accessibility for all students indicates the need for a guideline weighted for age and one for more vulnerable groups. For teens (12-year-olds and older) and young adults having normal speech processing in noise, ambient noise levels not exceeding 40 dBA are suggested as acceptable, and reverberation times of about 0.5 s are concluded to be optimum. Younger students, having normal speech processing in noise for their age, would require noise levels ranging from 39 dBA for 10-11-year-olds to only 28.5 dBA for 6-7-year-olds. By contrast, groups suspected of delayed speech processing in noise may require levels as low as only 21.5 dBA at age 6-7. As one would expect, these more vulnerable students would include the hearing-impaired in the course of language development and non-native listeners. <s> BIB003 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> In a series of experiments using monosyllabic words produced by a native and a non-native speaker of English, native English speakers monitored the word-initial consonants of the words to decide which of two consonants was present on each trial. In some of the experiments, a secondary task of a linguistic nature, deciding whether the target-bearing word was a noun or verb, was also required. When the words were presented in silence, the native and non-native stimuli were processed in a like manner. Specifically, when the secondary task was not required, phonemic decisions tended to be made on the basis of prelexical information, whereas when the secondary task was required they tended to be made on the basis of postlexical information (see Eimas, Marcovitz Hornstein, & Payton, 1990). However, when the listening conditions were degraded by presenting the words at a lower level and in noise, the two types of stimuli yielded different patterns. Native speech was processed as before, whereas for non-native speech phonemic decisions now tended to be made on the basis of postlexical information both when a secondary task was required and when it was not. The contrasting results for native and non-native speech are discussed in terms of models of phoneme processing. <s> BIB004 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> This study compared the intelligibility of native and foreign-accented English speech presented in quiet and mixed with three different levels of background noise. Two native American English speakers and four native Mandarin Chinese speakers for whom English is a second language each read a list of 50 phonetically balanced sentences (Egan, 1948). The authors identified two of the Mandarin-accented English speakers as high-proficiency speakers and two as lower proficiency speakers, based on their intelligibility in quiet (about 95% and 80%, respectively). Original recordings and noise-masked versions of 48 utterances were presented to monolingual American English speakers. Listeners were asked to write down the words they heard the speakers say, and intelligibility was measured as content words correctly identified. While there was a modest difference between native and high-proficiency speech in quiet (about 7%), it was found that adding noise to the signal reduced the intelligibility of high-proficiency accented speech significantly more than it reduced the intelligibility of native speech. Differences between the two groups in the three added noise conditions ranged from about 12% to 33%. This result suggests that even high-proficiency non-native speech is less robust than native speech when it is presented to listeners under suboptimal conditions. <s> BIB005 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> This study compared monosyllabic word recognition in quiet, noise, and noise with reverberation for 15 monolingual American English speakers and 12 Spanish–English bilinguals who had learned English prior to 6 years of age and spoke English without a noticeable foreign accent. Significantly poorer word recognition scores were obtained for the bilingual listeners than for the monolingual listeners under conditions of noise and noise with reverberation, but not in quiet. Although bilinguals with little or no foreign accent in their second language are often assumed by their peers, or their clinicians in the case of hearing loss, to be identical in perceptual abilities to monolinguals, the present data suggest that they may have greater difficulty in recognizing words in noisy or reverberant listening environments. <s> BIB006 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> This study examines how native language (L1) experience affects auditory–visual (AV) perception of nonnative (L2) speech. Korean, Mandarin and English perceivers were presented with English CV syllables containing fricatives with three places of articulation: labiodentals nonexistent in Korean, interdentals nonexistent in Korean and Mandarin, and alveolars occurring in all three L1s. The stimuli were presented as auditory-only, visual-only, congruent AV and incongruent AV. Results show that for the labiodentals which are nonnative in Korean, the Koreans had lower accuracy for the visual domain than the English and the Mandarin perceivers, but they nevertheless achieved native-level perception in the auditory and AV domains. For the interdentals nonexistent in Korean and Mandarin, while both nonnative groups had lower accuracy in the auditory domain than the native English group, they benefited from the visual information with improved performance in AV perception. Comparing the two nonnative groups, the Mandarin perceivers showed poorer auditory and AV identification for the interdentals and greater AV-fusion with the incongruent AV material than did the Koreans. These results indicate that nonnative perceivers are able to use visual speech information in L2 perception, although acquiring accurate use of the auditory and visual domains may not be similarly achieved across native groups, a process influenced by L1 experience. <s> BIB007 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> This study aimed to determine the relative processing cost associated with comprehension of an unfamiliar native accent under adverse listening conditions. Two sentence verification experiments were conducted in which listeners heard sentences at various signal-to-noise ratios. In Experiment 1, these sentences were spoken in a familiar or an unfamiliar native accent or in two familiar native accents. In Experiment 2, they were spoken in a familiar or unfamiliar native accent or in a nonnative accent. The results indicated that the differences between the native accents influenced the speed of language processing under adverse listening conditions and that this processing speed was modulated by the relative familiarity of the listener with the native accent. Furthermore, the results showed that the processing cost associated with the nonnative accent was larger than for the unfamiliar native accent. <s> BIB008 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> This study investigated the relative contribution of auditory and visual information to speech perception by looking at the effect of visual and auditory degradation on the weighting given to visual cues for native and non-native speakers. Multiple iterations of /ba/, /da/ and /ga/ by five Australian English and five Mandarin Chinese speakers were presented to Australian English, British English and Mandarin Chinese participants. Tokens were presented in auditory, visual and congruent/incongruent audiovisual (AV) modes, either in clear or with visual degradation (blurring), auditory degradation (noise) or combined degradations. In the AV clear condition, English-speaking participants showed greater visual weighting for non-native speakers, but this was not found for Chinese participants. In 'single-channel degradation' conditions, the weighting of the intact channel increased significantly, with little influence of speaker language. There was no strong evidence of native-language effects on the weighting of visual cues. The degree of visual weighting varied widely across individual participants, and was also affected by individual speaker characteristics. The weighting of auditory and visual cues is therefore highly flexible and dependent on the information load of each channel; non-native speaker and language-background effects may influence visual weighting but individual perceiver and speaker strategies also have a strong impact. <s> BIB009 </s> Non-native speech perception in adverse conditions: A review <s> Introduction <s> The study connects two major topics in current speech research: foreign accentedness and speech in adverse conditions. We parallel the research in intelligibility of non-native speech, but instead of linguistic unit recognition we focus on the perception of the foreign accent strength. First, the question of type and degree of perceptual deficiencies occurring along with certain types of signal degradation is tackled. Second, we measure correlations between the accent ratings and certain candidate phenomena that may influence them, e.g., articulation rate, temporal patterning, contrasts in sound pressure levels on selected syllables and F0 variation. The impacts of different types of signal degradation help to estimate the role of segmental/suprasegmental information in assessments of foreignness in Czech English. The full appreciation of the strength of foreign accent is apparently not possible without fine phonetic detail on the segmental level. However, certain suprasegmental features of foreignness are robust enough to manifest at severe levels of signal degradation. Pairwise variability indices of vowel durations and variation in F0 tracks seem to guide the listener even better in the degraded than in the 'clean' speech signal. <s> BIB010
For many of us, the first non-native (NN) language experience outside the classroom is a shock. Not only are the answers to the carefully-practised stock phrases not those that appeared in the textbook, but the raw acoustic material reaching our ears lacks the clarity of the speakers in the quiet language laboratory. Thus unprepared, we enter the real world of the non-native listener, characterised by the dual challenges of imperfect signal and imperfect knowledge. And the problem persists even as we gain experience, exposure and confidence in the non-native language. Use of the telephone seems harder than it should be. Conversations in restaurants and bars are difficult to follow and join. The television never seems quite loud enough. We continue to prefer hearing non-native speakers of English at international conferences rather than highly-fluent natives. We finally take solace in the fact that even "true" bilingual listeners never quite reach the ability of monolinguals in the presence of noise BIB002 BIB006 . Knowing about the extent of problems faced by nonnative listeners in adverse conditions is important in developing theories of general speech perception. Comparing adult, normal-hearing populations who differ only in their native-language experience has the potential to provide insights into the role of linguistic factors in speech decoding. Since all listeners routinely handle acoustically-complex scenarios containing competing sound sources, reverberant energy and other forms of distortion, the use of native and non-native populations allows us to explore the extent to which linguistic knowledge is used in tasks such as sound source separation and identification. To give an example, consider the processes used by listeners to handle variability in formant frequencies due to factors such as differences in vocal tract sizes. Can vocal tract length normalisation be performed purely on the basis of the speech signal itself, or does it depend on the identification of units such as vowels in the speech stream, thereby engaging higher level representations which differentiate between native and non-native listeners? More generally, studies which compare native and non-native listeners help determine what processes in speech understanding are universal and which are language-specific. The study of non-native speech perception in imperfect conditions has clear practical applications in a world where increased mobility means that large minorities work or study in a second or third language setting. Knowing the extent to which non-native listeners suffer in spaces with moderate-to-strong reverberation should be taken into account when designing classrooms and workspaces BIB003  . Understanding non-native deficits in noisy settings such as factories ought to lead to revised standards for acceptable noise output levels. Differential effects of transmission channels on native and non-native listeners for speech broadcast over public address systems need to be understood to optimise information transfer to all listener groups, particularly in safety-critical situations involving emergency procedures. Similarly, studying the effect on non-native learners of differences in speaking style, from casual to careful speech, will inform the design of materials, training programmes and guidelines for educators. This review focuses on studies involving non-native listener groups performing speech perception tasks in simulated adverse conditions. Work in this area is dominated by additive noise, with only a very limited number of reports employing reverberation or channel distortion. Added noise has been motivated both by a desire to reduce scores from ceiling level when comparing native and nonnative listeners, and more directly to study the effect of simulating everyday conditions in which speech perception takes place. We consider both types of study here. The review is limited to acoustic stimuli, and excludes the extra dimension brought in by audio-visual studies (e.g., BIB001 BIB007 BIB009 . Further due to the paucity of non-native studies, we do not review the effects of noise on speech production. Another area outside the scope of the review is the perception of foreign accent in noise (e.g.,  BIB004 BIB005 BIB008 BIB010 . The review is organised as follows. Three background sections describe the parameters of the task faced by listeners in processing speech (Section 2), what constitutes nonnative listening (Section 3), and how adverse listening conditions (noise, reverberation) affect the perception of speech (Section 4). In Section 5, we then provide a compre-hensive overview of studies of non-native perception in adverse conditions, and in Section 6 we compare across the studies, in particular in the light of the features of non-native speech perception which emerged from the earlier sections. This section highlights limitations of work to date, and concludes with suggestions of some areas for further studies.