Non-native speech perception in adverse conditions: A review <s> Non-native speech perception under informational masking <s> Although many researchers have examined the role that binaural cues play in the perception of spatially separated speech signals, relatively little is known about the cues that listeners use to segregate competing speech messages in a monaural or diotic stimulus. This series of experiments examined how variations in the relative levels and voice characteristics of the target and masking talkers influence a listener's ability to extract information from a target phrase in a 3-talker or 4-talker diotic stimulus. Performance in this speech perception task decreased systematically when the level of the target talker was reduced relative to the masking talkers. Performance also generally decreased when the target and masking talkers had similar voice characteristics: the target phrase was most intelligible when the target and masking phrases were spoken by different-sex talkers, and least intelligible when the target and masking phrases were spoken by the same talker. However, when the target-to-masker ratio was less than 3 dB, overall performance was usually lower with one different-sex masker than with all same-sex maskers. In most of the conditions tested, the listeners performed better when they were exposed to the characteristics of the target voice prior to the presentation of the stimulus. The results of these experiments demonstrate how monaural factors may play an important role in the segregation of speech signals in multitalker environments. <s> BIB001 </s> Non-native speech perception in adverse conditions: A review <s> Non-native speech perception under informational masking <s> In many studies, the influence of intelligibility of the interfering speech is avoided by reversing it in time. Usually, intelligibility with time-reversed interfering speech indeed is higher compared to that with normal interfering speech. However, due to the nature of speech, reversed speech also gives rise to increased forward masking. The latter will result in a decrease in intelligibility. Thus, differences in intelligibility as a consequence of reversing speech in time are due to two opposite effects. This paper describes a speech reception threshold (SRT) test with intelligible and unintelligible interfering speech played normally and time-reversed. With Dutch listeners, Swedish reversed interfering speech gave a rise in SRT of 2.3 dB compared with the Swedish interfering speech (played normally). The difference can be attributed to differences in forward masking. Dutch time-reversed interfering speech gave a decrease in SRT of 4.3 dB compared to (intelligible) Dutch interfering speech. The latter ... <s> BIB002 </s> Non-native speech perception in adverse conditions: A review <s> Non-native speech perception under informational masking <s> Do listeners process noisy speech by taking advantage of "glimpses"-spectrotemporal regions in which the target signal is least affected by the background? This study used an automatic speech recognition system, adapted for use with partially specified inputs, to identify consonants in noise. Twelve masking conditions were chosen to create a range of glimpse sizes. Several different glimpsing models were employed, differing in the local signal-to-noise ratio (SNR) used for detection, the minimum glimpse size, and the use of information in the masked regions. Recognition results were compared with behavioral data. A quantitative analysis demonstrated that the proportion of the time-frequency plane glimpsed is a good predictor of intelligibility. Recognition scores in each noise condition confirmed that sufficient information exists in glimpses to support consonant identification. Close fits to listeners' performance were obtained at two local SNR thresholds: one at around 8 dB and another in the range -5 to -2 dB. A transmitted information analysis revealed that cues to voicing are degraded more in the model than in human auditory processing. <s> BIB003 </s> Non-native speech perception in adverse conditions: A review <s> Non-native speech perception under informational masking <s> Studies of speech perception in various types of background noise have shown that noise with linguistic content affects listeners differently than nonlinguistic noise [e.g., Simpson, S. A., and Cooke, M. (2005). "Consonant identification in N-talker babble is a nonmonotonic function of N," J. Acoust. Soc. Am. 118, 2775-2778; Sperry, J. L., Wiley, T. L., and Chial, M. R. (1997). "Word recognition performance in various background competitors," J. Am. Acad. Audiol. 8, 71-80] but few studies of multi-talker babble have employed background babble in languages other than the target speech language. To determine whether the adverse effect of background speech is due to the linguistic content or to the acoustic characteristics of the speech masker, this study assessed speech-in-noise recognition when the language of the background noise was either the same or different from the language of the target speech. Replicating previous findings, results showed poorer English sentence recognition by native English listeners in six-talker babble than in two-talker babble, regardless of the language of the babble. In addition, our results showed that in two-talker babble, native English listeners were more adversely affected by English babble than by Mandarin Chinese babble. These findings demonstrate informational masking on sentence-in-noise recognition in the form of "linguistic interference." Whether this interference is at the lexical, sublexical, and/or prosodic levels of linguistic structure and whether it is modulated by the phonetic similarity between the target and noise languages remains to be determined. <s> BIB004 </s> Non-native speech perception in adverse conditions: A review <s> Non-native speech perception under informational masking <s> Studies comparing native and non-native listener performance on speech perception tasks can distinguish the roles of general auditory and language-independent processes from those involving prior knowledge of a given language. Previous experiments have demonstrated a performance disparity between native and non-native listeners on tasks involving sentence processing in noise. However, the effects of energetic and informational masking have not been explicitly distinguished. Here, English and Spanish listener groups identified keywords in English sentences in quiet and masked by either stationary noise or a competing utterance, conditions known to produce predominantly energetic and informational masking, respectively. In the stationary noise conditions, non-native talkers suffered more from increasing levels of noise for two of the three keywords scored. In the competing talker condition, the performance differential also increased with masker level. A computer model of energetic masking in the competing talker condition ruled out the possibility that the native advantage could be explained wholly by energetic masking. Both groups drew equal benefit from differences in mean F0 between target and masker, suggesting that processes which make use of this cue do not engage language-specific knowledge. <s> BIB005 </s> Non-native speech perception in adverse conditions: A review <s> Non-native speech perception under informational masking <s> Processing speech in a non-native language requires listeners to cope with influences from their first language and to overcome the effects of limited exposure and experience. These factors may be particularly important when listening in adverse conditions. However, native listeners also suffer in noise, and the intelligibility of speech in noise clearly depends on factors which are independent of a listener's first language. The current study explored the issue of language-independence by comparing the responses of eight listener groups differing in native language when confronted with the task of identifying English intervocalic consonants in three masker backgrounds, viz. stationary speech-shaped noise, temporally-modulated speech-shaped noise and competing English speech. The study analysed the effects of (i) noise type, (ii) speaker, (iii) vowel context, (iv) consonant, (v) phonetic feature classes, (vi) stress position, (vii) gender and (viii) stimulus onset relative to noise onset. A significant degree of similarity in the response to many of these factors was evident across all eight language groups, suggesting that acoustic and auditory considerations play a large role in determining intelligibility. Language-specific influences were observed in the rankings of individual consonants and in the masking effect of competing speech relative to speech-modulated noise. <s> BIB006 </s> Non-native speech perception in adverse conditions: A review <s> Non-native speech perception under informational masking <s> In this study, we asked whether native and non-native speakers of English use a similar balance of lexical knowledge and acoustic cues, e.g., juncture-specific allophones, to segment spoken English, and whether the two groups are equally affected by energetic masking (a competing talker) and by cognitive load (a simultaneous visual search task). In intact speech, as well as in both adverse conditions, non-native speakers gave relatively less weight to lexical plausibility than to acoustic cues. Under energetic masking, overall segmentation accuracy decreased, but this decrease was of comparable magnitude in native and non-natives speakers. Under cognitive load, native speakers relied relatively more on lexical plausibility than on acoustic cues. This lexical drift was not observed in the non-native group. These results indicate that non-native speakers pay less attention to lexical information-and relatively more attention to acoustic detail-than previously thought. They also suggest that the penetrability of the speech system by cognitive factors depends on listener's proficiency with the language, and especially their level of lexical-semantic knowledge. <s> BIB007
There are good reasons to expect informational masking to have a different impact on native versus non-native listeners. On the one hand, dealing with more than one intelligible speech source requires additional cognitive loading and the ability to correctly piece together fragments from each source to make a coherent interpretation, both of which might affect listeners more adversely when processing a second language. However, listeners might suffer more from competing attention if the masker is in a language with which they are familiar, while unfamiliar language interferers may be easier to block out. In other words: the first effect could cause more difficulty for nonnative listeners, while the second effect could cause more difficulty for native listeners. Several recent studies have started to measure the effect of intelligible maskers on native and non-native listeners. One paradigm has the same listener group identifying items in their native language in the presence of native and non-native language maskers (e.g. BIB002 BIB004 while another compares the effect of a single masking language and varies the L1 of the listener group BIB006 , or crosses masker language and listener group L1 (García Lecumberri and BIB003 . The first study to show an informational masking effect due to L1 interference was BIB002 , whose Dutch listeners gained a benefit of 4.3 dB from time-reversal of Dutch speech but only 2.3 dB for Swedish material. BIB004 demonstrated that native English listeners are more adversely affected by English babble than Mandarin babble for two-talker babble but not for 6-talker babble, suggesting that audible words in babble have a greater impact if they are in the listeners' L1. In García Lecumberri and BIB003 , monolingual native English listeners scored better on a consonant recognition task in the presence of a competing Spanish speech masker than for an English masker, while a non-native Spanish group of university-level English learners suffered equally from the two maskers. These studies all point to increased interference when the language of the masker consists of known, recognisable words, whereas unknown and unrecognisable speech is easier to block out. As  showed with native listeners, the more words potentially activated by the competing speech, the greater the interference. This effect thus causes more problems for native listeners. The other possibility raised above, that non-native listeners might suffer more in the presence of competing speech, is also borne out by two recent studies in which native and non-native listeners identified speech in the presence of a speech masker. BIB005 used a classic informational masking paradigm BIB001 where listeners heard pairs of simple syntactically-equivalent and semantically-neutral sentences such as "place red at B4 now" spoken by talkers with the same or different gender, or by the same talker, and presented at a range of SNRs. This task forces listeners to separate and track sentences based on low-level cues such as F0 and gender-related differences in formant spacing. In all speaker-pairing conditions (same/different gender, same talker) non-native listeners suffered significantly more than natives, with a disadvantage that increased markedly at higher masker levels. In BIB006 , eight listener groups differing in L1 identified consonants in a competing speech masker and in a speech-modulated noise maskers designed to produce the same amount of energetic masking. While scores for the native group were equivalent for the two maskers, most of the non-native listener groups showed a greater masking effect for the competing speaker. Moreover, the additional impact of competing speech showed a negative correlation with individual listener scores in noise, suggesting that competence in the target language also helps when dealing with the effects of a competing speaker. The influence of target and background language similarity on speech perception in competing talker conditions was tackled by Van Engen (2010), who compared native English and native Mandarin speakers in identifying English sentences in the presence of either English or Mandarin 2-talker babble. Both groups suffered more in the English babble condition, suggesting that a common foregroundbackground language is detrimental regardless of whether it is in a listener's L1 or L2. Recently, other forms of informational masking have been investigated. BIB007 tested the reliance of native and non-native participants on acoustic or lexical cues to word segmentation under conditions of cognitive load, provided by a simultaneous visual search task. Their results suggest that relative to native listeners, non-natives attend more to acoustic detail when a cognitive load is present, highlighting a reduced ability to make use of lexical information under noisy conditions, a finding compat-ible with the outcome of studies reviewed in the previous section. In summary, the few studies of informational masking on non-native speech perception to date thus support the idea of both a facilitating effect for non-natives due to release from L1 interference, and a degrading impact due to other factors such as increased cognitive load when processing pairs of L2 sentences or their lesser experience with the masker language in speech separation. The relative contribution of these factors has yet to be clarified, and is likely to vary as a function of both situation-dependent factors (e.g., SNR) and listener-dependent factors (e.g., proficiency).