Auditory Masking Effects On Non-native Speech Perception In Babble Noise

Natural spoken communication usually takes place in noise,which deteriorates the accuracy and efficiency to recognize the target signals for listeners,especially nonnative listeners.The perceptual difficulty caused by noise is mainly attributed to two types of masking effects produced by noise,that is,energetic masking and informational masking.Masking effects can reduce non-native speech intelligibility to different degrees due to varied factors,including noise types and levels,individual differences such as second language(L2)proficiency and so on.Therefore,in order to investigate how the two types of masking effects influence non-natives' Mandarin speech perception,the present study adopted forced-choice identification tasks in which participants were required to identify target speech sounds in noise.Babble noise with both acoustic cues and linguistic cues and babble-modulated noise with only acoustic cues were used as maskers so that both energetic masking and informational masking were taken into consideration.Two experiments were conducted in the present study.In Experiment 1,the target signals were presented without semantic context by using isolated vowel-tone phonemes in order to investigate the influence of masking effect in six-talker babble on Mandarin vowel-plus-tone identification.30 participants were recruited and equally divided into three groups: Chinese native group and Korean listeners respectively with high and medium Chinese proficiency.A 3�3�2�20 mixed factorial design was employed.It was found that Korean listeners significantly underperformed Chinesenative listeners mainly due to greater energetic masking,but they suffered from comparable informational masking with native listeners.Since no significant difference was found among informational masking effects of three listener groups,a follow-up experiment was designed by presenting target sounds in speech flows(sentences)with more semantic information in order to increase the weighting of informational masking.36 listeners were recruited and divided into the same groups as Experiment 1.A 3�2�6 mixed factorial design was employed.Numbers of talkers in noise were increased to five levels(one-different-gender babble,one-samegender babble,two-talker babble,four-talker babble,eight-talker babble)to test how different numbers of talkers affected the amount of masking effects.Results suggested that informational masking had greater influence than energetic masking on Mandarin speech perception in natural speech flows.Meanwhile,Chinese native listeners surprisingly suffered from more informational masking effects than non-native listeners when number of talkers in maskers were no less than 2.These results imply that the better listeners know a language,the more informational masking effects they may suffer from.Overall,listeners' identification performance was significantly reduced in noise due to the masking effects.Non-native groups significantly underperformed their native peers,but the non-native disadvantage in perceiving speech sounds in noise was only found between Chinese natives and Korean-native listeners with medium Chinese proficiency while Korean listeners with high Chinese proficiency showed comparable performance with Chinese natives in this study.This result indicated that non-native listeners with lower L2 proficiency may not only suffer from greater energetic masking and informational masking,but also have poorer ability to take advantage of the temporal modulations in noise so that the masking effects were not easy to be released.Results of the study have both theoretical and practical contributions.On the one hand,the study is a vital attempt to discuss phonetics,second language acquisition and audiology with an interdisciplinary approach,enriching the literature of non-native Mandarin speech perception in noise.One the other hand,regarding the pedagogical uses,teaching materials and environment for L2 learners should be more exquisitely designed due to their disadvantage of speech perception in noise.As for the clinical application,this study serves as new attempt to help design hearing aid devices which are more suitable for Chinese listeners.