English Vowel Discrimination and Perceptual Assimilation by Japanese Listeners.

This study examined whether the discrimination accuracy of nonnative vowels could be predicted by how listeners assimilate nonnative phones into their L1. The results demonstrated that Japanese listeners discriminated between English /æ/ and /ʌ/ better than they did between /ɑ/ and /ʌ/, although they categorized all those stimuli as the Japanese /a/. Given that the acoustic distance between stimuli was controlled to be identical, this result was attributed not to the acoustic difference but to the category-goodness difference. The goodness-of-fit to the Japanese /a/ phoneme differed between the English /æ/ and /ʌ/ but not between the English /ɑ/ and /ʌ/, suggesting that it is more difficult to discriminate between vowels when the category-goodness difference between two nonnative stimuli is smaller. In addition, this study examined the relationship between perceptual assimilation and the focalization effect. Focalization affects directional asymmetry in a manner that renders detecting a sound change from a more-focal to a less-focal vowel more difficult than detecting a change in the opposite direction. The results demonstrated that this directional asymmetry is only observed when listeners assimilate two nonnative phones into a single L1 phonemic category, with no category-goodness difference between the two nonnative phones.

Perception of noise-vocoded sine-wave speech of Japanese pitch-accent words.

The present study examined whether the identification accuracy of Japanese pitch-accent words increased after the sine-wave speech underwent noise vocoding, which eliminates the quasi-periodicity of the sine-wave speech. The results demonstrated that Japanese listeners were better at discriminating sine-wave speech than noise-vocoded sine-wave speech, with no significant difference in identification between the two conditions. They identify sine-wave pitch-accent words to some extent using acoustic cues other than the pitch accent. The noise vocoder used in the present study might not have been substantially effective for Japanese listeners to show a significant difference in the identification between the two conditions.

Audiovisual English /r/-/l/ Identification Training for Japanese-Speaking Adults and Children.

Purpose This study tested the hypothesis that audiovisual training benefits children more than it does adults and that it improves Japanese-speaking children's English /r/-/l/ perception to a native-like level. Method Ten sessions of audiovisual English /r/-/l/ identification training were conducted for Japanese-speaking adults and children. Assessments were made of age effects on the increase in identification accuracy in three testing conditions (audiovisual, visual only, and audio only) and auditory discrimination of the primary acoustic cue (F3 frequency). Results The results showed that both adults and children increased their identification accuracy in the audiovisual condition more than in the single-modality conditions (visual only and audio only). Their improvement in the visual-only condition was larger than that in the audio-only condition. Japanese-speaking adults and children improved their primary acoustic cue (F3) sensitivity to a similar extent. In addition, their identification improvement in the audiovisual condition was positively correlated with those in the audio-only and visual-only conditions. The improvement in the audio-only condition was also positively correlated with that in the visual-only condition and with primary acoustic cue sensitivity. Conclusion It was unclear whether children had an advantage over adults in improving their identification accuracy, but both age groups improved their auditory and visual perception of the English /r/-/l/ contrast and showed additive effects in the multisensory (i.e., audiovisual) condition.

Abstractness of human speech sound representations.

We argue, based on a study of brain responses to speech sound differences in Japanese, that memory encoding of functional speech sounds-phonemes-are highly abstract. As an example, we provide evidence for a theory where the consonants/p t k b d g/ are not only made up of symbolic features but are underspecified with respect to voicing or laryngeal features, and that languages differ with respect to which feature value is underspecified. In a previous study we showed that voiced stops are underspecified in English [Hestvik, A., & Durvasula, K. (2016). Neurobiological evidence for voicing underspecification in English. Brain and Language], as shown by asymmetries in Mismatch Negativity responses to /t/ and /d/. In the current study, we test the prediction that the opposite asymmetry should be observed in Japanese, if voiceless stops are underspecified in that language. Our results confirm this prediction. This matches a linguistic architecture where phonemes are highly abstract and do not encode actual physical characteristics of the corresponding speech sounds, but rather different subsets of abstract distinctive features.