Effects of formant proximity and stimulus prototypicality on the neural discrimination of vowels: Evidence from the auditory frequency-following response

Abstract

Cross-language speech perception experiments indicate that for many vowel contrasts, discrimination is easier when the same pair of vowels is presented in one direction compared to the reverse direction. According to one account, these directional asymmetries reflect a universal bias favoring “focal” vowels (i.e., vowels with prominent spectral peaks formed by the convergence of adjacent formants). An alternative account is that such effects reflect an experience-dependent bias favoring prototypical exemplars of native-language vowel categories. Here, we tested the predictions of these accounts by recording the auditory frequency-following response in English-speaking listeners to two synthetic variants of the vowel /u/ that differed in the proximity of their first and second formants and prototypicality, with stimuli arranged in oddball and reversed-oddball blocks. Participants showed evidence of neural discrimination when the more-focal/less-prototypic /u/ served as the deviant stimulus, but not when the less-focal/more-prototypic /u/ served as the deviant, consistent with the focalization account.

Asymmetries in Accessing Vowel Representations Are Driven by Phonological and Acoustic Properties: Neural and Behavioral Evidence From Natural German Minimal Pairs

“…Three contrasts showed facilitated and asymmetric discrimination on presenting a less peripheral vowel as standard and a more peripheral vowel as deviant. These results are in line with other behavioral and electrophysiological studies (e.g., Masapollo et al, 2015 , 2017b ; Zhao et al, 2019 ) that also report easier discrimination from a more central to a more peripheral vowel. Only one contrast could be explained within the underspecification approach.…”

Neurophysiological Correlates of Asymmetries in Vowel Perception: An English-French Cross-Linguistic Event-Related Potential Study

“…We clearly need further research into the relations between behavioral and neural levels of vowel processing in crosslinguistic studies with adults as well as infants early in development. Several recent ERP studies (Slabu et al, 2012;Zhao et al, 2019) focusing on subcortical auditory processing of speech sounds in adults have found evidence to corroborate some aspects of the existing behavioral data on directional asymmetries (Masapollo et al, 2017a). In the Zhao et al study, English listeners were presented with resynthesized (shortened) versions of the less-focal/English-prototypic /u/ and more-focal/Frenchprototypic /u/ identified by Masapollo et al (2017a) in a passive listening task.…”

“…While Zhao et al’s (2019) results revealed an intriguing parallel between subcortical ERP and behavioral measures of auditory vowel processing, the precise nature of the relations between these measures remain unclear in part because they were obtained under very different task demands and stimulus presentation speeds. The behavioral perceptual tasks utilized by Masapollo et al (2017a) and Liu et al (2021) were more demanding in terms of attention and memory than the passive oddball task used by Zhao et al (2019) .…”

“…While Zhao et al's (2019) results revealed an intriguing parallel between subcortical ERP and behavioral measures of auditory vowel processing, the precise nature of the relations between these measures remain unclear in part because they were obtained under very different task demands and stimulus presentation speeds. The behavioral perceptual tasks utilized by Masapollo et al (2017a) and Liu et al (2021) were more demanding in terms of attention and memory than the passive oddball task used by Zhao et al (2019). In the AX discrimination tasks, listeners were required to make overt similarity judgements about pairs of stimuli separated by relatively long inter-stimulus intervals (ISIs) (i.e., 1,500 ms), whereas in the ERP task, listeners attended to a silent video while passively listening to trains of vowel stimuli separated by very short ISIs (i.e., ∼50 ms).…”

Development of infants’ neural speech processing and its relation to later language skills: an MEG study

“…The potentially important role of subcortical processes in predicting later language outcomes parallels the significant developmental change in subcortical regions from 7-to 11-months in the whole brain analyses. Indeed, recent growth in the adult research literature has demonstrated repeatedly that early sensory encoding of speech in largely subcortical regions is highly relevant for speech discrimination and highly malleable through experience (Slabu, Grimm, & Escera, 2012;Zhao & Kuhl, 2018;Zhao, Masapollo, Polka, Ménard, & Kuhl, 2019). This result opens many more questions that future research will need to elucidate.…”