Caicai Zhang

Left hemisphere lateralization for lexical and acoustic pitch processing in Cantonese speakers as revealed by mismatch negativity

For nontonal language speakers, speech processing is lateralized to the left hemisphere and musical processing is lateralized to the right hemisphere (i.e., function-dependent brain asymmetry). On the other hand, acoustic temporal processing is lateralized to the left hemisphere and spectral/pitch processing is lateralized to the right hemisphere (i.e., acoustic-dependent brain asymmetry). In this study, we examine whether the hemispheric lateralization of lexical pitch and acoustic pitch processing in tonal language speakers is consistent with the patterns of function- and acoustic-dependent brain asymmetry in nontonal language speakers. Pitch contrast in both speech stimuli (syllable /ji/ in Experiment 1) and nonspeech stimuli (harmonic tone in Experiment 1; pure tone in Experiment 2) was presented to native Cantonese speakers in passive oddball paradigms. We found that the mismatch negativity (MMN) elicited by lexical pitch contrast was lateralized to the left hemisphere, which is consistent with the pattern of function-dependent brain asymmetry (i.e., left hemisphere lateralization for speech processing) in nontonal language speakers. However, the MMN elicited by acoustic pitch contrast was also left hemisphere lateralized (harmonic tone in Experiment 1) or showed a tendency for left hemisphere lateralization (pure tone in Experiment 2), which is inconsistent with the pattern of acoustic-dependent brain asymmetry (i.e., right hemisphere lateralization for acoustic pitch processing) in nontonal language speakers. The consistent pattern of function-dependent brain asymmetry and the inconsistent pattern of acoustic-dependent brain asymmetry between tonal and nontonal language speakers can be explained by the hypothesis that the acoustic-dependent brain asymmetry is the consequence of a carryover effect from function-dependent brain asymmetry. Potential evolutionary implication of this hypothesis is discussed.

Unequal effects of speech and nonspeech contexts on the perceptual normalization of Cantonese level tones

Context is important for recovering language information from talker-induced variability in acoustic signals. In tone perception, previous studies reported similar effects of speech and nonspeech contexts in Mandarin, supporting a general perceptual mechanism underlying tone normalization. However, no supportive evidence was obtained in Cantonese, also a tone language. Moreover, no study has compared speech and nonspeech contexts in the multi-talker condition, which is essential for exploring the normalization mechanism of inter-talker variability in speaking F0. The other question is whether a talkers full F0 range and mean F0 equally facilitate normalization. To answer these questions, this study examines the effects of four context conditions (speech/nonspeech × F0 contour/mean F0) in the multi-talker condition in Cantonese. Results show that raising and lowering the F0 of speech contexts change the perception of identical stimuli from mid level tone to low and high level tone, whereas nonspeech contexts only mildly increase the identification preference. It supports the speech-specific mechanism of tone normalization. Moreover, speech context with flattened F0 trajectory, which neutralizes cues of a talkers full F0 range, fails to facilitate normalization in some conditions, implying that a talkers mean F0 is less efficient for minimizing talker-induced lexical ambiguity in tone perception.

Achieving constancy in spoken word identification: time course of talker normalization.

This event-related potential (ERP) study examines the time course of context-dependent talker normalization in spoken word identification. We found three ERP components, the N1 (100-220 ms), the N400 (250-500 ms) and the Late Positive Component (500-800 ms), which are conjectured to involve (a) auditory processing, (b) talker normalization and lexical retrieval, and (c) decisional process/lexical selection respectively. Talker normalization likely occurs in the time window of the N400 and overlaps with the lexical retrieval process. Compared with the nonspeech context, the speech contexts, no matter whether they have semantic content or not, enable listeners to tune to a talkers pitch range. In this way, speech contexts induce more efficient talker normalization during the activation of potential lexical candidates and lead to more accurate selection of the intended word in spoken word identification.

Functionally integrated neural processing of linguistic and talker information: An event-related fMRI and ERP study

Speech signals contain information of both linguistic content and a talkers voice. Conventionally, linguistic and talker processing are thought to be mediated by distinct neural systems in the left and right hemispheres respectively, but there is growing evidence that linguistic and talker processing interact in many ways. Previous studies suggest that talker-related vocal tract changes are processed integrally with phonetic changes in the bilateral posterior superior temporal gyrus/superior temporal sulcus (STG/STS), because the vocal tract parameter influences the perception of phonetic information. It is yet unclear whether the bilateral STG is also activated by the integral processing of another parameter - pitch, which influences the perception of lexical tone information and is related to talker differences in tone languages. In this study, we conducted separate functional magnetic resonance imaging (fMRI) and event-related potential (ERP) experiments to examine the spatial and temporal loci of interactions of lexical tone and talker-related pitch processing in Cantonese. We found that the STG was activated bilaterally during the processing of talker changes when listeners attended to lexical tone changes in the stimuli and during the processing of lexical tone changes when listeners attended to talker changes, suggesting that lexical tone and talker processing are functionally integrated in the bilateral STG. It extends the previous study, providing evidence for a general neural mechanism of integral phonetic and talker processing in the bilateral STG. The ERP results show interactions of lexical tone and talker processing 500-800ms after auditory word onset (a simultaneous posterior P3b and a frontal negativity). Moreover, there is some asymmetry in the interaction, such that unattended talker changes affect linguistic processing more than vice versa, which may be related to the ambiguity that talker changes cause in speech perception and/or attention bias to talker changes. Our findings have implications for understanding the neural encoding of linguistic and talker information.

Toward an integrative model of talker normalization.

Successful speech perception requires accurate mapping of speech signals to linguistic categories despite talker variation in signals. Although factors like intrinsic and context cues have been identified, a full understanding of talker normalization remains to be achieved. In particular, it is important to examine the cocontribution of intrinsic, extrinsic and other cues in an integrative way. In Experiment 1, we examined the effect of intrinsic cues and typicality of a talkers F0 range relative to population F0 range on word identification in isolation. In Experiment 2, we compared the effects of 4 contexts to identify those that consistently facilitate talker normalization. We found that without contexts, word identification accuracy was low and variable depending on talker typicality. Contexts improved performance across all talkers regardless of typicality. But only meaningless and meaningful speech contexts with cues to a talkers acoustic-phonological space showed consistent effects. We proposed a new model, integrating talker typicality, talker familiarity, and context. Whereas speech signals from familiar or typical talkers may be accurately identified standing alone, a context with cues to a talkers acoustic-phonological space is necessary in the case of unfamiliar and atypical talkers. It is thus the first model that integrates memory and context effects. (PsycINFO Database Record

Neural bases of congenital amusia in tonal language speakers

&NA; Congenital amusia is a lifelong neurodevelopmental disorder of fine‐grained pitch processing. In this fMRI study, we examined the neural bases of congenial amusia in speakers of a tonal language – Cantonese. Previous studies on non‐tonal language speakers suggest that the neural deficits of congenital amusia lie in the music‐selective neural circuitry in the right inferior frontal gyrus (IFG). However, it is unclear whether this finding can generalize to congenital amusics in tonal languages. Tonal language experience has been reported to shape the neural processing of pitch, which raises the question of how tonal language experience affects the neural bases of congenital amusia. To investigate this question, we examined the neural circuitries sub‐serving the processing of relative pitch interval in pitch‐matched Cantonese level tone and musical stimuli in 11 Cantonese‐speaking amusics and 11 musically intact controls. Cantonese‐speaking amusics exhibited abnormal brain activities in a widely distributed neural network during the processing of lexical tone and musical stimuli. Whereas the controls exhibited significant activation in the right superior temporal gyrus (STG) in the lexical tone condition and in the cerebellum regardless of the lexical tone and music conditions, no activation was found in the amusics in those regions, which likely reflects a dysfunctional neural mechanism of relative pitch processing in the amusics. Furthermore, the amusics showed abnormally strong activation of the right middle frontal gyrus and precuneus when the pitch stimuli were repeated, which presumably reflect deficits of attending to repeated pitch stimuli or encoding them into working memory. No significant group difference was found in the right IFG in either the whole‐brain analysis or region‐of‐interest analysis. These findings imply that the neural deficits in tonal language speakers might differ from those in non‐tonal language speakers, and overlap partly with the neural circuitries of lexical tone processing (e.g. right STG). HighlightsCantonese amusics show abnormal neural activities in a widely distributed network;Relative pitch processing deficit in right superior temporal gyrus and cerebellum;Working memory and/or attention deficit in right middle frontal gyrus and precuneus;Neural bases of Cantonese amusics partly overlap with brain network of lexical tone;Neural bases of amusia in tonal languages differ from those in non‐tonal languages.

Effect of Noise on Lexical Tone Perception in Cantonese-Speaking Amusics.

Congenital amusia is a neurogenetic disorder affecting musical pitch processing. It also affects lexical tone perception. It is well documented that noisy conditions impact speech perception in second language learners and cochlear implant users. However, it is yet unclear whether and how noise affects lexical tone perception in the amusics. This paper examined the effect of multi-talker babble noise [1] on lexical tone identification and discrimination in 14 Cantonesespeaking amusics and 14 controls at three levels of signal-tonoise ratio (SNR). Results reveal that the amusics were less accurate in the identification of tones compared to controls in all SNR conditions. They also showed degraded performance in the discrimination, but less severe than in the identification. These results confirmed that amusia influences lexical tone processing. But the amusics were not influenced more by noise than the controls in either identification or discrimination. This indicates that the deficits of amusia may not be due to the lack of native-like language processing mechanisms or are mechanical in nature, as in the case of second language learners and cochlear implant users. Instead, the amusics may be impaired in the linguistic processing of native tones, showing impaired tone perception already under the clear condition.

Deficits of congenital amusia beyond pitch: Evidence from impaired categorical perception of vowels in Cantonese-speaking congenital amusics

Congenital amusia is a lifelong disorder of fine-grained pitch processing in music and speech. However, it remains unclear whether amusia is a pitch-specific deficit, or whether it affects frequency/spectral processing more broadly, such as the perception of formant frequency in vowels, apart from pitch. In this study, in order to illuminate the scope of the deficits, we compared the performance of 15 Cantonese-speaking amusics and 15 matched controls on the categorical perception of sound continua in four stimulus contexts: lexical tone, pure tone, vowel, and voice onset time (VOT). Whereas lexical tone, pure tone and vowel continua rely on frequency/spectral processing, the VOT continuum depends on duration/temporal processing. We found that the amusic participants performed similarly to controls in all stimulus contexts in the identification, in terms of the across-category boundary location and boundary width. However, the amusic participants performed systematically worse than controls in discriminating stimuli in those three contexts that depended on frequency/spectral processing (lexical tone, pure tone and vowel), whereas they performed normally when discriminating duration differences (VOT). These findings suggest that the deficit of amusia is probably not pitch specific, but affects frequency/spectral processing more broadly. Furthermore, there appeared to be differences in the impairment of frequency/spectral discrimination in speech and nonspeech contexts. The amusic participants exhibited less benefit in between-category discriminations than controls in speech contexts (lexical tone and vowel), suggesting reduced categorical perception; on the other hand, they performed inferiorly compared to controls across the board regardless of between- and within-category discriminations in nonspeech contexts (pure tone), suggesting impaired general auditory processing. These differences imply that the frequency/spectral-processing deficit might be manifested differentially in speech and nonspeech contexts in amusics—it is manifested as a deficit of higher-level phonological processing in speech sounds, and as a deficit of lower-level auditory processing in nonspeech sounds.

Impaired vowel discrimination in Mandarin-speaking congenital amusics

This paper investigates if individuals with amusia show deficits in the identification and discrimination of Mandarin vowels, with the aim of exploring whether the deficiency of the amusics lies in the acoustic processing of frequency, or in pitch processing. The results showed that the amusics performed comparably as the controls in vowel identification. For discrimination, both groups exhibited better discrimination for between-category pairs than within-category pairs, indicating that the amusics are not impaired in the categorical perception of vowels. However, amusics exhibited poorer accuracy than the controls in vowel discrimination across the board, irrespective of betweenor within-category vowel pairs. Moreover, the participants’ vowel discrimination accuracy is significantly correlated to their musical ability, as indexed by the Montreal Battery of Evaluation of Amusia (MBEA) scores. The results suggest that individuals with congenital amusia might be impaired in frequency processing in general, a deficiency broader than originally believed.

Is Congenital Amusia a Disconnection Syndrome? A Study Combining Tract- and Network-Based Analysis

Previous studies on congenital amusia mainly focused on the impaired fronto-temporal pathway. It is possible that neural pathways of amusia patients on a larger scale are affected. In this study, we investigated changes in structural connections by applying both tract-based and network-based analysis to DTI data of 12 subjects with congenital amusia and 20 demographic-matched normal controls. TBSS (tract-based spatial statistics) was used to detect microstructural changes. The results showed that amusics had higher diffusivity indices in the corpus callosum, the right inferior/superior longitudinal fasciculus, and the right inferior frontal-occipital fasciculus (IFOF). The axial diffusivity values of the right IFOF were negatively correlated with musical scores in the amusia group. Network-based analysis showed that the efficiency of the brain network was reduced in amusics. The impairments of WM tracts were also found to be correlated with reduced network efficiency in amusics. This suggests that impaired WM tracts may lead to the reduced network efficiency seen in amusics. Our findings suggest that congenital amusia is a disconnection syndrome.