Segmental and supra-segmental aspects of speech perception in familiar and unfamiliar languages: Influence of the listener's native language as revealed by Event-related potentials (ERPs)

The phonological structure differs between languages. Human brain structure subserving speech perception is shaped through early exposure to and long-term experience with one’s native language, so that the sensitivity to specific acoustic cues that are relevant in that language develops. Such adaptive process of brain plasticity facilitates to recognize phonemes and capture prosodic signals correctly in the native language, whereas it augments difficulty to perceive some linguistic cues in foreign languages. Speech phonology consists of segmental and suprasegmental components. Segmental components are expressed by formants defining phonemes, and suprasegmental components are defined by pitch (fundamental frequency: F0), intensity and temporal parameters (duration of phonemes and of pauses). The present studies are aimed at investigating cortical auditory processing of segmental and suprasegmental components of speech using the techniques of event-related brain potentials (ERPs). In Study I, two experiments were conducted to explore the auditory perception of vowels that belong or not to the phonemic inventory of listeners’ native language. The mismatch negativity (MMN) is an ERP component reflecting pre-attentive detection of auditory deviance compared with the integrated representation of standard features in the sensory memory (Naatanen et al., 2007; Kujala et al., 2007 for reviews). In the present study, this component was used to tap language-specific long-term memory traces for vowels (Naatanen et al., 1997; Cheour et al., 1998; Winkler et al., 1999a). An auditory sequence including four vowels (one standard and three deviants), each pronounced by three speakers, was presented in passive and active listening conditions. When all the vowels were distinctive in the native inventory (Experiment 1), the MMN was elicited by each deviant vowel category independently of speaker variability, demonstrating pre-attentive categorization based on long-term memory traces. By contrast, when a part of vowels did not belong to the native phonemic inventory (Experiment 2), deviant vowels did not elicit MMNs, indicating the lack of automatic categorization. Moreover, speaker’s variability interacted with vowel category only in the active listening condition, as reflected by behavioral data and cognitive ERP components, suggesting that listeners depended more on conscious acoustic analysis of each stimulus than on pre-attentive categorization, when the deviant to discriminate is physically similar to the standard or is not supported by the inventory in the native language. In Study II, another experiment (Experiment 3) was conducted to investigate the perception of small and large pitch changes embedded in sentences spoken in listeners’ native language, jabberwocky or a foreign language. Behavioral performance in a pitch change detection task and the ERP components elicited by pitch changes (an early centro-temporal negativity and a later positivity) were analyzed. Results showed that subjects processed phrasal pitch better in their native language than in the foreign language, while the results for jabberwocky sentences were intermediate, suggesting that both familiar prosodic patterns and natural and meaningful context in the native language help listeners to detect subtle changes in phrasal pitch contour. Overall results confirmed that long-term experience with one’s native language has effects from early stages of cortical auditory processing involved in speech perception, modulating conscious perception of speech stimuli in different languages.