Poster D82, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall
The use speech temporal cues in phonetic processing: an electrophysiological study with infants and adults
Monica Hegde1, Laurianne Cabrera1;1CNRS-Université Paris Descartes
The current project explores the interaction between auditory and speech perception abilities during early development. Before 10 months of age, we know that infants are not yet attuned to the consonant contrasts of their native language, meaning that, as compared to adults, they are sensitive to certain non-native phonological contrasts. We know, however, that the auditory system will continue to develop until late adolescence. How, then, are young infants able to detect such varied phonological contrasts? Psychoacoustic models suggest that the auditory system decomposes a complex speech signal in a series of narrowband signals modulated over time. According to these models, speech information is mainly conveyed by the temporal modulations at the output of cochlear filters. Particularly, these modulations can be described at two different time scales: a relatively fast one, the frequency modulations (FM) and a relatively slow one, amplitude modulations (AM). Speech analysis-synthesis tools called “vocoders” are used to generate a continuum of speech sounds with increasing/decreasing spectro-temporal complexity in order to assess the role of these modulations in speech perception. A myriad of studies have shown that adults are able to rely only on the slowest AM (< 8Hz) of speech to discriminate syllables. Recent behavioural studies have shown that 6-month-old infants may require faster fluctuations of AM cues in order to discriminate consonants. Such prior results suggest that infants weight fast AM cues more heavily than adults for speech perception. Yet, the neural underpinnings as to how such modulation cue weighting changes over the course of development are still unknown. To tackle this question, we used an Electroencephalography (EEG) paradigm to measure the Acoustic Change Complex (ACC) underlying auditory detection of native and non-native consonants in French-learning 6-month-old and native-French adult listeners. We used vocoders to process three Vowel-Consonant-Vowel syllables (VCV): French voiced /aba/, French unvoiced unaspirated /apa/, and an English aspirated /apha/. Three vocoder conditions were designed to: i) preserve original FM and AM, “Intact condition”, ii) reduce FM and preserve original AM, “Full AM condition”, and iii) reduce both FM and fast AM, “Slow AM Condition”. We hypothesize that with age, listeners rely more on modulation cues important for their native language as exposure to native phonological contrasts increases and their auditory system develops. Preliminary analyses with 8 infants show different ACC patterns for the different VCVs (e.g., later positive wave for “apa” compared to “aba”). Moreover, the vocoder manipulation seems to affect the ACC responses in more frontal regions (near F3, F4). Further analyses will be carried out on EEG data collected with 20 adults to investigate whether modulation cue weighting changes with age.
Themes: Speech Perception, Development
Method: Electrophysiology (MEG/EEG/ECOG)