The effect of literacy in the speech temporal modulation structure

• Autor(a) principal: Araújo, João Pedro Fonseca de
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.14/21898
• topic: Literacy; Speech envelope; Modulation spectrum; AM synchronisation; Psycholinguistics; Literacia; Envelope do discurso; Espectro de modulação; Sincronização de AMs; Psicolinguística; Domínio/Área Científica::Ciências Médicas::Ciências da Saúde

The temporal modulation structure of adult-directed speech is conceptualised as a modulation hierarchy comprising four temporal bands, delta, 1 – 3 Hz, theta, 4 – 8 Hz, beta, 15 – 30 Hz, and low gamma, 30 – 50 Hz. Neuronal oscillatory entrainment to amplitude modulations (AMs) in these four bands may provide a basis for speech encoding and parsing the continuous signal into linguistic units (delta – syllable stress patterns, theta – syllables, beta – onset-rime units, low gamma – phonetic information). While adult-directed speech is theta-dominant and shows tighter theta-beta/low gamma phase alignment, infant-directed speech is delta-dominant and shows tighter delta-theta phase alignment. Although this change in the speech representations could be maturational, it was hypothesized that literacy may also influence the structure of speech. In fact, literacy and schooling are known to change auditory speech entrainment, enhancing phonemic specification and augmenting the phonological detail of the lexicon’s representations. Thus, we hypothesized that a corresponding difference in speech production could also emerge. In this work, spontaneous speech samples were recorded from literate (with lower and higher literacy) and illiterate subjects and their energy modulation spectrum across delta, theta and beta/low gamma AMs as well as the phase synchronization between nested AMs analysed. Measures of the participants’ phonology skills and vocabulary were also retrieved and a specific task to confirm the sensitivity to speech rhythm of the analysis method used (S-AMPH) was conducted. Results showed no differences in the energy of delta, theta and beta/low gamma AMs in spontaneous speech. However, phase alignment between slower and faster speech AMs was significantly enhanced by literacy, showing moderately strong correlations with the phonology measures and literacy. Our data suggest that literacy affects not only cortical entrainment and speech perception but also the physical/rhythmic properties of speech production.