The temporal modulation structure of illiterate versus literate adult speech

Abstract

The temporal modulation structure of speech plays a key role in neural encoding of the speech signal. Amplitude modulations (AMs, quasi-rhythmic changes in signal energy or intensity) in speech are encoded by neuronal oscillations (rhythmic variations in neural excitability in large cell networks) that oscillate at matching temporal rates. To date, however, all neural studies have investigated adult-directed speech (ADS) as produced and perceived by highly literate adults. Whether temporal features of ADS vary with the skills of the speaker, for example literacy skills, is currently unknown. Here we analyse the temporal structure of ADS spoken by illiterate, low literate (≤ 4 years of literacy) and highly literate (≥ 12 years of literacy) adults. We find that illiterates produce speech differently. Spontaneous conversational speech produced by illiterate adults showed significantly less synchronised coupling between AM bands (less phase synchronisation) than conversational speech produced by low literate and highly literate adults, and contained significantly fewer syllables per second. There was also a significant relationship between years of literacy and the amount of theta-band energy in conversational speech. When asked to produce rhythmic proverbs learned in childhood, all groups could produce speech with similar AM phase synchronisation, suggesting that the differences in spontaneous conversational speech were not caused by physiological constraints. The data suggest that the temporal modulation structure of spoken language changes with the acquisition of cultural skills like literacy that are usually a product of schooling. There is a cultural effect on the temporal modulation structure of spoken language.

A neural oscillations perspective on phonological development and phonological processing in developmental dyslexia

“…The RL‐match comparison seeks to control for the effects of reading experience on the brain. Reading experience is known to affect phonological awareness and speech processing and indeed has recently been shown also to affect the amplitude modulation structure of conversational speech (illiterate adults speak differently, see Araujo, Flanagan, Castro‐Caldas, & Goswami, ). The significant difference in encoding accuracy compared to younger reading‐level matched children found by Power and his colleagues suggests a fundamental encoding deficit for slow AM speech information in developmental dyslexia, at least for English‐speaking dyslexic children.…”

“…This possibility could be explored by studying illiterate adults as well as by studying children (see Goswami, ). Indeed, the conversational speech of illiterate adults has been shown to contain less tightly synchronised AM information than the conversational speech of literate adults (Araujo et al, ). Accordingly, the mechanisms that are most important for speech perception by illiterates may differ as well.…”

“…This provides tentative evidence that matching of the modulation structure of music and language may be found in preliterate cultures. Currently, it is notable that almost the entire neural oscillatory literature regarding language processing depends on analysing the speech perception and production of university and college students (Araujo et al, ). This should be remedied in future studies, as millions of people in the world are illiterate.…”

The Temporal Statistics of Musical Rhythm across Western Genres: An Amplitude Modulation Phase Hierarchy Model

“…Music is a universal language. However, to date only one stress-timed language, English, and one syllabletimed language, Portuguese, have been modelled using the S-AMPH and PAD approaches [7][8][9]63]. Accordingly, further studies are necessary to understand how music interventions can contribute to improving speech processing in different languages.…”

“…For example, a direct comparison of IDS and ADS using the same speakers reported by [7] showed that the phase synchronisation (temporal alignment) of delta-and theta-rate AM bands was significantly greater in IDS than in ADS, while the phase synchronisation of theta- and beta/low gamma rate AM bands in ADS was significantly greater than in IDS. The low-frequency phase synchronisation of AM bands in ADS is also significantly greater for spontaneous speech spoken by literate adults than for spontaneous speech spoken by illiterate adults [11]. Accordingly, the temporal modulation structure of speech varies depending on whether an infant or an adult is being addressed, as well as with the literacy level of the speaker.…”