Acoustic-Emergent Phonology in the Amplitude Envelope of Child-Directed Speech
Acoustic-Emergent Phonology (AEP) in the Amplitude Envelope
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Leong, V., & Goswami, U. (2015). Acoustic-Emergent Phonology in the Amplitude Envelope of Child-Directed Speech. PLOS ONE, 10 (0144411)https://doi.org/10.1371/journal.pone.0144411
When acquiring language, young children may use acoustic spectro-temporal patterns in speech to derive phonological units in spoken language (e.g., prosodic stress patterns, syllables, phonemes). Children appear to learn acoustic-phonological mappings rapidly, without direct instruction, yet the underlying developmental mechanisms remain unclear. Across different languages, a relationship between amplitude envelope sensitivity and phonological development has been found, suggesting that children may make use of amplitude modulation (AM) patterns within the envelope to develop a phonological system. Here we present the Spectral Amplitude Modulation Phase Hierarchy (S-AMPH) model, a set of algorithms for deriving the dominant AM patterns in child-directed speech (CDS). Using Principal Components Analysis, we show that rhythmic CDS contains an AM hierarchy comprising 3 core modulation timescales. These timescales correspond to key phonological units: prosodic stress (Stress AM, ~2 Hz), syllables (Syllable AM, ~5 Hz) and onset-rime units (Phoneme AM, ~20 Hz). We argue that these AM patterns could in principle be used by naïve listeners to compute acoustic-phonological mappings without lexical knowledge. We then demonstrate that the modulation statistics within this AM hierarchy indeed parse the speech signal into a primitive hierarchically-organised phonological system comprising stress feet (proto-words), syllables and onset-rime units. We apply the S-AMPH model to two other CDS corpora, one spontaneous and one deliberately-timed. The model accurately identified 72-82% (freely-read CDS) and 90-98% (rhythmically-regular CDS) stress patterns, syllables and onset-rime units. This in-principle demonstration that primitive phonology can be extracted from speech AMs is termed Acoustic-Emergent Phonology (AEP) theory. AEP theory provides a set of methods for examining how early phonological development is shaped by the temporal modulation structure of speech across languages. The S-AMPH model reveals a crucial developmental role for stress feet (AMs ~2 Hz). Stress feet underpin different linguistic rhythm typologies, and speech rhythm underpins language acquisition by infants in all languages.
Amplitude modulation, temporal structure, AM hierarchy, language acquisition, statistical regularities
This research was funded by a Harold Hyam Wingate Foundation Research Scholarship and a Lucy Cavendish College Junior Research Fellowship to VL, and by a grant from the Medical Research Council to UG (G0902375). We thank Richard Turner for the use of his PCA scripts, and Michael Stone for the use of his code.
External DOI: https://doi.org/10.1371/journal.pone.0144411
This record's URL: https://www.repository.cam.ac.uk/handle/1810/252695
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Licence URL: http://creativecommons.org/licenses/by/4.0/