Oscillatory Dynamics Underlying Perceptual Narrowing of Native Phoneme Mapping from 6 to 12 Months of Age

Abstract

During the first months of life, human infants process phonemic elements from all languages similarly. However, by 12 months of age, as language-specific phonemic maps are established, infants respond preferentially to their native language. This process, known as perceptual narrowing, supports neural representation and thus efficient processing of the distinctive phonemes within the sound environment. Although oscillatory mechanisms underlying processing of native and non-native phonemic contrasts were recently delineated in 6-month-old infants, the maturational trajectory of these mechanisms remained unclear. A group of typically developing infants born into monolingual English families, were followed from 6 to 12 months and presented with English and Spanish syllable contrasts varying in voice-onset time. Brain responses were recorded with high-density electroencephalogram, and sources of event-related potential generators identified at right and left auditory cortices at 6 and 12 months and also at frontal cortex at 6 months. Time-frequency analyses conducted at source level found variations in both and ␥ ranges across age. Compared with 6-month-olds, 12-month-olds' responses to native phonemes showed smaller and faster phase synchronization and less spectral power in the range, and increases in left phase synchrony as well as induced high-␥ activity in both frontal and left auditory sources. These results demonstrate that infants become more automatized and efficient in processing their native language as they approach 12 months of age via the interplay between and ␥ oscillations. We suggest that, while oscillations support syllable processing, ␥ oscillations underlie phonemic perceptual narrowing, progressively favoring mapping of native over non-native language across the first year of life.

Critical period regulation across multiple timescales

“…Infants form phonemic categories via a process of perceptual narrowing to their native tongue, during a CP in the first year of life (8). At 6 mo, when environmental input is actively shaping phonemic maps, exposure to a native phonemic contrast leads to a rise in low gamma power; this rise is not observed after infants reach 1 y of age (77,78). Interestingly, the timing of both phoneme category formation and speech-induced gamma activity are maturationally constrained.…”

Synchronous, but not entrained: exogenous and endogenous cortical rhythms of speech and language processing

“…First, late in the womb and up to six months after birth, fetuses and neonates are able to distinguish both native and non-native phonemes (Gervain, 2015;Mahmoudzadeh et al, 2013); six months after birth and possibly earlier (Moon, Lagercrantz, & Kuhl, 2013), this perceptual ability narrows selectively towards native phonemes (Kuhl, 2000;Kuhl, Ramirez, Bosseler, Lin, & Imada, 2014). Such perceptual specialisation occurs both on the phonemic and syllabic level; strikingly, for phonemes, specialisation is associated with an enhancement of gamma-band entrainment (Ortiz-Mantilla, Hamalainen, Realpe-Bonilla, & Benasich, 2016), whereas for syllables, it is associated with an amplification of theta-band entrainment (Bosseler et al, 2013;Ortiz-Mantilla et al, 2016).…”

Synchronous, but not Entrained: Exogenous and Endogenous Cortical Rhythms of Speech and Language Processing

“…First, late in the womb and up to six months after birth, fetuses and neonates are able to distinguish both native and non-native phonemes (Gervain, 2015;Mahmoudzadeh et al, 2013); six months after birth and possibly earlier (Moon, Lagercrantz, & Kuhl, 2013), this perceptual ability narrows selectively towards native phonemes (Kuhl, 2000;Kuhl, Ramirez, Bosseler, Lin, & Imada, 2014). Such perceptual specialisation occurs both on the phonemic and syllabic level; strikingly, for phonemes, specialisation is associated with an enhancement of gamma-band entrainment (Ortiz-Mantilla, Hamalainen, Realpe-Bonilla, & Benasich, 2016), whereas for syllables, it is associated with an amplification of theta-band entrainment (Bosseler et al, 2013;Ortiz-Mantilla et al, 2016).…”