Abstract
Even prior to producing their first words, infants are developing a sophisticated speech processing system, with robust word recognition present by 4-6 months of age. These emergent linguistic skills, observed with behavioural investigations, are likely to rely on increasingly sophisticated neural underpinnings. The infant brain is known to robustly track the speech envelope, however to date no cortical tracking study could investigate the emergence of phonetic feature encoding. Here we utilise temporal response functions computed from electrophysiological responses to nursery rhymes to investigate the cortical encoding of phonetic features in a longitudinal cohort of infants when aged 4, 7 and 11 months, as well as adults. The analyses reveal an increasingly detailed and acoustically-invariant phonetic encoding over the first year of life, providing the first direct evidence that the pre-verbal human cortex learns phonetic categories. By 11 months of age, however, infants still did not exhibit adult-like encoding.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Conflicts of interest: none declared.
Funding sources: This project received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 694786) (A.A., U.G.). This research was conducted with the financial support of Science Foundation Ireland under Grant Agreement No. 13/RC/2106_P2 at the ADAPT SFI Research Centre at Trinity College Dublin (G.D.L., G.C.). ADAPT, the SFI Research Centre for AI-Driven Digital Content Technology, is funded by Science Foundation Ireland through the SFI Research Centres Programme. This work was also supported by the Science Foundation Ireland Career Development Award 15/CDA/3316 (G.D.L., R.R.). G.C. was supported by an Advanced European Research Council grant (NEUME, 787836) and by the FrontCog grant ANR-17-EURE-0017.