The Learning Objective Governs Perceptual Narrowing: A Cross-Lingual, Layer-Wise, Ten-Seed Study of Self-Supervised Speech Encoders

A study from arXiv (2608.00507v1) training a ~7M-parameter Transformer encoder on child-directed and read speech found that the learning objective, not architecture, determines perceptual narrowing in self-supervised speech encoders. Reconstruction (masked mel-prediction) degraded non-native phoneme discrimination by +0.051 in first-layer Mandarin ABX (p=3×10^-8), while prediction (frame-contrastive) improved it, with read speech producing a 3.6× steeper non-native decline. The study concludes that a single objective moves both languages the same way, failing to produce the full developmental signature.

arXiv:2608.00507v1 Announce Type: new Abstract: Perceptual narrowing---the developmental loss of non-native phoneme discrimination in the first year of life \citep{werker1984}---is a canonical developmental finding, yet \emph{what learning objective produces it} remains open. We train a \ \sim\ 7\,M-parameter Transformer encoder on child-directed and read speech and evaluate phoneme ABX in English, French, and Mandarin over ten seeds, the seed as the unit of replication. Six results. \textbf{ 1 }~The objective sets the direction of cross-lingual transfer: reconstruction masked mel-prediction degrades non-native discrimination, prediction frame-contrastive improves it---a same-encoder, same-data gap of \ +0.051\ in first-layer Mandarin ABX \ p=3\times10^{-8}\ , unanimous in sign across twenty runs. \textbf{ 2 }~That decline combines a large arm-intrinsic difficulty gradient with a smaller language-specialization effect matched vs.\ mismatched \ +0.022\ , \ p=10^{-4}\ , all four layers . \textbf{ 3 }~Against a language-symmetric raw-mel floor, reconstruction pushes the first layer \emph{below} the discriminability of its input; prediction pushes it \emph{above}. \textbf{ 4 }~Read speech gives a \ 3.6\times\ steeper non-native decline than child-directed speech. \textbf{ 5 }~The customary three-seed budget cannot see this reliably: an effect unambiguous at ten seeds is called significant by as few as 70\% of three-seed subsets. \textbf{ 6 }~Six objective configurations---sharpening, compression, consolidation, their composition, and word-level semantic grounding in two forms---fail to produce the full developmental signature native improves \emph{and} non-native declines : a single objective moves both languages the same way because it acts on a shared representation. We conclude that the objective, not the architecture, is the first-order determinant of narrowing-shaped representational change.