Acoustic measures of speech sound production in multilingual children: A scoping review protocol

In most societies, using more than one language or language variety is the norm, yet the reference data against which children's speech is judged derive largely from monolingual speakers. Systematic cross-linguistic variation is therefore liable to be read as atypical development, placing multilingual children at risk of misdiagnosis of speech sound disorder (SSD). This risk is most acute for closely related, understudied varieties, where difference and disorder overlap and community-specific data are scarce. Acoustic measures (e.g., voice onset time, vowel formants, segment durations) quantify fine-grained, continuous properties of speech production that categorical, transcription-based description obscures. No existing review, however, has mapped which acoustic measures have been applied to multilingual children, across which language varieties, or against which reference baselines their productions are interpreted. The objective of this review is to provide that map, showing where acoustic evidence is concentrated and where it is absent, to support clinical assessment and to identify where community-specific reference data are most needed. The review will follow updated Joanna Briggs Institute scoping review methodology and will be reported per the PRISMA Extension for Scoping Reviews. Searches will be conducted in MEDLINE (Ovid), Embase (Ovid), CINAHL (EBSCO), Web of Science Core Collection, and Linguistics and Language Behavior Abstracts, with grey literature sought through ProQuest Dissertations and Theses Global and conference proceedings; no date limits will be applied. Children from birth to 18 years are eligible regardless of clinical status, and a preschool subset (≤ 5;11) will be reported separately. After pilot calibration, two reviewers will independently screen and chart sources, resolving disagreements by discussion or a third reviewer. Charted data will be mapped through an acoustic-measure taxonomy crossed with language variety and reference baseline. This protocol has been registered on the Open Science Framework (OSF https://doi.org/10.17605/OSF.IO/R2EX5).