Best evidence across studies

Key takeaways (visualized as short structured bullets)

• Bilingual attention: L2 usage selectively modulates higher‑level attentional control (alpha-band ERS/ERD) while low‑level cortical speech envelope tracking (delta-driven) remains stable across usage groups Bilingual usage -> alpha modulation
• Hearing variability and sex: Large-scale audiometric datasets show greater male variance and higher male correlations across measures consistent with a role for X‑inactivation mosaicism in females; mean differences depend on dataset/context GMV and GMCs in hearing
• Clinical & applied studies in bundle: Several additional applied/clinical/education studies report robust real-world effects: NICU parent–infant closeness increased after staff training (≈+99 min/day presence; +24 min/day skin‑to‑skin) NICU closeness intervention, statin use rose among older adults with dementia but adherence and 3-year discontinuation were high Statin use & discontinuation in dementia.

Evidence quality, main limitations, and blindspots

• Most primary studies here are moderate quality (scores ~7–8) but include non-randomized or cross‑sectional designs (limits causal inference) — sample sizes vary (small EEG groups vs large audiometric cohorts) EEG study sample/limitsAudiometry datasets & limits.
• Common blindspots: reliance on self-report (usage), cross-sectional snapshots (not longitudinal plasticity), possible language-pair specificity (English–French), and environmental/test differences across large audiometric datasets.

What data would disprove key claims

• If larger, well-powered longitudinal studies find no relation between current L2 usage and alpha‑band modulation or behavioral interference resilience, the usage‑driven attentional adaptation claim would be falsified Falsifying bilingual usage effects.
• If audiometric re-analyses controlling for measurement context, age, noise exposure, and sampling show no consistent male > female variance advantage, the X‑inactivation explanatory preference would be weakened Falsifying X‑mosaicism link.

Practical implications (short)

1. For bilingual cognition research: emphasize longitudinal or within‑subject usage manipulations and combine behavioral, mTRF, and oscillatory metrics to dissociate low‑level encoding from top‑down control processes Design suggestion for bilingual studies.
2. For sex-difference research in sensory function: replicate GMV/GMC analyses across harmonized audiometric datasets and, where possible, link hearing variability to genotyped X-linked markers or mosaicism assays rather than infer solely from variance patterns Recommendation for genetics follow-up.