Infants tune to native sounds through social, not audio-only, input

Correct: B — Around 12 months, with social interaction substantially boosting learning relative to audio-only exposure

Kuhl (2010) synthesized behavioral, neuroimaging, and intervention work showing that infants younger than 6 months discriminate phonetic contrasts from any human language, but by 10–12 months they specialize for the contrasts of their native language and lose sensitivity to non-native ones. Critically, social exposure — a live tutor playing with the infant — produces statistical learning of the foreign-language contrasts, while equivalent audio or video alone does not. The findings reframed the 'critical period' as a socially gated, statistically driven tuning process rather than a clock-driven window.