fNIRS time courses at 1 month (light orange), 5 months (orange) and 18 months (dark orange) across Fam1NIRS (a), Fam2NIRS (b), Fam3NIRS (c), Novelty (d) and Post-test (e) epochs. Here, time courses of all infants contributing valid data for each cross-sectional age point are shown. Figures including only infants contributing fNIRS data to all three age points (N = 60) can be found in Supplementary Figure 2. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)