(a) Infant arousal around caregiver vocalisations, subdivided caregiver vocalisation intensity. (b) Infant arousal around caregiver vocalisations, subdivided by caregiver vocalisation type. (c) Identical to a, but examining the change in caregiver arousal, subdivided caregiver vocalisation intensity. (d) Identical to b, but examining the change in caregiver arousal, subdivided by caregiver vocalisation type. For all plots, shaded areas indicate standard error, and red highlights indicate areas of significant difference after correction for multiple comparisons (Figs a and b only).