Fig. 4.

Reducing rhythmic predictability reduces synchronized infant eye-looking. (A) Infant-directed singing presents predictable rhythmic cueing with relatively regular interbeat intervals (although, as noted, interbeat intervals in natural singing are not perfectly isochronous). To test the effects of reducing rhythmic predictability on infants’ looking, we experimentally manipulated the rhythm of caregiver cueing. We resampled the original audiovisual recordings and introduced jittering to the interval timing: in each song, two-thirds of the interbeat intervals were randomly varied by ±30% of their original duration. In this way, jittering disrupted the original rhythmic structure and reduced beat-to-beat predictability (bottom waveform). (B) Polar histogram showing the extent of variation in timing of interbeat intervals in original recordings (difference, in interbeat intervals relative to isochronous signal). (C) Polar histogram showing the extent of variation in the reduced predictability condition, after experimental manipulation. (D) In a replication cohort of 6 mo olds (see also SI Appendix, Fig. S4 for replication results), time-locked eye-looking is reduced when infants view singing with reduced predictability. White bars show response to original, predictable singing (data are repeated in SI Appendix, Fig. S4B and compared to the discovery cohort 6-mo-old results). Gray bars show response to reduced predictability condition. Dotted lines show 5th and 95th confidence intervals for change in eye-looking expected by chance (one-sided). (E) Phase plots of eye-looking for individual infants in the original and reduced predictability conditions, and (F) within-subject comparisons of individual phase response across conditions: diagonal lines connect phase responses of individual infants across original rhythm (top row) and reduced predictability (bottom row) conditions; two infants had usable data in one condition but not the other and so have no connecting line.