To meet the objectives described above, the Fellow carried out 10 experiments, tested 123 adult participants and 107 infants and analyzed synchronized movements to rhythmic stimuli of 160 babies who had already been tested in previous experiments on rhythm perception. The project developed a new way to measure spontaneous rhythmic coordination of perception and action, by looking at human pupils. The experimental results show that human pupils synchronize spontaneously to rhythms in speech and music – i.e. they fluctuate in size in synchrony with the perceived rhythm. This synchronization is driven by abstract rhythmic representations that are created in the human brain. We have experimentally shown that these synchronized pupillary changes are not sensitive to low-level acoustic differences between speech and music, suggesting that rhythm is perceived in the two domains through shared cognitive and neural resources. The results also show that rhythmic violations and disparities between rhythms in different domains are detected fast and overcome immediately. This is true for both adult participants as well as young infants during the first year of life.
The project also investigated rhythm synchronization in infants of different ages, ranging between 5- and 10-months-of-age. These ages are interesting because they correspond to different developmental milestones. For example, 5-month-old infants produce babbling sounds, are not thought to know many words and cannot yet fully control their hands and legs. By 7-months-of-age infants have acquired considerable finger dexterity to handle objects with agility, they already know many common nouns and have developed considerable rhythmic knowledge. Finally, at the end of the first-year infants begin to utter their first words, they begin to walk and they are thought to master the rhythms of their native tongue. It is therefore interesting that synchronized rhythmic behavior was observed in infants’ already in the youngest age group. Developmental changes to rhythm synchronization could therefore only be detected in a graded manner, with stronger results being observed for older infants and adults. This suggests that synchronized rhythm perception is fundamental for our congitivie repertoire from the earliest stages of development.
