The developing cognitive substrate of sequential action control in 9- to 12-month-olds: evidence for concurrent activation models.

Nine-month-olds start to perform sequential actions. Yet, it remains largely unknown how they acquire and control such actions. We studied infants' sequential-action control by employing a novel gaze-contingent eye tracking paradigm. Infants experienced occulo-motor action sequences comprising two elementary actions. To contrast chaining, concurrent and integrated models of sequential-action control, we then selectively activated secondary actions to assess interactions with the primary actions. Behavioral and pupillometric results suggest 12-month-olds acquire sequential action without elaborate strategy through exploration. Furthermore, the inhibitory mechanisms ensuring ordered performance develop between 9 and 12 months of age, and are best captured by concurrent models.