Procedural memory in infancy: evidence from implicit sequence learning in an eye-tracking paradigm

Procedural memory underpins the learning of skills and habits. It is often tested in children and adults with sequence learning on the serial reaction time (SRT) task, which involves manual motor control. However, due to infants’ slowly developing control of motor actions, most procedures that require motor control cannot be examined in infancy. Here, we investigated procedural memory using an SRT task adapted for infants. During the task, images appeared at one of three locations on a screen, with the location order following a five-item recurring sequence. Three blocks of recurring sequences were followed by a random-order fourth block and finally another block of recurring sequences. Eye movement data were collected for infants (n = 35) and adults (n = 31). Reaction time was indexed by calculating the saccade latencies for orienting to each image as it appeared. The entire protocol took less than 3 min. Sequence learning in the SRT task can be operationalized as an increase in latencies in the random block as compared with the preceding and following sequence blocks. This pattern was observed in both the infants and adults. This study is the first to report learning in an SRT task in infants as young as 9 months. This SRT protocol is a promising procedure for measuring procedural memory in infants.