Development of ordinal sequence perception in infancy.

Perception of the ordinal position of a sequence element is critical to many cognitive and motor functions. Here, the prediction that this ability is based on a domain-general perceptual mechanism and, thus, that it emerges prior to the emergence of language was tested. Infants were habituated with sequences of moving/sounding objects and then tested for the ability to perceive the invariant ordinal position of a single element (Experiment 1) or the invariant relative ordinal position of two adjacent elements (Experiment 2). Experiment 1 tested 4- and 6-month-old infants and showed that 4-month-old infants focused on conflicting low-level sequence statistics and, therefore, failed to detect the ordinal position information, but that 6-month-old infants ignored the statistics and detected the ordinal position information. Experiment 2 tested 6-, 8-, and 10-month-old infants and showed that only 10-month-old infants detected relative ordinal position information and that they could only accomplish this with the aid of concurrent statistical cues. Together, these results indicate that a domain-general ability to detect ordinal position information emerges during infancy and that its initial emergence is preceded and facilitated by the earlier emergence of the ability to detect statistical cues.