In the first year of life, infants possess two cognitive systems encoding numerical information: one for processing the numerosity of sets of 4 or more items, and the second for tracking up to 3 objects in parallel. While a previous study showed the former system to be already present a few hours after birth, it is unknown whether the latter system is functional at this age. Here, we adapt the auditory-visual matching paradigm that previously revealed sensitivity to large numerosities to test sensitivity to numerosities spanning the range from 2 to 12. Across studies, newborns discriminated pairs of large numerosities in a 3:1 ratio, even when the smaller numerosity was 3 (3 vs. 9). In contrast, newborn infants failed to discriminate pairs including the numerosity 2, even at the same ratio (2 vs. 6). These findings mirror the dissociation that has been reported with older infants, albeit with a discontinuity situated between numerosities 2 and 3. Two alternative explanations are compatible with our results: either newborn infants have a separate system for processing small sets, and the capacity of this system is limited to 2 objects; or newborn infants possess only one system to represent numerosities, and this system either is not functional or is extremely imprecise when it is applied to small numerosities.

Infants demonstrate robust audiovisual (AV) perception, detecting, for example, which visual face matches auditory speech in many paradigms. For simple phonetic segments, like vowels, previous work has assumed developmental stability in AV matching. This study shows dramatic differences in matching performance for different vowels across the first year of life: 3‐, 6‐, and 9‐month‐olds were familiarized for 40 sec with a visual face articulating a vowel in synchrony with auditory presentations of that vowel, but crucially, the mouth of the face was occluded. At test, infants were shown two still photos of the same face without occlusion for 1 min in silence. One face had a static articulatory configuration matching the previously heard vowel, while the other face had a static configuration matching a different vowel. Three auditory vowels were used: /a/, /i/, and /u/. Results suggest that AV matching performance varies according to age and to the familiarized vowel. Interestingly, results are not linked to the frequency of vowels in auditory input, but may instead be related to infants' ability to produce the target vowel. A speculative hypothesis is that vowel production in infancy modulates AV vowel matching.

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