Abstract Infants can compare large (3) and small (≤3) numerosities but face difficulty with cross-boundary comparisons (e.g., 1 vs. 4). This study examined 312 Chinese infants (11–24 months; 141 girls, data collection: 2022–2025) by using a forced-choice task to investigate when and how they overcome this challenge. Success emerged at 15 months for 1 vs. 4 (1:4 ratio). Older infants succeeded with the same (2 vs. 8) and smaller ratios (2 vs. 6; 1:3), but even at 24 months struggled with 2 vs. 4 (1:2). Performance was unrelated to vocabulary size, suggesting that cross-boundary success is independent from language development. These findings highlight the engagement of nonverbal approximate number processing for both small and large numerosities.
Mou et al. (Fri,) studied this question.