Newborns' asymmetrical processing of order from sequentially presented magnitudes

Four-month-old infants extract ordinal information in number-based and size-based visual sequences, provided that magnitude changes involve increasing relations. Here the ontogenetic origins of ordinal processing were investigated between 2018 and 2022 by testing newborns' discrimination of reversal in numerosity (Experiment 1, N = 22 White, 11 females), numerical order in the presence of redundant non-numerical quantitative cues (Experiment 2, N = 44 White, 23 females), or size-based order (Experiment 3, N = 44 White, 21 females). Newborns' post-habituation preferences revealed successful discrimination only when both numerical (items' number) and non-numerical (items' size) cues concurrently changed, and following habituation to increasing order (p = 0.017, η2p = 0.135). These findings, along with evidence from older infants and non-human animals, suggest continuity in magnitude representation across ontogenetic and phylogenetic levels.