A mental number line in human newborns

Abstract

Humans represent numbers on a mental number line with smaller numbers on the left and larger numbers on the right side. A left‐to‐right oriented spatial–numerical association, (SNA), has been demonstrated in animals and infants. However, the possibility that SNA is learnt by early exposure to caregivers’ directional biases is still open. We conducted two experiments: in Experiment 1, we tested whether SNA is present at birth and in Experiment 2, we studied whether it depends on the relative rather than the absolute magnitude of numerousness. Fifty‐five‐hour‐old newborns, once habituated to a number (12), spontaneously associated a smaller number (4) with the left and a larger number (36) with the right side (Experiment 1). SNA in neonates is not absolute but relative. The same number (12) was associated with the left side rather than the right side whenever the previously experienced number was larger (36) rather than smaller (4) (Experiment 2). Control on continuous physical variables showed that the effect is specific of discrete magnitudes. These results constitute strong evidence that in our species SNA originates from pre‐linguistic and biological precursors in the brain.

Commentary: A mental number line in human newborns

“…Therefore, when total perimeter but not SF content of the stimuli used to test numerosity effects is experimentally controlled, apparent numerical biases reflect natural lateralization of SF processing. If our SF explanation of Di Giorgio et al (2019) finding is correct, the resulting association "few-left" and "many-right" holds to the degree that numerosity and SF are correlated, e.g., when large numbers tend to be represented by smaller objects. Although our analysis holds for the above habituation study, the same SF filtering principle applies also to viewing stimuli prior to habituation.…”

“…MF and SS contributed to developing the idea. JL helped AF to perform computations on original stimuli used by Di Giorgio et al (2019) and participated in the discussions. MF supervised all steps of this work.…”

“…When we modeled this naturally-occurring visual filtering process on the very stimuli used by Di Giorgio et al (2019), their behavioral bias emerged from the hemispheric lateralization of SF processing: For any visual scene, patterns with relative few elements preferentially engage the right hemisphere, thus favoring leftward behavior. Conversely, patterns with relative many elements preferentially engage the left hemisphere, thus inducing rightward behavior ( Figure 1C).…”

Editorial: On the Development of Space-Number Relations: Linguistic and Cognitive Determinants, Influences, and Associations

“…In the first group of papers, McCrink and de Hevia outline a new theory on origins of directional SNAs. Their work attempts to integrate opposing views on directionality in SNAs: the nativist (e.g., Rugani et al, 2015;Di Giorgio et al, 2019) and culture related (Shaki et al, 2009;Patro et al, 2016a,b;Patro and Nuerk, 2017). According to their new proposal, left-to-right SNAs are inborn, but in humans they weaken at toddlerhood and then are further (re)shaped by cultural factors.…”

Transfer from number to size reveals abstract coding of magnitude in honeybees

“…According to this hypothesis, quantity representations in the various domains, (i.e., number, space and time), would be processed by a «common magnitude system», which represents these dimensions via the same unit of magnitude (6). Evidence that the temporal, spatial, and numerical features of a stimulus can interact with one another has been provided for vertebrates such as monkeys (7) and birds (8), and for prelinguistic human babies (9). Interestingly, honeybees have been shown to exhibit the numerical distance effect (i.e., the fact that the ability to discriminate between numbers improves as the numerical distance increases (e.g., zero vs. four is easier than zero vs. one, (5)).…”