Hatching with Numbers: Pre-natal Light Exposure Affects Number Sense and the Mental Number Line in young domestic chicks

Rugani, R.; Macchinizzi, M.; Zhang, Y.; Regolin, L.

doi:10.1101/2025.03.09.642211

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bioRxiv · 10.1101/2025.03.09.642211

Hatching with Numbers: Pre-natal Light Exposure Affects Number Sense and the Mental Number Line in young domestic chicks

Rugani, R.·Macchinizzi, M.·Zhang, Y.·Regolin, L.

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Abstract

Humans order numerosity along a left-to-right Mental Number Line (MNL), traditionally considered culturally rooted. Yet, some species at birth show Spatial-Numerical Associations, SNA, suggesting neural origins. Various accounts link SNA to brain lateralization, but lack evidence. We investigated brain lateralization effects on numerical spatialization in 100 newborn domestic chicks. In-ovo light exposure yielded strongly-lateralized brains in half the chicks and weakly-lateralized in the other half. Chicks learned to select the 4th item in a sagittal array. At test, the array was rotated 90{degrees}, with left and right 4th items correct. Strongly-lateralized chicks outperformed weakly-lateralized ones when ordinal and spatial cues were reliable (experiment 1), but not with unreliable spatial cues (experiment 2). Moreover, only strongly-lateralized chicks showed left-to-right directionality, suggesting the right hemispheres key role in integrating spatial and numerical cues. We demonstrate that brain lateralization is fundamental for developing a left-to-right oriented SNA.

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Rugani, R., Macchinizzi, M., Zhang, Y., Regolin, L.. 2025-03-11. Hatching with Numbers: Pre-natal Light Exposure Affects Number Sense and the Mental Number Line in young domestic chicks. https://doi.org/10.1101/2025.03.09.642211

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