Small on the left, large on the right: Numbers orient visual attention onto space in preverbal infants

Numbers are represented as ordered magnitudes along a spatially oriented number line. While culture and formal education modulate the direction of this number-space mapping, it is a matter of debate whether its emergence is entirely driven by cultural experience. By registering 8-9-month-old infants' eye movements, this study shows that numerical cues are critical in orienting infants' visual attention towards a peripheral region of space that is congruent with the number's relative position on a left-to-right oriented representational continuum. This finding provides the first direct evidence that, in humans, the association between numbers and oriented spatial codes occurs before the acquisition of symbols or exposure to formal education, suggesting that the number line is not merely a product of human invention. This work addresses the origins of the link between numbers and oriented spatial codes, as hypothesized under the'mental number line' model of numerical representation. Using a Posner-like task, we found that numerical (arrays of dots), but not non-numerical (size), cues orient 8-9 month-old infants' visual attention towards a peripheral region of space that is congruent with the number's relative position on a left-to-right oriented representational continuum. This evidence shows that a tendency to associate numbers onto spatial positions along a left-to-right oriented axis emerges before humans learn to read, write or count on their hands, and before acquisition of symbolic knowledge, supporting to the view that the number line is not merely a product of human invention.