Numerical magnitude, rather than individual bias, explains spatial numerical association in newborn chicks

We associate small numbers with the left side and large numbers with the right side of space. Recent evidence from human newborns and non-human animals has challenged the primary role assigned to culture, chiefly linked to reading and writing habits, in determining this spatial numerical association (SNA). Nevertheless, the effect of individual spatial biases has not been considered in previous research. Here we tested the effect of numerical magnitude in SNA and we also controlled for individual biases. We trained 3-day-old chicks (Gallus gallus) on a given numerical magnitude (i.e., 5). Then chicks could choose between two identical, left or right, stimuli both representing either 2, 8, or the familiar numerosity (5). We computed the percentage of Left-sided Choice (LC). We found that LC is explained by numerical magnitude: LC2vs.2 > LC5vs.5 > LC8vs.8, and not by individual lateral bias in the spatial task. This findings suggest that SNA originates from pre-linguistic precursors, and paves the way to the investigation of the neural correlates of the number space association.