Numbers Driving Space: Experience With Numerical Sequences Modulates Spatial Behavior in Newborn Chicks (Gallus gallus).

The preferential engagement of the right hemisphere in vertebrates biases visuospatial attention to the left. This attentional bias has been proposed as the basis for the organization of numbers along a left-to-right mental number line, with small numbers associated with the left and large ones with the right. In humans, this predisposition is modulated by culture, education, and even short exposure to spatial positions of numbers; yet data on animals are lacking. Here, in day-old chicks, we explore whether experience with increasing and decreasing numerical sequences influences the left-to-right visual exploration of numerosities. We conducted two experiments with day-old chicks (n = 70), training them to circumnavigate a sagittal sequence of three number sequences. In Experiment 1, chicks saw stimuli with either 2-5-8 (increasing-group) or 8-5-2 (decreasing-group) elements and then evaluated for searching behavior from left to right; in Experiment 2, we used larger numerosities, 8-20-32 or 32-20-8, and controlled for non-numerical cues. At test, chicks faced the stimuli arranged horizontally. We found that the increasing-group consistently approached the number stimuli from the left, regardless of the number arrangement. In contrast, the decreasing-group showed no directional preference. These results demonstrate that early exposure to numerical sequences can modulate the spontaneous left-to-right bias in newborn chicks, shedding light on the flexibility of cognitive biases in visuospatial and numerical cognition early in life.