Asymmetrical number-space mapping in the avian brain.

When trained to peck a selected position in a sagittally-oriented series of identical food containers, and then required to generalize to an identical series rotated by 90°, chicks identify as correct only the target position from the left end, while choosing the right one at chance. Here we show that when accustomed to systematic changes in inter-elements distances during training or faced with similar spatial changes at test, chicks identify as correct both the target positions from left and right ends. However, ordinal position is spontaneously encoded even when inter-element distances are kept fixed during training (in spite of the fact that distances between elements suffice for target identification without any numerical computation). We explain these findings in terms of intra-hemispheric coupling of bilateral numerical (ordinal) representation and unilateral (right hemispheric) spatial representation of the number line, producing differential allocation of attention in the left and right visual hemifields.