Logic in an asymmetrical (social) brain: Transitive inference in the young domestic chick

The ability of animals to perform transitive inference is associated with social group formation and dominance hierarchies. Brain lateralization is also linked to the selective pressures associated with social life. We investigated whether transitive inference is better performed by lateralized than non-lateralized brains. In the domestic chick (Gallus gallus) exposure of eggs to light before hatching leads to the development of lateralization of some visual functions. Thus, it is possible to obtain chicks with strong (light-incubated, Li-chicks) or weak (dark-incubated, Di-chicks) lateralization. Di- and Li-chicks were trained to discriminate stimulus pairs, in order to build a hierarchy (A < B < C < D < E). Chicks were subsequently tested on stimulus pairs never seen together before (AE and BD). Li-chicks performed the discrimination BD better than did Di-chicks, suggesting that exposure to light in the egg leads to an increased ability to carry out representational learning. Moreove...