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

Abstract

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. Moreover, lateralized chicks using their left eye only (right hemisphere) during test showed a better performance than did right eye only (left hemisphere) chicks on the BD task. Females also tended to perform better than males. Results demonstrate that chicks with lateralized brain hemispheres show greater inference, and this is under right hemisphere control: the brain hemisphere that is dominant in social interactions.

Keywords:

• Gallus gallus domesticus
• Chick
• Lateralization
• Brain hemisphere
• Transitive inference

This research is part of the project EDCBNL (Evolution and Development of Cognitive, Behavioural and Neural Lateralisation—2006–2009), supported by the Commission of the European Communities within the framework of the specific research and technological development programme “Integrating and strengthening the European Research Area” (“What it Means to be Human” initiative), through a financial grant to LR. The authors would like to thank Federico Del Gallo and Consuelo Besazza for their help with gathering data and caring for the chicks. We also thank two anonymous referees for helpful comments on the manuscript.