Low-rank Gallus gallus domesticus chicks are better at transitive inference reasoning.

A form of deductive reasoning, transitive inference, is thought to allow animals to infer relationships between members of a social group without having to remember all the interactions that occur. Such an ability means that animals can avoid direct confrontations which could be costly. Here we show that chicks perform a transitive inference task differently according to sex and rank. In female chicks, low-ranking birds performed better than did the highest ranked. Male chicks, however, showed an inverted U-shape of ability across rank, with the middle ranked chicks best able to perform the task. These results are explained according to the roles the sexes take within the group. This research directly links the abilities of transitive inference learning and social hierarchy formation and prompts further investigation into the role of both sex and rank within the dynamics of group living.

Time-dependent lateralization of social learning in the domestic chick (Gallus gallus domesticus): Effects of retention delays in the observed lateralization pattern.

Day-old chicks have been shown capable of learning to avoid pecking by observation only of a conspecific showing a disgust reaction after pecking a bitter-tasting bead. This learning is lateralized: access to the right hemisphere appears necessary for successful performance 30 min after training. This is in contrast to the non-social learning version of this learning task, in which the left hemisphere appears to play the dominant role, although both the left and right hemispheres are, in turn, subject to brief windows of "enhanced recall" during memory formation. In our present work we wished to investigate whether such recall events are also prevalent in the social learning task. We investigated 3 such windows; 25 min (a right hemisphere event), 32 min (left-hemisphere event) and 64 min (a possible left-hemisphere event following an interconnection of both hemispheres allowing memory transfer between the two hemispheres). At 32 and 64 min after training we found no evidence of functional lateralization. At 25 min, however, we found right hemisphere dominance. We suggest that a lateralization effect occurs in the social version of the PAL (passive avoidance learning) only at time points associated with right hemisphere dominance. It seems that lateralization is not able to emerge at time points where a left-hemisphere event is expected, because the two "lateralization effects" (right hemisphere dominance associated with the social task and left-hemisphere dominance associated with the PAL task) are in conflict.

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. 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.

Lateralization of social cognition in the domestic chicken (Gallus gallus).

In this paper, we report on the ongoing work in our laboratories on the effect of lateralization produced by light exposure in the egg on social cognition in the domestic chick (Gallus gallus). The domestic chick possesses a lateralized visual system. This has effects on the chick's perception towards and interaction with its environment. This includes its ability to live successfully within a social group. We show that there is a tendency for right brain hemisphere dominance when performing social cognitive actions. As such, chicks show a left hemispatial bias for approaching a signalled target object, tend to perceive gaze and faces of human-like masks more effectively when using their left eye, are able to inhibit a pecking response more effectively when viewing a neighbour tasting a bitter substance with their left eye, and are better able to perform a transitive inference task when exposed to light in the egg and when forced to use their left eye only compared to dark-hatched or right eye chicks. Some of these effects were sex specific, with male chicks tending to show an increased effect of lateralization on their behaviours. These data are discussed in terms of overall social cognition in group living.