Lateralized category-specific cognition in a “people-present/people- absent” discrimination task by pigeons

Herrnstein and Loveland (1964) showed that pigeons are capable of people-present/people-absent concept discrimination. Yamazaki et al. (2007) suggested that the use of concept-based strategy is lateralized in birds. In their study birds showed categorization superiority with the right eye (left hemisphere). To further our understanding of the role of each hemisphere in categorization behaviour, we examined concept discrimination in birds while one hemisphere or the other was deactivated. Pigeons were trained in a go/no- go procedure to discriminate pictures of humans and to transfer to novel exemplars. To examine which hemisphere was involved in categorization, an additional transfer test was conducted while the left or the right entopallium was blocked with Tetrodotoxin. On the transfer test, the birds were tested with both previously learned as well as novel people-present/people- absent instances. Discrimination of learned stimuli was not impaired when either the left or the right hemisphere was blocked. However, concept discrimination of the novel instances was impaired when the left hemisphere was blocked, although they still performed the discrimination above chance. This suggests that the left hemisphere was superior in category-specific processing, whereas the right hemisphere is just capable of discriminating between the known stimuli, thus relaying on a memorization strategy. Our findings of an asymmetrical cognitive architecture in birds are largely shared with humans and might have a long phylogenetic history