Visual lateralization as an indicator of animal welfare

Functional specialization of the brain hemispheres has been observed across the animal kingdom, with the left hemisphere being associated with positive emotions while the right hemisphere is associated with negative emotions. In vertebrates, contralateral eye use is indicative of which brain hemisphere is being used for processing and so may therefore reveal affective state. Using a within-subjects design, we investigated whether lateralized eye use could be used as a non-invasive welfare indicator in captive-bred lizards (Pogona vitticeps) housed in standard or enriched enclosures for four weeks. Eye use was recorded during basking, a key maintenance behaviour. We found that when lizards were housed in standard enclosures (an environment associated with reduced welfare) they exhibited significantly greater use of their left eye (right brain hemisphere) compared to when they were housed in enriched enclosures (an environment associated with improved welfare). These findings suggest that the negative affective state induced by housing conditions is reflected in lateralized eye use, making this a promising, non-invasive tool for assessing animal welfare that is likely to be of value across vertebrate species.