Lizards assess complex social signals by lateralizing colour but not motion detection.

Vertebrates lateralize many behaviours including social interactions. Social displays typically comprise multiple components, yet our understanding of how these are processed comes from studies that typically examine responses to the dominant component or the complex signal as a whole. Here, we examined laterality in lizard responses to determine whether receivers separate the processing of motion and colour signal components in different brain hemispheres. In Psammophilus dorsalis, males display colours that dynamically change during courtship and aggressive interactions. We tested the visual grasp reflex of both sexes using robotic stimuli that mimicked two signal components: (1) multiple speeds of head-bobbing behaviour and (2) multiple colours. We found no laterality in response to different motion stimuli, indicating that motion similarly attracts attention from the two visual fields across sexes. Notably, receivers showed left visual field dominance to colours, especially when males were exposed to 'aggression-specific' colours and females to 'courtship-specific' colours.