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Head bobs are downward movements of the head which signal the use of motion parallax, a monocular visual depth cue used by many animals, including humans. Mongolian gerbils (Meriones unguiculatus), the subjects of this study, typically execute a series of head bobs prior to jumping. Understanding how head bobs are used in different situations and controlled by the brain is important in comparing visual evolution and adaptation across species. We asked if head bobs are affected by the precise visual array, specifically ambient light level and distance to target. In addition, previous studies suggest that two brain areas, the temporal posterior cortical area (TP) and the superior colliculus (SC), have important roles in rodents’ ability to process visual motion cues. By correlating numbers of head bobs with the size of TP and SC of the gerbils, the study sought to establish the importance of these two areas in the processing of motion parallax for a specific visuomotor task. Head bob frequency was maximal overall when gerbils had to jump intermediate distances, where there was also an effect of light level. At short distances, average total head bobs (but not frequency) was maximal at low light. Head bob frequency was positively correlated with relative SC area. These results suggest that gerbils use motion parallax cues differentially under different conditions and specific brain areas contribute to this behavior.
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