Gaze tracking of large-billed crows (Corvus macrorhynchos) in a motion-capture system

Abstract

The visually guided behaviors of corvids (Corvidae) are often examined in previous studies because they provide important clues about their perception, attention, and cognition. However, the details regarding how they orient their heads toward the visual targets (or how they use their visual fields when attending to the visual targets) remain largely unclear. This study used a newly established motion capture system to examine the visual field use of large-billed crows (Corvus macrorhynchos). Study 1 employed an established ophthalmoscopic reflex technique to identify the visual field configuration, including the binocular width and optic axes, as well as the degree of eye movement. Study 2 used the motion capture system to track the head movements of freely moving crows and examined how they oriented their reconstructed visual fields toward attention-getting objects. When visual targets were moving, the crows used their binocular visual fields, particularly around the projection of the beak-tip. When the visual targets stopped moving, crows frequently used non-binocular visual fields, particularly around the regions where their optic axes were found in Study 1 (close to their visual axes). On such occasions, the crows slightly preferred the right eye. Overall, the visual field use of crows is clearly predictable. Thus, while the untracked eye movements could introduce some level of uncertainty (typically within 15 degrees), we demonstrated the feasibility of inferring a crow's attentional focus by 3D tracking of their heads. Our system represents a promising initial step towards establishing gaze tracking methods for studying corvid behavior and cognition.