Fig. 18

Estimation of gaze direction for the pursuit flight. The trajectory of the marker attached to the food reward in the gaze calibration trial is represented in two coordinate systems: one that translates with the headpack and is parallel to the motion capture coordinate system (a), and one fixed to the headpack (b). The estimated gaze direction \(\vec {v}_{gaze}\) is the orthogonal regression line (cyan) to the samples in the fixation phase (blue) in the headpack coordinate system (b). The samples outside this phase are shown for reference (black, semi-transparent). The food reward is presented to the bird at a distance between 0.5 and 1.5 m. Note how the position of the food marker in the fixation phase in (b) falls within a small region, in contrast to the curved trajectory it follows in (a), suggesting the bird is actively positioning the food reward on a small area of its visual field during that phase. Inset in (b) shows the approximate orientation of the headpack coordinate system relative to the bird’s head