Fig. 8: Compensatory eye movements in freely moving mice keep the focea ahead of the animal.

a Tracking of head tilt (pitch and roll) and left and right eye positions in a freely moving mouse (inset). Illustration of head pitch and roll axes (relative to the ground), eye torsion (white arrow), and pupil centers (white dots) in angular eye coordinates (blue and red arrows). b The spherical coordinate system used in this study with [azi = 0°, ele = 0°] pointing toward the animal’s nose. The arrows indicate the foceal projection of the right (purple) and left (green) eye. Distribution of angular foceal projections in the same reference frame for an example mouse during spontaneous locomotion in an open field environment (right). Light and dark shading indicate regions of low and high probability, respectively. Dots indicate circular median position of the focea for the left (green) and right (purple) eye. Dashed lines indicate monocular visual fields for the left and right eyes (same color schema; 180° visual collection angle for each eye) showing that the focea fell into the binocular zone. c Thirty-second segment showing elevation of left/right foceas (top), horizontal, and vertical eye position of left and right eye (middle) and head pitch and roll (bottom) for the example mouse in (b). Same conventions as in (a). Control condition (“Focea fixed in head”) in top panel shows what the elevation of the focea would have been in the absence of stabilizing eye movements. d Average circular mean elevation (top) and standard deviation (SD, bottom) of the left/right foceas for the same mice either head-fixed or in three different head-free contexts (open field, social interaction, object tracking). In all three contexts, eye movements counteracted head movements to stabilize the elevation of the focea relative to the ground. Same color schema as in panels a–c. Dark gray bars show means for the focea and light gray bars show means for the control condition (“Focea fixed in head” in panels a–c). Means computed across eyes and mice. Data from four mice. Mean ± SEM. e Optical flow field during locomotion (body speed >10 cm/s) for the left (top) and right (bottom) eye. Optical flow vectors were computed for discrete grid points (spacing 10°) centered at the focea using head and eye positions and the geometry of the environment. Black arrows show average flow vectors across four mice. Green/purple shaded circles illustrate pRF size at the focea. Gray circles, pRF size at an azimuth of 50°.