Eye-head coordination during free exploration in human and cat.

Eye, head, and body movements jointly control the direction of gaze and the stability of retinal images in most mammalian species. The contribution of the individual movement components, however, will largely depend on the ecological niche the animal occupies and the layout of the animal's retina, in particular its photoreceptor density distribution. Here the relative contribution of eye-in-head and head-in-world movements in cats is measured, and the results are compared to recent human data. For the cat, a lightweight custom-made head-mounted video setup was used (CatCam). Human data were acquired with the novel EyeSeeCam device, which measures eye position to control a gaze-contingent camera in real time. For both species, analysis was based on simultaneous recordings of eye and head movements during free exploration of a natural environment. Despite the substantial differences in ecological niche, photoreceptor density, and saccade frequency, eye-movement characteristics in both species are remarkably similar. Coordinated eye and head movements dominate the dynamics of the retinal input. Interestingly, compensatory (gaze-stabilizing) movements play a more dominant role in humans than they do in cats. This finding was interpreted to be a consequence of substantially different timescales for head movements, with cats' head movements showing about a 5-fold faster dynamics than humans. For both species, models and laboratory experiments therefore need to account for this rich input dynamic to obtain validity for ecologically realistic settings.