Contributions a l'etude des coordinations oculo-cephaliques chez l'homme et l'animal

A decade ago Bizzi and collaborators proposed the "linear summation" hypothesis mainly based on the vestibulo-ocular reflex to explain how subjects move their eyes and head simultaneously to acquire a peripheral visual target. We asked human subjects to make rapid horizontal gaze shifts to unpredictable visible or remembered targets situated at offsets ranging from 30$ sp circ$ to 160$ sp circ$. Different experimental paradigms were used to dissociate crucial variables and different perturbations were imposed to our subjects' head movements to test the interaction between the saccadic eye movement and the head displacement. Several assumptions of the "linear summation" hypothesis were questioned by the analysis of results and we proposed a more elaborated gaze control model to explain how subjects could reach a target accurately with their gaze shifts whatever the conditions, even when the target was beyond the subject's oculomotor range.In parallel with human experiments we developed a technique to record vestibular units in head-free cats during orienting eye-head movements. Preliminary results on several electrophysiologically identified cells show some particular discharge patterns in the head-free condition. They bring some insights to the behavioral results