Neural Mechanisms of Head Pursuit and Predictive Orienting

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Cats were trained to stand in a small box and to fixate at a light spot projected on a center of the panel and were required to orient or pursuit the light spot which moved from the fixation point to a target. When a light spot moved from a fixation point to the target with ramp-hold manner, cats moved their heads slowly toward the target with the concomitant controversive eye movements due to the vestibulo-ocular reflex, resulting in a flat gaze traces and then made rapid head movements and saccades toward the target to fixate it. Switching from moving to step (stationary) visual stimuli produced pronounced prolongation of latencies of orienting and reduction of head and gaze velocities with little effects on saccade velocities, suggesting that there are two types of orienting, i.e., volocity guided and position guided orienting, which utilize velocity and position signals of visual stimuli, respectively. Velocity guided orienting were further subdivided into two subtypes. In predictive orienting, head and eyes started to move during stimulation and the gaze reached the target slightly after the light spot reached its destination, indicating that they made an accurate prediction of the destination of the target light from the velocity of the moving visual stimulus. Regular orienting was characterized by longer latencies of both head and eye saccades than the predictive orienting, in which orienting was made after the light spot reached at the target using both positional and velocity information of stimuli. Cats pursued the light spot smoothly with multiple correction saccades for slow spot movements (head pursuit), which were suggested to be induced by a pathway of velocity guided orienting.