Abstract
To overcome internal processing delays, the oculomotor system uses a integration of prior stimulus movements and the current sensory input to adjust the initial eye speed. We investigated the roles of retinal and extra-retinal signals as prior information. Each trial consisted of a specific movement sequence: (1) a 15 deg/s baseline movement of a Gaussian blob across the screen, during which the participants kept fixating. (2) A prior movement, where the same physical target movement took place, but observers pursued the target. The starting position of the movement was chosen to create variability in the initial oculomotor behavior. Some trials were tracked with pure pursuit vs. some trials were tracked with pursuit and an additional forward corrective saccade, some trials with pursuit and an additional backward corrective saccade. (3) A 15 deg/s test movement to investigate the influence of the prior. This was the same as the baseline movement, but now observers pursued the target. For this movement, the starting position was chosen to minimize initial saccades. The occurrence of a corrective saccade during the prior movements allows to disentangle the contributions of extra-retinal and retinal information. A forward corrective saccade leads to higher extra-retinal velocity while reducing the retinal velocity compared to the same physical trial without a saccade. The results showed an effect of the corrective saccades in the prior movement on pursuit speed in the test phase. In comparison to trials with pure pursuit, the eye speed in the test movement was slower after prior movements with forward saccades, even though both eye speed and perceived speed were higher in this case. In contrast, trials with additional backward saccade produced the opposite pattern of results, suggesting that retinal speed seems to be more important in forming oculomotor priors than extra-retinal signals or perceived speed.