Elling Prediction in Ocular Pursuit

Abstract

It has been realised since the early work of Dallos and Jones (1963) that predictive behaviour must be present in human ocular pursuit for three main reasons: (1) performance is better in response to predictable periodic target motion than it is to more random stimuli; (2) when pursuing sinusoids, phase errors at frequencies above 0.5Hz are much less than would be expected from the time delay (100ms) in visual feedback (Carl and Gellman 1987); (3) in a linear velocity error feedback system a combination of high gain and a large time delay would lead to an unstable system. But evidence of predictive behaviour is not readily apparent because anticipatory smooth movements cannot normally be generated at will. Over recent years we have carried out experiments designed to facilitate the generation of anticipatory movements and investigate their role in predictive pursuit (Barnes et al. 1987; Barnes and Asselman 1991; Wells and Barnes 1998). The model presented here was developed on the basis of the results from these experiments and attempts to demonstrate how predictive processes reduce phase errors during periodic tracking through the short-term storage of pre-motor drive information and its subsequent release to form anticipatory smooth movements.