Predictive Mechanisms in Human Smooth Pursuit Movement

Abstract

If a human observer is presented with a target moving at constant speed he can, almost within a single reaction time period, “lock” onto this target and start to track with virtually no retinal slip. This ability is difficult to explain if one considers the pursuit system merely as a simple servo mechanism responding to velocity and position errors (Young, 1971). Therefore a variety of alternative mechanisms have been invoked, among them many which involve some form of “prediction”. Vossius and Werner (1969) for example have proposed an extrapolating prediction, based on a Taylor expansion of current target movement into future. They and others (e.g. Eckmiller, 1978) had observed that the smooth pursuit response can “bridge” short gaps of target presentation. Before the idea of predictive extrapolation can be pursued however, it needs a quantitative experimental basis. As a step toward such a basis the present report considers the smooth pursuit component that remains when a moving target is suddenly removed from sight.