SMOOTH-PURSUIT ALONG A SOLID LINE - A NEW VARIATION ON THE THEME OF EFFERENCE-COPY-BOUND EYE TRACKING

Theoretical considerations of the physiology of eye tracking have long implied that the kinematics of smooth pursuit need not parallel those of the pursued target, with pursuit in the absence of a physically mo ving target as an extreme case. Yet these theoretical implications hav e been largely ignored, with the consequence that observed kinematic d iscrepancies between target and pursuit have generally been presented as somewhat surprising, and this view has maintained unnecessary diver sity among reported smooth-pursuit phenomena. The case of yet another stimulus-discrepant smooth-pursuit phenomenon is presented and is used to suggest a role which recognized eye-tracking theory might advantag eously play in classifying smooth-pursuit phenomena. The new phenomeno n, smooth pursuit along a stationary solid straight line under continu ous illumination, was demonstrated in a study where eye movements were documented by continuous recordings of the electrooculogram. All twel ve subjects were able to initiate smooth pursuit along the line and to maintain it in the absence of any other source of stimulation, and al l reported experiencing apparent movement during smooth pursuit. It is suggested that smooth-pursuit phenomena can best be classified in ter ms of degree of efference-copy dependency.