Abstract
Smooth pursuit eye movements are usually measured on a homogeneous background. In normal situations, however, pursuit eye movements are performed over textured and often dynamic backgrounds. It is known that such textured backgrounds can influence the accuracy, or gain, of smooth pursuit eye movements: When a background moves in a direction opposite that of the smooth pursuit, the pursuit gain is less than one (gaze can trail behind the target), requiring catch-up saccades. When a textured background moves in the same direction as the pursuit, the gain can exceed one. While it is clear that background retinal motion information contributes to smooth pursuit, it is not clear how this occurs. Retinal motion of the textured background may only contribute to the control of eye movements when the background falls directly under the target. Alternatively, a textured background that is separated in space from the target might also influence pursuit gain. To test this, subjects pursued a target while a textured background was presented near, but separated from, the target. The background was either stationary or moved with or opposite to the direction of pursuit. Even though the background was only separated by ∼1.5 deg from the target, there was little influence of the textured moving background on pursuit. The results show that the influence of background retinal motion on pursuit is spatially restricted, and that pursuit eye movements do not necessarily require an integration of retinal motion over large areas of the visual field.
Supported by an NIH grant to D.W.