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Abstract: The extent of perceived blur produced by a moving retinal image is less when the image motion occurs during pursuit eye movements compared to fixation. This study examined the effect of this reduced perception of motion blur during pursuit on spatial-interval acuity. Observers judged during pursuit at 4 or 8deg/s whether the horizontal separation between two stationary lines was larger or smaller than a standard. Three different line separations were tested for each pursuit velocity. Each observer performed these judgments also during fixation, for spatial-interval stimuli that moved with the same mean and standard deviation of speeds as the distribution of eye velocities during pursuit. Spatial-interval acuity was better during pursuit than fixation for small or intermediate line separations. The results indicate that a reduction of perceived motion blur during pursuit eye movements can lead to improved visual performance. [Copyright &y& Elsevier]

Abstract: Movement of an image on the retina is necessary for the persistence of vision in vertebrates. Leopard frogs (Rana pipiens) do not show any obvious independent eye movements that could sustain perception of stationary objects when the animal itself is stationary. However, video recordings of normal, awake leopard frogs made through a dissecting microscope reveal that the animal''s whole head oscillates with an amplitude of 10–100μm in step with the breathing cycle. The retinal image shifts produced by these breathing movements could ensure continuous perception of the frog''s stationary environment. [Copyright &y& Elsevier]

Abstract: When our eyes track objects that are moving in a richly structured environment, the retinal image of the stationary visual scene inevitably moves over the retina in a direction opposite to the eye movement. Such self-motion-induced global retinal slip usually provides an ideal stimulus for the optokinetic reflex. This reflex operates to compensate for global image flow. However, during smooth pursuit eye movements it must be shut down so that the reflex does not counteract the voluntary pursuit of moving targets. Here, we asked if retinal information is sufficient for this cancellation of the optokinetic reflex during smooth pursuit eye movements. In a series of experiments, we show that neither the eye movement-induced retinal image motion per se nor the relative motion between the pursuit target and the background are sufficient for suppression of optokinesis. We, therefore, conclude that extra-retinal information about smooth pursuit eye movements is required for the cancellation of the optokinetic reflex. [Copyright &y& Elsevier]

Abstract: We measured perceived motion smear when retinal image motion was created either by a physically moving object or by movement of the eyes or head. Consistent with previous reports, the extent of perceived motion smear during an eye or head movement is less than that produced by physical object motion when the eyes are stationary. Moreover, perceived smear is substantially smaller when the motion of the retinal image is in the same direction as the eye or head movement compared to when image motion is in the opposite direction. These results imply that extra-retinal signals associated with eye and head movements contribute to a reduction of perceived motion smear, thereby fostering perceptual clarity. We hypothesize that the visual system uses a simple dichotomous strategy in applying these extra-retinal signals, based only on the direction of retinal image motion with respect to the ongoing eye or head movement. [Copyright &y& Elsevier]

Visual guidance is often critical during locomotion. To understand how the visual system performs this function it is necessary to know what pattern of retinal image motion neurons experience. If a locomoting observer maintains an angle of gaze that is constant relative to his body, retinal image motion will resemble Gibson''s (The Perception of the Visual World (1950)) well-known optic flow field. However, if a moving observer fixates and tracks a stationary feature of the environment, or shifts his gaze, retinal motion will be quite different. We have investigated gaze in cats during visually-guided locomotion. Because cats generally maintain their eyes centered in the orbits, their gaze can be monitored with reasonable accuracy by monitoring head position. Using a digital videocamera, we recorded head position in cats as they walked down a cluttered alley. For much of the time, cats maintained a downward angle of gaze that was constant relative to their body coordinates; these episodes averaged 240 ms in duration and occupied 48–71% of the total trial time. Constant gaze episodes were separated by gaze shifts, which often coincided with blinks. Only rarely did we observe instances when cats appeared to fixate and track stationary features of the alley. We hypothesize that walking cats acquire visual information primarily during episodes of constant gaze, when retinal image motion resembles Gibson''s conventional optic flow field. [Copyright &y& Elsevier]