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Purpose: The relationship between eye movements and the visual evoked potential (VEP) response was examined in two subjects with infantile nystagmus syndrome (INS). Changes in VEP amplitude were compared between periods of foveation versus periods of high-frequency nystagmus. An analysis is proposed that improves extraction of the checkerboard reversal VEP signal from subjects with INS. Methods: INS subjects were 2 healthy children (12-13 years old) with 20/40 or better corrected acuity. Optical coherence tomography confirmed the optic nerves, retina, and fovea were within normal variation. VEPs were recorded to checkerboard reversal and to onset/offset of horizontal gratings while simultaneously recording the electrooculogram (EOG). VEP epochs underwent Fourier analysis, and epochs were examined for phase consistency with the mean. Foveation periods were compared to video-oculography recordings from a separate session. Results: Optic nerve misrouting, such as crossed VEP asymmetry seen in albinism, or ipsilateral VEP asymmetry seen in achiasma, was not detected in either subject. By averaging only epochs in which EOG epochs showed foveation, VEP amplitude could be increased ≥59%. Averaging the VEP only on epochs with consistent phase at Oz increased VEP amplitude by ≥twofold; subsequent EOG epochs after this analysis mostly contained foveation periods or minimal EOG activity. Latency varied <14 ms across all analyses. Conclusions: The checkerboard reversal VEP signal is dependent on foveation periods in subjects with INS despite good visual acuity. Reduction in VEP amplitude due to retinal image motion induces noise and/or lack of phase locking in the VEP epochs. Selective averaging of epochs based on phase consistency improves the extraction of a VEP signal, likely when retinal image motion is minimized. [ABSTRACT FROM AUTHOR]

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]

Since normal human subjects can perform smooth-pursuit eye movements only in the presence of a moving target, the occurrence of these eye movements represents an ideal behavioural probe to monitor the successful processing of visual motion. It has been shown previously that subjects can execute smooth-pursuit eye movements to targets defined by luminance and colour, the first-order stimulus attributes, as well as to targets defined by derived, second-order stimulus attributes such as contrast, flicker or motion. In contrast to these earlier experiments focusing on steady-state pursuit, the present study addressed the course of pre-saccadic pursuit initiation (less than 100 ms), as this early time period is thought to represent open-loop pursuit, i.e. the eye movements are exclusively driven by visual inputs proceeding the onset of the eye movement itself. Eye movements of five human subjects tracking first- and second-order motion stimuli had been measured. The analysis of the obtained eye traces revealed that smooth-pursuit eye movements could be initiated to first-order as well as second-order motion stimuli, even before the execution of the first initial saccade. In contrast to steady-state pursuit, the initiation of pursuit was not exclusively determined by the movement of the target, but rather due to an interaction between dominant first-order and less-weighted second-order motion components. Based on our results, two conclusions may be drawn: first and specific for initiation of smooth-pursuit eye movements, we present evidence supporting the notion that initiation of pursuit reflects integration of all available visual motion information. Second and more general, our results further support the hypothesis that the visual system consists of more than one mechanism for the extraction of first-order and second-order motion. [ABSTRACT FROM AUTHOR]

With the easy attainability of hand-held laser devices and the burgeoning light emitting diode (LED) technology, safety standards for long-term viewing of continuous light sources are being scrutinized. Oneconcern is with quantifying the effect of head and eye movements on the distribution of energy over the retina. This experiment describestarget motion over the retina as a result of head and eye movements during a deliberate fixation task. Volunteers deliberately fixated, with (fettered) and without (unfettered) head and chin rest support, on LEDs that subtended a 0.1 min of arc visual angle. A Dual Purkinje Image Eyetracker measured eye position during each 100-s fixation trial. The data showed an elliptical retinal energy distribution, oriented on the temporal/nasal retinal axis, with a major axis 1.5 times greater than the minor. The average half-maximum diameter for the majoraxis was 40 mum for the fettered and 107 mum for the unfettered condition. The retinal area illuminated from head and eye movements showed a positive linear relationship with time. Peak retinal radiant exposure at 100 s was reduced by a factor of 10 as a result of eye movements and by a factor of 30 as a result of head and eye movements. Although the net result was a reduction in radiant exposure from a 'no-movement' baseline, the distribution of energy over the retina was wellwithin the 200 mum foveal boundary. The data suggest that the laser permissible exposure limits for long term viewing of a small continuous wave source include a factor that adjusts for this reduction in retinal radiant exposure with time. [ABSTRACT FROM AUTHOR]