Human fixation and pursuit in normal and open‐loop conditions: effects of central and peripheral retinal targets.

Abstract

SUMMARY1. Eye movements were recorded precisely with a scleral-coil method under three experimental conditions: (a) fixation of a central, stationary target; (b) pursuit of a central, moving target; (c) pursuit of eccentric, moving targets. Subjects were instructed to attend to and fixate the target and to pursue it when it moved.2. The target was presented either in darkness (no visible background), on a diffusely lighted background, or on a large, structured background. Target and/or background could be moved independently with single sinusoids, pseudo-random mixtures of sinusoids or triangular waves.3. The target was usually presented under normal viewing conditions, but in some measurements (interleaved with normal ones) retinal target motion was uncoupled from eye motion by electronical addition of the eye position to the target position (open-loop conditions).4. The gain and phase relations of eye movements induced by motion of the target and/or background were calculated for the total, composite (smooth and saccadic) eye movement and for the reconstructed cumulative smooth component separately.5. Horizontal motion of a large, structured background induced correlated smooth eye movements while subjects fixated a stationary point target. The induced horizontal movements were very small (gain about 0'05) when the target was seen normally, and larger (gain about 0 20) when the target was horizontally stabilized on the retina. The phase lag of the induced eye movements relative to the background movements was usually smaller than 90 deg.6. When the target moved vertically and the background horizontally, vertical pursuit was similar to that with a stationary background, but in addition horizontal smooth eye movements, correlated with the background movements, were elicited with a gain of about 0-1 and a phase lag which was usually smaller than 90 deg.7. Imposed pseudo-random retinal motion of a central target under open-loop conditions (retinal image motion uncoupled from eye movements) elicited highly idiosyncratic responses which varied too much among subjects to allow any general conclusions, other than that open-loop stimulation seems unsuitable as a tool for analyzing the response characteristics of the smooth pursuit system. 8. In the absence of a background, an eccentric target configuration (two vertically H. COLLEWIJN AND E. P. TAMMINGA aligned arrows with the points localized 5 deg above and 5 deg below the fovea) in horizontal motion was pursued equally well as a central target. A stationary, structured background (extending also through the foveal area) inhibited eccentric smooth pursuit strongly for targets moving at constant velocities below 5 deg/s, and moderately (gain decreased by 0113-024) for other types of target motion.9. It is concluded that, in agreement with previous, complementary work , foveal fixation and smooth pursuit of a distinct target are slightly degraded (by 5-10%) due to relative motion of a background. Eccentric targets can be pursued very well in the absence of conflicting...

Human optokinetic nystagmus: Competition between stationary and moving displays

“…These results confirm those published previously (Barnes & Crombie, 1985;Murasugi et al, 1986). They also are consonant with the report that peripheral targets are pursued less well than central targets over a textured background (Collewijn & Tamminga, 1986). We conclude that when there are competing motion signals in different parts of the visual field, those motion signals that arise from objects nearest the fovea tend to dominate the oculomotor response.…”

“…rubia (1983) reported a similar loss of gain at this velocity, but losses of up to about 20% for higher velocities. In a later paper, Collewijn and Tamminga (1986) reported that the ability to pursue targets 50 above and below the fovea was strongly degraded, even at low velocities, by the presence of a stationary structured background. In the present experiment, we were concerned with OKN; we were not interested in the limits to which voluntary pursuit may be pushed.…”

Using Open-Loop Experiments to Study Physiological Systems, With Examples From the Human Eye-Movement Systems

“…However, the results of these studies are confusing and seem to be contradictory. The responses of subjects in some open-loop studies have been varied enough to lead the investigators to state that the use of this systems analysis technique is "useless" (18) and "unsuitable as a tool for analyzing the response characteristics of the smooth pursuit system" (5). Thus some investigators have expressed dissatisfaction with a technique that has potential value not only for the oculomotor systems but also for the analysis of other physiological control systems.…”

Physiological Models, Development

“…This is the same effect as if the feedback loop had been no matter how you move your eye, you cannot eliminate the cut, as in Fig tor may be the influence of prior experience on subject perforand the 1-sec mark, the subject made a series of saccades trying to mance. Examining the results from several studies (28,30,31) catch the target. When this strategy did not work, he seemed to turn reveals that open-loop gains are larger in subjects with more off the saccadic system and produce only smooth-pursuit eye moveexperience in laboratory tracking tasks.…”