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A previous study showed that the initial ocular following responses elicited by sudden motion of a large random-dot pattern were only modestly attenuated when that whole pattern was shifted out of the plane of fixation by altering its horizontal binocular disparity, but the same disparity applied to a restricted region of the dots had a much more powerful effect [Vision Research 41 (2001) 3371]. Thus, if the dots were partitioned into horizontal bands, for example, and alternate bands were moved in opposite directions to the left or right then ocular following was very weak, but if the (conditioning) dots moving in one direction were all shifted out of the plane of fixation (by applying horizontal disparity to them) then strong ocular following was now seen in the direction of motion of the (test) dots in the plane of fixation, i.e., moving images became much less effective when they were given binocular disparity. We sought to determine if the greater impact of disparity with the partitioned images was because there were additional relative disparity cues. We used a similar partitioned display and found that the dependence of ocular following on the absolute disparity of the conditioning stimulus had a Gaussian form with an x-offset that was close to zero disparity and, importantly, this offset was almost unaffected by changing the absolute disparity of the test stimulus. We conclude from this that it is the absolute--rather than the relative--disparity that is important, and that ocular following has a strong preference for moving images whose absolute disparities are close to zero. This is consistent with the idea that ocular following selectively stabilizes the retinal images of objects in and around the plane of fixation and works in harmony with disparity vergence, which uses absolute disparity to bring objects of interest into the plane of fixation [Archives of Ophthalmology 55 (1956) 848].

We examined the velocity dependence of the vergence and version eye movements elicited by motion stimuli that were symmetric or asymmetric at the two eyes. Movements of both eyes were recorded with the scleral search coil technique. Vergence was computed as the difference in the positions of the two eyes (left-right) and version was computed as the average position of the two eyes ((left+right)/2). Subjects faced a large tangent screen onto which two identical random-dot patterns were back-projected. Each pattern was viewed by one eye only using crossed-polarizers and its position was controlled by X/Y mirror galvanometers. Viewing was always binocular and horizontal velocity steps (range, 5-240 deg/s) were applied to one (asymmetric stimulus) or both (symmetric stimulus) patterns approximately 50 ms after a centering saccade. With the symmetric stimulus, the motion at the two eyes could be either in the opposite direction (eliciting vergence responses) or in the same direction (eliciting version responses). The asymmetric stimuli elicited both vergence and version. In all cases, minimum response latencies were very short (<90 ms). Velocity tuning curves (based on the changes in vergence and version over the time period, 90-140 ms) were all sigmoidal and peaked when the monocular (i.e., retinal) image velocities were 30-60 deg/s. The vergence (version) responses to symmetric stimuli were linearly related to the vergence (version) responses to asymmetric stimuli when expressed in terms of the monocular rather than the binocular image velocities. We conclude that the dynamical limits for both vergence and version are imposed in the monocular visual pathways, before the inputs from the two eyes are combined.

Using the scleral search coil technique to monitor eye movements, we recorded short-latency ocular following responses to displacement steps of large random-dot patterns. On half of the trials, the luminance of the dots and background were reversed during the step, a procedure that is known to reverse the direction of the perceived motion ("reverse phi"). Steps without luminance reversal induced small but consistent ocular following in the direction of the steps at ultra-short latency (<80 ms). Steps with luminance reversal induced small but consistent tracking at the same latency but in the direction opposite to the actual displacement. Tuning curves describing the dependence of initial ocular following on the amplitude of the displacement had a form approximating the derivative of a Gaussian and were well fit by Gabor functions, the cosine term being phase shifted approximately 180 degrees by the luminance reversal. This result is consistent with the idea that the initial ocular following is mediated, at least in part, by first-order (luminance) motion-energy detectors.

We show that the initial ocular following responses elicited by motion of a large pattern are modestly attenuated when that pattern is shifted out of the plane of fixation by altering its binocular disparity. If the motion is applied to only restricted regions of the pattern, however, then altering the disparity of those regions severely attenuates their ability to generate ocular following. This sensitivity of the ocular tracking mechanism to local binocular disparity would help the observer who moves through a cluttered 3-D world to stabilize objects in the plane of fixation and ignore all others.

Nasal or temporal side of the cat's retina was stimulated with nasalward and temporalward moving patterns for investigating the neural control of the optokinetic nystagmus in the direct and indirect pathways of OKN. The experimental data demonstrated that there was a nasalward directional preference in cat's OKN system under both close loop and open loop conditions, and the nasalward OKN gain evoked by stimulation of nasal retina was much higher than that at temporal retina. This indicates that OKN nasalward preference is mainly derived from the nasal retina, i.e. the direct pathway of OKN dominates the indirect pathway in cat's OKN system. The gains of temporalward and nasalward OKN from temporal retina are much less than those of nasalward OKN from nasal retina. It is suggested that the indirect pathway of OKN in the cat only possesses a supplementary function, which probably plays an important role in temporalward OKN eye-movements in relation to binocular vision.

Small disparity stimuli applied to large random-dot patterns elicit machine-like vergence eye movements at short latency. We have examined the sensitivity of these eye movements to simulated orthogonal tropias in three normal subjects by recording (1) the effects of vertical disparities on the initial horizontal vergence responses elicited by 2° crossed and uncrossed (horizontal) disparity stimuli, and (2) the effects of horizontal disparities on the initial vertical vergence responses elicited by 1.2° left-hyper and 0.8° right-hyper (vertical) disparity stimuli. Initial vergence responses were strongest when the orthogonal disparity was close to zero, and decreased to zero as the orthogonal disparity increased to 3°–5°, i.e., there was only a limited tolerance for orthogonal disparity. Tuning curves describing the dependence of the initial change in the vergence angle on the orthogonal disparity were well fit by a Gaussian function. An additional subject, who had an esotropia of ∼10° in our experimental setup, showed almost no horizontal vergence responses but did show vertical vergence responses to vertical disparity stimuli at short latency (albeit slightly longer than normal) despite the fact that her esotropia resulted in uncrossed disparities that would have totally disabled the vertical vergence mechanism of a normal subject, cf., anomalous retinal correspondence. [Copyright &y& Elsevier]