Binocular co‐ordination of human vertical saccadic eye movements.

Abstract

SUMMARY1. The binocular co-ordination of human vertical saccades was analysed systematically over the full oculomotor range, with a precise and accurate scleral sensor coil technique. Effects of amplitude (1-25-70 deg), direction (upward vs. downward and centripetal vs. centrifugal), as well as position (upper or lower sector of vertical oculomotor range), were investigated systematically in three subjects.2. All saccades were made voluntarily between continuously presented pairs of targets, which subtended equal angles of target vergence.3. Vertical saccades were less accurate than horizontal saccades (as described by Collewijn, Erkelens & Steinman, 1988). For target distances between 10 and 70 deg, upward saccades undershot the target by about 10%, whereas downward saccades tended to overshoot the target. Downward saccades were about 1P5 deg larger than upward saccades between the same targets.4. Peak velocities continued to increase monotonically with saccadic amplitude up to 513 + 27 (S.D.) deg/s for 70 deg saccades; a distinct asymptotic level was not reached.5. Velocity profiles of upward and downward saccades, made symmetrically about the primary (straight-ahead) position, were very similar for amplitudes up to 30 deg. At larger amplitudes, velocity profiles of upward saccades remained single peaked, whereas those of downward saccades invariably developed a second velocity peak.6. Parameters of upward saccades depended heavily on the position of the eye. In the upper oculomotor range such saccades had lower maximum speeds, longer durations, and were more skewed than similar saccades in the lower oculomotor range (below primary). Downward saccades were almost independent of eye position.7 Vertical eye movements during vertical saccades were virtually identical in the two eyes. In contrast, disjunctive horizontal components were systematically present. Upward saccades, at all amplitudes, were associated with diverging eye movements. Converging eye movements occurred during downward saccades. These systematic effects suggest that the vergence subsystem is not turned off during saccades.H. COLLEWIJN, C. J. ERKELENS AND R. M. STEINMAN 8. These changes in vergence were followed by converging horizontal postsaccadic drift after upward saccades, and in diverging horizontal drift after downward saccades. Vertical post-saccadic drift consisted mainly of a conjugated component, directed towards the target position. We conclude that post-saccadic drift on the vertical meridian is effective in decreasing binocular fixation errors in a way similar to error reduction following horizontal saccades.

The Initial Direction and Landing Position of Saccades

“…We have observed from experimental recordings of ourselves and others (see for example Collewijn et al, 1988a;Collewijn et al, 1988b;Becker & Jfirgens, 1990;) that trajectories of saccades show a fair amount of variability. Present models predict a fixed trajectory between start and landing position of saccades.…”

“…A further extension of experimental data was obtained from accurate measurements of conjugate (Collewijn et al, 1988a;Collewijn et al, 1988b) and disjunctive (Erkelens et al, 1989) saccades in the two eyes together. The data showed that saccades are not as stereotyped as once has been thought.…”

Long-term nonconjugate adaptation of human saccades to anisometropic spectacles

“…Less detailed reports on nonconjugate adaptations have been issued before by the same authors (Collewijn, Erkelens & Steinman, 1988a), and also by Levi, Zee, Hain, Fletcher and Miller (1988), Schor, Gleason and Horner (1988), Horner, Gleason and Schor (1988), and by Zee and Levi (1989). Schor, Gleason and Horner (1990) recently published an extensive experimental study on short-term adaptation, while Oohira, Zee and Guyton (1991) recently studied nonconjugate adaptation in one case of long-standing anisometropic correction.…”

Peripheral Contour Grouping and Saccade Targeting: The Role of Mirror Symmetry

“…Finally, we also note that the tendency to undershoot the target cannot be taken as evidence for incomplete integration of the contour shape, as this is a general and well-documented property of human eye movements [39,40]. As a side note, the differences observed in our dependent measures between horizontal and vertical saccades and between upward and downward saccades should also not be interpreted as direct evidence for anisotropies in the contour integration mechanism, as they are due at least in part and perhaps entirely to direction-dependent differences in saccades per se [52].…”