Voluntary binocular gaze-shifts in the plane of regard: Dynamics of version and vergence

Abstract

We studied the dynamics of voluntary, horizontal, binocular gaze-shifts between pairs of continuously visible, real three-dimensional targets. Subjects were stabilized on a biteboard to allow full control of target angles, which were made to differ only in distance (pure vergence), only in direction (pure version; conjugate saccades) or in both distance and direction (disjunctive saccades). A wide range of changes in vergence (0-25 deg) and version (0-65 deg) was recorded to study the dynamics of disjunctive saccades, described until now for limited ranges, throughout the horizontal oculomotor range within manual working space, and to study the velocity-duration-amplitude relations ("main sequence") of disjunctive vs conjugate saccades. Pure vergence was almost never observed; divergence, especially, was always associated with saccades. Likewise, horizontal saccades were never strictly conjugate, they always contained a transient divergence-convergence sequence. The amplitude and velocity of these transient components varied systematically with saccadic size. In combined version-vergence movements, vergence was, in general, accelerated and shortened as a function of increasing version. This effect was fairly uniform for divergence, which appeared to increase in velocity by about as much as the transient peak divergent velocity of the version saccade. The intrasaccadic fraction of divergence increased from about 50% to close to 100% as a function of increasing version. For convergence, saccades up to about 20 deg were also accelerating; in this case it appeared as if the transient peak convergent velocity of the version saccade was added to the basic convergence velocity. For larger saccades this effect was partly counteracted by the penetration of an initial divergence associated with the saccade. This initial divergence delayed and slowed down convergence. The intrasaccadic fraction of convergence varied between about 40% and 70%. In disjunctive saccades the individual eyes did not follow the main-sequence parameters of conjugate saccades of comparable sizes, except for the eye that moved with the combination "abduction and divergence". For all other combinations of vergence and version, disjunctive saccades had lower peak velocities and longer durations than conjugate saccades. As a consequence, disjunctive version was also slower than conjugate version. Thus, while version accelerates vergence, vergence slows down version: in the generalized case of three-dimensional gaze-shifts, peak velocities and durations are in between those of the limiting cases of pure version and pure vergence. We conclude that, within manual working space, binocular gaze-shifts are effected by the highly integrated action of conjugate and disjunctive mechanisms, both of which are expressed preferentially in fast, saccadic movements.

The Brain Stem Saccadic Burst Generator Encodes Gaze in Three-Dimensional Space

“…However, numerous studies have provided results that argue against this view. Vergence velocities are greater than what would be predicted by a linear summation of a conjugate saccade with a saccade-free vergence movement, while conjugate velocities are decreased Mays 2003, 2005a;Collewijn et al 1995Collewijn et al , 1997Enright 1984Enright , 1992Erkelens et al 1989; Kenyon et al 1980;Kumar et al 2005;Maxwell and King 1992;Ono et al 1978;Oohira 1993;Zee et al 1992). Moreover, the amount of vergence facilitation is dependent on peak saccadic velocity (Busettini and Mays 2005a).…”

Prediction of saccadic amplitude during smooth pursuit eye movements

“…Furthermore, latencies were slightly longer when the eye moved to the right (258 vs. 245 ms; P`0X005). This is caused by measuring the orientation of the left eye only and the fact that temporally directed saccades are somewhat faster than nasally directed saccades (Collewijn, Erkelens, & Steinman, 1995). The ANOVA showed that besides these main eects only interaction eects with sign (left±right) were signi®cant.…”

Pontine Omnipause Activity During Conjugate and Disconjugate Eye Movements in Macaques

“…In studies with humans, horizontal saccades during vergence often showed slower velocities and resulted in longer durations than conjugate saccades of comparable size (Collewijn et al 1995;Erkelens et al 1989) but the effects of vergence on vertical saccades were less clear (van Leeuwen et al 1998). In monkeys, superior colliculus (tectal) long lead bursters (TLLBs) show reduced activity for both horizontal and vertical saccades during vergence (Walton and Mays 2003) and we have preliminary evidence (unpublished observations) that this is also seen in medium lead burst neurons (MLBs).…”

“…Several studies (Collewijn et al 1995;Erkelens et al 1989;van Leeuwen et al 1998) have noted that horizontal saccades are often slowed when combined with vergence eye movements. Such mixed saccadic-vergence movements are typical of refixations in depth.…”