Binocular co‐ordination of human horizontal saccadic eye movements.

Abstract

SUMMARY1. The binocular co-ordination of human horizontal saccades was analysed for the first time systematically over the full oculomotor range with a precise and accurate scleral sensor coil technique. Effects of amplitude (1X25-80 deg), direction (adduction vs. abduction and centrifugal vs. centripetal) and eccentricity (symmetrical about primary or between primary and secondary positions) were systematically investigated in three subjects).2. To minimize extraneous effects of stimulus presentation on the programming of saccades, subjects were instructed to voluntarily change their gaze between two continuously visible targets. These were positioned on an iso-vergence locus, and thus contained no stimulus for disjunctive eye movements. 3. Under these conditions the amplitudes of the primary saccades of the two eyes were remarkably accurate; undershooting of the target by about 0.5 deg (independent of amplitude in the range 10-70 deg) was typical. This finding contrasts with the undershooting by about 10% described in the literature as characteristic for other stimulus conditions. 4. Saccadic peak velocities saturated at a mean asymptotic level of 502 + 32 (S.D.) deg/s for saccades of 40 deg and larger. The duration was linearly related to amplitude for saccades up to 50 deg; for saccades of larger sizes the duration increased progressively more steeply. Skewness values (acceleration time as a fraction of total saccadic duration) decreased from about 0-45 for saccades up to 10 deg to about 0-20 for saccades of 50 deg and larger.5. Binocular saccades showed an abduction-adduction asymmetry and were not well yoked dynamically. The saccades of the abducting eye consistently had a larger size, a higher peak velocity, a shorter duration and were more skewed than the concomitant adducting saccades of the fellow eye. As a result, the eyes diverged transiently by as much as 3 deg during horizontal saccades.6. Saccades also showed a marked centrifugal-centripetal asymmetry. Peak velocities of saccades towards the primary position were about 10% higher than peak velocities of corresponding centrifugal saccades.7. These directional asymmetries were the main source of variability in the pool H. COLLEWIJN, C. J. ERKELENS AND R. M. STEINMAN of saccades. In comparison, intra-and intersubject variability was minor in our sample.8. Post-saccadic drift consisted of a vergence and a version component. The vergence component of this drift was a continuation of the vergence movement occurring during saccades. The version component, generally smaller than the vergence component, was directed towards the target position. The result of postsaccadic drift was that the fovea of each eye was guided towards the target. The net post-saccadic drift of the abducting eye was smaller than that of the adducting eye, a result appropriate to reduce fixation errors remaining at saccadic offset.9. A tight relationship between skewness and saccade duration was not found. For instance, velocity profiles of centrifugal saccades were more skewed than ...

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.…”

“…The basic idea was developed for describing the neural control of horizontal saccades made by a single eye. Experimental data of vertical and oblique saccades (van Gisbergen et al, 1985;Yee et al, 1985;King et al, 1986;Collewijn et al, 1988a; made available due to improved recording methods for vertical eye movements, caused extension of one-dimensional of models of saccades to two dimensions (van Gisbergen et al, 1985;Tweed & Vilis, 1985;Scudder, 1988;Becker & Ji~rgens, 1990). Although two-dimensional saccades created specific problems for the modeling of their neural control, the basic idea of Robinson was never questioned and incorporated in all models.…”

“…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.…”

The Main Sequence of Saccades Optimizes Speed-accuracy Trade-off

“…In primates this is usually accomplished by fast saccadic eye movements. The high speed of saccades precludes visual feedback, yet saccades have remarkably stereotyped trajectories (Bahill et al 1975;Collewijn et al 1988;Harwood et al 1999). The peak velocity and the duration increase systematically with the amplitude of the movement, and these relationships have been called the 'main sequence' (Bahill et al 1975).…”

Neurophysiological Models of Gaze Control in Humanoid Robotics

“…Equation ( 1) shows the relation between eye velocity and eye amplitude where V is the maximum velocity, x the saccadic amplitude α and β are the parameters of the exponential model which can be calculate as the minimum of the square error between the model and the data Collewijn et al, 1988). An example of saccadic movement is shows in Fig.…”