Biomedical subjects

H Collewijn

Publications and source records attributed to H Collewijn.

At least 73 records · Page 4Linked to original sources

PubMed1988

Binocular co-ordination of human vertical saccadic eye movements.

1. 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 1.5 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. 8. These changes in vergence were followed by converging horizontal post-saccadic drift after upward saccades, and in diverging horizontal drift after downward saccades.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1987

Visual and oculomotor function in optic chiasma-sectioned rabbits.

Anatomical and physiological findings indicate that the crossed optic fibres of the rabbit have a crucial role in binocular vision. In order to directly examine the visual functions of the uncrossed fibre system, a technique of sectioning the optic chiasma midsagitally was developed. Both normal and chiasma-sectioned rabbits were tested on a variety of visual discrimination tasks as well as such oculomotor control functions as the optokinetic and vestibulo-ocular reflexes. Following transection of all contralateral retinal projections, rabbits were found to retain the same visual capacity for detection of intensity and orientation differences as before the operation. There was, however, a complete loss of optokinetic reflexes and a 50% reduction of the vestibulo-ocular reflex both in the light and in the dark.

Animals↗

PubMed1987

Voluntary smooth eye movements with foveally stabilized targets.

We investigated the capacity of 6 humans to make voluntary smooth eye movements with a horizontally stabilized foveal point target. When the target was viewed on a dark field, all subjects were able to make smooth oscillatory eye movements when they attempted to imitate their own normal pursuit of sinusoidal target movement (0.2-0.7 Hz) directly preceding the stabilization on the fovea. The frequency of the imitating eye movement was in general lower than the frequency of normal pursuit by 2-35%. While fixating a foveally stabilized point target superimposed on a large, sinusoidally moving non-stabilized background, all subjects were able to make either no eye movements, eye movements nearly in phase with or eye movements nearly in counterphase with the background movement depending on the instruction to imagine the target as head-stationary, moving in phase, or moving in counterphase with the background. The accuracy of the frequency of the smooth eye movement with the stabilized target on the moving background was higher than during imitation of pursuit on the dark field but the precision of the frequency was lower than during normal pursuit. When the background moved pseudo-randomly all subjects could voluntarily inhibit their smooth eye movements or could make smooth eye movements in phase with the background. Only 2 subjects showed a limited ability to make smooth eye movements opposite to the pseudo-random background movement. The results suggest that with predictable background movement the volition of the subject rather than the movement of the background determines the eye movements when the subject looks at the foveally stabilized target.

Eye Movements↗

PubMed1987

A direct test of Listing's law--I. Human ocular torsion measured in static tertiary positions.

The validity of Listing's law was reinvestigated by means of a direct test. Horizontal, vertical and torsional eye movements were measured simultaneously with a recently developed scleral induction coil. Either eye of 4 subjects was measured monocularly. Eye position were measured in Fick coordinates and ocular torsion values were compared to the theoretical ones predicted by Listing's law. During consecutive measurements in the primary position torsion values were close to zero although considerable fluctuations of torsion were seen. Torsion values in the secondary positions were also close to zero. In the tertiary positions torsion in the direction as predicted by Listing's law and increasing with eccentricity was recorded. In the temporal quadrants mean torsion was quantitatively in agreement with Listing's law; torsion values in the nasal quadrants however showed systematically larger values and this discrepancy increased with eccentricity to more than 50%. Statistical support for this finding however, was seen only in 4 out of 8 eyes. Symmetry could be obtained by shifting the chosen horizontal primary position (gaze parallel to the midplane) in the temporal direction; as a consequence all measured torsion values would exceed the ones specified by Listing's law. Torsion values varied idiosyncratically among subjects and among the left and right eyes of any one subject. It is concluded that Listing's law specifies ocular torsion only approximately: physiological eye movements show considerable stochastical as well as systematical deviations from this law.

Eye Movements↗

PubMed1987

A direct test of Listing's law--II. Human ocular torsion measured under dynamic conditions.

Ocular torsion was recorded with a scleral search coil technique in five normal subjects. The dynamic aspects of torsion were investigated during monocular fixation, blinking, smooth pursuit and saccades. Torsion near the primary position showed considerable short-term (SD about 0.25 deg) and a much larger long-term fluctuation (SD about 2.3 deg). During saccades between diagonally opposite tertiary positions torsion transiently reached values approximating those in the sustained primary position. During smooth pursuit across the primary position, the minimal values of torsion varied with the direction and the trajectory of pursuit, in violation of Donder's law. Changes in torsion associated with horizontal and vertical saccades and during the aftermath of blinks often had a sluggish, exponential time course. During eye movements around a circular or square trajectory torsion showed hysteresis. During clockwise pursuit the right eye showed relative intorsion compared to counterclockwise pursuit. It is proposed that central nervous control of torsion is usually imprecise, and that the eye follows Listing's and Donder's laws only approximately.

Blinking↗

PubMed1987

Human gaze stability in the horizontal, vertical and torsional direction during voluntary head movements, evaluated with a three-dimensional scleral induction coil technique.

The stability of gaze in three dimensions (horizontal, vertical and torsion) was measured with a new type of scleral search coil in eight emmetropic observers. Subjects held the head still or oscillated it at 0.16-0.67 Hz (amplitude about 10 deg) in the horizontal, vertical or torsional plane while fixating a point target at optical infinity. Veridical gaze and head coordinates were calculated with full correction for non-linear goniometric relations and for cross-coupling artifacts due to misalignments of the coil on the eye. The amount of gaze instability in the horizontal and vertical direction was virtually identical. With the head still, in either of these directions the mean standard deviation of gaze position (inclusive saccades) was about 7 min arc; mean non-saccadic retinal image speeds were 20-30 min arc/sec. During head oscillation these values increased to about 16 min arc and 1 deg/sec; a mean of about 2.5% of the head motion remained uncorrected by the compensatory eye movements. These findings agree well with our earlier results for the horizontal plane; the effect of the corrections was relatively small because the adventitious cross-coupling of horizontal and vertical to torsional head movements proved to be usually smaller than 10%. However, the corrections were important when head torsion was deliberately produced. Gaze stability in the torsional plane was considerably inferior to that in the horizontal and vertical plane. With the head held still, the mean SD of torsional gaze position was about 17 min arc; mean torsional non-saccadic retinal image speed was about 46 min arc/sec. Gain of the torsional compensatory eye movements was frequency dependent and rose from about 0.26 in static conditions (0 Hz) to about 0.42 at 0.16 Hz and 0.64 at 0.67 Hz. Accordingly, position instability and speed of the retinal image in torsion were about an order of magnitude larger than in the horizontal and vertical direction.

Eye Movements↗

PubMed1986

Control of human optokinetic nystagmus by the central and peripheral retina: effects of partial visual field masking, scotopic vision and central retinal scotomata.

Optokinetic nystagmus (OKN) was elicited in humans by a horizontally moving grating covering the whole visual field. Selective stimulation of central or peripheral parts of the retina was achieved by partial masking or scotopic viewing conditions in normals; three patients with a unilateral central retinal scotoma were studied in addition. In all cases, the elimination of foveal stimulation was accompanied by a decrease in OKN slow phase velocity compared to whole field stimulation. Vertical masks with retinally stabilized edges were used to selectively occlude or stimulate central or peripheral sectors with a fixed retinal location. A central stimulus was always more effective than the complementary peripheral stimulus, until the central zone was narrowed down to a width of 5-10 degrees. This central dominance was found throughout the range of velocities (6-180 degrees/s) and spatial frequencies (0.05-0.5 cycles/deg) used. A horizontal central band of occlusion caused a smaller decrease of OKN than a vertical occlusion with the same width. Scotopic vision caused a uniform mild decrease in OKN gain throughout the velocity range, provided that the spatio-temporal frequency of the stimulus remained within the scotopic resolution range. The patients had a slightly lower OKN gain when viewing with the scotomatous eye than with the contralateral, normal eye. The normal slight preference for temporal-to-nasal motion was not accentuated by masking or scotopic vision in normal eyes, but was enhanced in the eyes with the pathological scotomata in two of the three patients. All responses were immediate; no slow build-up was seen under any condition.

Adult↗

PubMed1986

Human smooth pursuit: effects of stimulus extent and of spatial and temporal constraints of the pursuit trajectory.

We compared the quality of monocular smooth pursuit obtained with either a single point, a full-field stripe pattern or their combination as the target for unidirectional stimulus motion at velocities between 9 and 90 deg/sec. A point target moving in a fixed trajectory maximally constrains target selection as well as pursuit trajectory, whereas a full-field multicontoured pattern leaves the subject maximal freedom in these respects. To unconfound effects of pattern extent from those of spatial and temporal constraints, we presented point targets under conditions in which the subject was free to choose the location, extent and temporal structure of his pursuit trajectory ("free range"). Pursuit velocity gains were lowest for the point target moving in a fixed trajectory. Gain improved when the subject was free to pursue the same target moving at the same velocity in his own preferred range and rhythm. A further improvement was reached by showing the stripe pattern in addition to, and moving in conjunction with the spot. A final increase in gain occurred when the spot was removed, and the subject was allowed to pursue any feature of the uniformly moving, multicontoured pattern. No asymmetries were found between monocular pursuit with the right or the left eye, pursuit of rightward and leftward motion or between nasal- and temporalward motion. Effects of the type of target on the structure of the nystagmoid pursuit eye movements were slight or absent.

Eye Movements↗

PubMed1986

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

Eye movements were recorded precisely with a scleral-coil method under three experimental conditions: fixation of a central, stationary target; pursuit of a central, moving target; pursuit of eccentric, moving targets. Subjects were instructed to attend to and fixate the target and to pursue it when it moved. 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. 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). 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. 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. 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. 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 analysing the response characteristics of the smooth pursuit system. In the absence of a background, an eccentric target configuration (two vertically 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.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1986

Visual field defects for vergence eye movements and for stereomotion perception.

An objective visual field can be mapped in terms of stimulus-induced eye movement. The authors used the scleral coil technique to record vergence and conjugate eye movements while stimulating different visual field locations with a 3 X 3 deg target whose image vergence was oscillated. For each of three subjects tested there was a visual field location where vergence eye movements were much weaker than in a control location of equal retinal eccentricity. On the other hand, conjugate eye movements driven from these two locations by lateral motion were similar. Field defects for ocular vergence coincided with regions in which oscillating retinal disparity failed to produce a sensation of motion in depth, although visual responses to static disparity were normal, and psychophysical thresholds for lateral motion showed no defect with either binocular or monocular viewing. It was concluded, therefore, that the perceptual stereomotion scotomata were not due to a monocular loss, but to a defective binocular interaction between motion signals from the left and right eyes, and that this defective interaction was specific for opposed rather than parallel motion in the two eyes. Furthermore, the visual loss was specific for motion rather than for position. The correlation between the field defects for ocular vergence and stereomotion perception leads the authors to suggest that the same defect in binocular interaction is responsible for both the eye movement and sensory abnormalities. Two candidate hypotheses are proposed: one is framed in terms of a single population, and the other in terms of two populations of cortical neurons.

Blindness↗

PubMed1986

Necessary conditions for the perception of motion in depth.

This study investigated the relation between the perception of motion in depth and ocular vergence movements for a single foveally viewed dot, and for a 30 deg X 30 deg pattern of many dots. When the target's disparity was changed, it appeared to move in depth relative to stationary reference marks, but removing the reference marks completely abolished the sensation of motion in depth for the multi-dot target and left only a weak sensation of motion in depth for the single dot target. However, it is not the case that motion-in-depth sensation per se depends on the presence of reference marks; motion in depth generated by changing-size stimulation was unaffected by removing reference marks. Possible explanations for the loss of motion-in-depth sensation include ocular vergence exactly tracked stimulus motion; vergence changes and disparity changes, though unequal, produced equal and opposite motion-in-depth signals; vergence changes, though producing no motion-in-depth signals, suppressed the signals produced by disparity changes; motion-in-depth sensation requires relative motion. Explanation is rejected because vergence tracking errors were large. Explanation is rejected because vergence changes do not in themselves induce a sensation of motion in depth. Explanation is rejected because motion-in-depth threshold is not affected by vergence changes. Conclusions are as follows. For a single-dot target, visual sensitivity to motion in depth is much higher for changes in relative retinal disparity than for changes in absolute retinal disparity, while for a multi-dot target any residual sensitivity is abolished by an interaction between neighboring coherently moving dots. The authors suggest that the relative velocity elements proposed to explain sensitivity to changing size feed the stereomotion mechanism also.

Depth Perception↗

PubMed1985

Human ocular counterroll: assessment of static and dynamic properties from electromagnetic scleral coil recordings.

Static and dynamic components of ocular counterroll as well as cyclorotatory optokinetic nystagmus were measured with a scleral search coil technique. Static counterroll compensated for about 10% of head roll when the head was tilted to steady positions up to 20 deg from the upright position. The dynamic component of counterroll, which occurs only while the head is moving, is much larger. It consists of smooth compensatory cyclorotation opposite to the head rotation, interrupted frequently by saccades moving in the same direction as the head. During voluntary sinusoidal head roll, cyclorotation compensated from 40% to more than 70% of the head motion. In the range 0.16 to 1.33 Hz, gain increased with frequency and with the amount of visual information. The lowest values were found in darkness. The gain increased in the presence of a visual fixation point and a further rise was induced by a structured visual pattern. Resetting saccades were made more frequently in the dark than in the light. These saccades were somewhat slower than typical horizontal saccades. Cyclorotatory optokinetic nystagmus could be induced by a patterned disk rotating around the visual axis. It was highly variable even within a same subject and had in general a very low gain (mean value about 0.03 for stimulus velocities up to 30 deg/s). It is concluded that cyclorotational slip velocity on the retina is considerably reduced by counterroll during roll of the head, although the residual cyclorotation after the head has reached a steady position is very small.

Biomechanical Phenomena↗

PubMed1985

Eye movements and stereopsis during dichoptic viewing of moving random-dot stereograms.

The dynamic properties of the version and vergence system were studied in relation to stereopsis for movements of the whole visual scene. Large random-dot stereograms (30 X 30 deg arc), moving laterally, were viewed dichoptically by human subjects without a fixed visual frame of reference. Sinusoidal movements in counterphase of the two half-images constituting the stereogram induced sinusoidal ocular vergence movements. The gain of vergence depended on the frequency as well as the amplitude of stimulus movement, while the phase lag depended only on the frequency. Fusion and stereopsis were retained up to a maximal velocity of change in relative position of the two half-images between 6 and 13.5 deg/sec. Sinusoidal movement of one half-image while the other one remained stationary induced sinusoidal ocular version as well as vergence movements. For version gains were higher and phase lags were smaller than for vergence. At the retinal level, residual overall binocular disparities between the two half-images up to 2 deg arc were tolerated without loss of stereopsis. The presence of sinusoidally varying overall binocular disparities and ocular vergence movements without perception of motion in depth suggests that these variables are not adequate cues for perception of (change in) depth.

Convergence, Ocular↗

PubMed1985

Motion perception during dichoptic viewing of moving random-dot stereograms.

The relation between binocular and monocular motion perception was investigated. A random-dot stereogram (30 X 30 deg arc), containing a central figure seen in front of the background in stereoscopic vision, was viewed dichoptically by human subjects without a fixed visual frame of reference. The images seen by the right and left eye were moved laterally according to a triangular wave form, in counterphase, but with variable amplitude ratios. Under this condition only purely lateral movement and no motion in depth of the stereogram as a whole was perceived, while stereoscopic vision of the figure-background relation was maintained. The magnitude of the binocularly perceived lateral motion, signalled by manual tracking of the perceived displacement, equalled the algebraic mean of the monocular motion percepts. As a special case, when the two images forming the stereogram were moved with equal velocities but in opposite directions they were perceived as a completely stationary, fused image in stereoscopic depth. Only the addition of a stationary reference (a bar or grating seen by both eyes) resulted in the perception of motion in depth. We conclude that a visual frame of reference is essential for perception of motion in depth but not for perception of lateral movements. Moreover, it seems likely that not absolute binocular disparity (retinal locus differences) but relative binocular disparity (differences in angular distance between two or more corresponding features in the two retinal images) is a cue for perception of depth.

Convergence, Ocular↗

PubMed1985

Velocity step responses of the human gaze pursuit system. Experiments with sigma-movement.

By means of d.c.-electrooculography or the electromagnetic search coil technique, horizontal and vertical eye position signals were recorded in subjects (head fixed) attentively pursuing a rotating dot circle (dot distance Ps = 0.8 or 1.0 deg). In addition, circular eye pursuit movements were evoked by sigma-movement seen when the stationary dot circle was illuminated stroboscopically (flash frequency fs). The rotation velocity Vs or the velocity of sigma-movement (Ps X fs) was changed in positive or negative steps, leading to acceleration or deceleration of pursuit eye velocity. This step response of eye velocity could be well described by a linear second-order differential equation with an additional dead time of about 80-100 msec. When gaze position error signals were larger than 0.3-0.5 deg, correcting saccades were superimposed on the step response of the smooth pursuit system. Voluntary saccades across the rotating or apparently rotating circle did not lead to any impairment in successive pursuit eye movements or an interruption in the sigma-movement. The gaze tracking command signals (smooth pursuit and saccadic responses) are evidently related to the stimulus movement in the extrapersonal space and not to retinal movement signals.

Adult↗

PubMed1985

The oculomotor behaviour of human albinos.

Horizontal and vertical eye movements were recorded in 16 human albinos with a scleral search coil technique. Spontaneous nystagmus, responses to target steps, voluntary pursuit and optokinetic nystagmus (OKN) were assessed, including the effects of selective stimulation of the nasal or temporal halves of the retina. The results suggest a subdivision of albinos into three classes of oculomotor behaviour. Class I (n = 11) is characterized by vigorous spontaneous nystagmus (of the pendular unidirectional jerk or bidirectional jerk type), the absence of true horizontal OKN but the presence of the ability to control the direction of gaze in an imprecise way. In Class II (n = 2) there is a vigorous unidirectional jerk nystagmus which reverses in direction spontaneously or as a result of visual stimulation. Moving stimuli typically elicited inverted pursuit, the smooth eye movements having a direction opposite to that of the stimulus movement. Class III (n = 3) is characterized by very little or no spontaneous nystagmus and virtually normal oculomotor responses. Only pursuit of motion in the temporal direction, projected onto the temporal half retina, was defective. In all three classes, vertical eye movements were disturbed much less than horizontal. Anomalous visual projections (confirmed in all subjects by asymmetrical monocular visual evoked cortical potentials) are a likely basic cause underlying the oculomotor instability, but the large intersubject differences show that the eventual consequences of misrouting and secondary adaptations can vary widely among subjects.

Adolescent↗

PubMed1985

Aland eye disease: no albino misrouting.

Electrophysiological studies showed that a patient with Aland eye disease had no misrouting of the optic pathways which is always found in all forms of albinism as a consequence of the retino-geniculate anomaly. Also the spontaneous and optokinetic nystagmus did not resemble that of the large majority of human albinos. The marked asymmetry found in this patient seems to be typical for humans with a defective development of foveal binocular vision. These findings are in agreement with clinical, nystagmographic and EM findings that Aland eye disease is distinct from the Nettleship-Falls type of X-linked ocular albinism. Furthermore, Aland eye disease is different from X-chromosomal congenital stationary night blindness with myopia by the fact that the scotopic functions are only moderately affected and there is no restriction of the peripheral photopic visual fields. In addition, there is latent nystagmus of extraocular type that appears also in female carriers. There is no ophthalmoplegia, there is a progression of the myopia and the dyschromatopsia is of secondary type.

Adult↗

PubMed1985

Human eye movements associated with blinks and prolonged eyelid closure.

Eye movements associated with eyelid closure were recorded in human subjects with search coils, embedded in self-adhering scleral annuli, in a magnetic field. In contrast to classical notions, voluntary as well as reflex blinks were consistently accompanied by transient downward and nasalward movements of both eyes with amplitudes 1-5 degrees. These eye movements had a shorter duration than the upper lid movements, and the shapes of the spatial trajectories of eye and lid movements were not similar. The trajectory of the eye movements was only modestly affected by gaze eccentricities up to 15 degrees; there was a tendency for the downward component to be enhanced by looking upward, and vice versa. Restraining of the lids of one eye in the open or closed position did not significantly alter the eye movements during (attempted) blinks. Velocity-amplitude-duration relations of the down- and upward components were similar for the same eye before and after closure and for the closed eye and the contralateral unrestrained eye. The velocity-amplitude-duration characteristics of saccades were also unaffected by prolonged closure of the lids of one eye. Prolonged, voluntary closure of the lids was followed by a slow, tonic ocular deviation, which was consistently upward in half of the subjects and consistently downward in the other half. Additional horizontal components were highly variable even within subjects. In one subject the downward deviation was converted into upward deviation when lid closure was mechanically impeded. We conclude that elevation of the eye ball (Bell's phenomenon) does not occur during short blinks and only in about half of the subjects during voluntary unrestrained prolonged lid closure. Our evidence does not support the possibility that the transient eye movements during blinks are caused primarily by a mechanical interaction between the lids and the eye (or the scleral annulus). More likely, they are a secondary effect of an active cocontraction of extraocular muscles that primarily results in retraction of the eye.

Adult↗