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PubMed1967

Saccadic and smooth pursuit eye movements in the monkey.

1. Voluntary eye movements were measured in the chronic, unanaesthetized monkey. A training technique is described which conditions the animals to follow a large variety of target trajectories.2. The eye movements of the monkey are not qualitatively different from those of man. In response to random target motions the monkey also employs a combination of saccadic and smooth pursuit movements.3. Monkeys execute their saccades more rapidly than humans.4. Monkeys are capable of attaining smooth pursuit velocities which are twice as fast as those of man.5. Most of the critical experiments showing the separate nature of the saccadic and smooth pursuit modes in man have been performed on monkeys with similar results.6. Therefore, if one remains aware of the quantitative differences between the two primates, results of neurophysiological studies of the occulomotor system of the monkey can be expected to have considerable relevance when extrapolated to man.

Animals↗
PubMed1988

Eccentric fixation with macular scotoma.

People with macular scotoma tend to read and visually scan more slowly than others with equivalently reduced visual acuity but intact central fields. We measured fixation eye movements and considered the contribution of fixation variability and centripetal eye drift to poor visual performance. These factors might confound efforts to consistently use an optimum retinal locus outside of the macula. We measured monocular horizontal and vertical eye movements using a search coil eyetracker while subjects with naturally occurring central scotomata or control subjects with simulated scotomata eccentrically fixated a single character that was sized to their visual acuity. Motivated subjects with long-standing stable maculopathies were chosen to estimate attainable performance limits. During attempts to eccentrically fixate, an ubiquitous foveal pursuit or centripetal drift tendency was not found; rather a pattern of drift was idiosyncratic from subject to subject. This finding was confirmed by an analysis of eye drift of 32 eyes with long-standing bilateral macular scotomata. Moreover, the eye drift speeds (15-200 minarc/sec) were too low to be of functional significance. Drift speeds during eccentric fixation with a visible target were not significantly different than those after the target was extinguished; however, drift speeds were greater than during foveal fixation. This suggests that the fovea has a specialized control of slow eye movements. Fixation variability increased with scotoma size for both simulated and real scotomata, with an abrupt rise when scotomata diameters exceeded 20 degrees C. A significant minority of subjects (39%) adopted two or more distinct preferred retinal loci (PRL) during fixation. Multiple PRL were also more likely if scotoma size exceeded 20 degrees C. Reasonably steady fixation is thus attainable when central scotoma sizes are smaller than approximately 20 degrees C.

Adult↗
PubMed1983

Smooth pursuit eye movements under open-loop and closed-loop conditions.

We measured smooth pursuit eye movement responses to sinusoidal target motion in the open-loop condition (target motion stabilized on the retina) and the closed-loop condition (target motion fixed in space). We also predicted the closed-loop response for each subject from the open-loop data, using the relationship for a linear system. Predictions made in this way were very accurate, for both gain and phase lag, even though responses of a given subject usually differed idiosyncratically from those of another. The accuracy of prediction was observed over a broad frequency range (0.5-3Hz) and a moderate range of target amplitudes (2-6 deg, peak-to-peak).

Eye Movements↗
PubMed1996

Eye position and target amplitude effects on human visual saccadic latencies.

Gaze shifts vary in the extent of eye and head contribution; a large amplitude and/or an eccentric ocular orbital starting position alter the participation of head movement in the shift. The interval between eye onset and head onset determines compensatory counterrolling before and after the shift and the extent of vestibular ocular reflex reduction during the shift. The latency of eye saccades in the head-fixed condition was measured with respect to target amplitude and orbital position in order to establish base-line operations of these two variables as they apply to the head-free condition. Eye movements were measured during single-step saccades in nine young adult humans. The target step, hereafter called a jump, started from three possible fixation lights; e.g., rightward saccades started from the midline (0 degree) or from -20 or -40 degrees left of the midline, with a maximum amplitude of 80 degrees. The latency of saccades starting from the primary position increased with jump amplitude (amplitude-latency relation). When the eye started eccentrically, the latency was decreased (orbital position-latency relation), with the largest jump amplitudes most affected. These changes can be related to active eye-head coordination. Thus, with a leftward maximal orbital eccentricity, compensatory eye rotation would be impossible with a rightward head movement; however, incorporating the orbital position-latency relation, the forward ocular saccade is expedited by 90 ms. Conversely, with a primary starting position, the ocular component of an 80 degrees gaze saccade could be slowed 125 ms by incorporating the amplitude-latency relation, thus facilitating a head contribution to the gaze shift. The orbital position and amplitude-latency relations were prominent in those subjects with habitually large head contributions to the gaze shift and minimal in individuals with typically small head contributions.

Adult↗
PubMed1983

Tracking eye movements are normal in dyslexic children.

We measured saccadic and smooth eye tracking movements in 34 dyslexic and 35 control subjects and were unable to show differences in any of the tasks or parameters measured. Subjects were carefully screened for neurological, optometric, audiological, and behavioral problems before admission to the study. We suggest that differences between our results and those of previous investigators are based on sampling differences. We conclude that while there may be children with reading disorders secondary to visual or oculomotor deficits, dyslexia can and does exist independent of such deficits. Because, in this and other studies, we have ruled out peripheral involvement, we feel that dyslexia is primarily a deficit of central information processing of written or spoken material.

Child↗
PubMed1978

Ocular saccades in Duane's syndrome.

Since Hering's law might be affected when paradoxical innervation exists, 10 patients with Duane's syndrome were studied. Eye movements were measured by binocular recording of electro-oculogram. Our study shows clearly that the sound eye's motility is also affected. When adduction of the affected eye is present, Hering's law holds, whereas when adduction is limited this law cannot be demonstrated.

Adolescent↗
PubMed1976

Note on duration of stimulus exposure in experiments on covert scanning of laterally shown targets.

Prevention of contamination by eye movements is on methodological requirement in the choice of an exposure time in experiments on the covert scanning of stimuli, tachistoscopically exposed laterally. The use of measures of eye movement latency to set upper limits for exposure intervals seems questionable because latency does not index the total time (minimally, 200 msec.) required to obtain information through an eye movement. The foregoing requirement, however, is only one consideration in selection of an exposure time. Since covert encoding processes can only function while the stimulus is on and during the after-stimulation, duration of exposure delimits the operating time of these processes. Choice of an interval, therefore, should establish the setting required to study those aspects of covert scanning of experimental interest.

Attention↗
PubMed1991

Smooth pursuit and saccadic eye movements and neurological soft signs in obsessive-compulsive disorder.

Patients with obsessive-compulsive disorder (OCD) demonstrate an increased number of neurological soft signs as well as neuroanatomic abnormalities detected with modern imaging techniques. Quantitative analysis of eye movements has proved fruitful in investigations of other neuropsychiatric disorders with similar findings. Therefore, we studied the smooth pursuit and saccadic eye movements of 8 OCD patients and 12 normal controls using infrared oculography and computerized pattern recognition software. We also measured neurologic soft signs using a standardized rating instrument. Despite having an increased number of neurological soft signs, OCD patients' performance on a variety of measures of eye movement was not significantly impaired. Neither the severity of obsessions or compulsions nor the number of neurologic soft signs correlated with any of the parameters of eye movement function. We conclude that OCD patients do not have prominent oculomotor dysfunction and that eye movement dysfunction and neurologic soft signs are not inextricably linked.

Adult↗
PubMed1981

EEG sleep patterns in schizophrenic patients undergoing hemodialysis.

All-night electroencephalographic (EEG) sleep studies were obtained before and during a double-blind clinical trial of hemodialysis in six schizophrenic patients with normal renal functioning. No significant changes were observed in either clinical status or sleep, except for a significant reduction in rapid eye movement (REM) density, a measure of the number of eye movements per minute of REM sleep.

Adult↗
PubMed2005

Angular and linear vestibulo-ocular responses in humans.

A new technique is introduced to measure linear and angular vestibulo-ocular responses in three dimensions. Using a three-dimensional motion platform, human subjects underwent whole-body rotations and translations. Eye movements were measured with an infrared video recording device and/or with scleral search coils. Subjects were tested with sinusoidal stimulation and impulses under light and dark conditions. The results show that for sinusoidal stimulation, torsion compensatory eye movements (roll stimulation) have a low gain compared to horizontal (yaw) and vertical (pitch) compensatory eye movements. With impulses, we reliably assessed gain and delay for rotations in yaw, pitch, and roll. Under this stimulus condition the gain for roll (torsion eye movements) was also low compared to yaw and pitch (horizontal and vertical eye movements). For translations, the gain of eye-movement responses varied between 0.7 and 1 in the light. In the dark, responses were lower and more variable.

Calibration↗
PubMed1989

A case of Wallenberg's syndrome: ocular motor abnormalities.

Eye movements were measured objectively in a patient with Wallenberg's syndrome during the course of his 2-year recovery period. The patient exhibited a change in fixational and reading eye movement patterns consistent with concurrent reduction in symptoms. The results demonstrate the importance of clinical eye movement recordings in such patients to understand more fully the relationship between the visually related symptoms and the objective oculomotor correlates.

Eye Movements↗
PubMed2002

Fixational eye movements are not affected by abrupt onsets that capture attention.

Recent work shows that abrupt onsets reflexively capture attention and trigger saccades that compete with voluntary saccades. To test whether oculomotor capture occurs when no saccade is being planned, we measured fixational eye movements in the absence or presence of an abrupt onset at peripheral locations. We found no effect of abrupt onset location on the average pattern of eye movements during fixation. We conclude that the capture of eye movements by an abrupt onset only happens when the oculomotor system has been preset to make a saccade. This implies that the oculomotor system is not obligatorily driven by events in the visual array.

Adult↗
PubMed1985

Active and passive smooth eye movements: effects of stimulus size and location.

We measured active smooth pursuit eye movements and passive smooth eye movements in the open-loop condition as subjects viewed moving stimuli of different sizes and at various retinal loci. Active movements have high gain and relatively large phase lag. Passive movements have lower gain and smaller phase lag, and occur with either foveal or eccentric stimuli. They appear to be similar or identical to optokinetic movements. Although different, active and passive movements show a similar increase in amplitude and phase lag as the size of the stimulus was increased. From these findings we suggest that: (1) The stimuli for the active movements are target position and velocity; (2) the stimulus for passive movements is target velocity; and (3) the active response to target velocity is related, in part, to the passive response and thus is related to optokinesis.

Adult↗
PubMed2002

Spatial orientation of postrotatory nystagmus during static roll tilt in cats.

While the stimulation of otolith inputs reduces the duration of postrotatory nystagmus (PRN), there is still room for dialogue about the effect of static tilt on the orientation of PRN. We studied one possible influence of static roll tilt on the spatial orientation of PRN in cats. The animal was rotated about an earth-vertical axis (EVA) at a constant velocity of 100 deg/s with an acceleration and deceleration of 120 deg/s2. Within two seconds after stopping EVA rotation, the animal was passively tilted at 45 deg/s about its longitudinal axis by as much as +/- 90 deg in steps of 15 deg. Eye movements were measured with magnetic search coils. The angle of the PRN plane and its slow phase eye velocity were measured. The time constant of PRN decreased with an increase in roll tilt. The PRN plane remained earth horizontal within a range of +/- 30 deg roll tilt. Beyond this range, the velocity of PRN decreased too rapidly to measure any change in orientation. Our results indicate a spatially limited and temporally short interaction of the semicircular canal and otolith signals in the velocity storage mechanism of cat PRN. Our data, along with previous studies, suggest that different species show different solutions to the problem of the imbalance and spatial disorientation during contradictory stimuli.

Animals↗
PubMed1977

Abnormal saccades in paralytic strabismus.

Saccadic eye movements were measured in ten patients with unilateral limitation of function of an extraocular muscle. With the paretic eye fixating, there were a series of saccades when refixating in the direction opposite to the paralysis. Between each saccade, the eye drifted back toward the starting position; the drift rate decreased as the eye moved into the field of action of the strong agonist muscle. In one patient, the normal (covered) eye was immobilized during attempted refixations. In this case, the abnormal pattern of saccades made by the paretic eye persisted. Thus, the central nervous system uses innervation or efference to calculate the position of the eye in the orbit for saccadic eye movements.

Eye Movements↗
PubMed1991

The effects of flicker on eye movement control.

Groups of typists with extensive experience of screen-based editing and groups of students with no such experience carried out a reading task under three conditions of illumination (50-Hz flicker, 100-Hz flicker, and steady illumination). Subjects read a sentence, which was followed by the presentation of a single stimulus word on the same line to the right-hand side of the display. The task was to decide whether or not the stimulus was present in the sentence. Subjects were free to re-inspect the sentence when making the decision. Eye movements were measured as subjects completed the task. In comparison with students, typists adopted a more cautious reading style, making more right-to-left saccades, shorter saccades, and more corrective eye movements. Flicker affected the performance of both groups of subjects in the first pass, leading to shorter saccades. In the second pass, its effect for students was to shorten the extent of large saccades made to check the presence of the stimulus word. In the group of typists, flicker led to an increase in the variability of saccade extent and a doubling in the number of small corrective saccades. The results are consistent with the view that flicker has two distinct effects on reading, both of which are potentially disruptive. The first relates to an increase in the number of prematurely triggered saccades, which are, as a result, less accurate. The second is an increase in the number of saccades perturbed in flight, which land short of their intended target. These two mechanisms may have different consequences for readers, depending on their reading style.

Adult↗
PubMed1984

Interaction between saccade and tracking vergence.

Additivity of saccade and tracking vergence was examined. Binocular eye movements were measured photoelectrically while subjects tracked a target moving smoothly on a radial line with an interpolated step change to a new radial line. Examining the abrupt portions of the two eyes' movements, we found the durations were almost the same for the two eyes, but that there were reliable differences in the magnitudes which were too large to be understood by an additivity hypothesis.

Adult↗