Saccade Dynamics Research Articles

Horizontal Saccade Dynamics across the Human Life Span

To investigate saccade dynamics as a function of age to determine whether they follow the pattern of development and decline predicted by Weale's model of aging. One hundred ninety-five participants between the ages of 3 and 86 years made visually guided horizontal prosaccades ranging in size from 1 degrees to 60 degrees in response to dot stimuli. Eye movements were recorded binocularly with a video-based eye tracker, sampling at 120 Hz. Saccadic latency, accuracy, and velocity were measured and analyzed as a function of age. Mean saccadic latency decreased from 439 ms at 3 years to 172 ms at 14 years, followed by a period of relative stability to age 50 and finally, gradually increased to 264 ms at >or=80 years. For saccadic accuracy (amplitude gain), there was a statistically significant (P<0.05) interaction between saccade size and age. Participants made increasingly hypometric saccades as age and saccade size increased. Average age group saccadic asymptotic peak velocity (Vmax) increased during childhood from 446 deg/s at age 3, to a peak of 610 deg/s at 14 years and then gradually declined with age to approximately 345 deg/s for participants>or=80 years. Age affected saccadic latency, accuracy, and velocity. For each parameter there was a different pattern of development and decline probably related to the way in which the portion of the brain that controls each function develops and ages.

Saccade dynamics in peripheral vs central sixth nerve palsies

To investigate differences between peripheral idiopathic and central sixth nerve palsies from brainstem damage by comparing peak velocities and durations of horizontal saccades. Fourteen patients with unilateral incomplete sixth nerve palsies caused by idiopathic, presumed ischemic, peripheral damage, 5 with incomplete central (fascicular) palsy caused by brainstem lesions, and 10 controls were studied. Palsies under 1 month in duration were designated as acute and those of longer duration were chronic. Among peripheral palsies, five were acute, nine were chronic. Among central palsies, two were acute, three were chronic. Subjects made +/- 10 deg horizontal saccades while wearing search coils. Serial recordings were made in seven patients with acute palsy (five peripheral, two central). Centrifugal abducting saccadic velocities in the paretic eye were subnormal in both central and peripheral acute palsies, as anticipated from lateral rectus weakness. In chronic central palsies, abducting velocities in the paretic eye remained reduced. However, in chronic peripheral palsies, velocities became normal in the tested range of excursion, within 2 months of onset, despite persisting abduction deficit. Saccade peak velocities are reduced and their durations are prolonged in the field of action of acutely palsied peripheral and central nerves. Speeds remain reduced in chronic central (fascicular) palsies, consistent with limited regeneration within the brain. Saccade speeds are repaired in chronic peripheral palsies, probably by remyelination and axonal regeneration, and perhaps also by central monocular adaptation of innervation selectively to the paretic eye, in order to drive both eyes rapidly and simultaneously into the paretic field of motion.

Saccade–Vergence Interactions in Macaques. II. Vergence Enhancement as the Product of a Local Feedback Vergence Motor Error and a Weighted Saccadic Burst

In the accompanying paper we reported that intrasaccadic vergence enhancement during combined saccade-vergence eye movements reflects saccadic dynamics, which implies the involvement of saccadic burst signals. This involvement was not predicted by the Multiply Model of Zee et al. We propose a model wherein vergence enhancement is the result of a multiplicative interaction between a weighted saccadic burst signal and a nonvisual short-latency estimate of the vergence motor error at the time of the saccade. The enhancement of vergence velocity by saccades causes the vergence goal to be approached more rapidly than if no saccade had occurred. The adjustment of the postsaccadic vergence velocity to this faster reduction in vergence motor error occurred with a time course too fast for visual feedback. This implies the presence of an internal estimate of the progress of the movement and indicates that vergence responses are under the control of a local feedback mechanism. It also implies that the vergence enhancement signal is included in the vergence feedback loop and is an integral part of the vergence velocity command. Our multiplicative model is able to predict the peak velocity of the vergence enhancement as a function of cyclopean saccadic dynamics, smooth vergence dynamics, and saccade-vergence timing with remarkable precision. It performed equally well for both horizontal and vertical saccades with very similar parameters, suggesting a common mechanism for all saccadic directions. A saccade-vergence additive model is also presented, although it would require external switching elements. Possible neural implementations are discussed.

Saccades to Moving Targets

The metrics and dynamics of saccades to stationary and moving targets were observed in monkeys (Macaca mulatta). To isolate the effects of target speed on the saccade from contributions of smooth pursuit, saccade velocity was corrected for intrasaccadic pursuit velocity on a trial-by-trial basis prior to analysis. The effects of presaccadic retinal error and target speed on the saccadic velocity profile were determined by analyzing the partial correlations computed as a function of time after saccade onset. The main results are: (1) Saccade amplitude is determined not only by the retinal error sampled before the saccade, but also by the speed of the target during the latency period. (2) The dynamics of saccades, even if compensated for smooth-pursuit components, differ between forward- and backward-moving targets. (3) Whereas the presaccadic retinal error affects the eye velocity throughout the saccade, target speed has no effect before peak velocity. These results are discussed in the context of current models of saccade generation and their physiological substrates, in particular the role of the cerebellum in the local feedback loop.

Retention of Saccadic Adaptation in Humans

In the present study, we tested in human subjects the persistence of the oculomotor changes resulting from saccadic adaptation up to 19 days after exposure to the double step target protocol. The main results indicate that the reduction of saccade gain related to the adaptation session (mean gain change of 5 subjects = 22 +/- 4.7%) was partially but significantly retained after 1 day and 5 days (mean amount of retention = 36 +/- 17% and 19.7 +/- 13.3%, respectively) but was no longer significant at day 11 and 19. Unexpectedly, gain changes were larger for leftward than for rightward saccades. No change in saccade dynamics was observed. These data suggest that in humans, adaptive mechanisms induce long lasting changes in visually-guided saccade amplitude, probably reflecting plastic changes in the brain.

Application of rational power functions in analyses of saccadic velocity profiles.

The relationship between the product of peak velocity and duration (VmD) and saccadic amplitude is tightly correlated. The velocity profile of a saccade was referred as a triangular profile; whereas the saccadic amplitude is proportional to VmD. From our observation and derivation, in addition to the triangular profile, the rational power function can also be applied to explain the linear relationship between the saccadic amplitude and VmD. In this study, rational power functions were used for the analyses of saccadic dynamics. The results show that the rational power functions were fitted very well to the velocity profiles for three different amplitudes, i.e. 10deg, 20deg, and 30deg, with correlation coefficients are all greater than 0.99. Significant differences in shape parameters between experimental and simulated profiles were also observed. Additionally, we have found that the minimum variance model proposed based on the minimization of variance of post-saccadic eye position cannot simulate velocity profiles matched with the experimental results. In conclusion, rational power functions are efficient in describing the saccadic velocity profiles. The shape parameters are also efficient for describing the dynamics of saccadic velocity profiles.

Saccades to stationary and moving targets differ in the monkey

Saccade characteristics in response to moving and stationary targets were studied in three monkeys (Macaca mulatta) that had been trained to look at a target, which after an initial jump either remained in place or moved forward or backward with constant velocity (10 degrees /s). Eye movements were recorded using a search coil. The contribution of smooth pursuit to the saccade amplitude was small (<0.25 degrees ). Saccades having the same amplitude (5.67-6.83 degrees for different monkeys) to forward and backward moving targets were compared. Peak velocity was higher (37-42 degrees /s on average for different monkeys) and saccade duration was shorter (8-10 ms on average) for backward saccades than for forward saccades These differences were highly significant (t-test: P<0.001). Thus, forward and backward saccades are not on the same main sequence. This suggests that saccade dynamics are affected not only by the retinal position error but also by target motion. Further analysis revealed that saccade peak velocity mainly depends on the retinal position error, but saccade amplitude also depends on a stimulus-related velocity factor, which affects the saccade mainly during deceleration. This velocity factor could be retinal slip or target velocity, which was the same under our conditions. Our results experimentally support recent models that propose that the saccade acceleration in response to moving targets might be controlled by the superior colliculus, whereas the deceleration changes are fine-tuned by the cerebellum. This prediction must still be tested on a neuronal level.

Understanding cone distributions from saccadic dynamics. Is information rate maximised?

Understanding cone distributions from saccadic dynamics. Is information rate maximised?

Understanding cone distributions from saccadic dynamics. Is information rate maximised?

There is not yet a fully satisfactory and quantitative explanation as to why human cones have their particular distribution on the retina. If this distribution is to maximise the rate of the information transfer, it should be proportional to the probability distribution of locations of attended objects. We derive this probability distribution from experiment data on eye movements to test this hypothesis, which provides a quantitative link between saccadic dynamics and the cone distribution.

Task demands and binocular eye movements.

Humans make rapid movements of their eyes several times a second that enable them to examine objects located at different positions in space with both of their eyes. Much of our understanding of these binocular movements comes from studies using experienced observers performing repetitive, unnatural tasks. But what eye movements are made when naïve observers perform tasks demanding specific binocular visual information? We examined the binocular eye movements produced by observers performing two tasks differing in the visual information needed for their completion. Our motivation for doing this was to examine the role and function of binocular eye movements when making decisions. We considered the fixation strategies adopted by observers, the effects of the task on the dynamics of saccadic eye movements, and the combination of vergence and version in gaze shifts. We report that the task-dependent use of visual information can have a strong influence on the patterns of fixations, whilst not influencing saccade dynamics. Our data provide some support for the notion that observers choose and fixate a notional reference point in the scene when making judgments about depth structure.

THE PEAK VELOCITY AND SKEWNESS RELATIONSHIP FOR THE REFLEXIVE SACCADES

The main sequence relations of saccades stated that the duration was linearly correlated to the saccadic amplitude for a wide range, whereas the peak velocity correlated exponentially to the amplitude with saturation occurred at 30°-40°. Skewness was used efficiently in delineating the asymmetry between the acceleration and deceleration phases of the saccadic velocity profiles. It can be estimated from the shape parameter obtained by applying gamma function to the velocity profile. The relationship between peak velocity and skewness was derived according to the following observations. (1) At the same target amplitude and under the similar test conditions, data from previous investigations showed that great intra- and inter-subject variation of the peak velocity and the skewness were always observed. (2) Although the velocity was substantially decreased and the duration greatly increased, accuracy was not affected with the saccadic amplitude was almost unchanged for the subjects after diazepam had been taken. (3) The duration of acceleration phase is almost unchanged for different amplitudes. Fifteen normal subjects (range 21 to 26 years with mean of 23.6) without history of neurological disease were recruited and tested in this study. Electro-oculograph (EOG) was used for recording the eye movements with amplitudes ranging from 10° to 60°. The results show that the data were highly correlated to the derived peak velocity and skewness relation with correlation coefficient (R) as high as 0.66-0.92 for great amplitudes (&gt;30°). This study provides an alternative method in quantitative analysis of saccadic dynamics

Scleral search coils influence saccade dynamics.

The scleral search coil technique is commonly used for recording eye movements. The goal of this paper is to investigate to what extent the placement of scleral search coils onto the eyes influences the kinematics of saccades. To that end saccadic eye movements of human subjects were recorded with an infrared video system, while they wore coils and we compared the main sequence properties with recordings in which no coils were mounted on the eyes. It was found that saccades last longer (by about 8%) and become slower (by about 5%) when both eyes wear coils. This is truly due to the fact that the coils are on the eyes and not due to other factors that are part of this method, such as the scleral anesthesia. The influence of coils in both eyes was also observed when one coil was mounted on one eye only. Therefore the effect that the coils have on the eye movements cannot be attributed to purely mechanical factors, such as inertial load on the eyeball or increased friction. Rather the coils appear to change the oculomotor command signals that drive the saccadic eye movements.

Inactivation of macaque lateral intraparietal area delays initiation of the second saccade predominantly from contralesional eye positions in a double-saccade task.

Previous studies have shown that, although lateral intraparietal (LIP) area neurons have retinotopic receptive fields, the response strength of these cells is modulated by eye position. This combining of retinal and eye position information can form a distributed coding of target locations in a head-centered coordinate frame. Such an implicit head-centered coding offers one mechanism for maintaining spatial stability across eye movements and can be used to compute new oculomotor error vectors after each eye movement. An alternative mechanism is to use eye displacement signals rather than eye position signals to maintain spatial stability. The aim of this study was to distinguish which of these two extra-retinal signals (or perhaps both signals) are employed in a double saccade task, which required the monkey to use extraretinal information associated with the first saccade to localize a remembered target for a second saccade. By varying the direction and the end point of the first saccade and selectively inactivating area LIP in one hemisphere with muscimol injection, we were able to distinguish between the two mechanisms by observing how the second saccade was impaired in this task. The displacement mechanism predicts that, if the first saccade is in the contralesional direction, the second saccade will be impaired, and the end point of the first saccade would not be important. The eye position mechanism predicts that if the first saccade ended in the contralesional head-centered space, the second saccade will be impaired, no matter in which direction the first saccade is made. Results showed that, after area LIP lesion, when the first saccade stepped into the contralesional field, the error rate of the second saccade became higher and the latency longer. However, when the end point of the first saccade was constant, the direction of the first saccade had much less effect on the second saccade. These results suggest that eye position, and not eye displacement, is the more predominant factor in this task. In a different behavioral paradigm, the monkeys performed single visual and memory saccades from different initial eye positions. It was found that the impairment of either the metrics or dynamics of visual and memory saccades did not significantly vary with the different eye positions. It thus appears that the performance of single visual and memory saccades is best described in an oculocentric coordinate frame that does not rely on extraretinal signals. Altogether these results lend further support to the hypothesis that, by combining retinal and eye position signals, area LIP contains concurrent eye-centered and head-centered representations of the visual space. Depending on the task, either representation can be used.

The Difference in Saccadic Parameters Among Several Visually Guided Tasks

Purpose: The present study was undertaken to establish the effects of the five different paradigms (simultaneous, gap, overlap, delayed-memory, and anti-saccade tasks) on saccade dynamics (duration, peak velocity, and amplitude). Methods: We recorded ocular movements in 7 normal subjects, using infrared oculography with a visual stimulation system. Results: The distribution of saccade accuracy in gap and overlap tasks had about the same steepness as that in simultaneous tasks, but that in delayed-memory and anti-saccade tasks was broader than that in simultaneous tasks. The distribution in anti-saccade tasks had a marked intersubject variability, and the average values of accuracy were hypermetric in four subjects. The peak velocity/amplitude ratio in simultaneous and gap tasks were higher than those of other tasks. The relationship between average of peak velocity of abduction and adduction was different, adduction was higher than abduction in simultaneous and gap tasks, and abduction was lower than adduction in delayed-memory and anti-saccade tasks. Conclusions: The dynamics in simultaneous tasks had about the same characteristics as in gap tasks, but were different from those in overlap, delayed-memory, and anti-saccade tasks. These results indicated that the marked differences in dynamic properties among different saccade types may reflect processes in the visuomotor system.

Quantification analysis for saccadic eye movements.

Traditional parameters, such as latency and peak velocity, have been used for quantitative analysis of saccade dynamics. However, saccades of equal magnitude which differ substantially in dynamics may still have the same peak velocity. This lack of selectivity might degrade the efficacy of the peak velocity measurement in discriminating patients from normal subjects. In this study, an alternative parameter, the damping ratio of a second-order response, is proposed to concisely and accurately describe saccadic dynamics. A measurement of damping ratio is made by considering the response curve of saccade as the step response of a second-order transfer function. Using the least-mean-square algorithm, the second-order function has been optimized to fit the response of the saccade dynamics with the latency removed. Nineteen normal subjects (ten young and nine older) and 16 patients of Parkinson's disease (eight mildly affected and eight advanced affected) were tested for eye movements in response to pseudorandom saccadic stimuli. While the traditional peak velocity had difficulties in differentiating between the saccadic dynamics of normal and Parkinson subjects, the damping ratio is sensitive enough not only to highlight the difference between a group of patients mildly affected with Parkinson's disease and an age-matched normal group (p<0.01; abnormal versus normal), but also to distinguish between groups at different ages (p<0.01; younger versus older). It is proposed that the damping ratio could be a useful parameter in analyzing saccadic dynamics.

Effects of lesions of the oculomotor vermis on eye movements in primate: saccades.

We studied the effects on saccades of ablation of the dorsal cerebellar vermis (lesions centered on lobules VI and VII) in three monkeys in which the deep cerebellar nuclei were spared. One animal, with a symmetrical lesion, showed bilateral hypometric horizontal saccades. Two animals, with asymmetrical lesions, showed hypometric ipsilateral saccades, and saccades to vertically positioned targets were misdirected, usually deviating away from the side to which horizontal saccades were hypometric. Postlesion, all animals showed an increase (2- to 5-fold) in trial-to-trial variability of saccade amplitude. They also showed a change in the ratio of the amplitudes of centripetal to centrifugal saccades (orbital-position effect); usually centrifugal saccades became smaller. In the two animals with asymmetrical lesions, for saccades in the hypometric direction, latencies were markedly increased (up to approximately 500 ms). There was also an absence of express and anticipatory saccades in the hypometric direction. When overall saccade latency was increased, centrifugal saccades became relatively more delayed than centripetal saccades. The dynamic characteristics of saccades were affected to some extent in all monkeys with changes in peak velocity, eye acceleration, and especially eye deceleration. There was relatively little effect of orbital position on saccade dynamics, however, with the exception of one animal that showed an orbital position effect for eye acceleration. In a double-step adaptation paradigm, animals showed an impaired ability to adaptively adjust saccade amplitude, though increased amplitude variability postlesion may have played a role in this deficit. During a single training session, however, the latency to corrective saccades-which had been increased postlesion-gradually decreased and so enabled the animal to reach the final position of the target more quickly. Overall, both in the early postlesion period and during recovery, changes in saccade amplitude and latency tended to vary together but not with changes in saccade dynamics or adaptive capability, both of which behaved relatively independently. These findings suggest that the cerebellum can adjust saccade amplitude and saccade dynamics independently. Our results implicate the cerebellar vermis directly in every aspect of the on-line control of saccades: initiation (latency), accuracy (amplitude and direction), and dynamics (velocity and acceleration) and also in the acquisition of adaptive ocular motor behavior.

Effects of focal inactivation of dorsal or ventral layers of the lateral geniculate nucleus on cats' ability to see and fixate small targets.

To reveal contributions of different subdivisions of the lateral geniculate nucleus (LGN) to visuomotor behavior, segments of either layer A or the C layers were inactivated with microinjections of gamma-aminobutyric acid while cats made saccades to retinally stabilized spots of light placed either in affected regions of visual space or mirror-symmetric locations in the opposite hemifield. Inactivating layer A reduced the success rate for saccades to targets presented in affected locations from 82.4 to 26.8% while having no effect on saccades to the control hemifield. Saccades to affected sites had reduced accuracy and longer initiation latency and tended to be hypometric. In contrast, inactivating C layers did not affect performance. Data from all conditions fell along the same saccade velocity/amplitude function ("main sequence"), suggesting that LGN inactivations cause localization deficits, but do not interfere with saccade dynamics. Cerebral cortex is the only target of the A layers, so behavioral decrements caused by inactivating layer A must be related to changes in cortical activity. Inactivating layer A substantially reduces the activity of large subsets of corticotectal cells in areas 17 and 18, whereas few corticotectal cells depend on C layers for visually driven activity. The parallels between these behavioral and electrophysiological data along with the central role of the superior colliculus in saccadic eye movements suggests that the corticotectal pathway is involved in both deficits and remaining capacities resulting from blockade of layer A.

Properties of Horizontal Saccades Accompanied by Blinks

Using the magnetic search coil technique to record eye and lid movements, we investigated the effect of voluntary blinks on horizontal saccades in five normal human subjects. The main goal of the study was to determine whether changes in the dynamics of saccades with blinks could be accounted for by a superposition of the eye movements induced by blinks as subjects fixated a stationary target and saccadic movements made without a blink. First, subjects made voluntary blinks as they fixed on stationary targets located straight ahead or 20 degrees to the right or left. They then made saccades between two continuously visible targets 20 or 40 degrees apart, while either attempting not to blink, or voluntarily blinking, with each saccade. During fixation of a target located straight ahead, blinks induced brief downward and nasalward deflections of eye position. When subjects looked at targets located at right or left 20 degrees, similar initial movements were made by four of the subjects, but the amplitude of the adducted eye was reduced by 65% and was followed by a larger temporalward movement. Blinks caused substantial changes in the dynamic properties of saccades. For 20 degrees saccades made with blinks, peak velocity and peak acceleration were decreased by approximately 20% in all subjects compared with saccades made without blinks. Blinks caused the duration of 20 degrees saccades to increase, on average, by 36%. On the other hand, blinks had only small effects on the gain of saccades. Blinks had little influence on the relative velocities of centrifugal versus centripetal saccades, and abducting versus adducting saccades. Three of five subjects showed a significantly increased incidence of dynamic overshoot in saccades accompanied by blinks, especially for 20 degrees movements. Taken with other evidence, this finding suggests that saccadic omnipause neurons are inhibited by blinks, which have longer duration than the saccades that company them. In conclusion, the changes in dynamic properties of saccades brought about by blinks cannot be accounted for simply by a summation of gaze perturbations produced by blinks during fixation and saccadic eye movements made without blinks. Our findings, especially the appearance of dynamic overshoots, suggest that blinks affect the central programming of saccades. These effects of blinks need to be taken into account during studies of the dynamic properties of saccades.

Dissociated effects of botulinum toxin chemodenervation on ocular deviation and saccade dynamics in chronic lateral rectus palsy

AIMChanges in saccade velocity/amplitude characteristics (main sequence) and attenuation of distance esotropia in response to botulinum toxin (BTX-A) chemodenervation of the antagonist medial rectus were studied in a group of...

注視点と視標の有無による意識的サッカードの動特性変動と視覚依存性反射的サッカードとの比較

It was investigated whether the existence of a fixation point and saccade target influences the dynamics (peak velocity and duration) of voluntary saccades. In addition, the difference in dynamics between visually guided reflexive saccades, which reflexively occur oriented forward a suddenly appearing target, and visually guided voluntary saccades, which were voluntarily elicited toward the target, was investigated. Five experiments were conducted on young subjects in darkness. The results gave new findings as follows. (1) Independent of the fixation point the existence of the saccade target increases the peak velocity and reduces the duration of the voluntary saccades. (2) Independent of the existence of the saccade target the existence of the fixation point does not influence the dynamics of the voluntary saccades. (3) The visually guided reflexive saccade is larger in peak velocity and shorter in duration than the visually guided voluntary saccade.