Eye-hand interactions during goal-directed pointing movements

Saccadic eye and hand movements made to step displacements in target position were measured under conditions designed to dissociate the output of the ocular and manual motor systems. This was accomplished by having subjects look and point, either with or without vision of the hand (closed or open loop, respectively) at peripheral targets starting from independent initial positions. The results showed that the amplitude of open loop pointing responses increased in size when accompanied by saccades that were larger than the required hand movement. Providing the subject with visual feedback of the hand during the response or asking them to visually fixate caused this effect to disappear. Taken together, this pattern of results suggests that when vision of the hand is unavailable the programming of saccade metrics influences the control of simultaneously produced pointing movements in an on-line manner.     

Saccades induced electrically from the dorsomedial frontal cortex: evidence for a head-centered representation

The amplitude and direction of saccadic eye movements evoked electrically from the dorsomedial frontal cortex (DMFC) of monkeys vary with starting eye position. This observation has been used to argue that the DMFC codes saccadic eye movements in head-centered coordinates. Whether the amplitude and direction of the evoked saccades are also affected by changes in head position has never been demonstrated. Such a result would argue against a head-centered representation, and instead would suggest a representation anchored to another body part. Tests were conducted on rhesus monkeys to determine whether changing the position of the head with respect to the trunk or changing the position of the head with respect to the gravitational axis alters saccadic parameters. The amplitude and direction of saccadic eye movements remained invariant to such manipulations. These findings confirm the claim that the DMFC encodes saccadic eye movements in head-centered coordinates.     

Hydrothermal-electrochemical deposition of hydroxyapatite

Age-related differences in the trajectories of saccadic eye movements were examined. Younger and older adult subjects produced saccades to predictable target locations. Detailed features of the movements were examined such as the time of peak acceleration and the variability in the magnitude of the peak velocity. These and other measures reveal important details of the force pulses underlying the eye movements and the mental mechanisms that control them. Although minor differences were apparent between the eye movements of younger and older adults, the general patterns were the same across age groups. These results suggest that fundamental details of the brain mechanisms involved in the control of movement are the same for younger and older adults.     

Aging and movement: Variability of force pulses for saccadic eye movements.

Age-related differences in the trajectories of saccadic eye movements were examined. Younger and older adult subjects produced saccades to predictable target locations. Detailed features of the movements were examined such as the time of peak acceleration and the variability in the magnitude of the peak velocity. These and other measures reveal important details of the force pulses underlying the eye movements and the mental mechanisms that control them. Although minor differences were apparent between the eye movements of younger and older adults, the general patterns were the same across age groups. These results suggest that fundamental details of the brain mechanisms involved in the control of movement are the same for younger and older adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye-hand coordination: Oculomotor control in rapid aimed limb movements.

Three experiments are reported in which Ss produced rapid wrist rotations to a target while the position of their eyes was being monitored. In Experiment 1, Ss spontaneously executed a saccadic eye movement to the target around the same time as the wrist began to move. Experiment 2 revealed that wrist-rotation accuracy suffered if Ss were not allowed to move their eyes to the target, even when visual feedback about the moving wrist was unavailable. In Experiment 3, wrist rotations were equally accurate when Ss produced either a saccadic or a smooth-pursuit eye movement to the target. However, differences were observed in the initial-impulse and error-correction phases of the wrist rotations, depending on the type of eye movement involved. The results suggest that aimed limb movements use information from the oculomotor system about both the static position of the eyes and the dynamic characteristics of eye movements. Furthermore, the information that governs the initial impulse is different from that which guides final error corrections. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the oculomotor vermis in generating pursuit and saccades: effects of microstimulation

We studied the eye movements evoked by applying small amounts of current (2-50 microA) within the oculomotor vermis of two monkeys. We first compared the eye movements evoked by microstimulation applied either during maintained pursuit or during fixation. Smooth, pursuitlike changes in eye velocity caused by the microstimulation were directed toward the ipsilateral side and occurred at short latencies (10-20 ms). The amplitudes of these pursuitlike changes were larger during visually guided pursuit toward the contralateral side than during either fixation or visually guided pursuit toward the ipsilateral side. At these same sites, microstimulation also often produced abrupt, saccadelike changes in eye velocity. In contrast to the smooth changes in eye velocity, these saccadelike effects were more prevalent during fixation and during pursuit toward the ipsilateral side. The amplitude and type of evoked eye movements could also be manipulated at single sites by changing the frequency of microstimulation. Increasing the frequency of microstimulation produced increases in the amplitude of pursuitlike changes, but only up to a certain point. Beyond this point, the value of which depended on the site and whether the monkey was fixating or pursuing, further increases in stimulation frequency produced saccadelike changes of increasing amplitude. To quantify these effects, we introduced a novel method for classifying eye movements as pursuitlike or saccadelike. The results of this analysis showed that the eye movements evoked by microstimulation exhibit a distinct transition point between pursuit and saccadelike effects and that the amplitude of eye movement that corresponds to this transition point depends on the eye movement behavior of the monkey. These results are consistent with accumulating evidence that the oculomotor vermis and its associated deep cerebellar nucleus, the caudal fastigial, are involved in the control of both pursuit and saccadic eye movements. We suggest that the oculomotor vermis might accomplish this role by altering the amplitude of a motor error signal that is common to both saccades and pursuit.     

Quantitative evaluation of saccadic and smooth pursuit eye movements. Is it reliable?

PURPOSE: The authors evaluated the reliability of the coefficients of the (1) amplitude/duration and (2) amplitude/peak velocity relationships of the mean precision values and the mean latency values (saccadic eye movements) and the coefficients of the target velocity/gain relationship (smooth pursuit eye movements). They computed test-retest maximum variability limits for these parameters. METHODS: After a 1-week interval, saccadic and smooth pursuit eye movements were recorded twice from 20 healthy subjects; 12 of these subjects underwent a third recording session. The estimate of the intraclass coefficient of reliability, R, was adopted to evaluate the reliability of eye movement quantitative analysis. RESULTS: The data demonstrated that the reliability was fairly good for the amplitude/peak velocity relationship, was good for the precision, and was excellent for the amplitude/duration, the target velocity/gain relationships, and the latency. CONCLUSIONS: Quantitative analysis of both saccadic and smooth pursuit eye movements is reliable. One statistic used to estimate reliability, ie, the within-subjects mean square value, also enables the determination of test-retest normal variability values for both the variances and the differences of measurements.     

Initiation of disjunctive smooth pursuit in monkeys: evidence that Hering's law of equal innervation is not obeyed by the smooth pursuit system

Monkeys generated disjunctive smooth pursuit eye movements when they tracked visual targets that moved toward or away from them. Eye acceleration was computed during the initial 100 msec of pursuit (the open-loop interval) for various target trajectories. The initial acceleration of either eye was a function of the target's motion with respect to that eye, regardless of whether or not the pursuit was conjugate or disjunctive, or performed with one eye occluded. Eye movements produced by fusional vergence could be separated temporally from eye movements produced by smooth pursuit using step-ramp paradigms. The separation of the two responses demonstrates that the fusional vergence system operates in parallel with the smooth pursuit system, presumably to minimize disparity, but not to generate disjunctive components of smooth pursuit eye movements.     

Eye- and head movements in freely moving rabbits

1. Eye- and head movements were recorded in unrestrained, spontaneously behaving rabbits with a new technique, based upon phase detection of signals induced in implanted coils by a rotating magnetic field. 2. Movements of the eye in space were exclusively saccadic. In the intersaccadic intervals the eyes were stabilized in space, even during vigorous head movements. Most of this stability was maintained in darkness, except for the occurrence of slow drift. 3. Many saccades were initiated while the head was stationary. They were accompanied by a similar, but slower head rotation with approximately the same amplitude. The displacement of the eye in space was a pure step without appreciable under- or over-shoot. The deviation of the eye in the head was mostly transient. 4. Other saccades were started while the head was moving and were possibly fast phases of a vestibulo-ocular reflex. The time course of the eye movement in space was identical for all saccades, whether the head was moving prior to the saccade or not. Eye movements without any head movement were not observed. 5. Saccades were mostly large (average 20-6 +/- 12-4 degrees S.D.) and never smaller than 1 degree. The relations of maximal velocity and duration to amplitude were similar to those reported for man. 6. Visual pursuit of moving objects, when elicited, was only saccadic and never smooth. 7. It is concluded that the co-ordination and dynamics of the rabbit's head- and eye movements are similar to those of primates. In the absence of foveal specilization, the eye movements are restricted to a rather global redirection of the visual field, possibly in particular of the binocular area.     

Nucleotide sequences and functional characterization of two tobacco UAG suppressor tRNA(Gln) isoacceptors and their genes

The hypothesis was tested that peak velocity of saccadic eye movements in visual motor tasks varies with variables related to energy regulation. The hypothesis is based on the cognitive-energetical performance model of Sanders. An experimental paradigm was developed in which saccadic peak velocity of task-relevant eye movements is measured while a choice reaction task is carried out. Confounding factors of saccadic amplitude and movement direction were controlled. The task was designed in such a way that in each trial subjects performed a target saccade towards an imperative stimulus and a return saccade after the manual response back to the centre of the screen. For both types of saccades the experimental variables were foreperiod duration (short versus long), knowledge of results (with versus without), postsaccadic demand (low versus high) and time on task (five 30-min intervals). In two experiments, there are main and interaction effects of the task variables on peak saccadic velocity. Return saccades are slower than target saccades, but not in the case of high postsaccadic demand. Knowledge of results increases peak saccadic velocity, but more so for return than for target saccades. Time on task leads to a decrease in peak saccadic velocity, which is much stronger for return than for target saccades; furthermore this effect is more pronounced after short than after long foreperiods. Peak saccadic velocity is changed within seconds. The results support the hypothesis. Peak saccadic velocity of task related eye movements reflects energy regulation during task performance. The paradigm will be developed as a diagnostic tool in workload measurement.     

Programming saccadic eye movements.

This article addresses questions about the preparatory processes that immediately precede saccadic eye movements. Saccade latencies were measured in a task in which subjects were provided partial advance information about the spatial location of a target fixation. In one experiment, subjects were faster in initiating saccades when they knew either the direction or amplitude of the required movement in advance compared to a condition with equal uncertainty about the number of potential saccade targets but without knowledge of the parameters required to execute the movement. These results suggest that the direction and amplitude for an upcoming saccade were calculated separately, and not in a fixed serial order. In another experiment, subjects appear to have programmed the saccades more holistically—with computations of direction and amplitude parameters occurring simultaneously. The implications of these results for models of eye movement preparation are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two malate dehydrogenases in Methanobacterium thermoautotrophicum

PURPOSE: To study fixational eye movements as a function of visual acuity (VA) in patients with diabetic maculopathy and in patients with non-diabetic macular disease. MATERIAL: Two groups of patients each with VA ranging between 0.05-0.77 were studied, i.e. 24 patients with diabetic maculopathy and 23 patients with non-diabetic macular lesions. Fixational eye movements were quantified from video recordings of the ocular fundus obtained with the Rodenstock scanning laser ophthalmoscope. RESULTS: Within both groups of patients we found a similar significantly negative relation between the amplitude of fast saccadic eye movements and the VA. Patients with VA > 0.20 showed a normal directional pattern with larger amplitudes of the fast saccadic movements in the horizontal than in the vertical plane, whereas for patients with VA < or = 0.20 the amplitudes of the saccadic movements in the vertical plane had enlarged to equal the saccadic amplitude in the horizontal plane. Four patients with VA < or = 0.10 had the fixation centre located more than three degrees (approximately 500 microns at the retinal plane) from the centre of the foveal avascular zone, whereas the fixation centre of the remaining 43 patients was within one degree of the centre of this zone. CONCLUSION: Patients with VA < or = 0.20 may have retinal areas of fixation located more than 500 microns from the fovea. This fact should be taken into account when planning retinal photocoagulation in macular disease.     

Directional control of rapid arm movements: The role of the kinetic visual feedback system.

Examined how vision of initial, terminal, or complete arm trajectory affected the movement control and accuracy of 6 right-handed volunteers when the amplitude and directional task constraints were varied. Evidence was found for the significant contribution of vision during the initial phase of rapid pointing movements when this phase is under the control of the kinetic channel. Movements having directional requirements were more accurate when vision of the initial portion of the trajectory was available. Times-to-peak acceleration and velocity were shorter and their respective amplitudes were generally higher when vision was available for the 1st 3rd of the trajectory than when it was not. Vision of the entire trajectory did not yield better precision than when vision was available for the initial phase of the movements only. The data support the existence of 2 supportive visual feedback systems. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Speed and accuracy of saccadic eye movements: Characteristics of impulse variability in the oculomotor system.

Dynamic characteristics observed in the trajectories of saccadic eye movements revealed systematic variability of the force pulses used to move the eyes. This variability causes saccades to exhibit a linear speed–accuracy trade-off: As the average distance and duration of saccades toward specified target points increase, the standard deviations of saccadic-movement endpoints increase linearly with the saccades' average velocity. The linear trade-off, and other observed stochastic properties of saccades, may be attributed to noise in neuromotor processes and may be described in terms of an impulse-variability model originally designed for characterizing limb movements. According to the model, both eye and limb movements are controlled through stochastic force and time parameters that govern movement kinematics. Such an account may promote a unified conceptual framework for understanding a wide range of motor behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infant attention and the development of smooth pursuit tracking.

The effect of attention on smooth pursuit and saccadic tracking was studied in infants at 8, 14, 20, and 26 weeks of age. A small rectangle was presented moving in a sinusoidal pattern in either the horizontal or vertical direction. Attention level was distinguished with a recording of heart rate. There was an increase across age in overall tracking, the gain of the smooth pursuit eye movements, and an increase in the amplitude of compensatory saccades at faster tracking speeds. One age change was an increase in the preservation of smooth pursuit tracking ability as stimulus speed increased. A second change was the increasing tendency during attentive tracking to shift from smooth pursuit to saccadic tracking when the stimulus speed increased to the highest velocities. This study shows that the development of smooth pursuit and targeted saccadic eye movements is closely related to the development of sustained attention in this age range. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye movements in recovering substance abusers: a prospective study

Smooth-pursuit (SPEM) and saccadic (SEM) eye movements were studied in 11 cocaine-dependent and 4 alcohol-dependent patients after 1, 3, and 12 weeks of verified abstinence. Sixteen non-drug-dependent controls were studied after comparable intervals. SPEM tracking accuracy, estimated by the Ln (S/N) statistic, was higher among cocaine-dependent patients than among alcohol-dependent patients and normal controls. A microanalysis of SPEM tracking revealed that the superior accuracy of the cocaine-dependent group was due to a small increase in eye movements at the target frequency (0.4 Hz) and a small compensatory decrease in higher frequency eye movements (i.e., saccades). In contrast to the findings of the SPEM study, the findings of the SEM study revealed that alcohol-dependent patients constituted the only abnormal group. Alcohol-dependent patients exhibited slower saccade onset latencies than the other groups. There were no significant differences among the groups with respect to saccade velocity, amplitude, or duration.     

Accuracy of visually and memory-guided antisaccades in man

Primary saccades to remembered targets are generally not precise, but rather undershoot target position. The major source of this saccadic undershoot may be (a) a memory-related process or (b) a poor spatial resolution in those processes which transfer the retinotopic target information into an intermediate memory-linked representation of space. The aim of this study was to investigate whether distortions of eye positions in the antisaccade task, which are characterized by inherent co-ordinate transformation processes, may completely account for the spatial inaccuracies of memory-guided antisaccades. The results show that the spatial inaccuracy of primary and secondary eye movements in the visually guided antisaccade task was comparable to that in the memory-guided antisaccade task. In both conditions, the direction error component was less dysmetric than the amplitude error component. Secondary eye movements were significantly corrective. This increase of eye position accuracy was achieved by reducing the amplitude error only. It is concluded from this study that at least some of the distortion of memory-guided saccades is due to inaccuracies in the sensorimotor co-ordinate transformations.     

Detection of cortical activities on eye movement using functional magnetic resonance imaging

Cortical activity during eye movement was examined with functional magnetic resonance imaging. Horizontal saccadic eye movements and smooth pursuit eye movements were elicited in normal subjects. Activity in the frontal eye field was found during both saccadic and smooth pursuit eye movements at the posterior margin of the middle frontal gyrus and in parts of the precentral sulcus and precentral gyrus bordering the middle frontal gyrus (Brodmann's areas 8, 6, and 9). In addition, activity in the parietal eye field was found in the deep, upper margin of the angular gyrus and of the supramarginal gyrus (Brodmann's areas 39 and 40) during saccadic eye movement. Activity of V5 was found at the intersection of the ascending limb of the inferior temporal sulcus and the lateral occipital sulcus during smooth pursuit eye movement. Our results suggest that functional magnetic resonance imaging is useful for detecting cortical activity during eye movement.     

Binocular coordination in reading.

Measured the differences in time between the 2 eyes, using laboratory real-time computer methods to detect and measure the time between velocity peaks of binocular saccadic movements in reading. The hypothesis was that instead of being completely conjugate as indicated by prior methods of ocular measurement, the eyes must be coordinated in directional motion by small time differences that govern their feedback guidance and relative velocity. Results with 3 Ss indicate that the time differences between the eyes clustered around 3 values: (a) near synchrony, including no difference and left eye leading by 1 msec.; (b) left eye leading by 7-9 msec.; and (c) left eye leading by 14 msec. These time differences were not related to the difficulty of the reading material, but were changed significantly by 15– horizontal rotation of the reading display. Results change the established views that the eyes are perfectly conjugate in saccadic motion and provide initial suggestive data toward a dynamic feedback doctrine of coordinate eye motion and functional disabilities in visual perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Signal-dependent noise determines motor planning

When we make saccadic eye movements or goal-directed arm movements, there is an infinite number of possible trajectories that the eye or arm could take to reach the target. However, humans show highly stereotyped trajectories in which velocity profiles of both the eye and hand are smooth and symmetric for brief movements. Here we present a unifying theory of eye and arm movements based on the single physiological assumption that the neural control signals are corrupted by noise whose variance increases with the size of the control signal. We propose that in the presence of such signal-dependent noise, the shape of a trajectory is selected to minimize the variance of the final eye or arm position. This minimum-variance theory accurately predicts the trajectories of both saccades and arm movements and the speed-accuracy trade-off described by Fitt's law. These profiles are robust to changes in the dynamics of the eye or arm, as found empirically. Moreover, the relation between path curvature and hand velocity during drawing movements reproduces the empirical 'two-thirds power law. This theory provides a simple and powerful unifying perspective for both eye and arm movement control.