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PubMed2006

The role of eye movements in lateralised word recognition.

The present study examined the role of eye movements and attention in lateralised word recognition, where words and pseudowords are presented to the right or left of the fixation point, and participants are asked to decide whether or not the presented letter string is a word. In the move condition, our participants were instructed to launch a saccade towards the target letter string, which was erased from the screen after 100 ms (i.e., prior to the eyes reaching the target). It was assumed that a preparation of an eye movement simultaneously with an attention shift results in the attention being more readily allocated to the target. In the fixate condition, participants were asked to fixate on the central fixation point throughout the trial. The data on response accuracy demonstrated that word recognition in the LVF benefited from a preparation to make an eye movement, whereas the performance in the RVF did not benefit. The results are consistent with the attentional advantage account (Mondor & Bryden, 1992), according to which the performance deficit of RH for verbal stimuli may be overcome by orienting attention to the LVF prior to the presentation of a letter string.

Adult↗
PubMed1989

The effects of diet and sublingual provocative testing on eye movements with dyslexic individuals.

A double blind study was conducted utilizing the EDL/Biometrics Reading Eye Camera to determine if poor diets and altered reactions could have a detrimental effect on the eye movements of a group of dyslexic individuals. The study found that a poor diet, high in sugar, and a provocative challenge of cane sugar caused more erratic eye movements, while a good diet, without sugar, caused "normal" eye movements for the dyslexic individuals.

Adolescent↗
PubMed1998

Using the eye-movement system to control the head.

We tested the hypothesis that A.I., a subject who has total ophthalmoplegia, resulting in a lack of eye movements, used her head to orientate in a qualitatively similar way to eye-based orientating of control subjects. We used four classic eye-movement paradigms and measured A.I.'s head movements while she performed the tasks. These paradigms were (i) the gap paradigm, (ii) the remote-distractor effect, (iii) the anti-saccade paradigm, and (iv) tests of saccadic suppression. In all cases, A.I.'s head saccades were qualitatively similar to previously reported eye-movement data. We conclude that A.I.'s head movements are probably controlled by the same neural mechanisms that control eye movements in unimpaired subjects.

Adult↗
PubMed2006

Role of the human supplementary eye field in the control of saccadic eye movements.

The precise function of the supplementary eye field (SEF) is poorly understood. Although electrophysiological and functional imaging studies are important for demonstrating when SEF neurones are active, lesion studies are critical to establish the functions for which the SEF is essential. Here we report a series of investigations performed on an extremely rare individual with a highly focal lesion of the medial frontal cortex. High-resolution structural imaging demonstrated that his lesion was confined to the region of the left paracentral sulcus, the anatomical locus of the SEF. Behavioural testing revealed that the patient was significantly impaired when required to switch between anti- and pro-saccades, when there were conflicting rules governing stimulus-response mappings for saccades. Similarly, the results of an arbitrary stimulus-response associative learning task demonstrated that he was impaired when required to select the appropriate saccade from conflicting eye movement responses, but not for limb movements on an analogous manual task. When making memory-guided saccadic sequences, the patient demonstrated hypometria, like patients with Parkinson's disease, but had no significant difficulties in reproducing the order of saccades correctly on a task that emphasized accuracy with a wide temporal segregation between responses. These findings are consistent with the hypothesis that the SEF plays a key role in implementing control when there is conflict between several, ongoing competing saccadic responses, but not when eye movements need to be made accurately in sequence.

Association Learning↗
PubMedDate not supplied

The influence of combined visual and tactile information on finger and eye movements during shape tracing.

Adaptation experiments in shape tracing were conducted to investigate finger and eye movements in various conditions of visual and tactile information. Maximum velocity, mean velocity, maximum acceleration and reacceleration point were calculated from finger movements. Number of eye fixations and lead time of eye fixation to finger position were calculated from eye movements. The results showed that for the finger movement the values of the indices studied were higher in the combined visual and tactile condition than in the visual only condition. The number of eye fixations decreased when subjects repeated the tracing and was more marked in the combined visual and tactile condition than in the visual only condition. The results suggest that finger movements become faster and use of vision is reduced when both visual and tactile information are given.

Attention↗
PubMed2003

Stimulation-evoked eye movements with and without the lateral rectus muscle pulley.

Recent studies have suggested that extraocular muscle (EOM) pulleys, composed of collagen, elastin, and smooth muscle, are among the tissues surrounding the eye. High-resolution magnetic-resonance imaging appears to indicate that the pulleys serve to both constrain and alter the pulling paths of the EOMs. The active pulley hypothesis suggests that the orbital layer of the EOMs inserts on the pulley and serves to control it. Based on anatomical data, the active pulley hypothesis also suggests that the orbital layer does not rotate the eye within the orbit; this is done by the global layer of the muscle. However, no physiological data exist to confirm this hypothesis. Here we used stimulation-evoked eye movements in anesthetized monkeys and cats before and after destruction of the lateral rectus muscle pulley by removal of the lateral bony orbit and adjacent orbital tissue. The absence of these structures resulted in increased lateral, in the primate, and medial, in the cat, eye-movement amplitude and velocity. Vertical eye movements in the cat were not significantly affected. The results indicate that these increases, confined to horizontal eye-movement amplitude and velocity, may be attributed to passive properties within the orbit. In relation to the active pulley hypothesis, we could discern no clear impact (in terms of amplitude or velocity profile of the movements) of lateral eye exposure that could be directly attributable to the active lateral pulley system.

Animals↗
PubMed1983

The dynamics of vertical eye movements in normal human subjects.

We studied the dynamics of horizontal and vertical slow eye movements (vestibular, optokinetic, pursuit, and visual-vestibular) in 10 normal human subjects. Several differences between horizontal and vertical eye movements were found. The time constant (time required for the slow-phase eye velocity to decay to 37% of the peak value) of vertical postrotatory nystagmus (PRN) was, on average, 50% as long as the time constant of horizontal PRN; the mean phase lead of per-rotatory nystagmus during low-frequency sinusoidal rotation in the vertical plane was approximately twice the mean phase lead of per-rotatory nystagmus at the same frequency in the horizontal plane. Vertical optokinetic after-nystagmus (OKAN) was minimal compared to horizontal OKAN. Asymmetries in the dynamics of vertical eye movements were also noted. The mean time constant of PRN with upward slow phases was consistently longer than the mean time constant of PRN with downward slow phases and vertical OKAN only occurred when the optokinetic stimulus moved upward. Upward pursuit was better than downward pursuit and upward slow phases of vestibular nystagmus were poorly inhibited with fixation while downward slow phases were normally inhibited.

Electrooculography↗
PubMedDate not supplied

Change in rapid eye movement (REM) sleep in response to exposure to all-night noise and transient noise.

Several experiments conducted by the authors revealed certain characteristic changes in stage rapid-eye-movement sleep in response to noise exposure. Continuous and all-night exposure to noise first decreased the percentage of rapid-eye-movement stage at Leg 45dBA. In contrast, the threshold of shifts from the rapid-eye-movement stage in response to intermittent noise was higher than thresholds noted for slow-wave sleep or stage-2 sleep. We concluded that these results indicated that a silent environment is required to maintain the duration of rapid-eye-movement sleep, even though rapid-eye-movement sleep is stable and is not influenced easily by noise.

Adult↗
PubMed2003

The study of cytosolic phospholipase A2 gene polymorphism in schizophrenia using eye movement disturbances as an endophenotypic marker.

Phospholipase A(2) (PLA2) is a key enzyme of the phospholipid metabolism which shows alteration in schizophrenia. Eye movement disturbances occur in a majority of patients with schizophrenia and in a proportion of their first-degree relatives, and they have been suggested as an endophenotypic marker in genetic studies of this illness. Here we report an association between the BAN I polymorphism of the cytosolic PLA2 gene (single nucleotide polymorphism in the first intron of the gene) and the intensity of eye movement disturbances (fixation and smooth pursuit) observed in 126 schizophrenic patients. The mean intensity of both kinds of eye movement disturbances was significantly higher in individuals homozygous for the A2 genotype compared with the remaining phenotypes. There was also a trend for greater A2 allele frequency in schizophrenic patients with a higher degree of eye movement disturbances. The relative frequency of the A2/A2 genotype was higher in patients with a greater degree of eye movement disturbances occurring during both fixation and smooth pursuit tests. Our results correspond to the other studies showing an association between the cPLA2 polymorphism and schizophrenia (predominance of the A2 allele in schizophrenic subjects).

Adolescent↗
PubMedDate not supplied

Single-neuron activity in the dorsomedial frontal cortex during smooth-pursuit eye movements to predictable target motion.

A region of dorsomedial frontal cortex (DMFC) has been implicated in planning and executing saccadic eye movements; hence it has been referred to as a supplementary eye field (SEF). Recently, activity related to executing smooth-pursuit eye movements has been recorded from the DMFC, and microstimulation here has been shown to evoke smooth eye movements. This report documents neuronal activity present in smooth-pursuit tasks where the predictability of target motion was manipulated. The activity of many neurons in the DMFC reached a peak when a predictable change in target motion occurred. Furthermore, the peak activity of some cells was systematically shifted by manipulating the duration of the target event, indicating that the network these neurons were in could learn the temporal characteristics of new target motion. Finally, the activity of most neurons tested was greater when target motion was predictable than when it was unpredictable. The results suggest that the DMFC participates in planning smooth-pursuit eye movements based on past stimulus history.

Animals↗
PubMed1988

Human saccadic eye movements in the absence of the geniculocalcarine projection.

This paper describes the results of an investigation into the spatial and temporal properties of the saccadic eye-movement system in a subject with a 'blind' hemifield caused by accidental damage to the left geniculostriate projection. The results show that blind hemifield stimulation can elicit goal-directed saccades of short latency provided the contrast of the visual stimulus is above the threshold required for saccade generation at the corresponding stimulus eccentricity. Signal processing associated with blind hemifield pathways shows reduced sensitivity by comparison with the normal hemifield and greater dependence on stimulus size, eccentricity and mode of presentation. Higher contrast levels are always needed for blind field stimulation and larger variance in mean saccadic amplitudes and latencies is normally observed. Large stimulus eccentricities which would normally require corrective saccades exhibit a different response pattern to that observed in normal vision. The results show that the centre of gravity effect and the generation of rapid, 'express-saccades' observed in normal vision are not inevitable outcomes of midbrain processing of visual information. The subject's performance reveals strategic patterns of eye-movement responses which maximize the use of his normal hemifield. Visual performance in the control of saccadic eye-movement responses appears to be optimum when the detection of the visual stimulus is associated with both the geniculostriate and the midbrain pathways. Experiments designed to test for the effects of light scatter into the normal hemifield show that the subject's saccadic eye-movement performance following visual stimulation of the blind hemifield cannot be attributed either to the amount or the pattern of light scatter into the normal hemifield. The implications of present findings on the results of other studies of eye-movements in subjects with scotomas associated with cortical lesions are also examined.

Adult↗
PubMed1995

Antisaccades and smooth pursuit eye movements in schizophrenia.

Saccadic and smooth pursuit eye movements were recorded in schizophrenic patients, nonschizophrenic psychiatric patients, and normal controls. Both schizophrenic subjects and psychiatric controls demonstrated greater increases in error rates and greater delays in generating antisaccades than did normal controls. Schizophrenic patients with impaired smooth pursuit tracking showed greater increases in error rates in the antisaccade task than did schizophrenic patients with normal pursuit. Among psychiatric controls, increased errors on the antisaccade task were unrelated to pursuit performance. The small size of this group, however, reduces the power to detect a relation between smooth pursuit tracking and performance on the antisaccade task. Although most patients were receiving one or more medications, some of which can affect eye movements, medication state in this study did not account for differences we report in dependent variables.

Adult↗
PubMed1999

Rotation vector analysis of eye movement in three dimensions with an infrared CCD camera.

We have developed a new technique for analyzing the rotation vector of eye movement in three dimensions with an infrared CCD camera based on the following four assumptions; i) the eye rotates on a point; ii) the pupil edge is a circle; iii) the distance from the center of eye rotation to pupil circle remains unchanged despite the rotation; iv) the image of the eye by the CCD camera is projected onto a plane which is perpendicular to the camera axis. After taking digital images of voluntary circular eye movements, we first constructed a three-dimensional frame of reference fixed on the orbita of the subject wearing a goggle equipped with an infrared CCD camera, and determined the space coordinates of the center of eye rotation, the center of the pupil, and an iris freckle. We then took digital images of the eye movements during a saccade or vestibulo-ocular reflex (VOR) and analyzed the axis and angle of the eye movements by the trajectories of the center of the pupil and the iris freckle. Finally, Listing's plane of saccade and the gain and the phase of VOR were obtained. The suitability of this technique is examined.

Adult↗
PubMed2001

A model of eye movements and visual working memory during problem solving in geometry.

The Oculomotor Geometry Reasoning Engine (OGRE) was proposed to model eye movements and visual working memory during problem solving in geometry. OGRE postulates that geometrical elements from diagrams are added to visual working memory when they are scanned. Newly-added elements overwrite elements already in memory. The model was applied to eye-movement patterns of three subjects: two geometry experts and one non-expert. Their eye movements and verbal protocols were recorded as they solved geometry problems posed with diagrams. Subjects used highly redundant eye-movement patterns with multiple rescans of the same geometrical elements. OGRE's model of visual memory provided a good fit for the distribution of times between rescans. The model was used to estimate the size of visual working memory used in geometry. The estimates varied as a function of both problems and subjects, with means and standard deviations for each subject being: 5.3+/-1.4, 4.0+/-0.9 and 4.7+/-1.6.

Eye Movements↗
PubMed2003

Enhancement of rapid eye movement sleep in the rat by actions at A1 and A2a adenosine receptor subtypes with a differential sensitivity to atropine.

The adenosine agonist cyclohexaladenosine injected into the medial pontine reticular formation of the rat induces a long-lasting increase in rapid eye movement sleep. To investigate the adenosine receptor-subtype(s) mediating this effect, the dose-response relationships for increasing rapid eye movement sleep by two highly selective adenosine receptor agonists were compared. Rats were surgically prepared for chronic sleep recording and bilateral guide cannulae were aimed at medial sites in the caudal, oral pontine reticular formation. Injections were made unilaterally in 60 nl volumes within 1 h after lights-on. The adenosine agonists used were A1-selective cyclohexaladenosine (10(-6)-10(-4) M) and A2a-selective CGS 21680 (10(-7)-10(-3) M). Each animal also received a series of three, paired-consecutive injections of the muscarinic receptor antagonist atropine (4x10(-3) M) followed by the lowest effective dose of each agonist or saline as control. The A2a receptor agonist, CGS 21680, was one order of magnitude more potent than the A1 receptor agonist, cyclohexaladenosine, in inducing rapid eye movement sleep increases. Preinjection of atropine at a dose that did not itself affect rapid eye movement sleep resulted in antagonism of CGS 21680, but not cyclohexaladenosine-induced rapid eye movement sleep. The differential sensitivity of these ligands to antagonism by atropine supports the conclusion that both A1 and A2a adenosine receptor subtypes in the reticular formation subserve agonist-induced rapid eye movement sleep and that they do so by independent mechanisms. The A2a mechanism requires the cholinergic system and may act through the increased release of acetylcholine. The A1 mechanism operates at a different locus possibly through an inhibition of GABA neurotransmission.

Animals↗
PubMed1979

Quantitative studies of saccadic and pursuit eye movements in multiple sclerosis.

Ocular movements were studied in 108 patients with established or suspected multiple sclerosis using an on-line computer-based electro-oculographic technique. In one group of patients peak eye movement velocities alone were measured during horizontal refixation saccades. In a second group saccade reaction times and accuracies were measured in addition to velocities, while in a subgroup a quantitative analysis of horizontal pursuit eye movements was also carried out. With the saccade velocity test abnormalities were present in 44 per cent of cases studied and were subclinical in 18 per cent. Abnormalities were found in 57 per cent of cases in whom the detailed saccade analysis was performed, including 48 per cent of patients with clinically normal eye movements. Saccade reaction time and accuracy were more sensitive parameters than saccade velocity, and the highest yield of abnormalities was obtained when all three were taken into consideration. Abnormalities of pursuit movements were found in 71 per cent of cases studied and were frequently subclinical. Abnormalities of saccadic and pursuit movements were not always present together in the same patient, and the overall yield of abnormalities was higher when the results of both types of study were taken into account. The yield of abnormalities with the eye movement studies was somewhat lower than with the pattern-reversal VEP in the clinically definite multiple sclerosis group, but was higher in patients in the other categories. Subclinical abnormalities of eye movement were found in a significant number of patients with normal VEPs. The finding of such an abnormality in patients with spinal cord syndromes allowed reclassification of 14 patients to a category with a higher degree of diagnostic certainty. It is concluded that quantitative electro-oculography is a valuable adjunct to the clinical evaluation of eye movements and has an important role in the investigation of patients suspected of multiple sclerosis.

Adult↗
PubMed2000

Eye movement abnormalities during reading in patients with Alzheimer disease.

OBJECTIVE: This goal of this study was to evaluate reading ability by assessing eye movements during reading among patients with Alzheimer disease (AD) compared with normal elderly controls. BACKGROUND: Reading is disturbed in patients with AD. These patients may have changes in reading ability early in the course of their disease before clinical alexia or abnormalities are apparent on standard reading tasks. METHOD: Reading competence was evaluated by recording eye movements during reading in 14 patients with mild to moderate clinically probable AD and 14 age- and education-matched controls. RESULTS: All patients with AD could recognize letters and words and could understand written material of similar difficulty. Despite successful reading comprehension among the patients with AD, their oculographs showed slowed reading and irregular eye movements. Compared with controls, the patients with AD did not differ in saccadic duration; however, they had significantly longer fixation times, more forward saccades per line of text, and more saccadic regressions. In addition, increased reading difficulty significantly correlated with a scale of dementia severity in the patients with AD. CONCLUSIONS: This pattern of eye movements corresponds to increased text difficulty and probably represents difficulty with lexical-semantic access in AD. These results suggest that disordered eye movements can signal difficulties in reading ability in AD even before complaints of reading difficulty or abnormalities on reading tests and may be a means of identifying linguistic impairment early in this disorder.

Aged↗
PubMed1995

Eye movements in monkeys with local dopamine depletion in the caudate nucleus. I. Deficits in spontaneous saccades.

The basal ganglia contribute to the suppression and initiation of saccadic eye movements through the inhibitory connection from the substantia nigra pars reticulata (SNr) to the superior colliculus. This mechanism consists of serial and parallel connections, which are mostly inhibitory and GABAergic. Dopamine is known to exert powerful modulatory effects on the basal ganglia function, but its nature and mechanism are still unclear, especially in relation to voluntary behavior. The purpose of this series of investigation was to study the role of dopamine in the control of saccadic eye movements. We examined, in the monkey, whether and how the deficiency of the nigrostriatal dopaminergic innervation affects saccadic eye movements. The present article is focused on spontaneous saccades that the monkey made with no incentive to obtain reward; the next paper will describe task-specific saccades. Using an osmotic minipump we infused 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) unilaterally into the head-body junction of the caudate nucleus of monkeys where presaccadic neurons were clustered. Tyrosine hydroxylase activity, visualized using an immunohistochemical method, decreased locally around the injection site with some effects extending into the ipsilateral putamen and locally in the ipsilateral substantia nigra. Changes of eye movements started to appear 3-5 d after starting the infusion. Spontaneous saccades became less frequent. The area scanned by the saccades became narrower and shifted to the hemifield ipsilateral to the infusion site. The saccade amplitudes and peak velocities decreased; durations were prolonged. These effects were more prominent for saccades directed toward the side contralateral to the infusion site. These monkeys showed no obvious skeletomotor symptoms. These results suggest that the local deprivation of the dopaminergic innervation in the caudate nucleus facilitates neuronal activity of the SNr leading to suppression of saccadic eye movements.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗