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PubMed2005

A comparison between the magnetic scleral search coil and infrared reflection methods for saccadic eye movement analysis.

BACKGROUND: A non-invasive eye tracking system, based on pulsed infrared light (IR), was compared with the magnetic scleral search coil method (MSC) for saccadic eye movement recordings. METHODS: Ten normal subjects performed horizontal and vertical saccades recorded with both methods. Eight recordings were complete and analysed for maximum peak velocity (V(MAX)) and constant (C) of the main sequence curve. RESULTS: The IR recordings showed significantly higher peak velocity values than the MSC system and generally more inter-individual variability. No significant difference regarding peak velocity was detected between abducting and adducting saccades or between upward and downward saccades with either of the systems. Horizontal saccades had higher peak velocities with both techniques. CONCLUSIONS: Comparison of the main sequence plots of the IR and MSC eye tracking techniques reveals that the IR system yields higher values of maximum peak velocity and the constant, the differences being similar for eye movements in different directions. There are various possible explanations for the lower maximum velocity of the MSC recordings, e.g. slipping of the coil annulus on the surface of the eye and a change of the oculomotor command signal induced by wearing the coil. Also, artefacts associated with the IR recording system may cause over-estimations of the saccadic velocity and, furthermore, contribute to the higher variability of the IR recordings.

Adult↗
PubMed1984

Correlation between pulvinar-lateralis posterior complex unit activity and eye movements in the cat.

In 15 encéphale isolé cats, 130 units were recorded in the pulvinar-lateralis posterior complex (P-LP); 19 units responded in relation to horizontal eye movements (15%), 9 of which discharged when ipsiversive movements were recorded and the remaining 10 to contraversive movements. Three units discharged during spontaneous nystagnoid eye movement. All units always responded after initiation of the eye movement, with a latency range between 50 and 250 ms. The eye movement-related units were preferentially located (80%) in the border between the pulvinar and the lateralis posterior complex. Our results show the presence of eye movement-related units in the cat's P-LP, and their probable participation in ocular motility.

Animals↗
PubMed1980

Attention and saccadic eye movements.

Four threshold detection experiments addressed three issues concerning the relationship between movements of spatial attention and saccadic eye movements: (a) the time course of attention shifts wit saccades, (b) the response of the two systems to changes in stimulus parameters, and (c) the relationship of attention to saccadic suppression. These issues bear on the more general question of the degree of independence between the saccadic and attentional movement systems. The results of these experiments support the contention that the mechanisms that shift attention are separate from those that control saccadic eye movements. Relevant events in the visual field periphery, however, will trigger both a saccade and attention shift. The attentional response to such events does not appear to be under subjects' control. The implication of these results for theories of saccadic suppression is discussed.

Attention↗
PubMed1985

Vestibular nuclei activity and eye movements in the alert monkey during sinusoidal optokinetic stimulation.

In the alert monkey (Macaca fascicularis) vestibular nuclei neurons and eye movements were recorded during sinusoidal optokinetic stimulation in the horizontal plane at frequencies between 0.02-3.3 Hz. Maximal stimulus velocity was generally kept constant at 40 deg/s, except for frequencies above 1 Hz. Eye movements showed a nystagmus-like pattern up to 0.2 Hz with a gain (change in eye position/change in cylinder position) greater than 0.8; at frequencies above 1 Hz the gain dropped to 0.35 at 3.3 Hz. A decrease in gain was accompanied by an increasing phase lag. Recordings in the vestibular nuclei were obtained from 'vestibular only' and 'vestibular plus saccade' neurons. Neurons with a strong eye position signal ('vestibular plus position') were excluded. The vast majority (87%) of neurons were not modulated at 0.2 Hz or higher frequencies of sinusoidal optokinetic stimulation, and were classified as 'low-frequency' type neurons. Compared to the response at constant stimulus velocity, sensitivity (imp X s-1/deg X s-1) dropped to 72% at 0.03 Hz and 16% at 0.1 Hz. A few neurons (13%) responding at 0.2 Hz (sensitivity on average 65% of the constant velocity response) were classified as 'high-frequency' type neurons. They did not respond above 1.0 Hz and showed no modulation with individual eye movements. The results suggest that the activity in the groups of vestibular nuclei neurons tested here is insufficient to account for the eye movements in response to sinusoidal optokinetic stimulation at frequencies above 0.1 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Frontal 'oculomotor' area in alert cat. II. Unit discharges associated with eye movements and neck muscle activity.

(1) Unit activity in front 'oculomotor' cortex was recorded extracellularly from sites where subsequent electrical stimulation, using threshold current (50 microamperes), could elicit both eye movements and simultaneous neck EMG acitivity. (2) Of 103 cells, 19% were related to either eye movements or neck EMG activity. Cells could be grouped into three categories: (a) Directional (D) cells (31%) discharged before and during saccadic eye movements, whenever the eyes followed a target in one specific direction. Spontaneous saccades, or vestibularly driven nystagmus, in either the light or dark, elicited no responses. (b) Conditionally directional (CD) cells (43%) discharged following (i) tracking saccades; (ii) spontaneous saccades and (iii) the quick phase of nystagmus, in all directions. There usually was a slight discharge preference for one given direction, and this preference was enhanced whenever visual tracking was restricted to the preferred direction. One-third of CD cells responded to stimulation of the contralateralal biventer cervicis neck muscle (min lat. 20 msec). (c) Neck EMG (N) cells (26%) discharged in association with, and preceding, changes in neck muscle activity. These cells also responded to stimulation of the contralateral biventer cervicis muscle (min lat. 10 msec). (3) For points in the lateral 'oculomotor' region (as defined by stimulation: see ref. 17), the directions of evoked saccades, and the directions of spontaneous saccades associated with unit discharges, were sililar. In the medial region 17, the directions of evoked saccades were roughly opposite to the directions of spontaneous eye movements favoured by unit discharges.

Action Potentials↗
PubMed1995

A syntactic analysis method for eye movements of vestibulo-ocular reflex.

In this study a computer method is described which is designed to recognize these eye movements originating from vestibulo-ocular reflex signals. The corresponding head movement signal measured concurrently with eye movements serves as the stimulation signal which is utilized in the pattern recognition process and in the computation of gain and phase shift parameters. The recognition method is syntactic with a formal grammar and language applied to terminal symbols into which the measured signals are transformed in a preprocessing phase of the method after filtering. After preliminary tests in an otoneurological laboratory the method seems to function correctly and accurately, and has been taken into use for eye movement investigations of patients suffering from otoneurological diseases.

Eye Movements↗
PubMed1988

Fixational instability and saccadic eye movements of dyslexic children with subtle cerebellar dysfunction.

Fixational stability and saccadic eye movements were measured in 9- to 13-year-old dyslexics with signs of subtle cerebellar dysfunction and in a group of age-matched normal readers. This group of dyslexics was specifically chosen because cerebellar disorders are often associated with ocular motor dysfunction. Dyslexic children were found to exhibit significantly greater fixational instability than controls while viewing a simple, stationary stimulus. Although both groups of children showed disruption of fixational stability when viewing stationary targets against optokinetic backgrounds, gaze stability of dyslexics was more degraded than that of controls. However, latency and accuracy of saccadic eye movements of dyslexic children were not different from those of normal readers. The results suggest that poor maintenance of gaze stability, rather than inadequate control over saccadic eye movements, characterizes the ocular motor problems that may contribute to reading difficulties in this subgroup of dyslexics.

Cerebellar Diseases↗
PubMed2005

Patient and normal three-dimensional eye-movement responses to maintained (DC) surface galvanic vestibular stimulation.

HYPOTHESIS: That disease or dysfunction of vestibular end organs in human patients will reduce or eliminate the contribution of the affected end organs to the total eye-movement response to DC surface galvanic vestibular stimulation (GVS). BACKGROUND: It was assumed that DC GVS (at current of 5 mA) stimulates all vestibular end organs, an assumption that is strongly supported by physiological evidence, including the activation of primary vestibular afferent neurons by galvanic stimulation. Previous studies also have described the oculomotor responses to vestibular activation. Stimulation of individual semicircular canals results in eye movements parallel to the plane of the stimulated canal, and stimulation of the utricular macula produces changes in ocular torsional position. It was also assumed that the total three-dimensional eye-movement response to GVS is the sum of the contributions of the oculomotor drive of all the vestibular end organs. If a particular vestibular end organ were to be diseased or dysfunctional, it was reasoned that its contribution to the GVS-induced oculomotor response would be reduced or absent and that patients thus affected would have a systematic difference in their GVS-induced oculomotor response compared with the response of normal healthy individuals. METHODS: Three-dimensional video eye-movement recording was carried out in complete darkness on normal healthy subjects and patients with various types of vestibular dysfunction, as diagnosed by independent vestibular clinical tests. The eye-movement response to long-duration bilateral and unilateral surface GVS was measured. RESULTS: The pattern of horizontal, vertical, and torsional eye velocity and eye position during GVS of patients independently diagnosed with bilateral vestibular dysfunction, unilateral vestibular dysfunction, CHARGE syndrome (semicircular canal hypoplasia), semicircular canal occlusion, or inferior vestibular neuritis differed systematically from the responses of normal healthy subjects in ways that corresponded to the expectations from the conceptual approach of the study. CONCLUSION: The study reports the first data on the differences between the normal response to GVS and those of patients with a number of clinical vestibular conditions including unilateral vestibular loss, canal block, and vestibular neuritis. The GVS-induced eye-movement patterns of patients with vestibular dysfunction are consistent with the reduction or absence of oculomotor contribution from the end organs implicated in their particular disease condition.

Adolescent↗
PubMedDate not supplied

Eye movement pattern and accuracy during perceptual-motor performance in young and old adults.

Differences between young and old adults in matching a motor response to arrival of a moving stimulus may be partially attributable to age group differences in eye movements. In Experiment 1 the eye movement patterns used by young and old adults during performance of a coincidence-anticipation task were recorded. Age group differences in preferred pattern were noted but did not appear to be linked to task performance level. In Experiment 2, eye tracking error was recorded for young adults and many of the old adults tested in Experiment 1. Age group differences were attributable to task performance rather than eye tracking error. Further, the preferred eye movement pattern did not appear to be stable over time among the subjects retested. The eye-movement reaction time of the old adults was significantly longer than that of the young adults, but this did not appear to hamper the ability of the old adults to distinguish the stimulus speeds. Little evidence was found for linking visual search to task performance error.

Adult↗
PubMed1994

The application of smooth pursuit eye movement analysis to clinical medicine.

Pursuit tracking eye movements were analyzed from selected patients with neurological injuries and compared to the responses of 20 normal subjects. The patients/subjects tracked a small spot of light moving sinusoidally in the horizontal plane at a frequency of 0.4 Hz and a peak-to-peak amplitude of 40 degrees. Eye-movement responses were separated into a smooth-pursuit component and a saccadic component. The smooth-pursuit component was analyzed by calculating the gain, phase, and asymmetry. The saccadic component was quantified by calculating the percentage of the total tracking movement contributed by the saccadic system. The patients with smooth-pursuit impairment exhibited a higher percentage of saccadic tracking and a lower smooth pursuit gain compared to the normal subjects. One patient with a unilateral lesion exhibited significant asymmetry in the smooth-pursuit component. In this case, the direction of the asymmetry indicated the side of the lesion.

Adult↗
PubMed1997

Characterization of Purkinje cells in the goldfish cerebellum during eye movement and adaptive modification of the vestibulo-ocular reflex.

The discharge characteristics of Purkinje cells were analyzed in the goldfish cerebellum during eye movement and adaptation of the vestibulo-ocular reflex (VOR). Purkinje cells, identified by the simultaneous recording of complex and simple spikes, were recorded in the cerebellar area where electrical microstimulation elicited ipsiversive horizontal eye movements. Simple spikes of Purkinje cells displayed signals related to head and/or eye velocity as determined independently during either VOR suppression or optokinetic stimulation, respectively. Head velocity-only Purkinje cells (12%) increased their firing rate in relationship to ipsilateral head movements. Two types of eye velocity-only Purkinje cells (28%) were found that responded either in phase with ipsi- (16%) or contralateral (12%) eye movement, respectively. Purkinje cells combining both eye and head velocity (60%) were classified into two groups according to their preferred direction for eye movement. Eye velocity signals either added to (18%) or subtracted from (42%) head velocity during all visuo-vestibular interactions. Short term adaptive changes of the VOR were induced by oscillating goldfish in a moving visual surround that modified the ratio of eye to head velocity (gain) from a level of 1.0 (16 degrees/s) towards gains ranging from 2.5 (40 degrees/s) to -1.0 (-16 degrees/s). Simple spike modulation of individual Purkinje cells was shown to correlate well with VOR performance throughout adaptation irrespective of training direction. Purkinje cell behavior always equaled the algebraic summation of eye and head velocity signal sensitivity. Causality of signal generation was addressed by measuring Purkinje cell responses to both eye and head velocity separately throughout the time course of VOR adaptation. The sensitivity of each type of Purkinje cell was found to be independent of the VOR gain state. We therefore conclude that the changes responsible for short term VOR plasticity do not occur in the cerebellum. These observations suggest that Purkinje cells integrate corollary head and eye velocity signals to continuously adjust the set point of brainstem VOR interneurons that embrace the substantive site for adaptive plasticity.

Acclimatization↗
PubMed2002

Readers' eye movements distinguish anomalies of form and content.

Evidence is presented that eye-movement patterns during reading distinguish costs associated with the syntactic processing of sentences from costs associated with relating sentence meaning to real world probabilities. Participants (N = 30) read matching sets of sentences that differed by a single word, making the sentence syntactically anomalous (but understandable), pragmatically anomalous, or non-anomalous. Syntactic and pragmatic anomaly each caused perturbations in eye movements. Subsequent to the anomaly, the patterns diverged. Syntactic anomaly generated many regressions initially, with rapid return to baseline. Pragmatic anomaly resulted in lengthened reading times, followed by a gradual increase in regressions that reached a maximum at the end of the sentence. Evidence of rapid sensitivity to pragmatic information supports the use of timing data in resolving the debate over the autonomy of linguistic processing. The divergent patterns of eye movements support indications from neurocognitive studies of a principled distinction between syntactic and pragmatic processing procedures within the language processing mechanism.

Eye Movements↗
PubMed1998

Anticipatory saccades during smooth pursuit eye movements and familial transmission of schizophrenia.

BACKGROUND: Smooth pursuit eye movement (SPEM) abnormalities are a putative marker of genetic risk for schizophrenia. Accurate SPEM performance requires the subject to activate neural systems responsible for smooth pursuit tracking, while simultaneously suppressing activity of neurons responsible for saccadic movements that would move the eye ahead of the target. This study examined whether specific aspects of SPEM dysfunction cosegregate with genetic risk in parents of schizophrenic probands. METHODS: Eighteen probands and their parents had SPEM recorded. Parents with an ancestral history of schizophrenia were hypothesized to be more likely than their spouses without such a history to carry a genetic risk for schizophrenia. RESULTS: Ten families had a single parent with a positive ancestral history for schizophrenia. The frequency of anticipatory saccades, which were mostly small, and the fraction of total eye movement that they represented were the only measures that differentiated the more likely genetic carrier parents in these families from their spouses and age-matched normals. CONCLUSIONS: Failure to suppress saccadic anticipation of target motion during smooth pursuit appears an aspect of SPEM dysfunction related to presumed genetic risk for schizophrenia.

Adult↗
PubMed1992

Sensory response of cortical neurons in the anterior ectosylvian sulcus, including the area evoking eye movement.

The deep cortical tissue in the caudal portion of the anterior ectosylvian sulcus (AES) of cats anesthetized with alpha-chloralose was explored to examine the sensory response properties of neurons in this area, which is known to contain an area evoking eye movement. Of 873 neurons isolated, 262 (30.0%) were multimodal, i.e. responsive to two or more of the stimulus modalities of visual, auditory, or somatic. The ratio of multimodal neurons to total neurons in the eye-movement-evoking area was significantly larger than this ratio in other areas; 79 (39.5%) of 200 neurons in the eye-movement-evoking area were multimodal, while 183 (27.2%) of 673 neurons in other areas were multimodal. Neuronal minimal latency in response to visual stimulation was widely and bimodally distributed, showing two peaks at 35 ms and 60 ms, whereas latencies to auditory and somatic stimulation were narrowly distributed, with one peak at 10 ms and 15 ms, respectively. There was no remarkable difference either between unimodal neurons and multimodal neurons or between the neurons in the eye-movement-evoking area and those in other areas in distribution of latency. That there was a significant difference in ratio of multimodal to total neurons between the eye movement area and other areas suggests that some convergence or integration of different kinds of sensory input in relation to eye movement might be carried out in the caudal portion of the AES.

Animals↗
PubMed1995

Influence of target distance and acceleration level on eye movements evoked by lateral acceleration steps.

Lateral eye movements produced by linear acceleration along the inter-aural axis were studied in 6 normal subjects. They were seated upright, whole-body restrained, and were exposed to randomised rightward/leftward steps of 0.05 g. 0.1 g, 0.24 g of 600 ms duration. When viewing earth-fixed targets at 30, 60 or 280 cm from their eyes, mainly pure compensatory slow-phase eye movements were evoked at latencies around 50 ms measured for the closest viewing distances. At onset, slow-phase amplitude was modulated by acceleration and target distance. When the subjects were stationary and pursued moving targets at similar distances and accelerations, latencies around 140 ms were observed, and catch-up saccades were frequently made. From these experiments, we defined the dynamics of the otolith-ocular reflex for various levels of acceleration and viewing distances.

Adult↗
PubMed2006

Retinal image shifts, but not eye movements per se, cause alternations in awareness during binocular rivalry.

Particularly promising studies on visual awareness exploit a generally used perceptual bistability phenomenon, "binocular rivalry"--in which the two eyes' images alternately dominate--because it can dissociate the visual input from the perceptual output. To successfully study awareness, it is crucial to know the extent to which eye movements alter the input. Although there is convincing evidence that perceptual alternations can occur without eye movements, the literature on their exact role is mixed. Moreover, recent work has demonstrated that eye movements, first, correlate positively with perceptual alternations in binocular rivalry, and second, often accompany covert attention shifts (that were previously thought to be purely mental). Here, we asked whether eye movements cause perceptual alternations, and if so, whether it is either the execution of the eye movement or the resulting retinal image change that causes the alternation. Subjects viewed repetitive line patterns, enabling a distinction of saccades that did produce foveal image changes from those that did not. Subjects reported binocular rivalry alternations. We found that, although a saccade is not essential to initiate percept changes, the foveal image change resulting from a (micro)saccade is a deciding factor for percept dominance. We conclude that the foveal image must change to have a saccade cause a change in awareness. This sheds new light on the interaction between spatial attention shifts and perceptual alternations.

Awareness↗
PubMed1989

Eye movement perimetry in glaucoma.

Present-day computerized perimetry is often inaccurate and unreliable owing to the need to maintain central fixation over long periods while repressing the normal response to presentation of peripheral stimuli. We tested a new method of perimetry that does not require prolonged central fixation. During this test eye movements were encouraged on presentation of a peripheral target. Twenty-three eyes were studied with an Octopus perimeter, with a technician monitoring eye movements. The sensitivity was 100% and the specificity 23%. The low specificity was due to the technician's inability to accurately monitor small eye movements in the central 6 degrees field. If small eye movements are monitored accurately with an eye tracker, eye movement perimetry could become an alternative method to standard perimetry.

Eye Movements↗
PubMed1975

[Synkinesis of head and eye movements evoked by brainstem stimulation in the alert monkey].

The synkinesis of head and eye movements evoked by electrical stimulation of the tectum and tegmentum in the alert monkey is described. In positions where both head and eye movements can be evoked, the two are almost always parallel in direction and they are superimposed on rather than substituted for each other. The directiion of movement depends on the stimulated positions: tilt and turn reactions are distributed according to laterality, direction of vertical movements depends more on the stimulus parameter than the electrode position. Head movements release vestibulo-ocular reflexes, which are superimposed on the electrically evoked eye movements.

Animals↗