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PubMed1991

Adaptation and habituation of the vestibulo-ocular reflex in intact and inferior olive-lesioned rats.

The gain of the vestibulo-ocular reflex (VOR) of intact pigmented rats was adaptively modified by training protocols that created a visual-vestibular conflict. For training, head restrained animals were oscillated on a turntable in front of an optokinetic pattern projected onto a cylindrical wall. The optokinetic pattern either moved the same amplitude with the animal ("in-phase": 0.05 Hz +/- 20 degrees/s) or opposite in direction ("out-of-phase": turntable and pattern 0.05 Hz +/- 10 degrees/s each). VOR responses were tested in darkness before and after each 8 min training period for a duration of 40 min. During "out-of-phase" training the gain of compensatory eye movements measured in light was close to 2 from the beginning on and the VOR tested in darkness increased in gain progressively from 0.48 (+/- 0.12) to 0.9 (+/- 0.3; P less than 0.05) in 5 out of 7 rats. Two rats did not adapt their VOR gain. Phase values decreased slightly by about 10 degrees. During "in-phase" stimulation compensatory eye movements were almost completely suppressed (gain close to 0) from the beginning on and the VOR tested in darkness decreased gradually in gain from 0.62 (+/- 0.17) to 0.13 (+/- 0.1; P less than 0.001) in all 6 trained rats. Phase values decreased in parallel from 151 degrees to 119 degrees (P less than 0.01). The effectiveness of the "in-phase" training paradigm in the absence of compensatory eye movements indicates that retinal image slip is the relevant signal for adaptation. In seven rats with histologically verified almost complete inferior olive (IO) lesions (chemically induced at least 45 days prior to training), "out-of-phase" and "in-phase" stimulation evoked compensatory eye movements with gains comparable to those in intact rats. VOR parameters measured in darkness were altered with respect to those of control rats. Gain differed extremely between individuals and phase lag re acceleration was in all IO-lesioned rats larger than in intact rats. The time constant of the VOR in response to table velocity steps was significantly longer (17 s +/- 4) than in intact rats (11 s +/- 3). Training did not alter the gain of the VOR in 5 out of 7 IO-lesioned rats. One rat increased its gain during "out-of-phase" training in the first, but not during a second training session (and not during "in-phase" training) and another rat decreased its gain during "in-phase" training (but not during "out-of-phase" training).(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed2006

Neurophysiological endophenotypes of schizophrenia: the viability of selected candidate measures.

In an effort to reveal susceptibility genes, schizophrenia research has turned to the endophenotype strategy. Endophenotypes are characteristics that reflect the actions of genes predisposing an individual to a disorder, even in the absence of diagnosable pathology. Individual endophenotypes are presumably determined by fewer genes than the more complex phenotype of schizophrenia and would, therefore, reduce the complexity of genetic analyses. Unfortunately, despite there being rational criteria to define a viable endophenotype, the term is sometimes applied indiscriminately to characteristics that are deviant in affected individuals. Schizophrenia patients exhibit deficits in several neurophysiological measures of information processing that have been proposed as candidate endophenotypes. Successful processing of sensory inputs requires the ability to inhibit intrinsic responses to redundant stimuli and, reciprocally, to facilitate responses to less frequent salient stimuli. There is evidence to suggest that both these processes are "impaired" in schizophrenia. Measures of inhibitory failure include prepulse inhibition of the startle reflex, P50 auditory evoked potential suppression, and antisaccade eye movements. Measures of impaired deviance detection include mismatch negativity and the P300 event-related potential. The purpose of this review is to systematically evaluate the endophenotype candidacy of these key neurophysiological abilities. For each candidate, we describe typical experimental procedures, the current understanding of the underlying neurobiology, the nature of the abnormality in schizophrenia, the reliability, stability and heritability of the measure, and any reported gene associations. We conclude with a discussion of the few studies thus far that have employed a multivariate approach with these candidates.

Arousal↗
PubMed1982

Eye and contact lens movement measurement.

An accurate and relatively simple method of measuring eye and contact lens movement has been developed. A hidden ultra-high-speed motion picture camera, a digital film data analyzer, and computer data reduction are used to define and separate eye, head, and contact lens movements. The technique has an eye rotational accuracy of about 0.2 degrees and a linear translational accuracy of better than 0.05 mm over a field of view of more than 60 degrees. This procedure requires no extraneous hardware, fixtures, or eye restraints, so data can be obtained in a natural environment. It provides a method of evaluating motility training procedures, studying contact lens fitting methods, and investigating tear pumping mechanisms.

Computers↗
PubMed1989

Reduced vergence response velocities in dyslexics: a preliminary report.

Dyslexia is a developmental disorder characterized by a reduced ability to recognize or comprehend written or printed words. Two clinically diagnosed dyslexics and two normals served as subjects. Both dyslexic subjects showed reduced static accommodative and vergence ranges compared with normals and numerous regressions and fixation pauses during reading and target tracking tasks. The subjects were then presented with convergent and divergent ramp disparity stimuli ranging in speed from 1.33 to 32.0 deg/s and steps of either 2 or 4 degrees amplitude. The dyslexic subjects showed reduced vergence velocities and fewer step-ramp and multiple step responses than normals. These preliminary findings suggest that certain vergence control functions may be diminished or absent in dyslexics. However, the vergence deficit may parallel dyslexia and may not be a causative factor. Thus vergence eye movement measurements may be used to provide additional insight into the components of the central deficits associated with dyslexia.

Accommodation, Ocular↗
PubMed1989

Effects of VDT resolution on visual fatigue and readability: an eye movement approach.

The effects of VDT resolution on visual fatigue and readability were studied. Two kinds of displays with different resolutions (1664 x 1200 pixels and 720 x 350 pixels) and fonts were used. In the first experiment, the subjects read from each display for 1 h to induce fatigue. Reading speed and blink rate while reading were measured. Eye movements during visual smooth pursuit tracking tasks were studied before and after reading; quantitative scoring of eye movement performance showed no significant changes. In the second experiment, readability tests with three different character sizes on both displays were conducted and resulting reading eye movements were analysed. For readability of sufficiently large characters, no significant difference between the high and the standard VDT could be detected. However, for very small characters, higher resolution improved readability.

Adult↗
PubMed1996

A comparison of the sedative and amnestic effects of chlorpromazine and lorazepam.

The effects of single doses of chlorpromazine (100 mg) and lorazepam (0.5, 1 and 2 mg) were compared with placebo in a battery of tests of information processing, working and semantic memory. Peak saccadic velocity was used to provide a precise and reliable measure of sedation and its results were found to be consistent with those using visual analogue rating scales. Chlorpromazine 100 mg was equally sedative to lorazepam 2 mg. Lorazepam caused dose-dependent deterioration in performance in many of the memory tests, whereas an equally sedative dose of chlorpromazine did not. These data therefore support the view that benzodiazepine-induced amnesia is not secondary to sedation. Peak saccadic velocity has considerable advantages over visual analogue scales as a measure of sedation, since it is objective and has a demonstrated low coefficient of variation. It is suggested that saccadic eye movement measurement will permit considerably more reliable and precise separation of the sedative and amnestic effects of drugs and will allow investigation of amnesia caused by clinically relevant doses of psychotropic drugs.

Adult↗
PubMed1997

Patterns of eye movements during parallel and serial visual search tasks.

Eye movements were monitored while subjects performed parallel and serial search tasks. In Experiment 1a, subjects searched for an "O" among "X"s (parallel condition) and for a "T" among "L"s (serial condition). In the parallel condition in Experiment 1b, "[symbol: see text]" was the target, and "O"s were distractors; in the serial condition these stimuli switched roles. Displays contained 1, 12, or 24 stimuli, with both target-present and target-absent trials. RT and eye-movement measures (number of fixations, saccadic error, and latency to move) indicated that search efficiency was greatest in the parallel conditions, followed by the serial condition of experiment 1a and, finally, by the serial condition of Experiment 1b. This suggests that eye movements are correlated with the attentional processes underlying visual search.

Attention↗
PubMed2002

Characteristics of eye movement and cognition during simulated landing of aircraft.

Objective. To examine how the subject scans different parts of display panels and how the attention is distributed through the analysis of the eye movement principle and the cognition of the brain. Method. An experiment was conducted to simulate the airplane's landing course and eye movement data were recorded with eye movement measure system (EMMS). Result. There were three regions of interest (ROI) on which the subject's attention was concentrated. The subject's visual activity was active in the three ROIS and attention's shifting and distribution was between ROIS. Conclusion. Eye movement were driven by the top-down processing and the distribution of the attention. The consequence of the eye movement makes the subject maintain a continuous situation awareness.

Aircraft↗
PubMed2006

Fixations in natural scenes: interaction of image structure and image content.

Explorative eye movements specifically target some parts of a scene while ignoring others. Here, we investigate how local image structure--defined by spatial frequency contrast--and informative image content--defined by higher order image statistics-are weighted for the selection of fixation points. We measured eye movements of macaque monkeys freely viewing a set of natural and manipulated images outside a particular task. To probe the effect of scene content, we locally introduced patches of pink noise into natural images, and to probe the interaction with image structure, we altered the contrast of the noise. We found that fixations specifically targeted the natural image parts and spared the uninformative noise patches. However, both increasing and decreasing the contrast of the noise attracted more fixations, and, in the extreme cases, compensated the effect of missing content. Introducing patches from another natural image led to similar results. In all paradigms tested, the interaction between scene structure and informative scene content was the same in any of the first six fixations on an image, demonstrating that the weighting of these factors is constant during viewing of an image. These results question theories, which suggest that initial fixations are driven by stimulus structure whereas later fixations are determined by informative scene content.

Animals↗
PubMed2003

Pursuit of the ineffable: perceptual and motor reversals during the tracking of apparent motion.

Pursuit can be guided by perceived rather than physical motion, but the temporal relationship between motion perception and pursuit is unknown. We used an apparent motion stimulus consisting of a horizontal row of evenly spaced Kanizsa illusory squares (1.44 deg2): the illusory contours appeared at the midpoints of the illusory squares presented in the previous frame, producing bi-directional apparent motion of the illusory contours (21.5 deg/s) that could be reversed at will. We measured eye movements in five subjects asked to (1) track the motion of the illusory squares, and (2) reverse the perceived direction while continuing to track the squares. We measured the timing of the voluntary perceptual reversals and compared this to the time course of the reversal in tracking direction. We found that subjects could smoothly track the apparent motion of illusory squares and also produce saccade-free reversals in pursuit velocity. The time course of these motor reversals closely followed the measurements of the perceptual reversal and, on average, the perceptual reversals preceded the pursuit reversals by 53 ms, a delay shorter than when the perceptual reversal was visually guided. Smooth pursuit and the perception of motion direction were in temporal register and highly correlated, suggesting that pursuit can provide a real-time readout for the state of motion perception.

Adult↗
PubMed2005

The role of (micro)saccades and blinks in perceptual bi-stability from slant rivalry.

We exposed the visual system to an ambiguous 3D slant rivalry stimulus consisting of a grid for which monocular (perspective) and binocular (disparity) cues independently specified a slant about a horizontal axis. When those cues specified similar slants, observers perceived a single slant. When the difference between the specified slants was large, observers alternatively perceived a perspective- or a disparity-dominated slant. Eye movement measurements revealed that there was no positive correlation between a perceptual flip and both saccades (microsaccades as well as larger saccades) and blinks that occurred prior to a perceptual flip. We also found that changes in horizontal vergence were not responsible for perceptual flips. Thus, eye movements were not essential to flip from one percept to the other. After the moment of a perceptual flip the occurrence probabilities of both saccades and blinks were reduced. The reduced probability of saccades mainly occurred for larger voluntary saccades, rather than for involuntary microsaccades. We suggest that the reduced probability of voluntary saccades reflects a reset of saccade planning.

Blinking↗
PubMed1995

The human ocular torsion position response during yaw angular acceleration.

Recent results by Wearne [(1993) Ph.D. thesis] using the scleral search-coil method of measuring eye position indicate that changes in ocular torsion position (OTP) occur during yaw angular acceleration about an earth vertical axis. The present set of experiments, using an image processing method of eye movement measurement free from the possible confound of search coil slippage, demonstrates the generality and repeatability of this phenomenon and examines its possible causes. The change in torsion position is not a linear vestibulo-ocular reflex (LVOR) response to interaural linear acceleration stimulation of the otoliths, but rather the effect is dependent on the characteristics of the angular acceleration stimulus, commencing at the onset and decaying at the offset of the angular acceleration. In the experiments reported here, the magnitude of the angular acceleration stimulus was varied and the torsion position response showed corresponding variations. We consider that the change in torsion position observed during angular acceleration is most likely to be due to activity of the semicircular canals.

Acceleration↗
PubMed1989

Effect of a scotoma on eye movements during visual search.

Eye movements have been recorded during a free visual search task both with and without an artificial foveal scotoma. Results of the eye movement measurements show that neither fixation durations nor mean saccade amplitudes are significantly modified by the loss of foveal vision.

Analog-Digital Conversion↗
PubMed1984

The eye blink electro-oculogram.

An electro-oculogram (EOG) was derived from potentials recorded from electrodes placed above and below the eye during voluntary vertical eye movements. Concurrent measurement of the amplitude of eye blink potentials recorded from the same electrodes produced curves which were highly correlated with the EOG measured from stereotyped eye movements. Recordings from a patient with a missing globe, owing to trauma, revealed eye movement and blink responses only from the intact side. A patient with no light perception showed blink responses which were less variable than responses measured during attempts voluntarily to move the eyes vertically in 60 degrees excursions. An EOG calculated by measurement of eye blink potentials may be possible in clinical situations where traditional electro-oculography techniques are not feasible.

Adaptation, Ocular↗
PubMed1982

Human response to cyclofusional stimuli containing depth cues.

The cyclofusional response to stimuli containing depth cues was studied. Eye positions were monitored by an objective, binocular, eye movement measuring technique while a psychophysical method was used to measure the stereoscopic responses. We found that the overall response contains both stereoscopic and cyclofusional components and that the cyclofusional response includes a large nonmotor, or sensory, contribution. The composition of the response was unaffected by changes in stimulus size. Increased stimulus complexity elicited larger cyclotorsional eye movements and diminished the amount of perceived inclination which was observed in the fused percept.

Adult↗
PubMed2000

An eye movement technique for correlating fixational target eye movements with location on the retinal image.

Recent investigation demonstrate that ocular motility in eyes with retinal pathology may show a lower propensity to visit such areas of the retina as compared to non-pathological retinal sites. While current ophthalmic instruments with the ability to image both the retina and visual function test target placement on the retina have provided this observation, the ability to quantify in real time these images as an eye movement measurement is presently lacking and the objective of this paper. A Rodenstock confocal scanning ophthalmoscope (CSLO) was used to image the retina during the performance of a visual fixation task. Direct observation of acuity target placement at the retina under continuous viewing conditions was possible with this apparatus. Target fixation eye movement images of the retina were rapidly digitized from video tape records and registered using a specialized rapid retinal image tracking algorithm. Fixational eye movement pattern densities at the retina were derived from these data. Preliminary data obtained demonstrate the utility of this technique in quantifying fixation eye movement patterns observed in three human patients with vocation-related laser retinal injury. In all patients, areas of severe retinal damage was generally avoided. The density of ocular eye movement tends to reflect regions of retinal normality and avoidance of retinal regions with severe pathology. Variation in eye movement density may exist where pathology is less severe.

Eye Movements↗
PubMed2006

Eye movements cannot explain vibration-induced visual motion and motion aftereffect.

Eye movements are thought to account for a number of visual motion illusions involving stationary objects presented against a featureless background or apparent motion of the whole visual field. We tested two different versions of the eye movement account: (a) the retinal slip explanation and (b) the nystagmus-suppression explanation, in particular their ability to account for visual motion experienced during vibration of the neck muscles, and for the visual motion aftereffect following vibration. We vibrated the neck (ventral sternocleidomastoid muscles, bilaterally, or right dorsal muscles) and measured eye movements in conjunction with perceived illusory displacement of an LED presented in complete darkness (N=10). To test the retinal-slip explanation, we compared the direction of slow eye movements to the direction of illusory motion of the visual target. To test the suppression explanation, we estimated the direction of suppressed slow-phase eye movements and compared it to the direction of illusory motion. Two main findings show that neither actual nor suppressed eye movements cause the illusory motion and motion aftereffect. Firstly, eye movements do not reverse direction when the illusory motion reverses after vibration stops. Secondly, there are large individual differences with regards to the direction of eye movements in observers who all experience a similar visual illusion. We conclude that, rather than eye movements, a more global spatial constancy mechanism that takes into account head movement is responsible for the illusion. The results also argue against the notion of a single central signal that determines both perceptual experience and oculomotor behaviour.

Adult↗
PubMed1985

Properties of visual inputs that initiate horizontal smooth pursuit eye movements in monkeys.

Smooth pursuit eye movements allow primates to fixate and track small, slowly moving objects. Pursuit usually requires visual targets; our aim was to determine the properties of the visual signals transmitted to the pursuit motor system. Rhesus monkeys were rewarded for tracking spots of light that underwent discreet changes in velocity under a variety of visual conditions. We measured the resulting smooth eye acceleration in a 100-msec interval that began with the initiation of pursuit and ended before there had been time for visual feedback. This approach allowed us to vary the parameters of visual stimulation and measure eye movement responses in a way that provides estimates of the properties of signals transmitted by visual pathways. The initiation of pursuit showed different properties early and late in the interval we studied. In the first 20 msec of pursuit, eye acceleration was in the correct direction, but was independent of the initial position of the moving images, the velocity of the stimulus, or the presence or absence of background illumination. Thereafter, the initiation of pursuit depended strongly on all of the above parameters. Eye acceleration was highest when the moving images fell close to the fovea and decreased sharply as eccentricity was increased up to 21 degrees. When the background was diffusely illuminated, eye acceleration showed velocity selectivity; it was highest for a middle range of velocities (30 to 60 degrees/sec) and decreased for higher velocities. When the background was dark, eye acceleration increased as a function of target velocity up to 150 degrees/sec. We conclude that the initiation of pursuit has at least 2 visual components. The two components have different latencies and show quite different relationships to the visual properties of the stimulus, suggesting two cell populations that could provide the visual inputs for pursuit.

Animals↗