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PubMed1990

Eye-movement models for arithmetic and reading performance.

Three stochastic eye-movement models for arithmetic and reading performance have been proposed, one for arithmetic and two for reading. Each model characterizes a real-time stochastic process in terms of fixation durations and saccadic movement, but only direction and length of saccades are considered, not acceleration or velocity. Aspects of the models that are emphasized, partly because of their general neglect in the literature, are the probability distribution of fixation durations and the random walk of saccade directions. The distributions of fixation duration are approximately exponential, but systematic deviations can be accounted for in the models, even though the fit to data is not perfect. In the case of the arithmetic algorithms of addition and subtraction, the random walk of the normative model has only two possible moves. Data are also presented on backtracking, skipping and wandering eye movements, each of which has a significant relative frequency. The first reading model is called a minimal control model, because it does not take account of the effects of many local variables, e.g., word length, that have been extensively studied. The axioms on fixation duration for the minimal control model are the same as for the arithmetic model. Abstracting from the different arrangement of stimuli in arithmetic algorithms and in linear text, the axioms on saccadic motion for the two models are also essentially identical. The stochastic nature of both models is strongly supported by data on the independence of fixation durations from previous fixation durations. Additional detailed evidence is presented for the arithmetic model. To better account for a great variety of experimental results concerning significant effects on eye movements in reading, a text-dependent probabilistic model of reading is introduced. Significant local effects fall into three classes, identified as line, word and grammatical variables. The revised axioms embody five features of text known to be significant: (i) fixation duration depends on the number of letters in a word; (ii) a saccade is longer when a longer word is to the right; (iii) a saccade is longer when the current fixation is on a longer word; (iv) high-frequency fixation words have the highest probability of being skipped; (v) ambiguous or difficult grammatical structures increase backtracking.

Cognition↗
PubMed2004

The role of the frontal pursuit area in learning in smooth pursuit eye movements.

The frontal pursuit area (FPA) in the cerebral cortex is part of the circuit for smooth pursuit eye movements. The present paper asks whether the FPA is upstream, downstream, or at the site of learning in pursuit eye movements. Learning was induced by having monkeys repeatedly pursue targets that moved at one speed for 150 msec before changing speed. Single-cell recording showed no consistent correlate of pursuit learning in the responses of FPA neurons. Some neurons showed changes in firing in the same direction as the learning, others showed changes in the opposite direction, and many showed no changes at all. In contrast, the eye movements evoked by electrical stimulation of the FPA showed clear correlates of learning. Learning effects were observed when microstimulation was delivered during the initiation of pursuit and during fixation of a stationary target. In addition, learning caused changes in the degree to which stimulation of the FPA enhanced the eye velocity evoked by brief perturbations of a stationary target. The magnitude of the change in the stimulation-evoked eye movement in each tracking condition was proportional to the size of the eye movement evoked under that condition before learning. We conclude that learning occurs downstream from the FPA, possibly within the cerebellum, and that learning may be related to mechanisms that also control the gain of visual-motor responses on a rapid time scale.

Animals↗
PubMed1996

On the origin of eye movement desensitization and reprocessing: a response to Rosen.

Rosen argues that the eye movements experienced by Shapiro during the incident leading to her development of eye movement desensitization and reprocessing (EMDR) could not, as she later inferred, have been saccadic. The present author disputes Rosen's conclusion by showing that his arguments are based on a faulty understanding of the nature of saccadic eye movements or are irrelevant to Shapiro's claim.

Attention↗
PubMed1983

The effects of lowered temperature on spontaneous eye movements in a teleost fish.

A new opto-electronic method has been used to measure spontaneous eye movements in a lightly restrained unanaesthetized marine teleost fish (Parore). The normal scanning pattern of eye movement is similar to that previously described in goldfish. The effects of cooling on eye movements were investigated by 2 degrees C step changes down from ambient temperature (13-14 degrees C). Lowered temperature altered the scanning pattern, decreased saccade velocity, increased mean saccade amplitude and impaired the ability of the fish to hold the eye stationary between saccades. All eye movements stopped at temperatures around 6 degrees C, but could be restored by subsequent warming.

Animals↗
PubMed2005

Three-dimensional analysis of eye movements using four times high-speed video camera.

In order to record and analyze the rapid eye movement non-invasively in human subjects, a four times high-speed video camera (4TC) with a new computer software was developed and utilized. Nine healthy volunteers and four patients with vestibular dysfunction participated in this study. Caloric stimulation was applied to the healthy subjects and the eye movements were recorded using a standard camera (SC) and a 4TC. In four patients, the positional and/or positioning nystagmus was recorded using SC and 4TC. Analysis of the eye speed of the quick phase of nystagmus was performed manually from the print out of the chart. The quick phase of the caloric nystagmus was adequately analyzed from the data using 4TC. However, using SC the sampling rate was not sufficiently enough for this purpose, as prospected. The adaptability of the 4TC in clinical examination is exactly similar to that of SC, because of the size and weight of the camera. Although the time taken to analyze eye movements using 4TC is about four times longer than that using SC, this system is quite useful and adequate for analyzing the quick eye movements in vestibular nystagmus, in an out-patient clinic set up.

Adult↗
PubMed1992

The interstitial nucleus of Cajal is involved in generating downward fast eye movement in alert cats.

We examined whether or not the interstitial nucleus of Cajal (INC) is involved in generating vertical fast eye movement. We used a gamma-aminobutyric acid (GABA) agonist (muscimol) to deactivate the INC cell bodies bilaterally in alert head-fixed cats. The INC was identified by recording vertical eye position-related burst-tonic neurons. Following muscimol infusion into the bilateral INC, the cats were unable to hold eccentric upward eye position after saccades, and the mean time constant of postsaccadic drift was 0.4 sec. In addition, downward saccades were virtually lost without clear impairment of horizontal saccades. Muscimol infusion into the Forel's field H resulted in loss of both upward and downward fast eye movement as reported previously. Bilateral electrolytic INC lesions produced results similar to those after muscimol infusion into the INC, suggesting that the cutting of passing fibers in the INC alone cannot explain the selective loss of downward fast eye movement. These results indicate that the INC itself is involved in generating downward fast eye movement. We propose that the loss of activity in possible downward burster-driving neurons in the INC can explain the selective loss of downward fast eye movement after bilateral INC lesions.

Animals↗
PubMed1991

Spinocerebellar degeneration with slow eye movements and abducens nerve palsy.

A 51-year-old woman with spinocerebellar degeneration manifested an unusual disorder of eye movements. She presented with bilateral abducens palsy and slow eye movements in the horizontal plane. Slow eye movements typically are seen with supranuclear lesions, whereas abducens palsies are of nuclear or infranuclear origin. This unique combination of eye movement disorders is discussed, as well as other features of ophthalmoplegias associated with spinocerebellar degeneration.

Abducens Nerve↗
PubMed1976

Dominant direction of conjugate lateral eye movements and responsiveness to facial and verbal cues.

Responsiveness to facial versus verbal cues as a function of dominant direction of conjugate lateral eye movements and sex was tested in a 2 X 2 analysis of variance design. Ss were 81 student volunteers. Right-movers (n = 33) were more responsive to verbal cues; left-movers (n = 45) were more responsive to facial cues (p less than .05). The results are consistent with the hypothesized link between conjugate lateral eye movements and functional asymmetry of the cerebral hemispheres. Males were more responsive to verbal cues; females were more responsive to facial cues (p less than .05). Data relevant to reliability of the eye movements, the relationship between sex and eye movements, and the relationship between type of question and eye movements are also presented.

Adolescent↗
PubMed2001

Effect of stimulus contrast on performance and eye movements in visual search.

According to the visual span control hypothesis, eye movements are controlled in relation to the size of visual span. In reading, the decrease of contrast reduces visual span, saccade sizes, and reading speed. The purpose of the present study is to determine how stimulus contrast affects the speed of two-dimensional visual search and how changes in eye movements and visual span could explain changes in performance. The task of the observer was to search for, and identify, an uppercase letter from a rectangular array of characters in which the other items were numerals. Threshold search time, i.e. the duration of stimulus presentation required for search that is successful with a given probability, was determined by using a multiple-alternative staircase method. Eye movements were recorded simultaneously by using a video eye tracker. Four different set sizes (the sizes of stimulus array) (3x3-10x10), and five different contrasts (0.0186-0.412) were used. At all set sizes, threshold search time decreased with increasing contrast. Also the average number of fixations per search decreased with increasing contrast. At the smallest set size (3x3), only one fixation was needed except at the lowest contrast. Average fixation duration decreased and saccade amplitudes increased slightly with increasing contrast. The reduction of the number of fixations with increasing contrast suggests that visual span, i.e. the area from which information can be collected at one fixation, increases with increasing contrast. The reduction of the number of fixations together with reduced fixation duration result in reduced search times when contrast increases.

Analysis of Variance↗
PubMed1995

Visually guided eye movements in patients with Wallenberg's syndrome.

To determine the lesions and the lateralization in patients with Wallenberg's syndrome, visually-guided eye movements were quantitatively analysed and these findings were compared with a lesioned site as revealed by magnetic resonance imaging (MRI). The 8 patients could be clearly classified into two subgroups based on the functional test of eye movements. In 4 patients, optokinetic nystagmus (OKN), pursuit eye movements and fixation-suppression of caloric nystagmus (FS), utilizing the slow phase velocity as a parameter, were impaired toward the lesioned side in the medulla. In the remaining 4 patients, OKN and pursuit eye movements were impaired toward the side contralateral to the lesion, whereas FS toward the lesioned side, indicating a lesion affecting not only the medulla but also the inferior peduncle and/or the cerebellum. Therefore, the functional visually-guided eye movements can provide a useful test battery with which to detect the lesion site in Wallenberg's syndrome.

Angiography↗
PubMed2002

Short-latency eye movements evoked by near-threshold galvanic vestibular stimulation.

To investigate whether the primary planes of eye and body responses to galvanic vestibular stimulation (GVS) are congruent, we have measured the binocular, three-dimensional eye movements (scleral coil technique) to bilateral bipolar GVS in six normal human subjects. Stimulation intensities were kept deliberately low in order to characterize the response to near-threshold intensities of stimulation (0.1-0.9 mA) that had been used previously to characterise body postural responses. Stimuli were applied for 4 s, but only the early responses that occurred within the initial 300 ms of turning the current on or off were measured. At intensities of 0.1-0.7 mA the 'on' response consisted almost exclusively of a torsional slow phase eye movement in which the top of the eyes rotated towards the anode. The latency of the torsional response was ca. 46 ms. A weak polarity-dependent disconjugate response was also observed in which the intorting eye elevated and the extorting eye depressed ('skew eye deviation'). When the current was turned off similar responses occurred in the reverse direction. Removal of the visual fixation light-emitting diode (LED) had no consistent effect on the short-latency ocular responses. The direction of the ocular response was similar to that of the postural response and is compatible with GVS inducing an apparent dynamic roll-tilt of the head towards the cathode. However, weak horizontal eye movements, which became more prominent as the stimulus intensity was increased to 0.9 mA, were also observed. This suggests that an additional weak rotational component about the yaw axis, or a component of lateral translation in the frontal plane, is contained in the GVS-evoked signal. The overall pattern of eye movement suggests that semicircular canal afferents contribute to these low-intensity GVS responses.

Electric Stimulation↗
PubMed2004

Interference with spatial working memory: an eye movement is more than a shift of attention.

In the present experiments, we examined whether shifts of attention selectively interfere with the maintenance of both verbal and spatial information in working memory and whether the interference produced by eye movements is due to the attention shifts that accompany them. In Experiment 1, subjects performed either a spatial or a verbal working memory task, along with a secondary task requiring fixation or a secondary task requiring shifts of attention. The results indicated that attention shifts interfered with spatial, but not with verbal, working memory, suggesting that the interference is specific to processes within the visuospatial sketchpad. In Experiment 2, subjects performed a primary spatial working memory task, along with a secondary task requiring fixation, an eye movement, or an attention shift executed in the absence of an eye movement. The results indicated that both eye movements and attention shifts interfered with spatial working memory. Eye movements interfered to a much greater extent than shifts of attention, however, suggesting that eye movements may contribute a unique source of interference, over and above the interference produced by the attention shifts that accompany them.

Attention↗
PubMed1983

Eye movements in the human fetus and newborn.

The human oculomotor system becomes active long before birth. At about 16 weeks (post-menstrual age) the first slow changes of eye position can be observed with the aid of real time ultrasonography. At 18-20 weeks more rapid eye movements are detectable. There is a gradual decline in the percentage of time spent in rapid and slow eye movements from 32-40 weeks. These eye movements are organized in episodes of activity, divided by episodes of quiescence which are at first unrelated to cyclical changes in other variables (such as breathing movements, body movements and fetal heart rate patterns). At about 36 weeks gestation, REM and non-REM episodes become linked with other changes and then represent behavioural states identical to those seen in the newborn infant. This organization of behavioral states in the fetus is identical with that found in preterm infants of comparable age. Opening of eyelids is difficult to see before birth but the existence of episodes of wakefulness seems most probable. Hence fetal eye movements will be in part related to wakefulness. In the newborn at term, the interval distributions of REMs during sleep and of scanning eye movements during wakefulness are statistically different.

Eye Movements↗
PubMed2004

Cortical mechanisms of smooth pursuit eye movements with target blanking. An fMRI study.

Smooth pursuit eye movements are evoked by retinal image motion of visible moving objects and can also be driven by the internal representation of a target due to extraretinal mechanisms (e.g. efference copy). To delineate the corresponding neuronal correlates, functional magnetic resonance imaging at 1.5 T was applied during smooth pursuit at 10 degrees /s with continuous target presentation and target blanking for 1 s to 16 right-handed healthy males. Eye movements were assessed during scanning sessions by infra-red reflection oculography. Smooth pursuit performance was optimal when the target was visible but decreased to a residual velocity of about 30% of the velocity observed during continuous target presentation. Random effects analysis of the imaging data yielded an activation pattern for smooth pursuit in the absence of a visual target (in contrast to continuous target presentation) which included a number of cortical areas in which extraretinal information is available such as the frontal eye field, the superior parietal lobe, the anterior and the posterior intraparietal sulcus and the premotor cortex, and also the supplementary and the presupplementary eye field, the supramarginal gyrus, the dorsolateral prefrontal cortex, cerebellar areas and the basal ganglia. We suggest that cortical mechanisms such as prediction, visuo-spatial attention and transformation, multimodal visuomotor control and working memory are of special importance for maintaining smooth pursuit eye movements in the absence of a visible target.

Adult↗
PubMed1999

Kinematics of eye movements of cats to broadband acoustic targets.

Operant conditioning was used to train cats with their heads immobilized to localize sound by directing their eyes to the location of the sources. The kinematics of those eye movements were studied and compared with eye movements to visual targets at the same locations. The main finding of this study is that eye movements to broadband long-duration acoustic targets have two components: an initial slow phase of variable duration and a fast, normal saccade. The slow component is characterized by a persistent, shallow velocity ramp, while the saccadic component of the response falls on the main sequence computed from eye movements to visual targets. The slow component was shorter before saccades to long-duration stimuli performed under the delayed-saccade task and practically absent before saccades to transient acoustic stimuli. The results suggest that the initial slow component is used by cats to deal with uncertainty associated with the location of long-duration broadband targets and that the input to the saccade integrator(s) is similar under both visual and acoustic conditions.

Acoustic Stimulation↗
PubMed2000

Saccadic eye movements and cognition.

Scanning of the visual scene is an important selective process in visual perception. In this article we argue that eye-movement data provide an excellent on-line indication of the cognitive processes underlying visual search and reading. We outline some recent advances from physiological investigations of saccadic eye-movement control before focusing on eye-movement behaviour in visual search and reading studies. We consider factors that can affect the duration of fixations and the choice of saccade targets, emphasising continuities between biological and cognitive descriptions. We discuss different ways of measuring cognitive processing time from an eye-movement record and the relationship between attention and eye movements.

Journal Article↗
PubMed1991

Adaptive plasticity in the gaze stabilizing synergy of slow and saccadic eye movements.

When a normal human subject is briefly turned in total darkness while trying to "look" at a spatially fixed target, the vestibulo-ocular reflex (VOR) produces slow-phase compensatory eye movements tending to hold the eyes on target. However, slow-phase compensation per se is generally inadequate in these circumstances. Nevertheless it has recently been found, that even in the dark, this inadequacy tends to be corrected by supplementary saccades usually acting in the compensatory direction. The present study further investigates this phenomenon by measuring the respective contributions of saccadic, slow-phase and overall net compensation in 9 subjects tested before and after 30% adaptive attenuation of VOR slow-phase gain. In each test series, subjects attempted to stabilize their gaze on a previously seen target during each of 40 brief (approximately 0.5 s) whole body rotations (40 degrees/s, 20 degrees amp) conducted in complete darkness. The adaptive experience comprised 2 h of full-field visual suppression of the VOR during sinusoidal rotation of subject and surround at 1/6 Hz and 40 degrees/s velocity amplitude. Before adaptation, the cumulative slow-phase and cumulative saccadic components produced on average 78% and 14% respectively of the ideal (100%) compensation, thus yielding an overall net compensation which was 92% of the desired value. After adaptation, the corresponding values in the same population were 53%, 18% and 71% respectively. Thus after adaptation, the combined saccadic-slow-phase response brought the final gaze position to a point in space that was systematically shifted in the direction of head rotation (i.e. undercompensation). Subjects re-exposed to 30 min of normal visual-vestibular interaction displayed a variety of recovery patterns using different combinations of slow and saccadic eye movements. However, there was a consistent "synergistic" tendency for saccadic eye movements to improve slow-phase performance, regardless of the subject's adaptive state. In one subject, compensatory saccadic eye movements corrected a consistent directional asymmetry in the slow-phase response. It is suggested that a conscious vestibular percept of self-rotation might underlie the combined saccadic-slow-phase response, and that the net under performance after adaptation might reflect attenuation of this percept relative to the actual rotational stimulus.

Acclimatization↗
PubMed1995

Deficits in torsional and vertical rapid eye movements and shift of Listing's plane after uni- and bilateral lesions of the rostral interstitial nucleus of the medial longitudinal fasciculus.

The rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) contains burst neurons whose activity precedes rapid eye movements with a vertical and/or torsional component. To ascertain their causal role in the generation of conjugate eye movements, we placed uni- and bilateral kainic acid lesions in that region. Unilateral inactivation of the riMLF leads to a loss of all rapid eye movements with an ipsitorsional component (ipsitorsional is defined as movement of the upper pole of the ipsilateral eye in a temporal direction). Vertical eye movements are impaired in an asymmetric way, with downward movements slowed and upward movements little affected. Listing's plane is shifted in the contratorsional direction, i.e., we find a constant torsional offset for all eye positions. With bilateral lesions one observes a total loss of all vertical and torsional eye movements, while Listing's plane retains its shape and position. These results show that burst neurons in the riMLF play a decisive role in generating rapid eye movements with a vertical and torsional component.

Animals↗