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Eye movement abnormalities as a predictor of the acquired immunodeficiency syndrome dementia complex.

Using infrared oculography, we recorded the eye movements in a group of patients with acquired immunodeficiency syndrome (AIDS), with or without the AIDS dementia complex (ADC). Our aim was to determine whether the severity of dementia could be correlated with abnormalities of eye movement and whether eye movement abnormalities could be detected prior to the onset of clinical dementia. Abnormalities of eye movement were present in seven of seven patients with mild, moderate, or severe ADC and in six of seven AIDS or asymptomatic human immunodeficiency virus-seropositive patients without clinical dementia, but at risk for ADC. The eye movement abnormalities detected included disturbances of both saccadic and smooth-pursuit function, and their severity correlated strongly with the severity of dementia. The abnormalities were qualitatively similar to those that occur in Alzheimer's disease but quantitatively less severe. Recording of eye movements may be a valuable, noninvasive technique for the early detection of neurologic dysfunction in asymptomatic patients who are seropositive for human immunodeficiency virus or in patients with AIDS, even prior to other clinical evidence of ADC. In particular, it may be of use in selecting high-risk patients requiring antiviral therapy and in monitoring the neurologic response to such treatment.

Acquired Immunodeficiency Syndrome↗

Changes of vertical eye movements of goldfish for different otolith stimulation by linear acceleration.

Eye movements serves to hold the gaze steady or to shift the gaze to an object of interest. On Earth, signals from otoliths can be interpreted either as linear motion or as tilt with respect to gravity. In microgravity, static tilt will no longer give rise to changes in otolith activity. However, linear acceleration as well as angular acceleration stimulate the otolith organ. Therefore, during adaptation to microgravity, otolith-mediated response such as eye movements alter. In this study, we analyzed the eye movements of goldfish during linear acceleration. The eye movements during rectangular linear acceleration along the different body axis were video-recorded. The vertical eye rotations were analyzed frame by frame. In normal fish, leftward lateral acceleration induced downward eye rotation in the left eye and upward eye rotation in the right eye. Acceleration from caudal to rostral evoked downward eye rotation in both eyes. When the direction of acceleration was shifted 15 degrees left, the responses in the left eye disappeared. These results suggested that otolith organs in each side were stimulated differently.

Acceleration↗

Eye-movement-based memory effect: a reprocessing effect in face perception.

An eye-movement-based memory effect was demonstrated in 2 experiments showing different patterns of eye movements elicited to famous versus nonfamous faces, across a range of different processing tasks. The effects of prior exposure emerged early in viewing, within the first 5 fixations, and were observed on multiple measures of eye-movement behavior, reflecting a change in viewers' sampling behavior to the famous faces. Accordingly, the eye-movement-based memory effect can be seen as a change in the nature of processing of novel versus repeated items, with implications for other effects of prior exposure such as those seen in examples of repetition priming. The authors argue that the eye-movement-based memory effect is an obligatory consequence of previous exposure--a reprocessing effect caused by re-engaging the visual pattern analyzers and face processing machinery of the brain.

Brain↗

Ventilation during early and late rapid-eye-movement sleep in normal humans.

Because successive rapid-eye-movement (REM) sleep periods in the night are longer in duration and have more phasic events, ventilation during late REM sleep might be more affected than in earlier episodes. Despite the increase in eye movement density (EMD) in late REM sleep, average minute ventilation was, however, not reduced compared with that in early REM sleep. Decreases in rib cage motion (mean inspiratory flow of the rib cage) in association with increasing EMD were offset by increments in respiratory frequency. Apart from expiratory time, there were no significant changes in the slopes of the relationships between EMD and specific ventilatory components, from early to late REM sleep periods. However, there was an increase in the number of episodes when ventilation was reduced during late REM sleep. Changes in ventilatory pattern during late REM sleep are due to changes in the underlying nature of REM sleep. The ventilatory response during eye movements is, however, subject specific. Some subjects exhibit large decrements in mean inspiratory flow of the rib cage and increments in respiratory frequency during bursts of eye movement, whereas other individuals demonstrate only small changes in these ventilatory parameters.

Adult↗

MST neuronal responses to heading direction during pursuit eye movements.

As you move through the environment, you see a radial pattern of visual motion with a focus of expansion (FOE) that indicates your heading direction. When self-movement is combined with smooth pursuit eye movements, the turning of the eye distorts the retinal image of the FOE but somehow you still can perceive heading. We studied neurons in the medial superior temporal area (MST) of monkey visual cortex, recording responses to FOE stimuli presented during fixation and smooth pursuit eye movements. Almost all neurons showed significant changes in their FOE selective responses during pursuit eye movements. However, the vector average of all the neuronal responses indicated the direction of the FOE during both fixation and pursuit. Furthermore, the amplitude of the net vector increased with increasing FOE eccentricity. We conclude that neuronal population encoding in MST might contribute to pursuit-tolerant heading perception.

Analysis of Variance↗

Saccadic eye movements while reading music.

Subjects' eye movements were measured whilst they read and performed lines of music consisting of rhythmic information only, in conventional musical notation. The relationship between the spatial pattern of the notes displayed and of the fixations made in reading them is stochastic, and similar to that in ordinary reading, but with a tendency to fixate salient details of the notation such as notes and barlines rather than the spaces in between. Shorter notes are less likely to be fixated than longer ones, and this is determined by their performance length rather than their visual appearance. Despite the timing constraints imposed by the music, the time of execution of individual saccades appears to be entirely unrelated to the time of the execution of elements of the performance itself. However, as the tempo of performance of a given piece of music is increased, the average time between saccades decreases but their mean amplitude increases. These observations suggest a new model of the oculomotor and perceptual processes involved, in which an central, iconic representation of the fixated image is internally scanned and interpreted to a given criterion of accuracy, the scan ending when this criterion cannot be reached, and this end-point determining the position of the next fixation. It is proposed that the fullness of the buffer between the perceptual and motor processes determines the strictness of the criterion which is adopted, and hence the amplitude and timing of the eye movements.

Fixation, Ocular↗

Operant conditioning of vertical eye movements without visual feedback in the midpontine pretrigeminal cat.

An operant conditioning of vertical eye movements was achieved in the midpontine pretrigeminal cat in total darkness by contingent reinforcement of spontaneous eye movements with lateral hypothalamic (LHT) reward stimulation, when each movement (upward direction was chosen in this experiment) exceeded a preset amplitude. However, the response rates in the dark were lower than those in the light and the time to reach the peak response rate was much longer. Recording of evoked potentials to optic chiasma (OC) stimulation revealed enhancement of late components of the visual cortex (VC) and superior colliculus (SC) responses in relation to eye movements. Sequential records of the averaged evoked responses associated with eye movements indicated that the amplitudes of the late components of the VC and SC waves gradually increased in the course of establishment of the operant conditioning, and decreased gradually during extinction. In a yoked control test, increase in amplitudes of the late components was much less significant during non-contingent reinforcement given independently of the eye movements. These results suggest that 'corollary discharge' may play a critical role as a cue in acquisition of the operant conditioning of vertical eye movements when visual feedback is absent in total darkness.

Animals↗

Otolith-visual interaction in the control of eye movement produced by sinusoidal vertical linear acceleration in alert cats.

1. Eye movement responses were examined in alert cats during sinusoidal vertical linear acceleration. Stimulus frequencies of 0.20-0.85 Hz with a constant amplitude of 10.5 cm (corresponding to 0.02-0.31 g) were used. A random visual pattern was presented to give sinusoidal vertical optokinetic stimuli of similar amplitude and frequency to the up-down motion of the cat. 2. Sinusoidal linear acceleration in the presence of a stationary visual pattern produced robust eye movement responses with near compensatory phase at all stimulus frequencies tested. With both eyes covered, a vertical linear vestibulo-ocular reflex (LVOR) was frequently produced at a stimulus strength corresponding to 0.04-0.31 g. The evoked LVOR was always small, and the overall mean response phase values advanced by as much as 70 degrees at frequencies below 0.56 Hz, indicating that the otolith signals activated by sinusoidal linear acceleration were not, by themselves, converted into compensatory eye position signals under these experimental conditions. 3. Optokinetic stimulation alone produced more lag of response phase as stimulus frequency increased, and the gain of evoked eye movement responses was smaller at higher stimulus frequencies compared to the gain during linear acceleration in the light. Bilateral labyrinthectomies resulted in a significant change of the eye movement responses during linear acceleration when visual inputs were allowed: there was more phase lag at higher stimulus frequencies and a decreased gain at all frequencies tested. These results indicate that the interaction of otolith and visual inputs produces robust eye movement responses with near compensatory phase during sinusoidal linear acceleration in the light.

Acceleration↗

EEG cortical potentials preceding vergence and combined saccade-vergence eye movements.

Previous event-related potential (ERP) studies of eye movements were restricted to saccades, the rapid conjugate movements used to change direction of fixation. Our study explored ERP activity for vergence eye movements used for the adjustment of the angle of the visual axes to the distance of the object. These movements are essential when exploring the natural 3D world. Subjects made the following visually guided movements to LED targets: pure convergence or divergence along the median plane, pure lateral saccades within the same distance, and combined movements (lateral and divergent or convergent). ERPs were recorded from 14 surface electrodes and were analyzed for 200 ms prior to the onset of the eye movement. The highest activation was observed prior to vergence. Activation was diffused and peaked at 50 ms prior to the onset of vergence. Combined vergence and sacccadic movements revealed a composite pattern of ERP activity from both saccades and pure vergence. These findings suggest a cortical substrate for vergence eye movements in humans that is engaged in the natural exploration of visual space.

Adult↗

[Density of rapid eye movements during active sleep in preterm newborn infants].

Rapid eye movement (REM) density has been helpful as a reliable index of phasic eye movements activity during REM (active) sleep in adults. We evaluated this index in 28 newborns, at 34 to 39 weeks of conceptional age (CA). The 5 hours polysomnographic recording during sleep included electroencephalogram, electrooculogram, electrocardiogram, pneumogram, nasal thermistor for detecting airflow, and continuous oxygen saturation (tcPO2) monitoring. REM density was measured by two distinct criteria: REM density as the duration of phasic eye movements in relation to REM periods (REMP). Such index varied from 10.6 to 14.1% and was higher in the 36-37 weeks CA group. REM density was calculated as a percentage of 10-second epochs of REM sleep in which phasic eye movements occurred. This criterion confirmed the narrow range of such index in this age bracket (39.9-44.6%), was higher in the first REMP and in the 36-37 weeks CA group. Our data suggest that REM density is a consistent phasic REM sleep feature in preterm newborns with levels close to the adult population, in spite of the gradual decrease of REM sleep duration with age. Higher indices were also found in the first REMP and in the 36-37 weeks CA group by both methods.

Female↗

Transfer function of right- and leftward eye movements in patients with unilateral labyrinth.

In patients with loss of unilateral labyrinthine function, the dynamic characteristics of rightward eye movement and leftward eye movement induced by the healthy labyrinth were displayed respectively. In patients who were examined within a few months after loss of unilateral labyrinthine function, the gain of eye movement toward the healthy labyrinth was low compared with that of eye movement toward the opposite direction. These differences in the gain were remarkable in the frequency range from 0.01 to 0.1 Hz. But those differences in the gain were not detected in patients who were examined more than 3 months after loss of unilateral labyrinthine function.

Adult↗

Striate cortex potentials related to eye movements in the light and in darkness in the waking human.

Potentials in relation to eye movements were studied by means of direct recording of the striate cortex in a waking man. In a lighted environment, the usual evoked potential--lambda response--was obtained and was clearly visible after each eye movement. In complete darkness no individual potential was observable by means of visual analysis after each eye movement, but a slow potential of low amplitude could be obtained by superimposition and averaging of the cortical striate activity time-locked to the start of a series of eye movements. This eye-movement potential showed a longer latency and a lower amplitude than the lambda response. These data are discussed in reference to those obtained in the cat and the monkey; the significance of this eye-movement potential in darkness as a 'corollary discharge' is considered.

Darkness↗

Task demands and binocular eye movements.

Humans make rapid movements of their eyes several times a second that enable them to examine objects located at different positions in space with both of their eyes. Much of our understanding of these binocular movements comes from studies using experienced observers performing repetitive, unnatural tasks. But what eye movements are made when naïve observers perform tasks demanding specific binocular visual information? We examined the binocular eye movements produced by observers performing two tasks differing in the visual information needed for their completion. Our motivation for doing this was to examine the role and function of binocular eye movements when making decisions. We considered the fixation strategies adopted by observers, the effects of the task on the dynamics of saccadic eye movements, and the combination of vergence and version in gaze shifts. We report that the task-dependent use of visual information can have a strong influence on the patterns of fixations, whilst not influencing saccade dynamics. Our data provide some support for the notion that observers choose and fixate a notional reference point in the scene when making judgments about depth structure.

Adult↗

Pursuit eye movements and their neural control in the monkey.

1. Single units in the 3. and 6. nerve nuclei were recorded, together with the stimulus and eye movements in trained macaques during pursuit eye movements. 2. The relationship between the impulse rate of an oculomotor motoneuron and the corresponding eye movements can be described by a first order differential equation only, if distinctions are made between the modes of the oculomotor system (e.g., fixation or pursuit) and between the agonist phase and the antagonist phase of the corresponding eye muscle. 3. The trained monkeys showed a frequency response during pursuit eye movements, which was comparable to that of humans and which clearly indicates the existence of a predictor mechanism. 4. After sudden stimulus disappearance in the pursuit mode, both the neural impulse rate and the eye movement performed smooth changes for more than 1s. These slow post-pursuit eye movements were related to the time course before stimulus disappearance. 5. Our findings lead to the hypothesis, that pursuit eye movements in primates, if elicited by small moving visual stimuli, are generated by means of a feedback system consisting of a predictor mechanism, the parameters of which are continuously corrected by an updating process in the afferent visual system.

Animals↗

Eye movements do not reflect retrieval processes: limits of the eye-mind hypothesis.

This research investigated whether eye movements are informative about retrieval processes. Participants learned facts about persons and locations, and the number of facts (fan) learned about each person and location was manipulated. During a subsequent recognition test, participants made more gazes to high-fan facts than to low-fan facts, and gazes to high-fan facts had a longer duration than gazes to low-fan facts. However, there was no relation between the order in which items were fixated and the relative effect of person or location fan. The effect of person and location fan on gaze duration also did not differ with whether it was the person or location being fixated. A model assuming that the process of retrieval is independent of eye movements was successfully fit to the data on the distribution of gaze durations. According to this model, the effect of fan on number of gazes and gaze duration is an artifact of the longer retrieval times for high-fan facts.

Brain↗

[Three-dimensional analysis of eye movements induced by off-vertical axis rotation].

Off-vertical axis rotation (OVAR) is a method to stimulate the otolith organ. In order to elucidate the function of the otolith organ, we analyzed three-dimensional eye movements by video-oculographic technique during OVAR in 30 normal subjects. The eye movements induced by OVAR stimulation have two components: a constant horizontal deviation in the direction opposite to the rotation known as the bias component, and sinusoidal amplitude changes of eye movements known as the modulation component. Modulation components were detected in the horizontal, vertical, and torsional eye movements, but the bias components were only detected in the horizontal eye movements. The modulation components may compensate for changes in head orientation with respect to gravity. Since the bias component is caused by the velocity storage mechanism, the lack of bias components in vertical and torsional eye movements may suggest its specific relation to only horizontal eye movements. Our results also demonstrated that torsional and horizontal eye movements may originate from the utricle, whereas vertical eye movement may originate from the saccule. However, a lag phase between torsional and horizontal eye movements suggests that the most effective direction for stimulation of these two eye movements may be different.

Adult↗

Photoelectric technique for measuring eye movements.

By the system described, the movement of a stimulus and the correlated tracking movements of the eye are recorded simultaneously. The technique for measuring the eye movements consists of detecting and amplifying by photomultiplication the total amount of light passing through a small slit upon which is imaged a small portion of the light-dark field represented by the iris and sclera of the eye. This total amount of light varies directly with the angular position of the eye.

Electronics↗