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PubMed2002

Eye-tracking measures and human performance in a vigilance task.

BACKGROUND: Visual scanning is necessary for aviation safety and similar vigilance tasks, but little is known about its characteristics in such tasks, including possible changes with alertness and fatigue. We explored concurrent eye movements and human performance during a vigilance task designed to require frequent visual scanning. Effects of time and auditory stimuli were examined. METHOD: A corneal-reflectance, PC-based system (Eyegaze Development System, LC Technologies) provided eye movement measures. Stimuli were four digits in a rectangular array, changed at an event rate of 4 s for a task duration of 30 min. There were 20 subjects who were asked to respond to specific, infrequent signal arrays by bar press, under both 50 dBA white noise and 90 dBA intermittent and unpredictable sound-burst conditions, counterbalanced for order. RESULTS: With time-on-task, subjective fatigue ratings increased, dwell time defined as the total duration of fixations on target digits decreased, number of fixations decreased, and fixations were further from target digits in both conditions. Fixation durations [mean (M) = 258 ms; standard deviation (SD) = 54 ms] did not change significantly with time or condition. Off-target visual scan-paths were less frequently followed by hits than were on-target scan-paths in both conditions. With the sound-burst condition, fixations were closer to target digits and hit rates increased. CONCLUSIONS: Dwell time, number, and accuracy of fixations on target objects decreased with time on task, and inaccurate scan-paths were often associated with performance errors. Sound bursts increased fixation accuracy and hit rate. The results provide a basis for visual scan analyses during vigilance tasks, with applications to alertness monitoring and prediction.

Adult↗
PubMed1980

The cat's vestibulo-ocular reflex.

1. The conscious cat's vestibulo-ocular reflex (v.o.r.) has been studied using the electro-oculogram to measure eye movements. A servomotor was used to rotate the head horizontally while the body remained stationary. 2. The frequency content of natural head movements in the cat has been determined by Fourier analysis. The fastest and most kinked head movement profiles contain frequency components of significant power extending up to 7-10 Hz. 3. The transfer function of the v.o.r. slow-phase response was measured in the frequency range 0.2-7 Hz. At 1 Hz the average gain is 0.94 with a phase lead of 3 deg. At 7 Hz the gain has only fallen to 0.81 and the phase lag is 10 deg. This indicates that the v.o.r. can compensate to a considerable degree for the high-frequency components of natural head movements. 4. Rotation of the body around a stationary head in the absence of vision does not produce a measurable neck-ocular reflex. 5. The presence or absence of fast phases has no effect on the phase lead of the v.o.r. slow-phase response at 0.2 Hz. 6. V.o.r. fast phases never occur more frequently than 4/sec. 7. Fast phases do not function merely to recentre the eyes once a slow phase has driven them to extreme orbital eccentricities. Instead, fast phases occur early on and serve to offset gaze in the same direction as the head movement.

Animals↗
PubMed1992

Characterization and adaptive modification of the goldfish vestibuloocular reflex by sinusoidal and velocity step vestibular stimulation.

1. The normal and adapted vestibuloocular reflex (VOR) of goldfish was characterized by means of sinusoidal, velocity step, and position step head rotations about the vertical axis. VOR adaptation was induced by short-term, 1- to 4-h, presentation of visual and vestibular stimuli that altered the ratio of eye to head velocity. 2. The VOR response measured with sinusoidal oscillations in the dark was close to ideal compensatory values over 2 decades (1/32-2 Hz). Gain approximated unity, and phase, in relation to the head, was nearly 180 degrees. The VOR was linear within the range of head velocity tested (4-64 degrees/s). 3. Head velocity steps from 1/8 to 1 Hz produced steplike eye velocity profiles that could be divided into an early acceleration-related "dynamic" component and a later constant-velocity "sustained" period frequently separated by a sag at approximately 0.1-0.15 s from the initiation of eye movement. The sustained response exhibited no decay during the constant-velocity component of the step. 4. Higher temporal resolution of the dynamic response showed the adducting eye movement to have a shorter latency, faster rise time, and larger peak gain than the abducting eye movement. The characteristics of this directional asymmetry were similar for position steps and electrical stimulation of the vestibular nerve. However, the asymmetry was not observed during sinusoidal head rotation, the sustained component of the step response, or after electrical stimulation of the VIth and IIIrd nerves. We conclude that this directional asymmetry is of central origin and may be largely due to the parallel vestibular and abducens internuclear neuron pathways onto medial rectus motoneurons. 5. The VOR adaptation process for both higher and lower eye velocity exhibited an exponential time course with time constants of 55 and 45 min, respectively. After continuous sinusoidal training for 4 h, VOR gain reached an asymptotic level 5% away from perfect suppression in the low-gain training, but 19% away from the actual performance in the high-gain paradigm. The time constant for VOR gain reversal was 5 h, and an asymptotic level 40% less than performance was reached within 10 h. 6. Adapted VOR gain was symmetrical for both directions of eye movement measured either during sinusoidal rotation or the sustained part of the velocity step. VOR adaptation also produced a comparable gain change in the nasal and temporal directions of the dynamic component, but this reflected the asymmetric characteristics observed in the preadapted condition.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed2003

Neural processing of gravito-inertial cues in humans. IV. Influence of visual rotational cues during roll optokinetic stimuli.

Sensory systems often provide ambiguous information. For example, otolith organs measure gravito-inertial force (GIF), the sum of gravitational force and inertial force due to linear acceleration. However, according to Einstein's equivalence principle, a change in gravitational force due to tilt is indistinguishable from a change in inertial force due to translation. Therefore the central nervous system (CNS) must use other sensory cues to distinguish tilt from translation. For example, the CNS might use dynamic visual cues indicating rotation to help determine the orientation of gravity (tilt). This, in turn, might influence the neural processes that estimate linear acceleration, since the CNS might estimate gravity and linear acceleration such that the difference between these estimates matches the measured GIF. Depending on specific sensory information inflow, inaccurate estimates of gravity and linear acceleration can occur. Specifically, we predict that illusory tilt caused by roll optokinetic cues should lead to a horizontal vestibuloocular reflex compensatory for an interaural estimate of linear acceleration, even in the absence of actual linear acceleration. To investigate these predictions, we measured eye movements binocularly using infrared video methods in 17 subjects during and after optokinetic stimulation about the subject's nasooccipital (roll) axis (60 degrees /s, clockwise or counterclockwise). The optokinetic stimulation was applied for 60 s followed by 30 s in darkness. We simultaneously measured subjective roll tilt using a somatosensory bar. Each subject was tested in three different orientations: upright, pitched forward 10 degrees, and pitched backward 10 degrees. Five subjects reported significant subjective roll tilt (>10 degrees ) in directions consistent with the direction of the optokinetic stimulation. In addition to torsional optokinetic nystagmus and after nystagmus, we measured a horizontal nystagmus to the right during and following clockwise (CW) stimulation and to the left during and following counterclockwise (CCW) stimulation. These measurements match predictions that subjective tilt in the absence of real tilt should induce a nonzero estimate of interaural linear acceleration and, therefore, a horizontal eye response. Furthermore, as predicted, the horizontal response in the dark was larger for Tilters (n = 5) than for Non-Tilters (n = 12).

Adult↗
PubMed1999

Effects of static orientation upon human optokinetic afternystagmus.

"Normal" human subjects were placed in a series of 5 static orientations with respect to gravity and were asked to view an optokinetic display moving at a constant angular velocity. The axis of rotation coincided with the subject's rostro-caudal axis and produced horizontal optokinetic nystagmus and afternystagmus. Wall (1) previously reported that these optokinetic afternystagmus responses were not well characterized by parametric fits to slow component velocity. The response for nose-up, however, was larger than for nose-down. This suggested that the horizontal eye movements measured during optokinetic stimulation might include an induced linear VOR component as presented in the body of this paper. To investigate this hypothesis, another analysis of these data has been made using cumulative slow component eye position. Some subjects' responses had reversals in afternystagmus direction. These reversals were "filled in" by a zero slow component velocity. This method of analysis gives a much more consistent result across subjects and shows that, on average, responses from the nose-down horizontal (prone) orientation are greatly reduced (p < 0.05) compared to other horizontal and vertical orientations. Average responses are compared to responses predicted by a model previously used to predict successfully the responses to post-rotatory nystagmus after earth horizontal axis rotation. Ten of 11 subjects had larger responses in their supine than their prone orientation. Application of horizontal axis optokinetic afternystagmus for clinical otolith function testing, and implications for altered gravity experiments are discussed.

Gravitation↗
PubMed2003

Evidence-based ergonomics. A comparison of Japanese and American office layouts.

There is a variety of alternatives in office layouts. Yet the theoretical basis and criteria for predicting how well these layouts accommodate employees are poorly understood. The objective of this study was to evaluate criteria for selecting office layouts. Intensive computer workers worked in simulated office layouts in a controlled experimental laboratory. Eye movement measures indicate that knowledge work requires both concentration and interaction. Findings pointed to one layout as providing optimum balance between these 2 requirements. Recommendations for establishing a theoretical basis and design criteria for selecting office layouts based on work style are suggested.

Ergonomics↗
PubMed2005

Face processing and familiarity: evidence from eye-movement data.

How is information extracted from familiar and unfamiliar faces? Three experiments, in which eye-movement measures were used, examined whether there was differential sampling of the internal face region according to familiarity. Experiment 1 used a face familiarity task and found that whilst the majority of fixations fell within the internal region, there were no differences in the sampling of this region according to familiarity. Experiment 2 replicated these findings, using a standard recognition memory paradigm. The third experiment employed a matching task, and once again found that the majority of fixations fell within the internal region. Additionally, this experiment found that there was more sampling of the internal region when faces were familiar compared with when they were unfamiliar. The use of eye fixation measures affirms the importance of internal facial features in the recognition of familiar faces compared with unfamiliar faces, but only when viewers compare pairs of faces.

Adolescent↗
PubMed2005

Incidental visual memory for targets and distractors in visual search.

We explored incidental retention of visual details of encountered objects during search. Participants searched for conjunction targets in 32 arrays of 12 pictures of real-world objects and then performed a token discrimination task that examined their memory for visual details of the targets and distractors from the search task. The results indicate that even though participants had not been instructed to memorize the objects, the visual details of search targets and distractor objects related to the targets were retained after the search. Distractor objects unrelated to the search target were remembered more poorly. Eye-movement measures indicated that the objects that were remembered were looked at more frequently during search than those that were not remembered. These results provide support that detailed visual information is included incidentally in the visual representation of an object after the object is no longer in view.

Attention↗
PubMed2004

Naltrexone treatment of tardive dyskinesia in patients with schizophrenia.

OBJECTIVE: Treatment of dyskinetic disorders, in general, and of tardive dyskinesia (TD), in particular, is difficult. The opiate peptide enkephalin coexits with gamma aminobutyric acid in the projection neurons of striatum forming the "indirect" pathway. Several lines of preclinical evidence implicate this enkephalin-comediated pathway in the pathophysiology and therapeutics of dyskinesia. However, previous studies, most using relatively low doses of opioid antagonists, showed mixed results. The goal of the current study was to test whether moderately high doses of naltrexone, alone or in combination with a subtherapeutic dose of a gamma aminobutyric acid agonist, improve TD. METHODS: In 2 double-blind, placebo-controlled, randomized, crossover trials, effects of naltrexone alone (n = 9) and in combination with clonazepam (n = 14) were tested on TD. In both trials, patients' antipsychotic medication and dose remained unchanged through the trial. Naltrexone dose was increased over a period of 3 weeks to 200 mg/d and maintained at that dose for another week. In the second study, patients were first stabilized on low dose (0.25 to 0.5 mg) of clonazepam for 4 weeks or longer. In addition to the TD scores, saccadic peak velocity and latency, as measures of vigilance, and antisaccade error rate were obtained during the fourth week of placebo and naltrexone in a subgroup of patients. RESULTS: There were no significant effects of naltrexone alone on TD (mean +/- SD decrease in TD score = 0.1 +/- 4.8), psychosis scores, or eye movement measures. Low dose of clonazepam had no effect on TD. However, addition of naltrexone significantly improved TD (mean, SD decrease in TD score 4.0 +/- 3.6). There was no clinical or laboratory evidence of increased sedation during treatment with naltrexone compared to placebo. There were no significant effects on the antisaccade error rate or psychosis scores. CONCLUSION: These findings suggest effectiveness of a strategy of combining a GABA(gamma aminobutyric acid)mimetic drug with an enkephalin antagonist to treat dyskinesia.

Adult↗
PubMed2003

Using saccadic eye movements as objective measures of tolerance in methadone dependent individuals during the hydromorphone challenge test.

Substitute methadone prescribing is one of the main modes of treatment for opiate dependence. This study examined the relationship between methadone dose (measured by daily dose and methadone's active (R)-enantiomer blood levels) and opiate receptor function. Nine subjects on substitute methadone (30 - 90 mg daily) received three subcutaneous injections 1.5 hours apart (saline, 5 mg and 10 mg hydromorphone, a short-acting opiate agonist) followed by measures of functional response in particular saccadic eye movements (SEMs), as well as self-report measures. Ten mg of hydromorphone significantly slowed SEM parameters (peak velocity by 15%, p < 0.005; peak acceleration by 20%, p < 0.025; peak deceleration by 26%, p < 0.025) and the SEM velocity changes correlated significantly with (R)-methadone levels (r = 0.844, p < 0.005) and with the oral dose of methadone being taken (r = 0.829, p < 0.005). Although a similar trend was observed for 5 mg, this was not significant. These finding suggest that, at higher methadone doses (resulting in higher plasma concentrations), there is significant tolerance to the action of agonists. Such studies may help in refining our understanding of the actions of methadone and the SEM measure could help in defining the degree of tolerance in individuals using street heroin.

Adult↗
PubMed1983

Dyslexic children have normal vestibular responses to rotation.

We examined the rotational vestibular responses of carefully screened dyslexic and control populations (34 dyslexics and 33 controls). The subject groups had equivalent performance IQs but differed significantly on verbal IQ and on silent and oral reading. Children with significant neurologic, visual, or hearing deficits were excluded. We measured eye movements provoked by sinusoidal rotation of the subjects (in total darkness) at low frequencies (0.01 to 0.16 Hz). Gain, phase, and preponderance (asymmetry) of the responses were calculated from the eye velocity and stimulus velocity waveforms. There were no differences between the groups in any of these measures. We conclude that there are no clinically measurable differences in this aspect of vestibular function in our carefully selected populations of dyslexic and control children.

Child↗
PubMed1986

Effects of rectilinear acceleration, caloric and optokinetic stimulation of human subjects in the Spacelab D-1 mission.

A set of vestibular experiments was performed during the course of the German Spacelab D-1 mission from 30 October to 6 November 1985 by a consortium of experimenters from various european countries. Similar to the Spacelab SL-1 mission all of the scientific crew members were theoretically and practically trained for the experiments. Baseline measurements for all tests were collected 113, 86, 44, 30 and 18 days prior to the mission and compared with data taken inflight, on the landing day and the consecutive 7 to 14 days. The hardware comprised mainly a motordriven accelerating platform, the SPACE SLED, and the vestibular helmet, a multi-purpose instrument in support of a variety of vestibular experiments including air-calorisation of the ears, optokinetic stimulation pattern presentation and optical and nystagmographic recording of eye movements. Measurements of the threshold for the perception of detection of whole body movement did not reveal any dramatic changes in the 2 measured axes inflight when compared to preflight values. Early postflight values show a significantly elevated threshold for all axes in 3 out of 4 subjects. The caloric nystagmus, already found during the SL-1 mission, was confirmed on all three tested subjects during the D-1 mission. It's amplitude and in some instances it's direction were influenced by horizontal acceleration on the SLED. The amplitude of optokinetic nystagmus increased when subjects were allowed to free-float over that seen when subjects were fixed. Stimulation of the neck receptors by roll movements of the body against the fixated head resulted in illusory object motion to the contralateral side. Torsional movements of the eyes during such neck receptor stimulation was present inflight and postflight, while it had not been observed preflight. Most results point to a reduction of otolithic effects in favour of visual and proprioceptive influences for spatial orientation.

Acceleration↗
PubMed1990

Optokinetic nystagmus and afternystagmus in human beings: relationship to nonlinear processing of information about retinal slip.

In four normal human subjects we measured eye movements during full-field optokinetic stimulation (10-220 deg/s) and determined the relationship among retinal-slip velocity (drum velocity minus slow-phase eye velocity), the slow-phase velocity of optokinetic nystagmus (OKN) and the initial value of the slow-phase velocity of optokinetic afternystagmus (OKAN) measured in darkness. OKN and OKAN were maximum (63-84 and 11-19 deg/s, respectively) when retinal slip ranged from 30-100 deg/s. For higher values of retinal slip, OKN and OKAN fell (in 3 subjects) or reached a plateau (in the fourth). The amplitude of OKAN in human beings was much less than that reported in monkeys. The shape, however, of the curve relating retinal slip to the amplitude of OKAN was similar to that of monkeys. Furthermore, in both cases the curve resembles that obtained by plotting the results of experimental recordings of neural discharge in the nucleus of the optic tract as a function of retinal slip. These results imply that the processing of visual information for generation of OKAN is similar in monkeys and human beings but that the gain of the system is much less in human beings. We also found that fixation of a small target during optokinetic stimulation nearly completely prevented the development of OKAN while fixation of a small target for short periods after optokinetic stimulation did not alter the pattern of decay of OKAN. Thus, fixation may actively prevent the coupling of visual information into the velocity-storage mechanism.

Adult↗
PubMed2006

Combined gaze-angle and vergence variation in infantile nystagmus: two therapies that improve the high-visual-acuity field and methods to measure it.

PURPOSE: To investigate the convergence-induced waveform and high-acuity-field improvements resulting from different therapies in two subjects with infantile nystagmus (IN) that was damped by convergence and to report a new finding in one of the subjects. METHODS: Infrared reflection was used to measure eye movements during fixation of targets at different gaze and convergence angles and the expanded nystagmus acuity function (NAFX) to evaluate the IN waveform's foveation quality at all fixation points. RESULTS: Recordings demonstrated that, at far, both subjects exhibited classic nulls (high NAFX values) with NAFX reduction at gaze angles lateral to the null. S1 was treated with prisms and S2 with surgery. When converged at near or at far with base-out prisms (S1) or after bimedial recession and bilateral tenotomy surgery (S2), NAFX was higher at both the null and lateral gaze angles; the null region was broadened. The longest foveation domain (gaze angles where the NAFX is within 10% of its peak) at near was three times wider than at far for S1 and two times wider after than before surgery for S2. The therapeutic improvement domain (gaze angles where the posttherapy NAFX is higher than pretherapy) was even broader. At fixed gaze angles in the central 20 degrees of gaze, S1's NAFX variation with vergence exhibited hysteresis, higher during divergence than convergence; S2 exhibited no hysteresis after surgery. CONCLUSIONS: Damping IN by means of convergence, induced either surgically or with prisms, broadened the range of gaze angles with higher foveation quality, mimicking the null-broadening effects of tenotomy. The discovery of vergence hysteresis may reflect pulley movement and might allow higher acuity, if a near point is transiently fixated just before a far target. The acuity domains provide new and more comprehensive evaluations of both pre- and posttherapy visual function than do primary-position acuity measurements, suggesting that high-visual-acuity fields should be included in clinical measures of visual function in nystagmus.

Adolescent↗
PubMed2001

The effect of scleral search coil lens wear on the eye.

BACKGROUND/AIM: Scleral search coils are used to measure eye movements. A recent abstract suggests that the coil can affect the eye by decreasing visual acuity, increasing intraocular pressure, and damaging the corneal and conjunctival surface. Such findings, if repeated in all subjects, would cast doubt on the credibility of the search coil as a reliable investigative technique. The aim of this study was to reassess the effect of the scleral search coil on visual function. METHODS: Six volunteer subjects were selected to undergo coil wear and baseline measurements were taken of logMAR visual acuity, non-contact tonometry, keratometry, and slit lamp examination. Four drops of 0.4% benoxinate hydrochloride were instilled before insertion of the lens by an experienced clinician. The lens then remained on the eye for 30 minutes. Measurements of the four ocular health parameters were repeated after 15 and 30 minutes of lens wear. The lens was then removed and the health of the eye reassessed. RESULTS: No obvious pattern of change was found in logMAR visual acuity, keratometry, or intraocular pressure. The lens did produce changes to the conjunctival and corneal surfaces, but this was not considered clinically significant. CONCLUSION: Search coils do not appear to cause any significant effects on visual function. However, thorough prescreening of subjects and post-wear checks should be carried out on all coil wearers to ensure no adverse effects have been caused.

Adult↗
PubMed2003

Early morphological effects in reading: evidence from parafoveal preview benefit in Hebrew.

Hebrew words are composed of two interwoven morphemes: a triconsonantal root and a word pattern. We examined the role of the root morpheme in word identification by assessing the benefit of presentation of a parafoveal preview word derived from the same root as a target word. Although the letter information of the preview was not consciously perceived, a preview of a word derived from the same root morpheme as the foveal target word facilitated eye-movement measures of first-pass reading (i.e.,first fixation and gaze duration). These results are the first to demonstrate early morphological effects in the context of sentence reading in which no external task is imposed on the reader, and converge with previous findings of morphemic priming in Hebrew using the masked priming paradigm, and morphemic parafoveal preview benefit effects in a single-word identification task.

Eye Movements↗
PubMed2002

Eye movements and processing stages in reading: relative contribution of visual, lexical, and contextual factors.

The independent and the combined influence of word length, word frequency, and contextual predictability on eye movements in reading was examined across processing stages under two priming-context conditions. Length, frequency, and predictability were used as predictors in multiple regression analyses, with parafoveal, early, late, and spillover eye movement measures as the dependent variables. There were specific effects of: (a) length, both on where to look (how likely a word was fixated and in which location) and how long to fixate, across all processing stages; (b) frequency, on how long to fixate a word, but not on where to look, at an early processing stage; and (c) predictability, both on how likely a word was fixated and for how long, in late processing stages. The source of influence for predictability was related to global rather than to local contextual priming. The contribution of word length was independent of contextual source. These results are relevant to determine both the time course of the influence of visual, lexical, and contextual factors on eye movements in reading, and which main component of eye movements, that is, location or duration, is affected.

Eye Movements↗
PubMed1990

Frequency distribution of the time interval between quick phase nystagmic eye movements.

We measured the frequency distribution of the time interval between quick phases of nystagmic eye movements in 8 patients with congenital nystagmus. For each patient we recorded a 3- to 4-second long electro-oculographic (EOG) signal, repeating each session 22 times. The period of the nystagmic cycles was computed for each record, by evaluating the peak frequency of the nystagmic oscillations via spectral analysis of the EOGs. This period is a measure of the time interval between quick phases. Its distribution ranged between 100 and 600 ms and peaked at about 240 +/- 50 ms, with a gaussian shape for values less than about 300 ms. Our measurements were considered as providing the distribution of intersaccadic latencies in normal humans.

Adolescent↗