Reliability of smooth pursuit, fixation, and saccadic eye movements

Eye-Tracking in Physical Human-Robot Interaction: Mental Workload and Performance Prediction

BACKGROUND

In Physical Human-Robot Interaction (pHRI), the need to learn the robot's motor-control dynamics is associated with increased cognitive load. Eye-tracking metrics can help understand the dynamics of fluctuating mental workload over the course of learning.

OBJECTIVE

The aim of this study was to test eye-tracking measures' sensitivity and reliability to variations in task difficulty, as well as their performance-prediction capability, in physical human-robot collaboration tasks involving an industrial robot for object comanipulation.

METHODS

Participants (9M, 9F) learned to coperform a virtual pick-and-place task with a bimanual robot over multiple trials. Joint stiffness of the robot was manipulated to increase motor-coordination demands. The psychometric properties of eye-tracking measures and their ability to predict performance was investigated.

RESULTS

Stationary Gaze Entropy and pupil diameter were the most reliable and sensitive measures of workload associated with changes in task difficulty and learning. Increased task difficulty was more likely to result in a robot-monitoring strategy. Eye-tracking measures were able to predict the occurrence of success or failure in each trial with 70% sensitivity and 71% accuracy.

CONCLUSION

The sensitivity and reliability of eye-tracking measures was acceptable, although values were lower than those observed in cognitive domains. Measures of gaze behaviors indicative of visual monitoring strategies were most sensitive to task difficulty manipulations, and should be explored further for the pHRI domain where motor-control and internal-model formation will likely be strong contributors to workload.

APPLICATION

Future collaborative robots can adapt to human cognitive state and skill-level measured using eye-tracking measures of workload and visual attention.

Classification of short and long term mild traumatic brain injury using computerized eye tracking

Accurate, and objective diagnosis of brain injury remains challenging. This study evaluated useability and reliability of computerized eye-tracker assessments (CEAs) designed to assess oculomotor function, visual attention/processing, and selective attention in recent mild traumatic brain injury (mTBI), persistent post-concussion syndrome (PPCS), and controls. Tests included egocentric localisation, fixation-stability, smooth-pursuit, saccades, Stroop, and the vestibulo-ocular reflex (VOR). Thirty-five healthy adults performed the CEA battery twice to assess useability and test-retest reliability. In separate experiments, CEA data from 55 healthy, 20 mTBI, and 40 PPCS adults were used to train a machine learning model to categorize participants into control, mTBI, or PPCS classes. Intraclass correlation coefficients demonstrated moderate (ICC > .50) to excellent (ICC > .98) reliability (p < .05) and satisfactory CEA compliance. Machine learning modelling categorizing participants into groups of control, mTBI, and PPCS performed reasonably (balanced accuracy control: 0.83, mTBI: 0.66, and PPCS: 0.76, AUC-ROC: 0.82). Key outcomes were the VOR (gaze stability), fixation (vertical error), and pursuit (total error, vertical gain, and number of saccades). The CEA battery was reliable and able to differentiate healthy, mTBI, and PPCS patients reasonably well. While promising, the diagnostic model accuracy should be improved with a larger training dataset before use in clinical environments.

Eye tracking assessment of Parkinson's disease: a clinical retrospective analysis

Parkinson's disease (PD) presents a significant clinical challenge due to its profound motor and cognitive impacts. Early diagnosis is crucial for implementing effective, stage-based treatment strategies. Recently, eye-tracking technology has emerged as a promising tool for the non-invasive diagnosis and monitoring of various neurological disorders, including PD. This retrospective study analyzed eye-tracking parameters, specifically visually-guided saccades (VGS), in PD patients within a clinical setting. We reviewed eye-tracking data from 62 PD patients, focusing on eye movement performance in horizontal and vertical VGS tasks. Our findings revealed significant correlations between demographic profiles, Mini-Mental State Examination (MMSE) scores, pattern recognition, and spatial working memory tests with saccadic performance in PD patients. Despite the retrospective nature of the study, our results support the potential of eye-tracking technology as a valuable diagnostic tool in PD assessment and monitoring. Future research should prioritize longitudinal studies and more comprehensive assessments to further understand and enhance the clinical application of eye-tracking in PD.

Quantifying the Impact of Motions on Human Aiming Performance: Evidence from Eye Tracking and Bio-Signals

Working on a moving platform can significantly impede human performance. Previous studies on moving vehicles have often focused on the overall impact on general task performance, whereas our study's emphasis is on precise hand movements, exploring the interaction between body motion and the escalation of task difficulty. We recruited 28 participants to engage in reciprocal aiming tasks, following Paul Fitts's setting, under both in-motion and stationary conditions. The task index of difficulty (ID) was manipulated by varying the width of the targets and the distance between the targets. We measured participants' movement time (MT), performance errors, and monitored their eye movements using an eye-tracking device, heart rate (HR), and respiration rate (RR) during the tasks. The measured parameters were compared across two experimental conditions and three ID levels. Compared to the stationary conditions, the in-motion conditions degraded human aiming performance, resulting in significantly prolonged MT, increased errors, and longer durations of eye fixations and saccades. Furthermore, HR and RR increased under the in-motion conditions. Linear relationships between MT and ID exhibited steeper slopes under the in-motion conditions compared to the stationary conditions. This study builds a foundation for us to explore the control mechanisms of individuals working in dynamic and demanding environments, such as pilots in airplanes and paramedics in ambulances.

Normative tDCS over V5 and FEF reveals practice-induced modulation of extraretinal smooth pursuit mechanisms, but no specific stimulation effect

The neural networks subserving smooth pursuit eye movements (SPEM) provide an ideal model for investigating the interaction of sensory processing and motor control during ongoing movements. To better understand core plasticity aspects of sensorimotor processing for SPEM, normative sham, anodal or cathodal transcranial direct current stimulation (tDCS) was applied over visual area V5 and frontal eye fields (FEF) in sixty healthy participants. The identical within-subject paradigm was used to assess SPEM modulations by practice. While no specific tDCS effects were revealed, within- and between-session practice effects indicate plasticity of top-down extraretinal mechanisms that mainly affect SPEM in the absence of visual input and during SPEM initiation. To explore the potential of tDCS effects, individual electric field simulations were computed based on calibrated finite element head models and individual functional localization of V5 and FEF location (using functional MRI) and orientation (using combined EEG/MEG) was conducted. Simulations revealed only limited electric field target intensities induced by the applied normative tDCS montages but indicate the potential efficacy of personalized tDCS for the modulation of SPEM. In sum, results indicate the potential susceptibility of extraretinal SPEM control to targeted external neuromodulation (e.g., personalized tDCS) and intrinsic learning protocols.

Transforming Psychological Testing With Saccadic Responses: Internal Consistency is High for Rorschach and Facial Expressions

Psychologists have long been interested in the underlying visual perceptual processes associated with forming responses to certain psychological tests, including the Rorschach Ink Blot Test, which modern users conceptualize as a conceptual problem-solving task. Accordingly, we used eye tracking technology to assess the internal consistency of saccadic responses to both the Rorschach Ink Blot Test and a facial expression task. Internal consistency was highest for eye Fixation Duration (FD) and Saccade Amplitude (SA), and both FD and SA measures in the Rorschach were positively related to the same measures in the facial expression task. Given this high internal consistency of FD and SA for viewing Rorschach ink blots and viewing pictures from well-known collections of facial expressions, and given high correlations between these eye tracking measures across the two tasks, FD and SA may now be used in further studies of eye movements in visuo-attentive psychological/neuropsychological tests (e.g., the Thematic Apperception Test). Reliability of these eye movement measures across tasks enables their use for better understanding of underlying visual processes and improved interpretations of the meaning of behavioral responses to psychological/neuropsychological tests.

Visuomotor Synchronization: Military Normative Performance

INTRODUCTION

Cognitive processes such as perception and reasoning are preceded and dependent on attention. Because of the close overlap between neural circuits of attention and eye movement, attention may be objectively quantified with recording of eye movements during an attention-dependent task. Our previous work demonstrated that performance scores on a circular visual tracking task that requires dynamic synchronization of the gaze with the target motion can be impacted by concussion, sleep deprivation, and attention deficit/hyperactivity disorder. The current study examined the characteristics of performance on a standardized predictive visual tracking task in a large sample from a U.S. Military population to provide military normative data.

MATERIALS AND METHODS

The sample consisted of 1,594 active duty military service members of either sex aged 18-29 years old who were stationed at Fort Hood Army Base. The protocol was reviewed and approved by the U.S. Army Medical Research and Materiel Command Institutional Review Board. Demographic, medical, and military history data were collected using questionnaires, and performance-based data were collected using a circular visual tracking test and Trail Making Test. Differences in visual tracking performance by demographic characteristics were examined with a multivariate analysis of variance, as well as a Kolmogorov-Smirnov test and a rank-sum test. Associations with other measures were examined with a rank-sum test or Spearman correlations.

RESULTS

Robust sex differences in visual tracking performance were found across the various statistical models, as well as age differences in several isolated comparisons. Accordingly, norms of performance scores, described in terms of percentile standings, were developed adjusting for age and sex. The effects of other measures on visual tracking performance were small or statistically non-significant. An examination of the score distributions of various metrics suggested that strategies preferred by men and women may optimize different aspects of visual tracking performance.

CONCLUSION

This large-scale quantification of attention, using dynamic visuomotor synchronization performance, provides rigorously characterized age- and sex-based military population norms. This study establishes analytics for assessing normal and impaired attention and detecting changes within individuals over time. Practical applications for combat readiness and surveillance of attention impairment from sleep insufficiency, concussion, medication, or attention disorders will be enhanced with portable, easily accessible, fast, and reliable dynamic eye-tracking technologies.

Cerebral blood flow and immediate and sustained executive function benefits following single bouts of passive and active exercise

Passive exercise occurs when an individual's limbs are moved via an external force and is a modality that increases cerebral blood flow (CBF) and provides an immediate postexercise executive function (EF) benefit. To our knowledge, no work has examined for how long passive exercise benefits EF. Here, healthy young adults (N = 22; 7 female) used a cycle ergometer to complete three 20-min conditions: passive exercise (via mechanically driven flywheel), a traditional light intensity (37 W) "active" exercise condition (i.e., via volitional pedalling) and a non-exercise control condition. An estimate of CBF was obtained via transcranial Doppler ultrasound measurement of middle cerebral artery blood velocity (MCAv) and antisaccades (i.e., saccade mirror-symmetrical to a target) were completed prior to and immediately, 30- and 60-min following each condition to assess EF. Passive and active exercise increased MCAv; however, the increase was larger in the latter condition. In terms of antisaccades, passive and active exercise provided an immediate postexercise reaction time benefit. At the 30-min assessment, the benefit was observed for active but not passive exercise and neither produced a benefit at the 60-min assessment. Thus, passive exercise provided an evanescent EF "boost" and is a finding that may reflect a smaller cortical hemodynamic response.

Polygenic risk scores for schizophrenia are associated with oculomotor endophenotypes

BACKGROUND

Schizophrenia is a heterogeneous disorder with substantial heritability. The use of endophenotypes may help clarify its aetiology. Measures from the smooth pursuit and antisaccade eye movement tasks have been identified as endophenotypes for schizophrenia in twin and family studies. However, the genetic basis of the overlap between schizophrenia and these oculomotor markers is largely unknown. Here, we tested whether schizophrenia polygenic risk scores (PRS) were associated with oculomotor performance in the general population.

METHODS

Analyses were based on the data of 2956 participants (aged 30-95) of the Rhineland Study, a community-based cohort study in Bonn, Germany. Genotyping was performed on Omni-2.5 exome arrays. Using summary statistics from a recent meta-analysis based on the two largest schizophrenia genome-wide association studies to date, we quantified genetic risk for schizophrenia by creating PRS at different p value thresholds for genetic markers. We examined associations between PRS and oculomotor performance using multivariable regression models.

RESULTS

Higher PRS were associated with higher antisaccade error rate and latency, and lower antisaccade amplitude gain. PRS showed inconsistent patterns of association with smooth pursuit velocity gain and were not associated with saccade rate during smooth pursuit or performance on a prosaccade control task.

CONCLUSIONS

There is an overlap between genetic determinants of schizophrenia and oculomotor endophenotypes. Our findings suggest that the mechanisms that underlie schizophrenia also affect oculomotor function in the general population.

Assessing anxiety-linked impairment in attentional control without eye-tracking: The masked-target antisaccade task

Contemporary cognitive theories of anxiety and attention processing propose that heightened levels of anxiety vulnerability are associated with a decreasing ability to inhibit the allocation of attention towards task-irrelevant information. Existing performance-based research has most often used eye-movement assessment variants of the antisaccade paradigm to demonstrate such effects. Critically, however, eye-movement assessment methods are limited by expense, the need for expert training in administration, and limited mobility and scalability. These barriers have likely led to researchers' use of suboptimal methods of assessing the relationship between attentional control and anxiety vulnerability. The present study examined the capacity for a non-eye-movement-based variant of the antisaccade task, the masked-target antisaccade task (Guitton et al., 1985), to detect anxiety-linked differences in attentional control. Participants (N = 342) completed an assessment of anxiety vulnerability and performed the masked-target antisaccade task in an online assessment session. Greater levels of anxiety vulnerability predicted poorer performance on the task, consistent with findings observed from eye-movement methods and with cognitive theories of anxiety and attention processing. Results also revealed the task to have high internal reliability. Our findings indicate that the masked-target antisaccade task provides a psychometrically reliable, low-cost, mobile, and scalable assessment of anxiety-linked differences in attentional control.

One-year-later spontaneous EEG features predict visual exploratory human phenotypes

During visual exploration, eye movements are controlled by multiple stimulus- and goal-driven factors. We recently showed that the dynamics of eye movements -how/when the eye move- during natural scenes' free viewing were similar across individuals and identified two viewing styles: static and dynamic, characterized respectively by longer or shorter fixations. Interestingly, these styles could be revealed at rest, in the absence of any visual stimulus. This result supports a role of intrinsic activity in eye movement dynamics. Here we hypothesize that these two viewing styles correspond to different spontaneous patterns of brain activity. One year after the behavioural experiments, static and dynamic viewers were called back to the lab to record high density EEG activity during eyes open and eyes closed. Static viewers show higher cortical inhibition, slower individual alpha frequency peak, and longer memory of alpha oscillations. The opposite holds for dynamic viewers. We conclude that some properties of spontaneous activity predict exploratory eye movement dynamics during free viewing.

Blink duration is increased in concussed youth athletes: a validity study using eye tracking in male youth and adult athletes of selected contact sports

OBJECTIVE

Diagnosing a sports-related concussion (SRC) remains challenging, and research into diagnostic tools is limited. This study investigated whether selected eye tracking variables would be a valid tool to diagnose and monitor SRC in adult and youth participants in selected contact sports, such as Rugby Union (rugby) and football (soccer).

METHODS

This prospective cohort study, with 70 concussed and 92 non-concussed adult and youth athletes, assessed the validity of five previously selected eye tracking variables for SRC diagnostics and management. The performance between concussed and age-matched control (non-concussed) athletes, as well as between three successive testing sessions in the concussed athletes were compared. Self-paced saccade count in adult group; blink duration in the memory-guided saccade and sinusoidal smooth pursuit tasks, proportion of antisaccade errors, and gain of diagonal smooth pursuit in the youth group were assessed.

RESULTS

The youth concussed group had higher blink duration in the fast memory-guided saccades task (p = 0.001, η2 = 0.17) and a tendency for higher blink duration in the sinusoidal smooth pursuit task (p = 0.016, η2 = 0.06) compared to the youth control group. In both tasks the blink duration in the concussed youth group decreased from session 1 to session 2 by 24% and 18%, accordingly, although statistical significance was not reached. The concussed adult group demonstrated a lower number of self-paced saccades compared to controls (p = 0.05, η2 = 0.09), which gradually increased, with the largest difference between session 1 and session 3 (p = 0.02).

CONCLUSIONS

Blink duration in youth athletes holds promise as a valid metric for concussion diagnostics and monitoring. It is recommended to focus future studies on comparing eye tracking performance within the same concussed athletes over time rather than comparing them to healthy controls.

Cardiovascular reactivity during sadness induction predicts inhibitory control performance

Higher negative affectivity has an association with decreased executive function and cognitive control. Heart rate variability (HRV) serves as an index of cardiac vagal regulation differences in the autonomic nervous system for both cognition and emotion. The current study investigates this association using a classic as well as emotional antisaccade paradigm to study inhibitory control performance. Ninety participants completed affective questionnaires (Beck Depression Inventory-II, and Mood Scale), a 6-minute baseline electrocardiogram, and two different antisaccade tasks. After the baseline, subjects were presented with a video sequence with either neutral, sad, or emotionally arousing content. By subtracting the baseline from the video sequence, we computed HRV reactivity and tested whether the reactivity score could predict inhibitory control performance. We hypothesized that this would be the case in both the sadness and arousal group, but not in the neutral one. Furthermore, we awaited significant performance differences between experimental groups. Contrary to our assumption, inhibitory control performance did not differ between experimental groups. Moreover, there was no significant relation between affective measures and task performance. Nevertheless, cardiovascular reactivity in terms of HRV was predictive of error rates in both antisaccade tasks in the sadness group. We could find this effect neither in the neutral nor in the arousal group. In addition, BDI scores moderated the effect in the emotional task. Results indicate that emotional reactivity to a sad video stimulus as indexed by HRV as well as the interaction with current emotional state predict inhibitory control performance.

Eye Tracking in Patients with Parkinson’s Disease Treated with Nabilone–Results of a Phase II, Placebo-Controlled, Double-Blind, Parallel-Group Pilot Study

The topic of the therapeutic use of cannabinoids in Parkinson’s disease (PD) is broadly discussed and frequently comes up in the outpatient clinic. So far, there are only a few randomized clinical trials assessing the effects of cannabinoids in PD. We are able to demonstrate a reduction in non-motor symptom (NMS) burden after the administration of nabilone. As impairment of attention and working memory have been described earlier as possible side effects, we assess cognitive performance using saccadic paradigms measured by an eye tracker. We do not observe a significant difference in any of the saccadic paradigms between PD patients on placebo versus those treated with nabilone. We, therefore, conclude that top-down inhibitory control is not affected by the tetrahydrocannabinol analogue. Nabilone did not significantly worsen cognitive performance and appears to be safe to use in selected PD patients who suffer from disabling NMS.

Exploring Eye Movement Biometrics in Real-World Activities: A Case Study of Wayfinding

Eye movement biometrics can enable continuous verification for highly secure environments such as financial transactions and defense establishments, as well as a more personalized and tailored experience in gaze-based human–computer interactions. However, there are numerous challenges to recognizing people in real environments using eye movements, such as implicity and stimulus independence. In the instance of wayfinding, this research intends to investigate implicit and stimulus-independent eye movement biometrics in real-world situations. We collected 39 subjects’ eye movement data from real-world wayfinding experiments and derived five sets of eye movement features (the basic statistical, pupillary response, fixation density, fixation semantic and saccade encoding features). We adopted a random forest and performed biometric recognition for both identification and verification scenarios. The best accuracy we obtained in the identification scenario was 78% (equal error rate, EER = 6.3%) with the 10-fold classification and 64% (EER = 12.1%) with the leave-one-route-out classification. The best accuracy we achieved in the verification scenario was 89% (EER = 9.1%). Additionally, we tested performance across the 5 feature sets and 20 time window sizes. The results showed that the verification accuracy was insensitive to the increase in the time window size. These findings are the first indication of the viability of performing implicit and stimulus-independent biometric recognition in real-world settings using wearable eye tracking.

Positive and Negative Symptoms Are Associated with Distinct Effects on Predictive Saccades

The predictive saccade task is a motor learning paradigm requiring saccades to track a visual target moving in a predictable pattern. Previous research has explored extensively anti-saccade deficits observed across psychosis, but less is known about predictive saccade-related mechanisms. The dataset analysed came from the studies of Crawford et al, published in 1995, where neuroleptically medicated schizophrenia and bipolar affective disorder patients were compared with non-medicated patients and control participants using a predictive saccade paradigm. The participant groups consisted of medicated schizophrenia patients (n = 40), non-medicated schizophrenia patients (n = 18), medicated bipolar disorder patients (n = 14), non-medicated bipolar disorder patients (n = 18), and controls (n = 31). The current analyses explore relationships between predictive saccades and symptomatology, and the potential interaction of medication. Analyses revealed that the schizophrenia and bipolar disorder diagnostic categories are indistinguishable in patterns of predictive control across several saccadic parameters, supporting a dimensional hypothesis. Once collapsed into predominantly high-/low- negative/positive symptoms, regardless of diagnosis, differences were revealed, with significant hypometria and lower gain in those with more negative symptoms. This illustrates how the presentation of the deficits is homogeneous across diagnosis, but heterogeneous when surveyed by symptomatology; attesting that a diagnostic label is less informative than symptomatology when exploring predictive saccades.

Emotion-related impulsivity: Testing a model of arousal effects on cognitive control

The trait-based tendency to respond rashly to emotions is robustly tied to many forms of psychopathology and poor behavioural outcomes, including aggression and suicidality. Researchers have found associations between response inhibition and emotion-related impulsivity; however, effect sizes are often small. Because emotion-related impulsivity emerges in the context of heightened positive and negative emotions, arousal is a candidate trigger of impulsivity. The goals of the present study were to (1) replicate the association between emotion-related impulsivity and response inhibition, and (2) test whether emotion-related impulsivity is associated with arousal-induced decays in response inhibition performance. Participants (N = 55) completed a self-report measure of emotion-related impulsivity, and then completed a computer-based response inhibition task (the antisaccade task, in which participants must make a rapid saccadic eye movement away from a cue rather than toward it) before and after a well-validated stress induction (the Trier Social Stress Test). Psychophysiological indices of arousal were measured throughout the session. Findings provide partial support for the association between emotion-related impulsivity and pre-stress response inhibition. Contrary to hypotheses, emotion-related impulsivity did not interact with arousal to predict post-stress response inhibition performance after controlling for pre-stress response inhibition performance. Future research is needed to consider clinical samples and to assess whether emotion-related impulsivity is related to deficits in other facets of cognitive control and decision-making.

Sensory processing sensitivity predicts performance in an emotional antisaccade paradigm

Sensory Processing Sensitivity (SPS) is a common, heritable, and evolutionarily conserved trait, describing inter-individual differences in responsiveness and a more cautious approach to novel stimuli. It is associated with increased activation of brain regions involved in awareness, integration of sensory information, and empathy during processing of emotional faces. Furthermore, SPS is related to better performance in a visual detection task. Even though SPS is conceptualized to be closely related to traits characterized by pausing before acting, no study to date has assessed the relation between SPS and inhibitory control in a behavioral inhibition task. The present study fills this gap by investigating how SPS influences individual performance on two different antisaccade paradigms including emotional face stimuli. In addition, we assessed self-reported mood, anxiety, and depressiveness. Results showed that SPS was related to faster processing speed on the emotional, but not the classic antisaccade paradigm. Moreover, SPS predicted inhibitory control speed above mood and depressiveness. Our results provide evidence that higher SPS participants show superior inhibitory abilities, especially during the processing of emotional stimuli. This is in line with earlier findings showing better performance in a visual detection task as well as increased brain activation during emotional face processing.

Do emotional stimuli interfere with response inhibition? evidence from the antisaccade paradigm

When it comes to measuring cognitive control and inhibition, the antisaccade paradigm is a popular task to apply. Usually, simple, perceptually and affectively neutral stimuli, e.g. white circles, are used. Recently, researchers also employed a version of the paradigm displaying emotional faces. Differences in cognitive processing due to stimulus size and emotional valence have not been investigated yet. Thus, in the present study, we applied both versions of the antisaccade paradigm in a healthy sample. In addition, we used scrambled faces to control for stimulus size and emotional valence. We hypothesised slower reaction times and higher error rates for emotional face stimuli compared to circular and scrambled ones as well as significant differences between individual emotions. In contrast to our hypotheses, results showed faster reaction times fewer errors for emotional faces compared to circular and scrambled stimuli. Furthermore, ANOVA models showed no meaningful differences between different emotions. Our study shows specific patterns in inhibitory control due to stimulus size and valence in an antisaccade eye-tracking task.

Replicability and reliability of the background and target velocity effects in smooth pursuit eye movements

When we follow a slowly moving target with our eyes, we perform smooth pursuit eye movements (SPEM). Previous investigations point to significantly and robustly reduced SPEM performance in the presence of a stationary background and at higher compared to lower target velocities. However, the reliability of these background and target velocity effects has not yet been investigated systematically. To address this issue, 45 healthy participants (17 m, 28 f) took part in two experimental sessions 7 days apart. In each session, participants were instructed to follow a horizontal SPEM target moving sinusoidally between ±7.89° at three different target velocities, corresponding to frequencies of 0.2, 0.4 and 0.6 Hz. Each target velocity was presented once with and once without a stationary background, resulting in six blocks. The blocks were presented twice per session in order to additionally explore potential task length effects. To assess SPEM performance, velocity gain was calculated as the ratio of eye to target velocity. In line with previous research, detrimental background and target velocity effects were replicated robustly in both sessions with large effect sizes. Good to excellent test-retest reliabilities were obtained at higher target velocities and in the presence of a stationary background, whereas lower reliabilities occurred with slower targets and in the absence of background stimuli. Target velocity and background effects resulted in largely good to excellent reliabilities. These findings not only replicated robust experimental effects of background and target velocity at group level, but also revealed that these effects can be translated into reliable individual difference measures.

Cross-modal auditory priors drive the perception of bistable visual stimuli with reliable differences between individuals

It is a widely held assumption that the brain performs perceptual inference by combining sensory information with prior expectations, weighted by their uncertainty. A distinction can be made between higher- and lower-level priors, which can be manipulated with associative learning and sensory priming, respectively. Here, we simultaneously investigate priming and the differential effect of auditory vs. visual associative cues on visual perception, and we also examine the reliability of individual differences. Healthy individuals (N = 29) performed a perceptual inference task twice with a one-week delay. They reported the perceived direction of motion of dot pairs, which were preceded by a probabilistic visuo-acoustic cue. In 30% of the trials, motion direction was ambiguous, and in half of these trials, the auditory versus the visual cue predicted opposing directions. Cue-stimulus contingency could change every 40 trials. On ambiguous trials where the visual and the auditory cue predicted conflicting directions of motion, participants made more decisions consistent with the prediction of the acoustic cue. Increased predictive processing under stimulus uncertainty was indicated by slower responses to ambiguous (vs. non-ambiguous) stimuli. Furthermore, priming effects were also observed in that perception of ambiguous stimuli was influenced by perceptual decisions on the previous ambiguous and unambiguous trials as well. Critically, behavioural effects had substantial inter-individual variability which showed high test-retest reliability (intraclass correlation coefficient (ICC) > 0.78). Overall, higher-level priors based on auditory (vs. visual) information had greater influence on visual perception, and lower-level priors were also in action. Importantly, we observed large and stable differences in various aspects of task performance. Computational modelling combined with neuroimaging could allow testing hypotheses regarding the potential mechanisms causing these behavioral effects. The reliability of the behavioural differences implicates that such perceptual inference tasks could be valuable tools during large-scale biomarker and neuroimaging studies.

Perceptual-motor styles

Even for a stereotyped task, sensorimotor behavior is generally variable due to noise, redundancy, adaptability, learning or plasticity. The sources and significance of different kinds of behavioral variability have attracted considerable attention in recent years. However, the idea that part of this variability depends on unique individual strategies has been explored to a lesser extent. In particular, the notion of style recurs infrequently in the literature on sensorimotor behavior. In general use, style refers to a distinctive manner or custom of behaving oneself or of doing something, especially one that is typical of a person, group of people, place, context, or period. The application of the term to the domain of perceptual and motor phenomenology opens new perspectives on the nature of behavioral variability, perspectives that are complementary to those typically considered in the studies of sensorimotor variability. In particular, the concept of style may help toward the development of personalised physiology and medicine by providing markers of individual behaviour and response to different stimuli or treatments. Here, we cover some potential applications of the concept of perceptual-motor style to different areas of neuroscience, both in the healthy and the diseased. We prefer to be as general as possible in the types of applications we consider, even at the expense of running the risk of encompassing loosely related studies, given the relative novelty of the introduction of the term perceptual-motor style in neurosciences.

Inter-Visit Reliability of Smooth Pursuit Neck Torsion Test in Patients with Chronic Neck Pain and Healthy Individuals

Visual disturbances are commonly reported in patients with neck pain. Smooth pursuit neck torsion (SPNT) test performed in neutral position and with trunk rotated under the stationary head has been used to discriminate between those with cervical component and those without. However, no studies investigated the reliability of the SPNT-test in patients with chronic neck pain and healthy controls. The aim of this study was to assess inter-visit reliability of the SPNT-test while applying different amplitudes and velocities of target movement. Thirty-two controls and thirty-one patients were enrolled in the study. The SPNT-test was performed in neutral position and through 45° torsion positions. The test was performed at 20°/s, 30°/s and 40°/s velocities and at 30°, 40° and 50° amplitudes of cyclic sinusoidal target movements. Interclass correlation coefficient and smallest detectable change were calculated for parameters of gain and SPNT-differences. In patients, moderate to good reliability was observed for gain at 40° and 50° amplitudes and for 20°/s and 30°/s velocities, while moderate to excellent reliability for gain was observed in controls. Both groups presented with moderate to good reliability for SPNT-difference. Our findings imply that amplitudes of 40° and 50° and velocities of 20°/s and 30°/s are the most reliable and should be applied in future studies assessing oculomotor functions during the SPNT test.

Schizotypy, neuroticism, and saccadic eye movements: New data and meta-analysis

Deficits on saccade tasks, particularly antisaccade performance, have been reliably reported in schizophrenia. However, less evidence is available on saccade performance in relation to schizotypy, a personality constellation harboring risk for schizophrenia. Here, we report a large empirical study of the associations of schizotypy and neuroticism with antisaccade and prosaccade performance (Study I). Additionally, we carried out meta-analyses of the association between schizotypy and antisaccade error rate (Study II). In Study I, N = 526 healthy individuals from the general population aged 18-54 years completed prosaccade and antisaccade tasks as well as the Schizotypal Personality Questionnaire (SPQ). Schizotypy was significantly associated with increased antisaccade error rate, with the disorganized dimension emerging as strongest predictor (β = .118, p = .007). Neuroticism emerged as a significant predictor for prosaccade gain (β = .103, p = .023) and antisaccade latency (β = .101, p = .025). In Study II, random-effects meta-analyses were performed on the published data and those from Study I. Meta-analyses revealed significant associations (all p ≤ .003) of antisaccade error rate with positive (g = 0.37), negative (g = 0.26), disorganized (g = 0.36) and overall schizotypy (g = 0.37). Overall, the present work replicates the association between antisaccade direction errors and schizotypy. Significant findings from meta-analyses provide further evidence of the antisaccade error rate as a putative schizophrenia spectrum marker.

Aging Effects and Test-Retest Reliability of Inhibitory Control for Saccadic Eye Movements

Neuropsychological studies indicate that healthy aging is associated with a decline of inhibitory control of attentional and behavioral systems. A widely accepted measure of inhibitory control is the antisaccade task that requires both the inhibition of a reflexive saccadic response toward a visual target and the initiation of a voluntary eye movement in the opposite direction. To better understand the nature of age-related differences in inhibitory control, we evaluated antisaccade task performance in 78 younger (20-35 years) and 78 older (60-80 years) participants. In order to provide reliable estimates of inhibitory control for individual subjects, we investigated test-retest reliability of the reaction time, error rate, saccadic gain, and peak saccadic velocity and further estimated latent, not directly observable processed contributing to changes in the antisaccade task execution. The intraclass correlation coefficients (ICCs) for an older group of participants emerged as good to excellent for most of our antisaccade task measures. Furthermore, using Bayesian multivariate models, we inspected age-related differences in the performances of healthy younger and older participants. The older group demonstrated higher error rates, longer reaction times, significantly more inhibition failures, and late prosaccades as compared with young adults. The consequently lower ability of older adults to voluntarily inhibit saccadic responses has been interpreted as an indicator of age-related inhibitory control decline. Additionally, we performed a Bayesian model comparison of used computational models and concluded that the Stochastic Early Reaction, Inhibition and Late Action (SERIA) model explains our data better than PRO-Stop-Antisaccade (PROSA) that does not incorporate a late decision process.

Increased cerebral blood flow supports a single-bout postexercise benefit to executive function: evidence from hypercapnia

A single bout of aerobic exercise improves executive function; however, the mechanism for the improvement remains unclear. One proposal asserts that an exercise-mediated increase in cerebral blood flow (CBF) enhances the efficiency of executive-related cortical structures. To examine this, participants completed separate 10-min sessions of moderate- to heavy-intensity aerobic exercise, a hypercapnic environment (i.e., 5% CO₂), and a nonexercise and nonhypercapnic control condition. The hypercapnic condition was included because it produces an increase in CBF independent of metabolic demands. An estimate of CBF was achieved via transcranial Doppler ultrasound and near-infrared spectroscopy that provided measures of middle cerebral artery blood velocity (BV) and deoxygenated hemoglobin (HHb), respectively. Exercise intensity was adjusted to match participant-specific changes in BV and HHb associated with the hypercapnic condition. Executive function was assessed before and after each session via antisaccades (i.e., saccade mirror-symmetrical to a target) because the task is mediated via the same executive networks that demonstrate task-dependent modulation following single and chronic bouts of aerobic exercise. Results showed that hypercapnic and exercise conditions were associated with comparable BV and HHb changes, whereas the control condition did not produce a change in either metric. In terms of antisaccade performance, the exercise and hypercapnic, but not control, conditions demonstrated improved postcondition reaction times (RT), and the magnitude of the hypercapnic and exercise-based increase in estimated CBF was reliably related to the postcondition improvement in RT. Accordingly, results evince that an increase in CBF represents a candidate mechanism for a postexercise improvement in executive function.NEW & NOTEWORTHY Single-bout aerobic exercise "boosts" executive function, and increased cerebral blood flow (CBF) has been proposed as a mechanism for the benefit. In this study, participants completed 10 min of aerobic exercise and 10 min of inhaling a hypercapnic gas, a manipulation known to increase CBF independently of metabolic demands. Both exercise and hypercapnic conditions improved executive function for at least 20 min. Accordingly, an increase in CBF is a candidate mechanism for the postexercise improvement in executive function.

Development and validation of a high-speed video system for measuring saccadic eye movement

Laboratory-based retroreflective and magnetic scleral search-coil technologies are the current standards for collecting saccadometric data, but such equipment is costly and cumbersome. We have validated a novel, portable, high-speed video camera-based system (Exilim EX-FH20, Casio, Tokyo, Japan) for measuring saccade reaction time (RT) and error rate in a well-lit environment. This system would enable measurements of pro- and antisaccades in athletes, which is important because antisaccade metrics provide a valid tool for concussion diagnosis and determining an athlete's safe return to play. A total of 529 trials collected from 15 participants were used to compare saccade RT and error rate measurements of the high-speed camera system to a retroreflective video-based eye tracker (Eye-Trac 6: Applied Sciences Laboratories, Bedford, MA). Bland-Altman analysis revealed that the RT measurements made by the high-speed video system were 11 ms slower than those made by the retroreflective system. Error rate measurements were identical between the two systems. An excellent degree of reliability was found between the system measurements and in the ratings of independent researchers examining the video data. A strong association (r = .97) between the RTs determined via the retroreflective and high-speed camera systems was observed across all trials. Our high-speed camera system is portable and easily set up, does not require extensive equipment calibration, and can be used in a well-lit environment. Accordingly, the camera-based capture of saccadometric data may provide a valuable tool for neurological assessment following a concussive event and for the continued monitoring of recovery.

Differential benefits of olanzapine on executive function in schizophrenia patients: Preliminary findings

OBJECTIVE

Schizophrenia patients show executive function (EF) impairments in voluntary orienting as measured by eye-movements. We tested 14 inpatients to investigate the effects of the antipsychotic olanzapine on EF, as measured by antisaccade eye-movement performance.

METHODS

Patients were tested at baseline (before olanzapine), 3-5 days post-medication, and 12-14 days post-medication. Patients were also assessed on the Positive and Negative Syndrome Scale (PANSS) to measure the severity of schizophrenia-related symptoms, and administered the Stroop task, a test of EF. Nine matched controls were also tested on the antisaccade and Stroop.

RESULTS

Both groups showed improvement on Stroop and antisaccade; however, the schizophrenia group improved significantly more on antisaccade, indicating an additional benefit of olanzapine on EF performance. Patients with poorer baseline antisaccade performance (High-Deficit) showed significantly greater improvement on the antisaccade task than patients with better baseline performance (Low-Deficit), suggesting that baseline EF impairment predicts the magnitude of cognitive improvement with olanzapine. These subgroups showed significant and equivalent improvement on PANSS scores, indicating that improvement on the antisaccade task with olanzapine was not a result of differences in magnitude of clinical improvement.

CONCLUSIONS

This preliminary study provides evidence that olanzapine may be most advantageous for patients with greater baseline EF deficits.

Antisaccade and prosaccade eye movements in individuals clinically at risk for psychosis: comparison with first-episode schizophrenia and prediction of conversion

Saccadic eye movements are well-described markers of cerebral function and have been widely studied in schizophrenia spectrum populations. However, less is known about saccades in individuals clinically at risk for schizophrenia. Therefore, we studied individuals in an at-risk mental state (ARMS) (N = 160), patients in their first episode of schizophrenia (N = 32) and healthy controls (N = 75). N = 88 ARMS participants showed an early at-risk mental state (E-ARMS), defined by cognitive-perceptive basic symptoms (COPER) or a combination of risk and loss of function, whereas N = 72 were in a late at-risk mental state (L-ARMS), defined by attenuated psychotic symptoms or brief limited intermittent psychotic symptoms. We examined prosaccades, reflecting overt attentional shifts, and antisaccades, measuring inhibitory control, as well as their relationship as an indicator of the interplay of bottom-up and top-down influences. L-ARMS but not E-ARMS participants had increased antisaccade latencies compared to controls. First-episode patients had higher antisaccade error rates compared to E-ARMS participants and controls, and increased latencies compared to all other groups. Prosaccade latencies did not differ between groups. We observed the expected negative correlation between prosaccade latency and antisaccade error rate, indicating that individuals with shorter prosaccade latencies made more antisaccade errors. The magnitude of the association did not differ between groups. No saccadic measure predicted conversion to psychosis within 2 years. These findings confirm the existence of antisaccade impairments in patients with schizophrenia and provide evidence that volitional response generation in the antisaccade task may be affected even before onset of clinically overt psychosis.

One-year test-retest reliability of ten vision tests in Canadian athletes

Background: Vision tests are used in concussion management and baseline testing. Concussions, however, often occur months after baseline testing and reliability studies generally examine intervals limited to days or one week. Our objective was to determine the one-year test-retest reliability of these tests.

Methods: We assessed one-year test-retest reliability of ten vision tests in elite Canadian athletes followed by the Institut National du Sport du Quebec. We included athletes who completed two baseline (preseason) annual evaluations by one clinician within 365±30 days. We excluded athletes with any concussion or vision training in between the annual evaluations or presented with any factor that is believed to affect the tests (e.g. migraines). Data were collected from clinical charts. We evaluated test-retest reliability using Intraclass Correlation Coefficient (ICC) and 95% limits of agreement (LoA).

Results: We examined nine female and seven male athletes with a mean age of 22.7 (SD 4.5) years. Among the vision tests, we observed excellent test-retest reliability in Positive Fusional Vergence at 30cm (ICC=0.93) but this dropped to 0.53 when an outlier was excluded in a sensitivity analysis. There was good to moderate reliability in Negative Fusional Vergence at 30cm (ICC=0.78), Phoria at 30cm (ICC=0.68), Near Point of Convergence break (ICC=0.65) and Saccades (ICC=0.61). The ICC for Positive Fusional Vergence at 3m (ICC=0.56) also decreased to 0.45 after removing two outliers. We found poor reliability in Near Point of Convergence (ICC=0.47), Gross Stereoscopic Acuity (ICC=0.03) and Negative Fusional Vergence at 3m (ICC=0.0). ICC for Phoria at 3m was not appropriate because scores were identical in 14/16 athletes. 95% LoA of the majority of tests were ±40% to ±90%.

Conclusions: Five tests had good to moderate one-year test-retest reliability. The remaining tests had poor reliability. The tests would therefore be useful only if concussion has a moderate-large effect on scores.

Clinical Utility of Oculomotor and Electrophysiological Measures in Identifying Concussion History

OBJECTIVE

To examine whether oculomotor and electrophysiological measures improve the clinical performance of the typical concussion protocol for classifying collegiate athletes with a history of concussion.

DESIGN

Cross-sectional.

SETTING

University Athletic Medicine and Research Facility.

PARTICIPANTS

Forty-five varsity collegiate athletes.

INDEPENDENT VARIABLES

Collegiate varsity athletes with or without a history of a diagnosed concussion.

MAIN OUTCOME MEASURES

Multivariate receiver operating curve and area under the curve (AUC) analyses tested the clinical performance of the typical concussion protocol (symptoms, postural control, neuropsychological abilities). We examined differences in clinical performance between this protocol and after adding reflexive saccade and event-related potential (ERP) indices. Hypotheses were formed after data collection.

RESULTS

Significant AUCs were demonstrated for the typical concussion protocol (model 1: AUC = 0.75, P = 0.007), after adding reflexive saccade eye excursion gain (model 2: AUC = 0.80, P = 0.001), and ERPs (model 3: AUC = 0.79, P = 0.002). The AUC for reflexive saccades and ERPs was significant (model 4: AUC = 0.70, P = 0.030). Model 2's increased clinical performance compared with model 1 was nonsignificant, χ(2) = 1.871, P = 0.171.

CONCLUSIONS

All 4 models demonstrated adequate sensitivity and specificity for classifying athletes with a previous concussion. Adding reflexive saccades and ERPs did not significantly increase clinical performance of the typical concussion protocol. Future research should determine the clinical utility of saccades and ERPs for acute postconcussion assessments.

Individual differences in visual salience vary along semantic dimensions

What determines where we look? Theories of attentional guidance hold that image features and task demands govern fixation behavior, while differences between observers are interpreted as a "noise-ceiling" that strictly limits predictability of fixations. However, recent twin studies suggest a genetic basis of gaze-trace similarity for a given stimulus. This leads to the question of how individuals differ in their gaze behavior and what may explain these differences. Here, we investigated the fixations of >100 human adults freely viewing a large set of complex scenes containing thousands of semantically annotated objects. We found systematic individual differences in fixation frequencies along six semantic stimulus dimensions. These differences were large (>twofold) and highly stable across images and time. Surprisingly, they also held for first fixations directed toward each image, commonly interpreted as "bottom-up" visual salience. Their perceptual relevance was documented by a correlation between individual face salience and face recognition skills. The set of reliable individual salience dimensions and their covariance pattern replicated across samples from three different countries, suggesting they reflect fundamental biological mechanisms of attention. Our findings show stable individual differences in salience along a set of fundamental semantic dimensions and that these differences have meaningful perceptual implications. Visual salience reflects features of the observer as well as the image.

Saccadic eye movements in different dimensions of schizophrenia and in clinical high-risk state for psychosis

BACKGROUND

Oculomotor dysfunction is one of the most replicated findings in schizophrenia. However the association between saccadic abnormalities and particular clinical syndromes remains unclear. The assessment of saccadic movements in schizophrenia patients as well as in clinical high-risk state for psychosis individuals (CHR) as a part of schizophrenia continuum may be useful in validation of saccadic movements as a possible biomarker.

METHODS

The study included 156 patients who met the ICD-10 criteria for schizophrenia: 42 individuals at clinical high-risk-state for psychosis and 61 healthy controls. The schizophrenia patients had three subgroups based on the sum of the global SAPS and SANS scores: (1) patients with predominantly negative symptoms (NS, n = 62); (2) patients with predominantly positive symptoms (PS, n = 54) (3) patients with predominantly disorganization symptoms (DS, n = 40). CHR subjects were characterized by the presence of one of the groups of criteria: (1) Ultra High Risk criteria, (2) Basic Symptoms criteria or (3) negative symptoms and formal thought disorders. Horizontal eye movements were recorded by using videonystagmograph. We measured peak velocity, latency and accuracy in prosaccade, antisaccade and predictive saccade tasks as well as error rates in the antisaccade task.

RESULTS

Schizophrenia patients performed worse than controls in predictive, reflexive and antisaccade tasks. Oculomotor parameters of NS were different from the other groups of patients. Latencies of predictive and reflexive saccades were significantly longer than in controls only in the NS group. The accuracy of predictive saccades was also different from controls only in the NS schizophrenia group. More prominent loss of accuracy of reflexive saccades was found in the DS group and it significantly differed from the one in other groups. Participants from DS group made more errors in antisaccade task compared to NS and PS groups. CHR subjects performed worse than controls as measured by the accuracy of reflexive saccades and antisaccades.

CONCLUSIONS

The study confirms the existence of different relations between the symptom dimensions of schizophrenia and saccades tasks performances. Saccadic abnormalities were revealed in the clinical (schizophrenia) and pre-clinical (clinical high risk) populations that provide further evidence for assessing saccadic abnormalities as a possible neurobiological marker for schizophrenia.

Language-driven anticipatory eye movements in virtual reality

Predictive language processing is often studied by measuring eye movements as participants look at objects on a computer screen while they listen to spoken sentences. This variant of the visual-world paradigm has revealed that information encountered by a listener at a spoken verb can give rise to anticipatory eye movements to a target object, which is taken to indicate that people predict upcoming words. The ecological validity of such findings remains questionable, however, because these computer experiments used two-dimensional stimuli that were mere abstractions of real-world objects. Here we present a visual-world paradigm study in a three-dimensional (3-D) immersive virtual reality environment. Despite significant changes in the stimulus materials and the different mode of stimulus presentation, language-mediated anticipatory eye movements were still observed. These findings thus indicate that people do predict upcoming words during language comprehension in a more naturalistic setting where natural depth cues are preserved. Moreover, the results confirm the feasibility of using eyetracking in rich and multimodal 3-D virtual environments.

Working Memory and Attention Influence Antisaccade Error Rate in Schizophrenia

Objectives: Antisaccade error rate has been proposed to be one of the most promising endophenotypes for schizophrenia. Increased error rate in patients has been associated with working memory, attention and other executive function impairments. The relationship between antisaccade error rate and other neuropsychological processes in patients compared to healthy controls has not been explored in depth. This study aimed to replicate the finding of heightened antisaccade error rate in patients and determine which cognitive processes were most strongly associated with antisaccade error rate in both patients and controls. In addition, the study investigated whether different antisaccade task paradigms engage different cognitive processes. Methods: One hundred and ninety-one participants (54 patients with schizophrenia/schizoaffective disorder and 137 controls) completed the antisaccade task, which included both gap and step task parameters. Neuropsychological measures were obtained using the MCCB and the Stroop task. Results: The current study replicated a pronounced antisaccade error rate deficit in patients. In patients, working memory variance was most significantly associated with antisaccade errors made during the step condition, while attentional processes were most associated with errors made during the gap condition. In controls, overall global cognitive performance was most associated with antisaccade rates for both gap and step conditions. Conclusions: The current study demonstrates that in schizophrenia patients, but not controls, elevated antisaccade error rate is associated with attention and working memory, but not with global cognitive impairment or psychopathological processes. Our novel findings demonstrate that the gap and step conditions of the antisaccade task engage different cognitive processes. (JINS, 2019, 25, 174-183).

Subclinical Saccadic Eye Movement Dysfunction in Pediatric Multiple Sclerosis

BACKGROUND

Efferent visual dysfunction in children could lead to impaired quality of life at home and school. Eye-tracking can detect subtle efferent dysfunction missed on bedside examination but has not been validated in the pediatric multiple sclerosis population.

OBJECTIVE

We sought to determine the feasibility of eye-tracking in children and associations with multiple sclerosis.

METHODS

Participants meeting criteria for pediatric multiple sclerosis without acute efferent vision abnormalities and healthy controls were recruited. Multiple sclerosis participants underwent a clinical assessment and saccade and antisaccade testing paradigms. Intraclass correlation coefficients were generated for intertest repeatability. Adjusting for age and intereye correlations, generalized estimating equations compared latencies with case status, Expanded Disability Status Scale and Symbol Digit Modalities Test (SDMT) scores.

RESULTS

We eye-tracked 15 children with multiple sclerosis (n = 30 eyes, mean age 15.6 ± 2.1, mean disease duration 3.9 years, median Expanded Disability Status Scale 1.5) compared to 6 healthy controls (n = 12 eyes, age 14.3 ± .95). The intraclass correlation coefficient for repeated trials was 0.85. Adjusting for age, saccadic latency was 60 milliseconds (ms) longer for cases than controls (95% confidence interval = 26.4, 93.8; P = .0005). For antisaccadic latency, we observed a similar trend of 60 ms longer for cases than controls ( P = .06).

CONCLUSION

Eye-tracking is a short noninvasive examination, and high intertest repeatability supports use of eye-tracking technology in pediatric multiple sclerosis. Longer saccadic latencies were seen in children with multiple sclerosis despite short disease duration and low Expanded Disability Status Scale scores.

Task-Related Differences in Eye Movements in Individuals With Aphasia

Background: Neurotypical young adults show task-based modulation and stability of their eye movements across tasks. This study aimed to determine whether persons with aphasia (PWA) modulate their eye movements and show stability across tasks similarly to control participants.

Methods: Forty-eight PWA and age-matched control participants completed four eye-tracking tasks: scene search, scene memorization, text-reading, and pseudo-reading.

Results: Main effects of task emerged for mean fixation duration, saccade amplitude, and standard deviations of each, demonstrating task-based modulation of eye movements. Group by task interactions indicated that PWA produced shorter fixations relative to controls. This effect was most pronounced for scene memorization and for individuals who recently suffered a stroke. PWA produced longer fixations, shorter saccades, and less variable eye movements in reading tasks compared to controls. Three-way interactions of group, aphasia subtype, and task also emerged. Text-reading and scene memorization were particularly effective at distinguishing aphasia subtype. Persons with anomic aphasia showed a reduction in reading saccade amplitudes relative to their respective control group and other PWA. Persons with conduction/Wernicke’s aphasia produced shorter scene memorization fixations relative to controls or PWA of other subtypes, suggesting a memorization specific effect. Positive correlations across most tasks emerged for fixation duration and did not significantly differ between controls and PWA.

Conclusion: PWA generally produced shorter fixations and smaller saccades relative to controls particularly in scene memorization and text-reading, respectively. The effect was most pronounced recently after a stroke. Selectively in reading tasks, PWA produced longer fixations and shorter saccades relative to controls, consistent with reading difficulty. PWA showed task-based modulation of eye movements, though the pattern of results was somewhat abnormal relative to controls. All subtypes of PWA also demonstrated task-based modulation of eye movements. However, persons with anomic aphasia showed reduced modulation of saccade amplitude and smaller reading saccades, possibly to improve reading comprehension. Controls and PWA generally produced stabile fixation durations across tasks and did not differ in their relationship across tasks. Overall, these results suggest there is potential to differentiate among PWA with varying subtypes and from controls using eye movement measures of task-based modulation, especially reading and scene memorization tasks.

The Area under the Main Sequence as an Alternative Method to Measure Saccadic Dynamics

SIGNIFICANCE

This study shows that the area under the main sequence (MSAREA) is a valid alternative to the standard peak-velocity main sequence in measuring saccadic dynamics. A one-parameter area model, MSAREA = GPW = 1.55 × SACSIZE, with SACSIZE as the size of the saccade, 1.55 as a power factor, and GPW = 1.55 as a gain parameter, is presented.

PURPOSE

SACPEAK = Vmax × (1 - e) is the traditional model used to describe the saccadic main sequence, the relationship between the size of the movement and its peak velocity (SACPEAK). In the previous article, we have shown that there is a strong linear correlation between the two parameters Vmax and SAT, which severely affects the model's clinical applicability. The purpose of this study is to see if, by using the MSAREA as an alternative approach, we can overcome the limitations of the traditional model.

METHODS

Participants and main sequence data are the same as the previous study. A trapezoidal integration was used to estimate the MSAREAs as a function of SACSIZE.

RESULTS

A two-parameter area model was computed to determine the range of variability of its parameters and R values. These were then used as reference values in the search for one-parameter alternatives. The one-parameter model MSAREA = GPW = 1.55 × SACSIZE performed well for all data sets. We tested its validity by performing a comparison with other one-parameter area models.

CONCLUSIONS

Area models are superior to peak-velocity models in terms of R and stability and can be reduced to robust one-parameter expressions with only limited degradation in R. This not only greatly simplifies the determination if a set is inside or outside a reference population but also allows for direct comparisons between sets, with the saccadic dynamics expressed by a simple linear gain factor (GPW = 1.55).

Association of Visual Tracking Metrics With Post-concussion Symptomatology

Attention impairment may provide a cohesive neurobiological explanation for clusters of clinical symptoms that occur after a concussion; therefore, objective quantification of attention is needed. Visually tracking a moving target is an attention-dependent sensorimotor function, and eye movement can be recorded easily and objectively to quantify performance. Our previous work suggested the utility of gaze-target synchronization metrics of a predictive visual tracking task in concussion screening and recovery monitoring. Another objectively quantifiable performance measure frequently suggested for concussion screening is simple visuo-manual reaction time (simple reaction time, SRT). Here, we used visual tracking and SRT tasks to assess changes between pre- and within-2-week post-concussion performances and explore their relationships to post-concussion symptomatology. Athletes participating in organized competitive sports were recruited. Visual tracking and SRT records were collected from the recruited athlete pool as baseline measures over a 4-year period. When athletes experienced a concussion, they were re-assessed within 2 weeks of their injury. We present the data from a total of 29 concussed athletes. Post-concussion symptom burden was assessed with the Rivermead Post-Concussion Symptoms Questionnaire and subscales of the Brain Injury Screening Questionnaire. Post-concussion changes in visual tracking and SRT performance were examined using a paired t-test. Correlations of changes in visual tracking and SRT performance to symptom burden were examined using Pearson's coefficients. Post-concussion changes in visual tracking performance were not consistent among the athletes. However, changes in several visual tracking metrics had moderate to strong correlations to symptom scales (r up to 0.68). On the other hand, while post-concussion SRT performance was reduced (p < 0.01), the changes in the performance metrics were not meaningfully correlated to symptomatology (r ≤ 0.33). Results suggest that visual tracking performance metrics reflect clinical symptoms when assessed within 2 weeks of concussion. Evaluation of concussion requires assessments in multiple domains because the clinical profiles are heterogeneous. While most individuals show recovery within a week of injury, others experience prolonged recovery periods. Visual tracking performance metrics may serve as a biomarker of debilitating symptoms of concussion implicating attention as a root cause of such pathologies.

Device-Embedded Cameras for Eye Tracking-Based Cognitive Assessment: Validation With Paper-Pencil and Computerized Cognitive Composites

BACKGROUND

As eye tracking-based assessment of cognition becomes more widely used in older adults, particularly those at risk for dementia, reliable and scalable methods to collect high-quality data are required. Eye tracking-based cognitive tests that utilize device-embedded cameras have the potential to reach large numbers of people as a screening tool for preclinical cognitive decline. However, to fully validate this approach, more empirical evidence about the comparability of eyetracking-based paradigms to existing cognitive batteries is needed.

OBJECTIVE

Using a population of clinically normal older adults, we examined the relationship between a 30-minute Visual Paired Comparison (VPC) recognition memory task and cognitive composite indices sensitive to a subtle decline in domains associated with Alzheimer disease. Additionally, the scoring accuracy between software used with a commercial grade eye tracking camera at 60 frames per second (FPS) and a manually scored procedure used with a laptop-embedded web camera (3 FPS) on the VPC task was compared, as well as the relationship between VPC task performance and domain-specific cognitive function.

METHODS

A group of 49 clinically normal older adults completed a 30-min VPC recognition memory task with simultaneous recording of eye movements by a commercial-grade eye-tracking camera and a laptop-embedded camera. Relationships between webcam VPC performance and the Preclinical Alzheimer Cognitive Composite (PACC) and National Institutes of Health Toolbox Cognitive Battery (NIHTB-CB) were examined. Inter-rater reliability for manually scored tests was analyzed using Krippendorff's kappa formula, and we used Spearman's Rho correlations to investigate the relationship between VPC performance scores with both cameras. We also examined the relationship between VPC performance with the device-embedded camera and domain-specific cognitive performance.

RESULTS

Modest relationships were seen between mean VPC novelty preference and the PACC (r=.39, P=.007) and NIHTB-CB (r=.35, P=.03) composite scores, and additional individual neurocognitive task scores including letter fluency (r=.33, P=.02), category fluency (r=.36, P=.01), and Trail Making Test A (-.40, P=.006). Robust relationships were observed between the 60 FPS eye tracker and 3 FPS webcam on both trial-level VPC novelty preference (r=.82, P<.001) and overall mean VPC novelty preference (r=.92 P<.001). Inter-rater agreement of manually scored web camera data was high (kappa=.84).

CONCLUSIONS

In a sample of clinically normal older adults, performance on a 30-minute VPC task correlated modestly with computerized and paper-pencil based cognitive composites that serve as preclinical Alzheimer disease cognitive indices. The strength of these relationships did not differ between camera devices. We suggest that using a device-embedded camera is a reliable and valid way to assess performance on VPC tasks accurately and that these tasks correlate with existing cognitive composites.

A standardized protocol for quantification of saccadic eye movements: DEMoNS

OBJECTIVE

Quantitative saccadic testing is a non-invasive method of evaluating the neural networks involved in the control of eye movements. The aim of this study is to provide a standardized and reproducible protocol for infrared oculography measurements of eye movements and analysis, which can be applied for various diseases in a multicenter setting.

METHODS

Development of a protocol to Demonstrate Eye Movement Networks with Saccades (DEMoNS) using infrared oculography. Automated analysis methods were used to calculate parameters describing the characteristics of the saccadic eye movements. The two measurements of the subjects were compared with descriptive and reproducibility statistics.

RESULTS

Infrared oculography measurements of all subjects were performed using the DEMoNS protocol and various saccadic parameters were calculated automatically from 28 subjects. Saccadic parameters such as: peak velocity, latency and saccade pair ratios showed excellent reproducibility (intra-class correlation coefficients > 0.9). Parameters describing performance of more complex tasks showed moderate to good reproducibility (intra-class correlation coefficients 0.63-0.78).

CONCLUSIONS

This study provides a standardized and transparent protocol for measuring and analyzing saccadic eye movements in a multicenter setting. The DEMoNS protocol details outcome measures for treatment trial which are of excellent reproducibility. The DEMoNS protocol can be applied to the study of saccadic eye movements in various neurodegenerative and motor diseases.

Effects of task repetition but no transfer of inhibitory control training in healthy adults

Executive functions (EFs) comprise the updating, shifting and inhibition dimensions. According to the Unity and Diversity Model, the inhibition dimension is fully accounted for by a general EFs factor. This suggests that training of inhibition should transfer, in part, to updating and shifting. Therefore, we tested the effectiveness of a three-week inhibition training (high-conflict Stroop task) and explored near transfer effects to an untrained inhibition task (antisaccade task) and far transfer effects to untrained tasks demanding task-set shifting (number-letter-task), working memory updating (n-back task) and planning abilities (Stockings of Cambridge task). We employed a randomized pretest/treatment/posttest study design in n = 102 healthy young adults, assigned to an intensive Stroop training (n = 38), an active control condition (n = 34) or no training intervention (n = 30). In the Stroop training group, Stroop performance improved with practice, while performance in the active control group remained unchanged. The Stroop training group showed improvements in overall Stroop task performance from pretest to posttest, but we observed neither near nor far transfer effects. Additionally, specifically stronger gains on incongruent Stroop trials compared to congruent trials were observed in the Stroop training group when color bar trials were excluded from the pretest-posttest-analysis. Generally, there were substantial improvements from pretest to posttest independent of training condition in all transfer tasks. In sum, our data do not support the existence of transfer effects from inhibition training in healthy young adults.

Effects of Dopamine and Norepinephrine on Exercise-induced Oculomotor Fatigue

INTRODUCTION

Fatigue-induced impairments in the control of eye movements are detectable via reduced eye movement velocity after a bout of prolonged, strenuous exercise. Slower eye movements caused by neural fatigue within the oculomotor system can be prevented by caffeine, and the upregulation of central catecholamines may be responsible for this effect. This study explored the individual contribution of dopamine and norepinephrine to fatigue-related impairments in oculomotor control.

METHODS

The influence of a dopamine reuptake inhibitor (methylphenidate) and a norepinephrine reuptake inhibitor (reboxetine) was assessed in 12 cyclists performing 180 min of stationary cycling within a placebo-controlled crossover design. Eye movement kinematics (saccades, smooth pursuit, and optokinetic nystagmus) were measured using infrared oculography. Visual attention was assessed with overt and covert spatial attention tasks.

RESULTS

Exercise-induced fatigue was associated with a 6% ± 8% reduction in the peak velocity of visually guided, reflexive prosaccades. Importantly, both dopamine reuptake inhibition and norepinephrine reuptake inhibition prevented fatigue-related decrements in the peak velocity of prosaccades. Pursuit eye movements, optokinetic nystagmus, and visual attention tasks were unaffected by exercise or drug treatments.

CONCLUSION

Overall, our findings suggest that alterations in norepinephrinergic and dopaminergic neurotransmission are linked with the development of fatigue within circuits that control eye movements. Psychiatric medications that target central catecholamines can exert a protective effect on eye movements after prolonged exercise.

Impaired Antisaccades in Obsessive-Compulsive Disorder: Evidence From Meta-Analysis and a Large Empirical Study

Increasing evidence indicates that patients with obsessive-compulsive disorder (OCD) exhibit alterations in fronto-striatal circuitry. Performance deficits in the antisaccade task would support this model, but results from previous small-scale studies have been inconclusive as either increased error rates, prolonged antisaccade latencies, both or neither have been reported in OCD patients. In order to address this issue, we investigated antisaccade performance in a large sample of OCD patients (n = 169) and matched control subjects (n = 183). As impaired antisaccade performance constitutes a potential endophenotype of OCD, unaffected first-degree relatives of OCD patients (n = 100) were assessed, as well. Furthermore, we conducted a quantitative meta-analysis to integrate our data with previous findings. In the empirical study, OCD patients exhibited significantly increased antisaccade latencies, intra-subject variability (ISV) of antisaccade latencies, and antisaccade error rates. The latter effect was driven by errors with express latency (80-130 ms), as patients did not differ significantly from controls with regards to regular errors (>130 ms). Notably, unaffected relatives of OCD patients showed elevated antisaccade express error rates and increased ISV of antisaccade latencies, as well. Antisaccade performance was not associated with state anxiety within groups. Among relatives, however, we observed a significant correlation between antisaccade error rate and harm avoidance. Medication status of OCD patients, symptom severity, depressive comorbidity, comorbid anxiety disorders and OCD symptom dimensions did not significantly affect antisaccade performance. Meta-analysis of 10 previous and the present empirical study yielded a medium-sized effect (SMD = 0.48, p < 0.001) for higher error rates in OCD patients, while the effect for latencies did not reach significance owing to strong heterogeneity (SMD = 0.51, p = 0.069). Our results support the assumption of impaired antisaccade performance in OCD, although effects sizes were only moderately large. Furthermore, we provide the first evidence that increased antisaccade express error rates and ISV of antisaccade latencies may constitute endophenotypes of OCD. Findings regarding these more detailed antisaccade parameters point to potentially underlying mechanisms, such as early pre-stimulus inhibition of the superior colliculus.

Behavioural and computational varieties of response inhibition in eye movements

Response inhibition is the ability to override a planned or an already initiated response. It is the hallmark of executive control as its deficits favour impulsive behaviours, which may be detrimental to an individual's life. This article reviews behavioural and computational guises of response inhibition. It focuses only on inhibition of oculomotor responses. It first reviews behavioural paradigms of response inhibition in eye movement research, namely the countermanding and antisaccade paradigms, both proven to be useful tools for the study of response inhibition in cognitive neuroscience and psychopathology. Then, it briefly reviews the neural mechanisms of response inhibition in these two behavioural paradigms. Computational models that embody a hypothesis and/or a theory of mechanisms underlying performance in both behavioural paradigms as well as provide a critical analysis of strengths and weaknesses of these models are discussed. All models assume the race of decision processes. The decision process in each paradigm that wins the race depends on different mechanisms. It has been shown that response latency is a stochastic process and has been proven to be an important measure of the cognitive control processes involved in response stopping in healthy and patient groups. Then, the inhibitory deficits in different brain diseases are reviewed, including schizophrenia and obsessive-compulsive disorder. Finally, new directions are suggested to improve the performance of models of response inhibition by drawing inspiration from successes of models in other domains.This article is part of the themed issue 'Movement suppression: brain mechanisms for stopping and stillness'.

Acute impairment of saccadic eye movements is associated with delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage

OBJECTIVE

Delayed cerebral ischemia (DCI) causing cerebral infarction remains a significant cause of morbidity and mortality following aneurysmal subarachnoid hemorrhage (aSAH). Early brain injury in the first 72 hours following rupture is likely to play a key role in the pathophysiology underlying DCI but remains difficult to quantify objectively. Current diagnostic modalities are based on the concept of vasoconstriction causing cerebral ischemia and infarction and are either invasive or have a steep learning curve and user variability. The authors sought to determine whether saccadic eye movements are impaired following aSAH and whether this measurement in the acute period is associated with the likelihood of developing DCI.

METHODS

As part of a prospective, observational cohort study, 24 male and female patients (mean age 53 years old, range 31–70 years old) were recruited. Inclusion criteria included presentation with World Federation of Neurosurgical Societies (WFNS) Grades 1 or 2 (“good grade”) aSAH on admission and endovascular treatment within 72 hours of aneurysmal rupture. DCI and DCI-related cerebral infarction were defined according to consensus guidelines. Saccadometry data were collected at 3 time points in patients: in the first 72 hours, between Days 5 and 10, and at 3 months after aSAH. Data from 10 healthy controls was collected on 1 occasion for comparison.

RESULTS

Age-adjusted saccadic latency in patients was significantly prolonged in the first 72 hours following aSAH when compared with controls (188.7 msec [95% CI 176.9–202.2 msec] vs 160.7 msec [95% CI 145.6–179.4 msec], respectively; p = 0.0054, t-test). By 3 months after aSAH, there was no significant difference in median saccadic latency compared with controls (188.7 msec [95% CI 176.9–202.2 msec] vs 180.0 msec [95% CI 165.1–197.8 msec], respectively; p = 0.4175, t-test). Patients diagnosed with cerebral infarction due to DCI had a significantly higher age-adjusted saccadic latency in the first 72 hours than those without infarction (240.6 msec [95% CI 216.7–270.3 msec] vs 204.1 msec [95% CI 190.7–219.5 msec], respectively; p = 0.0157, t-test). This difference was more pronounced during Days 5–10 following aSAH, the peak incidence for DCI (303.7 msec [95% CI 266.7–352.7 msec] vs 207.6 msec [95% CI 193.7–223.6 msec], respectively; p < 0.0001, t-test). A binary generalized linear model showed that latency in the first 72 hours was the only significant predictor of cerebral infarction (p = 0.0185).

CONCLUSIONS

This is the first study to use saccadometry to measure the saccadic latency of eye movements in patients with aSAH during the acute period following aneurysm rupture. The results showed that median saccadic latency is associated with the risk of developing cerebral infarction due to DCI and may act as a potential objective biomarker to guide the need for intensive care admission and treatment. Future studies will look to formally validate saccadic latency as a biomarker of DCI in a larger cohort and assess whether the addition of saccades improves current clinical models for predicting patients at risk.

Caffeine increases the velocity of rapid eye movements in unfatigued humans

BACKGROUND

Caffeine is a widely used dietary stimulant that can reverse the effects of fatigue on cognitive, motor and oculomotor function. However, few studies have examined the effect of caffeine on the oculomotor system when homeostasis has not been disrupted by physical fatigue. This study examined the influence of a moderate dose of caffeine on oculomotor control and visual perception in participants who were not fatigued.

METHODS

Within a placebo-controlled crossover design, 13 healthy adults ingested caffeine (5 mg·kg^-1 body mass) and were tested over 3 h. Eye movements, including saccades, smooth pursuit and optokinetic nystagmus, were measured using infrared oculography.

RESULTS

Caffeine was associated with higher peak saccade velocities (472 ± 60° s^-1) compared to placebo (455 ± 62° s^-1). Quick phases of optokinetic nystagmus were also significantly faster with caffeine, whereas pursuit eye movements were unchanged. Non-oculomotor perceptual tasks (global motion and global orientation processing) were unaffected by caffeine.

CONCLUSIONS

These results show that oculomotor control is modulated by a moderate dose of caffeine in unfatigued humans. These effects are detectable in the kinematics of rapid eye movements, whereas pursuit eye movements and visual perception are unaffected. Oculomotor functions may be sensitive to changes in central catecholamines mediated via caffeine's action as an adenosine antagonist, even when participants are not fatigued.

Plasticity of prefrontal cortex connectivity in schizophrenia in response to antisaccade practice

People with schizophrenia exhibit difficulties in cognitive control that are often attributed to deficits in prefrontal cortex (PFC) circuitry. Practice paradigms have been used to improve these PFC-mediated deficits. The neural consequences of practice on task-based PFC activation have been addressed. Effects on task-based PFC connectivity, however, are largely unknown. We recruited people with schizophrenia and controls to practice antisaccades, a measure of PFC-mediated cognitive control that is disrupted in people with schizophrenia. Subjects performed antisaccades during functional magnetic resonance imaging (fMRI) before and after eight days of antisaccade practice. A group (schizophrenia, controls) × time (pre-, post-test) repeated measures ANOVA on the results of a psychophysiological interaction (PPI) analysis was used to evaluate changes in PFC connectivity; a similar model was used to evaluate changes in antisaccade behavior. After practice, antisaccade behavior improved and PFC connectivity with insular/temporal regions (involved in bottom-up orienting processes) increased in the schizophrenia group. The level of connectivity at post-test in the schizophrenia group was similar to that seen at pre-test in controls and positively correlated with antisaccade performance. Increases in connectivity between bottom-up and top-down regions may underlie behavioral improvements in people with schizophrenia after cognitive control practice.