EXPRESS: Word length and frequency effects in natural Chinese reading: Evidence for character representations in lexical identification.

Word length and frequency are two of the "big three" factors that affect eye movements in natural reading (Clifton et al., 2016). Whilst these factors have been extensively investigated, all previous studies manipulating word length have been confounded with changes in visual complexity (longer words have more letters and are more visually complex). We controlled stroke complexity across one-character (short) and two-character (long) high- and low-frequency Chinese words (to avoid complexity confounds) and recorded readers' eye movements during sentence reading. Both word length and frequency yielded strong main effects for fixation time measures. For saccadic targeting and skipping probability, word length effects, but not word frequency effects, occurred. Critically, the interaction was not significant regardless of stroke complexity, indicating that word length and frequency independently influence lexical identification and saccade target selection during Chinese reading. The results provide evidence for character level representations during Chinese word recognition in natural reading.

EXPRESS: Navigating the Mind's Eye: Understanding Gaze Shifts in Visuospatial Bootstrapping.

Visuo-spatial bootstrapping refers to the well-replicated phenomena in which serial recall in a purely verbal task is boosted by presenting digits within the familiar spatial layout of a typical telephone keypad. The visuo-spatial bootstrapping phenomena indicates that additional support comes from long-term knowledge of a fixed spatial pattern, and prior experimentation supports the idea that access to this benefit depends on the availability of the visuo-spatial motor system (e.g., Allen et al., 2015). We investigate this by tracking participants' eye movements during encoding and retention of verbal lists to learn whether gaze patterns support verbal memory differently when verbal information is presented in the familiar visual layout. Participants' gaze was recorded during attempts to recall lists of seven digits in three formats: centre of the screen, typical telephone keypad, or a spatially identical layout with randomized number placement. Performance was better with the typical than with the novel layout. Our data show that eye movements differ when encoding and retaining verbal information that has a familiar layout compared with the same verbal information presented in a novel layout, suggesting recruitment of different spatial rehearsal strategies. However, no clear link between gaze pattern and recall accuracy was observed, which suggests that gazes play a limited role in retention, at best.

Evaluation of motor capacity and neuromotor control for tapping and sliding movements reveals differences in visuomotor control.

The Fitts' task is a simple and effective method for evaluating motor capacity that can be used to reveal detailed aspects of visuomotor control when hand and eye kinematics are recorded simultaneously. With advances in technology, the classical Fitts' reciprocal tapping task was modified for use with digitizer tablets and computer screens that require sliding rather than tapping hand movements, which may rely on different visuomotor control strategies. Given the ubiquity of digital devices and touchscreens that often require execution of sliding movements, it is important to compare the underlying visuomotor control and eye-hand coordination involved in reciprocal sliding and tapping movements, which was the aim of the current study. Twelve young adults performed both tasks while their hand and eye movements were recorded. Results revealed motor capacity was significantly higher (p < 0.0001, d = 2.67) in the tapping task (19.62 ± 5.89 bits/s) compared to the sliding task (7.87 ± 2.02 bits/s). Examining hand kinematics showed the deceleration interval was significantly longer in the sliding compared to the tapping task at the lowest task difficulty (ID 2.28: 0.160 s ± 0.026 vs 0.129 s ± 0.017; p < 0.01), which was exacerbated as task difficulty increased (ID 6.97: 0.355 s ± 0.059 vs 0.226 s ± 0.020, p < 0.0001), indicating greater reliance on visual feedback during the sliding task. Examining temporal eye-hand coordination pattern showed that hand movement initiation tended to precede eye movement in both tasks. Overall, the results of this study provide a comprehensive examination of eye and hand kinematics demonstrating salient differences in visuomotor control between tapping and sliding movements. The findings also reveal a novel insight into the temporal pattern of eye-hand coordination for reciprocal tapping and sliding movements, which is in contrast to previous studies that examined discrete (rather than reciprocal) target-directed pointing movements where the eyes typically precede the hand by approximately 100 ms. In conclusion, the current study revealed substantial differences between the two tasks, one major finding being the sliding movements were performed slower compared to parabolic tapping hand movements, which may have implications for designing interactive digital devices and assessment of eye-hand coordination.

Kinematically distinct saccades are used in a context-dependent manner by larval zebrafish.

Saccades are rapid eye movements that are used by all species with good vision. In this study, we set out to characterize the complete repertoire of larval zebrafish horizontal saccades to gain insight into their contributions to visually guided behavior and underlying neural control. We identified five saccade types, defined by systematic differences in kinematics and binocular coordination, which were differentially expressed across a variety of behavioral contexts. Conjugate saccades formed a large group that serves at least four functions. These include fast phases of the optokinetic nystagmus, visual scanning in stationary animals, and shifting gaze in coordination with body turns. In addition, we discovered a previously undescribed pattern of eye-body coordination in which small conjugate saccades partially oppose head rotation to maintain gaze during forward locomotion. Convergent saccades were coordinated with body movements to foveate prey targets during hunting. Detailed kinematic analysis showed that conjugate and convergent saccades differed in the millisecond coordination of the eyes and body and followed distinct velocity main sequence relationships. This challenges the prevailing view that all horizontal saccades are controlled by a common brainstem circuit and instead indicates saccade-type-specific neural control.

Future movement plans interact in sequential arm movements.

Real-world actions often comprise a series of movements that cannot be entirely planned before initiation. When these actions are executed rapidly, the planning of multiple future movements needs to occur simultaneously with the ongoing action. How the brain solves this task remains unknown. Here, we address this question with a new sequential arm reaching paradigm that manipulates how many future reaches are available for planning while controlling execution of the ongoing reach. We show that participants plan at least two future reaches simultaneously with an ongoing reach. Further, the planning processes of the two future reaches are not independent of one another. Evidence that the planning processes interact is twofold. First, correcting for a visual perturbation of the ongoing reach target is slower when more future reaches are planned. Second, the curvature of the current reach is modified based on the next reach only when their planning processes temporally overlap. These interactions between future planning processes may enable smooth production of sequential actions by linking individual segments of a long sequence at the level of motor planning.

Writing direction influences the spatial representations of past- and future-tense forms: Evidence from eye tracking.

The present study tests the hypothesis that the directionality of reading habits (left-to-right or right-to-left) impacts individuals' representation of nonspatial events. Using the blank screen paradigm, we examine whether eye movements reflect culture-specific spatial biases in processing temporal information, specifically, grammatical tense in Russian and Hebrew. Sixty-two native speakers of Russian (a language with a left-to-right reading and writing system) and 62 native speakers of Hebrew (a language with a right-to-left reading and writing system) listened to verbs in the past or future tense while their spontaneous gaze positions were recorded. Following the verb, a visual spatial probe appeared in one of the five locations of the screen, and participants responded manually to indicate its position. While participants' response latencies to the spatial probe revealed no significant effects, their gaze positions along the horizontal axis for past- and future-tensed verbs aligned with the reading and writing direction in their language. These results provide novel evidence that eye movements during auditory processing of grammatical tense are influenced by culturally specific reading and writing conventions, shifting leftward or rightward on the horizontal plane depending on the stimuli's time reference (past or future) and the participants' language (Russian or Hebrew). This spatial bias indicates a common underlying cognitive mechanism that uses spatial dimensions to represent temporal constructs.

Corrigendum: Childhood cerebral visual impairment subtype classification based on an extensive versus a limited test battery.

[This corrects the article DOI: 10.3389/fnins.2023.1266201.].

Reaching into the future.

When carrying out a sequence of movements, humans can plan several steps in advance to make the movement smooth.

Effects of lorazepam on saccadic eye movements - evidence from prosaccade and free viewing tasks.

RATIONALE: Peak velocities of saccadic eye movements are reduced after benzodiazepine administration. Even though this is an established effect, past research has only examined it in horizontal prosaccade tasks. OBJECTIVES: The spectrum of saccadic eye movements, however, is much larger. Therefore, we aimed to make a first attempt at filling this research gap by testing benzodiazepine effects on saccades under different experimental task conditions. METHODS: 1 mg lorazepam or placebo was administered (within-subjects, double-blind, in randomised order) to n = 30 healthy adults. Participants performed an extended version of the prosaccade task, including vertical saccade directions and different stimulus eccentricities, as well as a free viewing task. RESULTS: Results from the prosaccade task confirmed established effects of benzodiazepines as well as saccade direction on saccadic parameters but additionally showed that the drug effect on peak velocity was independent of saccade direction. Remarkably, in the free viewing task peak velocities as well as other saccade parameters were unaffected by lorazepam. Furthermore, exploration patterns during free viewing did not change under lorazepam. CONCLUSIONS: Overall, our findings further consolidate the peak velocity of prosaccades as a biomarker of sedation. Additionally, we suggest that sedative effects of low doses of benzodiazepines may be compensated in tasks that more closely resemble natural eye movement behaviour, possibly due to the lack of time constraints or via neurophysiological processes related to volition.

Automated visual acuity estimation by optokinetic nystagmus using a stepped sweep stimulus.

PURPOSE: To describe an automatic system for objective measurement of visual acuity (VA) using optokinetic nystagmus (OKN). This pilot study tested the system's sensitivity and specificity for detecting reduced VA in healthy adults by comparing VA-OKN to VA with an Early Treatment of Diabetic Retinopathy Study (ETDRS) chart (VA-ETDRS). METHODS: Adult participants (age 30 ± 12 years) with either reduced VA (n = 11, VA-ETDRS > 0.20 logMAR) or normal VA (n = 12, VA-ETDRS ≤ 0.20 logMAR) completed monocular VA-OKN measurements in each eye. The VA-OKN stimulus was an array of drifting (5°/s) vanishing discs presented in descending/ascending size order (0.00-1.00 logMAR in 0.10 steps). The stimulus was stepped every 2 s, and 10 sweeps were shown per eye (five ascending and five descending). Eye-tracking data determined when OKN activity ceased (descending sweep) or began (ascending sweep), which was used to determine VA-OKN for each sweep. The estimates were averaged across sweeps to produce an automated VA-OKN. The automated sweeps were then provided in randomised order to a reviewer blinded to the VA-ETDRS findings who determined a final VA-OKN for an eye. RESULTS: A single randomly selected eye from each observer was used for analysis. The sensitivity and specificity of VA-OKN using the same 0.20 logMAR threshold as VA-ETDRS was 100%. Comparisons between the VA-OKN and VA-ETDRS measures were made for participants in the reduced VA group. There was no significant difference between VA-OKN and VA-ETDRS (p = 0.55) and the two measures produced comparable values (r2 = 0.84, 95% limits of agreement = 0.19 logMAR, intra-class correlation coefficient = 0.90 [95% CI:0.68-0.97]). CONCLUSIONS: Visual acuity using optokinetic nystagmus correctly identified a VA deficit in adults and for those with a VA deficit, VA-OKN was strongly correlated with the gold-standard clinical measure of VA. OKN is a promising method which has the potential for use in cognitively impaired adults and pre-verbal children.

Direct lexical control of eye movements in Chinese reading: Evidence from the co-registration of EEG and eye tracking.

The direct-lexical-control hypothesis stipulates that some aspect of a word's processing determines the duration of the fixation on that word and/or the next. Although the direct lexical control is incorporated into most current models of eye-movement control in reading, the precise implementation varies and the assumptions of the hypothesis may not be feasible given that lexical processing must occur rapidly enough to influence fixation durations. Conclusive empirical evidence supporting this hypothesis is therefore lacking. In this article, we report the results of an eye-tracking experiment using the boundary paradigm in which native speakers of Chinese read sentences in which target words were either high- or low-frequency and preceded by a valid or invalid preview. Eye movements were co-registered with electroencephalography, allowing standard analyses of eye-movement measures, divergence point analyses of fixation-duration distributions, and fixated-related potentials on the target words. These analyses collectively provide strong behavioral and neural evidence of early lexical processing and thus strong support for the direct-lexical-control hypothesis. We discuss the implications of the findings for our understanding of how the hypothesis might be implemented, the neural systems that support skilled reading, and the nature of eye-movement control in the reading of Chinese versus alphabetic scripts.

Oculometric biomarkers of visuomotor deficits in clinically asymptomatic patients with systemic lupus erythematosus undergoing long-term hydroxychloroquine treatment.

Introduction: This study examines a set of oculomotor measurements, or "oculometric" biomarkers, as potential early indicators of visual and visuomotor deficits due to retinal toxicity in asymptomatic Systemic Lupus Erythematosus (SLE) patients on long-term hydroxychloroquine (HCQ) treatment. The aim is to identify subclinical functional impairments that are otherwise undetectable by standard clinical tests and to link them to structural retinal changes. Methods: We measured oculomotor responses in a cohort of SLE patients on chronic HCQ therapy using a previously established behavioral task and analysis technique. We also examined the relationship between oculometrics, OCT measures of retinal thickness, and standard clinical perimetry measures of visual function in our patient group using Bivariate Pearson Correlation and a Linear Mixed-Effects Model (LMM). Results: Significant visual and visuomotor deficits were found in 12 asymptomatic SLE patients on long-term HCQ therapy compared to a cohort of 17 age-matched healthy controls. Notably, six oculometrics were significantly different. The median initial pursuit acceleration was 22%, steady-state pursuit gain 16%, proportion smooth 7%, and target speed responsiveness 31% lower, while catch-up saccade amplitude was 46% and fixation error 46% larger. Excluding the two patients with diagnosed mild toxicity, four oculometrics, all but fixation error and proportion smooth, remained significantly impaired compared to controls. Across our population of 12 patients (24 retinae), we found that pursuit latency, initial acceleration, steady-state gain, and fixation error were linearly related to retinal thickness even when age was accounted for, while standard measures of clinical function (Mean Deviation and Pattern Standard Deviation) were not. Discussion: Our data show that specific oculometrics are sensitive early biomarkers of functional deficits in SLE patients on HCQ that could be harnessed to assist in the early detection of HCQ-induced retinal toxicity and other visual pathologies, potentially providing early diagnostic value beyond standard visual field and OCT evaluations.

A tutorial: Analyzing eye and head movements in virtual reality.

This tutorial provides instruction on how to use the eye tracking technology built into virtual reality (VR) headsets, emphasizing the analysis of head and eye movement data when an observer is situated in the center of an omnidirectional environment. We begin with a brief description of how VR eye movement research differs from previous forms of eye movement research, as well as identifying some outstanding gaps in the current literature. We then introduce the basic methodology used to collect VR eye movement data both in general and with regard to the specific data that we collected to illustrate different analytical approaches. We continue with an introduction of the foundational ideas regarding data analysis in VR, including frames of reference, how to map eye and head position, and event detection. In the next part, we introduce core head and eye data analyses focusing on determining where the head and eyes are directed. We then expand on what has been presented, introducing several novel spatial, spatio-temporal, and temporal head-eye data analysis techniques. We conclude with a reflection on what has been presented, and how the techniques introduced in this tutorial provide the scaffolding for extensions to more complex and dynamic VR environments.

Rapid Eye Movements during REM Sleep Differentiate PSP from Parkinson's Disease.

BACKGROUND: Little is known about the characteristics and occurrence frequencies of rapid eye movements (REMs) during REM sleep in movement disorders. OBJECTIVES: The aim of this study was to detect and characterize REMs during polysomnographically defined REM sleep as recorded by electro-oculography (EOG) in 12 patients with progressive supranuclear palsy (PSP), 13 patients with Parkinson's disease (PD) and 12 healthy controls. METHODS: Using a modified EOG montage, we developed an algorithm that automatically detects and characterizes REMs during REM sleep based on their presumptive saccadic kinematics. RESULTS: Compared to PD and healthy controls, REM densities and REM peak velocities were significantly reduced in PSP. These effects were most pronounced in vertical REMs. CONCLUSION: Ocular motor dysfunction, one of the cardinal features of PSP, seems to be equally at play during REM sleep and wakefulness. For future studies, we provide a novel tool for the unbiased analysis of REMs during REM sleep in movement disorders.

Quantitative patterns of visual impairment and recovery in children with brain injury.

Brain injury can cause many distinct types of visual impairment in children, but these deficits are difficult to quantify due to co-morbid deficits in communication and cognition. Clinicians must instead rely on low-resolution, subjective judgements of simple reactions to handheld stimuli, which limits treatment potential. We have developed an interactive assessment program called the Visual Ladder, which uses gaze-based responses to intuitive, game-like tasks to address the lack of broad-spectrum quantified data on the visual abilities of children with brain injury. Here, we present detailed metrics on eye movements, field asymmetries, contrast sensitivity, and other critical visual abilities measured longitudinally using the Ladder in hospitalized children with varying types and degrees of brain injury, many of whom were previously considered untestable. Our findings show which abilities are most likely to exhibit recovery and reveal how distinct patterns of task outcomes defined unique diagnostic clusters of visual impairment.

Openness to experience predicts eye movement behavior during scene viewing.

Individuals' abilities to perform goal-directed spatial deployments of attention are distinguishable from their broader preferences for how they use spatial attention when circumstances do not compel a specific deployment strategy. Although these preferences are likely to play a major role in how we interact with the visual world during daily life, they remain relatively understudied. This exploratory study investigated two key questions about these preferences: firstly, are individuals consistent in their preferences for how they deploy their spatial attention when making shifts of attention versus adopting an attentional breadth? Secondly, which other factors are associated with these preferences? Across two experiments, we measured how participants preferred to deploy both attentional breadth (using an adapted Navon task) and eye movements (using a free-viewing task). We also measured participants' working memory capacities (Experiment 1), and their personalities and world beliefs (Experiment 2). In both experiments, there were consistent individual differences in preference for attentional breadth and eye movement characteristics, but these two kinds of preference were unrelated to each other. Working memory capacity was not linked to these preferences. Conversely, the personality trait of Openness to Experience robustly predicted two aspects of eye movement behavior preference, such that higher levels of Openness predicted smaller saccades and shorter scan paths. This suggests that personality dimensions may predict preferences for more absorbed engagement with visual information. However, it appears that individuals' preferences for shifts of attention during scene viewing do not necessarily relate to the breadth of attention they choose to adopt.

The role of morphology in novel word learning: a registered report.

The majority of the new words that we learn every day as adults are morphologically complex; yet, we do not know much about the role of morphology in novel word learning. In this study, we tackle this issue by comparing the learning of: (i) suffixed novel words (e.g. flibness); (ii) novel words that end in non-morphological, but frequent letter chunks (e.g. fliban); and (iii) novel words with non-morphological, low-frequency endings (e.g. flibov). Words are learned incidentally through sentence reading, while the participants' eye movements are monitored. We show that morphology has a facilitatory role compared with the other two types of novel words, both during learning and in a post-learning recognition memory task. We also showed that participants attributed meaning to word parts (if flibness is a state of happiness, then flib must mean happy), but this process was not specifically triggered by the presence of a suffix (flib must also mean happy in fliban and flibov), thus suggesting that the brain tends to assume similar meanings for similar words and word parts.

Eye-Movement Suppression in the Visual World Paradigm.

Eye movements in the visual world paradigm are known to depend not only on linguistic input but on such factors as task, pragmatic context, affordances, etc. However, the degree to which eye movements may depend on task rather than on linguistic input is unclear. The present study for the first time tests how task constraints modulate eye movement behavior in the visual world paradigm by probing whether participants could refrain from looking at the referred image. Across two experiments with and without comprehension questions (total N = 159), we found that when participants were instructed to avoid looking at the referred images, the probability of fixating these reduced from 58% to 18% while comprehension scores remained high. Although language-mediated eye movements could not be suppressed fully, the degree of possible decoupling of eye movements from language processing suggests that participants can withdraw at least some looks from the referred images when needed. If they do so to different degrees in different experimental conditions, comparisons between conditions might be compromised. We discuss some cases where participants could adopt different viewing behaviors depending on the experimental condition, and provide some tentative ways to test for such differences.

Oculomotor Behaviour in Individuals with Long COVID-19.

OBJECTIVE: To determine, the impact of long COVID-19 on oculomotor behaviour. DESIGN: A case-control study. SETTING: Spanish Association of Persistent COVID. PARTICIPANT: Participants were 75 cases (64 women, 11 men, mean age 46.4 years ±8.9) and 42 controls (22 women, 20 men, mean age 53.5 years ±13.13). INTERVENTION: An eye-tracking test based on visual search paradigm and the Adult Developmental Eye Movement Test were used to evaluate the participants. MAIN MEASURES: The primary outcomes in the Adult Developmental Eye Movement Test were horizontal reading time, vertical reading time, and their ratio. And for the eye-tracking test the time to find the target, the duration, and the number of eye fixations. RESULTS: In cases and controls, eye movement test results were horizontal(Hadj) reading time 74.2 ± 22.7 s vs 52.0 ± 6.1 s (p < .0001); vertical(Vadj) reading time 67.6 ± 17.8 s vs 50.4 ± 6.9 s (p < .0001); Hadj/Vadj ratio 0.9 ± 0.1 vs 1.0 ± 0 (p = .0032), respectively; and eye-tracking test results were fixation number 11.3 ± 3.07 vs 3.51 ± 2.57 (p < .0001); fixation duration 2.01 ± 0.79 s vs 1.5 ± 0.4 s (p = .0013), and time to find target 24.5 ± 8.0 vs 18 ± 9.4 (p = .0034), respectively. CONCLUSIONS: Data showed a lower performance in oculomotor behaviour in people with long COVID-19, compared to healthy individuals. It cannot be affirmed an ocular musculature dysfunction; the differentiated behaviour could be associated to cognitive alterations affected in these people. Both tests used could be an useful tool for the clinical assessment of these participants. Further studies are needed to explore the utility of these procedures.