Microsaccades as an overt measure of covert attention shifts

Coupling of saccade plans to endogenous attention during urgent choices

The neural mechanisms that willfully direct attention to specific locations in space are closely related to those for generating targeting eye movements (saccades). However, the degree to which the voluntary deployment of attention to a location necessarily activates a corresponding saccade plan remains unclear. One problem is that attention and saccades are both automatically driven by salient sensory events; another is that the underlying processes unfold within tens of milliseconds only. Here, we use an urgent task design to resolve the evolution of a visuomotor choice on a moment-by-moment basis while independently controlling the endogenous (goal-driven) and exogenous (salience-driven) contributions to performance. Human participants saw a peripheral cue and, depending on its color, either looked at it (prosaccade) or looked at a diametrically opposite, uninformative non-cue (antisaccade). By varying the luminance of the stimuli, the exogenous contributions could be cleanly dissociated from the endogenous process guiding the choice over time. According to the measured time courses, generating a correct antisaccade requires about 30 ms more processing time than generating a correct prosaccade based on the same perceptual signal. The results indicate that saccade plans elaborated during fixation are biased toward the location where attention is endogenously deployed, but the coupling is weak and can be willfully overridden very rapidly.

Attentional shifts bias microsaccade direction but do not cause new microsaccades

Brain circuitry that controls where we look also contributes to attentional selection of visual contents outside current fixation, or content within the spatial layout of working memory. A behavioural manifestation of this contribution comes from modulations in microsaccade direction that accompany spatial attention shifts. Here, we address whether such modulations come about because attention shifts trigger new microsaccades or whether, instead, spatial attention only biases the direction of ongoing microsaccades that would have been made whether or not attention was also shifted. We utilised an internal-selective-attention task that has recently been shown to yield robust spatial microsaccade modulations and compared microsaccade rates following colour retrocues that were carefully matched for sensory input, but differed in whether they invited an attention shift or not. If attention shifts trigger new microsaccades then we would expect more microsaccades following attention-directing cues than following neutral cues. In contrast, we found no evidence for an increase in overall microsaccade rate, despite robust modulations in microsaccade direction. This implies that shifting spatial attention biases the direction of ongoing microsaccades without changing the probability of microsaccade occurrence. These findings help to explain why microsaccades and visual-spatial shifts of attention are often correlated but not obligatorily linked.

Preselection of potential target spaces based on partial information by the supplementary eye field

Before selecting a saccadic target, we often acquire partial information about the location of the forthcoming target and preselect a region of visual space even before the target becomes visible. To determine whether the supplementary eye field (SEF) represents information signifying the potential target space, we examined neuronal activity in the SEF of monkeys performing a behavioral task designed to isolate the process of visuospatial preselection under uncertainty from the process of selecting a specified location. Our data showed that the activity of SEF neurons represented information about the potential target space instructed by symbolic cues. Increased activity of visuospatially selective SEF neurons encoded the potential target space, which could be a mechanism facilitating subsequent selection of an appropriate target. Furthermore, electrical stimulation of the SEF during the preselection period disrupted subsequent target selection. These results demonstrate that the SEF contributes to the preselection of potential target spaces based on partial information.

The role of the peripheral target in stimulating eye movements

The present study investigated the role of top-down and bottom-up processes during a deceptive sports strategy called "no-look passes" and how microsaccades and small saccades modulate these processes. The first experiment examined the role of expertise in modulating the shift of covert attention with the bottom-up procedure. Results showed more saccades of greater amplitude and faster peak velocity in amateur than in expert groups. In the second experiment, the shift of covert attention between top-down and bottom-up conditions was investigated in a group of expert basketball players. Analysis showed that athletes make more microsaccades during the bottom-up condition; meanwhile, during the top-down condition, they were pushed to make more small saccades to decide where to send the ball. The findings suggested that the top-down process stimulates the eyes to move more concerning the bottom-up condition. It could be explained by the fact that during the top-down condition, athletes do not have an "eyehold" that stimulates their attention. During the top-down condition, athletes had to shift their attention to both sides before making the pass, resulting in their eyes being more "hesitant" concerning the situation in which they are peripherally stimulated.

Sense of agency at a temporally-delayed gaze-contingent display

The subjective feeling of being the author of one's actions and the subsequent consequences is referred to as a sense of agency. Such a feeling is crucial for usability in human-computer interactions, where eye movement has been adopted, yet this area has been scarcely investigated. We examined how the temporal action-feedback discrepancy affects the sense of agency concerning eye movement. Participants conducted a visual search for an array of nine Chinese characters within a temporally-delayed gaze-contingent display, blurring the peripheral view. The relative delay between each eye movement and the subsequent window movement varied from 0 to 4,000 ms. In the control condition, the window played a recorded gaze behavior. The mean authorship rating and the proportion of "self" responses in the categorical authorship report ("self," "delayed self," and "other") gradually decreased as the temporal discrepancy increased, with "other" being rarely reported, except in the control condition. These results generally mirror those of prior studies on hand actions, suggesting that sense of agency extends beyond the effector body parts to other modalities, and two different types of sense of agency that have different temporal characteristics are simultaneously operating. The mode of fixation duration shifted as the delay increased under 200-ms delays and was divided into two modes at 200-500 ms delays. The frequency of 0-1.5° saccades exhibited an increasing trend as the delay increased. These results demonstrate the influence of perceived action-effect discrepancy on action refinement and task strategy.

Inter-individual variability (but intra-individual stability) of overt versus covert rehearsal strategies in a digital Corsi task

The Corsi (block-tapping) paradigm is a classic and well-established visuospatial working memory task in humans involving internal computations (memorizing of item sequences, organizing and updating the memorandum, and recall processes), as well as both overt and covert shifts of attention to facilitate rehearsal, serving to maintain the Corsi sequences during the retention phase. Here, we introduce a novel digital version of a Corsi task in which i) the difficulty of the memorandum (using sequence lengths ranging from 3 to 8) was controlled, ii) the execution of overt and/or covert attention as well as the visuospatial working memory load during the retention phase was manipulated, and iii) shifts of attention were quantified in all experimental phases. With this, we present behavioral data that demonstrate, characterize, and classify the individual effects of overt and covert strategies used as a means of encoding and rehearsal. In a full within-subject design, we tested 28 participants who had to solve three different Corsi conditions. While in condition A neither of the two strategies were restricted, in condition B the overt and in condition C the overt as well as the covert strategies were suppressed. Analyzing Corsi span, (eye) exploration index, and pupil size (change), data clearly show a continuum between overt and covert strategies over all participants (indicating inter-individual variability). Further, all participants showed stable strategy choice (indicating intra-individual stability), meaning that the preferred strategy was maintained in all three conditions, phases, and sequence lengths of the experiment.

Saccades and Microsaccades Coupling During Free-Throw Shots in Basketball Players

We investigated the role of saccades and microsaccades when different levels of basketball players were engaged in an ecological free-throw condition. All participants made more correct than incorrect shoots, with a movement time initiation shorter in amateurs than in near-expert groups. Near-experts had more stable gaze fixation than amateurs, with higher microsaccade rate and duration and lower peak velocity. Amateurs showed higher saccade rate, peak velocity, and amplitude than near-experts. The temporal sequence of near-experts' microsaccade rate increased after the saccade peak; on the contrary, in amateurs, the saccade peak is shown after the decrement in microsaccade rates. The spatiotemporal characteristics of microsaccades and saccades may reflect an optimal sampling method by which the brain discretely acquires visual information and can differentiate between participants who use a fixation before the critical movement time and participants who move their eyes to catch more visual cues to make decisions.

Do microsaccades vary with discriminability around the visual field?

Microsaccades-tiny fixational eye movements-improve discriminability in high-acuity tasks in the foveola. To investigate whether they help compensate for low discriminability at the perifovea, we examined microsaccade characteristics relative to the adult visual performance field, which is characterized by two perceptual asymmetries: horizontal-vertical anisotropy (better discrimination along the horizontal than vertical meridian) and vertical meridian asymmetry (better discrimination along the lower than upper vertical meridian). We investigated whether and to what extent microsaccade directionality varies when stimuli are at isoeccentric locations along the cardinals under conditions of heterogeneous discriminability (Experiment 1) and homogeneous discriminability, equated by adjusting stimulus contrast (Experiment 2). Participants performed a two-alternative forced-choice orientation discrimination task. In both experiments, performance was better on trials without microsaccades between ready signal onset and stimulus offset than on trials with microsaccades. Across the trial sequence, the microsaccade rate and directional pattern were similar across locations. Our results indicate that microsaccades were similar regardless of stimulus discriminability and target location, except during the response period-once the stimuli were no longer present and target location no longer uncertain-when microsaccades were biased toward the target location. Thus, this study reveals that microsaccades do not flexibly adapt as a function of varying discriminability in a basic visual task around the visual field.

Low and high beta rhythms have different motor cortical sources and distinct roles in movement control and spatiotemporal attention

Low and high beta frequency rhythms were observed in the motor cortex, but their respective sources and behavioral correlates remain unknown. We studied local field potentials (LFPs) during pre-cued reaching behavior in macaques. They contained a low beta band (<20 Hz) dominant in primary motor cortex and a high beta band (>20 Hz) dominant in dorsal premotor cortex (PMd). Low beta correlated positively with reaction time (RT) from visual cue onset and negatively with uninstructed hand postural micro-movements throughout the trial. High beta reflected temporal task prediction, with selective modulations before and during cues, which were enhanced in moments of increased focal attention when the gaze was on the work area. This double-dissociation in sources and behavioral correlates of motor cortical low and high beta, with respect to both task-instructed and spontaneous behavior, reconciles the largely disparate roles proposed for the beta rhythm, by suggesting band-specific roles in both movement control and spatiotemporal attention.

Sense of agency at a gaze-contingent display with jittery temporal delay

Introduction

Inconsistent jittery temporal delays between action and subsequent feedback, prevalent in network-based human-computer interaction (HCI), have been insufficiently explored, particularly regarding their impact on the sense of agency (SoA). This study investigates the SoA in the context of eye-gaze HCI under jittery delay conditions.

Methods

Participants performed a visual search for Chinese characters using a biresolutional gaze-contingent display, which displayed a high-resolution image in the central vision and a low-resolution in the periphery. We manipulated the delay between eye movements and display updates using a truncated normal distribution (μ to μ + 2 σ) with μ ranging from 0 to 400 ms and σ fixed at 50 ms. Playback of recorded gaze data provided a non-controllable condition.

Results

The study revealed that both reported authorship and controllability scores, as well as the fixation count per second, decreased as μ increased, aligning with trends observed under constant delay conditions. The subjective authorship weakened significantly at a μ of 94 ms. Notably, the comparison between jittery and constant delays indicated the minimum value (μ) of the distribution as a critical parameter influencing both authorship perception and visual search time efficiency.

Discussion

This finding underscores the importance of the shortest delay in modulating SoA. Further examining the relative distribution for fixation duration and saccade amplitude suggests an adaptation in action planning and attention distribution in response to delay. By providing a systematic examination of the statistical attributes of jittery delays that most significantly affect SoA, this research offers valuable implications for the design of efficient, delay-tolerant eye-gaze HCI, expanding our understanding of SoA in technologically mediated interactions. Moreover, our findings highlight the significance of considering both constant and variable delay impacts in HCI usability design, marking a novel contribution to the field.

Jointly looking to the past and the future in visual working memory

Working memory enables us to bridge past sensory information to upcoming future behaviour. Accordingly, by its very nature, working memory is concerned with two components: the past and the future. Yet, in conventional laboratory tasks, these two components are often conflated, such as when sensory information in working memory is encoded and tested at the same location. We developed a task in which we dissociated the past (encoded location) and future (to-be-tested location) attributes of visual contents in working memory. This enabled us to independently track the utilisation of past and future memory attributes through gaze, as observed during mnemonic selection. Our results reveal the joint consideration of past and future locations. This was prevalent even at the single-trial level of individual saccades that were jointly biased to the past and future. This uncovers the rich nature of working memory representations, whereby both past and future memory attributes are retained and can be accessed together when memory contents become relevant for behaviour.

A Pilot Study to Improve Cognitive Performance and Pupil Responses in Mild Cognitive Impaired Patients Using Gaze-Controlled Gaming

Mild cognitive impairment (MCI) may progress to severe forms of dementia, so therapy is needed to maintain cognitive abilities. The neural circuitry for oculomotor control is closely linked to that which controls cognitive behavior. In this study, we tested whether training the oculomotor system with gaze-controlled video games could improve cognitive behavior in MCI patients. Patients played a simple game for 2-3 weeks while a control group played the same game using a mouse. Cognitive improvement was assessed using the MoCA screening test and CANTAB. We also measured eye pupil and vergence responses in an oddball paradigm. The results showed an increased score on the MoCA test specifically for the visuospatial domain and on the Rapid Visual Information Processing test of the CANTAB battery. Pupil responses also increased to target stimuli. Patients in the control group did not show significant improvements. This pilot study provides evidence for the potential cognitive benefits of gaze-controlled gaming in MCI patients.

Common structure of saccades and microsaccades in visual perception

We obtain large amounts of external information through our eyes, a process often considered analogous to picture mapping onto a camera lens. However, our eyes are never as still as a camera lens, with saccades occurring between fixations and microsaccades occurring within a fixation. Although saccades are agreed to be functional for information sampling in visual perception, it remains unknown if microsaccades have a similar function when eye movement is restricted. Here, we demonstrated that saccades and microsaccades share common spatiotemporal structures in viewing visual objects. Twenty-seven adults viewed faces and houses in free-viewing and fixation-controlled conditions. Both saccades and microsaccades showed distinctive spatiotemporal patterns between face and house viewing that could be discriminated by pattern classifications. The classifications based on saccades and microsaccades could also be mutually generalized. Importantly, individuals who showed more distinctive saccadic patterns between faces and houses also showed more distinctive microsaccadic patterns. Moreover, saccades and microsaccades showed a higher structure similarity for face viewing than house viewing and a common orienting preference for the eye region over the mouth region. These findings suggested a common oculomotor program that is used to optimize information sampling during visual object perception.

Visual Feature Tuning Properties of Short-Latency Stimulus-Driven Ocular Position Drift Responses during Gaze Fixation

Ocular position drifts during gaze fixation are significantly less well understood than microsaccades. We recently identified a short-latency ocular position drift response, of ∼1 min arc amplitude, that is triggered within <100 ms by visual onsets. This systematic eye movement response is feature-tuned and seems to be coordinated with a simultaneous resetting of the saccadic system by visual stimuli. However, much remains to be learned about the drift response, especially for designing better-informed neurophysiological experiments unraveling its mechanistic substrates. Here we systematically tested multiple new feature tuning properties of drift responses. Using highly precise eye tracking in three male rhesus macaque monkeys, we found that drift responses still occur for tiny foveal visual stimuli. Moreover, the responses exhibit size tuning, scaling their amplitude (both up and down) as a function of stimulus size, and they also possess a monotonically increasing contrast sensitivity curve. Importantly, short-latency drift responses still occur for small peripheral visual targets, which additionally introduce spatially directed modulations in drift trajectories toward the appearing peripheral stimuli. Drift responses also remain predominantly upward even for stimuli exclusively located in the lower visual field and even when starting gaze position is upward. When we checked the timing of drift responses, we found it was better synchronized to stimulus-induced saccadic inhibition than to stimulus onset. These results, along with a suppression of drift response amplitudes by peristimulus saccades, suggest that drift responses reflect the rapid impacts of short-latency and feature-tuned visual neural activity on final oculomotor control circuitry in the brain.

Contralateral delay activity and alpha lateralization reflect retinotopic and screen-centered reference frames in visual memory

The visual system represents objects in a lateralized manner, with contralateral cortical hemispheres responsible for left and right visual hemifields. This organization extends to visual short-term memory (VSTM), as evidenced by electrophysiological indices of VSTM maintenance: contralateral delay activity (CDA) and alpha-band lateralization. However, it remains unclear if VSTM represents object locations in gaze-centered (retinotopic) or screen-centered (spatiotopic) coordinates, especially after eye movements. In two experiments, participants encoded the colors of target objects and made a lateral saccade during the maintenance interval, thereby shifting the object's location on the retina. A non-lateralized probe stimulus was then presented at the new fixation for a change detection task. The CDA maintained lateralization towards the target's original retinotopic location, unaffected by subsequent saccades, and did not invert polarity even when a saccade brought that location into the opposite hemifield. We also found conventional alpha lateralization towards the target's location before a saccade. After a saccade, however, alpha was lateralized towards the screen center regardless of the target's original location, even in a control condition without any memory requirements. This suggests that post-saccadic alpha-band lateralization reflects attentional processes unrelated to memory, while pre- and post-saccade CDA reflect VSTM maintenance in a retinotopic reference frame.

Microsaccades reflect attention shifts: a mini review of 20 years of microsaccade research

Microsaccades are small, involuntary eye movements that occur during fixation. Since the 1950s, researchers have conducted extensive research on the role of microsaccades in visual information processing, and found that they also play an important role in human advanced visual cognitive activities. Research over the past 20 years further suggested that there is a close relationship between microsaccades and visual attention, yet lacking a timely review. The current article aims to provide a state-of-the-art review and bring microsaccades studies into the sight of attention research. We firstly introduce basic characteristics about microsaccades, then summarized the empirical evidence supporting the view that microsaccades can reflect both external (perception) and internal (working memory) attention shifts. We finally conclude and highlight three promising avenues for future research.

Dissociable components of attention exhibit distinct neuronal signatures in primate visual cortex

Attention can be deployed in multiple forms and facilitates behavior by influencing perceptual sensitivity and choice bias. Attention is also associated with a myriad of changes in sensory neural activity. Yet, the relationship between the behavioral components of attention and the accompanying changes in neural activity remains largely unresolved. We examined this relationship by quantifying sensitivity and bias in monkeys performing a task that dissociated eye movement responses from the focus of covert attention. Unexpectedly, bias, not sensitivity, increased at the focus of covert attention, whereas sensitivity increased at the location of planned eye movements. Furthermore, neuronal activity within visual area V4 varied robustly with bias, but not sensitivity, at the focus of covert attention. In contrast, correlated variability between neuronal pairs was lowest at the location of planned eye movements, and varied with sensitivity, but not bias. Thus, dissociable behavioral components of attention exhibit distinct neuronal signatures within the visual cortex.

Geometry of visuospatial working memory information in miniature gaze patterns

Stimulus-dependent eye movements have been recognized as a potential confound in decoding visual working memory information from neural signals. Here we combined eye-tracking with representational geometry analyses to uncover the information in miniature gaze patterns while participants (n = 41) were cued to maintain visual object orientations. Although participants were discouraged from breaking fixation by means of real-time feedback, small gaze shifts (<1°) robustly encoded the to-be-maintained stimulus orientation, with evidence for encoding two sequentially presented orientations at the same time. The orientation encoding on stimulus presentation was object-specific, but it changed to a more object-independent format during cued maintenance, particularly when attention had been temporarily withdrawn from the memorandum. Finally, categorical reporting biases increased after unattended storage, with indications of biased gaze geometries already emerging during the maintenance periods before behavioural reporting. These findings disclose a wealth of information in gaze patterns during visuospatial working memory and indicate systematic changes in representational format when memory contents have been unattended.

Cognitive Vergence Recorded with a Webcam-Based Eye-Tracker during an Oddball Task in an Elderly Population

(1) Background: Our previous research provides evidence that vergence eye movements may significantly influence cognitive processing and could serve as a reliable measure of cognitive issues. The rise of consumer-grade eye tracking technology, which uses sophisticated imaging techniques in the visible light spectrum to determine gaze position, is noteworthy. In our study, we explored the feasibility of using webcam-based eye tracking to monitor the vergence eye movements of patients with Mild Cognitive Impairment (MCI) during a visual oddball paradigm. (2) Methods: We simultaneously recorded eye positions using a remote infrared-based pupil eye tracker. (3) Results: Both tracking methods effectively captured vergence eye movements and demonstrated robust cognitive vergence responses, where participants exhibited larger vergence eye movement amplitudes in response to targets versus distractors. (4) Conclusions: In summary, the use of a consumer-grade webcam to record cognitive vergence shows potential. This method could lay the groundwork for future research aimed at creating an affordable screening tool for mental health care.

Oculomotor inhibition markers of working memory load

Involuntary eye movements occur constantly even during fixation and were shown to convey information about cognitive processes. They are inhibited momentarily in response to external stimuli (oculomotor inhibition, OMI), with a time and magnitude that depend on stimulus saliency, attention, and expectations. It was recently shown that the working memory load for numbers modulates the microsaccade rate; however, the generality of the effect and its temporal properties remain unclear. Our goal was to investigate the relationship between OMI and the working memory load for simple colored shapes. Participants (N = 26) maintained their fixation while their eyes were tracked; they viewed briefly flashed colored shapes accompanied by small arrows indicating the shapes to be memorized (1/2/3). After a retention period, a probe shape appeared for matching. The microsaccade rate modulation and temporal properties were analyzed for the memory encoding, maintenance, and retrieval phases. Microsaccade inhibition was stronger when more shapes were memorized, and performance improved when microsaccades were suppressed during maintenance and retrieval. This occurred even though the physical stimuli were identical in number under all conditions. Thus, oculomotor inhibition may play a role in silencing the visual input while processing current stimuli and is generally related to processing time and load.

Do microsaccades vary with discriminability around the visual field?

Microsaccades-tiny fixational eye movements- improve discriminability in high acuity tasks in the foveola. To investigate whether they help compensate for low discriminability at perifovea, we examined MS characteristics relative to the adult visual performance field, which is characterized by two perceptual asymmetries: Horizontal-Vertical Anisotropy (better discrimination along the horizontal than vertical meridian), and Vertical Meridian Asymmetry (better discrimination along the lower- than upper-vertical meridian). We investigated whether and to what extent microsaccade directionality varies when stimuli are at isoeccentric locations along the cardinals under conditions of heterogeneous discriminability (Experiment 1) and homogeneous discriminability, equated by adjusting stimulus contrast (Experiment 2). Participants performed a two-alternative forced-choice orientation discrimination task. In both experiments, performance was better on trials without microsaccades between ready signal onset and stimulus offset than on trials with microsaccades. Across the trial sequence the microsaccade rate and directional pattern were similar across locations. Our results indicate that microsaccades were similar regardless of stimulus discriminability and target location, except during the response period-once the stimuli were no longer present and target location no longer uncertain-when microsaccades were biased toward the target location. Thus, this study reveals that microsaccades do not flexibly adapt as a function of varying discriminability in a basic visual task around the visual field.

Ultra-fine resolution of pre-saccadic attention in the fovea

Microsaccades, the tiny gaze relocations that occurr during fixation, have been linked to covert attention deployed degrees away from the center of gaze. However, the link between attention and microsaccades is deeper in that it also unfolds at the foveal scale. Here, we have examined the spatial grain of pre-microsaccadic attention across the 1° foveola. Through the use of high-precision eye-tracking and gaze-contingent display system that achieves arcminute precision in gaze localization, we have shown that the spotlight of attention at this scale can reach a strikingly high resolution, in the order of 0.17°. Further, when a microsaccade occurs, vision is modulated in a peculiar way across the foveola; whereas fine spatial vision is enhanced at the microsaccade goal location, it drops at the very center of gaze, where acuity is normally highest. These results reveal the finesse of the visuomotor system and of the interplay between eye movements and attention.

Spatial and Temporal Abnormalities of Spontaneous Fixational Saccades and Their Correlates With Positive and Cognitive Symptoms in Schizophrenia

BACKGROUND AND HYPOTHESIS

Visual fixation is a dynamic process, with the spontaneous occurrence of microsaccades and macrosaccades. These fixational saccades are sensitive to the structural and functional alterations of the cortical-subcortical-cerebellar circuit. Given that dysfunctional cortical-subcortical-cerebellar circuit contributes to cognitive and behavioral impairments in schizophrenia, we hypothesized that patients with schizophrenia would exhibit abnormal fixational saccades and these abnormalities would be associated with the clinical manifestations.

STUDY DESIGN

Saccades were recorded from 140 drug-naïve patients with first-episode schizophrenia and 160 age-matched healthy controls during ten separate trials of 6-second steady fixations. Positive and negative symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). Cognition was assessed using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB).

STUDY RESULTS

Patients with schizophrenia exhibited fixational saccades more vertically than controls, which was reflected in more vertical saccades with angles around 90° and a greater vertical shift of horizontal saccades with angles around 0° in patients. The fixational saccades, especially horizontal saccades, showed longer durations, faster peak velocities, and larger amplitudes in patients. Furthermore, the greater vertical shift of horizontal saccades was associated with higher PANSS total and positive symptom scores in patients, and the longer duration of horizontal saccades was associated with lower MCCB neurocognitive composite, attention/vigilance, and speed of processing scores. Finally, based solely on these fixational eye movements, a K-nearest neighbors model classified patients with an accuracy of 85%. Conclusions: Our results reveal spatial and temporal abnormalities of fixational saccades and suggest fixational saccades as a promising biomarker for cognitive and positive symptoms and for diagnosis of schizophrenia.

Microsaccades Track Location-Based Object Rehearsal in Visual Working Memory

Besides controlling eye movements, the brain's oculomotor system has been implicated in the control of covert spatial attention and the rehearsal of spatial information in working memory. We investigated whether the oculomotor system also contributes to rehearsing visual objects in working memory when object location is never asked about. To address this, we tracked the incidental use of locations for mnemonic rehearsal via directional biases in microsaccades while participants maintained two visual objects (colored oriented gratings) in working memory. By varying the stimulus configuration (horizontal, diagonal, and vertical) at encoding, we could quantify whether microsaccades were more aligned with the configurational axis of the memory contents, as opposed to the orthogonal axis. Experiment 1 revealed that microsaccades continued to be biased along the axis of the memory content several seconds into the working memory delay. In Experiment 2, we confirmed that this directional microsaccade bias was specific to memory demands, ruling out lingering effects from passive and attentive encoding of the same visual objects in the same configurations. Thus, by studying microsaccade directions, we uncover oculomotor-driven rehearsal of visual objects in working memory through their associated locations.

No obligatory trade-off between the use of space and time for working memory

Space and time can each act as scaffolds for the individuation and selection of visual objects in working memory. Here we ask whether there is a trade-off between the use of space and time for visual working memory: whether observers will rely less on space, when memoranda can additionally be individuated through time. We tracked the use of space through directional biases in microsaccades after attention was directed to memory contents that had been encoded simultaneously or sequentially to the left and right of fixation. We found that spatial gaze biases were preserved when participants could (Experiment 1) and even when they had to (Experiment 2) additionally rely on time for object individuation. Thus, space remains a profound organizing medium for working memory even when other organizing sources are available and utilized, with no evidence for an obligatory trade-off between the use of space and time.

Visual feature tuning properties of stimulus-driven saccadic inhibition in macaque monkeys

Saccadic inhibition refers to a short-latency transient cessation of saccade generation after visual sensory transients. This oculomotor phenomenon occurs with a latency that is consistent with a rapid influence of sensory responses, such as stimulus-induced visual bursts, on oculomotor control circuitry. However, the neural mechanisms underlying saccadic inhibition are not well understood. Here, we exploited the fact that macaque monkeys experience robust saccadic inhibition to test the hypothesis that inhibition time and strength exhibit systematic visual feature tuning properties to a multitude of visual feature dimensions commonly used in vision science. We measured saccades in three monkeys actively controlling their gaze on a target, and we presented visual onset events at random times. Across seven experiments, the visual onsets tested size, spatial frequency, contrast, orientation, motion direction, and motion speed dependencies of saccadic inhibition. We also investigated how inhibition might depend on the behavioral relevance of the appearing stimuli. We found that saccadic inhibition starts earlier, and is stronger, for large stimuli of low spatial frequencies and high contrasts. Moreover, saccadic inhibition timing depends on motion direction and orientation, with earlier inhibition systematically occurring for horizontally drifting vertical gratings. On the other hand, saccadic inhibition is stronger for faster motions and when the appearing stimuli are subsequently foveated. Besides documenting a range of feature tuning dimensions of saccadic inhibition to the properties of exogenous visual stimuli, our results establish macaque monkeys as an ideal model system for unraveling the neural mechanisms underlying a ubiquitous oculomotor phenomenon in visual neuroscience.NEW & NOTEWORTHY Visual onsets dramatically reduce saccade generation likelihood with very short latencies. Such latencies suggest that stimulus-induced visual responses, normally jump-starting perceptual and scene analysis processes, can also directly impact the decision of whether to generate saccades or not, causing saccadic inhibition. Consistent with this, we found that changing the appearance of the visual onsets systematically alters the properties of saccadic inhibition. These results constrain neurally inspired models of coordination between saccade generation and exogenous sensory stimulation.

An eye for detail: Eye movements and attention at the foveal scale

Human vision relies on a tiny region of the retina, the 1-deg foveola, to achieve high spatial resolution. Foveal vision is of paramount importance in daily activities, yet its study is challenging, as eye movements incessantly displace stimuli across this region. Here I will review work that, building on recent advances in eye-tracking and gaze-contingent display, examines how attention and eye movements operate at the foveal level. This research highlights how exploration of fine spatial detail unfolds following visuomotor strategies reminiscent of those occurring at larger scales. It shows that, together with highly precise control of attention, this motor activity is linked to non-homogenous processing within the foveola and selectively modulates sensitivity both in space and time. Overall, the picture emerges of a highly dynamic foveal perception in which fine spatial vision, rather than simply being the result of placing a stimulus at the center of gaze, is the result of a finely tuned and orchestrated synergy of motor, cognitive, and attentional processes.

Effects of others' gaze and facial expression on an observer's microsaccades and their association with ADHD tendencies

BACKGROUND

The aim of this study was to examine the effect of others' gaze on an observer's microsaccades. We also aimed to conduct preliminary investigations on the relationship between the microsaccadic response to a gaze and a gazer's facial expression and attention-deficit/hyperactivity disorder (ADHD) tendencies.

METHODS

Twenty healthy undergraduate and graduate students performed a peripheral target detection task by using unpredictable gaze cues. During the task, the participants' eye movements, along with changes in pupil size and response times for target detection, were recorded. ADHD tendencies were determined using an ADHD questionnaire.

RESULTS

We found that consciously perceiving the gaze of another person induced the observer's attention; moreover, microsaccades were biased in the direction opposite to the gaze. Furthermore, these microsaccade biases were differentially modulated, based on the cognitive processing of the facial expressions of the gaze. Exploratory correlation analysis indicated that microsaccade biases toward gazes with fearful expressions may specifically be correlated with participant characteristics, including inattention.

CONCLUSIONS

Our findings support that microsaccades reflect spatial attention processing and social cognitive processing. Moreover, the exploratory correlation analysis results suggested the potential benefit of using microsaccade bias toward spatial attention to assess pathophysiological responses associated with ADHD tendencies.

Human microsaccade cueing modulation in visual- and memory-delay saccade tasks after theta burst transcranial magnetic stimulation over the frontal eye field

Microsaccades that occur during periods of fixation are modulated by various cognitive processes and have an impact on visual processing. A network of brain areas is involved in microsaccade generation, including the superior colliculus and frontal eye field (FEF) which are involved in modulating microsaccade rate and direction after the appearance of a visual cue (referred to as microsaccade cueing modulation). Although the neural mechanisms underlying microsaccade cueing modulations have been demonstrated in monkeys, limited research has investigated a causal role of these areas in humans. By applying continuous theta-burst transcranial magnetic stimulation (cTBS) over the right FEF and vertex, we investigated the role of human FEF in modulating microsaccade responses after the appearance of a visual target in a visual- and memory-delay saccade task. After target appearance, microsaccade rate was initially suppressed but then increased in both cTBS conditions. More importantly, in the visual-delay task, microsaccades after target appearance were directed to the ipsilateral side more often with FEF, compared to vertex stimulation. Moreover, microsaccades were directed towards the target location, then to the opposite location of the target in both tasks, with larger effects in the visual-, compared to, memory-delay task. This microsaccade direction modulation was delayed after FEF stimulation in the memory-delay task. Overall, some microsaccade cueing modulations were moderately disrupted after FEF cTBS, suggesting a causal role for involvement of the human FEF in microsaccade generation after presentation of salient stimuli.

Fixation offset decreases pupillary inhibition of return

Inhibition of return (IOR) is reflected as a slower manual or saccadic response to a cued rather than an uncued target (manual IOR and saccadic IOR, respectively), and as a pupillary dilation when a bright, relative to a dark side of a display is cued (pupillary IOR). The aim of this study was to investigate the relation between an IOR and oculomotor system. According to the predominant view, only the saccadic IOR is strictly related to the visuomotor process, and the manual and pupillary IORs depend on non-motor factors (e.g., short-term visual depression). Alternatively, the after-effect of the covert-orienting hypothesis postulates that IOR is strictly related to the oculomotor system. As fixation offset affects oculomotor processes, this study investigated whether fixation offset also affects pupillary and manual IORs. The results show that fixation offset decreased IOR in pupillary but not manual responses, and provides support for the hypothesis that at least the pupillary IOR is tightly linked to eye movement preparation.

Posterior Parietal Cortex Plays a Causal Role in Abstract Memory-Based Visual Categorical Decisions

Neural activity in the lateral intraparietal cortex (LIP) correlates with both sensory evaluation and motor planning underlying visuomotor decisions. We previously showed that LIP plays a causal role in visually-based perceptual and categorical decisions, and preferentially contributes to evaluating sensory stimuli over motor planning. In that study, however, monkeys reported their decisions with a saccade to a colored target associated with the correct motion category or direction. Since LIP is known to play a role in saccade planning, it remains unclear whether LIP's causal role in such decisions extend to decision-making tasks which do not involve saccades. Here, we employed reversible pharmacological inactivation of LIP neural activity while two male monkeys performed delayed match to category (DMC) and delayed match to sample (DMS) tasks. In both tasks, monkeys needed to maintain gaze fixation throughout the trial and report whether a test stimulus was a categorical match or nonmatch to the previous sample stimulus by releasing a touch bar. LIP inactivation impaired monkeys' behavioral performance in both tasks, with deficits in both accuracy and reaction time (RT). Furthermore, we recorded LIP neural activity in the DMC task targeting the same cortical locations as in the inactivation experiments. We found significant neural encoding of the sample category, which was correlated with monkeys' categorical decisions in the DMC task. Taken together, our results demonstrate that LIP plays a generalized role in visual categorical decisions independent of the task-structure and motor response modality.SIGNIFICANCE STATEMENT Neural activity in the lateral intraparietal cortex (LIP) correlates with perceptual and categorical decisions, in addition to its role in mediating saccadic eye movements. Past work found that LIP is causally involved in visual decisions that are rapidly reported by saccades in a reaction time based decision making task. Here we use reversible inactivation of LIP to test whether LIP is also causally involved in visual decisions when reported by hand movements during delayed matching tasks. Here we show that LIP inactivation impaired monkeys' task performance during both memory-based discrimination and categorization tasks. These results demonstrate that LIP plays a generalized role in visual categorical decisions independent of the task-structure and motor response modality.

Patterns of small involuntary fixation saccades (SIFSs) in different neurodegenerative diseases: the role of noise

During the attempt to steadily fixate at a single spot, sequences of small involuntary fixation saccades (SIFSs, known also as microsaccades οr intrusions) occur which form spatio-temporal patterns such as square wave jerks (SWJs), a pattern characterised by alternating centrifugal and centripetal movements of similar magnitude. In many neurodegenerative disorders, SIFSs exhibit elevated amplitudes and frequencies. Elevated SIFS amplitudes have been shown to favour the occurrence of SWJs ("SWJ coupling"). We analysed SIFSs in different subject groups comprising both healthy controls (CTR) and patients with amyotrophic lateral sclerosis (ALS) and progressive supranuclear palsy (PSP), i.e. two neurodegenerative diseases with completely different neuropathological basis and different clinical phenotypes. We show that, across these groups, the relations between SIFS amplitude and the relative frequency of SWJ-like patterns and other SIFS characteristics follow a common law. As an explanation, we propose that physiological and technical noise comprises a small, amplitude-independent component that has little effect on large SIFSs, but causes considerable deviations from the intended amplitude and direction of small ones. Therefore, in contrast to large SIFSs, successive small SIFSs have a lower chance to meet the SWJ similarity criteria. In principle, every measurement of SIFSs is affected by an amplitude-independent noise background. Therefore, the dependence of SWJ coupling on SIFS amplitude will probably be encountered in almost any group of subjects. In addition, we find a positive correlation between SIFS amplitude and frequency in ALS, but none in PSP, suggesting that the elevated amplitudes might arise at different sites in the two disorders.

Microsaccades transiently lateralise EEG alpha activity

The lateralisation of 8-12 Hz alpha activity is a canonical signature of human spatial cognition that is typically studied under strict fixation requirements. Yet, even during attempted fixation, the brain produces small involuntary eye movements known as microsaccades. Here we report how spontaneous microsaccades - made in the absence of incentives to look elsewhere - can themselves drive transient lateralisation of EEG alpha power according to microsaccade direction. This transient lateralisation of posterior alpha power occurs similarly following start and return microsaccades and is, at least for start microsaccades, driven by increased alpha power ipsilateral to microsaccade direction. This reveals new links between spontaneous microsaccades and human electrophysiological brain activity. It highlights how microsaccades are an important factor to consider in studies relating alpha activity - including spontaneous fluctuations in alpha activity - to spatial cognition, such as studies on visual attention, anticipation, and working memory.

Rhythmic attentional scanning

Sensory processing, short-term memory, and decision-making often deal with multiple items, or options, simultaneously. I review evidence suggesting that the brain handles such multiple items by "rhythmic attentional scanning (RAS)": each item is processed in a separate cycle of the theta rhythm, involving several gamma cycles, to reach an internally consistent representation in the form of a gamma-synchronized neuronal group. Within each theta cycle, items that are extended in representational space are scanned by traveling waves. Such scanning might go across small numbers of simple items linked into a chunk.

Microsaccades are directed towards the midpoint between targets in a variably cued attention task

Reliable, non-invasive biomarkers that reveal the internal state of a subject are an invaluable tool for neurological diagnoses. Small fixational eye movements, called microsaccades, are a candidate biomarker thought to reflect a subject's focus of attention (1, 2). The linkage between the direction of microsaccades and attention has mainly been demonstrated using explicit and unambiguous attentional cues. However, the natural world is seldom predictable and rarely provides unambiguous information. Thus, a useful biomarker must be robust to such changes in environmental statistics. To determine how well microsaccades reveal visual-spatial attention across behavioral contexts, we analyzed these fixational eye movements in monkeys performing a conventional change detection task. The task included two stimulus locations and variable cue validities across blocks of trials. Subjects were adept at the task, showing precise and graded modulations of visual attention for subtle target changes and performing better and faster when the cue was more reliable (3). However, over tens of thousands of microsaccades, we found no difference in microsaccade direction between cued locations when cue variability was high nor between hit and miss trials. Instead, microsaccades were made towards the midpoint of the two target locations, not towards individual targets. Our results suggest that the direction of microsaccades should be interpreted with caution and may not be a reliable measure of covert spatial attention in more complex viewing conditions.

Significance Statement

Small fixational eye movements called microsaccades are thought to "point" towards a location that is being attended in the visual periphery. This phenomenon has largely been studied using visual cues that unambiguously indicate the location of the upcoming stimulus change. Because the natural world is rarely unambiguous, we studied the relationship between microsaccade direction and spatial attention using less reliable cues. We found that monkeys' microsaccade directions in a standard visuospatial attention task did not indicate the animals' focus of attention, despite behavioral and neuronal evidence of spatial attention. Instead, microsaccades were made towards the midpoint between the target locations in both animals, suggesting a more complex relationship between microsaccades and attention in naturalistic settings.

The influence of scene tilt on saccade directions is amplitude dependent

When exploring a visual scene, humans make more saccades in the horizontal direction than any other direction. While many have shown that the horizontal saccade bias rotates in response to scene tilt, it is unclear whether this effect depends on saccade amplitude. We addressed this question by examining the effect of image tilt on the saccade direction distributions recorded during freely viewing natural scenes. Participants (n = 20) viewed scenes tilted at -30°, 0°, and 30°. Saccade distributions during free viewing rotated by an angle of 12.1° ± 6.7° (t(19) = 8.04, p < 0.001) in the direction of the image tilt. When we partitioned the saccades according to their amplitude we found that small amplitude saccades occurred most in the horizontal direction while large amplitude saccades were more oriented to the scene tilt (p < 0.001). To further study the characteristics of small saccades and how they are affected by scene tilt, we looked at the effect of image tilt on small fixational saccades made while fixating a central target amidst a larger scene and found that fixational saccade distributions did not rotate with scene tilt (-0.3° ±1.7° degrees; t(19) = -0.8, p = 0.39). These results suggest a combined effect of two reference frames in saccade generation: one egocentric reference frame that dominates for small saccades, biases them horizontally, and may be common for different tasks, and another allocentric reference frame that biases larger saccades along the orientation of an image during free viewing.

Eye movements during optic flow perception

Optic flow is an important visual cue for human perception and locomotion and naturally triggers eye movements. Here we investigate whether the perception of optic flow direction is limited or enhanced by eye movements. In Exp. 1, 23 human observers localized the focus of expansion (FOE) of an optic flow pattern; in Exp. 2, 18 observers had to detect brief visual changes at the FOE. Both tasks were completed during free viewing and fixation conditions while eye movements were recorded. Task difficulty was varied by manipulating the coherence of radial motion from the FOE (4 %-90 %). During free viewing, observers tracked the optic flow pattern with a combination of saccades and smooth eye movements. During fixation, observers nevertheless made small-scale eye movements. Despite differences in spatial scale, eye movements during free viewing and fixation were similarly directed toward the FOE (saccades) and away from the FOE (smooth tracking). Whereas FOE localization sensitivity was not affected by eye movement instructions (Exp. 1), observers' sensitivity to detect brief changes at the FOE was 27 % higher (p <.001) during free-viewing compared to fixation (Exp. 2). This performance benefit was linked to reduced saccade endpoint errors, indicating the direct beneficial impact of foveating eye movements on performance in a fine-grain perceptual task, but not during coarse perceptual localization.

Targeting displacement as an indicator of binocular fixation in normal Chinese adults

Purpose

The stability of fixation is crucial for the development of visual function. In this study, we quantify the deviation of visual target during fixational and saccadic tasks using eye-tracking technology, reflecting the control ability and characteristics of fixational displacement among healthy adults in a convenient method.

Methods

One hundred healthy participants aged between 18 and 55 years were recruited in the study. All participants underwent a complete ophthalmic assessment. The eye positions in the fixational and saccadic tasks were documented and analyzed by the Tobii eye-tracking system. Participants were grouped by age and gender. Targeting displacement (TD), defined as the average displacement between visual target and the mean of fixation points corresponding to that stimuli, was used to quantitatively observe fixational displacement in the horizontal and vertical directions.

Result

There was a strong reproducibility of TD as an indicator of fixation (ICC 0.812 to 0.891, p < 0.001). The TD in fixational task was significantly smaller than that of the saccadic task (3.884 ± 0.525 vs. 4.484 ± 0.509, p < 0.001) among normal people. Moreover, the difference of TD in the horizontal and vertical meridians was related to the nature of the task: In the fixational task, the TD in horizontal was smaller than that in the vertical (p < 0.001), whereas the TD in horizontal was larger than that in vertical in the saccadic task (p = 0.003). In the different age and gender groups: There was no significant difference between different gender and age groups in fixational task. However, during the saccadic task, males had smaller TD in the vertical direction than females (4.061 ± 0.495 vs. 4.404 ± 0.484, p = 0.002), and the average TD increased with age, mainly in the vertical direction (all p < 0.05). The fixation stability decreased significantly in the group over 50-years-old.

Conclusion

By reporting the fixational displacement of different genders and ages in fixational and saccadic tasks, as well as different longitude lines among normal people, our study might provide an objective, quantitative and convenient reference index for the evaluation of fixation stability in visual impairment diseases and aging phenomenon of visual function.

Emerging order of anomalous eye movements with progressive drowsiness

It has been widely recognized that human alertness is reflected in the eyes (e.g., when drowsiness, miosis, slow saccades, divergence, less compensatory vestibulo-ocular reflex, and less-accurate optokinetic response and smooth pursuit emerge). Previous studies that discovered these pupil/oculomotor anomalous behaviors along with lowering alertness evaluated only one or a few of them simultaneously, thus their emergence order is yet unknown. Presently, we focused on the following five pupil/oculomotor behaviors that can be evaluated under a natural stationary environment without giving external sensory stimulations: saccades, slow-phase eye movements, vergence, pupil diameter, and blinks. We demonstrate that their anomalous behaviors emerge in the following order: first: frequent saccades; second: slow saccades; third: divergence & miosis, then slow eye movement, while elongated eyelid closure duration emerges randomly in this sequence. These results provide a basis for the oculo-pupillometry-enabling objective monitoring of progressive drowsiness.

A Narrative Literature Review About the Role of Microsaccades in Sports

In many daily and sport situations, people have to simultaneously perceive and process multiple objects and scenes in a short amount of time. A wrong decision may lead to a disadvantage for a team or for a single athlete, and during daily life (i.e., driving, surgery), it could have more dangerous consequences. Considering the results of different studies, the ability to distribute visual attention depends on different levels of expertise and environment-related constraints. This article is a narrative review of the current scientific evidence in the field of eye movements in sports, focusing on the role of microsaccades in sporting task situations. Over the past 10 years, microsaccades have become one of the most increasing areas of research in visual and oculomotor studies and even in the area of sport science. Here, we review the latest findings and discuss the relationships between microsaccades and attention, perception, and action in sports.

Face familiarity revealed by fixational eye movements and fixation-related potentials in free viewing

Event-related potentials (ERPs) and the oculomotor inhibition (OMI) in response to visual transients are known to be sensitive to stimulus properties, attention, and expectation. We have recently found that the OMI is also sensitive to face familiarity. In natural vision, stimulation of the visual cortex is generated primarily by saccades, and it has been recently suggested that fixation-related potentials (FRPs) share similar components with the ERPs. Here, we investigated whether FRPs and microsaccade inhibition (OMI) in free viewing are sensitive to face familiarity. Observers freely watched a slideshow of seven unfamiliar and one familiar facial images presented randomly for 4-s periods, with multiple images per identity. We measured the occipital fixation-related N1 relative to the P1 magnitude as well as the associated fixation-triggered OMI. We found that the average N1-P1 was significantly smaller and the OMI was shorter for the familiar face, compared with any of the seven unfamiliar faces. Moreover, the P1 was suppressed across saccades for the familiar but not for the unfamiliar faces. Our results highlight the sensitivity of the occipital FRPs to stimulus properties such as face familiarity and advance our understanding of the integration process across successive saccades in natural vision.

V1-bypassing suppression leads to direction-specific microsaccade modulation in visual coding and perception

Microsaccades play a critical role in refreshing visual information and have been shown to have direction-specific influences on human perception. However, the neural mechanisms underlying such direction-specific effects remains unknown. Here, we report the emergence of direction-specific microsaccade modulation in the middle layer of V2 but not in V1: responses of V2 neurons after microsaccades moved toward their receptive fields were stronger than those when microsaccades moved away. The decreased responses from V1 to V2, which are correlated with the amplitude of microsaccades away from receptive fields, suggest topographically location-specific suppression from an oculomotor source. Consistent with directional effects in V2, microsaccades function as a guide for monkeys' behavior in a peripheral detection task; both can be explained by a dynamic neural network. Our findings suggest a V1-bypassing suppressive circuit for direction-specific microsaccade modulation in V2 and its functional influence on visual sensitivity, which highlights the optimal sampling nature of microsaccades.

Deja Vu: semantics-aware recording and replay of high-speed eye tracking and interaction data to support cognitive studies of software engineering tasks-methodology and analyses

The paper introduces a fundamental technological problem with collecting high-speed eye tracking data while studying software engineering tasks in an integrated development environment. The use of eye trackers is quickly becoming an important means to study software developers and how they comprehend source code and locate bugs. High quality eye trackers can record upwards of 120 to 300 gaze points per second. However, it is not always possible to map each of these points to a line and column position in a source code file (in the presence of scrolling and file switching) in real time at data rates over 60 gaze points per second without data loss. Unfortunately, higher data rates are more desirable as they allow for finer granularity and more accurate study analyses. To alleviate this technological problem, a novel method for eye tracking data collection is presented. Instead of performing gaze analysis in real time, all telemetry (keystrokes, mouse movements, and eye tracker output) data during a study is recorded as it happens. Sessions are then replayed at a much slower speed allowing for ample time to map gaze point positions to the appropriate file, line, and column to perform additional analysis. A description of the method and corresponding tool, Deja Vu, is presented. An evaluation of the method and tool is conducted using three different eye trackers running at four different speeds (60 Hz, 120 Hz, 150 Hz, and 300 Hz). This timing evaluation is performed in Visual Studio, Eclipse, and Atom IDEs. Results show that Deja Vu can playback 100% of the data recordings, correctly mapping the gaze to corresponding elements, making it a well-founded and suitable post processing step for future eye tracking studies in software engineering. Finally, a proof of concept replication analysis of four tasks from two previous studies is performed. Due to using the Deja Vu approach, this replication resulted in richer collected data and improved on the number of distinct syntactic categories that gaze was mapped on in the code.

Microsaccadic correlates of covert attention and crowding

Spatial crowding occurs when an object is cluttered among other objects in space and is a ubiquitous factor affecting object recognition in the peripheral visual field. Crowding is typically tested by presenting crowded stimuli at an eccentric location while having observers fixate at a point in space. However, even during fixation, our eyes are not perfectly steady but instead make small-scale eye movements (microsaccades) that have recently been suggested to be affected by shifts in attentional allocation. In the current study, we monitored microsaccadic behavior (a possible attentional correlate) to understand naturally occurring shifts in attention that occur following the presentation of a crowded stimulus. A tracking scanning laser ophthalmoscope (TSLO) was used to image the right eye of each observer during a psychophysical task. The stimuli consisted of Sloan numbers (0-9) presented briefly, either unflanked or surrounded by Sloan numbers at one of four nominal spacings. The extent of crowding was found to decrease by 26% on trials with the presence of incongruent microsaccades (proposed to suggest attentional capture). These findings complement the existing body of literature on the beneficial impact of explicit shifts of spatial attention to the location of a crowded stimulus.

Measurement of Fixational Eye Movements With the Head-Mounted Perimeter Imo

Purpose

Although visual field testing is conducted with the subject gazing at a fixation target, constant minute eye movements, called fixational eye movements, do occur during fixation. We examined dynamic changes in fixational eye movements associated with stimulus presentation during visual field testing.

Methods

We used the head-mounted perimeter imo, which is capable of measurement under binocular conditions, with the frame rate of its fixation monitoring camera improved to 300 Hz, to assess fixational eye movements in 18 healthy individuals. We measured changes in fixational eye movements during testing under monocular and binocular conditions and analyzed these changes based on the bivariate contour ellipse area (BCEA). We also assessed the changes in the horizontal and vertical microsaccade rates separately.

Results

Both the BCEA and horizontal microsaccade rates were higher at 400 to 600 msec after stimulus presentation than during stimulus presentation (P < 0.01). Additionally, the BCEA and vertical microsaccade rates were significantly lower in the binocular condition than in the monocular condition (P < 0.01 and P < 0.05, respectively). We did not observe a significant correlation between the test locations and microsaccade direction during visual field testing.

Conclusions

Fixational eye movements, especially vertical microsaccade rates, were lower in the binocular condition than in the monocular condition. Visual field testing under binocular conditions is a useful method for suppressing fixational eye movements and stabilizing the fixation during testing and may improve the reliability of the test results.

Translational Relevance

Visual field testing under binocular conditions can make the fixation more stable during the testing compared with monocular conditions.

Functional but not obligatory link between microsaccades and neural modulation by covert spatial attention

Covert spatial attention is associated with spatial modulation of neural activity as well as with directional biases in fixational eye movements known as microsaccades. We studied how these two 'fingerprints' of attention are interrelated in humans. We investigated spatial modulation of 8-12 Hz EEG alpha activity and microsaccades when attention is directed internally within the spatial layout of visual working memory. Consistent with a common origin, spatial modulations of alpha activity and microsaccades co-vary: alpha lateralisation is stronger in trials with microsaccades toward versus away from the memorised location of the to-be-attended item and occurs earlier in trials with earlier microsaccades toward this item. Critically, however, trials without attention-driven microsaccades nevertheless show clear spatial modulation of alpha activity - comparable to trials with attention-driven microsaccades. Thus, directional biases in microsaccades correlate with neural signatures of spatial attention, but they are not necessary for neural modulation by spatial attention to be manifest.

Optic Flow Speed and Retinal Stimulation Influence Microsaccades

Microsaccades are linked with extraretinal mechanisms that significantly alter spatial perception before the onset of eye movements. We sought to investigate whether microsaccadic activity is modulated by the speed of radial optic flow stimuli. Experiments were performed in the dark on 19 subjects who stood in front of a screen covering 135 × 107° of the visual field. Subjects were instructed to fixate on a central fixation point while optic flow stimuli were presented in full field, in the foveal, and in the peripheral visual field at different dot speeds (8, 11, 14, 17, and 20°/s). Fixation in the dark was used as a control stimulus. For almost all tested speeds, the stimulation of the peripheral retina evoked the highest microsaccade rate. We also found combined effects of optic flow speed and the stimulated retinal region (foveal, peripheral, and full field) for microsaccade latency. These results show that optic flow speed modulates microsaccadic activity when presented in specific retinal portions, suggesting that eye movement generation is strictly dependent on the stimulated retinal regions.

Fixation-related saccadic inhibition in free viewing in response to stimulus saliency

Microsaccades that occur during fixation were studied extensively in response to transient stimuli, showing a typical inhibition (Oculomotor Inhibition, OMI), and a later release with a latency that depends on stimulus saliency, attention, and expectations. Here, we investigated the hypothesis that in free viewing every saccade provides a new transient stimulation that should result in a stimulus-dependent OMI like a flashed presentation during fixation. Participants (N = 16) freely inspected static displays of randomly oriented Gabor texture images, with varied contrast and spatial frequency (SF) for periods of 10 s each. Eye tracking recordings were divided into epochs triggered by saccade landing (> 1 dva), and microsaccade latency relative to fixation onset was computed (msRT). We found that the msRT in free viewing was shorter for more salient stimuli (higher contrast or lower SF), as previously found for flashed stimuli. It increased with saccade size and decreased across successive saccades, but only for higher contrast, suggesting contrast-dependent repetition enhancement in free viewing. Our results indicate that visual stimulus-dependent inhibition of microsaccades also applies to free viewing. These findings are in agreement with the similarity found between event-related and fixation-related potentials and open the way for studies combining both approaches to study natural vision.

Do your eye movements reveal your performance on an IQ test? A study linking eye movements and socio-demographic information to fluid intelligence

Understanding the main factors contributing to individual differences in fluid intelligence is one of the main challenges of psychology. A vast body of research has evolved from the theoretical framework put forward by Cattell, who developed the Culture-Fair IQ Test (CFT 20-R) to assess fluid intelligence. In this work, we extend and complement the current state of research by analysing the differential and combined relationship between eye-movement patterns and socio-demographic information and the ability of a participant to correctly solve a CFT item. Our work shows that a participant’s eye movements while solving a CFT item contain discriminative information and can be used to predict whether the participant will succeed in solving the test item. Moreover, the information related to eye movements complements the information provided by socio-demographic data when it comes to success prediction. In combination, both types of information yield a significantly higher predictive performance than each information type individually. To better understand the contributions of features related to eye movements and socio-demographic information to predict a participant’s success in solving a CFT item, we employ state-of-the-art explainability techniques and show that, along with socio-demographic variables, eye-movement data. Especially the number of saccades and the mean pupil diameter, significantly increase the discriminating power. The eye-movement features are likely indicative of processing efficiency and invested mental effort. Beyond the specific contribution to research on how eye movements can serve as a means to uncover mechanisms underlying cognitive processes, the findings presented in this work pave the way for further in-depth investigations of factors predicting individual differences in fluid intelligence.

Gaze-cued shifts of attention and microsaccades are sustained for whole bodies but are transient for body parts

Gaze direction is an evolutionarily important mechanism in daily social interactions. It reflects a person’s internal cognitive state, spatial locus of interest, and predicts future actions. Studies have used static head images presented foveally and simple synthetic tasks to find that gaze orients attention and facilitates target detection at the cued location in a sustained manner. Little is known about how people’s natural gaze behavior, including eyes, head, and body movements, jointly orient covert attention, microsaccades, and facilitate performance in more ecological dynamic scenes. Participants completed a target person detection task with videos of real scenes. The videos showed people looking toward (valid cue) or away from a target (invalid cue) location. We digitally manipulated the individuals in the videos directing gaze to create three conditions: whole-intact (head and body movements), floating heads (only head movements), and headless bodies (only body movements). We assessed their impact on participants’ behavioral performance and microsaccades during the task. We show that, in isolation, an individual’s head or body orienting toward the target-person direction led to facilitation in detection that is transient in time (200 ms). In contrast, only the whole-intact condition led to sustained facilitation (500 ms). Furthermore, observers executed microsaccades more frequently towards the cued direction for valid trials, but this bias was sustained in time only with the joint presence of head and body parts. Together, the results differ from previous findings with foveally presented static heads. In more real-world scenarios and tasks, sustained attention requires the presence of the whole-intact body of the individuals dynamically directing their gaze.