Regular Saccades Research Articles

Impairment of Visual Fixation and Preparatory Saccade Control in Borderline Personality Disorder With and Without Comorbid Attention-Deficit/Hyperactivity Disorder

BackgroundBorderline personality disorder (BPD) is associated with heightened impulsivity, evidenced by increased substance abuse, self-harm, and suicide attempts. Addressing impulsivity in individuals with BPD is a therapeutic objective, but its underlying neural basis in this clinical population remains unclear, partly due to its frequent comorbidity with attention-deficit/hyperactivity disorder (ADHD). MethodsWe used a response inhibition paradigm—the interleaved pro-/antisaccade task—among adolescents diagnosed with BPD with and without comorbid ADHD (n = 25 and n = 24, respectively) during concomitant video-based eye tracking. We quantified various eye movement response parameters reflective of impulsive action during the task, including delay to fixation acquisition, fixation breaks, anticipatory saccades, and direction errors with express saccade (saccade reaction time: 90–140 ms) and regular saccade latencies (saccade reaction time > 140 ms). ResultsIndividuals with BPD exhibited deficient response preparation, as evidenced by reduced visual fixation on task cues and greater variability of saccade responses (i.e., saccade reaction time and peak velocity). The ADHD/BPD group shared these traits and made more anticipatory responses and direction errors with express saccade latencies and reduced error correction. ConclusionsSaccadic deficits in BPD and ADHD/BPD stemmed not from an inability to execute antisaccades but rather from inadequate preparation for the upcoming task set. These distinctions may arise due to abnormal signaling in cortical areas like the frontal eye fields, posterior parietal cortex, and anterior cingulate cortex. Understanding these mechanisms could provide insights into targeted interventions focusing on task set preparation to manage response inhibition deficits in BPD and ADHD/BPD.

Microsaccade rate activity during the preparation of pro- and antisaccades.

Microsaccades belong to the category of fixational micromovements and may be crucial for image stability on the retina. Eye movement paradigms typically requirefixational control, but this does not eliminate all oculomotor activity. The antisaccade task requires a planned eye movement in the direction opposite of an onset, allowing separation of planning and execution. We build on previous studies of microsaccades in the antisaccade task using a combination of fixed and mixed pro- and antisaccade blocks. We hypothesized that microsaccade rates may be reduced prior to the execution of antisaccades as compared with regular saccades (prosaccades). In two experiments, we measured microsaccades in four conditions across three trial blocks: one block each of fixed prosaccade and antisaccade trials, and a mixed block where both saccade types were randomized. We anticipated that microsaccade rates would be higher prior to antisaccades than prosaccades due to the need to preemptively suppress reflexive saccades during antisaccade generation. In Experiment 1, with monocular eye tracking, there was an interaction between the effects of saccade and block type on microsaccade rates, suggesting lower rates on antisaccade trials, but only within mixed blocks. In Experiment 2, eye tracking was binocular, revealing suppressed microsaccade rates on antisaccade trials. A cluster permutation analysis of the microsaccade rate over the course of a trial did not reveal any particular critical time for this difference in microsaccade rates. Our findings suggest that microsaccade rates reflect the degree of suppression of the oculomotor system during the antisaccade task.

An improved algorithm for saccadic intrusion qualification under air traffic control situation

Saccadic intrusions are saccadic deviations that interrupt fixations. Saccadic intrusions have the unique characteristics of regular saccades and a small amplitude and round trip, providing a foundation for accurately identifying and quantifying saccadic intrusions. However, currently, rapid and accurate identification algorithms for saccadic intrusions of air traffic controllers are lacking. This study aimed to improve Tokuda's quantification algorithm for saccadic eye movement deviation in terms of data preprocessing, saccadic eye movement identification, and saccade amplitude threshold. The eye movement data were recorded using an eye tracker at a frequency of 100 Hz and obtained from the control simulation experiment. A total of 20 participants with basic control knowledge participated in this study, and finally 54 sets of data were obtained. The analysis of eye movement data showed that the saccadic intrusion quantification value of 36 of 54 sets of data obtained by the improved algorithm was closer to the value output by the manual identification method compared with the original algorithm. The results showed that these improvements had positive effects on the algorithm.

The role of fixation disengagement and oculomotor preparation in gap saccade task is gap-duration dependent.

The influence of internal brain state on behavioral performance is well illustrated by the gap saccade task, in which saccades might be initiated with short latency (express saccade) or with long latency (regular saccade) even though the external visual condition is identical. Accumulated evidence has demonstrated that the internal brain state is different before the initiation of an express saccade than a regular saccade. However, the reported origin of the fluctuation of internal brain state is disputed among previous studies, e.g., the fixation disengagement theory versus the oculomotor preparation theory. The present study examined these two theories by analyzing the rate and direction of fixational saccades, i.e., small amplitude saccades during fixation, because they could be modulated by the internal brain state. Since fixation disengagement is not spatially tuned, it might affect the rate but not the direction of fixational saccades. In contrast, oculomotor preparation can contain spatial information for the upcoming saccade and thus affect fixational saccade direction. We found that the different spatiotemporal characteristics of fixational saccades among tasks with different gap durations reveal diverse driving force to change the internal brain state. Under short gap duration (100 ms), fixation disengagement plays a primary role in switching internal brain states. Conversely, oculomotor preparation plays a primary role under medium (200 ms) and long (400 ms) gap durations. These results suggest that both fixation disengagement and oculomotor preparation can change the internal brain state, but their relative contributions are gap-duration dependent.NEW & NOTEWORTHY While performing the gap saccade task, the role of fixation disengagement and oculomotor preparation in modulating the internal brain state is gap-duration dependent. Fixation disengagement plays a primary role when gap duration is shorter (100 ms), whereas oculomotor preparation plays a primary role when gap duration is longer (200 ms and 400 ms).

Visual selective attention and the control of tracking eye movements: a critical review.

People's eyes are directed at objects of interest with the aim of acquiring visual information. However, processing this information is constrained in capacity, requiring task-driven and salience-driven attentional mechanisms to select few among the many available objects. A wealth of behavioral and neurophysiological evidence has demonstrated that visual selection and the motor selection of saccade targets rely on shared mechanisms. This coupling supports the premotor theory of visual attention put forth more than 30 years ago, postulating visual selection as a necessary stage in motor selection. In this review, we examine to which extent the coupling of visual and motor selection observed with saccades is replicated during ocular tracking. Ocular tracking combines catch-up saccades and smooth pursuit to foveate a moving object. We find evidence that ocular tracking requires visual selection of the speed and direction of the moving target, but the position of the motion signal may not coincide with the position of the pursuit target. Further, visual and motor selection can be spatially decoupled when pursuit is initiated (open-loop pursuit). We propose that a main function of coupled visual and motor selection is to serve the coordination of catch-up saccades and pursuit eye movements. A simple race-to-threshold model is proposed to explain the variable coupling of visual selection during pursuit, catch-up and regular saccades, while generating testable predictions. We discuss pending issues, such as disentangling visual selection from preattentive visual processing and response selection, and the pinpointing of visual selection mechanisms, which have begun to be addressed in the neurophysiological literature.

Saccadic intrusion recognition intelligent algorithms based on different eye movement date classification methods

The saccadic intrusion recognition algorithm proposed by Tokuda doesn’t take into account individual differences and also, since the accuracy is not high enough, three aspects in this regard have been vastly improved. Firstly, the algorithm is tailored to deal with three types of missing data such as low confidence, not on the screen, and time missing, which improves the data fault tolerance of the algorithm. Secondly, the improved algorithm refers to the E&K algorithm, utilizing the ratio of saccade speed to overall speed. Then, the adaptive speed threshold has been determined accurately, which improves the sensitivity of the algorithm. Finally, the algorithm adds the upper limit of the amplitude for identifying regular saccades and filters out rapid retrospectives with large amplitude. A combination of all three minor improvements boosts the overall accuracy of the algorithm. In addition, the N-back task experiment provided data, which has been processed by the improved algorithm, and aided in arriving at a conclusion consistent with the previous ones. The experimental data compares the effect of the improved algorithm and DBSCAN in identifying fixation points. Furthermore, the results demonstrate the improved algorithm being significantly better than the DBSCAN algorithm in regard to sequence and sensitivity of data points.

Sensitivity of express saccades to the expected value of the target.

Express saccades, a distinct fast mode of visually guided saccades, are probably underpinned by a specific pathway that is at least partially different from the one underlying regular saccades. Whether and how this pathway deals with information on the subjective value of a saccade target is unknown. We studied the influence of varying reward expectancies and compared it with the impact of a temporal gap between the disappearance of the fixation dot and the appearance of the target on the visually guided saccades of two rhesus macaques (Macaca mulatta). We found that increasing reward expectancy increased the probability and decreased the reaction time of express saccades. The latter influence was stronger in the later parts of the reaction time distribution of express saccades, satisfactorily captured by a linear shift model of change in the saccadic reaction time distribution. Although different in strength, increasing reward expectancy and inserting a temporal gap resulted in similar effects on saccadic reaction times, suggesting that these two factors summon the same mechanism to facilitate saccadic reaction times.NEW & NOTEWORTHY Express saccades are the fastest visually driven way of shifting gaze to targets of interest. We examined whether the pathway underlying these saccades has access to information on the value of saccade targets. We found that not only regular saccades but also express saccades occur earlier in case of higher expectations of reward. Yet, the sensitivity of express saccades to reward decreases linearly when approaching the earliest possible reaction time.

Transsaccadic perception is affected by saccade landing point deviations after saccadic adaptation.

Whenever we move our eyes, some visual information obtained before a saccade is combined with the visual information obtained after a saccade. Interestingly, saccades rarely land exactly on the saccade target, which may pose a problem for transsaccadic perception as it could affect the quality of postsaccadic input. Recently, however, we showed that transsaccadic feature integration is actually unaffected by deviations of saccade landing points. Possibly, transsaccadic integration remains unaffected because the presaccadic shift of attention follows the intended saccade target and not the actual saccade landing point during regular saccades. Here, we investigated whether saccade landing point errors can in fact alter transsaccadic perception when the presaccadic shift of attention follows the saccade landing point deviation. Given that saccadic adaptation not only changes the saccade vector, but also the presaccadic shift of attention, we combined a feature report paradigm with saccadic adaptation. Observers reported the color of the saccade target, which occasionally changed slightly during a saccade to the target. This task was performed before and after saccadic adaptation. The results showed that, after adaptation, presaccadic color information became less precise and transsaccadic perception had a stronger reliance on the postsaccadic color estimate. Therefore, although previous studies have shown that transsaccadic perception is generally unaffected by saccade landing point deviations, our results reveal that this cannot be considered a general property of the visual system. When presaccadic shifts of attention follow altered saccade landing points, transsaccadic perception is affected, suggesting that transsaccadic feature perception might be dependent on visual spatial attention.

Saccadic inhibition in a guided saccade task.

The eye movement system reacts very systematically to visual transients that are presented during the planning phase of a saccade. About 50 to 70 ms after the onset of a transient, the number of saccades that are started decreases, a phenomenon that has been termed saccadic inhibition. Saccades started just before this time window are hypometric compared to regular saccades, presumably because the presentation of the transient stops them in mid-flight. Recent research investigating the properties of repeated saccades to fixed locations found that these early saccades were additionally faster than expected from the main sequence relation, suggesting that a saccadic dead time during which saccades can no longer be modified does not exist. The present study investigated the properties of saccades to random locations in a guided saccade task. As expected, early saccades starting just before the saccadic inhibition dip in frequency were hypometric. Their velocity profiles implied that these saccades were actively stopped after reaching peak velocity. However, the peak velocities of these saccades did not generally deviate from the main sequence relation. The question whether an active stop of early saccades is incompatible with the idea of a saccadic dead time is open to debate.

The influence of distractors on express saccades.

It is well known that regular target-driven saccades are affected by the presence of close and remote distractors. Distractors close to the target affect the saccade landing position (known as the global effect), while remote distractors prolong saccade latencies to the target (known as the remote-distractor effect). Little is known about whether a different population of saccades known as express saccades (saccades with very short latencies between 80 and 130 ms) is similarly affected by close and remote distractors, as these saccades are considered to be the result of advanced preparation of an oculomotor program toward the target. We designed a task in which we were able to generate a large number of express saccades, as evidenced by a separate and very early peak in the saccade-latency distribution-a distribution that was different from that of regular saccades. Our results show that irrelevant and unexpected visual input had a large effect on express saccades. We found a global and a remote-distractor effect which were similar to those seen in regular saccades. Even though our findings confirm the existence of very-short-latency saccades in humans, it is questionable whether they represent a different population of saccades, as they were equally affected by the presence of distractors as are regular saccades.

Disrupted Saccade Control in Chronic Cerebral Injury: Upper Motor Neuron-Like Disinhibition in the Ocular Motor System.

Saccades rapidly direct the line of sight to targets of interest to make use of the high acuity foveal region of the retina. These fast eye movements are instrumental for scanning visual scenes, foveating targets, and, ultimately, serve to guide manual motor control, including eye–hand coordination. Cerebral injury has long been known to impair ocular motor control. Recently, it has been suggested that alterations in control may be useful as a marker for recovery. We measured eye movement control in a saccade task in subjects with chronic middle cerebral artery stroke with both cortical and substantial basal ganglia involvement and in healthy controls. Saccade latency distributions were bimodal, with an early peak at 60 ms (anticipatory saccades) and a later peak at 250 ms (regular saccades). Although the latencies corresponding to these peaks were the same in the two groups, there were clear differences in the size of the peaks. Classifying saccade latencies relative to the saccade “go signal” into anticipatory (latencies up to 80 ms), “early” (latencies between 80 and 160 ms), and “regular” types (latencies longer than 160 ms), stroke subjects displayed a disproportionate number of anticipatory saccades, whereas control subjects produced the majority of their saccades in the regular range. We suggest that this increase in the number of anticipatory saccade events may result from a disinhibition phenomenon that manifests as an impairment in the endogenous control of ocular motor events (saccades) and interleaved fixations. These preliminary findings may help shed light on the ocular motor deficits of neurodegenerative conditions, results that may be subclinical to an examiner, but clinically significant secondary to their functional implications.

Eye tracking and EEG synchronization to analyze microsaccades during a workload task.

Electroencephalography (EEG) and eye tracking are two fields that have evolved independently to study topics such as mental workload, attention and fatigue in cognitive neuroscience. However, little research has been devoted to integrating data from these two fields. In this paper, we investigate the utility of a specific type of eye movement, microsaccades, to analyze cognitive activity. We assess mental workload using event related potentials (ERPs) correlated with microsaccades during experiments where task complexity is designed to be greater with an increase in visual degradation. We also develop a modified eye movement algorithm to identify microsaccades during tasks that permit regular saccades and blinks. We compare ERPs at microsaccade onset locked epochs to those of stimulus onset locked epochs. Our results show a clear correlation of ERP activations to both latency and activation areas. These findings provide important insights for analyzing sophisticated tasks in a non-invasive fashion.

Micro and regular saccades across the lifespan during a visual search of “Where’s Waldo” puzzles

Despite the fact that different aspects of visual-motor control mature at different rates and aging is associated with declines in both sensory and motor function, little is known about the relationship between microsaccades and either development or aging. Using a sample of 343 individuals ranging in age from 4 to 66 and a task that has been shown to elicit a high frequency of microsaccades (solving Where’s Waldo puzzles), we explored microsaccade frequency and kinematics (main sequence curves) as a function of age. Taking advantage of the large size of our dataset (183,893 saccades), we also address (a) the saccade amplitude limit at which video eye trackers are able to accurately measure microsaccades and (b) the degree and consistency of saccade kinematics at varying amplitudes and directions. Using a modification of the Engbert–Mergenthaler saccade detector, we found that even the smallest amplitude movements (0.25–0.5°) demonstrate basic saccade kinematics. With regard to development and aging, both microsaccade and regular saccade frequency exhibited a very small increase across the life span. Visual search ability, as per many other aspects of visual performance, exhibited a U-shaped function over the lifespan. Finally, both large horizontal and moderate vertical directional biases were detected for all saccade sizes.

Parietal Cortical Neuronal Activity Is Selective for Express Saccades

Saccadic eye movements are central to primate behavior and serve to move the eyes to visual objects of interest. Express saccades, unlike regular saccades, occur with very short reaction times, a behavior necessary for speeded reactions in goal-directed behavior. Previous studies have shown that introduction of a blank interval (gap) between the fixation point offset and the saccadic target onset leads to an increase in the number of express saccades and that the superior colliculus plays a crucial role in the generation of express saccades. A longstanding hypothesis asserted that express saccades are mediated largely by a subcortical circuit, circumventing extrastriate visual cortex. An alternative "posterior pathway" hypothesis proposed the involvement of posterior parietal cortex. In the present study, using a gap saccade task, we investigated the role of nonhuman primate's lateral intraparietal cortex (LIP) in generation of express saccades. We show that roughly half of recorded LIP neurons were modulated during the gap interval. Moreover, a group of neurons with persistent activity in a memory-guided saccade task enhanced their activity during express saccades relative to that during regular saccades. After reducing the target's certainty by increasing the potential target locations, neuronal activity remained in the similar level during express saccades but markedly reduced during regular saccades that correlated with the increase of saccadic reaction time in the regular saccade. Our results suggest that area LIP is directly involved in generating saccades in express mode.

Covert attention regulates saccadic reaction time by routing between different visual-oculomotor pathways

Covert attention modulates saccadic performance, e.g., the abrupt onset of a task-irrelevant visual stimulus grabs attention as measured by a decrease in saccadic reaction time (SRT). The attentional advantage bestowed by the task-irrelevant stimulus is short-lived: SRT is actually longer ~200 ms after the onset of a stimulus than it is when no stimulus appears, known as inhibition of return. The mechanism by which attention modulates saccadic reaction is not well-understood. Here, we propose two possible mechanisms: by selective routing of the visuomotor signal through different pathways (routing hypothesis) or by general modulation of the speed of visuomotor transformation (shifting hypothesis). To test them, we designed a cue gap paradigm in which a 100-ms gap was introduced between the fixation point disappearance and the target appearance to the conventional cued visual reaction time paradigm. The cue manipulated the location of covert attention, and the gap interval resulted in a bimodal distribution of SRT, with an early mode (express saccade) and a late mode (regular saccade). The routing hypothesis predicts changes in the proportion of express saccades vs. regular saccades, whereas the shifting hypothesis predicts a shift of SRT distribution. The addition of the cue had no effect on mean reaction time of express and regular saccades, but it changed the relative proportion of two modes. These results demonstrate that the covert attention modification of the mean SRT is largely attributed to selective routing between visuomotor pathways rather than general modulation of the speed of visuomotor transformation.

Deficit of inhibition motor control in untreated patients with schizophrenia: Further support from visually guided saccade paradigms

In addition to classical delusional, negative, and cognitive deficit, schizophrenia has consistently been associated with impairments in saccadic eye movements, e.g., an increased error rate in the antisaccade task. We hypothesized that a deficit in inhibitory control is a core defect in untreated patients with schizophrenia leading to impairment in different oculomotor paradigms. Ten drug-free or drug-naïve patients with schizophrenia were matched in age and gender to 11 healthy controls with no psychoactive substance use or abuse. They were explored using reflexive saccades with unpredictable targets with or without the gap procedure, predictive saccades and a fixation/distracter paradigm. Patients with schizophrenia displayed shorter latency in reflexive and predictive saccades. In the GAP condition, patients made more anticipatory saccades, fewer regular saccades, and had a shorter latency of express saccades than controls. In addition, patients had an increased error rate in the fixation/distracters task. Altogether, these results provide new evidence of reduced prefrontal inhibitory regulation of subcortical and brainstem systems involved in the control of saccades.

Human EEG Potentials before Express Saccades

Abstract Using EEG backward averaging method there were fast negative and positive potentials found before regular short latency saccades and express-saccades. These potentials can reflect different stages of presaccadic preparation which include processes of saccadic system release of central fixation, attention disengagement from the central stimulus, decision making and activation of premotor cortical and subcortical structures. There were two schemes of visual stimulus presentation used–“step” and with a 200-ms “gap”. Analysis of parameters and spatiotemporal dynamics of potentials allowed us to assume that express-saccades appear in conditions when the previously selected motor programm and prediction of the target location coincides with the real coordinates of the target. At that optimum preparation of neuronal structure and a high level of readiness and attention are necessary. Decreasing an express-saccade latency can be the result of participation of main oculomotor areas of motor and saccadic planning in express-saccades initiation, particularly by direct signal transferring from the cortex to the saccadic brainstem generator, by-passing superior colliculus. Moreover, to successfully start initiation process and generate express-saccades, release from central fixation and attention disengagement has to begin in advance.

Conditions that alter saccadic eye movement latencies and affect target choice to visual stimuli and to electrical stimulation of area V1 in the monkey

In this study, we examined procedures that alter saccadic latencies and target selection to visual stimuli and electrical stimulation of area V1 in the monkey. It has been shown that saccadic eye movement latencies to singly presented visual targets form a bimodal distribution when the fixation spot is turned off a number of milliseconds prior to the appearance of the target (the gap period); the first mode has been termed express saccades and the second regular saccades. When the termination of the fixation spot is coincident with the appearance of the target (0 ms gap), express saccades are rarely generated. We show here that a bimodal distribution of saccadic latencies can also be obtained when an array of visual stimuli is presented prior to the appearance of the visual target, provided the elements of the array overlap spatially with the visual target. The overall latency of the saccadic eye movements elicited by electrical stimulation of area V1 is significantly shortened both when a gap is introduced between the termination of the fixation spot and the stimulation and when an array is presented. However, under these conditions, the distribution of saccadic latencies is unimodal. When two visual targets are presented after the fixation spot, introducing a gap has no effect on which target is chosen. By contrast, when electrical stimulation is paired with a visual target, introducing a gap greatly increases the frequency with which the electrical stimulation site is chosen.

Blind Saccades: An Asynchrony between Seeing and Looking

Saccades may not always wait for the completion of the perceptual analysis. By taking advantage of a motion-induced illusion of position and of the spontaneous scatter of saccade latency, we showed that in normal observers, regular saccades (latency, approximately 200 ms) were accurately directed to the target, whereas at higher latencies, saccades were increasingly biased by visual motion until they reflected the perceptual illusion. We reconstructed the time course of saccadic direction coding and identified an early phase in which saccades are mostly predictive (latencies less than approximately 100 ms), followed by a phase in which saccades are guided by the target position signal (latencies approximately 100-250 ms), and a later phase associated with the buildup of mislocalization (approximately 250-450 ms). This transient dissociation between action and perception indicates that seeing and looking are based on asynchronous processes, possibly because of independent thresholds for saccades and perceptual localization. The metrics of a saccade would then reflect the evolution of cortical visual signals from a predictive state to a perceptual state, passing through an intermediate visuomotor state. If saccades occur during the visuomotor state, they escape the tricks of perception.

Effects of uncertainty and target displacement on the latency of express saccades in man

Saccadic eye movements generated in response to a gap paradigm in which the fixation light spot was extinguished 200 ms prior to presentation of the target light spot showed appreciably shorter latencies than for the overlap paradigm in which the target light spot was presented 200 ms prior to extinction of the fixation light spot. When there was unpredictability in the direction of target presentation, i.e., to the left or right of the fixation light spot, the gap paradigm evoked mainly fast regular saccades of peak latency of 155 ms with relatively few express saccades which were defined as having latencies of less than 120 ms. By contrast, when the target always appeared to the right, a substantial population of express saccades with peak latency 95 ms was now generated. There was also a change in the relationship between saccadic latency and target angular displacement which covered the range 5–35 °. With the overlap paradigm and unpredictability of target direction, the latencies of the slow regular saccades increased markedly with target angular displacement. This was not the case with the same target direction when the latency of slow regular, fast regular, and express saccades remained constant with increasing target angular displacement. This indicates for targets appearing in the same hemifield that the ocular motor system operates with shortest latency irrespective of target angular displacement.