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Richard J Krauzlis - One of the best experts on this subject based on the ideXlab platform.
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A Neural Mechanism for Microsaccade Generation in the
2016Co-Authors: Primate Superior Colliculus, Ziad M Hafed, Laurent Goffart, Richard J KrauzlisAbstract:During fixation, the eyes are not still but often exhibit microsaccadic movements. The function of Microsaccades is controversial, largely because the neural mechanisms responsible for their generation are unknown. Here, we show that the superior colliculus (SC), a retinotopically organized structure involved in voluntary-saccade target selection, plays a causal role in Microsaccade generation. Neurons in the foveal portion of the SC increase their activity before and during Microsaccades with sizes of only a few minutes of arc and exhibit selectivity for the direction and amplitude of these movements. Reversible inactivation of these neurons significantly reduces Microsaccade rate without otherwise compromising fixation. These results, coupled with computational modeling of SC activity, demonstrate that Microsaccades are controlled by the SC and explain the link between Microsaccades and visual attention. Microsaccades are the very small (typi-cally <12 min arc), involuntary, fasteye movements that occur during fixation (1–3). The behavioral properties and functional role of Microsaccades have been extensively studied, and sometimes vigorously debated, for many years (1–14). However, th
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superior colliculus inactivation alters the relationship between covert visual attention and Microsaccades
European Journal of Neuroscience, 2013Co-Authors: Ziad M Hafed, Richard J Krauzlis, Lee P. LovejoyAbstract:Microsaccades are tiny saccades that occur during gaze fixation. Whereas these movements have traditionally been viewed as random, it was recently discovered that Microsaccade directions can be significantly biased by covertly attended visual stimuli. The detailed mechanisms mediating such a bias are neither known nor immediately obvious, especially because the amplitudes of the movements influenced by attentional cueing could be up to two orders of magnitude smaller than the eccentricity of the attended location. Here, we tested whether activity in the peripheral superior colliculus (SC) is necessary for this correlation between attentional cueing and Microsaccades. We reversibly and focally inactivated SC neurons representing peripheral regions of visual space while rhesus monkeys performed a demanding covert visual attention task. The normal bias of Microsaccade directions observed in each monkey before SC inactivation was eliminated when a cue was placed in the visual region affected by the inactivation; Microsaccades were, instead, biased away from the affected visual space. When the cue was placed at another location unaffected by SC inactivation, the baseline cue-induced bias of Microsaccade directions remained mostly intact, because the cue was in unaffected visual space, and any remaining changes were again explained by a repulsion of Microsaccades away from the inactivated region. Our results indicate that peripheral SC activity is required for the link between Microsaccades and the cueing of covert visual attention, and that it could do so by altering the probability of triggering Microsaccades without necessarily affecting the motor generation of these movements.
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similarity of superior colliculus involvement in Microsaccade and saccade generation
Journal of Neurophysiology, 2012Co-Authors: Ziad M Hafed, Richard J KrauzlisAbstract:The characteristics of Microsaccades, or small fixational saccades, and their influence on visual function have been studied extensively. However, the detailed mechanisms for generating these movements are less understood. We recently found that the superior colliculus (SC), a midbrain structure involved in saccade generation, also plays a role in Microsaccade generation. Here we compared the dynamics of neuronal activity in the SC associated with Microsaccades to those observed in this structure in association with larger voluntary saccades. We found that Microsaccade-related activity in the SC is characterized by a gradual increase in firing rate starting ∼100 ms prior to Microsaccade onset, a peak of neuronal discharge just after movement onset, and a subsequent gradual decrease in firing rate until ∼100 ms after movement onset. These properties were shared with saccade-related SC neurons, recorded from the same monkeys but preferring larger eye movements, suggesting that at the level of the SC the neuronal control of Microsaccades is similar to that for larger voluntary saccades. We also found that neurons exhibiting Microsaccade-related activity often also exhibited saccade-related activity for slightly larger movements of similar direction, suggesting a continuity of the spatial representation in the SC, in both amplitude and direction, down to the smallest movements. Our results indicate that the mechanisms controlling Microsaccades may be fundamentally the same as those for larger saccades, and thus shed new light on the functional role of these eye movements and their possible influence on sensory and sensory-motor processes.
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Modulation of Microsaccades in Monkey during a Covert Visual Attention Task
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2011Co-Authors: Ziad M Hafed, Lee P. Lovejoy, Richard J KrauzlisAbstract:The use of awake, fixating monkeys in neuroscience has allowed significant advances in understanding numerous brain functions. However, fixation is an active process, with the occurrence of incessant eye movements, including rapid ones called Microsaccades. Even though Microsaccades have been shown to be modulated by stimulus and cognitive processes in humans, it is not known to what extent these results are similar in monkeys or why they occur. Here, we analyzed the stimulus-, context-, and attention-related changes in Microsaccades while monkeys performed a challenging visual attention task. The distributions of Microsaccade times were highly stereotypical across thousands of trials in the task. Moreover, in epochs of the task in which animals anticipated the occurrence of brief stimulus probes, Microsaccade frequency decreased to a rate of less than one movement per second even on long multisecond trials. These effects were explained by the observation that Microsaccades occurring at the times of the brief probes were sometimes associated with reduced perceptual performance. Microsaccade directions also exhibited temporal modulations related to the attentional demands of the task, like earlier studies in humans, and were more likely to be directed toward an attended location on successfully performed trials than on unsuccessfully completed ones. Our results show that Microsaccades in nonhuman primates are correlated with the allocation of stimulus-evoked and sustained covert attention. We hypothesize that involvement of the superior colliculus in Microsaccade generation and attentional allocation contributes to these observations. More importantly, our results clarify the potential role of these eye movements in modifying behavior and neural activity.
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microsaccadic suppression of visual bursts in the primate superior colliculus
The Journal of Neuroscience, 2010Co-Authors: Ziad M Hafed, Richard J KrauzlisAbstract:Saccadic suppression, a behavioral phenomenon in which perceptual thresholds are elevated before, during, and after saccadic eye movements, is an important mechanism for maintaining perceptual stability. However, even during fixation, the eyes never remain still, but undergo movements including Microsaccades, drift, and tremor. The neural mechanisms for mediating perceptual stability in the face of these “fixational” movements are not fully understood. Here, we investigated one component of such mechanisms: a neural correlate of microsaccadic suppression. We measured the size of short-latency, stimulus-induced visual bursts in superior colliculus neurons of adult, male rhesus macaques. We found that Microsaccades caused ∼30% suppression of the bursts. Suppression started ∼70 ms before Microsaccade onset and ended ∼70 ms after Microsaccade end, a time course similar to behavioral measures of this phenomenon in humans. We also identified a new behavioral effect of microsaccadic suppression on saccadic reaction times, even for continuously presented, suprathreshold visual stimuli. These results provide evidence that the superior colliculus is part of the mechanism for suppressing self-generated visual signals during Microsaccades that might otherwise disrupt perceptual stability.
Stephen L Macknik - One of the best experts on this subject based on the ideXlab platform.
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Changes in visibility as a function of spatial frequency and Microsaccade occurrence.
The European journal of neuroscience, 2017Co-Authors: Francisco M. Costela, Stephen L Macknik, Michael B. Mccamy, Mary Coffelt, Jorge Otero-millan, Susana Martinez-condeAbstract:Fixational eye movements (FEMs), including Microsaccades, drift, and tremor, shift our eye position during ocular fixation, producing retinal motion that is thought to help visibility by counteracting neural adaptation to unchanging stimulation. Yet, how each FEM type influences this process is still debated. Recent studies found little to no relationship between Microsaccades and visual perception of spatial frequencies (SF). However, these conclusions were based on coarse analyses that make it hard to appreciate the actual effects of Microsaccades on target visibility as a function of SF. Thus, how Microsaccades contribute to the visibility of stimuli of different SFs remains unclear. Here, we asked how the visibility of targets of various SFs changed over time, in relationship with concurrent Microsaccade production. Participants continuously reported on changes in target visibility, allowing us to time-lock ongoing changes in Microsaccade parameters to perceptual transitions in visibility. Microsaccades restored/increased the visibility of low SF targets more efficiently than that of high SF targets. Yet, Microsaccade rates rose before periods of increased visibility, and dropped before periods of diminished visibility, for all the SFs tested, suggesting that Microsaccades boosted target visibility across a wide range of SFs. Our data also indicate that visual stimuli fade/become harder to see less often in the presence of Microsaccades. In addition, larger Microsaccades restored/increased target visibility more effectively than smaller Microsaccades. These combined results support the proposal that Microsaccades enhance visibility across a broad variety of SFs.
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Unsupervised clustering method to detect Microsaccades.
Journal of vision, 2014Co-Authors: Jorge Otero-millan, Stephen L Macknik, José Luis Alba Castro, Susana Martinez-condeAbstract:Microsaccades, small involuntary eye movements that occur once or twice per second during attempted visual fixation, are relevant to perception, cognition, and oculomotor control and present distinctive characteristics in visual and oculomotor pathologies. Thus, the development of robust and accurate Microsaccade-detection techniques is important for basic and clinical neuroscience research. Due to the diminutive size of Microsaccades, however, automatic and reliable detection can be difficult. Current challenges in Microsaccade detection include reliance on set, arbitrary thresholds and lack of objective validation. Here we describe a novel Microsaccade-detecting method, based on unsupervised clustering techniques, that does not require an arbitrary threshold and provides a detection reliability index. We validated the new clustering method using real and simulated eye-movement data. The clustering method reduced detection errors by 62% for binocular data and 78% for monocular data, when compared to standard contemporary Microsaccade-detection techniques. Further, the clustering method's reliability index was correlated with the Microsaccade-detection error rate, suggesting that the reliability index may be used to determine the comparative precision of eye-tracking devices.
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highly informative natural scene regions increase Microsaccade production during visual scanning
The Journal of Neuroscience, 2014Co-Authors: Michael B. Mccamy, Jorge Oteromillan, Stephen L Macknik, Leandro L Di Stasi, Susana MartinezcondeAbstract:Classical image statistics, such as contrast, entropy, and the correlation between central and nearby pixel intensities, are thought to guide ocular fixation targeting. However, these statistics are not necessarily task relevant and therefore do not provide a complete picture of the relationship between informativeness and ocular targeting. Moreover, it is not known whether either informativeness or classical image statistics affect Microsaccade production; thus, the role of Microsaccades in information acquisition is also unknown. The objective quantification of the informativeness of a scene region is a major challenge, because it can vary with both image features and the task of the viewer. Thus, previous definitions of informativeness suffered from subjectivity and inconsistency across studies. Here we developed an objective measure of informativeness based on fixation consistency across human observers, which accounts for both bottom-up and top-down influences in ocular targeting. We then analyzed fixations in more versus less informative image regions in relation to classical statistics. Observers generated more Microsaccades on more informative than less informative image regions, and such regions also exhibited low redundancy in their classical statistics. Increased Microsaccade production was not explained by increased fixation duration, suggesting that the visual system specifically uses Microsaccades to heighten information acquisition from informative regions.
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Distinctive features of Microsaccades in Alzheimer’s disease and in mild cognitive impairment
Age (Dordrecht Netherlands), 2013Co-Authors: Zoï Kapoula, Stephen L Macknik, Jorge Otero-millan, Qing Yang, Shifu Xiao, Alexandre Lang, Marc Verny, Susana Martinez-condeAbstract:During visual fixation, the eyes are never completely still, but produce small involuntary movements, called “fixational eye movements,” including Microsaccades, drift, and tremor. In certain neurological disorders, attempted fixation results in abnormal fixational eye movements with distinctive characteristics. Thus, determining how normal fixation differs from pathological fixation has the potential to aid early and differential noninvasive diagnosis of neurological disease as well as the quantification of its progression and response to treatment. Here, we recorded the eye movements produced by patients with Alzheimer’s disease, patients with mild cognitive impairment, and healthy age-matched individuals during attempted fixation. We found that Microsaccade magnitudes, velocities, durations, and intersaccadic intervals were comparable in the three subject groups, but Microsaccade direction differed in patients versus healthy subjects. Our results indicate that Microsaccades are more prevalently oblique in patients with Alzheimer’s disease or mild cognitive impairment than in healthy subjects. These findings extended to those Microsaccades paired in square-wave jerks, supporting the hypothesis that Microsaccades and square-wave jerks form a continuum, both in healthy subjects and in neurological patients.
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Microsaccades restore the visibility of minute foveal targets.
PeerJ, 2013Co-Authors: Francisco M. Costela, Stephen L Macknik, Michael B. Mccamy, Jorge Otero-millan, Susana Martinez-condeAbstract:Stationary targets can fade perceptually during steady visual fixation, a phenomenon known as Troxler fading. Recent research found that Microsaccades—small, involuntary saccades produced during attempted fixation—can restore the visibility of faded targets, both in the visual periphery and in the fovea. Because the targets tested previously extended beyond the foveal area, however, the ability of Microsaccades to restore the visibility of foveally-contained targets remains unclear. Here, subjects reported the visibility of low-to-moderate contrast targets contained entirely within the fovea during attempted fixation. The targets did not change physically, but their visibility varied intermittently during fixation, in an illusory fashion (i.e., foveal Troxler fading). Microsaccade rates increased significantly before the targets became visible, and decreased significantly before the targets faded, for a variety of target contrasts. These results support previous research linking Microsaccade onsets to the visual restoration of peripheral and foveal targets, and extend the former conclusions to minute targets contained entirely within the fovea. Our findings suggest that the involuntary eye movements produced during attempted fixation do not always prevent fading—in either the fovea or the periphery—and that Microsaccades can restore perception, when fading does occur. Therefore, Microsaccades are relevant to human perception of foveal stimuli.
Ziad M Hafed - One of the best experts on this subject based on the ideXlab platform.
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dependence of the stimulus driven Microsaccade rate signature on visual stimulus polarity
bioRxiv, 2020Co-Authors: Tatiana Malevich, Antimo Buonocore, Ziad M HafedAbstract:Microsaccades have a steady rate of occurrence during maintained gaze fixation, which gets transiently modulated by abrupt sensory stimuli. Such modulation, characterized by a rapid reduction in Microsaccade frequency followed by a stronger rebound phase of high Microsaccade rate, is often described as the microsaccadic rate signature, owing to its stereotyped nature. Here we investigated the impacts of stimulus polarity (luminance increments or luminance decrements relative to background luminance) and size on the microsaccadic rate signature. We presented brief visual flashes consisting of large or small white or black stimuli over an otherwise gray image background. Both large and small stimuli caused robust early microsaccadic inhibition, but only small ones caused a subsequent increase in Microsaccade frequency above baseline Microsaccade rate. Critically, small black stimuli were always associated with stronger modulations in Microsaccade rate after stimulus onset than small white stimuli, particularly in the post-inhibition rebound phase of the microsaccadic rate signature. Because small stimuli were also associated with expected direction oscillations to and away from their locations of appearance, these stronger rate modulations in the rebound phase meant higher likelihoods of Microsaccades opposite the black flash locations relative to the white flash locations. Our results demonstrate that the microsaccadic rate signature is sensitive to stimulus polarity, and they point to dissociable neural mechanisms underlying early microsaccadic inhibition after stimulus onset and later microsaccadic rate rebound at longer times thereafter. These results also demonstrate early access of oculomotor control circuitry to sensory representations, particularly for momentarily inhibiting saccade generation.
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Memory-guided Microsaccades.
Nature communications, 2019Co-Authors: Konstantin F. Willeke, Xiaoguang Tian, Antimo Buonocore, Joachim Bellet, Araceli Ramirez-cardenas, Ziad M HafedAbstract:Despite strong evidence to the contrary in the literature, Microsaccades are overwhelmingly described as involuntary eye movements. Here we show in both human subjects and monkeys that individual Microsaccades of any direction can easily be triggered: (1) on demand, based on an arbitrary instruction, (2) without any special training, (3) without visual guidance by a stimulus, and (4) in a spatially and temporally accurate manner. Subjects voluntarily generated instructed “memory-guided” Microsaccades readily, and similarly to how they made normal visually-guided ones. In two monkeys, we also observed midbrain superior colliculus neurons that exhibit movement-related activity bursts exclusively for memory-guided Microsaccades, but not for similarly-sized visually-guided movements. Our results demonstrate behavioral and neural evidence for voluntary control over individual Microsaccades, supporting recently discovered functional contributions of individual Microsaccade generation to visual performance alterations and covert visual selection, as well as observations that Microsaccades optimize eye position during high acuity visually-guided behavior. Microsaccades are small-amplitude, fixational eye movements that are largely thought to be involuntary. Here, the authors demonstrate that monkeys (and humans) can be easily trained to respond to a remembered target location with a volitional Microsaccade, and that a population of superior colliculus neurons is selectively associated with them.
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Memory-guided Microsaccades
2019Co-Authors: Konstantin F. Willeke, Xiaoguang Tian, Antimo Buonocore, Joachim Bellet, Araceli Ramirez-cardenas, Ziad M HafedAbstract:Abstract Despite strong evidence to the contrary in the literature, Microsaccades are overwhelmingly described as involuntary eye movements. Here we show in both human subjects and monkeys that individual Microsaccades of any direction can easily be triggered: (1) “on demand”, based on an arbitrary instruction, (2) without any special training, (3) without visual guidance by a stimulus, and (4) in a spatially and temporally accurate manner. Subjects voluntarily generated instructed “memory-guided” Microsaccades readily, and similarly to how they made normal visually-guided ones. In two monkeys, we also observed midbrain superior colliculus neurons that exhibit movement-related activity bursts exclusively for memory-guided Microsaccades, but not for similarly-sized visually-guided movements. Our results demonstrate behavioral and neural evidence for voluntary control over individual Microsaccades, supporting recently discovered functional contributions of individual Microsaccade generation to visual performance alterations and covert visual selection, as well as observations that Microsaccades optimize eye position during high acuity visually-guided behavior.
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A Neural Mechanism for Microsaccade Generation in the
2016Co-Authors: Primate Superior Colliculus, Ziad M Hafed, Laurent Goffart, Richard J KrauzlisAbstract:During fixation, the eyes are not still but often exhibit microsaccadic movements. The function of Microsaccades is controversial, largely because the neural mechanisms responsible for their generation are unknown. Here, we show that the superior colliculus (SC), a retinotopically organized structure involved in voluntary-saccade target selection, plays a causal role in Microsaccade generation. Neurons in the foveal portion of the SC increase their activity before and during Microsaccades with sizes of only a few minutes of arc and exhibit selectivity for the direction and amplitude of these movements. Reversible inactivation of these neurons significantly reduces Microsaccade rate without otherwise compromising fixation. These results, coupled with computational modeling of SC activity, demonstrate that Microsaccades are controlled by the SC and explain the link between Microsaccades and visual attention. Microsaccades are the very small (typi-cally <12 min arc), involuntary, fasteye movements that occur during fixation (1–3). The behavioral properties and functional role of Microsaccades have been extensively studied, and sometimes vigorously debated, for many years (1–14). However, th
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A Causal Role for the Cortical Frontal Eye Fields in Microsaccade Deployment.
PLoS biology, 2016Co-Authors: Tyler R. Peel, Ziad M Hafed, Suryadeep Dash, Stephen G. Lomber, Brian D. CorneilAbstract:Microsaccades aid vision by helping to strategically sample visual scenes. Despite the importance of these small eye movements, no cortical area has ever been implicated in their generation. Here, we used unilateral and bilateral reversible inactivation of the frontal eye fields (FEF) to identify a cortical drive for Microsaccades. Unexpectedly, FEF inactivation altered Microsaccade metrics and kinematics. Such inactivation also impaired Microsaccade deployment following peripheral cue onset, regardless of cue side or inactivation configuration. Our results demonstrate that the FEF provides critical top-down drive for Microsaccade generation, particularly during the recovery of Microsaccades after disruption by sensory transients. Our results constitute the first direct evidence, to our knowledge, for the contribution of any cortical area to Microsaccade generation, and they provide a possible substrate for how cognitive processes can influence the strategic deployment of Microsaccades.
Ralf Engbert - One of the best experts on this subject based on the ideXlab platform.
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Microsaccades: Empirical Research and Methodological Advances:
Journal of Eye Movement Research, 2019Co-Authors: Susana Martinez-conde, Ralf Engbert, Rudolf GronerAbstract:Recent technical developments and increased affordability of high-speed eye tracking devices have brought Microsaccades to the forefront of research in many areas of sensory, perceptual, and cognitive processes. The present thematic issue on “Microsaccades: Empirical Research and Methodological Advances” invited authors to submit original research and reviews encompassing measurements and data analyses in fundamental, translational, and applied studies. We present the first volume of this special issue, comprising 14 articles by research teams around the world. Contributions include the characterization of fixational eye movements and saccadic intrusions in neurological impairments and in visual disease, methodological developments in Microsaccade detection, the measurement of fixational eye movements in applied and ecological scenarios, and advances in the current understanding of the relationship between Microsaccades and cognition. When fundamental research on Microsaccades experienced a renaissance at the turn of the millennium (c.f. Martinez-Conde, Macknik, & Hubel, 2004), one could hardly have been so bold as to predict the manifold applications of research on fixational eye movements in clinic and practice. Through this great variety of areas of focus, some main topics emerge. One such theme is the applicability of Microsaccade measures to neurological and visual disease. Whereas Microsaccade quantifications have been largely limited to participants with intact visual and oculomotor systems, recent research has extended this interest into the realm of neural and ophthalmic impairment (see Alexander, Macknik, & Martinez-Conde, 2018, for a review). In this volume, Becker et al analyze “Saccadic intrusions in amyotrophic lateral sclerosis (ALS)” and Kang et al study “Fixational eye movement waveforms in amblyopia”, delving into the characteristics of fast and slow eye movements. Two other articles focus on how the degradation of visual information, which is relevant to many ophthalmic pathologies, affects microsaccadic features. Tang et al investigate the “Effects of visual blur on Microsaccades on visual exploration” and conclude that the precision of an image on the fovea plays an important role in the calibration of Microsaccade amplitudes during visual scanning. Otero-Millan et al use different kinds of visual stimuli and viewing tasks in the presence or absence of simulated scotomas, to determine the contributions of foveal and peripheral visual information to Microsaccade production. They conclude that “Microsaccade generation requires a foveal anchor”. The link between microsaccadic characteristics and cognitive processes has been a mainstay of Microsaccade research for almost two decades, since studies in the early 2000s connected Microsaccade directions to the spatial location of covert attentional cues (Engbert & Kliegl, 2003; Hafed & Clark, 2002). In the present volume, Dalmaso et al report that “Anticipation of cognitive conflict is reflected in Microsaccades”, providing new insights about the top-down modulation of Microsaccade dynamics. Ryan et al further examine the relationship between “Microsaccades and covert attention” during the performance of a continuous, divided-attention task, and find preliminary evidence that Microsaccades track the ongoing allocation of spatial attention. Krueger et al discover that Microsaccade rates modulate with visual attention demands and report that “Microsaccades distinguish looking from seeing”. Taking the ecological validity of Microsaccade investigations one step further, Barnhart et al evaluate Microsaccades during the observation of magic tricks and conclude that “Microsaccades reflect the dynamics of misdirected attention in magic”. Two articles examine the role of individual differences and intraindividual variability over time on microsaccadic features. In “Reliability and correlates of intra-individual variability in the oculomotor system” Perquin and Bompas find evidence for intra-individual reliability over different time points, while cautioning that its use to classify self-reported individual differences remains unclear. Stafford et al provide a counterpoint in “Can Microsaccade rate predict drug response?” by supporting the use of Microsaccade occurrence as both a trait measure of individual differences and as a state measure of response to caffeine administration. Methodological and technical advances are the subjects of three papers in this volume. In “Motion tracking of iris features to detect small eye movements” Chaudhary and Pelz describe a new video-based eye tracking methodology that relies on higher-order iris texture features, rather than on lower-order pupil center and corneal reflection features, to detect Microsaccades with high confidence. Munz et al present an open source visual analytics system called “VisME: Visual Microsaccades explorer” that allows users to interactively vary Microsaccade filter parameters and evaluate the resulting effects on Microsaccade behavior, with the goal of promoting reproducibility in data analyses. In “What makes a Microsaccade? A review of 70 years research prompts a new detection method” Hauperich et al review the Microsaccade properties reported between the 1940s and today, and use the stated range of parameters to develop a novel method of Microsaccade detection. Lastly, Alexander et al switch the focus from the past of Microsaccade research to its future, by discussing the recent and upcoming applications of fixational eye movements to ecologically-valid and real-world scenarios. Their review “Microsaccades in applied environments: real-world applications of fixational eye movement measurements” covers the possibilities and challenges of taking Microsaccade measurements out of the lab and into the field. Microsaccades have engaged the interest of scientists from different backgrounds and disciplines for many decades and will certainly continue to do so. One reason for this fascination might be Microsaccades’ role as a link between basic sensory processes and high-level cognitive phenomena, making them an attractive focus of interdisciplinary research and transdisciplinary applications. Thus, research on Microsaccades will not only endure, but keep evolving as the present knowledge base expands. Part 2 of the special issue on Microsaccades is already in progress with articles currently under review and will be published in 2021. References Alexander, R.G., Macknik, S.L., & Martinez-Conde, S. (2018). Microsaccade characteristics in neurological and ophthalmic disease. Frontiers in Neurology, 9:144. Engbert, R. & Kliegl, R. (2003). Microsaccades uncover the orientation of covert attention. Vision Research, 43, 1035–1045. Hafed, Z. M. & Clark, J. J. (2002). Microsaccades as an overt measure of covert attention shifts. Vision Research, 42, 2533–2545. Martinez-Conde, S., Macknik, S.L., & Hubel, D.H. (2004). The role of fixational eye movements in visual perception. Nature Reviews Neuroscience, 5(3), 229-40.
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Saccadic facilitation by modulation of Microsaccades in natural backgrounds
The Mind Research Repository, 2014Co-Authors: Petra Sinn, Ralf EngbertAbstract:Saccades move objects of interest into the center of the visual field for high-acuity visual analysis. White, Stritzke, and Gegenfurtner ( Current Biology, 18 , 124 – 128, 2008 ) have shown that saccadic latencies in the context of a structured background are much shorter than those with an unstructured background at equal levels of visibility. This effect has been explained by possible preactivation of the saccadic circuitry whenever a structured background acts as a mask for potential saccade targets. Here, we show that background textures modulate rates of Microsaccades during visual fixation. First, after a display change, structured backgrounds induce a stronger decrease of Microsaccade rates than do uniform backgrounds. Second, we demonstrate that the occurrence of a Microsaccade in a critical time window can delay a subsequent saccadic response. Taken together, our findings suggest that Microsaccades contribute to the saccadic facilitation effect, due to a modulation of micro- saccade rates by properties of the background. Attention, Perception, & Psychophysics
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Computational Modeling of Collicular Integration of Perceptual Responses and Attention in Microsaccades
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012Co-Authors: Ralf EngbertAbstract:During visual fixation on a target object, our eyes are not motionless but generate slow fixational eye movements and Microsaccades. Effects of visual attention have been observed in both Microsaccade rates and spatial directions. Experimental results, however, range from early ( 600 ms) effects combined with cue-congruent as well as cue-incongruent Microsaccade directions. On the basis of well characterized neural circuitry in superior colliculus, we construct a dynamical model of neural activation that is modulated by perceptual input and visual attention. Our results show that additive integration of low-level perceptual responses and visual attention can explain Microsaccade rate and direction effects across a range of visual cueing tasks. These findings suggest that the patterns of Microsaccade direction observed in experiments are compatible with a single dynamical mechanism. The basic principles of the model are highly relevant to the general problem of integration of low-level perception and top-down selective attention.
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Saccadic facilitation by modulation of Microsaccades in natural backgrounds
Attention Perception & Psychophysics, 2011Co-Authors: Petra Sinn, Ralf EngbertAbstract:Saccades move objects of interest into the center of the visual field for high-acuity visual analysis. White, Stritzke, and Gegenfurtner ( Current Biology, 18 , 124–128, 2008 ) have shown that saccadic latencies in the context of a structured background are much shorter than those with an unstructured background at equal levels of visibility. This effect has been explained by possible preactivation of the saccadic circuitry whenever a structured background acts as a mask for potential saccade targets. Here, we show that background textures modulate rates of Microsaccades during visual fixation. First, after a display change, structured backgrounds induce a stronger decrease of Microsaccade rates than do uniform backgrounds. Second, we demonstrate that the occurrence of a Microsaccade in a critical time window can delay a subsequent saccadic response. Taken together, our findings suggest that Microsaccades contribute to the saccadic facilitation effect, due to a modulation of Microsaccade rates by properties of the background.
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Microsaccade characterization using the continuous wavelet transform and principal component analysis
Journal of Eye Movement Research, 2010Co-Authors: Mario Bettenbühl, Ralf Engbert, Reinhold Kliegl, Konstantin Mergenthaler, Claudia Paladini, Matthias HolschneiderAbstract:During visual fixation on a target, humans perform miniature (or fixational) eye movements consisting of three components, i.e., tremor, drift, and Microsaccades. Microsaccades are high velocity components with small amplitudes within fixational eye movements. However, Microsaccade shapes and statistical properties vary between individual observers. Here we show that Microsaccades can be formally represented with two significant shapes which we identfied using the mathematical definition of singularities for the detection of the former in real data with the continuous wavelet transform. For character-ization and model selection, we carried out a principal component analysis, which identified a step shape with an overshoot as first and a bump which regulates the overshoot as second component. We conclude that Microsaccades are singular events with an overshoot component which can be detected by the continuous wavelet transform.
Susana Martinez-conde - One of the best experts on this subject based on the ideXlab platform.
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Microsaccades: Empirical Research and Methodological Advances:
Journal of Eye Movement Research, 2019Co-Authors: Susana Martinez-conde, Ralf Engbert, Rudolf GronerAbstract:Recent technical developments and increased affordability of high-speed eye tracking devices have brought Microsaccades to the forefront of research in many areas of sensory, perceptual, and cognitive processes. The present thematic issue on “Microsaccades: Empirical Research and Methodological Advances” invited authors to submit original research and reviews encompassing measurements and data analyses in fundamental, translational, and applied studies. We present the first volume of this special issue, comprising 14 articles by research teams around the world. Contributions include the characterization of fixational eye movements and saccadic intrusions in neurological impairments and in visual disease, methodological developments in Microsaccade detection, the measurement of fixational eye movements in applied and ecological scenarios, and advances in the current understanding of the relationship between Microsaccades and cognition. When fundamental research on Microsaccades experienced a renaissance at the turn of the millennium (c.f. Martinez-Conde, Macknik, & Hubel, 2004), one could hardly have been so bold as to predict the manifold applications of research on fixational eye movements in clinic and practice. Through this great variety of areas of focus, some main topics emerge. One such theme is the applicability of Microsaccade measures to neurological and visual disease. Whereas Microsaccade quantifications have been largely limited to participants with intact visual and oculomotor systems, recent research has extended this interest into the realm of neural and ophthalmic impairment (see Alexander, Macknik, & Martinez-Conde, 2018, for a review). In this volume, Becker et al analyze “Saccadic intrusions in amyotrophic lateral sclerosis (ALS)” and Kang et al study “Fixational eye movement waveforms in amblyopia”, delving into the characteristics of fast and slow eye movements. Two other articles focus on how the degradation of visual information, which is relevant to many ophthalmic pathologies, affects microsaccadic features. Tang et al investigate the “Effects of visual blur on Microsaccades on visual exploration” and conclude that the precision of an image on the fovea plays an important role in the calibration of Microsaccade amplitudes during visual scanning. Otero-Millan et al use different kinds of visual stimuli and viewing tasks in the presence or absence of simulated scotomas, to determine the contributions of foveal and peripheral visual information to Microsaccade production. They conclude that “Microsaccade generation requires a foveal anchor”. The link between microsaccadic characteristics and cognitive processes has been a mainstay of Microsaccade research for almost two decades, since studies in the early 2000s connected Microsaccade directions to the spatial location of covert attentional cues (Engbert & Kliegl, 2003; Hafed & Clark, 2002). In the present volume, Dalmaso et al report that “Anticipation of cognitive conflict is reflected in Microsaccades”, providing new insights about the top-down modulation of Microsaccade dynamics. Ryan et al further examine the relationship between “Microsaccades and covert attention” during the performance of a continuous, divided-attention task, and find preliminary evidence that Microsaccades track the ongoing allocation of spatial attention. Krueger et al discover that Microsaccade rates modulate with visual attention demands and report that “Microsaccades distinguish looking from seeing”. Taking the ecological validity of Microsaccade investigations one step further, Barnhart et al evaluate Microsaccades during the observation of magic tricks and conclude that “Microsaccades reflect the dynamics of misdirected attention in magic”. Two articles examine the role of individual differences and intraindividual variability over time on microsaccadic features. In “Reliability and correlates of intra-individual variability in the oculomotor system” Perquin and Bompas find evidence for intra-individual reliability over different time points, while cautioning that its use to classify self-reported individual differences remains unclear. Stafford et al provide a counterpoint in “Can Microsaccade rate predict drug response?” by supporting the use of Microsaccade occurrence as both a trait measure of individual differences and as a state measure of response to caffeine administration. Methodological and technical advances are the subjects of three papers in this volume. In “Motion tracking of iris features to detect small eye movements” Chaudhary and Pelz describe a new video-based eye tracking methodology that relies on higher-order iris texture features, rather than on lower-order pupil center and corneal reflection features, to detect Microsaccades with high confidence. Munz et al present an open source visual analytics system called “VisME: Visual Microsaccades explorer” that allows users to interactively vary Microsaccade filter parameters and evaluate the resulting effects on Microsaccade behavior, with the goal of promoting reproducibility in data analyses. In “What makes a Microsaccade? A review of 70 years research prompts a new detection method” Hauperich et al review the Microsaccade properties reported between the 1940s and today, and use the stated range of parameters to develop a novel method of Microsaccade detection. Lastly, Alexander et al switch the focus from the past of Microsaccade research to its future, by discussing the recent and upcoming applications of fixational eye movements to ecologically-valid and real-world scenarios. Their review “Microsaccades in applied environments: real-world applications of fixational eye movement measurements” covers the possibilities and challenges of taking Microsaccade measurements out of the lab and into the field. Microsaccades have engaged the interest of scientists from different backgrounds and disciplines for many decades and will certainly continue to do so. One reason for this fascination might be Microsaccades’ role as a link between basic sensory processes and high-level cognitive phenomena, making them an attractive focus of interdisciplinary research and transdisciplinary applications. Thus, research on Microsaccades will not only endure, but keep evolving as the present knowledge base expands. Part 2 of the special issue on Microsaccades is already in progress with articles currently under review and will be published in 2021. References Alexander, R.G., Macknik, S.L., & Martinez-Conde, S. (2018). Microsaccade characteristics in neurological and ophthalmic disease. Frontiers in Neurology, 9:144. Engbert, R. & Kliegl, R. (2003). Microsaccades uncover the orientation of covert attention. Vision Research, 43, 1035–1045. Hafed, Z. M. & Clark, J. J. (2002). Microsaccades as an overt measure of covert attention shifts. Vision Research, 42, 2533–2545. Martinez-Conde, S., Macknik, S.L., & Hubel, D.H. (2004). The role of fixational eye movements in visual perception. Nature Reviews Neuroscience, 5(3), 229-40.
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Changes in visibility as a function of spatial frequency and Microsaccade occurrence.
The European journal of neuroscience, 2017Co-Authors: Francisco M. Costela, Stephen L Macknik, Michael B. Mccamy, Mary Coffelt, Jorge Otero-millan, Susana Martinez-condeAbstract:Fixational eye movements (FEMs), including Microsaccades, drift, and tremor, shift our eye position during ocular fixation, producing retinal motion that is thought to help visibility by counteracting neural adaptation to unchanging stimulation. Yet, how each FEM type influences this process is still debated. Recent studies found little to no relationship between Microsaccades and visual perception of spatial frequencies (SF). However, these conclusions were based on coarse analyses that make it hard to appreciate the actual effects of Microsaccades on target visibility as a function of SF. Thus, how Microsaccades contribute to the visibility of stimuli of different SFs remains unclear. Here, we asked how the visibility of targets of various SFs changed over time, in relationship with concurrent Microsaccade production. Participants continuously reported on changes in target visibility, allowing us to time-lock ongoing changes in Microsaccade parameters to perceptual transitions in visibility. Microsaccades restored/increased the visibility of low SF targets more efficiently than that of high SF targets. Yet, Microsaccade rates rose before periods of increased visibility, and dropped before periods of diminished visibility, for all the SFs tested, suggesting that Microsaccades boosted target visibility across a wide range of SFs. Our data also indicate that visual stimuli fade/become harder to see less often in the presence of Microsaccades. In addition, larger Microsaccades restored/increased target visibility more effectively than smaller Microsaccades. These combined results support the proposal that Microsaccades enhance visibility across a broad variety of SFs.
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Unsupervised clustering method to detect Microsaccades.
Journal of vision, 2014Co-Authors: Jorge Otero-millan, Stephen L Macknik, José Luis Alba Castro, Susana Martinez-condeAbstract:Microsaccades, small involuntary eye movements that occur once or twice per second during attempted visual fixation, are relevant to perception, cognition, and oculomotor control and present distinctive characteristics in visual and oculomotor pathologies. Thus, the development of robust and accurate Microsaccade-detection techniques is important for basic and clinical neuroscience research. Due to the diminutive size of Microsaccades, however, automatic and reliable detection can be difficult. Current challenges in Microsaccade detection include reliance on set, arbitrary thresholds and lack of objective validation. Here we describe a novel Microsaccade-detecting method, based on unsupervised clustering techniques, that does not require an arbitrary threshold and provides a detection reliability index. We validated the new clustering method using real and simulated eye-movement data. The clustering method reduced detection errors by 62% for binocular data and 78% for monocular data, when compared to standard contemporary Microsaccade-detection techniques. Further, the clustering method's reliability index was correlated with the Microsaccade-detection error rate, suggesting that the reliability index may be used to determine the comparative precision of eye-tracking devices.
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Distinctive features of Microsaccades in Alzheimer’s disease and in mild cognitive impairment
Age (Dordrecht Netherlands), 2013Co-Authors: Zoï Kapoula, Stephen L Macknik, Jorge Otero-millan, Qing Yang, Shifu Xiao, Alexandre Lang, Marc Verny, Susana Martinez-condeAbstract:During visual fixation, the eyes are never completely still, but produce small involuntary movements, called “fixational eye movements,” including Microsaccades, drift, and tremor. In certain neurological disorders, attempted fixation results in abnormal fixational eye movements with distinctive characteristics. Thus, determining how normal fixation differs from pathological fixation has the potential to aid early and differential noninvasive diagnosis of neurological disease as well as the quantification of its progression and response to treatment. Here, we recorded the eye movements produced by patients with Alzheimer’s disease, patients with mild cognitive impairment, and healthy age-matched individuals during attempted fixation. We found that Microsaccade magnitudes, velocities, durations, and intersaccadic intervals were comparable in the three subject groups, but Microsaccade direction differed in patients versus healthy subjects. Our results indicate that Microsaccades are more prevalently oblique in patients with Alzheimer’s disease or mild cognitive impairment than in healthy subjects. These findings extended to those Microsaccades paired in square-wave jerks, supporting the hypothesis that Microsaccades and square-wave jerks form a continuum, both in healthy subjects and in neurological patients.
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Microsaccades restore the visibility of minute foveal targets.
PeerJ, 2013Co-Authors: Francisco M. Costela, Stephen L Macknik, Michael B. Mccamy, Jorge Otero-millan, Susana Martinez-condeAbstract:Stationary targets can fade perceptually during steady visual fixation, a phenomenon known as Troxler fading. Recent research found that Microsaccades—small, involuntary saccades produced during attempted fixation—can restore the visibility of faded targets, both in the visual periphery and in the fovea. Because the targets tested previously extended beyond the foveal area, however, the ability of Microsaccades to restore the visibility of foveally-contained targets remains unclear. Here, subjects reported the visibility of low-to-moderate contrast targets contained entirely within the fovea during attempted fixation. The targets did not change physically, but their visibility varied intermittently during fixation, in an illusory fashion (i.e., foveal Troxler fading). Microsaccade rates increased significantly before the targets became visible, and decreased significantly before the targets faded, for a variety of target contrasts. These results support previous research linking Microsaccade onsets to the visual restoration of peripheral and foveal targets, and extend the former conclusions to minute targets contained entirely within the fovea. Our findings suggest that the involuntary eye movements produced during attempted fixation do not always prevent fading—in either the fovea or the periphery—and that Microsaccades can restore perception, when fading does occur. Therefore, Microsaccades are relevant to human perception of foveal stimuli.