Saccade Parameters Research Articles

Improvement of saccadic functions after dosing with methadone in opioid addicted individuals

ABSTRACTIn the current experiment, we used the saccadometric test to study the effect of a single therapeutic dose of methadone on the integrity of cortico-subcortical brain functioning. In this prospective study, we used the Saccadometer System (Advanced Clinical Instrumentation, Cambridge, UK). The saccadometric test was performed before and 1.5 hours after methadone dosing. We analyzed the following saccadic parameters: latency, duration, amplitude, average and peak velocity, and processing performance (promptness) as well as a number of different types of saccades (like correct/incorrect, under/overshoot, and left-sided/right-sided). The sample consists of 40 subjects with an average 18 years of opioid addiction. The mean age is 35.3 ± 7 (80% males and 20% females). The mean period of heroin dependence is 15.3 ± 6.3 years. The mean daily dose of methadone in substitution therapy is 90 ± 26.5 mg. After administration of a single therapeutic dose of methadone, there were statistically significant differences in the values of saccade duration and latency when compared to the values before the drug administration. Average duration of saccade was significantly longer [51.40 ± 8.75 ms versus 48.93 ± 6.91 ms, z = 2.53, p = .01] and average latency was significantly longer [198.85 ± 52.57 ms versus 183.05 ± 30.95 ms, z = 2.09 p < .03]. This is the first study to test the therapeutic effect of daily methadone dosing on the integrity of the cortico-subcortical brain functions as measured by the saccadometry. More research is needed to explore the effect of illicit opioid use on the integrity of brain structures and functions, and the protective effect of opioid agonist therapy on reversing the damaging effects of illicit opioid use.

Visual mislocalization during double-step saccades.

Visual objects presented briefly at the time of saccade onset appear compressed toward the saccade target. Compression strength depends on the presentation of a visual saccade target signal and is strongly reduced during the second saccade of a double-step saccade sequence (Zimmermann et al., 2014b). Here, I tested whether perisaccadic compression is linked to saccade planning by contrasting two double-step paradigms. In the same-direction double-step paradigm, subjects were required to perform two rightward 10° saccades successively. At various times around execution of the saccade sequence a probe dot was briefly flashed. Subjects had to localize the position of the probe dot after they had completed both saccades. I found compression of visual space only at the time of the first but not at the time of the second saccade. In the reverse-direction paradigm, subjects performed first a rightward 10° saccade followed by a leftward 10° saccade back to initial fixation. In this paradigm compression was found in similar magnitude during both saccades. Analysis of the saccade parameters did not reveal indications of saccade sequence preplanning in this paradigm. I therefore conclude that saccade planning, rather than saccade execution factors, is involved in perisaccadic compression.

Saccadic Movements in subjects with cerebellar disorders

SummarySaccades are part of the electrooculography tests battery. The cerebellum has important connections with the brainstem and thalamic structures involved in the generation of saccades.Aimto study saccadic movements in subjects with cerebellar disorders.Study MethodProspective clinical study.Materials and Methods11 subjects with cerebellar disorders were selected, together with a control group with 27 normal subjects. The patients of both groups had their saccadic movements registered (fixed and randomized). We compared and quantitatively analyzed the responses from both groups.ResultsWe did not find any differences among the quantitative parameters between the two. Age and gender did not influence these values. Despite these findings, the morphologies of the saccadic curves were very different between the two groups.ConclusionQuantitative parameters of horizontal saccades from individuals with cerebellar diseases do not differ from those presented by normal subjects. Gender and age also did not influence these parameters.

Visual updating across saccades by working memory integration

We explore the visual world through saccadic eye movements, but saccades also present a challenge to visual processing, by shifting externally-stable objects from one retinal location to another. The brain could solve this problem in two ways: by overwriting preceding input and starting afresh with each new fixation, or by storing a representation of pre-saccadic visual features in memory and updating it with new information from the spatiotopically-matched location. When multiple objects are present in a scene, the planning of eye movements profoundly alters the precision of their working memory representations, transferring memory resources from fixation toward the saccadic target. Here we show that enacting a saccade updates not only the precision of representations but also their contents. When multiple item colours are shifted imperceptibly during a saccade, the perceived colours are found to fall between pre- and post-saccadic values, with the weight given to each input varying continuously with item location, and fixed relative to saccade parameters. Increasing sensory uncertainty, by adding colour noise, biases updating towards the more reliable input, consistent with an optimal integration of pre-saccadic working memory with a post-saccadic update signal. We recover this update signal and show it to be tightly-focused on the vicinity of the saccade target. These results reveal how the nervous system accumulates detailed visual information from multiple views of the same object or scene. Meeting abstract presented at VSS 2015

Early Changes in Saccadic Eye Movement in Hemiparkinsonian MPTP-Treated Monkeys.

The saccadic eye movements declining given the development of Parkinson's disease (PD) still deserves thorough analysis. Recent studies confirmed that PD patients show poor saccadic control in visuomotor tasks. The purpose of this study was to investigate the dynamics of saccades parameters at the development of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. The gradual decline of saccadic control was studied in two monkeys that executed the visuomotor task with low doses of MPTP being injected at a prolonged period of time. The experiment included investigating the horizontal, vertical, oblique visually guided saccades as well as the corrective saccades triggered by stimuli onset in various loci within a two-dimensional visual field in the Gap-Step-Overlap paradigm. Our study revealed that the execution of visually guided saccades with small amplitude and corrective saccades changed dramatically with MPTP-model progressing. These changes are also confirmed statistically at the presymptomatic stage of MPTP syndrome. Not only our study gives a robust report of PD dynamics development and saccadic control but the obtained data could also be helpful in developing methods for the early diagnosis of PD.

Feeling good, searching the bad: Positive priming increases attention and memory for negative stimuli on webpages

Emotional impacts on attention arises in the form of externally and internally loaded forms. The former relates to the emotional valence of the sensory stimulus. The latter refers to the emotional state of the subject. We investigated their influence and interaction. Seventy-two subjects had been emotionally primed by a sequence of positive or negative images before they observed webpages of an online news portal. Each webpage contained positive and negative emotion-laden stimuli to be recalled in a memory test. We captured effects on overt attention, saccadic parameters, and explorative behavior. Furthermore, we related memory performance to characteristic gaze behavior. We found an attentional preference and a better memory performance for negative stimuli that was more pronounced after a positive mood induction. Importantly, increased attention correlated positively with recall performance on an individual level, but only after a positive mood induction. Moreover, the evaluation of the news-portal’s hedonic quality and overall appeal, but not of usability, was affected by subjects’ emotional states. We concluded that in contrast to previously reported mood-congruent preferences in young adults’ attention, there are complementary effects of internally and externally loaded emotions with the tendency that positive priming increases attention and memory for negative stimuli.

Evidence for Optimal Integration of Visual Feature Representations across Saccades.

This study examines the consequences of saccadic eye movements for the internal representation of visual objects. A saccade shifts the image of a stable visual object from one part of the retina to another. We show that visual representations are built up over these different views of the same object, by combining information obtained before and after each saccade. The weights given to presaccadic and postsaccadic information are determined by the relative reliability of each input. This provides evidence that the visual system combines inputs over time in a statistically optimal way.

11.4: Study on the Saccadic Eye Movement Metric of Visual Fatigue Induced By 3D Displays

Developing a valid measurement of visual fatigue induced by 3D display remains a big challenge and is beneficial for optimizing the system design. In this paper, effects of 3D visual fatigue on the dynamics of saccadic eye movements are examined. Thirteen subjects participate in a random dot stereogram (RDS) based task, the performing of the task by the subjects is assumed to directly influence the level of visual fatigue that is evaluated using subjective ratings, optometric tests and eye movement indices. The results of critical fusion frequency (CFF) and accommodation measurement (ACC) show that the proposed experiment setup can induce visual fatigue. According to the subjective ratings, the visual fatigue accumulated in the experiment is mostly related to the binocular vision stress of 3D display. The peak velocity‐magnitude relationship of saccadic eye movements decreases after the experiment, and no significant differences are observed in the other saccadic parameters. Our conclusion is that saccadic eye movement, particularly the peak velocity‐magnitude relationship, is a sensitive indicator for visual fatigue caused by 3D display and has the potential to help the establishment of a valid on‐line measure for the detection of 3D visual fatigue.

Fixational saccades during grating detection and discrimination

We investigated the patterns of fixational saccades in human observers performing two classical perceptual tasks: grating detection and discrimination. First, participants were asked to detect a vertical or tilted grating with one of three spatial frequencies and one of four luminance contrast levels. In the second experiment, participants had to discriminate the spatial frequency of two supra-threshold gratings. The gratings were always embedded in additive, high- or low-contrast pink noise. We observed that the patterns of fixational saccades were highly idiosyncratic among participants. Moreover, during the grating detection task, the amplitude and the number of saccades were inversely correlated with stimulus visibility. We did not find a systematic relationship between saccade parameters and grating frequency, apart from a slight decrease of saccade amplitude during grating discrimination with higher spatial frequencies. No consistent changes in the number and amplitude of fixational saccades with performance accuracy were reported. Surprisingly, during grating detection, saccade number and amplitude were similar in grating-with-noise and noise-only displays. Grating orientation did not affect substantially saccade direction in either task. The results challenge the idea that, when analyzing low-level spatial properties of visual stimuli, fixational saccades can be adapted in order to extract task-relevant information optimally. Rather, saccadic patterns seem to be overall modulated by task context, stimulus visibility and individual variability.

Saccade kinematics modulate perisaccadic perception.

Around the time of execution of an eye movement, participants systematically misperceive the spatial location of briefly flashed visual stimuli. This phenomenon, known as perisaccadic mislocalization, is thought to involve an active process that takes into account the motor plan (efference copy) of the upcoming saccade. While it has been proposed that the motor system anticipates and informs the visual system about the upcoming eye movements, at present the type and detail of information carried by this motor signal remains unclear. Some authors have argued that the efference copy conveys only coarse information about the direction of the eye movement, while a second theoretical view proposes that it provides specific details about the direction, amplitude, and velocity of the saccade to come. To test between these alternatives, we investigated the influence of saccade parameters on a perisaccadic unmasking task in which performance in discriminating the identity of a target (face or house) followed by a trailing mask is dramatically improved around the time of saccade onset. We found that the amplitude and peak velocity of the upcoming saccade modulated target perception, even for stimuli presented well before saccadic onset. We developed a predictive model for the generation of the efference copy that incorporates both saccade amplitude and saccade velocity planning prior to saccade execution. Overall, these results suggest that the efference copy stores specific information about the parameters of upcoming eye movement and that these parameters influence perception even prior to saccade onset.

Effects of aging on eye movements in the real world.

The effects of aging on eye movements are well studied in the laboratory. Increased saccade latencies or decreased smooth-pursuit gain are well established findings. The question remains whether these findings are influenced by the rather untypical environment of a laboratory; that is, whether or not they transfer to the real world. We measured 34 healthy participants between the age of 25 and 85 during two everyday tasks in the real world: (I) walking down a hallway with free gaze, (II) visual tracking of an earth-fixed object while walking straight-ahead. Eye movements were recorded with a mobile light-weight eye tracker, the EyeSeeCam (ESC). We find that age significantly influences saccade parameters. With increasing age, saccade frequency, amplitude, peak velocity, and mean velocity are reduced and the velocity/amplitude distribution as well as the velocity profile become less skewed. In contrast to laboratory results on smooth pursuit, we did not find a significant effect of age on tracking eye-movements in the real world. Taken together, age-related eye-movement changes as measured in the laboratory only partly resemble those in the real world. It is well-conceivable that in the real world additional sensory cues, such as head-movement or vestibular signals, may partially compensate for age-related effects, which, according to this view, would be specific to early motion processing. In any case, our results highlight the importance of validity for natural situations when studying the impact of aging on real-life performance.

Antisaccades and executive dysfunction in early drug-naive Parkinson's disease: The discovery study.

Cognitive impairment is well recognized in Parkinson's disease (PD), but when it begins to develop is unclear. The aim of this study was to identify early signs of cognitive impairment along with abnormalities in saccadic behavior in newly diagnosed unmedicated PD patients. Nineteen drug-naive PD patients and 20 controls were examined using a battery of tests, including an antisaccade task, phonemic and semantic verbal fluencies, and a switching and rule finding task. With simple tasks, no differences were found between the two groups. However, cognitive performance of the two groups diverged with more complex tasks, occurring independently of PD-related motor impairment. Patients exhibited higher antisaccadic error rates and switch costs in the task switching test, and performed significantly worse in the rule finding task. Certain cognitive domains and saccadic parameters are already significantly impoverished in newly diagnosed Parkinson's patients, even before the initiation of medication.

Effects of spatial congruency on saccade and visual discrimination performance in a dual-task paradigm.

The present study investigated the coupling of selection-for-perception and selection-for-action during saccadic eye movement planning in three dual-task experiments. We focused on the effects of spatial congruency of saccade target (ST) location and discrimination target (DT) location and the time between ST-cue and Go-signal (SOA) on saccadic eye movement performance. In two experiments, participants performed a visual discrimination task at a cued location while programming a saccadic eye movement to a cued location. In the third experiment, the discrimination task was not cued and appeared at a random location. Spatial congruency of ST-location and DT-location resulted in enhanced perceptual performance irrespective of SOA. Perceptual performance in spatially incongruent trials was above chance, but only when the DT-location was cued. Saccade accuracy and precision were also affected by spatial congruency showing superior performance when the ST- and DT-location coincided. Saccade latency was only affected by spatial congruency when the DT-cue was predictive of the ST-location. Moreover, saccades consistently curved away from the incongruent DT-locations. Importantly, the effects of spatial congruency on saccade parameters only occurred when the DT-location was cued; therefore, results from experiments 1 and 2 are due to the endogenous allocation of attention to the DT-location and not caused by the salience of the probe. The SOA affected saccade latency showing decreasing latencies with increasing SOA. In conclusion, our results demonstrate that visuospatial attention can be voluntarily distributed upon spatially distinct perceptual and motor goals in dual-task situations, resulting in a decline of visual discrimination and saccade performance.

F02 Cognitive And Oculomotor Performance In Premanifest Huntington Disease: One-year Follow-up

Background Cognitive and oculomotor performance have been extensively studied in Huntington Disease (HD), but evidence for significant deficits in premanifest gene carriers is still controversial. Moreover, their role as markers of disease status and progression is not yet convincingly established. Aims This study aims to understand the evolution of neuropsychological and saccadic performance in premanifest HD (preHD) over a course of 3 years. The results of the baseline assessment and preliminary longitudinal data regarding the one-year follow-up visit of the preHD group are shown here. Methods 15 preHD participants and 22 controls completed the baseline assessment. 10 preHD participants have completed the second visit so far. A comprehensive neuropsychological test battery was used to evaluate the overall cognitive functioning of the participants. An experimental paradigm was designed to assess oculomotor function. Participants completed four different horizontal saccadic tasks with an increasing executive/memory load: prosaccade, antisaccade, 1-or-2 back memory prosaccade and antisaccade. Success rate (percentage of error free trials), latency, directional and timing errors were calculated. Results No significant differences were found between preHD and controls in any of the neuropsychological tests, suggesting a similar overt cognitive baseline at visit #1. The cognitive results of the preHD group at visits #1 and #2 showed that their performance improved in some of the tests used. Concerning saccadic parameters, the preHD group exhibited at baseline a significantly faster response time compared to controls, specifically in memory antisaccades. At visit #2, preHD participants showed a lower success rate and an increased latency, particularly in tasks involving inhibitory processes. Conclusions These data suggest that oculomotor performance of the preHD group may rely on more automatic responses when an executive/memory load is added to the task, deteriorates in time, and also that temporal saccade properties can mark the presence of early neurodegeneration in HD. Furthermore, despite an already evident decline in the saccadic performance of preHD individuals after one year, this is not paralleled by overt cognitive deficits as measured by conventional neuropsychological tests.

J26 Portable Oculometric System for Quantitative Assessmentof Horizontal and Vertical Saccades in HD Monitoring

<h3>Background</h3> Saccadic eye movement parameters, such as its dynamics, latency and error rate are considered as a quantitative biomarkers of disease severity in HD. They possess potential for quick, non-invasive, objective assessment of cortical and sub-cortical function and when repeated systematically may allow easy tracking of disease progression or evaluation of novel therapies. Subjective evaluation of saccadic function is already included in UHDRS scale, however, most subtle features of saccadic movement cannot be observed without the instrumentation. On the other hand, application of the oculometric equipment is limited by its significantly high costs and complicated testing procedures. <h3>Methods/techniques</h3> Authors present Saccadometer Research XY, an integrated system dedicated for rapid, quantitative assessment of horizontal and vertical saccadic eye movement metrics in clinical environment. Subject’s eye movements are captured by a small factor, photo-electric sensor, designed for minimal setup and robust measurement. The stimuli is presented by an integrated, 8-targets laser stimuli generator, bound with the subject’s head, so that external stimuli display and head restraint are not required. The system provides pre programmed set of experiments for both reflex and volitional saccadic responses as well as build-in expert system for automatic saccade detection and classification. It allows to complete the testing procedure within several minutes. <h3>Conclusions</h3> Previous Saccadometer models have already proven its usefulness in examination of HD patients. The newest addition allows the measurement of vertical saccades, which are reported now to be more affected in HD than the horizontal.

Effects of mild to moderate sedation on saccadic eye movements

Sedatives alter the metrics of saccadic eye movements. If these effects are nonspecific consequences of sedation, like drowsiness and loss of attention to the task, or differ between sedatives is still unresolved. A placebo-controlled multi-step infusion of one of three sedatives, propofol or midazolam, both GABA-A agonists, or dexmedetedomidine, an α2-adrenergic agonist, was adopted to compare the effects of these three drugs in exactly the same experimental conditions. 60 healthy human volunteers, randomly divided in 4 groups, participated in the study. Each infusion step, delivered by a computer-controlled infusion pump, lasted 20min. During the last 10min of each step, the subject executed a saccadic task. Target concentration was doubled at each step. This block was repeated until the subject was too sedated to continue or for a maximum of 6 blocks. Subjects were unaware which infusion they were receiving. A video eye tracker was used to record the movements of the right eye. Saccadic parameters were modeled as a function of block number, estimated sedative plasma concentration, and subjective evaluation of sedation. Propofol and midazolam had strong effects on the dynamics and latency of the saccades. Midazolam, and to a less extent, propofol, caused saccades to become increasingly hypometric. Dexmedetedomidine had less impact on saccadic metrics and presented no changes in saccadic gain. Suppression of the sympathetic system associated with dexmedetomidine has different effects on eye movements from the increased activity of the inhibitory GABA-A receptors by propofol and midazolam even when the subjects reported similar sedation level.

Saccadic eye movements in juvenile variant of Huntington disease

Background and purposeHuntington disease (HD) is a neurodegenerative disease leading to involuntary movements, cognitive and behavior decline. The juvenile variant of HD (JHD) manifests in people younger than 21 and is characterized by a different clinical presentation, i.e. rigidity and bradykinesia. Rapid eye movements were not extensively studied in patients with JHD. Aims of our study were to describe the saccadic eye movements in JHD patients and to find a correlation between the saccade abnormalities, severity of the disease and cognitive and behavior deterioration. Materials and methodsWe studied 10 patients with JHD and 10 healthy subjects. Reflexive and volitional saccades were assessed with the Saccadometer Advanced. The battery of cognitive and behavior tests was performed as well. ResultsWe found a prolonged latency, slowness and decreased velocity of reflexive and voluntary saccades and reduced amplitude of voluntary saccades. Moreover, patients with JHD executed a significantly lower number of volitional saccades and made more incorrect cued saccades than controls. We noted a significant correlation between prolonged latency of reflexive saccades with gap task and disease severity and significant inverse correlation between prolonged latency of reflexive saccades with overlap task, an increased number of incorrect saccades made on a cue and impairment in working memory. ConclusionAbnormalities of saccade eye movements in patients with JHD were similar to those reported in patients with HD. Our findings did not confirm abnormalities previously reported in patients with early onset HD. Abnormal saccade parameters correlated also with a disease severity and cognitive deterioration.

Effect od a single dose of Methadone on saccadic refixations in Opioid addicted subjects

Introduction: Eye movements are closely related to cognitive and emotional functions. Information on saccadic dynamics during certain tasks may indicate disorders of mental functions, which can help to explain the neurobiology of sensory-motor systems and can be useful in neuropsychiatric diagnosis. Aims/ Objectives: The study aims at assessing the impact of a single therapeutic dose of methadone on eye movements (saccades) dynamics in HIV(+) and HIV(-) opioid addicted subjects. Methods: Sixty patients from the substitution program were examined. The Latency Test (LT), carried out with the use of saccadometer diagnostic system, was conducted twice: before and 1.5 hours after the administration of a therapeutic dose of methadone. In both parts of the test mean peak velocity, mean latency, mean duration, mean amplitude were measured. Results: The mean duration of latency in HIV(-) subjects measured by LT after the administration of a therapeutic dose of methadone was statistically significantly increased whereas the mean peak velocity was decreased. The mean peak velocity latency in HIV(+) subjects is not statistically significant. The mean duration and the amplitude of latency after the administration of a therapeutic dose of methadone is statistically significant in opioid addicted HIV(+) subjects . It was found that the mean peak velocity before the administration of a therapeutic dose of methadone was statistically significantly different in HIV(-) subjects as compared to HIV(+) ones. Conclusion: An increase in the values of saccadic refixation parameters in opioid addicted subjects after the administration of a therapeutic dose of methadone was observed. An improvement in saccadic refixations parameter in HIV(-) subjects after the administration of a therapeutic dose of methadone was concluded.

Adaptation of naturally paced saccades.

In the natural environment, humans make saccades almost continuously. In many eye movement experiments, however, observers are required to fixate for unnaturally long periods of time. The resulting long and monotonous experimental sessions can become especially problematic when collecting data in a clinical setting, where time can be scarce and subjects easily fatigued. With this in mind, we tested whether the well-studied motor learning process of saccade adaptation could be induced with a dramatically shortened intertrial interval. Observers made saccades to targets that stepped left or right either ∼250 ms or ∼1,600 ms after the saccade landed. In experiment I, we tested baseline saccade parameters to four different target amplitudes (5°, 10°, 15°, and 20°) in the two timing settings. In experiments II and III, we adapted 10° saccades via 2° intrasaccadic steps either backwards or forwards, respectively. Seven subjects performed eight separate adaptation sessions (2 intertrial timings × 2 adaptation direction × 2 session trial lengths). Adaptation proceeded remarkably similarly in both timing conditions across the multiple sessions. In the faster-paced sessions, robust adaptation was achieved in under 2 min, demonstrating the efficacy of our approach to streamlining saccade adaptation experiments. Although saccade amplitudes were similar between conditions, the faster-paced condition unexpectedly resulted in significantly higher peak velocities in all subjects. This surprising finding demonstrates that the stereotyped "main sequence" relationship between saccade amplitude and peak velocity is not as fixed as originally thought.

Saccadic eye movements in Parkinson's disease.

This review focuses on saccadic eye movement research in Parkinson's disease (PD) patients. Results from various studies related to Parkinson disease and saccades have been discussed in terms of various saccadic parameters like latency, amplitude, velocity and gain. Neural circuitry of saccadic eye movements and cognitive processes and it's relation with altered saccadic performance in Parkinson disease has been discussed here. This article also covers various research paradigms commonly used to study saccades. Effects of medication on saccadic parameters in PD patients have also been discussed along with the effects of deep brain stimulation of subthalamic nucleus on saccadic performance in PD patients. Literature review was done using online Pubmed search engine and National Medical Library.