Fixational eye movements in passive versus active sustained fixation tasks
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ABSTRACT:
SUBMITTER: Bowers N
PROVIDER: S-EPMC8556553 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:PurposeFixational saccades shift the foveal image to counteract visual fading related to neural adaptation. Drifts are slow eye movements between two adjacent fixational saccades. We quantified fixational saccades and asked whether their changes could be attributed to pathologic drifts seen in amblyopia, one of the most common causes of blindness in childhood.MethodsThirty-six pediatric subjects with varying severity of amblyopia and eleven healthy age-matched controls held their gaze on a visual target. Eye movements were measured with high-resolution video-oculography during fellow eye-viewing and amblyopic eye-viewing conditions. Fixational saccades and drifts were analyzed in the amblyopic and fellow eye and compared with controls.ResultsWe found an increase in the amplitude with decreased frequency of fixational saccades in children with amblyopia. These alterations in fixational eye movements correlated with the severity of their amblyopia. There was also an increase in eye position variance during drifts in amblyopes. There was no correlation between the eye position variance or the eye velocity during ocular drifts and the amplitude of subsequent fixational saccade. Our findings suggest that abnormalities in fixational saccades in amblyopia are independent of the ocular drift.DiscussionThis investigation of amblyopia in pediatric age group quantitatively characterizes the fixation instability. Impaired properties of fixational saccades could be the consequence of abnormal processing and reorganization of the visual system in amblyopia. Paucity in the visual feedback during amblyopic eye-viewing condition can attribute to the increased eye position variance and drift velocity.
| S-EPMC4773232 | biostudies-literature
Project description:We perceive the world based on visual information acquired via oculomotor control,1 an activity intertwined with ongoing cognitive processes.2,3,4 Cognitive influences have been primarily studied in the context of macroscopic movements, like saccades and smooth pursuits. However, our eyes are never still, even during periods of fixation. One of the fixational eye movements, ocular drifts, shifts the stimulus over hundreds of receptors on the retina, a motion that has been argued to enhance the processing of spatial detail by translating spatial into temporal information.5 Despite their apparent randomness, ocular drifts are under neural control.6,7,8 However little is known about the control of drift beyond the brainstem circuitry of the vestibulo-ocular reflex.9,10 Here, we investigated the cognitive control of ocular drifts with a letter discrimination task. The experiment was designed to reveal open-loop effects, i.e., cognitive oculomotor control driven by specific prior knowledge of the task, independent of incoming sensory information. Open-loop influences were isolated by randomly presenting pure noise fields (no letters) while subjects engaged in discriminating specific letter pairs. Our results show open-loop control of drift direction in human observers.
| S-EPMC10133196 | biostudies-literature
Project description:During steady fixation, observers make small fixational saccades at a rate of around 1-2 per second. Presentation of a visual stimulus triggers a biphasic modulation in fixational saccade rate-an initial inhibition followed by a period of elevated rate and a subsequent return to baseline. Here we show that, during passive viewing, this rate signature is highly sensitive to small changes in stimulus contrast. By training a linear support vector machine to classify trials in which a stimulus is either present or absent, we directly compared the contrast sensitivity of fixational eye movements with individuals' psychophysical judgements. Classification accuracy closely matched psychophysical performance, and predicted individuals' threshold estimates with less bias and overall error than those obtained using specific features of the signature. Performance of the classifier was robust to changes in the training set (novel subjects and/or contrasts) and good prediction accuracy was obtained with a practicable number of trials. Our results indicate a tight coupling between the sensitivity of visual perceptual judgements and fixational eye control mechanisms. This raises the possibility that fixational saccades could provide a novel and objective means of estimating visual contrast sensitivity without the need for observers to make any explicit judgement.
| S-EPMC4633872 | biostudies-literature
Project description:When we fixate a stationary target, our eyes generate miniature (or fixational) eye movements involuntarily. These fixational eye movements are classified as slow components (physiological drift, tremor) and microsaccades, which represent rapid, small-amplitude movements. Here we propose an integrated mathematical model for the generation of slow fixational eye movements and microsaccades. The model is based on the concept of self-avoiding random walks in a potential, a process driven by a self-generated activation field. The self-avoiding walk generates persistent movements on a short timescale, whereas, on a longer timescale, the potential produces antipersistent motions that keep the eye close to an intended fixation position. We introduce microsaccades as fast movements triggered by critical activation values. As a consequence, both slow movements and microsaccades follow the same law of motion; i.e., movements are driven by the self-generated activation field. Thus, the model contributes a unified explanation of why it has been a long-standing problem to separate slow movements and microsaccades with respect to their motion-generating principles. We conclude that the concept of a self-avoiding random walk captures fundamental properties of fixational eye movements and provides a coherent theoretical framework for two physiologically distinct movement types.
| S-EPMC3182695 | biostudies-literature
Project description:All known photoreceptor cells adapt to constant light stimuli, fading the retinal image when exposed to an immobile visual scene. Counter strategies are therefore necessary to prevent blindness, and in mammals this is accomplished by fixational eye movements. Cubomedusae occupy a key position for understanding the evolution of complex visual systems and their eyes are assumedly subject to the same adaptive problems as the vertebrate eye, but lack motor control of their visual system. The morphology of the visual system of cubomedusae ensures a constant orientation of the eyes and a clear division of the visual field, but thereby also a constant retinal image when exposed to stationary visual scenes. Here we show that bell contractions used for swimming in the medusae refresh the retinal image in the upper lens eye of Tripedalia cystophora. This strongly suggests that strategies comparable to fixational eye movements have evolved at the earliest metazoan stage to compensate for the intrinsic property of the photoreceptors. Since the timing and amplitude of the rhopalial movements concur with the spatial and temporal resolution of the eye it circumvents the need for post processing in the central nervous system to remove image blur.
| S-EPMC3679052 | biostudies-literature
Project description:Under natural viewing conditions the input to the retina is a complex spatiotemporal signal that depends on both the scene and the way the observer moves. It is commonly assumed that the retina processes this input signal efficiently by taking into account the statistics of the natural world. It has recently been argued that incessant microscopic eye movements contribute to this process by decorrelating the input to the retina. Here we tested this theory by measuring the responses of the salamander retina to stimuli replicating the natural input signals experienced by the retina in the presence and absence of fixational eye movements. Contrary to the predictions of classic theories of efficient encoding that do not take behavior into account, we show that the response characteristics of retinal ganglion cells are not sufficient in themselves to disrupt the broad correlations of natural scenes. Specifically, retinal ganglion cells exhibited strong and extensive spatial correlations in the absence of fixational eye movements. However, the levels of correlation in the neural responses dropped in the presence of fixational eye movements, resulting in effective decorrelation of the channels streaming information to the brain. These observations confirm the predictions that microscopic eye movements act to reduce correlations in retinal responses and contribute to visual information processing.
| S-EPMC4364215 | biostudies-literature
Project description:Involuntary eye movement during gaze (GZ) fixation, referred to as fixational eye movement (FEM), consists of two types of components: a Brownian motion like component called drifts-tremor (DRT) and a ballistic component called microsaccade (MS) with a mean saccadic amplitude of about 0.3° and a mean inter-MS interval of about 0.5 s. During GZ fixation in healthy people in an eccentric position, typically with an eccentricity more than 30°, eyes exhibit oscillatory movements alternating between centripetal drift and centrifugal saccade with a mean saccadic amplitude of about 1° and a period in the range of 0.5-1.0 s, which has been known as the physiological gaze-evoked nystagmus (GEN). Here, we designed a simple experimental paradigm of GZ fixation on a target shifted horizontally from the front-facing position with fewer eccentricities. We found a clear tendency of centripetal DRT and centrifugal MS as in GEN, but with more stochasticity and with slower drift velocity compared to GEN, even during FEM at GZ positions with small eccentricities. Our results showed that the target shift-dependent balance between DRT and MS achieves the GZ bounded around each of the given targets. In other words, GZ relaxes slowly with the centripetal DRT toward the front-facing position during inter-MS intervals, as if there always exists a quasi-stable equilibrium posture in the front-facing position, and MS actions pull GZ intermittently back to the target position in the opposite direction to DRT.
| S-EPMC9133340 | biostudies-literature
Project description:PurposePatients with amblyopia are known to have fixation instability, which arises from alteration of physiologic fixation eye movements (FEMs) and nystagmus. We assessed the effects of monocular, binocular, and dichoptic viewing on FEMs and eye alignment in patients with and without fusion maldevelopment nystagmus (FMN).MethodsThirty-four patients with amblyopia and seven healthy controls were recruited for this study. Eye movements were recorded using infrared video-oculography during (1) fellow eye viewing (FEV), (2) amblyopic eye viewing (AEV), (3) both eye viewing (BEV), and (4) dichoptic viewing (DcV) at varying fellow eye (FE) contrasts. The patients were classified per the clinical type of amblyopia and FEM waveforms into those without nystagmus, those with nystagmus with and without FMN. Fixational saccades and intersaccadic drifts, quick and slow phases of nystagmus, and bivariate contour ellipse area were analyzed in the FE and amblyopic eye (AE).ResultsWe found that FEMs are differentially affected with increased amplitude of quick phases of FMN observed during AEV than BEV and during DcV at lower FE contrasts. Increased fixation instability was seen in anisometropic patients at lower FE contrasts. Incomitance of eye misalignment was seen with the greatest increase during FEV. Strabismic/mixed amblyopia patients without FMN were more likely to demonstrate a fixation switch where the AE attends to the target during DcV than patients with FMN.ConclusionsOur findings suggest that FEM abnormalities modulate with different viewing conditions as used in various amblyopia therapies. Increased FEM abnormalities could affect the visual function deficits and may have treatment implications.
| S-EPMC8883146 | biostudies-literature
Project description:The present review is addressed to researchers in the field of reading and psycholinguistics who are both familiar with and new to co-registration research of eye movements (EMs) and fixation related-potentials (FRPs) in reading. At the outset, we consider a conundrum relating to timing discrepancies between EM and event related potential (ERP) effects. We then consider the extent to which the co-registration approach might allow us to overcome this and thereby discriminate between formal theoretical and computational accounts of reading. We then describe three phases of co-registration research before evaluating the existing body of such research in reading. The current, ongoing phase of co-registration research is presented in comprehensive tables which provide a detailed summary of the existing findings. The thorough appraisal of the published studies allows us to engage with issues such as the reliability of FRP components as correlates of cognitive processing in reading and the advantages of analysing both data streams (i.e., EMs and FRPs) simultaneously relative to each alone, as well as the current, and limited, understanding of the relationship between EM and FRP measures. Finally, we consider future directions and in particular the potential of analytical methods involving deconvolution and the potential of measurement of brain oscillatory activity.
| S-EPMC7157570 | biostudies-literature
Project description:Smooth pursuit and motion perception have mainly been investigated with stimuli moving along linear trajectories. Here we studied the quality of pursuit movements to curved motion trajectories in human observers and examined whether the pursuit responses would be sensitive enough to discriminate various degrees of curvature. In a two-interval forced-choice task subjects pursued a Gaussian blob moving along a curved trajectory and then indicated in which interval the curve was flatter. We also measured discrimination thresholds for the same curvatures during fixation. Motion curvature had some specific effects on smooth pursuit properties: trajectories with larger amounts of curvature elicited lower open-loop acceleration, lower pursuit gain, and larger catch-up saccades compared with less curved trajectories. Initially, target motion curvatures were underestimated; however, ∼300 ms after pursuit onset pursuit responses closely matched the actual curved trajectory. We calculated perceptual thresholds for curvature discrimination, which were on the order of 1.5 degrees of visual angle (°) for a 7.9° curvature standard. Oculometric sensitivity to curvature discrimination based on the whole pursuit trajectory was quite similar to perceptual performance. Oculometric thresholds based on smaller time windows were higher. Thus smooth pursuit can quite accurately follow moving targets with curved trajectories, but temporal integration over longer periods is necessary to reach perceptual thresholds for curvature discrimination.NEW & NOTEWORTHY Even though motion trajectories in the real world are frequently curved, most studies of smooth pursuit and motion perception have investigated linear motion. We show that pursuit initially underestimates the curvature of target motion and is able to reproduce the target curvature ∼300 ms after pursuit onset. Temporal integration of target motion over longer periods is necessary for pursuit to reach the level of precision found in perceptual discrimination of curvature.
| S-EPMC5596124 | biostudies-literature