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Causal Inference for Spatial Constancy across Saccades

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  • Ref Causal Inference for Spatial Constancy across Saccades

    Causal Inference for Spatial Constancy across Saccades

    http://journals.plos.org/ploscompbio...l.pcbi.1004766

    Abstract

    Our ability to interact with the environment hinges on creating a stable visual world despite the continuous changes in retinal input. To achieve visual stability, the brain must distinguish the retinal image shifts caused by eye movements and shifts due to movements of the visual scene. This process appears not to be flawless: during saccades, we often fail to detect whether visual objects remain stable or move, which is called saccadic suppression of displacement (SSD). How does the brain evaluate the memorized information of the presaccadic scene and the actual visual feedback of the postsaccadic visual scene in the computations for visual stability? Using a SSD task, we test how participants localize the presaccadic position of the fixation target, the saccade target or a peripheral non-foveated target that was displaced parallel or orthogonal during a horizontal saccade, and subsequently viewed for three different durations. Results showed different localization errors of the three targets, depending on the viewing time of the postsaccadic stimulus and its spatial separation from the presaccadic location. We modeled the data through a Bayesian causal inference mechanism, in which at the trial level an optimal mixing of two possible strategies, integration vs. separation of the presaccadic memory and the postsaccadic sensory signals, is applied. Fits of this model generally outperformed other plausible decision strategies for producing SSD. Our findings suggest that humans exploit a Bayesian inference process with two causal structures to mediate visual stability.
    Last edited by Jo Bowyer; 25-03-2016, 12:35 AM.
    Jo Bowyer
    Chartered Physiotherapist Registered Osteopath.
    "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

  • #2
    Saccadic Eye Movements in Anorexia Nervosa

    http://journals.plos.org/plosone/art...l.pone.0152338

    Abstract
    Background

    Anorexia Nervosa (AN) has a mortality rate among the highest of any mental illness, though the factors involved in the condition remain unclear. Recently, the potential neurobiological underpinnings of the condition have become of increasing interest. Saccadic eye movement tasks have proven useful in our understanding of the neurobiology of some other psychiatric illnesses as they utilise known brain regions, but to date have not been examined in AN. The aim of this study was to investigate whether individuals with AN differ from healthy individuals in performance on a range of saccadic eye movements tasks.

    Methods

    24 females with AN and 25 healthy individuals matched for age, gender and premorbid intelligence participated in the study. Participants were required to undergo memory-guided and self-paced saccade tasks, and an interleaved prosaccade/antisaccade/no-go saccade task while undergoing functional magnetic resonance imaging (fMRI).

    Results

    AN participants were found to make prosaccades of significantly shorter latency than healthy controls. AN participants also made an increased number of inhibitory errors on the memory-guided saccade task. Groups did not significantly differ in antisaccade, no-go saccade or self-paced saccade performance, or fMRI findings.

    Discussion

    The results suggest a potential role of GABA in the superior colliculus in the psychopathology of AN.
    Jo Bowyer
    Chartered Physiotherapist Registered Osteopath.
    "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

    Comment


    • #3
      Saccadic Impairment Associated With Remote History of Mild Traumatic Brain Injury

      http://neuro.psychiatryonline.org/do...psych.15100243

      Abstract
      Evidence suggests that mild traumatic brain injury (TBI) is associated with long-term changes in brain function, but conventional neurocognitive tools are often insensitive to deficits after 90 days. Eye movements have been proposed as a means to identify more chronic forms of impairment. In this study, saccadic, manual, and conventional neuropsychological measures were compared between participants with remote mild TBI and well-matched control participants. Saccadic impairment was more frequent within the mild TBI group, and a history of multiple injuries or high symptom burden appeared to compound this risk. However, other neurocognitive measures did not differ by group, number of injuries, or symptom severity. These results suggest that saccadic impairment may reflect chronic effects of mild TBI that conventional measures are unable to detect.
      Jo Bowyer
      Chartered Physiotherapist Registered Osteopath.
      "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

      Comment


      • #4
        Superior Colliculus Responses to Attended, Unattended, and Remembered Saccade Targets during Smooth Pursuit Eye Movements

        http://journal.frontiersin.org/artic...016.00034/full

        In realistic environments, keeping track of multiple visual targets during eye movements likely involves an interaction between vision, top-down spatial attention, memory, and self-motion information. Recently we found that the superior colliculus (SC) visual memory response is attention-sensitive and continuously updated relative to gaze direction. In that study, animals were trained to remember the location of a saccade target across an intervening smooth pursuit (SP) eye movement (Dash et al., 2015). Here, we modified this paradigm to directly compare the properties of visual and memory updating responses to attended and unattended targets. Our analysis shows that during SP, active SC visual vs. memory updating responses share similar gaze-centered spatio-temporal profiles (suggesting a common mechanism), but updating was weaker by ~25%, delayed by ~55 ms, and far more dependent on attention. Further, during SP the sum of passive visual responses (to distracter stimuli) and memory updating responses (to saccade targets) closely resembled the responses for active attentional tracking of visible saccade targets. These results suggest that SP updating signals provide a damped, delayed estimate of attended location that contributes to the gaze-centered tracking of both remembered and visible saccade targets.
        Jo Bowyer
        Chartered Physiotherapist Registered Osteopath.
        "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

        Comment


        • #5
          Pay Attention! Researchers Uncover Mechanism That May Clarify Meaning of Attention

          http://neurosciencenews.com/eye-move...oscience-4070/

          Neuroscientists from Tübingen and Okasaki show that tiny eye movements filter “important” stimuli and relay them to the brain.

          Neuroscientists from Tübingen and Okasaki (Japan) have uncovered a mechanism that might clarify the meaning of “attention”. This often non-quantifiable term is supposed to describe how strongly we react to a visual stimulus. An international team of neuroscientists from the Tübingen Werner Reichardt Centre for Integrative Neuroscience (CIN) and the Okasaki National Institute for Physiological Sciences (NIPS) now explain the mechanism of “attention”, not by looking at the visual system, but into the rhythm and direction of tiny eye movements that we constantly make. Their hypotheses and experimental validations are published in two back-to-back articles recently published in Frontiers in System Neuroscience. Results from four decades of research are now cast in a very different light.

          Good science is supposed to be “frugal”, i.e., it ought to make use of as few assumptions and abstractions as possible. In neuroscience, the abstract concept of “attention” is a concept that is considerably less frugal than would be desirable. It is basically a black box and does not necessarily explain which processes in the brain it actually addresses – a central question of perception research today.

          For several decades, “attention” was thought to be a barely definable state of certain brain regions. In visual perception, for instance, eye movements towards a stimulus are triggered in the Superior Colliculus, a part of the midbrain. The direction of attention in the brain does not react equally to all stimuli, though: when there is a high level of “attention in the sensory system, reactions are swift and intense; neuroscientists call this state “attentional capture”. A state of slow and comparatively weak reactions, on the other hand, is called “inhibition of return” (IOR). Attentional capture and IOR both follow an alternating pattern, which rides on a rhythm with approximately 10 oscillations per second.

          But what causes this rhythm, and how does “attention” control it? The international research team have now been able to depict the processes which might be responsible in a surprisingly simple model. These CIN and NIPS neuroscientists have been cooperating for several years now, headed by Dr. Ziad Hafed (Tübingen). They are investigating a phenomenon whose importance for visual perception has long been underestimated: tiny eye movements, so-called microsaccades. These small adjustments constantly correct the axis of vision when the gaze fixates an object. In earlier studies, Hafed and colleagues had found that microsaccades are generated in the Superior Colliculus in a stable rhythm that is reset by new stimuli entering the visual field. Microsaccades also change direction with each iteration.

          Following up on these observations, Hafed and his team arrived at a hypothesis: what if the rhythm and direction of microsaccades directly trigger attentional capture and IOR? They developed a theoretical and computer model based on this assumption, employing a wide range of parameters to see what predictions the model could make. Testing the model’s predictions in experiments, the researchers surprised even themselves: they found that besides microsaccades, no additional factors were necessary in the model to explain attentional capture and IOR.

          Ziad Hafed states that “attention” may be explained quite “parsimoniously”. He believes that the brain filters “important” stimuli simply based on saccadic corrections of the direction of gaze. These eye movements directly produce the phenomena which have so far been described as attentional capture and IOR. Which of these two occurs depends on the timing and direction of the stimulus relative to the microsaccadic rhythm and direction. ‘These findings are a strong argument that the mechanism of “attention” is based on a very simple principle’, says Hafed. ‘Should they be validated by further studies, results from decades of research would have to be seen in a very different light.’
          Jo Bowyer
          Chartered Physiotherapist Registered Osteopath.
          "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

          Comment


          • #6
            How Much Do We Really See?

            http://neurosciencenews.com/visual-p...iousness-4084/

            Glance out the window and then close your eyes. What did you see? Maybe you noticed it’s raining and there was a man carrying an umbrella. What color was it? What shape was its handle? Did you catch those details? Probably not. Some neuroscientists would say that, even though you perceived very few specifics from the window scene, your eyes still captured everything in front of you. But there are flaws to this logic, MIT researchers argue in an Opinion published April 19, 2016 in Trends in Cognitive Sciences. It may be that our vision only reflects the gist of what we see.
            Jo Bowyer
            Chartered Physiotherapist Registered Osteopath.
            "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

            Comment


            • #7
              A State Space Model for Spatial Updating of Remembered Visual Targets during Eye Movements

              http://journal.frontiersin.org/artic...016.00039/full

              In the oculomotor system, spatial updating is the ability to aim a saccade toward a remembered visual target position despite intervening eye movements. Although this has been the subject of extensive experimental investigation, there is still no unifying theoretical framework to explain the neural mechanism for this phenomenon, and how it influences visual signals in the brain. Here, we propose a unified state-space model (SSM) to account for the dynamics of spatial updating during two types of eye movement; saccades and smooth pursuit. Our proposed model is a non-linear SSM and implemented through a recurrent radial-basis-function neural network in a dual Extended Kalman filter (EKF) structure. The model parameters and internal states (remembered target position) are estimated sequentially using the EKF method. The proposed model replicates two fundamental experimental observations: continuous gaze-centered updating of visual memory-related activity during smooth pursuit, and predictive remapping of visual memory activity before and during saccades. Moreover, our model makes the new prediction that, when uncertainty of input signals is incorporated in the model, neural population activity and receptive fields expand just before and during saccades. These results suggest that visual remapping and motor updating are part of a common visuomotor mechanism, and that subjective perceptual constancy arises in part from training the visual system on motor tasks.
              Jo Bowyer
              Chartered Physiotherapist Registered Osteopath.
              "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

              Comment


              • #8
                VOR gain is related to compensatory saccades in healthy older adults

                http://journal.frontiersin.org/artic...00150/abstract

                Objective: Vestibulo-ocular reflex (VOR) gain is well-suited for identifying rotational vestibular dysfunction, but may miss partial progressive decline in age-related vestibular function. Since compensatory saccades might provide an alternative method for identifying subtle vestibular decline, we describe the relationship between VOR gain and compensatory saccades in healthy older adults.

                Methods: Horizontal VOR gain was measured in 243 subjects age 60 and older from the Baltimore Longitudinal Study of Aging using video head impulse testing (HIT). Saccades in each HIT were identified as either “compensatory” or “compensatory back-up,” i.e. same or opposite direction as the VOR response respectively. Saccades were also classified as “covert” (occurring during head movement) and “overt” (occurring after head movement). The relationship between VOR gain and percentage of HITs with saccades, as well as the relationship between VOR gain and saccade latency and amplitude, were evaluated using regression analyses adjusting for age, gender, and race.

                Results: In adjusted analyses, the percentage of HITs with compensatory saccades increased 4.5% for every 0.1 decrease in VOR gain (p<0.0001). Overt compensatory saccade amplitude decreased 0.6 degrees (p<0.005) and latency increased 90ms (p<0.001) for every 0.1 increase in VOR gain. Covert back-up compensatory saccade amplitude increased 0.4 degrees for every 0.1 increase in VOR gain.

                Conclusions: We observed significant relationships between VOR gain and compensatory saccades in healthy older adults. Lower VOR gain was associated with larger amplitude, shorter latency compensatory saccades. Compensatory saccades reflect underlying rotational vestibular hypofunction, and may be particularly useful at identifying partial vestibular deficits as occur in aging adults.
                Keywords: Head Impulse Testing, vor, vestibular, healthy aging, Compensatory saccades
                Jo Bowyer
                Chartered Physiotherapist Registered Osteopath.
                "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

                Comment


                • #9
                  Saccadic adaptation is associated with starting eye position

                  http://journal.frontiersin.org/artic...00322/abstract

                  Saccadic adaptation is the motor learning process that keeps saccade amplitudes on target. This process is eye position specific: amplitude adaptation that is induced for a saccade at one particular location in the visual field transfers incompletely to saccades at other locations. In our current study, we investigated wether this eye position signal corresponds to the initial or to the final eye position of the saccade. Each case would have different implications on the mechanisms of adaptation. The initial eye position is not directly available, when the adaptation driving post saccadic error signal is received. On the other hand the final eye position signal is not available, when the motor command for the saccade is calculated. In six human subjects we adapted a saccade of 15 deg amplitude that started at a constant position. We then measured the transfer of adaptation to test saccades of 10 deg and 20 deg amplitude. In each case we compared test saccades that matched the start position of the adapted saccade to those that matched the target of the adapted saccade. We found significantly more transfer of adaptation to test saccades with the same start position than to test saccades with the same target position. The results indicate that saccadic adaptation is specific to the initial eye position. This is consistent with a previously proposed effect of gain field modulated input from areas like the frontal eye field, the lateral intraparietal area and the superior colliculus into the cerebellar adaptation circuitry.
                  Keywords: saccadic adaptation, motor learning, oculomotor control, gain fields, Eye Position Signal
                  Jo Bowyer
                  Chartered Physiotherapist Registered Osteopath.
                  "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

                  Comment


                  • #10
                    Saccades influence the visibility of targets in rapid stimulus sequences: the roles of mislocalization, retinal distance and remapping

                    http://journal.frontiersin.org/artic...00058/abstract

                    Briefly presented targets around the time of a saccade are mislocalized towards the saccadic landing point. This has been taken as evidence for a remapping mechanism that accompanies each eye movement, helping maintain visual stability across large retinal shifts. Previous studies have shown that spatial mislocalization is greatly diminished when trains of brief stimuli are presented at a high frequency rate, which might help to explain why mislocalization is rarely perceived in everyday viewing. Studies in the laboratory have shown that mislocalization can reduce metacontrast masking by causing target stimuli in a masking sequence to be perceived as shifted in space towards the saccadic target and thus more easily discriminated. We investigated the influence of saccades on target discrimination when target and masks were presented in a rapid serial visual presentation (RSVP), as well as with forward masking and with backward masking. In a series of experiments, we found that performance was influenced by the retinal displacement caused by the saccade itself but that an additional component of un-masking occurred even when the retinal location of target and mask was matched. These results speak in favor of a remapping mechanism that begins before the eyes start moving and continues well beyond saccadic termination.
                    Keywords: Eye Movements, perisaccadic perception, forward masking, Mislocalization, rapid serial visual presentation




                    Pre-saccadic perception: Separate time courses for enhancement and spatial pooling at the saccade target

                    http://journals.plos.org/plosone/art...l.pone.0178902

                    Abstract

                    We interact with complex scenes using eye movements to select targets of interest. Studies have shown that the future target of a saccadic eye movement is processed differently by the visual system. A number of effects have been reported, including a benefit for perceptual performance at the target (“enhancement”), reduced influences of backward masking (“un-masking”), reduced crowding (“un-crowding”) and spatial compression towards the saccade target. We investigated the time course of these effects by measuring orientation discrimination for targets that were spatially crowded or temporally masked. In four experiments, we varied the target-flanker distance, the presence of forward/backward masks, the orientation of the flankers and whether participants made a saccade. Masking and randomizing flanker orientation reduced performance in both fixation and saccade trials. We found a small improvement in performance on saccade trials, compared to fixation trials, with a time course that was consistent with a general enhancement at the saccade target. In addition, a decrement in performance (reporting the average flanker orientation, rather than the target) was found in the time bins nearest saccade onset when random oriented flankers were used, consistent with spatial pooling around the saccade target. We did not find strong evidence for un-crowding. Overall, our pattern of results was consistent with both an early, general enhancement at the saccade target and a later, peri-saccadic compression/pooling towards the saccade target.
                    Update 16/06/2017
                    Last edited by Jo Bowyer; 16-06-2017, 06:04 PM.
                    Jo Bowyer
                    Chartered Physiotherapist Registered Osteopath.
                    "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

                    Comment


                    • #11
                      Impaired Oculomotor Behavior of Children with Developmental Dyslexia in Antisaccades and Predictive Saccades Tasks

                      http://journal.frontiersin.org/artic...016.00987/full

                      Analysis of eye movement patterns during tracking tasks represents a potential way to identify differences in the cognitive processing and motor mechanisms underlying reading in dyslexic children before the occurrence of school failure. The current study aimed to evaluate the pattern of eye movements in antisaccades, predictive saccades and visually guided saccades in typical readers and readers with developmental dyslexia. The study included 30 children (age M = 11; SD = 1.67), 15 diagnosed with developmental dyslexia (DG) and 15 regular readers (CG), matched by age, gender and school grade. Cognitive assessment was performed prior to the eye-tracking task during which both eyes were registered using the Tobii® 1750 eye-tracking device. The results demonstrated a lower correct antisaccades rate in dyslexic children compared to the controls (p < 0.001, DG = 25%, CC = 37%). Dyslexic children also made fewer saccades in predictive latency (p < 0.001, DG = 34%, CG = 46%, predictive latency within −300–120 ms with target as 0 point). No between-group difference was found for visually guided saccades. In this task, both groups showed shorter latency for right-side targets. The results indicated altered oculomotor behavior in dyslexic children, which has been reported in previous studies. We extend these findings by demonstrating impaired implicit learning of target's time/position patterns in dyslexic children.
                      Jo Bowyer
                      Chartered Physiotherapist Registered Osteopath.
                      "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

                      Comment


                      • #12
                        The Eyes Are the Window to the Brain

                        http://neurosciencenews.com/saccades...ovements-4747/

                        Our eyes are constantly moving, whether we notice or not. They jump from one focus point to another and even when we seem to be focused on one point, the eyes continue to reflexively move. These types of eye movements are called saccades. During saccades, even if we are not actively thinking about moving our eyes, our brain is still quickly working to land our focus precisely on spots that hold important information, such as the eyes of a person that you are talking to. The saccade is an example of sensorimotor coordination – how we coordinate our movement with what we sense -and has a far-reaching impact on motor control. Therefore, it is important to understand what is happening in the brain during saccades.


                        To Wait or Not to Wait—Separate Mechanisms in the Oculomotor Circuit of Basal Ganglia

                        http://journal.frontiersin.org/artic...017.00035/full

                        We reach a goal immediately after detecting the target, or later by withholding the immediate action. Each time, we choose one of these actions by suppressing the other. How does the brain control these antagonistic actions? We hypothesized that the output of basal ganglia (BG), substantia nigra pars reticulata (SNr), suppresses antagonistic oculomotor signals by sending strong inhibitory output to superior colliculus (SC). To test this hypothesis, we trained monkeys to perform two kinds of saccade task: Immediate (visually guided) and delayed (visually-withheld but memory-guided) saccade tasks. In both tasks, we applied one-direction-reward (1DR) procedure to modify the level of goal-reaching motivation. We identified SNr neurons that projected to SC by their antidromic activation from SC. We stimulated SC on both sides because SNr neurons projecting to the ipsilateral SC (ipsiSC) and those projecting to the contralateral SC (contraSC) might have antagonistic functions. First, we found that ipsiSC-projecting neurons were about 10 times more than contraSC-projecting neurons. More importantly, ipsiSC-projecting SNr neurons were roughly divided into two groups which would control immediate and delayed saccades separately. The immediate-type SNr neurons were clearly inhibited by a visual target on the contralateral side in both visual- and memory-1DR tasks. The inhibition would disinhibit SC neurons and facilitate a saccade to the contralateral target. This is goal-directed in visual-1DR task, but is erroneous in memory-1DR task. In contrast, the delayed-type SNr neurons tended to be excited by a visual target (especially on the contralateral side), which would suppress the immediate saccade to the target. Instead, they were inhibited before a delayed (memory-guided) saccade directed to the contralateral side, which would facilitate the saccade. ContraSC-projecting SNr neurons were more variable with no grouped features, although some of them may contribute to the saccade to the ipsilateral target. Finally, we found that some ipsiSC-projecting SNr neurons were inhibited more strongly when reward was expected, which was associated with shortened saccade reaction times. However, many SNr neurons showed no reward-expectation effect. These results suggest that two separate oculomotor circuits exist in BG, both of which contribute to goal-directed behavior, but in different temporal contexts.
                        Introduction
                        Eye movement guides one’s body toward a goal. In ecological environment the resources are limited; therefore, animals (or humans) should reach a goal promptly once they find it. However, the goal is sometimes unreachable and they need to withhold the action for a while. These two actions are conflicting because immediate action does not give the animal enough time to examine if the target is reachable or not. To control these antagonistic actions, the brain should hold two separate mechanisms competing with each other.

                        The basal ganglia (BG) can contribute to the selection of behavior because their outputs are powerfully inhibitory and can suppress antagonistic actions (Mink, 1996). A prominent mechanism of the BG is to select a saccadic eye movement (Hikosaka et al., 2000, 2014) which guides us to reach a valuable object (Land and Hayhoe, 2001). This is performed by the inhibitory connection from the substantia nigra pars reticulata (SNr) to the superior colliculus (SC) in macaque monkeys (Hikosaka and Wurtz, 1983b). SNr neurons can thus facilitate a saccade by reducing the inhibition and suppress other saccades by enhancing the inhibition. Indeed, this selection mechanism may be at work, since SNr neurons increase and/or decrease their activity during a reward-biased saccade task (Sato and Hikosaka, 2002). However, it was not shown whether those signals were transmitted from SNr to SC.

                        Another elusive issue is the crossed connection of the SNr-SC pathway. Anatomical studies have shown that a small proportion of SNr neurons project to the contralateral side of SC, while many SNr neurons project to the ipsilateral side of SC (Jayaraman et al., 1977; Beckstead et al., 1981; Gerfen et al., 1982; Rhoades et al., 1982; Huerta et al., 1991). In terms of uncrossed connection, Hikosaka and Wurtz (1983a) examined the neuronal signal of SC-projecting SNr neurons, focusing on their inhibitory responses during visual and memory-guided saccade tasks. Our recent study showed that the uncrossed SNr-SC pathway operates to choose or avoid visual objects by their reward-associated values (Yasuda et al., 2012). However, the crossed SNr-SC pathway may work differently, according to Jiang et al. (2003).
                        Update 14/04/2017
                        Last edited by Jo Bowyer; 14-04-2017, 07:25 PM.
                        Jo Bowyer
                        Chartered Physiotherapist Registered Osteopath.
                        "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

                        Comment


                        • #13
                          Eye movements affect postural control in young and older females

                          http://journal.frontiersin.org/artic...00216/abstract

                          Visual information is used for postural stabilization in humans. However, little is known about how eye movements prevalent in everyday life interact with the postural control system in older individuals. Therefore, the present study assessed the effects of stationary gaze fixations, smooth pursuits and saccadic eye movements, with combinations of absent, fixed and oscillating large-field visual backgrounds to generate different forms of retinal flow, on postural control in healthy young and older females. Participants were presented with computer generated visual stimuli, whilst postural sway and gaze fixations were simultaneously assessed with a force platform and eye tracking equipment, respectively. The results show that fixed backgrounds and stationary gaze fixations attenuated postural sway. In contrast, oscillating backgrounds and smooth pursuits increased postural sway. There were no differences regarding saccades. There were also no differences in postural sway or gaze errors between age groups in any visual condition. The stabilizing effect of the fixed visual stimuli show how retinal flow and extraocular factors guide postural adjustments. The destabilizing effect of oscillating visual backgrounds and smooth pursuits may be related to more challenging conditions for determining body shifts from retinal flow, and more complex extraocular signals, respectively. Because the older participants matched the young group's performance in all conditions, decreases of posture and gaze control during stance may not be a direct consequence of healthy aging. Further research examining extraocular and retinal mechanisms of balance control and the effects of eye movements, during locomotion, is needed to better inform fall prevention interventions.
                          Keywords: balance, Elderly, eye tracking, Gaze accuracy, saccadic, smooth pursuit, visual input
                          Jo Bowyer
                          Chartered Physiotherapist Registered Osteopath.
                          "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

                          Comment


                          • #14
                            The Role of the Oculomotor System in Updating Visual-Spatial Working Memory across Saccades

                            http://journals.plos.org/plosone/art...l.pone.0161829

                            Abstract

                            Visual-spatial working memory (VSWM) helps us to maintain and manipulate visual information in the absence of sensory input. It has been proposed that VSWM is an emergent property of the oculomotor system. In the present study we investigated the role of the oculomotor system in updating of spatial working memory representations across saccades. Participants had to maintain a location in memory while making a saccade to a different location. During the saccade the target was displaced, which went unnoticed by the participants. After executing the saccade, participants had to indicate the memorized location. If memory updating fully relies on cancellation driven by extraretinal oculomotor signals, the displacement should have no effect on the perceived location of the memorized stimulus. However, if postsaccadic retinal information about the location of the saccade target is used, the perceived location will be shifted according to the target displacement. As it has been suggested that maintenance of accurate spatial representations across saccades is especially important for action control, we used different ways of reporting the location held in memory; a match-to-sample task, a mouse click or by making another saccade. The results showed a small systematic target displacement bias in all response modalities. Parametric manipulation of the distance between the to-be-memorized stimulus and saccade target revealed that target displacement bias increased over time and changed its spatial profile from being initially centered on locations around the saccade target to becoming spatially global. Taken together results suggest that we neither rely exclusively on extraretinal nor on retinal information in updating working memory representations across saccades. The relative contribution of retinal signals is not fixed but depends on both the time available to integrate these signals as well as the distance between the saccade target and the remembered location.
                            It has been proposed that maintenance of accurate spatial representations across saccades is especially important for actions, but is less critical for perception [42]. The ability to keep track of a continuously present object does not necessarily require a precise prediction of its post-saccadic location. However, in order to act upon objects and to avoid obstacles, the updating of spatial movement goals is crucial.
                            Imo highly relevent for those working with movement, for which the ability to maintain equilibrium is essential.
                            Jo Bowyer
                            Chartered Physiotherapist Registered Osteopath.
                            "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

                            Comment


                            • #15
                              Saccadic Velocity in the New Suppression Head Impulse Test: A New Indicator of Horizontal Vestibular Canal Paresis and of Vestibular Compensation

                              http://journal.frontiersin.org/artic...016.00160/full

                              Objective: To determine whether saccadic velocity in the suppression head impulse paradigm (SHIMP) test is a reliable indicator of vestibular loss at the acute and at the chronic stage in patients suffering from different vestibular pathologies.

                              Methods: Thirty-five normal subjects and 57 patients suffering from different vestibular pathologies associated with unilateral vestibular loss (UVL) or bilateral vestibular loss (BVL) were tested in the SHIMPs paradigm. SHIMPs were performed by turning the head 10 times at high velocities to the left or right side, respectively. The patients were instructed to fixate on a red spot generated by a head-fixed laser projected on the wall. In this SHIMPs paradigm, healthy subjects made a large anti-compensatory saccade at the end of the head turn (a SHIMP saccade). The peak saccadic velocity, the percentage of the trials completed with saccades in 10 trials, and the latency of the saccades were quantified in each group. A video-head impulse test (v-HIT) was systematically performed in all of our subjects as well as a caloric test. The dizziness handicap inventory questionnaire was also given to chronic UVL and BVL patients.

                              Results: At the acute stage after a complete UVL, patients had zero or a few anti-compensatory saccades for low velocity head turns toward the lesioned side. These saccades had lower velocity than the anti-compensatory saccades recorded during head rotation toward the intact side and/or compared with the saccades measured in control subjects. At the chronic stage, some of the patients recovered the ability to perform SHIMP saccades at each head turn toward the lesioned side, but very often these saccades were of significantly lower velocity. In BVL patients, no anti-compensatory saccades, or only significantly smaller ones, could be detected for head turns to both sides.

                              Conclusion: SHIMP is a specific and sensitive test to detect a complete horizontal canal loss at the acute stage. In addition, it reflects the ability of patients with moderate horizontal vestibulo–ocular reflex gain decrease to generate anti-compensatory saccades in the chronic stage. In association with v-HIT, it allows determination of the residual vestibular function and to detect anti-compensatory saccades.
                              Jo Bowyer
                              Chartered Physiotherapist Registered Osteopath.
                              "Out beyond ideas of wrongdoing and rightdoing,there is a field. I'll meet you there." Rumi

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