Predication-Error-Based Intrinsically Motivated Saccade Learning

The quick, simultaneous movements of both eyes in the same direction is called a saccade, and the process of developing an internal model for the eyes’ movement-control based on visual stimuli is called saccade learning. All humans use this type of eye motion to bring salient objects to the foveal locations of the retina, even if the objects are located randomly in the surrounding environment. To begin with, infants are not able to perform this type of eye motion, but sensory information motivates them to start learning saccadic behavior. In this paper, a sensory prediction-error-based intrinsically motivated model is proposed for learning saccadic eye movements, and this approach is more consistent with biological systems for saccade learning. Predicted Coding/Biased Competition using Divisive Input Modulation (PC/BC-DIM) network is used for saccade learning using sensory prediction errors. The quantification of sensory prediction errors provides an intrinsic reward. A simulated humanoid agent, iCub, is used to assess and quantify the performance of the proposed model. The performance metrics used for this purpose are percentage mean post-saccadic distance and standard deviation. The mean post-saccadic distance for the proposed model was less than 1°, which is biologically plausible.

Two cases of neuronopathic form of Gaucher disease – diagnostic difficulties

Background: Gaucher disease is one of the most common inherited lysosomal storage diseases caused by the deficiency of the enzyme β-glucocerebrosidase, leading to the accumulation of glucocerebroside. Depending on the clinical manifestations, two different forms of the disease are distinguished – the non-neuronopathic form (type 1) with a variety of presentations – from asymptomatic to symptomatic patients (characterized by hepatosplenomegaly, thrombocytopenia, anemia and osteopenia), and the neuronopathic form (known as types 2 and 3). Besides visceral, osseous, and hematopoietic organ lesions, neuronopathic forms are associated with central nervous system involvement (bulbar and pyramidal signs, horizontal saccadic eye movements, myoclonic epilepsy, progressive development delay). In type 2, the neurological symptoms appear earlier and are more severe, the survival time is shorter. In type 3, the neurological symptoms are milder and allow patients to live a fully productive life. Case presentation: This article includes a review of two cases of neuronopathic Gaucher disease: type 2 and severe type 3. Both patients presented symptoms during infancy and the manifestations were similar but varied in intensity and the dynamics of progress. Enzyme replacement therapy was started in both cases, which decreased visceral symptoms. Conclusions: Both described cases indicate the lack of knowledge and the tendency of doctors to disregard the possibility of Gaucher disease in their paediatrics patients.

Intrinsic bursts facilitate learning of Lévy flight movements in recurrent neural network models

Isolated spikes and bursts of spikes are thought to provide the two major modes of information coding by neurons. Bursts are known to be crucial for fundamental processes between neuron pairs, such as neuronal communications and synaptic plasticity. Deficits in neuronal bursting can also impair higher cognitive functions and cause mental disorders. Despite these findings on the roles of bursts, whether and how bursts have an advantage over isolated spikes in the network-level computation remains elusive. Here, we demonstrate in a computational model that not isolated spikes but intrinsic bursts can greatly facilitate learning of Lévy flight random walk trajectories by synchronizing burst onsets across neural population. Lévy flight is a hallmark of optimal search strategies and appears in cognitive behaviors such as saccadic eye movements and memory retrieval. Our results suggest that bursting is a crucial component of sequence learning by recurrent neural networks in the brain.

Urgency forces stimulus-driven action by overcoming cognitive control

Intelligent behavior requires to act directed by goals despite competing action tendencies triggered by stimuli in the environment. For eye movements, it has recently been discovered that this ability is briefly reduced in urgent situations (Salinas et al., 2019). In a time-window before an urgent response, participants could not help but look at a suddenly appearing visual stimulus, even though their goal was to look away from it. Urgency seemed to provoke a new visual–oculomotor phenomenon: A period in which saccadic eye movements are dominated by external stimuli, and uncontrollable by current goals. This period was assumed to arise from brain mechanisms controlling eye movements and spatial attention, such as those of the frontal eye field. Here, we show that the phenomenon is more general than previously thought. We found that also in well-investigated manual tasks, urgency made goal-conflicting stimulus features dominate behavioral responses. This dominance of behavior followed established trial-to-trial signatures of cognitive control mechanisms that replicate across a variety of tasks. Thus together, these findings reveal that urgency temporarily forces stimulus-driven action by overcoming cognitive control in general, not only at brain mechanisms controlling eye movements.

Eye-Movement does not reduce ratings of vividness and emotionality or the number of intrusive thoughts of unpleasant memories: Implications for Eye-Movement Desensitisation and Reprocessing (EMDR)

<p>Eye-Movement Desensitisation and Reprocessing (EMDR) is a psychotherapy that incorporates the use of saccadic Eye-Movements (EM) to alleviate distress caused by traumatic memories. Although EMDR is recognised as a front-line treatment for individuals suffering from Posttraumatic Stress Disorder (PTSD), the mechanisms underlying the efficacy of the EM component remain a point of contention. The aim of the current research was to investigate first, whether EM reduced ratings of memory vividness and emotionality by taxing Working Memory (WM) capacity, and second, to examine whether EM lowered the number of intrusive thoughts under two opposing suppression conditions. In two experiments, 244 non-clinical participants were asked to recall an unpleasant memory while simultaneously engaging in fast-EM, slow-EM or a no-EM control. Participants then received an instruction to intentionally avoid thinking about the memory, or to think about whatever came to mind. Relative to no-EM, fast-EM and slow-EM had no significant effect on vividness and emotionality ratings, nor did they influence the number of intrusive thoughts. In addition, the level of suppression intent had no impact on memory outcomes. Overall, the results from these two experiments oppose earlier findings in support of WM theory, and a significant body of research that has demonstrated the efficacy of the EM component. Implications for the EM component in EMDR are discussed, and an alternative explanation for EM is offered.</p>

Eye-Movement does not reduce ratings of vividness and emotionality or the number of intrusive thoughts of unpleasant memories: Implications for Eye-Movement Desensitisation and Reprocessing (EMDR)

<p>Eye-Movement Desensitisation and Reprocessing (EMDR) is a psychotherapy that incorporates the use of saccadic Eye-Movements (EM) to alleviate distress caused by traumatic memories. Although EMDR is recognised as a front-line treatment for individuals suffering from Posttraumatic Stress Disorder (PTSD), the mechanisms underlying the efficacy of the EM component remain a point of contention. The aim of the current research was to investigate first, whether EM reduced ratings of memory vividness and emotionality by taxing Working Memory (WM) capacity, and second, to examine whether EM lowered the number of intrusive thoughts under two opposing suppression conditions. In two experiments, 244 non-clinical participants were asked to recall an unpleasant memory while simultaneously engaging in fast-EM, slow-EM or a no-EM control. Participants then received an instruction to intentionally avoid thinking about the memory, or to think about whatever came to mind. Relative to no-EM, fast-EM and slow-EM had no significant effect on vividness and emotionality ratings, nor did they influence the number of intrusive thoughts. In addition, the level of suppression intent had no impact on memory outcomes. Overall, the results from these two experiments oppose earlier findings in support of WM theory, and a significant body of research that has demonstrated the efficacy of the EM component. Implications for the EM component in EMDR are discussed, and an alternative explanation for EM is offered.</p>

Saccadic Eye Movements in Elderly Depressed Patients With Suicidal Behaviors: An Exploratory Eye-Tracking Study

Suicidal behaviors (SBs) are often associated with impaired performance on neuropsychological executive functioning (EF) measures that encourage the development of more specific and reliable tools. Recent evidence could suggest that saccadic movement using eye tracking can provide reliable information on EF in depressive elderly. The aim of this study was to describe oculomotor performances in elderly depressed patients with SB. To achieve this aim, we compared saccadic eye movement (SEM) performances in elderly depressed patients (N = 24) with SB and with no SB in prosaccade (PS) and antisaccade (AS) tasks under the gap, step, and overlap conditions. All participants also underwent a complete neuropsychological battery. Performances were impaired in patients with SB who exhibited less corrected AS errors and longer time to correct them than patients with no SB. Moreover, both groups had a similar performance for PS latencies and correct AS. These preliminary results suggested higher cognitive inflexibility in suicidal patients compared to non-suicidal. This inflexibility may explain the difficulty of the depressed elderly in generating solutions to the resurgence of suicidal ideation (SI) to respond adequately to stressful environments. The assessment of eye movement parameters in depressed elderly patients may be a first step in identifying high-risk patients for suicide.

The effect of subliminal incentives on goal-directed eye movements

Over the last decades, several studies have demonstrated that conscious and unconscious reward incentives both affect performance in physical and cognitive tasks, suggesting that goal-pursuit can arise from an unconscious will. Whether the planning of goal-directed saccadic eye movements during an effortful task can also be affected by subliminal reward cues has not been systematically investigated. We employed a novel task where participants made several eye movements back and forth between a fixation point and a number of peripheral targets. The total number of targets visited by the eyes in a fixed amount of time determined participants' monetary gain. The magnitude of the reward at stake was briefly shown at the beginning of each trial and masked by pattern images superimposed in time so that at shorter display durations participants perceived reward incentives subliminally. We found a main effect of reward across all display durations as higher reward enhanced participants' oculomotor effort measured as the frequency and peak velocity of saccades. This effect was strongest for consciously perceived rewards but also occurred when rewards were subliminally perceived. Although we did not find a statistically significant dissociation between the reward-related modulation of different saccadic parameters, across two experiments the most robust effect of subliminal rewards was observed for the modulation of the saccadic frequency but not the peak velocity. These results suggest that multiple indices of oculomotor effort can be incentivized by subliminal rewards and that saccadic frequency may provide the most sensitive indicator of subliminal incentivization of eye movements.

A sensory memory to preserve visual representations across eye movements

Saccadic eye movements (saccades) disrupt the continuous flow of visual information, yet our perception of the visual world remains uninterrupted. Here we assess the representation of the visual scene across saccades from single-trial spike trains of extrastriate visual areas, using a combined electrophysiology and statistical modeling approach. Using a model-based decoder we generate a high temporal resolution readout of visual information, and identify the specific changes in neurons’ spatiotemporal sensitivity that underly an integrated perisaccadic representation of visual space. Our results show that by maintaining a memory of the visual scene, extrastriate neurons produce an uninterrupted representation of the visual world. Extrastriate neurons exhibit a late response enhancement close to the time of saccade onset, which preserves the latest pre-saccadic information until the post-saccadic flow of retinal information resumes. These results show how our brain exploits available information to maintain a representation of the scene while visual inputs are disrupted.