14 results on '"Lefèvre, Philippe"'
Search Results
2. Oculomotor prediction of accelerative target motion during occlusion: long-term and short-term effects
- Author
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Bennett, Simon J., Orban de Xivry, Jean-Jacques, Lefèvre, Philippe, and Barnes, Graham R.
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- 2010
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3. A model that integrates eye velocity commands to keep track of smooth eye displacements
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Blohm, Gunnar, Optican, Lance M., and Lefèvre, Philippe
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- 2006
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4. Integration of past and current visual information during eye movements in amblyopia
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Deravet, Nicolas, Yüksel, Demet, Orban de Xivry, Jean-Jacques, Lefèvre, Philippe, Ramat, S, Shaikh, AG, UCL - SST/ICTM/INMA - Pôle en ingénierie mathématique, UCL - SSS/IONS/COSY - Systems & cognitive Neuroscience, UCL - SSS/IONS/NEUR - Clinical Neuroscience, and UCL - (SLuc) Service d'ophtalmologie
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Science & Technology ,genetic structures ,Clinical Neurology ,Neurosciences ,Visual information ,Amblyopia ,Unilateral functional amblyopia ,Catch-up saccades ,Reliability-based integration ,Mathematical & Computational Biology ,Neurosciences & Neurology ,Smooth pursuit ,Life Sciences & Biomedicine ,Kalman filtering - Abstract
Combination of signals based on their reliability is an increasingly popular model for sensorimotor processing. However, how reliability is estimated, or how such estimation is affected by prolonged exposure to noisy inputs, is still unknown. In this study, we compare patients with unilateral functional amblyopia with control subjects tracking either a reliable target, or a blurry, unreliable target, in a task of repeated, sustained smooth pursuit. We provide evidence for a lower weight of visual information during smooth pursuit in amblyopic and control subjects tracking a blurry target, with no significant difference of prior information weight. In contrast, we found no evidence of lower visual information weight in the catch-up saccades of amblyopic subjects. We conclude that oculomotor performance in unilateral amblyopia mostly lays within the continuum between our control groups, without significant differences in the relative weights of prior and visual information. However, smooth pursuit exhibits additional deficits that might result from abnormal visual development. ispartof: MATHEMATICAL MODELLING IN MOTOR NEUROSCIENCE: STATE OF THE ART AND TRANSLATION TO THE CLINIC. OCULAR MOTOR PLANT AND GAZE STABILIZATION MECHANISMS vol:248 pages:45-63 ispartof: location:Univ Pavia, Pavia, ITALY status: published
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- 2019
5. Evidence for high-velocity smooth pursuit in the trained cat
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Missal, Marcus, Lefèvre, Philippe, Crommelinck, Marc, and Roucoux, André
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- 1995
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6. Computations underlying the visuomotor transformation for smooth pursuit eye movements.
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Murdison, T. Scott, Leclercq, Guillaume, Lefèvre, Philippe, and Blohm, Gunnar
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EYE movements ,VISUOMOTOR coordination ,RETINAL (Visual pigment) ,ARTIFICIAL neural networks ,GAZE - Abstract
Smooth pursuit eye movements are driven by retinal motion and enable us to view moving targets with high acuity. Complicating the generation of these movements is the fact that different eye and head rotations can produce different retinal stimuli but giving rise to identical smooth pursuit trajectories. However, because our eyes accurately pursue targets regardless of eye and head orientation (Blohm G, Lefèvre P. J Neurophysiol 104: 2103-2115, 2010), the brain must somehow take these signals into account. To learn about the neural mechanisms potentially underlying this visual-to-motor transformation, we trained a physiologically inspired neural network model to combine twodimensional (2D) retinal motion signals with three-dimensional (3D) eye and head orientation and velocity signals to generate a spatially correct 3D pursuit command. We then simulated conditions of 1) head roll-induced ocular counterroll, 2) oblique gaze-induced retinal rotations, 3) eccentric gazes (invoking the half-angle rule), and 4) optokinetic nystagmus to investigate how units in the intermediate layers of the network accounted for different 3D constraints. Simultaneously, we simulated electrophysiological recordings (visual and motor tunings) and microstimulation experiments to quantify the reference frames of signals at each processing stage. We found a gradual retinal-to-intermediate-to-spatial feedforward transformation through the hidden layers. Our model is the first to describe the general 3D transformation for smooth pursuit mediated by eye- and head-dependent gain modulation. Based on several testable experimental predictions, our model provides a mechanism by which the brain could perform the 3D visuomotor transformation for smooth pursuit. [ABSTRACT FROM AUTHOR]
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- 2015
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7. Accounting for direction and speed of eye motion in planning visually guided manual tracking.
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Leclercq, Guillaume, Blohm, Gunnar, and Lefèvre, Philippe
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SENSORIMOTOR integration ,EYE movements ,PERCEPTUAL motor learning ,NEURONS ,MOTOR learning - Abstract
Accurate motor planning in a dynamic environment is a critical skill for humans because we are often required to react quickly and adequately to the visual motion of objects. Moreover, we are often in motion ourselves, and this complicates motor planning. Indeed, the retinal and spatial motions of an object are different because of the retinal motion component induced by self-motion. Many studies have investigated motion perception during smooth pursuit and concluded that eye velocity is partially taken into account by the brain. Here we investigate whether the eye velocity during ongoing smooth pursuit is taken into account for the planning of visually guided manual tracking. We had 10 human participants manually track a target while in steady-state smooth pursuit toward another target such that the difference between the retinal and spatial target motion directions could be large, depending on both the direction and the speed of the eye. We used a measure of initial arm movement direction to quantify whether motor planning occurred in retinal coordinates (not accounting for eye motion) or was spatially correct (incorporating eye velocity). Results showed that the eye velocity was nearly fully taken into account by the neuronal areas involved in the visuomotor velocity transformation (between 75% and 102%). In particular, these neuronal pathways accounted for the nonlinear effects due to the relative velocity between the target and the eye. In conclusion, the brain network transforming visual motion into a motor plan for manual tracking adequately uses extraretinal signals about eye velocity. [ABSTRACT FROM AUTHOR]
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- 2013
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8. Want to win a bowling game? Beware of even one glass of alcohol!
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Lefèvre, Philippe
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BOWLS (Game) , *SACCADIC eye movements , *ALCOHOL , *EYE movements - Abstract
Keywords: alcohol; bowling; eye movements; pupil; saccades; smooth pursuit EN alcohol bowling eye movements pupil saccades smooth pursuit 1017 1018 2 02/17/21 20210215 NES 210215 Most of us already experienced the consequences of alcohol consumption, if only by observing it. This study sheds new light on the influence of alcohol on human behaviour by reporting a very robust and significant effect of alcohol at ultra-low blood-alcohol levels on eye movements. Alcohol, bowling, eye movements, pupil, saccades, smooth pursuit. [Extracted from the article]
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- 2021
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9. How Do Primates Anticipate Uncertain Future Events?
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De Hemptinne, Coralie, Nozaradan, Sylvie, Duvivier, Quentin, Lefèvre, Philippe, and Missal, Marcus
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EYE movements ,PSYCHOPHYSICS ,MACAQUES ,PRIMATES ,PSYCHOPHYSIOLOGY - Abstract
The timing of an upcoming event depends on two factors: its temporal position, proximal or distal with respect to the present moment, and the unavoidable stochastic variability around this temporal position. We searched for a general mechanism that could describe how these two factors influence the anticipation of an upcoming event in an oculomotor task. Monkeys were trained to pursue a moving target with their eyes. During a delay period inserted before target motion onset, anticipatory pursuit responses were frequently observed. We found that anticipatory movements were altered by the temporal position of the target. Increasing the timing uncertainty associated with the stimulus resulted in an increase in the width of the latency distribution of anticipatory pursuit. These results show that monkeys relied on an estimation of the changing probability of target motion onset as time elapsed during the delay to decide when to initiate an anticipatory smooth eye movement. [ABSTRACT FROM AUTHOR]
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- 2007
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10. Spontaneous improvement in oculomotor function of children with cerebral palsy.
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Ego, Caroline, Orban de Xivry, Jean-Jacques, Nassogne, Marie-Cécile, Yüksel, Demet, and Lefèvre, Philippe
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HUMAN abnormalities , *CEREBRAL palsy , *EYE movement disorders , *EYE movements , *MOVEMENT disorders in children , *HEMIPLEGIA , *THERAPEUTICS - Abstract
Eye movements are essential to get a clear vision of moving objects. In the present study, we assessed quantitatively the oculomotor deficits of children with cerebral palsy (CP). We recorded eye movements of 51 children with cerebral palsy (aged 5-16 years) with relatively mild motor impairment and compared their performance with age-matched control and premature children. Overall eye movements of children with CP are unexpectedly close to those of controls even though some oculomotor parameters are biased by the side of hemiplegia. Importantly, the difference in performance between children with CP and controls decreases with age, demonstrating that the oculomotor function of children with CP develops as fast as or even faster than controls for some visual tracking parameters. That is, oculomotor function spontaneously improves over the course of childhood. This evolution highlights the ability of lesioned brain of children with CP to compensate for impaired motor function beyond what would be achieved by normal development on its own. [ABSTRACT FROM AUTHOR]
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- 2015
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11. Biological motion influences the visuomotor transformation for smooth pursuit eye movements
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Coppe, Sébastien, Xivry, Jean-Jacques Orban de, Missal, Marcus, and Lefèvre, Philippe
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VISUAL pathways , *EYE movements , *VISUAL perception , *COGNITION , *PSYCHOLOGY of movement , *STIMULUS satiation , *MEMORY - Abstract
Abstract: Humans are very sensitive to the presence of other living persons or animals in their surrounding. Human actions can readily be perceived, even in a noisy environment. We recently demonstrated that biological motion, which schematically represents human motion, influences smooth pursuit eye movements during the initiation period (). This smooth pursuit response is driven both by a visuomotor pathway, which transforms retinal inputs into motor commands, and by a memory pathway, which is directly related to the predictive properties of smooth pursuit. To date, it is unknown which of these pathways is influenced by biological motion. In the present study, we first use a theoretical model to demonstrate that an influence of biological motion on the visuomotor and memory pathways might both explain its influence on smooth pursuit initiation. In light of this model, we made theoretical predictions of the possible influence of biological motion on smooth pursuit during and after the transient blanking of the stimulus. These qualitative predictions were then compared with recordings of eye movements acquired before, during and after the transient blanking of the stimulus. The absence of difference in smooth pursuit eye movements during blanking of the stimuli and the stronger visually guided smooth pursuit reacceleration after reappearance of the biological motion stimuli in comparison with control stimuli suggests that biological motion influences the visuomotor pathway but not the memory pathway. [ABSTRACT FROM AUTHOR]
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- 2010
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12. Integration processes of oculomotor memory in the normal and pathological brain
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Deravet, Nicolas, UCL - SST/ICTM/INMA - Pôle en ingénierie mathématique, UCL - SSS/IONS/COSY - Systems & cognitive Neuroscience, UCL - Ecole Polytechnique de Louvain, Lefèvre, Philippe, Blohm, Gunnar, Ivanoiu, Adrian, Montagnini, Anna, Orban de Xivry, Jean-Jacques, Yüksel, Demet, and Keunings, Roland
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genetic structures ,Integration ,FTD ,Prior information ,Amblyopia ,Reliability ,eye diseases ,Eye movements ,Bayesian integration ,Memory ,Reliability-based integration ,Saccades ,Short-term prior ,Learning ,Dementia ,Short-term memory ,Smooth pursuit ,Oculomotor memory ,Primary progressive aphasia ,FTLD ,PPA ,Frontotemporal dementia - Abstract
Vision is an extremely important sense, and the eye movements that allow us to make use of it involve neural pathways across most major areas of our brain. The wide distribution of these pathways has made the study of eye movements a valuable window into the inner workings of our brains. In this thesis, we investigate the eye movements of healthy and pathological participants, first to validate and challenge a current theoretical and computational model of these movements, then to further our understanding of complex disorders that can affect the brain. In particular, we first investigate model-driven predictions by presenting participants with noisy visual information, in the form of a moving target having a Gaussian distribution of luminosity, and with variable levels of prior information about target motion. Through this, we validate a prediction of our reference model by showing reliability-weighted integration of visual and memory inputs in the control of eye movements. Then, we expand our investigation to pathological participants presenting one of two disorders thought to compromise brain areas involved in this process: either a developmental disorder that affects visual processing, amblyopia, or a degenerative disorder affecting the control of behavior and speech, fronto-temporal dementia. Using healthy participants as a reference, we discuss their performance in eye-movements tasks, highlight specific deficits, then draw parallels with the brain areas involved and our reference model. (FSA - Sciences de l'ingénieur) -- UCL, 2019
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- 2019
13. Maturation of visual tracking in typically developing children and individuals with cerebral palsy and autism spectrum disorder
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Ego, Caroline, UCL - SST/ICTM/INMA - Pôle en ingénierie mathématique, UCL - SSS/IONS/COSY - Systems & cognitive Neuroscience, UCL - Ecole Polytechnique de Louvain, Lefèvre, Philippe, Jungers, Raphaël, Bleyenheuft, Yannick, Gordon, Andrew, Masson, Guillaume, Nassogne, Marie-Cécile, Orban de Xivry, Jean-Jacques, and Yüksel, Demet
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Eye movements ,genetic structures ,Saccade ,Cerebral palsy ,Smooth pursuit ,Autism spectrum disorder ,Development ,eye diseases - Abstract
Vision is probably our most essential sense. One particularity of our environment is that it is made of moving objects. In order to get a clear vision of what surrounds us, we need a good ability to visually track moving targets. In this thesis, we studied the development of visual tracking abilities using oculomotor tasks that combine the two essential types of orienting eye movements that are smooth pursuit and saccades. As eye movements are controlled by muscles commanded through complex brain circuits, the goal was to better understand the development of oculomotor control with age. The evaluation of the typical development is also essential to detect deficits. In particular, we were interested in this thesis in characterizing the potential disorders of eye movements in children with cerebral palsy or autism spectrum disorder. Altogether, this thesis illustrates how eye movements can be used to better understand some developmental processes and disabilities. (FSA - Sciences de l'ingénieur) -- UCL, 2015
- Published
- 2015
14. Tracking the invisible requires prediction and internal models
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Orban de Xivry, Jean-Jacques, UCL - FSA/INMA - Département d'ingénierie mathématique, Lefèvre, Philippe, Blondel, Vincent, Thier, Peter, Stone, Leland, Missal, Marcus, and Barnes, Graham
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Occlusion ,Saccades ,Smooth pursuit ,Prediction ,Internal models - Abstract
In order to grasp an object in their visual field, humans orient their visual axis to targets of interest. While scanning their environment, humans perform multiple saccades (rapid eye movements that correct for a position error between eye and target) to align their visual axis with objects of interest. Humans are also able to track objects that move in their environment by means of smooth pursuit eye movements (slow eye movements that correct for any velocity error between eye and target, i.e. for any retinal slip). The appearance of a moving stimulus in the environment elicits smooth pursuit eye movements with a latency of around 100ms. Accordingly, the smooth pursuit system accounts for a change in the trajectory of a moving target with a similar delay. Due to this delay, the oculomotor system needs to develop strategies to avoid the build up of position error during tracking of a moving target. To do so, the oculomotor system uses prediction to try and anticipate the future target trajectory. However, this strategy is limited to conditions where target trajectory is predictable. Otherwise, primates have to combine pursuit and saccades in visual tracking of unpredictable moving targets to avoid large position error. This thesis focuses on both the prediction mechanisms and the interactions between saccades and pursuit. In order to investigate prediction mechanisms, we asked human subjects to pursue a moving target when it was transiently occluded. During occlusions, subjects continued to pursue the invisible target. This thesis demonstrates that this predictive pursuit response is based on a dynamic internal representation of target motion, i.e. a representation that evolves with time. This internal representation could be either built up by repetition of the same target motion or extrapolated on the basis of the pre-occlusion target motion. In addition, it is shown that during occlusions, saccades are adjusted in order to account for the large variability of the smooth pursuit response. As a consequence, it shows that the smooth pursuit command is used by internal models in order to predict future smooth pursuit response. These results demonstrate that both prediction and internal models are necessary to track the invisible and the visible. (FSA 3) -- UCL, 2007
- Published
- 2007
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