The understanding of the subjective experience of a visually stable world despite the occurrence of an observer's eye movements has been the focus of extensive research for over 20 years. These studies have revealed fundamental mechanisms such as anticipatory receptive field (RF) shifts and the saccadic suppression of stimulus displacements, yet there currently exists no single explanatory framework for these observations. We show that a previously presented neuro-computational model of peri-saccadic mislocalization accounts for the phenomenon of predictive remapping and for the observation of saccadic suppression of displacement (SSD). This converging evidence allows us to identify the potential ingredients of perceptual stability that generalize beyond different data sets in a formal physiology-based model. In particular we propose that predictive remapping stabilizes the visual world across saccades by introducing a feedback loop and, as an emergent result, small displacements of stimuli are not noticed by the visual system. The model provides a link from neural dynamics, to neural mechanism and finally to behavior, and thus offers a testable comprehensive framework of visual stability.

Regarder ou saisir un objet constituent, à première vue, des actes simples et triviaux. De tels mouvements nécessitent, entre autres, l’existence de complexes processus entre entrées sensorielles et sorties motrices afin de compenser l’effet de la variabilité sensorimotrice inhérente au système. Un concept clé décrit ces processus de contrôle : les modèles internes. Il s’agit de représentations dynamiques de l’état de nos appareils sensorimoteurs, inscrites au sein d’un réseau d’aires cérébrales, permettant la comparaison entre un mouvement désiré (parfait) et le mouvement réalisé (bruité). Lorsqu’une différence est perçue suite à cette comparaison, un signal d’erreur motrice (EM) serait envoyé afin d’ajuster le mouvement en cours d’exécution. Nous avons réalisé une première étude chez l’Homme afin de définir le rôle des modèles internes lors d’un acte sensorimoteur simple: la saccade oculaire. Une tâche originale nous a permis d’introduire du bruit moteur artificiel (saut de cible intrasaccadique) durant une séquence saccadique. Les résultats valident l’existence d’un mécanisme de contrôle sensorimoteur optimal et confirme la prédiction d’un modèle basé sur la théorie des filtres de Kalman, pondérant la «confiance» accordée aux mouvements désirés versus réalisés en fonction de leur fiabilité (l’inverse de leur variance). Nous nous sommes alors attachés à rechercher les substrats cérébraux du calcul de l’EM en adaptant nos paradigmes chez le macaque rhésus. Nous avons enregistré l’activité électrophysiologique neuronale unitaire puis réalisé des inactivations réversibles au sein de l’aire latérale intrapariétale (LIP), région clé pour l’intégration visuo-saccadique. Nos résultats suggèrent que le cortex pariétal serait impliqué dans l’ajustement moteur du système saccadique. Le cortex pariètal pourrait ainsi accumuler des évidences (signaux d’erreur donnés par la copie d’efférence et les retours sensoriels) quant à la présence d’erreur oculomotrice puis inciter le reste du réseau saccadique à corriger cette dernière. Ce mécanisme permettrait alors d’optimiser la plupart des actions motrices réalisées dans des contextes sensorimoteurs constamment bruités / Looking at or grasping an object are simple and trivial actions. However, these types of movements require complex processing of sensory and motor information in order to compensate for the natural variability within the sensorimotor system. A key concept describes these control processes: internal models. These models are dynamical representations of the state of our effectors, supported by a network of cerebral areas, which allow the comparison between the desired movement (perfect) and the realised movement (noisy). When a difference is perceived, a motor error (ME) signal is sent in order to adjust the ongoing movement. We performed a first study with human subjects to define the role of internal models during a simple sensorimotor action: a saccade. We developed an original task in order to introduce artificial motor noise (intrasaccadic target jump) during a sequence of saccades. These results validates the existence of an optimal sensorimotor control mechanism and confirms the predictions of a model based on the Kalman filter theory. This optimal control implies a balance between the reliability given to the desired movements versus the executed movements as a function of their uncertaincy (correlate to their variability). We then investigated the neural substrates of the ME estimation by adapting our protocols for use with rhesus monkeys. We recorded the electrophysiological activity of unitary neurons and performed reversible inactivations in the lateral intraparietal area (LIP), a key area for visuo-saccadic integration. Our results suggest, therefore, that the parietal cortex plays a role in the motor adjustment of the saccadic system. We postulate that parietal cortex could accumulate evidence (i.e. error signal given by efferent copy and sensorial feedback) on the necessity to perform a corrective saccade. When the amount of evidence exceeds an error threshold, the decision to trigger a correction could be made. This process could allow the optimization of these motor actions within noisy sensorimotor context

Une façon d'explorer visuellement notre monde consiste à déplacer très rapidement nos yeux pour en analyser le contenu. Dans certaines circonstances, ces mouvements oculaires, appelés saccades, peuvent perdre de leur précision. Fort heureusement notre cerveau est capable de corriger cette imprécision en ajustant progressivement la taille de ces saccades grâce à des mécanismes de plasticité cérébrale : c'est l'adaptation saccadique. L'adaptation saccadique est souvent utilisée comme modèle d'étude des mécanismes de plasticité visuo-motrice. Nous faisons également l'hypothèse qu'elle puisse servir d'outil thérapeutique. Dans cette thèse, nous nous sommes essentiellement intéressés à l'adaptation des saccades volontaires en augmentation d'amplitude chez des sujets contrôles et chez des patients souffrant d'une amputation homonyme du champ visuel (hémianopsie latérale homonyme). Les expériences 1 à 3, réalisées chez le sujet contrôle, ont permis de découvrir les repères utilisés par le cerveau pour réaliser cette adaptation sensori-motrice et coder l' environnement visuel (expérience 1 ), et les mécanismes d'adaptation saccadique quand la cible visuelle n'est pas directement codée (remapping dans l'expérience 2 et cible virtuelle dans l'expérience 3). Enfin l'expérience 4 propose une application clinique du protocole d'adaptation des anti-saccades utilisé lors de l'expérience 3, dans un but thérapeutique de rééducation comportementale de patients hémianopsiques / One way to visually explore our environment consists to rapidly displace our eyes to analyze its content. Under certain circumstances, these ocular movements called saccades can become inaccurate. Fortunately our brain is able to correct this inaccuracy by progressively adjusting the size of saccades thanks to plasticity mechanisms called saccadic adaptation. Saccadic adaptation is often used as a model to study visuo-motor plasticity. We also suggest that it could be used as a rehabilitation tool. ln this thesis, we were interested in outward adaptation of voluntary saccades in healthy subjects and patients suffering from a half visual field loss for both eyes (lateral homonymous hemianopia). Experiments 1 to 3, performed on healthy subjects, gave us opportunity to acquired complementary knowledge on the reference frame used by the brain to code its environment (experience 1) and on adaptation mechanisms when a visual target is not directly coded (remapping in experiment 2 virtual target in experiment 3). Finally, experiment 4 suggests to clinically implement the anti-saccades adaptation protocol used in experiment 3, as a new rehabilitation tool tested in hemianopie patients

O objetivo do estudo foi avaliar parâmetros da cinemática palpebral durante o piscar espontâneo e movimentos sacádicos palpebrais em pacientes com ptose congênita submetidos à correção cirúrgica pela técnica de suspensão frontal com fáscia muscular. Com um sistema de câmeras de captação infravermelha para análise tridimensional de movimentos foi feito registro simultâneo de movimentos de supercílio e de pálpebra. Para análise do piscar espontâneo foram avaliados 17 pacientes com ptose congênita que realizaram correção cirúrgica pela técnica de suspensão frontal com utilização de fáscia muscular autógena (n=14), e fáscia lata preservada (n=3), e para o estudo do movimento sacádico palpebral, a avaliação foi dos 14 pacientes que utilizaram apenas fáscia autógena. Um grupo controle com 17 indivíduos normais também foi medido. Para análise do piscar espontâneo um programa foi utilizado para medidas de amplitude e velocidade máxima de movimento durante a observação de um filme comercial por 5 minutos. Para análise do movimento sacádico palpebral foram realizadas medidas em 10, 20, 30, 40 e 50 graus do olhar para baixo. A avaliação da superfície ocular em lâmpada de fenda com utilização de fluoresceína foi realizada nos pacientes que apresentavam ou não lagoftalmo. O número de piscadelas foi significativamente diminuído nos pacientes. A distribuição do intervalo entre as piscadelas foi similar nos dois grupos. A média de amplitude da fase descendente do piscar dos pacientes foi apenas 38% da média do grupo controle. A inclinação da reta da \"main sequence\" para o piscar espontâneo para os pacientes foi mais baixa. Nos controles o movimento do supercilio foi muito pequeno e insignificante durante o piscar espontâneo. Nos pacientes, a média de amplitude do movimento do supercílio foi cinco vezes maior que nos controles chegando a 45% da amplitude do piscar. Os movimentos sacádicos palpebrais mostraram uma importante restrição e não aumentou além de 30 graus do olhar para baixo. A velocidade máxima da pequena amplitude dos movimentos sacádicos palpebral foi muito baixa. Enquanto a movimentação do supercilio no grupo controle ficou entre 3,3 e 9,3% do movimento sacadico palpebral, nos pacientes a movimentação do supercílio foi responsável por 43,5 a 57,4% do movimento palpebral. Lagoftalmo foi encontrado em 13 (76,5%) dos pacientes. Apenas 3 (23%) mostraram sinais de ceratopatia superficial inferior, apesar da presença do fenômeno de Bell. A amplitude e velocidade do piscar espontâneo está severamente diminuída em pacientes com suspensão frontal com fáscia muscular. Esse tipo de material causa um efeito restritivo permanente nas propriedades elásticas das pálpebras. Após a cirurgia a amplitude do piscar é dependente da amplitude do movimento do supercílio. O lagoftalmo é uma consequência natural da suspensão frontal com fáscia muscular. / The purpose of the present investigation was to measure lid kinematics parameters in spontaneous blink metrics and downward eyelid saccadic movements in patients with congenital ptosis operated with frontalis slings with muscles fascia. A optoeletronic system was employed with infrared 3-dimensional video motion analyzer to simultaneously measure brow motion and spontaneous blinks in 17 patients with congenital ptosis who underwent frontalis sling with autogeneous muscle fascia (n=14) and banked fascia lata (n=3). Downward eyelid saccadic movements were analyzed only in the 14 patients with autogeneous muscle fascia. A control group of equal number of healthy subjects was also measured. For analyses of spontaneous blinks, a customized software identified and quantified the amplitude and maximum velocity during 5 minutes observation of a commercial movie. For downward eyelid saccadic movements, 10, 20, 30, 40 and 50 degrees of downgaze were measure. The corneal status of the patients with and without lagophthalmos was evaluated with slit lamp biomicroscopy with fluorescein staining. Blink rate was significantly diminished in the patients. The distribution of interblink time was similar in both groups. The mean amplitude of the down phase of the patients\' blinks was only 38% of the controls. The main sequence slope of the patients´ blinks was abnormally low. In controls brow motion was a minute and random event no related to blinks. In the patients, the means brow amplitude was 5 times higher than in controls reaching 45% of the blink amplitude. The lid saccades of the patients were severely restricted and did not increase beyond 30 degrees of downgaze. The maximum velocity of the small amplitude lid saccades was also abnormally low. While in controls brow motion accounted for about 3,3 to 9,3% of the lid saccades, in the patients brow motion was responsible for more than 43,5% to 57,4% lid movements. Lagophthalmos was detected on 13 (76,5%) patients. Out of these 3 (23%) showed signs of inferior superficial keratopathy despite the presence of normal. Spontaneous blink amplitude and velocity are severely impaired in patients with fascia slings. This material has a permanent restrictive effect on the elastic properties of the lids. After surgery blinking amplitude is linearly related to the amplitude of brow motion. Postoperative lagophthalmos is a natural consequence of the slings with muscle fascia.

Le système visuel humain est complexe par son organisation anatomique et par son fonctionnement incomplètement élucidé. Il est fonctionnellement divisé en deux systèmes. Le premier système est destiné à la vision consciente communément appelée voie visuelle principale ou en anglais « image forming visual pathways ». Le second, appelé système secondaire ou accessoire, n’apporte pas d’information visuelle consciente, il est dit « non image forming visual pathway ». Ce dernier apporte à notre cerveau une information sur l’environnement telle que la sensation jour/nuit. Ses fonctions sont sous-tendues par l’afflux d’informations rétiniennes non visuelles sur des structures de l’hypothalamus comme le noyau supra-chiasmatique. Les deux systèmes visuels ont un substratum anatomique complexe faisant intervenir de nombreuses structures anatomiques au sein des différents étages du cerveau cortical et sous-cortical comme les noyaux gris centraux dits « Basal Ganglias » (BG). Le système visuel secondaire intervient aussi comme une structure de contrôle des mouvements oculomoteurs tels que la poursuite ou les saccades nécessaires pour explorer notre environnement. Ainsi les saccades oculomotrices sont sous le contrôle modulateur des BG. De ce fait l’étude des saccades apparait comme un très bon modèle pour explorer le fonctionnement du système extrapyramidal au cours des maladies neuro-dégénératives. Les connaissances actuelles sur ce système de contrôle des saccades proviennent essentiellement des études sur le primate non humain et sur des observations cliniques chez l’homme au cours de pathologies dégénératives ou toxiques des BG. L’observation des structures anatomiques, en particulier du réseau de la substance blanche cérébrale qui supporte les connections axonales, n’est pas accessible à l’imagerie clinique de routine. Pour décrire et étudier ces réseaux de connections, la notion de connectomique a été introduite il y a un dizaine d’années. Dans ce travail, nous nous sommes donné l’objectif de décrire le connectome des saccades oculomotrices sur un plan structurel. Nous avons exploré les structures sous-corticales intervenant dans le contrôle des saccades comme les BG, le colliculus supérieur et le pulvinar. Pour ce faire, nous avons utilisé l’imagerie IRM structurelle en diffuseur de tension (DTI) chez deux groupes de patients présentant une maladie neuro-dégénérative : un groupe souffrant de maladie de Parkinson chez qui une atteinte des BG et une dysfonction des saccades sont reconnues, et un groupe de trembleurs essentiels reconnu pour ne pas présenter de dysfonction des saccades et chez qui les BG sont épargnés. Le résultat de ce travail a permis pour la première fois une description in vivo du connectome des saccades chez l’Homme. Il a de plus montré des différences dans la structure du connectome dans les deux groupes de patients. Une meilleure connaissance de ce connectome pourrait permettre de mieux comprendre certains troubles oculomoteurs et aussi de suivre l’évolution de certaines maladies neurodegeneratives. / Visual system is complex by its anatomy and its function. Neuro-anatomists have been interested in understanding the link between the visual pathways and the brain for centuries. Classical brain fixation and dissection methods were used to describe the visual pathways identifiable macroscopically. Non–image visual pathway, particularly the part involves in saccadic eye movements network in human is still not mastered. Our current knowledge in SCM is based on animal studies, anatomic dissection and brain histopathology examination of specimens from patients with clinical basal ganglia (BG) disorders. Saccadic eye movements (SCM) are under the control of the basal ganglia (BG) and SCM circuitry within the BG represents a good model for studying pathology in the extra-pyramidal system. The diagnosis of Parkinson’s disease (PD), which affects SEM and its distinction from non-dopaminergic, essential tremor (ET) where SEM are not impaired can be challenging and still relies on clinical observations. Diffusion tensor imaging and fiber tractography (DTI-FT), a new MRI technology, can be used to evaluate the presence and integrity of white matter tracts using directional diffusion patterns of water. The purpose of this study is to use DTI-FT to analyse SEM networks within BG and compare the SEM neural pathways or connectome of patients clinically diagnosed with PD and ET. To date, there are no studies, using DTI-FT for the extensive exploration of non-image visual pathways and SCM circuits, notably the deep brain connections. For this goal, we introduced the concept of SCM connectomes, derived from the general concept of connectome. Our study used structural MRI to identify nuclei and fascicles of the SCM connectome in PD and ET patients; imageries were acquired in routine clinical conditions fitted for DBS surgery. We found a reduction of the fiber number in two fascicles of the connectome in PDcompared to ET group.

Background: Estrogen has been reported to enhance well-being and quality of life during the climacteric phase. In women with an intact uterus estrogen treatment is always combined with progestins in order to protect the endometrium from hyperplasia and malignancies. However, in certain women the addition of progestins causes cyclicity in negative mood symptoms and physical symptoms similar to those encountered during ovulatory cycles in women with premenstrual dysphoric disorder (PMDD). The ovarian hormones estradiol and progesterone have profound effects on a number of neurotransmitter systems in the brain, such as the gamma aminobutyric acid (GABA) system and the serotonergic system. Progesterone metabolites, such as allopregnanolone and pregnanolone (also referred to as neurosteroids) modify the GABAA receptor in the central nervous system (CNS) and enhance GABAergic inhibitory transmission. Neurosteroid sensitivity in human studies can be studied by saccadic eye movement measurements using pharmacodynamic challenges with pregnanolone. Altered neurosteroid sensitivity has been suggested as a possible contributory factor to the progesterone/progestin-induced adverse mood effects of hormone replacement therapy (HRT). There is also evidence of estrogen treatment affecting the serotonergic system in postmenopausal women, although progestin addition has been less well studied. Aims and method: The aim was to investigate whether the negative mood symptoms experienced during the progestin or progesterone phase of HRT were associated with changes in neurosteroid sensitivity, or changes in platelet serotonin uptake site (transporter) and serotonin2A (5-HT2A) receptor binding. The intention was also to investigate whether hormonal changes during the normal menstrual cycle affect these peripheral serotonergic parameters. Postmenopausal women with climacteric symptoms were given HRT in two randomized, double-blinded, placebo-controlled crossover studies. The women received 2 mg estradiol (E2) continuously during 28- day cycles. Synthetic progestins or natural progesterone were added sequentially during the last 14 days, and compared to a placebo addition. Before treatment, as well as during the last week of each treatment cycle the pharmacodynamic response to pregnanolone was assessed using saccadic eye movement measurements. Throughout the studies daily symptom ratings were made. In the study regarding synthetic progestins, platelet serotonin transporter and 5-HT2A receptor binding were assayed before entering the study, as well as during the last week of each treatment cycle. In the study on reproductive women, blood samples were collected for analysis of platelet serotonin transporter and 5-HT2A receptor binding at six different points in time during the menstrual cycle. Results and conclusion: The addition of synthetic progestins to estrogen treatment increased negative mood symptoms and physical symptoms, whereas positive symptoms decreased. The addition of progestins also increased the sensitivity to pregnanolone. The addition of natural progesterone to estrogen treatment increased the sensitivity to pregnanolone. However, in this study the pregnanolone sensitivity was enhanced also during estrogen treatment. Women expressing cyclicity in negative mood symptoms were more sensitive to pregnanolone than women without symptom cyclicity. Thus, it is evident that mood deterioration during HRT is associated with altered neurosteroid sensitivity. Platelet serotonin transporter and 5-HT2A receptor binding did not change during the different treatment conditions in HRT. Thus, we were unable to explain the negative mood changes of HRT by use of these peripheral serotonergic parameters. In the study on reproductive women however, it was clear that the serotonergic variables did change during the menstrual cycle. Binding to the serotonin transporter was higher in the late follicular phase than in the ovulatory, early luteal or mid-luteal phases. Binding to the 5-HT2A receptor was higher in the early follicular phase and the early luteal phase than in the mid-luteal phase. These findings may provide a link between the ovarian steroids, and the GABAergic and serotonergic neurotransmitter systems, which in turn, could explain part of the specific vulnerability that women have for the development of adverse mood effects during HRT, mood and anxiety disorders and for the deterioration of mood so frequently seen during the luteal phase.

Gamma oscillations of local field potentials (LFP) in the basal ganglia and thalamus had not been studied during saccades. Eleven patients were studied during deep brain stimulation (DBS); 6 were in the subthalamic nucleus (STN); 3 in the globus pallidus interna (GPi); and 2 in the thalamic ventralis intermedius nucleus (Vim). Patients performed horizontal saccades to visual targets while LFPs from DBS electrodes, scalp electroencephalogram (EEG), and electrooculogram (EOG) were recorded. Wavelet spectrograms were generated and saccade onset and event-related gamma synchronizations (ERS) were compared to baseline without eye motion. ERS were recorded at and after saccade onset in the STN, GPi and Vim, EEGs and EOGs; but were absent during target light illumination without saccades. ERS were symmetric in all DBS contacts and appeared identical in DBS LFPs, frontal EEGs and EOGs. These findings indicate their origin from extraocular muscle spike potentials rather than brain neural activity.

Gamma oscillations of local field potentials (LFP) in the basal ganglia and thalamus had not been studied during saccades. Eleven patients were studied during deep brain stimulation (DBS); 6 were in the subthalamic nucleus (STN); 3 in the globus pallidus interna (GPi); and 2 in the thalamic ventralis intermedius nucleus (Vim). Patients performed horizontal saccades to visual targets while LFPs from DBS electrodes, scalp electroencephalogram (EEG), and electrooculogram (EOG) were recorded. Wavelet spectrograms were generated and saccade onset and event-related gamma synchronizations (ERS) were compared to baseline without eye motion. ERS were recorded at and after saccade onset in the STN, GPi and Vim, EEGs and EOGs; but were absent during target light illumination without saccades. ERS were symmetric in all DBS contacts and appeared identical in DBS LFPs, frontal EEGs and EOGs. These findings indicate their origin from extraocular muscle spike potentials rather than brain neural activity.

La saccade oculaire, i.e. mouvement très rapide des yeux, permet d’amener l’objet d’intérêt sur la fovéa, afin que le système visuel puisse analyser ses propriétés. Malgré l’importance du cortex occipital dans le traitement de l’information visuelle, son rôle dans la génération de saccades est encore peu connu. Pour ce faire, l’hémianopsie latérale homonyme consécutive à une atteinte unilatérale du cortex occipital (i.e. amputation de l’hémichamp visuel controlésionnel) peut être considérée comme modèle d’étude. En effet, malgré la perte de la vision consciente, certains patients sont capables de répondre à un stimulus présenté dans l’hémichamp controlésionnel. Ces capacités préservées, appelées vision aveugle, peuvent être de nature attentionnelle et/ou motrice. Le but de cette thèse est ainsi d’étudier l’implication du cortex occipital dans la génération de saccades. En manipulant les propriétés spatiales et temporelles du point de fixation, de la cible ou d’un distracteur, les paramètres des saccades de ces patients ont été examinés en étudiant différents types de saccades (volontaires et réactives) ainsi que des effets connus pour moduler les paramètres saccadiques (effets d’un distracteur et adaptation saccadique). Parallèlement, les capacités de vision aveugle ont été examinées à partir de différentes tâches perceptives (détection et discrimination), nécessitant une réponse verbale, manuelle (appui-bouton) et/ou oculomotrice (saccade et fixation). Malgré la perte de la conscience visuelle du stimulus présenté dans l’hémichamp controlésionnel, des capacités de vision aveugle sont attestées par la réalisation d’une action oculomotrice sur ce stimulus. La dichotomie observée dans ces capacités en fonction de la nécessité de réaliser une action sur la stimulation visuelle suppose une implication du cortex occipital dans les mécanismes de sélection pour l’action et pour la perception. Par ailleurs, une dissociation est observée dans l’atteinte des paramètres saccadiques. Si l’initiation de la saccade – reflétée par la latence - est altérée dans les deux hémichamps ipsi- et controlésionnel, le calcul de la métrique de la saccade – reflétée par l’amplitude - est spécifiquement altéré dans l’hémichamp controlésionnel. Ainsi, nos résultats sont en faveur d’une implication du cortex occipital dans la génération des saccades oculaires ainsi qu’en faveur d’un modèle fonctionnel de génération de saccades à deux voies de traitement parallèles dédiées respectivement à l’initiation et à la métrique de la saccade. / Saccadic eye movements are rapid and necessary to targeting the interesting object in our visual environment. Despite the crucial role of the occipital cortex in the visual process, its implication in the saccadic generation is poorly studied. To examine this, we can use one pathological model, the homonymous hemianopia (i.e. loss of contralateral visual hemifield to unilateral occipital lesion). Despite the loss of conscious vision, some patients can be able to react at one stimulus presented in the contralesional hemifield. These residual abilities, named blindsight, can be observed in attentional and/or motor tasks. The aim of this thesis is examine the parameters of saccades in hemianopic patients, through the study of saccade types (voluntary and reflexive saccades) and classical effects on the modulation of saccadic parameters (gap effect and distractor effects, by manipulating the spatial and temporal characteristics of the fixation point, the target or a distractor). Furthermore, the residual abilities are investigated by perceptual tasks (detection or discrimination) with different types of response: verbal, manual (key press) and motor (saccade or fixation). Overall, despite the loss of conscious perception of the target presented in the contralesional hemifield, residual abilities are found as showed by the saccadic execution toward the target, with a dichotomy depending on the need to perform an action on the visual stimulation. This suggests that the role of the occipital cortex is not the same in the selection mechanism for the action and the perception. Concerning to saccadic programming, dissociation is found in the saccadic parameters. The saccadic initiation, studied by with the saccade latency, is altered in both ipsi- and contralesional hemifields but the saccade metric, studied by the saccade amplitude, is altered in the contralesional hemifield. This suggests that the occipital cortex is implicated in the saccade generation and that saccade programing involves two pathways for the initiation and the metric of saccades.

Obwohl Blickbewegungen einen elementaren Bestandteil des natürlichen Sehens darstellen, werden hirnelektrische Korrelate der visuellen Verarbeitung im Elektroenzephalogramm (EEG) zumeist während passiver Stimulation des ruhenden Auges erfasst. Ein alternativer methodischer Zugang ist die Kopplung des EEG an Beginn oder Ende natürlich auftretender Augenbewegungen mit Hilfe simultanen, hochauflösenden Eye-Trackings (ET). Die resultierenden sakkaden- bzw. fixationskorrelierten Potentiale (SRPs/FRPs) wurden in zwei Forschungskontexten untersucht und angewendet. Der erste Teil der Arbeit (Publikation 1 & 2) befasst sich mit den elektrophysiologischen Korrelaten von Mikrosakkaden, unwillkürlichen Fixationsaugenbewegungen die auch während traditioneller EEG-Messungen auftreten. Es wird gezeigt, dass Mikrosakkaden trotz ihrer geringen Amplitude eine wesentliche, aber mit herkömmlichen Methoden kaum auszuschließende Quelle muskulärer und kortikaler Aktivität im EEG darstellen (mikrosakkadische SRPs), welche in der Mehrzahl experimenteller Durchgängen aktiv ist, und zur Fehlinterpretation reizgekoppelter Potentiale führen kann. Der zweite Teil der Arbeit demonstriert die Machbarkeit und Nützlichkeit von FRP-Analysen zur Untersuchung hirnelektrischer Prozesse beim Lesen. In Publikation 3 werden Einflüsse verschiedener Messartefakte sowie visuell-evozierter, motorischer und kognitiv modulierter Potentiale auf die FRP-Wellenform beschrieben und Methoden zur Signaloptimierung vorgeschlagen. Wir zeigen, dass sich im natürlichen Satzlesen der klassische N400 Wortvorhersagbarkeitseffekt reproduzieren und in Bezug zu Maßen der Fixationsdauer setzen lässt. In Publikation 4 wurde mittels FRPs das Ausmaß der parafovealen Wortverarbeitung bestimmt. Simultanes ET ist eine sinnvolle Ergänzung zur bestehenden EEG-Methodik, sowohl zur Kontrolle von Mikroaugenbewegungen, als auch zur Erforschung natürlichen Blickbewegungsverhaltens und Integration von Befunden der ET- und EEG-Forschung. / Although natural vision involves an active sampling of the environment with several saccadic eye movements per second, electroencephalographic (EEG) correlates of visual cognition are predominantly recorded under artificial conditions of prolonged fixation. An alternative approach to EEG analysis, explored in the present thesis, is to time-lock the signal not to passive stimulations, but to the on- or offsets of naturally occurring eye movements, yielding saccade- and fixation-related potentials (SRPs/FRPs). Using simultaneous high-resolution eye-tracking (ET), this technique was applied in two contexts. The first part of the thesis (publications 1 & 2) investigated brain-electric correlates of microsaccades, small involuntary eye movements, which occur despite attempted fixation during traditional EEG paradigms. In a series of experiments, we show that SRPs from microsaccades present a significant, but normally hidden source of visuocortical potentials that is active in most trials and can confound the interpretation of stimulus-locked data under specific conditions. The second part of the thesis assessed the feasibility and utility of using FRPs in the study of natural reading. Publication 3 provides a review of artifact sources, low-level factors, and high-level influences determining the FRP waveform in free viewing and proposes methods to optimize signal quality. We then replicate the N400 word predictability effect, a cornerstone of neurolinguistic research, in left-to-right sentence reading and relate N400 amplitude to measures of fixation time. In publication 4, the FRP technique was combined with gaze-contingent display manipulations to investigate the depth of parafoveal preprocessing in fluent reading. Our results show that simultaneous recordings improve the understanding of electrophysiological data recorded during fixation, extend the EEG’s methodological scope to naturalistic viewing scenarios, and help to integrate findings from EEG and ET research.