Pour percevoir le monde qui nous entoure, nous effectuons des mouvements rapides des yeux afin de placer les objets d'intérêt en fovéa, région de l'oeil où l'acuité visuelle est maximale. Ces mouvements oculaires, appelés saccades, sont précis malgré leur rapidité d'exécution. Le mécanisme assurant leur précision tout au long de la vie est l'adaptation saccadique. L'adaptation saccadique peut être facilement induite en laboratoire grâce au paradigme non invasif de double saut de la cible (McLaughlin, 1967) qui simule une « imprécision » de la visée d'une cible en déplaçant celle-ci pendant la saccade de manière répétée. Le système saccadique corrige progressivement l'erreur de visée induite artificiellement, la saccade amenant directement l'oeil vers la nouvelle position de la cible après seulement une cinquantaine d'essais. A ce jour, si les paramètres saccadiques (latence, amplitude, durée, vitesse moyenne et pic de vitesse) sont très bien documentés chez l'adulte, ils restent peu décrits chez le très jeune enfant. De plus, aucune étude n'a examiné la plasticité du système saccadique chez les enfants de moins de huit ans. Le but de ce travail de thèse est double. Il vise d'une part à caractériser les paramètres saccadiques chez le très jeune enfant. Pour ce faire, les mouvements oculaires d'un groupe de 115 bébés âgés de 7 à 42 mois ont été enregistrés pendant 140 essais (Etude 2). Nous avons mis au point un protocole expérimental original adapté à l'âge de ces jeunes participants que nous avons préalablement validé chez des adultes (Etude 1). D'autre part, nous avons étudié si la plasticité du système oculomoteur des bébés de cet âge possède les mêmes caractéristiques que celle des adultes en induisant, grâce au paradigme de double saut de la cible, une adaptation en diminution d'amplitude (Etude 3) et une adaptation en augmentation d'amplitude de la saccade (Etude 4). Les résultats reposant sur plus d'une centaine de saccades consécutives par participant montrent que les bébés sont capables de sélectionner un stimulus visuel comme cible et d'effectuer une saccade oculaire vers celle-ci. Le système oculomoteur est cependant immature à cet âge puisque les saccades des bébés ont des latences plus longues et sont plus hypométriques, i.e. moins précises que celles des adultes. Cependant, les performances saccadique des bébés s'améliorent avec l'âge pour la latence et, contre toute attente, au fur et à mesure des essais pour la précision de leur visée. Par ailleurs, les modifications adaptatives en réponse au saut intra-saccadique de la cible sont présentes chez un plus grand nombre d'adultes que d'enfants en diminution d'amplitude et inversement en augmentation d'amplitude. Cependant, l'efficacité de l'adaptation saccadique est similaire chez les deux groupes de participants. Nos études contribuent à la compréhension du développement du contrôle oculomoteur : le déclenchement de la saccade devient plus rapide (latence) avec l'âge mais la forte hypométrie de la saccade reste la même entre 7 et 42 mois. De façon inattendue, la précision saccadique s'améliore au cours de la session expérimentale suggérant une capacité d'apprentissage à court terme (Etude 2). Dans les Etudes 3 et 4, la plasticité du système oculomoteur est révélée pour la première fois chez des enfants d'âge préscolaire, signant des mécanismes adaptatifs fonctionnels chez le jeune enfant qui ne leur permettent cependant pas d'obtenir la précision saccadique des adultes. / To perceive the world around us, we perform rapid eye movements to bring objects of interest into the fovea, the eye region where visual acuity is optimal. These eye movements, called saccades, are accurate despite their high velocity. The mechanism that ensures accuracy throughout life is called saccadic adaptation. Saccadic adaptation can be easily induced in the laboratory by using the noninvasive double-step target paradigm (McLaughlin, 1967) that simulates targeting errors of the saccade by displacing repeatedly the target during the saccade. The saccadic system progressively reduces the error induced artificially so that after only fifty trials, the eyes rech the new position of the target. Today, if saccadic parameters (latency, amplitude, duration, average velocity and peak velocity) are well documented in adults, they remain poorly described in the very young children. Moreover, no study has examined the plasticity of the saccadic system in children aged under eight years-old. The goal of this thesis is twofold. On the one hand, it aims at characterizing saccadic parameters in very young children. To do this, the eye movements of a group of 115 babies aged 7-42 months-old were recorded during 140 trials (Study 2). We developed an original experimental protocol adapted to the age of these young participants, which first validated in adults (Study 1). One the other hand, we investigated whether the plasticity of the babies' oculomotor system has the same characteristics as adults' by inducing an adaptive shortening of saccade amplitude (backward adaptation; Study 3) and an adaptive lengthening of saccade amplitude (forward adaptation; Study 4). The results based on more than a hundred consecutive saccades per participant show that babies are able to select a stimulus as a visual target and generate a saccade toward it. However, the oculomotor system is immature at this age because babies' saccades have longer latencies and are more hypometric, i.e. less accurate than saccades in adults. Nevertheless, saccade latency improves with age in the child group. Unexpectedly, saccade accuracy improves over trials. Furthermore, adaptive changes in response to the intra-saccadic target step are present in a larger number of adults than children for backward adaptation and conversely for forward adaptation. However, the efficiency of saccadic adaptation is similar in the two groups of participants. Our studies allow to better understanding the development of oculomotor control: saccades are initiated faster with age but the high saccade hypometria remains the same between the age of 7 and 42 months. Unexpectedly, saccade accuracy improves over the course of the experimental session suggesting a short-term learning ability (Study 2). In Studies 3 and 4, the plasticity of the oculomotor system is revealed for the first time in preschool children. These results suggest that adaptive mechanisms are functional in young children. This ability however does not allow them to be as accurate as adults.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第17778号 / 医博第3804号 / 新制||医||999(附属図書館) / 30585 / 京都大学大学院医学研究科医学専攻 / (主査)教授 大森 治紀, 教授 髙橋 良輔, 教授 吉村 長久 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Sakkadische Blickbewegungen sind die häufigsten und schnellsten aller menschlichen Bewegungen und führen zur wiederholtem und rapiden Verschiebung von Objektprojektionen über die Retina. Entgegen der verbreiteten Annahme der Suppression untersucht diese Arbeit Ausmaß und Funktion intrasakkadischer visueller Wahrnehmung. Studie I beschreibt eine individuell gefertigte LED-Installation zur ausschließlich intrasakkadischen Präsentation von Text und Bildern, während Studie II einen Algorithmus zur Detektion von Sakkaden vorstellt, welcher blickkontingente Stimulusmanipulationen mithilfe eines DLP Projektionssystems mit einer Bildwiederholungsrate von 1440 Hz ermöglicht. Studien III und IV untersuchten ob visuelle Bewegungsspuren (sog. motion streaks), welche durch die schnelle Bewegung von Objekten über die Retina erzeugt werden, Korrespondenz zwischen Objekten über Sakkaden hinweg herstellen könnten. Diese Bewegungsspuren erlaubten Versuchsteilnehmern nicht nur einen präsakkadischen Stimulus aus zwei identischen postsakkadischen Stimuli zu identifizieren, während diese Fähigkeit von der Deutlichkeit der Bewegungsspur abhing, sondern auch Korrektursakkaden zu einem ursprünglichen präsakkadischen Stimulus zu erleichtern, falls dieser während der Sakkade versetzt wurde. Studie V untersuchte die subjektive Wahrnehmung und Lokalisierung von intrasakkadischen Bewegungsspuren, indem Teilnehmer gezeichnete Berichte angaben. Die Modellierung letzterer ergab, dass retinale Positionssignale mit einer zeitlich gedämpften mentalen Repräsentation von Augenposition kombiniert wurden, um eine Lokalisation in weltzentrierten Koordinaten zu ermöglichen. Diese Ergebnisse legen nahe, dass intrasakkadische visuelle Signale einen Einfluss auf transsakkadische perzeptuelle und motorische Prozesse haben könnten. Letztlich werden die mögliche Funktionen intrasakkadischer Wahrnehmung, sowie Möglichkeiten für zukünftige wissenschaftliche Untersuchungen, diskutiert. / Rapid eye movements, so-called saccades, are the fastest and most frequent human movements and cause projections of objects in the world to constantly shift across the retina at high velocities, thereby producing large amounts of motion blur. In contrast to accounts of saccadic suppression, this work explores the extent and potential functional role of intra-saccadic perception. As saccades are fast and brief events, technical challenges were addressed. Study I describes a custom LED-based anorthoscopic presentation setup capable of displaying text and images strictly during saccades. In study II, a novel online saccade detection algorithm enabled rapid, gaze-contingent display changes using a DLP projection system running at 1440 fps. Studies III and IV investigated whether intra-saccadic motion streaks, i.e., blurred traces routinely induced by stimuli moving at saccadic speeds, could serve as cues to establishing object correspondence across saccades. Motion streaks not only enabled perceptual matching of pre- and post-saccadic object locations, while performance depended strongly on streak efficiency, but also facilitated gaze correction in response to intra-saccadic target displacements, that was previously found to be mainly driven by objects’ surface features. Finally, study V explored the subjective appearance and localization of intra-saccadic motion streaks, tasking observers to reproduce their trajectories. Computational modeling of resulting response patterns suggested that retinal positions over time were combined with a damped eye position signal to readily localize intra-saccadic input in world-centered coordinates. Taken together, these results invite the intriguing hypothesis that intra-saccadic visual signals are not discarded from processing and might affect trans-saccadic perceptual and motor processes. The potential role of intra-saccadic perception for active vision, as well as directions for future research, are discussed.

No description available.

<p>This thesis explored the development of infants’ ability to preserve spatio-temporal continuity of moving objects in situations where they disappeared completely (Study I & II) or partially (Study III) behind other objects (occluders). We recorded infants gaze direction with the help of two different techniques: 1) infants’ gaze shifts in Study I were measured with electro-oculogram (EOG) in combination with a motion analyzing system (Qualisys) that recorded the reflected infrared light from markers placed on the infant’s head and the moving object; 2) in Studies II and III a cornea reflection eye tracker was used (Tobii 1750) . </p><p>The results presented in this thesis demonstrate that 4-month-old infants are able to represent the temporal aspects of object motion during different periods of complete occlusion (Study I). At 6 months of age infants are able not only to predict the time when a moving object will reappear after complete occlusion but they are also capable to extrapolate pre-occlusion trajectory of the moving object and, thus, to accurately predict its reappearance (Study II). Moreover, in the situation where a linear pre-occlusion trajectory of the moving object is violated (the object turns by 90 degrees behind the occluder), infants at this age are capable of rapidly learning this new experience and base their future gaze shifts over occluder on the newly acquired knowledge. They are also able to preserve this new experience over a 24-hour period. </p><p>In the situations where occlusion is not complete and some visual information is still available (Study III), 9-month-old infants and to a lesser extent 5-month-old infants are able to reconstruct the moving pattern and to follow its direction of motion with the smooth eye movements. Moreover, 9-month-olds are capable to produce such smooth pursuit at an adult-like level.</p>

This thesis explored the development of infants’ ability to preserve spatio-temporal continuity of moving objects in situations where they disappeared completely (Study I &amp; II) or partially (Study III) behind other objects (occluders). We recorded infants gaze direction with the help of two different techniques: 1) infants’ gaze shifts in Study I were measured with electro-oculogram (EOG) in combination with a motion analyzing system (Qualisys) that recorded the reflected infrared light from markers placed on the infant’s head and the moving object; 2) in Studies II and III a cornea reflection eye tracker was used (Tobii 1750) . The results presented in this thesis demonstrate that 4-month-old infants are able to represent the temporal aspects of object motion during different periods of complete occlusion (Study I). At 6 months of age infants are able not only to predict the time when a moving object will reappear after complete occlusion but they are also capable to extrapolate pre-occlusion trajectory of the moving object and, thus, to accurately predict its reappearance (Study II). Moreover, in the situation where a linear pre-occlusion trajectory of the moving object is violated (the object turns by 90 degrees behind the occluder), infants at this age are capable of rapidly learning this new experience and base their future gaze shifts over occluder on the newly acquired knowledge. They are also able to preserve this new experience over a 24-hour period. In the situations where occlusion is not complete and some visual information is still available (Study III), 9-month-old infants and to a lesser extent 5-month-old infants are able to reconstruct the moving pattern and to follow its direction of motion with the smooth eye movements. Moreover, 9-month-olds are capable to produce such smooth pursuit at an adult-like level.

Šiame tyrime buvo tiriama trikdžio įtaka sakadiniams akių judesiams. Eksperimentų serijoje, tiriamieji sekė taikinį, kai kartu su taikiniu atsirasdavo ir trikdis. Trikdis atsirasdavo arčiau taikinio per vidurį kelio arba arčiau fiksacijos taško. Visi trikdžiai buvo ant trajektorijos nuo fiksacijos iki taikinio. Taip pat trikdžių atsiradimo laikas skirdavosi. Siekiamieji akių judesiai buvo paveikti trikdžių. Rezultatai parodė kad trikdis labiau įtakoja horizontalius akies judesius ir kad akių judesiai buvo labiau paveikti kai trikdis buvo per vidurį trajektorijos iki taikinio. / In this research distracter influence for saccadic eye movements was studied. In a series of experiments, participants reached to targets in the presence of visual distracters that were either adjacent to the target or either adjacent to the fixation point. Distracters were located through the reach path. The distracters were presented at different times too. The reaching eye movements were affected by the presence of the distracters The results showed that the distracters affects more horizontal eye movements. And the eyes movements are more affected when distracters were in a middle of path to the target.

The visual system has evolved to deal with the consequences of our own movements onour perception. In particular, evolution has given us the ability to perceive our visual world as stableand continuous despite large shift of the image on our retinas when we move our eyes, head orbody. Animal studies have recently shown that in some cortical and sub-cortical areas involved inattention and saccade control, neurons are able to anticipate the consequences of voluntary eyemovements on their visual input. These neurons predict how the world will look like after a saccadeby remapping the location of each attended object to the place it will occupy following a saccade.In a series of studies, we first showed that remapping could be evaluated in a non-invasive fashion in human with simple apparent motion targets. Using eye movement recordingsand psychophysical methods, we evaluated the distribution of remapping errors across the visualfield and found that saccade compensation was fairly accurate. The pattern of errors observedsupport a model of space constancy based on a remapping of attention pointers and excluded otherknown models. Then using targets that moved continuously while a saccade was made across themotion path, we were able to directly visualize the remapping processes. With this novel method wedemonstrated again the existence of systematic errors of correction for the saccade, best explainedby an inaccurate remapping of expected moving target locations. We then extended our model toother body movements, and studied the contribution of sub-cortical receptors (otoliths and semi-circular canals) in the maintenance of space constancy across head movements. Contrary tostudies reporting almost perfect compensations for head movements, we observed breakdowns ofspace constancy for head tilt as well as for head translation. Then, we tested remapping of targetlocations to correct for saccades at the very edge of the visual field, remapping that would place theexpected target location outside the visual field. Our results suggest that visual areas involved inremapping construct a global representation of space extending out beyond the traditional visualfield. Finally, we conducted experiments to determine the allocation of attention across saccades.We demonstrated that the attention captured by a brief transient was remapped to the correctspatial location after the eye movement and that this shift can be observed even before thesaccade.Taken together these results demonstrate the management of attention pointers to therecovery of target locations in space as well as the ability of behavioral measurements to address atopic pioneered by eletrophysiologists.

Part of the aim of this thesis was to explore a model for producing very fast saccade latencies in the 80 to 120ms range. Its primary motivation was to explore a possible interaction by uniquely combining three independent saccade factors: the gap effect, target-feature-discrimination, and saccadic inhibition of return (IOR). Its secondary motivation was to replicate (in a more conservative and tightly controlled design) the surprising findings of Trottier and Pratt (2005), who found that requiring a high resolution task at the saccade target location speeded saccades, apparently by disinhibition. Trottier and Pratt’s finding was so surprising it raised the question: Could the oculomotor braking effect of saccadic IOR to previously viewed locations be reduced or removed by requiring a high resolution task at the target location? Twenty naïve untrained undergraduate students participated in exchange for course credit. Multiple randomised temporal and spatial target parameters were introduced in order to increase probability of exogenous responses. The primary measured variable was saccade latency in milliseconds, with the expectation of higher probability of very fast saccades (i.e. 80-120ms). Previous research suggested that these very fast saccades could be elicited in special testing circumstances with naïve participants, such as during the gap task, or in highly trained observers in non-gap tasks (Fischer & Weber, 1993). Trottier and Pratt (2005) found that adding a task demand that required naïve untrained participants to obtain a feature of the target stimulus (and to then make a discriminatory decision) also produced a higher probability of very fast saccade latencies. They stated that these saccades were not the same as saccade latencies previously referred to as express saccades produced in the gap paradigm, and proposed that such very fast saccades were normal. Carpenter (2001) found that in trained participants the probability of finding very fast saccades during the gap task increased when the horizontal direction of the current saccade continued in the same direction as the previous saccade (as opposed to reversing direction) – giving a distinct bimodality in the distribution of latencies in five out of seven participants, and likened his findings to the well known IOR effect. The IOR effect has previously been found in both manual key-press RT and saccadic latency paradigms. Hunt and Kingstone (2003) stated that there were both cortical top-down and oculomotor hard-wired aspects to IOR. An experiment was designed that included obtain-target-feature and oculomotor-prior-direction, crossed with two gap level offsets (0ms & 200ms-gap). Target-feature discrimination accuracy was high (97%). Under-additive main effects were found for each factor, with a three-way interaction effect for gap by obtain-feature by oculomotor-prior-direction. Another new three-way interaction was also found for anticipatory saccade type. Anticipatory saccades became significantly more likely under obtain-target-feature for the continuing oculomotor direction. This appears to be a similar effect to the increased anticipatory direction-error rate in the antisaccade task. These findings add to the saccadic latency knowledge base and in agreement with both Carpenter and Trottier and Pratt, laboratory testing paradigms can affect saccadic latency distributions. That is, salient (meaningful) targets that follow more natural oculomotor trajectories produce higher probability of very fast latencies in the 80-120ms range. In agreement with Hunt and Kingstone, there appears to be an oculomotor component to IOR. Specifically, saccadic target-prior-location interacts differently for obtain-target-feature under 200-ms gap than under 0ms-gap, and is most likely due predominantly to a predictive disinhibitory oculomotor momentum effect, rather than being due to the attentional inhibitory effect proposed for key-press IOR. A new interpretation for the paradigm previously referred to as IOR is offered that includes a link to the smooth pursuit system. Additional studies are planned to explore saccadic interactions in more detail.

Indiana University-Purdue University Indianapolis (IUPUI) / Huntington disease (HD) is an autosomal dominant disorder characterized by progressive decline of motor, cognitive, and behavioral function. Saccades (rapid, gaze-shifting eye movements) are affected before a clinical diagnosis of HD is certain (i.e. during the premanifest period of the disease). Fundamental questions remain regarding the neural substrates of abnormal saccades and the course of premanifest disease. This work addressed these questions using magnetic resonance imaging (MRI) and a longitudinal study of premanifest disease progression. Gray matter atrophy is a characteristic of HD that can be reliably detected during the premanifest period, but it is not known how such changes influence saccadic behavior. We evaluated antisaccades (AS) and memory guided saccades (MG) in premanifest and manifest HD, then tested for associations between impaired saccadic measures and gray matter atrophy in brain regions involved in these saccadic tasks. The results suggest that slowed vertical AS responses indicate cortical and subcortical atrophy and may be a noninvasive marker of atrophic changes in the brain. We also investigated the brain changes that underlie AS impairment using an event-related AS design with functional MRI (fMRI). We found that, in premanifest and manifest HD, blood oxygenation level dependent (BOLD) response was abnormally absent in the pre-supplementary motor area and dorsal anterior cingulate cortex following incorrect AS responses. These results are the first to suggest that abnormalities in an error-related response network underlie early disease-related saccadic changes, and they emphasize the important influence of regions outside the striatum and frontal cortex in disease manifestations. Though saccadic abnormalities have been repeatedly observed cross sectionally, they have not yet been studied longitudinally in premanifest HD. We found different patterns of decline; for some measures the rate of decline increased as individuals approached onset, while for others the rate was constant throughout the premanifest period. These results establish the effectiveness of saccadic measures in tracking premanifest disease progression, and argue for their use in clinical trials. Together, these studies establish the utility of saccade measures as a marker of HD neurodegeneration and suggest that they would be a valuable component of batteries evaluating the efficacy of neuroprotective therapies.