<p> This thesis is concerned with the systematic variation of stimulus movement and complexity in order to investigate developmental changes in visual fixation. It was shown that there is a developmental transition in the way in which infants extract visual information from the environment, with younger infants responding primarily through length of fixation, and older infants through the number of fixations. It was demonstrated that the faster a stimulus moves, the more fixation it elicits from infants; that older infants appear to be more responsive to differences in speed than younger infants; and that the more complex the stimulus, the greater the visual response to it. Percent measures were found to be more reliable than absolute measures in making age comparisons. </p> / Thesis / Doctor of Philosophy (PhD)

Os primeiros meses de vida são críticos para o desenvolvimento normal do sistema visual. Nesse período, os recém-nascidos desenvolvem habilidades visuais, algumas delas presentes ao nascimento, que serão refinadas durante a infância e utilizadas ao longo de toda a vida. A literatura mostra que em recém-nascidos as habilidades visuais, como fixação visual e acuidade visual, são desenvolvidas em períodos diferentes. Embora o desenvolvimento da acuidade visual seja semelhante entre recém-nascidos prematuros e termos quando se considera a idade corrigida para a prematuridade (IGc), ou seja, o tempo em semanas que o recém-nascido teria se nascesse com 40 semanas, não se sabe ao certo como se desenvolvem outras habilidades que dependem do sistema visual nesses recém-nascidos. O presente estudo, de caráter observacional, avaliou o desempenho visual através da medida do tempo de fixação visual para a face humana, baseado nos estímulos desenvolvidos por Fantz - face construída com padrões internos semelhantes à face humana (FC) e face desconstruída com padrões internos que não formavam face humana (FD), mas com contraste e luminância idênticos à face construída. Foram incluídos no estudo apenas os recém-nascidos com acuidade visual de resolução de grades, medida através dos cartões de Teller, dentro do esperado para a idade corrigida. Os participantes foram 50 recém-nascidos, 21 (idade média = 13,1 ± 7,1 semanas; peso ao nascimento = 3109 ± 468,9 g), nascidos a partir de 37 semanas de gestação (termo; idade média = 39,1 ± 1,2 semanas), e 29 (idade média = 11,1 ± 6,8 semanas; peso ao nascimento = 1544,3 ± 505,5g), nascidos antes de 37 semanas de gestação (prematuros; idade média = 31,7 ± 2,6 semanas). Os recém-nascidos foram avaliados no Setor de Neonatologia e Pediatria do Hospital Universitário da Universidade de São Paulo (HU-USP) e no Serviço de Neonatologia e Pediatria do Hospital das Clínicas de São Paulo (HCFMUSP). Durante a avaliação os recém-nascidos eram posicionados no bebê conforto, semi-elevados frente a um anteparo que impedia visualização do entorno para o teste de fixação das características faciais e no colo do responsável durante o teste de acuidade visual de Teller. O tempo médio de fixação à FC (termo = 56,9 ± 54,4 segundos; prematuros = 49,3 ± 42,8 segundos) e à FD (termo = 34,8 ± 41,5 segundos; prematuros = 44,1± 31,1 segundos) foi semelhante para recém-nascidos a termo e prematuros (FC: p = 0,723 e FD: p = 0,637). Entretanto, o tempo de fixação à FC foi estatisticamente superior (p = 0,014) ao tempo de fixação à FD para os recém-nascidos a termo, enquanto prematuros apresentaram tempos semelhantes (p = 0,75). A atenção às características faciais humanas possui papel fundamental no contexto diário dos recém-nascidos, pois influencia o desempenho de algumas habilidades que serão desenvolvidas posteriormente, como a comunicação e a interação visual, o reconhecimento de objetos, a resposta social e a orientação espacial. Os resultados do presente estudo mostram que contrariamente aos recém-nascidos a termo cuja preferência pela face humana construída é estatisticamente maior que pela face desconstruída, recém-nascidos prematuros não apresentam preferência pela face humana construída. Os achados indicam os efeitos da prematuridade na fixação à face humana e ressaltam a importância de se identificar alterações em habilidades que poderiam ser estimuladas precocemente / The first months of life are critical for the normal development of the visual system. In this period, newborns develop visual skills, some of which are present at birth, which will be refined during childhood and used throughout the life. The literature shows that in newborns some visual abilities, such as visual fixation and visual acuity, are developed in different periods. Although the development of visual acuity is similar between preterm newborns and terms when considering the corrected age for prematurity (the time in weeks that the newborn would have been born at 40 weeks), the development of other abilities that depend on the visual system in these preterm newborns is unknown. The present observational study evaluated visual performance by measuring the time of visual fixation to the human face, based on the Fantz real face with internal patterns similar to the human face and scrambled face with internal patterns that do not form a face, but with contrast and luminance identical to the real face. Only newborns with visual acuity as expected for the corrected age, as measured by Teller cards, were included in the study. Participants were 50 infants, 21 (mean age = 13.1 ± 7.1 weeks, birth weight = 3109 ± 468.9g) born after 37 weeks gestation (terms, mean age = 39.1 ± 1.2 weeks), and 29 (mean age = 11.1 ± 6.8 weeks, birth weight = 1544.3 ± 505.5g), born before 37 weeks gestation (preterms, mean age = 31, 7 ± 2.6 weeks). The newborns were evaluated in the Neonatology and Pediatrics Sector of the University Hospital (HU-USP) and in the Neonatology and Pediatrics Service of the Hospital das Clinicas de São Paulo (HCFMUSP) at the University of São Paulo. During the evaluation the newborns were placed in the comfort baby, semi-elevated against a bulkhead that prevented visualization of the surroundings to test the time of fixation for the facial characteristics and in the lap of his/her responsible during the visual acuity test. The mean fixation time to the real face (term = 56.9 ± 54.4 seconds, premature = 49.3 ± 42.8 seconds) and to the scrambled face (term = 34.8 ± 41.5 seconds, preterm = 44.1 ± 31.1 seconds) was similar for term and preterm newborns (p = 0.723 and FD: p = 0.637). However, the fixation time to the real face was statistically superior (p = 0.014) to the fixation time to the scrambled face for term newborns, whereas preterm infants presented similar times (p = 0.75). Fixation to human facial features plays a key role in the daily context of newborns, as it influences the performance of some skills that are in development, such as communication and visual interaction, object recognition, social response and spatial orientation. The results of the present study show that, contrary to the term newborns whose preference for the real human face is significantly higher than the scrambled face, preterm newborns have no preference for the real human face. The findings indicate the effects of prematurity on fixation to the human face and emphasize the importance of identifying changes in abilities that could be early stimulated

In normal everyday viewing, we perform large eye movements (saccades) and miniature or fixational eye movements. Most of our visual perception occurs while we are fixating. However, our eyes are perpetually in motion. Properties of these fixational eye movements, which are partly controlled by the brainstem, change depending on the task and the visual conditions. Currently, fixational eye movements are poorly understood because they serve the two contradictory functions of gaze stabilization and counteraction of retinal fatigue. In this dissertation, we investigate the spatial and temporal properties of time series of eye position acquired from participants staring at a tiny fixation dot or at a completely dark screen (with the instruction to fixate a remembered stimulus); these time series were acquired with high spatial and temporal resolution. First, we suggest an advanced algorithm to separate the slow phases (named drift) and fast phases (named microsaccades) of these movements, which are considered to play different roles in perception. On the basis of this identification, we investigate and compare the temporal scaling properties of the complete time series and those time series where the microsaccades are removed. For the time series obtained during fixations on a stimulus, we were able to show that they deviate from Brownian motion. On short time scales, eye movements are governed by persistent behavior and on a longer time scales, by anti-persistent behavior. The crossover point between these two regimes remains unchanged by the removal of microsaccades but is different in the horizontal and the vertical components of the eyes. Other analyses target the properties of the microsaccades, e.g., the rate and amplitude distributions, and we investigate, whether microsaccades are triggered dynamically, as a result of earlier events in the drift, or completely randomly. The results obtained from using a simple box-count measure contradict the hypothesis of a purely random generation of microsaccades (Poisson process). Second, we set up a model for the slow part of the fixational eye movements. The model is based on a delayed random walk approach within the velocity related equation, which allows us to use the data to determine control loop durations; these durations appear to be different for the vertical and horizontal components of the eye movements. The model is also motivated by the known physiological representation of saccade generation; the difference between horizontal and vertical components concurs with the spatially separated representation of saccade generating regions. Furthermore, the control loop durations in the model suggest an external feedback loop for the horizontal but not for the vertical component, which is consistent with the fact that an internal feedback loop in the neurophysiology has only been identified for the vertical component. Finally, we confirmed the scaling properties of the model by semi-analytical calculations. In conclusion, we were able to identify several properties of the different parts of fixational eye movements and propose a model approach that is in accordance with the described neurophysiology and described limitations of fixational eye movement control. / Während des alltäglichen Sehens führen wir große (Sakkaden) und Miniatur- oder fixationale Augenbewegungen durch. Die visuelle Wahrnehmung unserer Umwelt geschieht jedoch maßgeblich während des sogenannten Fixierens, obwohl das Auge auch in dieser Zeit ständig in Bewegung ist. Es ist bekannt, dass die fixationalen Augenbewegungen durch die gestellten Aufgaben und die Sichtbedingungen verändert werden. Trotzdem sind die Fixationsbewegungen noch sehr schlecht verstanden, besonders auch wegen ihrer zwei konträren Hauptfunktionen: Das stabilisieren des Bildes und das Vermeiden der Ermüdung retinaler Rezeptoren. In der vorliegenden Dissertation untersuchen wir die zeitlichen und räumlichen Eigenschaften der Fixationsbewegungen, die mit hoher zeitlicher und räumlicher Präzision aufgezeichnet wurden, während die Versuchspersonen entweder einen sichtbaren Punkt oder aber den Ort eines verschwundenen Punktes in völliger Dunkelheit fixieren sollten. Zunächst führen wir einen verbesserten Algorithmus ein, der die Aufspaltung in schnelle (Mikrosakkaden) und langsame (Drift) Fixationsbewegungen ermöglicht. Den beiden Typen von Fixationsbewegungen werden unterschiedliche Beiträge zur Wahrnehmung zugeschrieben. Anschließend wird für die Zeitreihen mit und ohne Mikrosakkaden das zeitliche Skalenverhalten untersucht. Für die Fixationsbewegung während des Fixierens auf den Punkt konnten wir feststellen, dass diese sich nicht durch Brownsche Molekularbewegung beschreiben lässt. Stattdessen fanden wir persistentes Verhalten auf den kurzen und antipersistentes Verhalten auf den längeren Zeitskalen. Während die Position des Übergangspunktes für Zeitreihen mit oder ohne Mikrosakkaden gleich ist, unterscheidet sie sich generell zwischen horizontaler und vertikaler Komponente der Augen. Weitere Analysen zielen auf Eigenschaften der Mikrosakkadenrate und -amplitude, sowie Auslösemechanismen von Mikrosakkaden durch bestimmte Eigenschaften der vorhergehenden Drift ab. Mittels eines Kästchenzählalgorithmus konnten wir die zufällige Generierung (Poisson Prozess) ausschließen. Des weiteren setzten wir ein Modell auf der Grundlage einer Zufallsbewegung mit zeitverzögerter Rückkopplung für den langsamen Teil der Augenbewegung auf. Dies erlaubt uns durch den Vergleich mit den erhobenen Daten die Dauer des Kontrollkreislaufes zu bestimmen. Interessanterweise unterscheiden sich die Dauern für vertikale und horizontale Augenbewegungen, was sich jedoch dadurch erklären lässt, dass das Modell auch durch die bekannte Neurophysiologie der Sakkadengenerierung, die sich räumlich wie auch strukturell zwischen vertikaler und horizontaler Komponente unterscheiden, motiviert ist. Die erhaltenen Dauern legen für die horizontale Komponente einen externen und für die vertikale Komponente einen internen Kontrollkreislauf dar. Ein interner Kontrollkreislauf ist nur für die vertikale Kompoente bekannt. Schließlich wird das Skalenverhalten des Modells noch semianalytisch bestätigt. Zusammenfassend waren wir in der Lage, unterschiedliche Eigenschaften von Teilen der Fixationsbewegung zu identifizieren und ein Modell zu entwerfen, welches auf der bekannten Neurophysiologie aufbaut und bekannte Einschränkungen der Kontrolle der Fixationsbewegung beinhaltet.

Les insectes sont capables de prouesses remarquables lorsqu’il s’agit d’éviter des obstacles,voler en environnement perturbé ou poursuivre une cible. Cela laisse penser que leurs capacités de traitement, aussi minimalistes soient-elles, sont parfaitement optimisées pour le vol. A cela s’ajoute des mécanismes raffinés, comme la stabilisation de la vision par rapport au corps, permettant d’améliorer encore plus leurs capacités de vol.Ces travaux de thèse présentent l’élaboration d’un micro drone de type quadrirotor, qui ressemble fortement à un insecte sur le plan perceptif (vibration rétinienne) et reprend des points structurels clés, tels que le découplage mécanique entre le corps et le système visuel. La conception du quadrirotor (de type open-source), son pilotage automatique et son système occulo-moteur sont minutieusement détaillés.Des traitements adaptés permettent, malgré un très faible nombre de pixels (24 pixels seulement), de poursuivre finement du regard une cible en mouvement. A partir de là, nous avons élaboré des stratégies basées sur le pilotage par le regard, pour stabiliser le robot en vol stationnaire, à l’aplomb d’une cible et asservir sa position ; et ce, en se passant d’une partie des capteurs habituellement utilisés en aéronautique tels que les magnétomètres et les accéléromètres. Le quadrirotor décolle, se déplace et atterrit de façon autonome en utilisant seulement ses gyromètres, son système visuel original mimant l’oeil d’un insecte et une mesure de son altitude. Toutes les expérimentations ont été validées dans une arène de vol, équipée de caméras VICON.Enfin, nous décrivons une nouvelle toolbox qui permet d’exécuter en temps réel des modèles Matlab/Simulink sur des calculateurs Linux embarqués de façon complètement automatisée (http://www.gipsalab.fr/projet/RT-MaG/). Cette solution permet d’écrire les modèles, de les simuler, d’élaborer des lois de contrôle pour enfin, piloter en temps réel, le robot sous l’environnement Simulink. Cela réduit considérablement le "time-to-flight" et offre une grande flexibilité (possibilité de superviser l’ensemble des données de vol, de modifier en temps réel les paramètres des contrôleurs, etc.). / Insects, like hoverflies are able of outstanding performances to avoid obstacles, reject disturbances and hover or track a target with great accuracy. These means that fast sensory motor reflexes are at work, even if they are minimalist, they are perfectly optimized for the flapping flight at insect scale. Additional refined mechanisms, like gaze stabilization relative to the body, allow to increase their flight capacity.In this PhD thesis, we present the design of a quadrotor, which is highly similar to an insect in terms of perception (visual system) and implements a bio-inspired gaze control system through the mechanical decoupling between the body and the visual system. The design of the quadrotor (open-source), itspilot and its decoupled eye are thoroughly detailed. New visual processing algorithms make it possible to faithfully track a moving target, in spite of a very limited number of pixels (only 24 pixels). Using this efficient gaze stabilization, we developed new strategies to stabilize the robot above a target and finely control its position relative to the target. These new strategies do not need classical aeronautic sensors like accelerometers and magnetometers. As a result, the quadrotor is able to take off, move and land automatically using only its embedded rate-gyros, its insect-like eye, and an altitude measurement. All these experiments were validated in a flying arena equipped with a VICON system. Finally, we describe a new toolbox, called RT-MaG toolbox, which generate automatically a real-time standalone application for Linux systems from a Matlab/Simulink model (http://www.gipsalab.fr/projet/RT-MaG/). These make it possible to simulate, design control laws and monitor the robot’s flight in real-time using only Matlab/Simulink. As a result, the "time-to-flight" is considerably reduced and the final application is highly reconfigurable (real-time monitoring, parameter tuning, etc.).