Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Оптична система виявлення динамічних об'єктів для БПЛА

This work presents an optical flow based method for obstacle detection by using a single CCDcamera. Computed optical flow is used to detect dynamic obstacles in front of the camera and toadjust rotor's control to avoid them. The proposed system is based on optical flow estimation with weighted image blocks from the streamed video. Hardware simulation is performed to prove theapplicability of this system. Methods and algorithms described in this paper are versatile enough andcan be implemented for various vehicles with autonomous navigation system. The feasibility of theproposed system for UAVs is discussedВ работе представлена технология на основе метода оптического потока ПЗС-камеры. Оптический поток используется для обнаружения динамических препятствий перед камерой, спомощью которого формируется сигнал управления на облет препятствия. Предлагаемая система основана на оценке оптического потока с взвешенными блоков изображения в потоко-вый видеопоследовательности. Проведенные практические испытания доказывают работоспособность этой системы. Методы и алгоритмы, описанные в данной роботе, являются достаточно универсальными и реализуются в различных областях, которые используют автономную систему навигации. Система разрабатывалась для использования на БПЛАУ роботі представлена технологія на основі методу оптичного потоку ПЗС-камери. Оптичний потік використовується для виявлення динамічних перешкод перед камерою, за допомогою якого формується сигнал управління на обліт перешкоди. Пропонована система заснована наоцінці оптичного потоку з зваженими блоків зображення в потоковій відео послідовності. Проведені практичні випробування доводять робото спроможність цієї системи. Методи і алгоритми, описані в даній роботі, є досить універсальними і реалізуються в різних областях, які використовують автономну систему навігації. Система розробляється для використанняна БПЛ

Estimating motion and time to contact in 3D environments: Priors matter

[eng] Until the present moment, an extensive amount of research has been done on how humans estimate motion or parameters of a task, such as the timeto- contact in simple scenarios. However, most avoid questioning how we extract 3D information from 2D optic information. A Bayesian approach based on a combination of optic and prior knowledge about statistical regularities of the environment would allow solving the ambiguity when translating 2D into 3D estimates. The present dissertation aims to analyse if the estimation of motion and time-to-contact in complex 3D environments is compatible with a combination of visual and prior information. In the first study, we analyse the predictions of a Bayesian model with a preference for slow speeds to estimate the direction of an object. The information available to judge movement in depth is much less precise than information about the lateral movement. Thus, combining both sources of information with a prior with preference for low speeds, estimates of motion in depth will be proportionally more attracted to low speeds than estimates of lateral motion. Thus, the perceived direction would depend on stimulus speed when estimating the ball’s direction. Our experimental results showed that the bias in perceived direction increased at higher speeds, which would be congruent with increasingly less precise motion estimates (consistent with Weber’s law). In the second study, we analyse the existing evidence on using a priori knowledge of the Earth’s gravitational acceleration and the size of objects to estimate the time to contact in parabolic trajectories. We analysed the existing evidence for using knowledge of the Earth’s gravity and the size of an object in the interaction with the surrounding environment. Next, we simulate predictions of the GS model. This model allows predicting the time to contact based on a combination of a priori variables (gravity and ball size) and optic variables. We compare the accuracy of the predictions of time-to-contact with an alternative only using optic variables, showing that relying on priors of gravitation and ball size solves the ambiguity in the estimation of the time-to-contact. Finally, we offer scenarios where the GS model would lead to predictions with systematic errors, which we will test in the following studies. In the third study, we created trajectories for which the GS model gives accurate predictions of the time to contact at different flight times but provides different systematic errors at any other time. We hypothesized that if the ball’s visibility is restricted to a short time window, the participants would prefer to see the ball during the time windows in which the model predictions are accurate. Our results showed that observers preferred to use a relatively constant ball viewing time. However, we showed evidence that the direction of the errors made by the participants for the different trajectories tested corresponded to the direction predicted by the GS model. In the fourth and final study, we investigated the role of a priori knowledge of the Earth’s gravitational acceleration and ball size in estimating the time of flight and the direction of motion of an observer towards the interception point. We introduced our participants in an environment where both gravitational acceleration and ball size was randomized trial-to-trial. The observers’ task was to move towards the interception point and predict the remaining flight time after a short occlusion. Our results provide evidence for using prior knowledge of gravity and ball size to estimate the time-to-contact. We also find evidence that gravitational acceleration may play a role in guiding locomotion towards the interception point. In summary, in this thesis, we contribute to answering a fundamental question in Perception: how we interpret information to act in the world. To do so, we show evidence that humans apply their knowledge about regularities in the environment in the form of a priori knowledge of the Earth’s gravitational acceleration, the size of the ball, or that objects stand still in the world when interpreting visual information.[spa] Hasta el momento, se ha realizado una gran cantidad de investigación sobre como el ser humano estima el movimiento o los parámetros de una tarea como el tiempo de contacto en escenarios simples. Sin embargo, la mayoría evita preguntarse cómo se extrae la información 3D a partir de la información óptica 2D. Un enfoque bayesiano basado en una combinación de información óptica y a priori sobre regularidades estadísticas del entorno interiorizadas en forma de conocimiento permitiría resolver la ambigüedad a la hora de traducir claves ópticas en 2D a estimaciones sobre propiedades del mundo en 3D. El objetivo de esta tesis es analizar si la estimación del movimiento y del tiempo de contacto en entornos 3D complejos es compatible con una combinación de información visual y a priori. En el primer estudio, se analizan las predicciones de un modelo bayesiano con preferencia por las velocidades lentas para la estimación de la dirección de un objeto. La información disponible para juzgar el movimiento en profundidad es mucho menos precisa que la información sobre el movimiento lateral. Así, cuando se combinan ambas fuentes de información con un prior con preferencia por la velocidad baja, las estimaciones del movimiento en profundidad serán proporcionalmente más atraídas por el prior que las estimaciones del movimiento lateral. Por lo tanto, la dirección percibida dependería de la velocidad del estímulo. Nuestros resultados experimentales mostraron que el sesgo en la dirección percibida aumentaba a velocidades más altas, lo que sería congruente con estimaciones de movimiento cada vez menos precisas (consistente con la ley de Weber). En el segundo estudio, analizamos las evidencias existentes sobre el uso del conocimiento a priori de la aceleración gravitatoria de la Tierra y el tamaño de los objetos para estimar el tiempo de contacto en trayectorias parabólicas. Analizamos las pruebas existentes sobre el uso del conocimiento de la gravedad de la Tierra y el tamaño de un objeto en la interacción con el entorno. A continuación, simulamos las predicciones del modelo GS, un modelo que permite predecir el tiempo de contacto a partir de una combinación de variables a priori (gravedad y tamaño de pelota) y variables ópticas. Comparamos la precisión de las predicciones del tiempo de contacto con una alternativa que solo utiliza variables ópticas, mostrando que basarse en las variables a priori de la gravedad y el tamaño de la bola resuelve la ambigüedad en la estimación del tiempo de contacto. Por último, mostramos varios escenarios en los que el modelo GS conduciría a predicciones con errores sistemáticos; escenarios que pondremos a prueba en los siguientes estudios. En el tercer estudio, creamos trayectorias para las que el modelo GS da predicciones precisas del tiempo hasta el contacto en diferentes tiempos de vuelo, pero proporciona diferentes errores sistemáticos en cualquier otro momento. Hipotetizamos que, si la visibilidad de la pelota está restringida a una ventana de tiempo corta, los participantes preferirían ver la pelota durante las ventanas de tiempo en las que las predicciones del modelo son precisas. Nuestros resultados mostraron que los observadores preferían utilizar un tiempo de visualización de la pelota relativamente constante. Por otra parte, mostramos pruebas de que la dirección de los errores cometidos por los participantes para las diferentes trayectorias probadas se correspondía con la dirección predicha por el modelo GS. En el cuarto y último estudio, investigamos el papel del conocimiento a priori de la aceleración gravitatoria de la Tierra y del tamaño de la pelota en la estimación del tiempo de vuelo y la dirección de movimiento de un observador hacia el punto de interceptación. Introdujimos a nuestros participantes en un entorno en el que tanto la aceleración gravitatoria como el tamaño de la pelota se asignaban aleatoriamente ensayo a ensayo. La tarea de los observadores consistía en desplazarse hacia el punto de interceptación y predecir el tiempo de vuelo restante tras una breve oclusión. Nuestros resultados proporcionan pruebas del uso del conocimiento previo de la gravedad y el tamaño de la pelota para estimar el tiempo de contacto. También encontramos pruebas de que la aceleración gravitatoria puede desempeñar un papel en la orientación de la locomoción hacia el punto de intercepción. En resumen, en esta tesis contribuimos a responder a una cuestión fundamental en la Percepción: como interpretamos la información para actuar en el mundo. Para ello, mostramos evidencias de que los humanos aplican sus conocimientos sobre regularidades del entorno en forma de conocimiento a priori de la aceleración gravitatoria de la tierra, del tamaño de la pelota o de la estabilidad del mundo a nuestro alrededor para interpretar la información visual

Figure-Ground Segmentation Using Multiple Cues

The theme of this thesis is figure-ground segmentation. We address the problem in the context of a visual observer, e.g. a mobile robot, moving around in the world and capable of shifting its gaze to and fixating on objects in its environment. We are only considering bottom-up processes, how the system can detect and segment out objects because they stand out from their immediate background in some feature dimension. Since that implies that the distinguishing cues can not be predicted, but depend on the scene, the system must rely on multiple cues. The integrated use of multiple cues forms a major theme of the thesis. In particular, we note that an observer in our real environment has access to 3-D cues. Inspired by psychophysical findings about human vision we try to demonstrate their effectiveness in figure-ground segmentation and grouping also in machine vision

Perceptual modelling for 2D and 3D

Livrable D1.1 du projet ANR PERSEECe rapport a été réalisé dans le cadre du projet ANR PERSEE (n° ANR-09-BLAN-0170). Exactement il correspond au livrable D1.1 du projet

3D motion : encoding and perception

The visual system supports perception and inferences about events in a dynamic, three-dimensional (3D) world. While remarkable progress has been made in the study of visual information processing, the existing paradigms for examining visual perception and its relation to neural activity often fail to generalize to perception in the real world which has complex dynamics and 3D spatial structure. This thesis focuses on the case of 3D motion, developing dynamic tasks for studying visual perception and constructing a neural coding framework to relate neural activity to perception in a 3D environment. First, I introduce target-tracking as a psychophysical method and develop an analysis framework based on state space models and the Kalman filter. I demonstrate that target-tracking in conjunction with a Kalman filter analysis framework produce estimates of visual sensitivity that are comparable to those obtained with a traditional forced-choice task and a signal detection theory analysis. Next, I use the target-tracking paradigm in a series of experiments examining 3D motion perception, specifically comparing the perception of frontoparallel motion with the perception of motion-through-depth. I find that continuous tracking of motion-through-depth is selectively impaired due to the relatively small retinal projections resulting from motion-through-depth and the slower processing of binocular disparities. The thesis then turns the neural representation of 3D motion and how that underlies perception. First I introduce a theoretical framework that extends the standard neural coding approach, incorporating the environment-to-retina transformation. Neural coding typically treats the visuals stimulus as a direct proxy for the pattern of stimulation that falls on the retina. Incorporating the environment-to-retina transformation results in a neural representation fundamentally shaped by the projective geometry of the world onto the retina. This model explains substantial anomalies in existing neurophysiological recordings in primate visual cortical neurons during presentations of 3D motion and in psychophysical studies of human perception. In a series of psychophysical experiments, I systematically examine the predictions of the model for human perception by observing how perceptual performance changes as a function of viewing distance and eccentricity. Performance in these experiments suggests a reliance on a neural representation similar to the one described by the model. Taken together, the experimental and theoretical findings reported here advance the understanding of the neural representation and perception of the dynamic 3D world, and adds to the behavioral tools available to vision scientists.Neuroscienc

Vision-based localization methods under GPS-denied conditions

This paper reviews vision-based localization methods in GPS-denied environments and classifies the mainstream methods into Relative Vision Localization (RVL) and Absolute Vision Localization (AVL). For RVL, we discuss the broad application of optical flow in feature extraction-based Visual Odometry (VO) solutions and introduce advanced optical flow estimation methods. For AVL, we review recent advances in Visual Simultaneous Localization and Mapping (VSLAM) techniques, from optimization-based methods to Extended Kalman Filter (EKF) based methods. We also introduce the application of offline map registration and lane vision detection schemes to achieve Absolute Visual Localization. This paper compares the performance and applications of mainstream methods for visual localization and provides suggestions for future studies.Comment: 32 pages, 15 figure

Gravity and known size calibrate visual information to time parabolic trajectories

Catching a ball in a parabolic flight is a complex task in which the time and area of interception are strongly coupled, making interception possible for a short period. Although this makes the estimation of time-to-contact (TTC) from visual information in parabolic trajectories very useful, previous attempts to explain our precision in interceptive tasks circumvent the need to estimate TTC to guide our action. Obtaining TTC from optical variables alone in parabolic trajectories would imply very complex transformations from 2D retinal images to a 3D layout. We propose based on previous work and show by using simulations that exploiting prior distributions of gravity and known physical size makes these transformations much simpler, enabling predictive capacities from minimal early visual information. Optical information is inherently ambiguous, and therefore, it is necessary to explain how these prior distributions generate predictions. Here is where the role of prior information comes into play: it could help to interpret and calibrate visual information to yield meaningful predictions of the remaining TTC. The objective of this work is: (1) to describe the primary sources of information available to the observer in parabolic trajectories; (2) unveil how prior information can be used to disambiguate the sources of visual information within a Bayesian encoding-decoding framework; (3) show that such predictions might be robust against complex dynamic environments; and (4) indicate future lines of research to scrutinize the role of prior knowledge calibrating visual information and prediction for action control

Visuelle Detektion unabhängig bewegter Objekte durch einen bewegten monokularen Beobachter

The development of a driver assistant system supporting drivers in complex intersection situations would be a major achievement for traffic safety, since many traffic accidents happen in such situations. While this is a highly complex task, which is still not accomplished, this thesis focused on one important and obligatory aspect of such systems: The visual detection of independently moving objects. Information about moving objects can, for example, be used in an attention guidance system, which is a central component of any complete intersection assistant system. The decision to base such a system on visual input had two reasons: (i) Humans gather their information to a large extent visually and (ii) cameras are inexpensive and already widely used in luxury and professional vehicles for specific applications. Mimicking the articulated human head and eyes, agile camera systems are desirable. To avoid heavy and sensitive stereo rigs, a small and lightweight monocular camera system mounted on a pan-tilt unit has been chosen as input device. In this thesis information about moving objects has been used to develop a prototype of an attention guidance system. It is based on the analysis of sequences from a single freely moving camera and on measurements from inertial sensors rigidly coupled with the camera system.Die Entwicklung eines Fahrerassistenzsystems, welches den Fahrer in komplexen Kreuzungssituationen unterstützt, wäre ein wichtiger Beitrag zur Verkehrssicherheit, da sehr viele Unfälle in solchen Situationen passieren. Dies ist eine hochgradig komplexe Aufgabe und daher liegt der Fokus dieser Arbeit auf einen wichtigen und notwendigen Aspekt solcher Systeme: Die visuelle Detektion unabhängig bewegter Objekte. Informationen über bewegte Objekte können z.B. für ein System zur Aufmerksamkeitssteuerung verwendet werden. Solch ein System ist ein integraler Bestandteil eines jeden kompletten Kreuzungsassistenzssystems. Zwei Gründe haben zu der Entscheidung geführt, das System auf visuellen Daten zu stützen: (i) Der Mensch sammelt seine Informationen zum Großteil visuell und (ii) Kameras sind zum Einen günstig und zum Anderen bereits jetzt in vielen Fahrzeugen verfügbar. Agile Kamerasysteme sind nötig um den beweglichen menschlichen Kopf zu imitieren. Die Wahl einer kleinen und leichten monokularen Kamera, die auf einer Schwenk-Neige-Einheit montiert ist, vermeidet die Verwendung von schweren und empfindlichen Stereokamerasystemen. Mit den Informationen über bewegte Objekte ist in dieser Arbeit der Prototyp eines Fahrerassistenzsystems Aufmerksamkeitssteuerung entwickelt worden. Das System basiert auf der Analyse von Bildsequenzen einer frei bewegten Kamera und auf Messungen von der mit der Kamera starr gekoppelten Inertialsensorik