Position Affects Performance in Multiple-Object Tracking in Rugby Union Players.

We report an experiment that examines the performance of rugby union players and a control group composed of graduate student with no sport experience, in a multiple-object tracking task. It compares the ability of 86 high level rugby union players grouped as Backs and Forwards and the control group, to track a subset of randomly moving targets amongst the same number of distractors. Several difficulties were included in the experimental design in order to evaluate possible interactions between the relevant variables. Results show that the performance of the Backs is better than that of the other groups, but the occurrence of interactions precludes an isolated groups analysis. We interpret the results within the framework of visual attention and discuss both, the implications of our results and the practical consequences.

The effect of object familiarity on the perception of motion.

Humans are capable of picking up the invariance of an object's physical speed regardless of the distance from which it is seen. This ability is known as speed constancy. Typically the studies of speed constancy focus on the spatiotemporal cues present in the stimulus. In this work we present a series of experiments that introduce the object's familiarity in combination with other cues to study the speed constancy. The results of the first experiment show that human observers use said familiarity in the estimation of the physical speed of the objects. When distance cues are added to the stimulus, the results show that familiarity helps the system to achieve speed constancy. In the second experiment we remove the contextual cues and show the effect of familiarity on speed constancy. Finally, we propose that familiarity needs to be included in the analysis of speed constancy perhaps by considering the prototypical size of the objects.

Effect of disparity on the perception of motion-defined contours

We present three experiments that explored the effect of binocular disparity on the perception of contours defined by motion in a Spatiotemporal Boundary Formation. Depending on the disparity, the stimulus is perceived as an object that moves behind a holed surface (occluded configuration) or as a luminous transparency that moves over a surface that contains dots (occluding configuration). In all of the experiments, we used a Vernier task to assess the strength of contour perception. In the first experiment, we measured acuity as a function of disparity for a range of speeds and dot densities. The results showed that, despite the difference in the percepts, acuity was similar in both situations, replicating the dependence on speed and dot density demonstrated in previous studies. In the second experiment, the results showed that the dynamics of contour integration were identical for both occluded and occluding configurations. In the third experiment, we tested whether the mechanism of contour integration works independently from the interpretation of the scene. In this experiment, we inverted the disparity during stimulus presentation so that the stimulus switched between occluded and occluding configurations. The results showed that the switch of the depth order increased the threshold to the value obtained with a shorter presentation time. This might be produced by a resetting of the integration process driven by the change of depth order. The results are discussed within a conceptual model that places the process of contour integration in the context of the perception of objects in a Spatiotemporal Boundary Formation...

Effect of disparity on the perception of motion-defined contours

We present three experiments that explored the effect of binocular disparity on the perception of contours defined by motion in a Spatiotemporal Boundary Formation. Depending on the disparity, the stimulus is perceived as an object that moves behind a holed surface (occluded configuration) or as a luminous transparency that moves over a surface that contains dots (occluding configuration). In all of the experiments, we used a Vernier task to assess the strength of contour perception. In the first experiment, we measured acuity as a function of disparity for a range of speeds and dot densities. The results showed that, despite the difference in the percepts, acuity was similar in both situations, replicating the dependence on speed and dot density demonstrated in previous studies. In the second experiment, the results showed that the dynamics of contour integration were identical for both occluded and occluding configurations. In the third experiment, we tested whether the mechanism of contour integration works independently from the interpretation of the scene. In this experiment, we inverted the disparity during stimulus presentation so that the stimulus switched between occluded and occluding configurations. The results showed that the switch of the depth order increased the threshold to the value obtained with a shorter presentation time. This might be produced by a resetting of the integration process driven by the change of depth order. The results are discussed within a conceptual model that places the process of contour integration in the context of the perception of objects in a Spatiotemporal Boundary Formation.(AU)

Effect of glare on reaction time for peripheral vision at mesopic adaptation.

When a bright light is present in the field of view, visibility is dramatically reduced. Many studies have investigated the effect of glare on visibility considering foveal vision. However, the effects on peripheral vision have received little attention. In a previous work [J. Opt. Soc. Am. A 25, 1790 (2008)], we showed that the effect of glare on reaction time (RT) for foveal vision at mesopic adaptation depends on the stimulus spatial frequency. In this work, we extend this study to peripheral vision. We measured the RT of achromatic sinusoidal gratings as a function of contrast for a range of spatial frequency, and eccentricity, and for two glare levels, in addition to the no-glare condition. Data were fitted with Piéron's law, following a linear relationship. We found that glare increases the slope of these lines for all conditions. These slopes seem to depend critically on eccentricity for 4 cycles/degree (c/deg), but not for 1 and 2 c/deg. We explain our results in terms of the contrast sensitivity (gain) of the underlying detection mechanisms.

Constancia de velocidad en imágenes naturales / Velocity constancy in natural images / Constance de vitesse dans les images naturelles / Constância de velocidade em imagens naturais

La investigación sobre el sistema visual condujo a la emergencia de modelos basados en los componentes neurales de dicho sistema, que permiten describir el modo en que es extraída la información de velocidad contenida en una escena con movimiento. El hecho de que estos modelos sean sensibles al tamaño de los estímulos presentados en la retina en combinación con el cambio de tamaño debido a la distancia a la cual se presentan los objetos, llevó a la pregunta acerca de cómo es posible la percepción de una velocidad constante, independientemente de la distancia a la cual se desplazan los objetos. En este trabajo revisamos las investigaciones realizadas sobre la constancia de la velocidad percibida e indagamos acerca de la importancia de la familiaridad de los objetos en movimiento. Por medio de experimentos psicofísicos con imágenes naturales, mostramos que la familiaridad juega un rol importante al momento de asignar perceptualmente la velocidad de un objeto en movimiento.

The investigation of the visual system produced models based on the neural components of such system, capable of describing the way in which the velocity information contained in a scene with movement is extracted. The fact that these models are sensitive to the size of the stimuli in combination with the distance to which the objects are presented on the retina, led to the question about how it could be possible the perception of a velocity independent from the object distance. In this work, we revised the investigations about velocity constancy and explore the effect of familiarity on the perception of speed. We performed a series of psychophysical experiments by using natural images and show that familiarity plays an important role in the assignment of a perceived speed to moving objects.

Recherche sur le système visuel l'a conduit à l'émergence de modèles basés sur les composants du système nerveux. Ces modèles peuvent décrire la façon dont il est extrait des informations de vitesse contenue dans une scène émouvante. Le fait que ces modèles sont sensibles à la taille des stimuli présentés dans la rétine, avec le changement de taille en raison de la distance à laquelle les objets sont présentés, ont conduit à la question de comment la perception d'une vitesse constante quelle que soit la distance à laquelle les objets se déplacent. Ici nous passons en revue la recherche sur le constance de vitesse perçue et en savoir davantage sur l'importance de la familiarité des objets en mouvement. Grâce à des expériences psychophysiques avec des images naturelles montrent que la familiarité joue un rôle important dans la détermination de la vitesse de perception d'un objet en mouvement.

A pesquisa sobre o sistema visual tem levado à emergência de modelos baseados nos componentes neurais de dito sistema, que permitem descrever o modo como é extraída a informação de velocidade contida numa cena com movimento. O fato de que estes modelos sejam sensíveis ao tamanho dos estímulos apresentados na retina, em combinação com a mudança de tamanho devida à distância à qual são apresentados os objetos, levou à pergunta de como é possível a percepção de uma velocidade constante, independentemente da distância pela qual se movimentam os objetos. Neste trabalho, revisamos as investigações realizadas sobre a constância da velocidade percebida e indagamos acerca da importância da familiaridade dos objetos em movimento. Mediante experimentos psicofísicos com imagens naturais, mostramos que a familiaridade tem um papel importante na hora de atribuir perceptualmente a velocidade de um objeto em movimento.

Constancia de velocidad en imágenes naturales / Velocity constancy in natural images / Constance de vitesse dans les images naturelles / Constância de velocidade em imagens naturais

La investigación sobre el sistema visual condujo a la emergencia de modelos basados en los componentes neurales de dicho sistema, que permiten describir el modo en que es extraída la información de velocidad contenida en una escena con movimiento. El hecho de que estos modelos sean sensibles al tamaño de los estímulos presentados en la retina en combinación con el cambio de tamaño debido a la distancia a la cual se presentan los objetos, llevó a la pregunta acerca de cómo es posible la percepción de una velocidad constante, independientemente de la distancia a la cual se desplazan los objetos. En este trabajo revisamos las investigaciones realizadas sobre la constancia de la velocidad percibida e indagamos acerca de la importancia de la familiaridad de los objetos en movimiento. Por medio de experimentos psicofísicos con imágenes naturales, mostramos que la familiaridad juega un rol importante al momento de asignar perceptualmente la velocidad de un objeto en movimiento(AU)

The investigation of the visual system produced models based on the neural components of such system, capable of describing the way in which the velocity information contained in a scene with movement is extracted. The fact that these models are sensitive to the size of the stimuli in combination with the distance to which the objects are presented on the retina, led to the question about how it could be possible the perception of a velocity independent from the object distance. In this work, we revised the investigations about velocity constancy and explore the effect of familiarity on the perception of speed. We performed a series of psychophysical experiments by using natural images and show that familiarity plays an important role in the assignment of a perceived speed to moving objects(AU)

Recherche sur le système visuel l'a conduit à l'émergence de modèles basés sur les composants du système nerveux. Ces modèles peuvent décrire la façon dont il est extrait des informations de vitesse contenue dans une scène émouvante. Le fait que ces modèles sont sensibles à la taille des stimuli présentés dans la rétine, avec le changement de taille en raison de la distance à laquelle les objets sont présentés, ont conduit à la question de comment la perception d'une vitesse constante quelle que soit la distance à laquelle les objets se déplacent. Ici nous passons en revue la recherche sur le constance de vitesse perçue et en savoir davantage sur l'importance de la familiarité des objets en mouvement. Grâce à des expériences psychophysiques avec des images naturelles montrent que la familiarité joue un rôle important dans la détermination de la vitesse de perception d'un objet en mouvement(AU)

A pesquisa sobre o sistema visual tem levado à emergência de modelos baseados nos componentes neurais de dito sistema, que permitem descrever o modo como é extraída a informação de velocidade contida numa cena com movimento. O fato de que estes modelos sejam sensíveis ao tamanho dos estímulos apresentados na retina, em combinação com a mudança de tamanho devida à distância à qual são apresentados os objetos, levou à pergunta de como é possível a percepção de uma velocidade constante, independentemente da distância pela qual se movimentam os objetos. Neste trabalho, revisamos as investigações realizadas sobre a constância da velocidade percebida e indagamos acerca da importância da familiaridade dos objetos em movimento. Mediante experimentos psicofísicos com imagens naturais, mostramos que a familiaridade tem um papel importante na hora de atribuir perceptualmente a velocidade de um objeto em movimento(AU)

The effect of chromatic and luminance information on reaction times.

We present a series of experiments exploring the effect of chromaticity on reaction time (RT) for a variety of stimulus conditions, including chromatic and luminance contrast, luminance, and size. The chromaticity of these stimuli was varied along a series of vectors in color space that included the two chromatic-opponent-cone axes, a red-green (L-M) axis and a blue-yellow [S - (L + M)] axis, and intermediate noncardinal orientations, as well as the luminance axis (L + M). For Weber luminance contrasts above 10-20%, RTs tend to the same asymptote, irrespective of chromatic direction. At lower luminance contrast, the addition of chromatic information shortens the RT. RTs are strongly influenced by stimulus size when the chromatic stimulus is modulated along the [S - (L + M)] pathway and by stimulus size and adaptation luminance for the (L-M) pathway. RTs are independent of stimulus size for stimuli larger than 0.5 deg. Data are modeled with a modified version of Pieron's formula with an exponent close to 2, in which the stimulus intensity term is replaced by a factor that considers the relative effects of chromatic and achromatic information, as indexed by the RMS (square-root of the cone contrast) value at isoluminance and the Weber luminance contrast, respectively. The parameters of the model reveal how RT is linked to stimulus size, chromatic channels, and adaptation luminance and how they can be interpreted in terms of two chromatic mechanisms. This equation predicts that, for isoluminance, RTs for a stimulus lying on the S-cone pathway are higher than those for a stimulus lying on the L-M-cone pathway, for a given RMS cone contrast. The equation also predicts an asymptotic trend to the RT for an achromatic stimulus when the luminance contrast is sufficiently large.

Learning motion: human vs. optimal Bayesian learner.

We used the optimal perceptual learning paradigm (Eckstein, Abbey, Pham, & Shimozaki, 2004) to investigate the dynamics of human rapid learning processes in motion discrimination tasks and compare it to an optimal Bayesian learner. This paradigm consists of blocks of few trials defined by a set of target attributes, and it has been shown its ability to detect learning effects appearing as soon as after the first trial. In the present task a sequence consisting of four patches containing random-dot patterns is presented at four separate locations equidistant from a fixation point. On each trial, the random dots in three patches moved with a mean speed and the fourth, target patch, could move either with slower or faster mean speed. Observers' task was to indicate what speed, faster or slower, was present in the display. The mean direction of the target patch was kept invariant along a block of trials. Observers learned the target relevant motion direction through indirect feedback, leading to an improvement in speed identification performance ranging from 15% to 30% which is greater than previously studied contrast defined targets and faces. However, comparison to an ideal learner revealed incomplete or partial learning for the motion task which was lower than previously measured for contrast defined targets and faces. A sub-optimal model that included inefficiencies in the updating of motion direction weights due to memory effects could account for the human learning. Finally, the similarity of the rapid learning effect observed here for motion perception with that found for contrast defined targets for localization and identification tasks could be suggesting a general strategy for learning in the human visual system and some common limitations such as memory.

The effect of spatial layout on motion segmentation.

We present a series of experiments exploring the effect of the stimulus spatial configuration on speed discrimination and two different types of segmentation, for random dot patterns. In the first experiment, we find that parsing the image produces a decrease of speed discrimination thresholds such as was first shown by Verghese and Stone [Verghese, P., & Stone, L. (1997). Spatial layout affects speed discrimination threshold. Vision Research, 37(4), 397-406; Verghese, P., & Stone, L. S. (1996). Perceived visual speed constrained by image segmentation. Nature, 381, 161-163] for sinusoidal gratings. In the second experiment, we study how the spatial configuration affects the ability of a subject in localizing an illusory contour defined by two surfaces with different speeds. Results show that the speed difference necessary to localize the contour decreases as the stimulus patches are separated. The third experiment involves transparency. Our results show a little or null effect for this condition. We explain the first and second experiment in the framework of the model of Bravo and Watamaniuk [Bravo, M., & Watamaniuk, S. (1995). Evidence for two speed signals: a coarse local signal for segregation and a precise global signal for discrimination. Vision Research, 35(12), 1691-1697] who proposed that motion computation consists in, at least, two stages: a first computation of coarse local speeds followed by an integration stage. We propose that the more precise estimate of speed obtained from the integration stage is used to produce a new refined segmentation of the image perhaps, through a feedback loop. Our data suggest that this third stage would not apply to the processing of transparency.