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José Antonio Aznar-Casanova

University of Barcelona, Cogntion, Development and Education Psychology, Faculty Member

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My first research interest is about how our brain represents Visual Space, i.e., how the world is represented in the brain. Spatial perception, which is the way for constructing an internal representation of perceived space, uses both visual and motor information. The nature of this representation and the neural mechanisms underlying it, have become a topic of great interest in both psychophysics and cognitive neuroscience. From these two approaches we try to understand how the brain rebuilds such spatial representations or Visual Space. To understand the intrinsic geometry that the brain uses to represent the perceived visual space we perform experiments on the mapping between the Physical Space (objectively measured with devices) and the Visual Space (subjectively obtained by using psychophysical methods). More specifically we aim at:"(1) verifying how different depth cues are integrated in order to structure a spatial metric system based on distance and visual direction (polar coordinates). (2) Studying how Visual System solve the conflict between depth cues, which take place in the most of the linear visual illusions and (3) Examining the influence of the certain constraints implemented in the Visual System (the oblique effect and the anisotropy of the vertical-horizontal meridians) on the accuracy and precision perceiving distances, sizes, orientations, etc.
Address: Passeig de la Vall d'Hebron, 171
ES-08035-Barcelona (Spain)

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J. Antonio Aznar Casanova

Elton Matsushima

UFF - Universidade Federal Fluminense

Manuel Esteban Moreno

Rochester Institute of Technology

Patricia DeLucia

Texas Tech University

Julian Hochberg

Columbia University

Christine Moroni

Université Lille 3, Res Fabrum

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Books by José Antonio Aznar-Casanova

Brief_CV_Aznar-Casanova_Enero_2019.pdf

Curriculum vitae

La Consciencia: la interfaz polinómica de la subjetividad

La Consciencia: la interfaz polinómica de la subjetividad, 2017

En esta obra, examinamos la Consciencia desde cuatro ejes o dimensiones: a) filosofía de la mente... more En esta obra, examinamos la Consciencia desde cuatro ejes o dimensiones: a) filosofía de la mente, b) evolucionista, c) bio-neurofisiológica, d) cognitivo-emocional. Y el uso metafórico de la consciencia como el interfaz de la subjetividad se refiere a un dispositivo capaz de transformar las señales generadas en un sistema (el mundo físico), codificadas en señales fisiológicas, que se hacen significativas como un mundo de qualias, con base en el cual se construye una realidad psíquica. Así, en esta obra se ponen en relación tres niveles o planos de la existencia: a) físico, b) fisiológico, c) psíquico. Donde lo fisiológico parece operar como un interfaz entre el mundo real y el mundo mental. En este libro he reunido gran cantidad de material que, aunque no explica la naturaleza de la consciencia ayudan a clarificar esta compleja noción. Este libro va dirigido a un público interesado, en particular, en las relaciones mente-cerebro y, en general, en la interacción entre el individuo con las realidades (física, virtual, social, cibernética, etc.), desde un enfoque interdisciplinar. Es decir, apunta hacia el sector de los estudiosos de la mente y su cerebro: Psicólogos, Neurocientíficos, Filósofos de la Ciencia y demás curiosos de la mente. Las ideas que aquí se tratan proporcionaran al lector un marco integrador de nociones que confluyen en este objeto de estudio: percepción-acción, atención, agencia (el yo), presencia (en la realidad), la subjetividad, la consciencia fenoménica, la autoconsciencia. En el libro se responden a unas cuantas preguntas pero, principalmente, se sugieren posibilidades para introducirse en un abordaje experimental del principal reto que tiene planteada la Ciencia del s. XXI, a saber, esclarecer la naturaleza de esta entidad y cómo surge.

Neurocomputacion en el Sistema Visual Humano

"Esta monografía representa el enfoque de la Neurociencia Computacional, que trata de integrar de... more "Esta monografía representa el enfoque de la Neurociencia Computacional, que trata de integrar de modo coherente, en un modelo explicativo, los hallazgos convergentes provenientes de la Neurofisiología, la Psicofísica y la Inteligencia Artificial (aplicada a la visión), procurando mantener la plausibilidad biológica. Es decir, que el modelo sea una explicación cabal de la visión en los sistemas visuales de los seres vivos y no sólo una serie de algoritmos computacionales que pretenden como objetivo lograr la máxima eficiencia en el procesamiento de información icónica.
Desde el enfoque neurocomputacional, aquí adoptado, se defiende la tesis de David Marr, según la cual si algún aspecto dl procesamiento visual puede explicarse mediante procesamiento de abajo-a-arriba, ó de bajo nivel, no hay por qué apelar al procesamiento guiado conceptualmente, ó de alto nivel. Ello implica que el cerebro visual debe tener una estructura modular, a saber, que las funciones visuales se hallan repartidas en módulos cerebrales, independientes unos de otros, operando en paralelo. Pero también, implica que la imagen (tal como suele entenderse este concepto) desaparece una vez que la información que han captado las células foto-receptoras de la retina empaquetan, en el haz de fibras del nervio óptico (axones de la células ganglionares), la distribución espaciotemporal de la energía luminosa, la cual contiene jugosa información de lo que hay ahí fuera, en el mundo exterior. A partir de su salida por el punto ciego, la tasa de impulsos bio-eléctricos por unidad de tiempo recodifica, en el dominio frecuencial, la información que llevaba la imagen, sin pérdida de detalles. El procesamiento en este dominio es mucho más rápido que el que puede ocurrir en el dominio espacial y, además, facilita el principal trabajo del sistema visual: el filtrado de detalles que distribuirán la información en múltiples escalas y resoluciones espaciales que operan a modo de lente zoom. Así, diferentes representaciones espectrales representan la información de la imagen, ya sea atenuando o excluyendo cierta información “irrelevante” para el perceptor”, ya sea realzando (bordes, contrastes, etc.) o rellenando (filling in) información de la imagen. No obstante, estas representaciones visuales multiescala, no trasparentes para el que percibe, son susceptibles de ser trasformadas, de nuevo, al dominio espacial, del cual somos conscientes. Así, a partir de la comprensión de las primeras etapas de la visión, se pone de manifiesto la idea original de D. Marr de que la visión es, esencialmente calculo, operaciones aplicadas a representaciones, que transforman sucesivamente la imagen que captó la retina, es decir: neuro-computación. Sin olvidar, que en el llamado ‘procesamiento visual tardío’ se añadirá un plus de información a la generada en la etapa de procesamiento inicial o temprano, también referida como ‘etapa de bajo nivel’."

Percepción del contraste: procesamiento de bajo nivel (Capitulo 8).

Introducción a la psicofísica

Anteriormente a la utilización de la introspección analítica y formal como método de la psicologí... more Anteriormente a la utilización de la introspección analítica y formal como método de la psicología experimental, apareció la psicofísica con el fin de estudiar las relaciones entre lo físico y lo psíquico, introduciéndose de este modo la medición en psicología. La paternidad indiscutible de esta metodología corresponde a E.H. Weber (1795-1878) y a G.T. Fechner (1801-1887) y, sin duda, la obra fundacional de la psicofísica clásica es "Elementos de la psicofísica", publicada por Fechner en 1860.

Alternativas teóricas en percepción: Raíces, orígenes y actualidad

Practicas Experimentales en Percepción Visual

Autor: J.Antonio Aznar-Casanova (Facultat de Psicologia. U.B.)

Psicología de la percepción visual

Resumen Se trata de una introducción a la percepción visual, en soporte informático, que pretende... more

... | Ayuda. Percepció. Información general. Autores: José Antonio Aznar Casanova; Editores: Univ... more

Human Visual Field and Navigational Strategies.

Informes de evaluación: un modelo informático para la enseñanza

... | Ayuda. Informes de evaluación : un modelo informático para la enseñanza. Información genera... more

Papers by José Antonio Aznar-Casanova

Chapter 9 Precision in Matching Oriented Lines Is Influenced by Perspective and Viewing Frames

Orientation is one of the main elements that form our perceptual space. Many studies have shown t... more Orientation is one of the main elements that form our perceptual space. Many studies have shown that people misjudge orientation in the frontoparallel plane. Here we examined precision in matching oriented lines in a 3D environment. In Experiment 1 we used perspective as a pictorial cue to provide the impression of a surface inclined in depth. In the first task we applied ―direct perspective‖ where observers had to draw lines on apparently inclined surfaces, in the second task we applied ―inverse perspective‖ where observers had to transform a perspective drawing onto a frontoparallel surface. Results showed two patterns, one related to inverse perspective, where precision matching oriented lines (PMOL) were modulated by the inclination of the surface. Here the observers had to perform more than one spatial transformation to solve the tasks. Another different pattern was found for direct perspective, in which observers had to perform only one spatial (cognitive) transformation. In E...

Dynamic Visual Acuity Lluïsa Quevedo

We present a review on the visual ability to discriminate fi ne details of moving objects (DVA: D... more We present a review on the visual ability to discriminate fi ne details of moving objects (DVA: Dynamic Visual Acuity), showing the most relevant differences, which have been attributed to this visual capacity in comparison to SVA (static visual acuity). It is known that the correlation between SVA and DVA is low. Moreover, when DVA is measured, not only the minimum spatial separation that the visual system can resolve is evaluated, but also the functionality of the oculomotor system. Therefore, assessing DVA also involves measuring the ability of the eye to actively seek information. Nowadays, it is known that DVA is one of the best indicators of success in certain sports specialties (table tennis, baseball, etc...) and that it negatively correlates with accident rates in traffi c scenarios. The investigated factors that produce a signifi cant reduction in dynamic spatial resolution are: (a) the speed of the stimulus, affecting both vertical and horizontal trajectories; (b) the sti...

Attention to Monocular Images Bias Binocular Rivalry

Frontiers in Systems Neuroscience, 2019

When monocular images cannot be fused, perception alternates between the two (or more) possible i... more When monocular images cannot be fused, perception alternates between the two (or more) possible images. This phenomenon, binocular rivalry (BR), is driven by the physical properties of the stimuli (size, contrast, spatial frequency, etc.) but it can also be modulated by attention to features of one of the rival stimuli (Chong et al., 2005; Dieter et al., 2016) and by attentional demands independent of the BR assessment (Paffen et al., 2008). Instead of the perceptually demanding tasks previously used to bias BR, we designed a simple counting task. We monocularly presented a number of trials (around 10 min) with a set of symbols and asked participants to count them. We found that after this task, dominance durations decreased for the unattended channel, and did not change for the attended channel. The results parallel those of Paffen et al. (2008) and square nicely with Levelt's second proposition, suggesting that the counting task effectively increased the sensibility of one channel which led to increased strength of the images presented to that channel. Alternatively, the results could be explained assuming that the non-attended channel was inhibited during the counting task, and the inhibition was carried over to the BR task.

The role of vertical disparities in the oblique effect

A great deal of studies using different visual tasks (e.g., Vernier acuity tasks, tilt illusion, ... more A great deal of studies using different visual tasks (e.g., Vernier acuity tasks, tilt illusion, crowding, etc) have revealed that our perception is strongly influenced by the orientation of the stimulus. Most studies have investigated visual acuity in twodimensional visual spaces (2D) but little is known about the effect of line orientation in depth perception (3D). In one experiment, Vernier Acuity (VA) in frontoparallel (2D) and medial (3D) planes was investigated. We used a virtual reality setup inducing inter-ocular disparities to simulate a 3D visual space, and a common computer screen to present stimuli in the frontal plane. In the experiment, by using the method of constant stimuli, the observer compared VA in the 2D and 3D visual spaces as a function of the stimulus orientation. Results showed that only judgments in the 3D condition were affected by the well-known 'oblique effect', and some impairment in stereoacuity (lines in depth plane) in comparison to 2D acuity (lines in frontal plane) was observed. We attributed the cause for such deterioration in stereoacuity to changes in vertical disparities.

¿Es el espacio visualmente percibido un espacio métrico?

Estudios de Psicología, 2009

... 1999; Indow, 2004; Koenderink y van Doorn, 2008a; Loomis, Da Silva, Fujita y Fukusima, 1992; ... more

Can exocentric direction be dissociated from its exocentric distance in virtual environments?

Perception & Psychophysics, 2008

Most studies that investigate the metrics of visual space use tasks in which observers need to co... more

One-Dimensional and Multi-Dimensional Studies of the Exocentric Distance Estimates in Frontoparallel Plane, Virtual Space, and Outdoor Open Field

The Spanish Journal of Psychology, 2006

The aim of this study is twofold: on the one hand, to determine how visual space, as assessed by ... more The aim of this study is twofold: on the one hand, to determine how visual space, as assessed by exocentric distance estimates, is related to physical space. On the other hand, to determine the structure of visual space as assessed by exocentric distance estimates. Visual space was measured in three environments: (a) points located in a 2-D frontoparallel plane, covering a range of distances of 20 cm; (b) stakes placed in a 3-D virtual space (range ≈ 330 mm); and (c) stakes in a 3-D outdoors open field (range = 45 m). Observers made matching judgments of distances between all possible pairs of stimuli, obtained from 16 stimuli (in a regular squared 4 × 4 matrix). Two parameters from Stevens' power law informed us about the distortion of visual space: its exponent and its coefficient of determination (R2). The results showed a ranking of the magnitude of the distortions found in each experimental environment, and also provided information about the efficacy of available visual cu...

Aurora Torrents Gómez

The influence of background topography on stereo-acuity*

New evidence of visual space anisotropy with autostereograms

Psychology and Neuroscience, 2014

Numerous research efforts have been directed toward determining the origin of anisotropies of vis... more Numerous research efforts have been directed toward determining the origin of anisotropies of visual space, in contrast to real space. Recent neurophysiological studies have placed the origin in the primary visual cortex (V1) or beyond. The present study sought to provide new psychophysical evidence of the origin of these anisotropies using auto-stereograms as visual stimuli in a relative depth judgment task. The observers were presented with a hidden three-dimensional shape that consisted of two pairs of parallel line segments that were located in different depth planes and oriented at 0° (horizontal line segments), 45°, and 90° (vertical line segments). The influence of orientation on the visual performance of five observers was evaluated. The encountered differences at 45° compared with cardinal orientations revealed a non-conclusive trend toward a negative impact of oblique orientation on the observers' performance. Significant differences were found in accuracy between the horizontal and vertical orientations, and the best scores corresponded to vertical line segments. This finding may be interpreted as the expression of vertical-horizontal anisotropy in depth. The perception of hidden three-dimensional shapes in auto-stereograms occurs beyond the primary visual cortex in the dorsal stream, and the present findings provide psychophysical evidence of the location of vertical-horizontal anisotropy in non-retinotopic areas beyond V1.

Brief_CV_Aznar-Casanova_Enero_2019.pdf

Curriculum vitae

La Consciencia: la interfaz polinómica de la subjetividad

La Consciencia: la interfaz polinómica de la subjetividad, 2017

En esta obra, examinamos la Consciencia desde cuatro ejes o dimensiones: a) filosofía de la mente... more En esta obra, examinamos la Consciencia desde cuatro ejes o dimensiones: a) filosofía de la mente, b) evolucionista, c) bio-neurofisiológica, d) cognitivo-emocional. Y el uso metafórico de la consciencia como el interfaz de la subjetividad se refiere a un dispositivo capaz de transformar las señales generadas en un sistema (el mundo físico), codificadas en señales fisiológicas, que se hacen significativas como un mundo de qualias, con base en el cual se construye una realidad psíquica. Así, en esta obra se ponen en relación tres niveles o planos de la existencia: a) físico, b) fisiológico, c) psíquico. Donde lo fisiológico parece operar como un interfaz entre el mundo real y el mundo mental. En este libro he reunido gran cantidad de material que, aunque no explica la naturaleza de la consciencia ayudan a clarificar esta compleja noción. Este libro va dirigido a un público interesado, en particular, en las relaciones mente-cerebro y, en general, en la interacción entre el individuo con las realidades (física, virtual, social, cibernética, etc.), desde un enfoque interdisciplinar. Es decir, apunta hacia el sector de los estudiosos de la mente y su cerebro: Psicólogos, Neurocientíficos, Filósofos de la Ciencia y demás curiosos de la mente. Las ideas que aquí se tratan proporcionaran al lector un marco integrador de nociones que confluyen en este objeto de estudio: percepción-acción, atención, agencia (el yo), presencia (en la realidad), la subjetividad, la consciencia fenoménica, la autoconsciencia. En el libro se responden a unas cuantas preguntas pero, principalmente, se sugieren posibilidades para introducirse en un abordaje experimental del principal reto que tiene planteada la Ciencia del s. XXI, a saber, esclarecer la naturaleza de esta entidad y cómo surge.

Neurocomputacion en el Sistema Visual Humano

"Esta monografía representa el enfoque de la Neurociencia Computacional, que trata de integrar de... more "Esta monografía representa el enfoque de la Neurociencia Computacional, que trata de integrar de modo coherente, en un modelo explicativo, los hallazgos convergentes provenientes de la Neurofisiología, la Psicofísica y la Inteligencia Artificial (aplicada a la visión), procurando mantener la plausibilidad biológica. Es decir, que el modelo sea una explicación cabal de la visión en los sistemas visuales de los seres vivos y no sólo una serie de algoritmos computacionales que pretenden como objetivo lograr la máxima eficiencia en el procesamiento de información icónica.
Desde el enfoque neurocomputacional, aquí adoptado, se defiende la tesis de David Marr, según la cual si algún aspecto dl procesamiento visual puede explicarse mediante procesamiento de abajo-a-arriba, ó de bajo nivel, no hay por qué apelar al procesamiento guiado conceptualmente, ó de alto nivel. Ello implica que el cerebro visual debe tener una estructura modular, a saber, que las funciones visuales se hallan repartidas en módulos cerebrales, independientes unos de otros, operando en paralelo. Pero también, implica que la imagen (tal como suele entenderse este concepto) desaparece una vez que la información que han captado las células foto-receptoras de la retina empaquetan, en el haz de fibras del nervio óptico (axones de la células ganglionares), la distribución espaciotemporal de la energía luminosa, la cual contiene jugosa información de lo que hay ahí fuera, en el mundo exterior. A partir de su salida por el punto ciego, la tasa de impulsos bio-eléctricos por unidad de tiempo recodifica, en el dominio frecuencial, la información que llevaba la imagen, sin pérdida de detalles. El procesamiento en este dominio es mucho más rápido que el que puede ocurrir en el dominio espacial y, además, facilita el principal trabajo del sistema visual: el filtrado de detalles que distribuirán la información en múltiples escalas y resoluciones espaciales que operan a modo de lente zoom. Así, diferentes representaciones espectrales representan la información de la imagen, ya sea atenuando o excluyendo cierta información “irrelevante” para el perceptor”, ya sea realzando (bordes, contrastes, etc.) o rellenando (filling in) información de la imagen. No obstante, estas representaciones visuales multiescala, no trasparentes para el que percibe, son susceptibles de ser trasformadas, de nuevo, al dominio espacial, del cual somos conscientes. Así, a partir de la comprensión de las primeras etapas de la visión, se pone de manifiesto la idea original de D. Marr de que la visión es, esencialmente calculo, operaciones aplicadas a representaciones, que transforman sucesivamente la imagen que captó la retina, es decir: neuro-computación. Sin olvidar, que en el llamado ‘procesamiento visual tardío’ se añadirá un plus de información a la generada en la etapa de procesamiento inicial o temprano, también referida como ‘etapa de bajo nivel’."

Percepción del contraste: procesamiento de bajo nivel (Capitulo 8).

Introducción a la psicofísica

Anteriormente a la utilización de la introspección analítica y formal como método de la psicologí... more Anteriormente a la utilización de la introspección analítica y formal como método de la psicología experimental, apareció la psicofísica con el fin de estudiar las relaciones entre lo físico y lo psíquico, introduciéndose de este modo la medición en psicología. La paternidad indiscutible de esta metodología corresponde a E.H. Weber (1795-1878) y a G.T. Fechner (1801-1887) y, sin duda, la obra fundacional de la psicofísica clásica es "Elementos de la psicofísica", publicada por Fechner en 1860.

Alternativas teóricas en percepción: Raíces, orígenes y actualidad

Practicas Experimentales en Percepción Visual

Autor: J.Antonio Aznar-Casanova (Facultat de Psicologia. U.B.)

Psicología de la percepción visual

Resumen Se trata de una introducción a la percepción visual, en soporte informático, que pretende... more

... | Ayuda. Percepció. Información general. Autores: José Antonio Aznar Casanova; Editores: Univ... more

Human Visual Field and Navigational Strategies.

Informes de evaluación: un modelo informático para la enseñanza

... | Ayuda. Informes de evaluación : un modelo informático para la enseñanza. Información genera... more

Chapter 9 Precision in Matching Oriented Lines Is Influenced by Perspective and Viewing Frames

Orientation is one of the main elements that form our perceptual space. Many studies have shown t... more Orientation is one of the main elements that form our perceptual space. Many studies have shown that people misjudge orientation in the frontoparallel plane. Here we examined precision in matching oriented lines in a 3D environment. In Experiment 1 we used perspective as a pictorial cue to provide the impression of a surface inclined in depth. In the first task we applied ―direct perspective‖ where observers had to draw lines on apparently inclined surfaces, in the second task we applied ―inverse perspective‖ where observers had to transform a perspective drawing onto a frontoparallel surface. Results showed two patterns, one related to inverse perspective, where precision matching oriented lines (PMOL) were modulated by the inclination of the surface. Here the observers had to perform more than one spatial transformation to solve the tasks. Another different pattern was found for direct perspective, in which observers had to perform only one spatial (cognitive) transformation. In E...

Dynamic Visual Acuity Lluïsa Quevedo

We present a review on the visual ability to discriminate fi ne details of moving objects (DVA: D... more We present a review on the visual ability to discriminate fi ne details of moving objects (DVA: Dynamic Visual Acuity), showing the most relevant differences, which have been attributed to this visual capacity in comparison to SVA (static visual acuity). It is known that the correlation between SVA and DVA is low. Moreover, when DVA is measured, not only the minimum spatial separation that the visual system can resolve is evaluated, but also the functionality of the oculomotor system. Therefore, assessing DVA also involves measuring the ability of the eye to actively seek information. Nowadays, it is known that DVA is one of the best indicators of success in certain sports specialties (table tennis, baseball, etc...) and that it negatively correlates with accident rates in traffi c scenarios. The investigated factors that produce a signifi cant reduction in dynamic spatial resolution are: (a) the speed of the stimulus, affecting both vertical and horizontal trajectories; (b) the sti...

Attention to Monocular Images Bias Binocular Rivalry

Frontiers in Systems Neuroscience, 2019

When monocular images cannot be fused, perception alternates between the two (or more) possible i... more When monocular images cannot be fused, perception alternates between the two (or more) possible images. This phenomenon, binocular rivalry (BR), is driven by the physical properties of the stimuli (size, contrast, spatial frequency, etc.) but it can also be modulated by attention to features of one of the rival stimuli (Chong et al., 2005; Dieter et al., 2016) and by attentional demands independent of the BR assessment (Paffen et al., 2008). Instead of the perceptually demanding tasks previously used to bias BR, we designed a simple counting task. We monocularly presented a number of trials (around 10 min) with a set of symbols and asked participants to count them. We found that after this task, dominance durations decreased for the unattended channel, and did not change for the attended channel. The results parallel those of Paffen et al. (2008) and square nicely with Levelt's second proposition, suggesting that the counting task effectively increased the sensibility of one channel which led to increased strength of the images presented to that channel. Alternatively, the results could be explained assuming that the non-attended channel was inhibited during the counting task, and the inhibition was carried over to the BR task.

The role of vertical disparities in the oblique effect

A great deal of studies using different visual tasks (e.g., Vernier acuity tasks, tilt illusion, ... more A great deal of studies using different visual tasks (e.g., Vernier acuity tasks, tilt illusion, crowding, etc) have revealed that our perception is strongly influenced by the orientation of the stimulus. Most studies have investigated visual acuity in twodimensional visual spaces (2D) but little is known about the effect of line orientation in depth perception (3D). In one experiment, Vernier Acuity (VA) in frontoparallel (2D) and medial (3D) planes was investigated. We used a virtual reality setup inducing inter-ocular disparities to simulate a 3D visual space, and a common computer screen to present stimuli in the frontal plane. In the experiment, by using the method of constant stimuli, the observer compared VA in the 2D and 3D visual spaces as a function of the stimulus orientation. Results showed that only judgments in the 3D condition were affected by the well-known 'oblique effect', and some impairment in stereoacuity (lines in depth plane) in comparison to 2D acuity (lines in frontal plane) was observed. We attributed the cause for such deterioration in stereoacuity to changes in vertical disparities.

¿Es el espacio visualmente percibido un espacio métrico?

Estudios de Psicología, 2009

... 1999; Indow, 2004; Koenderink y van Doorn, 2008a; Loomis, Da Silva, Fujita y Fukusima, 1992; ... more

Can exocentric direction be dissociated from its exocentric distance in virtual environments?

Perception & Psychophysics, 2008

Most studies that investigate the metrics of visual space use tasks in which observers need to co... more

One-Dimensional and Multi-Dimensional Studies of the Exocentric Distance Estimates in Frontoparallel Plane, Virtual Space, and Outdoor Open Field

The Spanish Journal of Psychology, 2006

The aim of this study is twofold: on the one hand, to determine how visual space, as assessed by ... more The aim of this study is twofold: on the one hand, to determine how visual space, as assessed by exocentric distance estimates, is related to physical space. On the other hand, to determine the structure of visual space as assessed by exocentric distance estimates. Visual space was measured in three environments: (a) points located in a 2-D frontoparallel plane, covering a range of distances of 20 cm; (b) stakes placed in a 3-D virtual space (range ≈ 330 mm); and (c) stakes in a 3-D outdoors open field (range = 45 m). Observers made matching judgments of distances between all possible pairs of stimuli, obtained from 16 stimuli (in a regular squared 4 × 4 matrix). Two parameters from Stevens' power law informed us about the distortion of visual space: its exponent and its coefficient of determination (R2). The results showed a ranking of the magnitude of the distortions found in each experimental environment, and also provided information about the efficacy of available visual cu...

Aurora Torrents Gómez

The influence of background topography on stereo-acuity*

New evidence of visual space anisotropy with autostereograms

Psychology and Neuroscience, 2014

Numerous research efforts have been directed toward determining the origin of anisotropies of vis... more Numerous research efforts have been directed toward determining the origin of anisotropies of visual space, in contrast to real space. Recent neurophysiological studies have placed the origin in the primary visual cortex (V1) or beyond. The present study sought to provide new psychophysical evidence of the origin of these anisotropies using auto-stereograms as visual stimuli in a relative depth judgment task. The observers were presented with a hidden three-dimensional shape that consisted of two pairs of parallel line segments that were located in different depth planes and oriented at 0° (horizontal line segments), 45°, and 90° (vertical line segments). The influence of orientation on the visual performance of five observers was evaluated. The encountered differences at 45° compared with cardinal orientations revealed a non-conclusive trend toward a negative impact of oblique orientation on the observers' performance. Significant differences were found in accuracy between the horizontal and vertical orientations, and the best scores corresponded to vertical line segments. This finding may be interpreted as the expression of vertical-horizontal anisotropy in depth. The perception of hidden three-dimensional shapes in auto-stereograms occurs beyond the primary visual cortex in the dorsal stream, and the present findings provide psychophysical evidence of the location of vertical-horizontal anisotropy in non-retinotopic areas beyond V1.

Visual mechanisms governing the perception of auto‐stereograms

Clinical and Experimental Optometry, 2011

Single image random dot stereograms (SIRDS) have been used to study diverse visual parameters and... more Single image random dot stereograms (SIRDS) have been used to study diverse visual parameters and skills. The aim of the present study was to identify the main optometric factors involved in the perception of SIRDS and to obtain a discriminant model to categorise our participants in terms of their skill in perceiving SIRDS. Response time was determined to assess the ability of 69 participants to perceive the hidden three-dimensional shape in an auto-stereogram presented under controlled conditions, whereupon three skill level groups were defined. The same participants were administered a battery of optometric tests to evaluate various aspects of accommodation and convergence, as well as stereopsis and phoria. Linear discriminant analysis, which served to examine the relationship between response times and the evaluated visual parameters and skills, provided a set of discriminant functions (or model), thus allowing for the categorisation of participants according to their skill to perceive SIRDS. Two discriminant functions were obtained, which allowed for an overall predictive accuracy of 66.67 per cent (p = 0.024), with a higher predictive accuracy for groups 1 (minimum time less than 10 seconds, 78.26 per cent) and 2 (minimum time greater than 10 seconds, 75.86 per cent) than for group 3 (SIRDS not perceived, 35.29 per cent). Stereoacuity, negative relative convergence, phoria at near and, to a lesser extent, the accommodative convergence and accommodation ratio were found to be the most relevant discriminant variables, although between-group statistically significant differences were only disclosed for stereoacuity (p = 0.001) and negative relative convergence (p = 0.003). The ability to perceive SIRDS was related to many visual parameters and skills, including, but not limited to, stereoacuity and negative relative convergence. It is uncertain whether SIRDS might be considered a useful tool in clinical practice.

Visual fatigue while watching 3D stimuli from different positions

Journal of optometry, Jan 17, 2016

When observers focus their stereoscopic visual system for a long time (e.g., watching a 3D movie)... more When observers focus their stereoscopic visual system for a long time (e.g., watching a 3D movie) they may experience visual discomfort or asthenopia. We tested two types of models for predicting visual fatigue in a task in which subjects were instructed to discriminate between 3D characters. One model was based on viewing distance (focal distance, vergence distance) and another in visual direction (oculomotor imbalance). A 3D test was designed to assess binocular visual fatigue while looking at 3D stimuli located in different visual directions and viewed from two distances from the screen. The observers were tested under three conditions: (a) normal vision; (b) wearing a lens (-2 diop.); (c) wearing a base-out prism (2▿) over each eye. Sensitivity and specificity were calculated (as Signal Detection Theory parameters: SDT). An ANOVA and SDT analyses revealed that impaired visual performance were directly related to short distance and larger deviation in visual direction, particular...

Influencia de la topografía del fondo sobre la estéreo-agudeza

Human depth perception can be strongly affected by the characteristics of the environment. Previo... more Human depth perception can be strongly affected by the characteristics of the environment. Previous studies have assessed visual acuity in the frontoparallel plane but little is known about the effect of background topography on stereoacuity. In the present experiment, based on alignment tasks, we analyzed how stimulus orientation and 3D background configuration influence stereoscopic vision. An experiment was designed to investigate the influence of stimulus orientation (0, 45 and 90 degrees) and background configuration (flat, black, concave and convex) on precision in 3D visual alignment tasks in a virtual environment. Background was found to result in an underestimation of stereoacuity, with the highest and lowest precision scores in comparison judgment tasks corresponding to convex and concave backgrounds, respectively. In addition, a significant orientation by background interaction was discovered. We conclude that background local depth cues are integrated with our target sti...

Dynamic Visual Acuity

We present a review on the visual ability to discriminate ¿ ne details of moving objects (DVA: Dy... more We present a review on the visual ability to discriminate ¿ ne details of moving objects (DVA: Dynamic Visual Acuity), showing the most relevant differences, which have been attributed to this visual capacity in comparison to SVA (static visual acuity). It is known that the correlation between SVA and DVA is low. Moreover, when DVA is measured, not only the minimum spatial separation that the visual system can resolve is evaluated, but also the functionality of the oculomotor system. Therefore, assessing DVA also involves measuring the ability of the eye to actively seek information. Nowadays, it is known that DVA is one of the best indicators of success in certain sports specialties (table tennis, baseball, etc...) and that it negatively correlates with accident rates in traf¿ c scenarios. The investigated factors that produce a signi¿ cant reduction in dynamic spatial resolution are: the speed of the stimulus, affecting both vertical and horizontal trajectories; the stimulus expos...

The Emotional Attentional Blink as a Measure of Patriotism

The Spanish Journal of Psychology, 2020

This study aims to explore whether the implicit processing of emotional symbols related to patrio... more This study aims to explore whether the implicit processing of emotional symbols related to patriotic feeling may exert some effects on attention. Here, we have conducted an experiment using two interrelated tasks. First, we use flags with different meanings to participants for measuring the strength of the emotional attentional blink (EAB) within a rapid serial visual presentation (RSVP) paradigm. Then, we use a “congruency judgments” subjective test, where we confront participants to judge the affinity between pairs of politician leaders and flags of different sign for community participants, while recording two physiological measures (Heart Rate Variance and Galvanic Skin Response) to evaluate the variations elicited by that confrontation. Results on the EAB task show a significant emotion induced blindness for emotional stimuli representing Catalan and Spanish patriotism (α = .05), while the effect does not appear for the stimulus representing neutral patriotism. The interaction ...

Creació d'una xarxa virtual col· laborativa de recursos d'aprenentatge

New evidences of the anisotropy of visual space in depth judgement tasks

Optica Pura y Aplicada, 2013

Utilizando un estímulo virtual consistente en dos segmentos de rectas paralelas que se visualizab... more Utilizando un estímulo virtual consistente en dos segmentos de rectas paralelas que se visualizaban tridimensionalmente mediante gafas estereoscópicas, se evaluó la relación entre el rendimiento visual de 12 observadores en juicios de profundidad relativa entre los citados segmentos, y la orientación espacial de los mismos, que se hizo variar entre 0º y 90º respecto a la horizontal. El peor rendimiento visual se obtuvo para las orientaciones más alejadas de las cardinales y, además, el rendimiento a 90º resultó mejor que a 0º. Por otra parte, la correlación encontrada entre el rendimiento visual de los observadores y la disparidad binocular vertical de los estímulos constituye una nueva evidencia de la contribución de dicha disparidad a la percepción de la profundidad.

Human Visual Field and Navigational Strategies

Applications of Virtual Reality, 2012

Two stages of programming eye gaze shifts in 3-D space

Vision Research, 2013

Accurate saccadic and vergence eye movements towards selected visual targets are fundamental to p... more Accurate saccadic and vergence eye movements towards selected visual targets are fundamental to perceive the 3-D environment. Despite this importance, shifts in eye gaze are not always perfect given that they are frequently followed by small corrective eye movements. The oculomotor system receives distinct information from various visual cues that may cause incongruity in the planning of a gaze shift. To test this idea, we analyzed eye movements in humans performing a saccade task in a 3-D setting. We show that saccades and vergence movements towards peripheral targets are guided by monocular (perceptual) cues. Approximately 200 ms after the start of fixation at the perceived target, a fixational saccade corrected the eye positions to the physical target location. Our findings suggest that shifts in eye gaze occur in two phases; a large eye movement toward the perceived target location followed by a corrective saccade that directs the eyes to the physical target location.

Comparison of Dynamic Visual Acuity Between Water Polo Players and Sedentary Students

Research Quarterly for Exercise and Sport, 2011

In this study, we examined differences in dynamic visual acuity between elite and subelite water ... more In this study, we examined differences in dynamic visual acuity between elite and subelite water polo players and sedentary students. To measure dynamic visual acuity binocularly, we asked participants to indicate the orientation of a broken ring, similar to the Landolt C, which increased in size as it moved across a computer screen. Two different speeds, three possible trajectories, and two different levels of contrast were evaluated. There were statistically significant differences between elite players and sedentary students for each combination of speed, contrast, and trajectory. Elite players achieved better dynamic visual acuity scores, and results also improved for some combinations of speed, contrast, and trajectory. Comparison between elite and subelite groups failed to reveal any

A Role of Eye Vergence in Covert Attention

PLoS ONE, 2013

Covert spatial attention produces biases in perceptual and neural responses in the absence of ove... more Covert spatial attention produces biases in perceptual and neural responses in the absence of overt orienting movements. The neural mechanism that gives rise to these effects is poorly understood. Here we report the relation between fixational eye movements, namely eye vergence, and covert attention. Visual stimuli modulate the angle of eye vergence as a function of their ability to capture attention. This illustrates the relation between eye vergence and bottom-up attention. In visual and auditory cue/no-cue paradigms, the angle of vergence is greater in the cue condition than in the no-cue condition. This shows a top-down attention component. In conclusion, observations reveal a close link between covert attention and modulation in eye vergence during eye fixation. Our study suggests a basis for the use of eye vergence as a tool for measuring attention and may provide new insights into attention and perceptual disorders.