Visual fatigue while watching 3D stimuli from different positions / Fatiga visual al observar estímulos en 3D desde diferentes posiciones

Purpose: 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). Method: 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). Results: An ANOVA and SDT analyses revealed that impaired visual performance were directly related to short distance and larger deviation in visual direction, particularly when the stimuli were located nearer and at more than 24◦ to the centre of the screen in dextroversion and beyond. Conclusion: This results support a mixed model, combining a model based on the visual angle (related to viewing distance) and another based on the oculomotor imbalance (related to visual direction). This mixed model could help to predict the distribution of seats in the cinema room ranging from those that produce greater visual comfort to those that produce more visual discomfort. Also could be a first step to pre-diagnosis of binocular vision disorders (AU)

Objetivo: Cuando los observadores centran su sistema visual estereoscópico durante un tiempo prolongado (ej.: viendo una película en 3D), pueden experimentar molestias visuales o astenopia. Probamos dos tipos de modelos de predicción de la fatiga visual en un estudio, en el que se solicitaba a los sujetos que discriminaran entre caracteres en 3D. Un modelo se basaba en la visión lejana (distancia focal, distancia de vergencia), y el otro en la dirección visual (desequilibrio oculomotor). Método: Se diseñó una prueba en 3D para valorar la fatiga visual binocular mientras se observaban estímulos en 3D situados en diferentes direcciones visuales, y se veían a dos distancias de la pantalla. Se realizó la prueba a los observadores bajo tres situaciones: a) visión normal, b) utilizando una lente (-2 dioptrías); c) utilizando un prisma base externa (2▽) en cada ojo. Se calcularon la sensibilidad y especificidad (como parámetros de la Teoría de la Detección de Señales: TDS). Resultados: Los análisis ANOVA y TDS revelaron que el deterioro del desempeño visual guardaba una relación directa con la distancia corta y una mayor desviación de la dirección visual, en especial cuando los estímulos se situaban más cerca, y a más de 24◦ del centro de la pantalla en dextroversión y valores superiores. Conclusión: Estos resultados respaldan un modelo mixto, que combina un modelo basado en el ángulo visual (relacionado con la visión lejana) y otro basado en el desequilibrio oculomotor (relacionado con la dirección visual). Este modelo mixto podría ayudar a predecir la distribución de las butacas en las salas de cine, que oscila entre aquellas que producen un mayor confort visual y aquellas que producen más molestias visuales. También podría constituir un primer paso para el diagnóstico previo de los trastornos de la visión binocular (AU)

New evidence of visual space anisotropy with auto-stereograms

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 0º (horizontal line segments), 45º, and 90º (vertical line segments). The influence of orientation on the visual performance of five observers was evaluated. The encountered differences at 45º 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.(AU)

New evidence of visual space anisotropy with auto-stereograms

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 0º (horizontal line segments), 45º, and 90º (vertical line segments). The influence of orientation on the visual performance of five observers was evaluated. The encountered differences at 45º 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.