Agudeza Visual Dinámica / Acuidade Visual Dinâmica / Dynamic Visual Acuity

Resumen Presentamos una revisión del tema relativo a la habilidad visual para discriminar detalles sutiles sobre objetos en movimiento (AVD: Agudeza Visual Dinámica), mostrando las diferencias más relevantes, que han sido atribuidas a esta capacidad visual en comparación con la AVE (AV estática). Actualmente, es sabido que la correlación entre AVE y AVD es baja. Además, al medir la AVD no solo evaluamos la mínima separación espacial que el sistema visual puede resolver, sino también la funcionalidad del sistema oculomotor. De este modo, valorar la AVD implica medir la capacidad del ojo como buscador activo de información. Hoy sabemos que la AVD es uno de los mejores indicadores de éxito en ciertas especialidades deportivas (tenis de mesa, baseball, etc.) y que correlaciona negativamente con la siniestralidad en accidentes de tráfico. Entre los factores investigados que producen una reducción significativa de la resolución espacial dinámica destacan: (a) la velocidad del estímulo, afectando tanto a trayectorias verticales como horizontales; (b) el tiempo de exposición del estímulo; (c) la iluminación ambiental; (d) la disminución del contraste y e) la edad del sujeto. Por otra parte, se ha verificado que esta capacidad visual es susceptible de mejorar con el entrenamiento.

Resumo Apresentamos uma revisão do tema referente a habilidade visual para discriminar sutís detalhes diante de objetos em movimento (AVD: Acuidade Visual Dinâmica), mostrando as diferenças mais relevantes, que foram atribuídas a esta capacidade visual em comparação com a AVE (AV estática). Atualmente sabemos que a correlação entre AVE e AVD é baixa. Sendo assim, ao medir a AVD não somente avaliamos a mínima separação espacial que o sistema visual pode resolver, também avaliamos a funcionalidade do sistema oculomotor. Desse modo, para avaliar a AVD requer medir a capacidade do olho como buscador ativo de informação. Hoje sabemos que a AVD é um dos melhores indicadores de êxito em certas especialidades desportivas (tênis de mesa, baseball, etc.) e que se correlaciona negativamente com sinistralidade nos acidentes de trânsito. Entre os fatores investigados que produzem una redução significativa da resolução espacial dinâmica destacam: (a) a velocidade do estímulo, que afeta tanto as trajetórias verticais como horizontais; (b) o tempo de exposição do estímulo; (c) a iluminação ambiental; (d) a diminuição do contraste e (e) a idade do sujeito. Por outro lado, verificou-se que esta capacidade visual é suscetível a melhorar com treinamento.

Abstract We present a review on the visual ability to discriminate fine 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 traffic scenarios. The investigated factors that produce a significant reduction in dynamic spatial resolution are: (a) the speed of the stimulus, affecting both vertical and horizontal trajectories; (b) the stimulus exposure time; (c) ambient illumination; (d) reduction in contrast and (e) subject age. Moreover, it has been verified that this visual capacity is likely to improve with training.

Attentional blink in children with attention deficit hyperactivity disorder

Objective: To explore the temporal mechanism of attention in children with attention deficit hyperactivity disorder (ADHD) and controls using a rapid serial visual presentation (RSVP) task in which two letters (T1 and T2) were presented in close temporal proximity among distractors (attentional blink [AB]). Method: Thirty children aged between 9 and 13 years (12 with ADHD combined type and 18 controls) took part in the study. Both groups performed two kinds of RSVP task. In the single task, participants simply had to identify a target letter (T1), whereas in the dual task, they had to identify a target letter (T1) and a probe letter (T2). Results: The ADHD and control groups were equivalent in their single-task performance. However, in the dual-task condition, there were significant between-group differences in the rate of detection of the probe letter (T2) at lag + 1 and lag + 4. The ADHD group exhibited a larger overall AB compared with controls. Conclusion: Our findings provide support for a link between ADHD and attentional blink. .

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.

Are first-order disparity gradients spatial primitives of the orientation of lines on the ground plane?

The present study investigated the mechanisms involved in processing orientation on the frontal and ground planes. The stimuli comprised two yellow circles conceived as the endpoints of a segment and depicted on a black background. In Experiment 1, the observers performed two tasks on both planes (frontal and ground). In Task 1 they were asked to indicate the absolute location of the two endpoints, presented one at a time (successive task). In Task 2 they had to locate the relative position of the endpoints presented simultaneously (simultaneous task). Relative and absolute errors were analyzed according to a cyclopean coordinate system derived from the geometry of the visual scene. These two kinds of errors were studied within the framework of the hypothesis that each kind of task would minimize the error related to its codification. The results showed greater absolute errors in the simultaneous task than in the successive task and greater relative errors in which the successive task seemingly activated a more accurate way of codification of the orientation. In Experiment 2 we controlled the availability of visual depth cues by changing the presentation time (50 and 3000 ms) and viewing conditions (monocular and binocular) in the simultaneous task. The results showed that the precision of orientation judgments was poorer on the ground plane than on the frontal plane, except when the observers used binocular vision. These results suggest that the orientation of a segment, at least on the ground plane, can be conceptualized as a gradient of disparities.

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, crowding, etc) have revealed that our perception is strongly influenced by the orientation of the stimulus. Most studies have investigated visual acuity in two-dimensional 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.

Models of brain asymmetry in emotional processing

Two models of brain asymmetry in emotional processing were reviewed: the right hemisphere and the valence hypotheses. The first states a dominant role for the right hemisphere in emotional processing, whereas the second assumes that the left hemisphere is dominant for positive emotions and the right hemisphere for negative ones. Different methods, such as the divided visual field technique, have supported both hypotheses. The amygdala and the prefrontal cortex are presented as important structures involved on brain asymmetry in emotional processing. The paper ends pointing out new perspectives for the study of the neural subtrates of different components of emotions.