Influence of background on precision of 3D depth judgment tasks in a real environment.

Presently, little is known about the effect of curved backgrounds against which the target stimulus is presented on precision in stereoacuity. The experiment analyzed the influence of stimulus orientation and 3D background configuration on stereoscopic vision. Participants were instructed to perform 3D visual alignment tasks on a modified version of the Howard-Dolman apparatus, whereupon precision in depth perception for different curved backgrounds (flat, black, concave, and convex) was evaluated. In addition, the influence of stimulus orientation (0 degrees, 45 degrees, and 90 degrees) on precision was examined. The findings revealed an underestimation in the perceived depth in all background configurations, indicating highest and lowest precision outcomes for convex and concave backgrounds, respectively. In addition, a significant interaction of background and orientation was found. It was concluded that, in a real environment, background local depth cues are integrated with target stimuli to contribute to depth perception.

Mental rotation of mirrored letters: evidence from event-related brain potentials.

Event-related brain potentials (ERPs) were recorded while participants (n=13) were presented with mirrored and normal letters at different orientations and were asked to make mirror-normal letter discriminations. As it has been suggested that a mental rotation out of the plane might be necessary to decide on mirrored letters, we wanted to determine whether this rotation occurs after the plane rotation in mirror rotated letters. The results showed that mirrored letters in the upright position elicited a negative-going waveform over the right hemisphere in the 400-500 ms window. A similar negativity was also present in mirrored letters at 30 degrees, 60 degrees, and 90 degrees, but in these cases it was delayed. Moreover, the well-known orientation effect on the amplitude of the rotation-related negativity was also found, although it was more evident for normal than for mirrored letters. These results indicate that the processing of mirrored letters differs from that of normal letters, and suggest that a rotation out of the plane after the plane rotation may be involved in the processing of mirror rotated letters.

Attention to Monocular Images Bias Binocular Rivalry.

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.

Generalisation decrement and not overshadowing by associative competition among pairs of landmarks in a navigation task with humans.

In three experiments, a virtual preparation for humans of the Morris water task (VMWT) was used. Experiment 1 established that four landmarks were of similar salience. Then, in Experiments 2 and 3, participants were trained to locate a hidden platform in the presence or either two or four of the previous landmarks. In Experiment 2, one pair of groups was trained with four visual landmarks spaced at equal intervals around the edge of the pool, while a second pair was trained with two landmarks only, either relatively close to or far from the hidden platform. After training, a reciprocal overshadowing effect was found: on a test without the platform with two landmarks only (either close to or far from the platform position), the participants trained with four landmarks spent less time in the platform quadrant than those trained with only two. Finally, Experiment 3 showed that at least participants trained with two landmarks relatively close to the platform and then tested with four also performed worse on test than those trained and tested with two close landmarks only. This result suggests that generalisation decrement, rather than associative competition, could provide a sufficient explanation for the overshadowing observed in Experiment 2 in the proximal groups. The present set of experiments extend, although only partially, the generalisation decrement results documented in rats to human participants.

[Familiarity and recollection in fictitious face recognition: implications for recognition models]. / Familiaridad y recuerdo en el reconocimiento de rostros ficticios: implicaciones para los modelos de reconocimiento.

Using the <> paradigm, participants were engaged in a fictitious face recognition experiment in which three between-subject conditions were manipulated by either adding or not adding wrinkles on the faces between the study and the recognition tasks (no change, single change, double change). Our hypothesis was that this procedure would maximize judgments based on familiarity, thus determining whether data provided better fit to the models based on the signal detection theory or to predictions of dual models. In global terms, our results support the signal detection model predictions, although we discuss whether these models better fit tasks based on familiarity or tasks based on recollection.

Visual fatigue while watching 3D stimuli from different positions.

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.

One-dimensional and multi-dimensional studies of the exocentric distance estimates in frontoparallel plane, virtual space, and outdoor open field.

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 x 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 cues of spatial layout. Furthermore, our data are in agreement with previous findings showing systematic perceptual errors, such as the further the stimuli, the larger the distortion of the area subtended by perceived distances between stimuli. Additionally, we measured the magnitude of distortion of visual space relative to physical space by a parameter of multidimensional scaling analyses, the RMSE. From these results, the magnitude of such distortions can be ranked, and the utility or efficacy of the available visual cues informing about the space layout can also be inferred.

Distance perception in a natural outdoor setting: is there a developmental trend to overconstancy?

The main purpose of the present study was to investigate whether in natural environment, using very large physical distances, there is a trend to overconstancy for distance estimates during development. One hundred and twenty-nine children aged 5 to 13 years old and twenty-one adults (in a control group), participated as observers. The observer's task was to bisect egocentric distances, ranging from 1.0 to 296.0 m, presented in a large open field. The analyses focused on two parameters, constant errors and variable errors, such as measuring accuracy and precision, respectively. A third analysis focused on the developmental pattern of shifts in constancy as a function of age and range of distances. Constant error analysis showed that there are two relevant parameters for accuracy, age, and range of distances. For short distances, there are three developmental stages: 5-7 years, when children have unstable responses, 7-11, underconstancy, and 13 to adulthood, when accuracy is reached. For large distances, there is a two-stage development: 5-11 years, with severe underconstancy, and beyond this age, with mild underconstancy. Variable errors analyses indicate that precision is noted for 7 year-old children, independently of the range of distances. The constancy analyses indicated that there is a shift from constancy (or slightly overconstancy) to underconstancy as a function of physical distance for all age groups. The age difference is noted in the magnitude of underconstancy that occurs in larger distances, where adults presented lower levels of underconstancy than children. The present data were interpreted as due to a developmental change in cognitive processing rather than to changes in visual space perception.

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.

Assessing Attention Deficit by Binocular Rivalry.

OBJECTIVE: To determine whether the frequency and duration of the periods of suppression of a percept in a binocular rivalry (BR) task can be used to distinguish between participants with ADHD and controls. METHOD: A total of 122 participants (6-15 years) were assigned to three groups: ADHD-Combined (ADHD-C), ADHD-Predominantly Inattentive (ADHD-I), and controls. They each performed a BR task and two measures were recorded: alternation rate and duration of exclusive dominance periods. RESULTS: ADHD-C group presented fewer alternations and showed greater variability than did the control group; results for the ADHD-I group being intermediate between the two. The duration of dominance periods showed a differential profile: In control group, it remained stable over time, whereas in the clinical groups, it decreased logarithmically as the task progressed. CONCLUSION: The differences between groups in relation to the BR indicators can be attributed to the activity of involuntary inhibition.

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.

A role of eye vergence in covert attention.

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.

Difference in visual processing assessed by eye vergence movements.

Orienting visual attention is closely linked to the oculomotor system. For example, a shift of attention is usually followed by a saccadic eye movement and can be revealed by micro saccades. Recently we reported a novel role of another type of eye movement, namely eye vergence, in orienting visual attention. Shifts in visuospatial attention are characterized by the response modulation to a selected target. However, unlike (micro-) saccades, eye vergence movements do not carry spatial information (except for depth) and are thus not specific to a particular visual location. To further understand the role of eye vergence in visual attention, we tested subjects with different perceptual styles. Perceptual style refers to the characteristic way individuals perceive environmental stimuli, and is characterized by a spatial difference (local vs. global) in perceptual processing. We tested field independent (local; FI) and field dependent (global; FD) observers in a cue/no-cue task and a matching task. We found that FI observers responded faster and had stronger modulation in eye vergence in both tasks than FD subjects. The results may suggest that eye vergence modulation may relate to the trade-off between the size of spatial region covered by attention and the processing efficiency of sensory information. Alternatively, vergence modulation may have a role in the switch in cortical state to prepare the visual system for new incoming sensory information. In conclusion, vergence eye movements may be added to the growing list of functions of fixational eye movements in visual perception. However, further studies are needed to elucidate its role.

Psychometric properties of a test for ADHD based on binocular rivalry.

The psychometric properties of a Binocular Rivalry (BR)-based test on a group of 159 participants (57 with attention deficit hyperactivity disorder, ADHD) aged between 6 and 15 years are presented. Two factors, which explained 56.82% of the variance, were obtained by exploratory factor analysis: (a) Alternations and Duration of exclusive dominances, and (b) Decision time. Reliability was excellent (Cronbach's α = .834 and .884). The ADHD group showed fewer alternations and longer duration of dominances and decision time than the control group. Correlations between measures of BR, IQ, working memory, and processing speed of the WISC-IV, and ADHD symptoms, assessed by parents and teachers, ranged between low and medium.

Onset time of binocular rivalry and duration of inter-dominance periods as psychophysical markers of ADHD.

Attention deficit hyperactivity disorder (ADHD) is one of the main neurobiological disorders in young children. Despite its prevalence, current diagnosis is debated. In this study we tested whether measures of binocular rivalry (BR) can contribute to the diagnosis of ADHD. BR is a phenomenon that is produced when two different images are presented to the two eyes simultaneously. Under these conditions the image presented to one eye competes with that presented to the other eye in seeking to achieve perceptual dominance. This competition is resolved through the activation of a given percept coupled with the suppression of the percept that had predominated until that point. We assume that the difficulty with inhibiting responses of ADHD children also affects their ability to inhibit the dominant image in a BR context. We analyzed the time to rivalry onset and the inter-dominance periods as measures of the temporal cost of resolving how long it takes for the brain to select (or suppress) one percept over the other. Our results show that the time to onset of rivalry (the first dominance) was longer in the clinical groups (ADHD-C and ADHD-I) than in the control group. As regards the inter-dominance periods, these were longer in the ADHD-C group than among controls, with the shortest period corresponding to the ADHD-I group. This study shows that BR can be used as a tool to develop a behavioral indicator of ADHD.

Visual mechanisms governing the perception of auto-stereograms.

BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSION: 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.

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. .

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.

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.

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.