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.

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.

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.