Proceedings Article | 11 February 2008
KEYWORDS: Visualization, Target detection, Contrast sensitivity, Eye, Eye models, Retina, Visual process modeling, Spatial frequencies, Statistical analysis, Injuries
Macular scotomas, affecting visual functioning, characterize many eye and neurological diseases like AMD, diabetes
mellitus, multiple sclerosis, and macular hole. In this work, foveal visual field defects were modeled, and their effects
were evaluated on spatial contrast sensitivity and a task of stimulus detection and aiming. The modeled occluding scotomas, of different size, were superimposed on the stimuli presented on the computer display, and were stabilized on the retina using a mono Purkinje Eye-Tracker. Spatial contrast sensitivity was evaluated using
square-wave grating stimuli, whose contrast thresholds were measured using the method of constant stimuli with "catch
trials". The detection task consisted of a triple conjunctive visual search display of: size (in visual angle), contrast and
background (simple, low-level features vs. complex, high-level features). Search/aiming accuracy as well as R.T.
measures used for performance evaluation. Artificially generated scotomas suppressed spatial contrast sensitivity in a size dependent manner, similar to previous studies. Deprivation effect was dependent on spatial frequency, consistent with retinal inhomogeneity models. Stimulus detection time was slowed in complex background search situation more than in simple background. Detection speed was dependent on scotoma size and size of stimulus. In contrast, visually guided aiming was more sensitive to scotoma effect in simple background search situation than in complex background. Both stimulus aiming R.T. and accuracy (precision targeting) were impaired, as a function of scotoma size and size of stimulus. The data can be explained by models distinguishing between saliency-based, parallel and serial search processes, guiding visual attention, which are supported by underlying retinal as well as neural mechanisms.
