Visual search in virtual 3D space: the relation of multiple targets and distractors

Effect of attention on ensemble perception: Comparison between exogenous attention, endogenous attention, and depth

Ensemble perception is an important ability of human beings that allows one to extract summary information for scenes and environments that contain information that far exceeds the processing limit of the visual system. Although attention has been shown to bias ensemble perception, two important questions remain unclear: (1) whether direct manipulations on different types of spatial attention could produce similar effects on ensembles and (2) whether factors potentially influencing the attention distribution, such as depth perception, could evoke an indirect effect of attention on ensemble representation. This study aims to address these questions. In Experiments 1 and 2, two types of precues were used to evoke exogenous and endogenous attention, respectively, and the ensemble color perceptions were examined. We found that both exogenous and endogenous attention biased ensemble representation towards the attended items, and the latter produced a greater effect. In Experiments 3 and 4, we examined whether depth perception could affect color ensembles by indirectly influencing attention allocation in 3D space. The items were separated in two depth planes, and no explicit cues were applied. The results showed that color ensemble was biased to closer items when depth information was task relevant. This suggests that ensemble perception is naturally biased in 3D space, probably through the mechanism of attention. Computational modeling consistently showed that attention exerted a direct shift on the ensemble statistics rather than averaging the feature values over the cued and noncued items, providing evidence against an averaging process of individual perception.

Object-based inhibition of return in three-dimensional space: From simple drawings to real objects

Cued to an object in space, inhibition of the attended location can spread to the entire object. Although object-based inhibition of return (IOR) studies in a two-dimensional plane have been documented, the IOR has not been explored when objects cross depth in three-dimensional (3D) space. In the present study, we used a virtual reality technique to adapt the double-rectangle paradigm to a 3D space, and manipulated the cue validity and target location to examine the difference in object-based IOR between far and near spaces under different object representations. The study showed that the object-based IOR of simple drawings existed only in near space, whereas object-based IOR of real objects existed only in far space at first, and as the object similarity decreases, it appeared in both far and near spaces.

Historical, Diagnostic, and Chromatic Treatment in Visual Snow Syndrome: A Retrospective Analysis

PURPOSE

This study aimed to determine the historical, diagnostic, and treatment aspects in patients with documented visual snow syndrome/visual snow in an academic, optometric setting.

METHODS

A retrospective analysis was performed in patients (N = 40, aged 12 to 55 years) with documented visual snow syndrome/visual snow examined over a 4-year period. Information was collected by a detailed case history and the Visual Snow Syndrome Symptom Survey. Treatment assessment was performed using the Intuitive Colorimeter, and a wide selection of chromatic tints was assessed under the most provocative/exacerbating and other conditions.

RESULTS

Visual snow was typically constant and monochromatic, with it being present on average 6.43 years. Bright and dark surfaces were the most provocative/exacerbating/revealing conditions, along with the viewing of computer screens. The most common etiology was mild traumatic brain injury. The most common primary and secondary symptoms were photosensitivity and tinnitus, respectively. There was a high frequency of occurrence of oculomotor deficits, especially accommodative and vergence insufficiency (~40 to 50%). Eighty percent of the patients were prescribed a chromatic tint with subjective visual reduction of visual snow ranging from 15 to 100% (mean, 45%).

CONCLUSIONS

The present information will help in understanding this unusual medicoperceptual condition, especially with respect to simple treatment frequently using readily available chromatic tints.

Top-down control of attention by stereoscopic depth

Stereoscopic depth has a mixed record as a guiding attribute in visual attention. Visual search can be efficient if the target lies at a unique depth; whereas automatic segmentation of search arrays into different depth planes does not appear to be pre-attentive. These prior findings describe bottom-up, stimulus-driven depth guidance. Here, we ask about the top-down selection of depth information. To assess the ability to direct attention to specific depth planes, Experiment 1 used the centroid judgment paradigm which permits quantitative measures of selective processing of items of different depths or colors. Experiment 1 showed that a subset of observers could deploy specific attention filters for each of eight depth planes, suggesting that at least some observers can direct attention to a specific depth plane quite precisely. Experiment 2 used eight depth planes in a visual search experiment. Observers were encouraged to guide their attention to far or near depth planes with an informative but imperfect cue. The benefits of this probabilistic cue were small. However, this may not be a specific problem with guidance by stereoscopic depth. Equivalently poor results were obtained with color. To check and prove that depth guidance in search is possible, Experiment 3 presented items in only two depth planes. In this case, information about the target depth plane allows observers to search more efficiently, replicating earlier work. We conclude that top-down guidance by stereoscopic depth is possible but that it is hard to apply the full range of our stereoscopic ability in search.