How does attention spread across objects oriented in depth?

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.

Orienting attention across binocular disparity

The spatial distribution of covert visual attention following an exogenous cue is often described as a spotlight, which disregards depth. Here, we study the orienting of attention across binocular disparity, a key depth cue in primates. A small Gabor patch target was displayed at ±12-arcmin horizontal offset in each eye independently, resulting in four possible 3D locations. With some latency relative to target onset (0-300 ms), an attentional cue was displayed at one of five binocular locations, resulting in various combinations of relative azimuth (horizontal position) and disparity (depth). Observers' task was to discriminate the orientation of the target. Observers' performance decreased as the relative azimuth between the cue and the target increased. Performance also decreased with the difference in disparity, even when the azimuth remained constant. Performance varied with the delay between the cue and the target and was maximal between 100 and 150 ms. The orienting of attention in azimuth and depth followed the same time course. We mapped the 3D shape of attentional focus over time and found that the spatial envelope was approximately a Gaussian modulated in time. These results could not be explained by monocular confounds nor by eye movements. We conclude that exogenous cues direct attention not only to their visual direction but also to their depth and that binocular disparity is sufficient to define that depth. The identical time course and interaction between azimuth and depth suggest a shared mechanism, and therefore that visual attention to spatial location is an intrinsically 3D process.

The flickering spotlight of visual attention: Characterizing abnormal object-based attention in schizophrenia

Schizophrenia is associated with deficits in both object perception and visual attention. However, few studies in schizophrenia have investigated object-based attention, which is dissociable from other forms of visuospatial attention. Recent research in healthy populations has shown that the 'spotlight' of sustained visual attention flickers in a rhythmic, oscillatory fashion at specific frequencies in the 4-12 Hz range. In healthy samples, this oscillatory signature has been used to investigate spatiotemporal dynamics of object-based attention, showing that the attentional spotlight spreads to uncued locations within cued objects, and also periodically alternates focus between cued and uncued objects. In this study, we adapted a performance-based visual object cueing task to investigate object-based attention in individuals with a schizophrenia diagnosis and healthy controls. In controls, spatiotemporal patterns of object-based attention closely resembled those reported in previous studies of healthy individuals. In the schizophrenia group, the oscillatory signature of attention also appeared in the location of the cue and on uncued objects, similar to the effects in controls. Indeed, the oscillatory signature of attention at the spatial location of the cue was stronger in the schizophrenia group than in controls. However, attention did not spread across the cued object in schizophrenia; rather, attention appeared to remain hyperfocused at the spatial location of the cue. These findings provide the first evidence that visual attention has oscillatory characteristics in schizophrenia, as in the general population. The results also show that the fundamental process of attentional spreading which underlies object-based attention is abnormal in schizophrenia.

Reversible-figure perception: Why is voluntary control limited?

Observers can voluntarily avoid reversals of an ambiguous, reversible figure, extending the duration of an intended percept. This is usually attributed to high-level, top-down attentional processes. However, voluntary control is limited. Reversals occur despite attempts to avoid them. In two experiments, observers demonstrated significant, but limited, voluntary control over Necker cube perception. Cube size and cube completeness, variables associated with stimulus-driven processes involving neural adaptation, influenced the frequency of reversals regardless of observers' intentions. Results are consistent with the hybrid hypothesis that both top-down and bottom-up processes contribute to Necker-cube perception and support the hypothesis that the contribution of bottom-up processes is responsible for the limitation on voluntary control.

Object-based attention generalizes to multisurface objects

When a part of an object is cued, targets presented in other locations on the same object are detected more rapidly and accurately than are targets on other objects. Often in object-based attention experiments, cues and targets appear not only on the same object but also on the same surface. In four psychophysical experiments, we examined whether the "object" of attentional selection was the entire object or one of its surfaces. In Experiment 1, facilitation effects were found for targets on uncued, adjacent surfaces on the same object, even when the cued and uncued surfaces were oriented differently in depth. This suggests that the "object-based" benefits of attention are not restricted to individual surfaces. Experiments 2a and 2b examined the interaction of perceptual grouping and object-based attention. In both experiments, cuing benefits extended across objects when the surfaces of those objects could be grouped, but the effects were not as strong as in Experiment 1, where the surfaces belonged to the same object. The cuing effect was strengthened in Experiment 3 by connecting the cued and target surfaces with an intermediate surface, making them appear to all belong to the same object. Together, the experiments suggest that the objects of attention do not necessarily map onto discrete physical objects defined by bounded surfaces. Instead, attentional selection can be allocated to perceptual groups of surfaces and objects in the same way as it can to a location or to groups of features that define a single object.

Fixating at far distance shortens reaction time to peripheral visual stimuli at specific locations

The purpose of the present study was to examine whether the fixation distance in real three-dimensional space affects manual reaction time to peripheral visual stimuli. Light-emitting diodes were used for presenting a fixation point and four peripheral visual stimuli. The visual stimuli were located at a distance of 45cm and at 25° in the left, right, upper, and lower directions from the sagittal axis including the fixation point. Near (30cm), Middle (45cm), Far (90cm), and Very Far (300cm) fixation distance conditions were used. When one of the four visual stimuli was randomly illuminated, the participants released a button as quickly as possible. Results showed that overall peripheral reaction time decreased as the fixation distance increased. The significant interaction between fixation distance and stimulus location indicated that the effect of fixation distance on reaction time was observed at the left, right, and upper locations but not at the lower location. These results suggest that fixating at far distance would contribute to faster reaction and that the effect is specific to locations in the peripheral visual field. The present findings are discussed in terms of viewer-centered representation, the focus of attention in depth, and visual field asymmetry related to neurological and psychological aspects.

Orienting of visuo-spatial attention in complex 3D space: Search and detection

The ability to detect changes in the environment is necessary for appropriate interactions with the external world. Changes in the background go more unnoticed than foreground changes, possibly because attention prioritizes processing of foreground/near stimuli. Here, we investigated the detectability of foreground and background changes within natural scenes and the influence of stereoscopic depth cues on this. Using a flicker paradigm, we alternated a pair of images that were exactly same or differed for one single element (i.e., a color change of one object in the scene). The participants were asked to find the change that occurred either in a foreground or background object, while viewing the stimuli either with binocular and monocular cues (bmC) or monocular cues only (mC). The behavioral results showed faster and more accurate detections for foreground changes and overall better performance in bmC than mC conditions. The imaging results highlighted the involvement of fronto‐parietal attention controlling networks during active search and target detection. These attention networks did not show any differential effect as function of the presence/absence of the binocular cues, or the detection of foreground/background changes. By contrast, the lateral occipital cortex showed greater activation for detections in foreground compared to background, while area V3A showed a main effect of bmC vs. mC, specifically during search. These findings indicate that visual search with binocular cues does not impose any specific requirement on attention‐controlling fronto‐parietal networks, while the enhanced detection of front/near objects in the bmC condition reflects bottom‐up sensory processes in visual cortex. Hum Brain Mapp 36:2231–2247, 2015. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.