Crowding, grouping, and object recognition: A matter of appearance.
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ABSTRACT:
SUBMITTER: Herzog MH
PROVIDER: S-EPMC4429926 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Crowding is the impairment of peripheral target perception by nearby flankers. A number of recent studies have shown that crowding shares many features with grouping. Here, we investigate whether effects of crowding and grouping on target perception are related by asking whether they operate over the same spatial scale. A target letter T had two sets of flanking Ts of varying orientations. The first set was presented close to the target, yielding strong crowding. The second set was either close enough to cause crowding on their own or too far to cause crowding on their own. The Ts of the second set had the same orientation that either matched the target's orientation (Grouped condition) or not (Ungrouped condition). In Experiment 1, the Grouped flankers reduced crowding independently of their distance from the target, suggesting that grouping operated over larger distances than crowding. In Experiments 2 and 3 we found that grouping did not affect sensitivity but produced a strong bias to report that the grouped orientation was present at the target location whether or not it was. Finally, we investigated whether this bias was a response or perceptual bias, rejecting the former in favor of a perceptual grouping explanation. We suggest that the effect of grouping is to assimilate the target to the identity of surrounding flankers when they are all the same, and that this shape assimilation effect differs in its spatial scale from the integration effect of crowding.
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Project description:Crowding is the breakdown in object recognition that occurs in cluttered visual environments and the fundamental limit on peripheral vision, affecting identification within many visual modalities and across large spatial regions. Though frequently characterized as a disruptive process through which object representations are suppressed or lost altogether, we demonstrate that crowding systematically changes the appearance of objects. In particular, target patches of visual noise that are surrounded ("crowded") by oriented Gabor flankers become perceptually oriented, matching the flankers. This was established with a change-detection paradigm: under crowded conditions, target changes from noise to Gabor went unnoticed when the Gabor orientation matched the flankers (and the illusory target percept), despite being easily detected when they differed. Rotation of the flankers (leaving target noise unaltered) also induced illusory target rotations. Blank targets led to similar results, demonstrating that crowding can induce apparent structure where none exists. Finally, adaptation to these stimuli induced a tilt aftereffect at the target location, consistent with signals from the flankers "spreading" across space. These results confirm predictions from change-based models of crowding, such as averaging, and establish crowding as a regularization process that simplifies the peripheral field by promoting consistent appearance among adjacent objects.
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Project description:Contour interpolation automatically binds targets with distractors to impair multiple object tracking (Keane, Mettler, Tsoi, & Kellman, 2011). Is interpolation special in this regard or can other features produce the same effect? To address this question, we examined the influence of eight features on tracking: color, contrast polarity, orientation, size, shape, depth, interpolation, and a combination (shape, color, size). In each case, subjects tracked 4 of 8 objects that began as undifferentiated shapes, changed features as motion began (to enable grouping), and returned to their undifferentiated states before halting. We found that intertarget grouping improved performance for all feature types except orientation and interpolation (Experiment 1 and Experiment 2). Most importantly, target-distractor grouping impaired performance for color, size, shape, combination, and interpolation. The impairments were, at times, large (>15% decrement in accuracy) and occurred relative to a homogeneous condition in which all objects had the same features at each moment of a trial (Experiment 2), and relative to a "diversity" condition in which targets and distractors had different features at each moment (Experiment 3). We conclude that feature-based grouping occurs for a variety of features besides interpolation, even when irrelevant to task instructions and contrary to the task demands, suggesting that interpolation is not unique in promoting automatic grouping in tracking tasks. Our results also imply that various kinds of features are encoded automatically and in parallel during tracking.
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Project description:Crowding, the phenomenon of impeded object identification due to clutter, is believed to be a key limiting factor of form vision in the peripheral visual field. The present study provides a characterization of object crowding in age-related macular degeneration (AMD) measured at the participants' respective preferred retinal loci with binocular viewing. Crowding was also measured in young and age-matched controls at the same retinal locations, using a fixation-contingent display paradigm to allow unlimited stimulus duration. With objects, the critical spacing of crowding for AMD participants was not substantially different from controls. However, baseline contrast energy thresholds in the noncrowded condition were four times that of the controls. Crowding further exacerbated deficits in contrast sensitivity to three times the normal crowding-induced contrast energy threshold elevation. These findings indicate that contrast-sensitivity deficit is a major limiting factor of object recognition for individuals with AMD, in addition to crowding. Focusing on this more tractable deficit of AMD may lead to more effective remediation and technological assistance.
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Project description:Object recognition in the peripheral visual field is limited by crowding: the disruptive influence of nearby clutter. Despite its severity, little is known about the cortical locus of crowding. Here, we examined the neural correlates of crowding by combining event-related fMRI adaptation with a change-detection paradigm. Crowding can change the appearance of objects, such that items become perceptually matched to surrounding objects; we used this change in appearance as a signature of crowding and measured brain activity that correlated with the crowded percept. Observers adapted to a peripheral patch of noise surrounded by four Gabor flankers. When crowded, the noise appears oriented and perceptually indistinguishable from the flankers. Consequently, substitution of the noise for a Gabor identical to the flankers ("change-same") is rarely detected, whereas substitution for an orthogonal Gabor ("change-different") is rarely missed. We predicted that brain areas representing the crowded percept would show repetition suppression in change-same trials but release from adaptation in change-different trials. This predicted pattern was observed throughout cortical visual areas V1-V4, increasing in strength from early to late visual areas. These results depict crowding as a multistage process, involving even the earliest cortical visual areas, with perceptual consequences that are increasingly influenced by later visual areas.
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