Mixture model investigation of the inner-outer asymmetry in visual crowding reveals a heavier weight towards the visual periphery.
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ABSTRACT:
SUBMITTER: Shechter A
PROVIDER: S-EPMC7822962 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:In peripheral vision, objects in clutter are difficult to identify. The exact cause of this "crowding" effect is unclear. To perceive coherent shapes in clutter, the visual system must integrate certain local features across receptive fields while preventing others from being combined. It is believed that this selective feature integration-segmentation process is impaired in peripheral vision, leading to crowding. We used functional magnetic resonance imaging (fMRI) to investigate the neural origin of crowding. We found that crowding was associated with suppressed fMRI signal as early as V1, regardless of whether attention was directed toward or away from a target stimulus. This suppression in early visual cortex was greatest for stimuli that produced the strongest crowding. In contrast, the pattern of activity was mixed in higher level visual areas, such as the lateral occipital cortex. These results support the view that the deficiency in feature integration and segmentation in peripheral vision is present at the earliest stages of cortical processing.
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Project description:In peripheral vision, objects that are easily discriminated on their own become less discriminable in the presence of surrounding clutter. This phenomenon is known as crowding.The neural mechanisms underlying crowding are not well understood. Better insight might come from single-neuron recording in nonhuman primates, provided they exhibit crowding; however, previous demonstrations of crowding have been confined to humans. In the present study, we set out to determine whether crowding occurs in rhesus macaque monkeys. We found that animals trained to identify a target letter among flankers displayed three hallmarks of crowding as established in humans. First, at a given eccentricity, increasing the spacing between the target and the flankers improved recognition accuracy. Second, the critical spacing, defined as the minimal spacing at which target discrimination was reliable, was proportional to eccentricity. Third, the critical spacing was largely unaffected by object size. We conclude that monkeys, like humans, experience crowding. These findings open the door to studies of crowding at the neuronal level in the monkey visual system.
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Project description:Crowding by nearby features causes identification failures in the peripheral visual field. However, prominent visual features can sometimes fail to reach awareness, causing scenes to be incorrectly interpreted. Here we examine whether awareness of the flanking features is necessary for crowding to occur. Flankers that were physically present were rendered perceptually absent with adaptation-induced blindness. In a letter identification task, targets were presented unflanked or with up to four flanker letters. On each trial, observers reported both the number of letters they perceived and the identity of a target letter. This paradigm allowed trial-by-trial assessment of awareness and crowding and ensured that both targets and flankers were attended. Target-letter identification performance was correlated with the number of flanking letters that were perceived on a given trial, regardless of the number that were physically present. Our data demonstrate that crowding can be released when flanking elements at attended locations are suppressed from visual awareness.
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Project description:Visual crowding, the phenomenon in which the ability to distinguish objects is hindered in cluttered environments, has critical implications for various ophthalmic and neurological disorders. Traditional methods for assessing crowding involve time-consuming and attention-demanding psychophysical tasks, making routine examination challenging. This study sought to compare trial-based Alternative Forced-Choice (AFC) paradigms using either manual or eye movement responses and a continuous serial search paradigm employing eye movement responses to evaluate their efficiency in rapidly assessing peripheral crowding. In all paradigms, we manipulated the orientation of a central Gabor patch, which could be presented alone or surrounded by six Gabor patches. We measured participants' target orientation discrimination thresholds using adaptive psychophysics to assess crowding magnitude. Depending on the paradigm, participants either made saccadic eye movements to the target location or responded manually by pressing a key or moving a mouse. We compared these paradigms in terms of crowding magnitude, assessment time, and paradigm demand. Our results indicate that employing eye movement-based paradigms for assessing peripheral visual crowding yields results faster compared to paradigms that necessitate manual responses. Furthermore, when considering similar levels of confidence in the threshold measurements, both a novel serial search paradigm and an eye movement-based 6AFC paradigm proved to be the most efficient in assessing crowding magnitude. Additionally, crowding estimates obtained through either the continuous serial search or the 6AFC paradigms were consistently higher than those obtained using the 2AFC paradigms. Lastly, participants did not report a clear difference between paradigms in terms of their perceived demand. In conclusion, both the continuous serial search and the 6AFC eye movement response paradigms enable a fast assessment of visual crowding. These approaches may potentially facilitate future routine crowding assessment. However, the usability of these paradigms in specific patient populations and specific purposes should be assessed.
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Project description:Processing of shape information in human peripheral visual fields is impeded beyond what can be expected by poor spatial resolution. Visual crowding, the inability to identify objects in clutter, has been shown to be the primary factor limiting shape perception in peripheral vision. Despite the well-documented effects of crowding, its underlying causes remain poorly understood. Given that spatial attention both facilitates learning of image statistics and directs saccadic eye movements, we propose that the acquisition of image statistics in peripheral visual fields is confounded by eye-movement artifacts. Specifically, the image statistics acquired under a peripherally deployed spotlight of attention are systematically biased by saccade-induced image displacements. These erroneously represented image statistics lead to inappropriate contextual interactions in the periphery and cause crowding.
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