Visual crowding is a combination of an increase of positional uncertainty, source confusion, and featural averaging

Harrison, William J.; Bex, Peter J.

doi:10.1038/srep45551

Cited by 20 publications

(20 citation statements)

References 66 publications

(102 reference statements)

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“…Such perceptual interference would degrade the encoding of memoranda due to their persistent overlapping cortical representations. Indeed, the nature of errors in these previous studies of working memory are consistent with those in visual crowding paradigms with minimal working memory demands ( Ester et al, 2014 ; Harrison and Bex, 2015 , 2017 ). The combination of target duration and interstimulus interval used by Pertzov et al (2014) (500 ms) thus sets a lower bound on the time required to transform a sensory signal into a memory representation.…”

Section: Discussionsupporting

confidence: 77%

“…This model is also consistent with the results of Tamber-Rosenau et al (2015) , who found that the frequency of swap errors for simultaneously presented memoranda depends on the degree of perceptual crowding. Because visual crowding increases positional uncertainty ( Harrison and Bex, 2017 ), a conjunctive code that binds spatial location with orientation will produce more swap errors under strongly crowded conditions than weakly crowded conditions, as was observed by Tamber-Rosenau et al (2015) . The Schneegans and Bays' (2017) model therefore suggests an important role of location in binding nonspatial features when items are presented simultaneously, but leaves open the question of how to account for the present findings with sequentially presented memoranda.…”

Section: Discussionmentioning

confidence: 92%

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Visual Working Memory Is Independent of the Cortical Spacing Between Memoranda

Harrison

Bays

2018

J. Neurosci.

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The sensory recruitment hypothesis states that visual short-term memory is maintained in the same visual cortical areas that initially encode a stimulus' features. Although it is well established that the distance between features in visual cortex determines their visibility, a limitation known as crowding, it is unknown whether short-term memory is similarly constrained by the cortical spacing of memory items. Here, we investigated whether the cortical spacing between sequentially presented memoranda affects the fidelity of memory in humans (of both sexes). In a first experiment, we varied cortical spacing by taking advantage of the log-scaling of visual cortex with eccentricity, presenting memoranda in peripheral vision sequentially along either the radial or tangential visual axis with respect to the fovea. In a second experiment, we presented memoranda sequentially either within or beyond the critical spacing of visual crowding, a distance within which visual features cannot be perceptually distinguished due to their nearby cortical representations. In both experiments and across multiple measures, we found strong evidence that the ability to maintain visual features in memory is unaffected by cortical spacing. These results indicate that the neural architecture underpinning working memory has properties inconsistent with the known behavior of sensory neurons in visual cortex. Instead, the dissociation between perceptual and memory representations supports a role of higher cortical areas such as posterior parietal or prefrontal regions or may involve an as yet unspecified mechanism in visual cortex in which stimulus features are bound to their temporal order.SIGNIFICANCE STATEMENT Although much is known about the resolution with which we can remember visual objects, the cortical representation of items held in short-term memory remains contentious. A popular hypothesis suggests that memory of visual features is maintained via the recruitment of the same neural architecture in sensory cortex that encodes stimuli. We investigated this claim by manipulating the spacing in visual cortex between sequentially presented memoranda such that some items shared cortical representations more than others while preventing perceptual interference between stimuli. We found clear evidence that short-term memory is independent of the intracortical spacing of memoranda, revealing a dissociation between perceptual and memory representations. Our data indicate that working memory relies on different neural mechanisms from sensory perception.

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Section: Discussionsupporting

confidence: 77%

Section: Discussionmentioning

confidence: 92%

Visual Working Memory Is Independent of the Cortical Spacing Between Memoranda

Harrison

Bays

2018

J. Neurosci.

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“…In particular, bar flankers produce less pronounced reductions in task accuracy than letter flankers, perhaps because bars are dissimilar to letters (Song, Levi, & Pelli, 2014). Furthermore, bar flankers may reduce positional uncertainty by cuing the position of the flanked target, an effect that does not occur for flanking letters (Harrison & Bex, 2017), which represent viable alternative responses. Reduced positional uncertainty induced by bar flankers may have counteracted any effect of fixational eye movements on the recognition of flanked stimuli because fixational eye movements are likely to increase positional uncertainty.…”

Section: Discussionmentioning

confidence: 99%

“…For example, Falkenberg, Rubin & Bex (2007) reported that crowding was unaffected by different levels of simulated fixation instability in normal peripheral vision, and Greenwood, Szinte, Sayim, & Cavanagh (2017) found no association between the magnitude of crowding and saccadic precision in peripheral vision. Moreover, there are models that consider positional uncertainty or confusion between target and flankers (Strasburger & Malania, 2013) or a combination of both uncertainty and confusion (Harrison & Bex, 2017) to explain the effect of crowding. The lack of an association between reduced fixation stability and crowding suggests that fixational eye movements are not a source of positional uncertainty in observers with normal vision.…”

Section: Discussionmentioning

confidence: 99%

Reduced fixation stability induced by peripheral viewing does not contribute to crowding

2020

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Attending to peripheral visual targets while maintaining central fixation, a process that involves covert attention, reduces fixation stability. Here, we tested the hypothesis that changes in fixation stability induced by peripheral viewing contribute to crowding in peripheral vision by increasing positional uncertainty. We first assessed whether fixation was less stable during peripheral versus central (foveal) viewing for both crowded and uncrowded stimuli. We then tested whether fixation stability during peripheral viewing was associated with the extent of crowding. Fourteen participants performed a tumbling E orientation discrimination task at three different eccentricities (0°, 5°, 10°). The target was presented with or without flankers. Fixational eye movements were measured using an infrared video-based eyetracker. A central fixation cross was provided for the two peripheral viewing conditions, and optotype size was scaled for each eccentricity. Discrimination of appropriately scaled uncrowded stimuli was unaffected by eccentricity, whereas discrimination of crowded stimuli deteriorated dramatically with eccentricity, despite scaling. Both crowded and uncrowded peripheral stimuli were associated with reduced fixation stability, increased microsaccadic amplitude, and a greater proportion of horizontal microsaccades relative to centrally presented stimuli. However, these effects were not associated with the magnitude of crowding. This suggests that reduced fixation stability due to peripheral viewing does not contribute to crowding in peripheral vision.

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“…A prominent hypothesis suggests that it is a limitation of bottom-up processes involved in feature integration (e.g. Greenwood et al (2009), Harrison and Bex (2017), Parkes et al (2001), and Pelli et al (2004)). According to this account, when an object is presented in isolation or far from other objects, its features are detected and appropriately combined to produce a recognisable object representation.…”

Section: Introductionmentioning

confidence: 99%

Response selection modulates crowding: a cautionary tale for invoking top-down explanations

Reuther

Chakravarthi

2019

Atten Percept Psychophys

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Object recognition in the periphery is limited by clutter. This phenomenon of visual crowding is ameliorated when the objects are dissimilar. This effect of inter-object similarity has been extensively studied for low-level features and is thought to reflect bottom-up processes. Recently, crowding was also found to be reduced when objects belonged to explicitly distinct groups; that is, crowding was weak when they had low group membership similarity. It has been claimed that top-down knowledge is necessary to explain this effect of group membership, implying that the effect of similarity on crowding cannot be a purely bottom-up process. We tested the claim that the effect of group membership relies on knowledge in two experiments and found that neither explicit knowledge about differences in group membership nor the possibility of acquiring knowledge about target identities is necessary to produce the effects. These results suggest that top-down processes need not be invoked to explain the effect of group membership. Instead, we suggest that differences in flanker reportability that emerge from the differences in group membership are the source of the effect. That is, when targets and flankers are sampled from distinct groups, flankers cannot be inadvertently reported, leading to fewer errors and hence weaker crowding. Further, we argue that this effect arises at the stage of response selection. This conclusion is well supported by an analytical model based on these principles. We conclude that previously observed effects in crowding attributed to top-down or higher level processes might instead be due to post-perceptual response selection strategies.

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Visual crowding is a combination of an increase of positional uncertainty, source confusion, and featural averaging

Cited by 20 publications

References 66 publications

Visual Working Memory Is Independent of the Cortical Spacing Between Memoranda

Visual Working Memory Is Independent of the Cortical Spacing Between Memoranda

Reduced fixation stability induced by peripheral viewing does not contribute to crowding

Response selection modulates crowding: a cautionary tale for invoking top-down explanations

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