Parietal cortex mediates perceptual Gestalt grouping independent of stimulus size

Grassi, Palazzo; Zaretskaya, Natalia; Bartels, Andreas

doi:10.1016/j.neuroimage.2016.03.008

Cited by 20 publications

(14 citation statements)

References 91 publications

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“…coherent pattern. This interpretation is consistent with the fMRI results from a recent study that used a similar asymmetric bistable stimulus revealing V5ϩ/MTϩ and parietal involvement during the alternative perception of two segmented surfaces moving inward compared with the default perception of one surface moving downward (Duarte et al, 2017).…”

Section: Plaidsupporting

confidence: 91%

“…The enhancement of activity in the PPC during non-default interpretations is in line with an increasing number of studies that reported the involvement of the PPC in high-level visual tasks like perceptual grouping (Yokoi and Komatsu, 2009;Zaretskaya et al, 2013;Reichert et al, 2014;Grassi et al, 2016;Liu et al, 2017), motion segmentation (Duarte et al, 2017), object processing (Konen and Kastner, 2008), and 3D form extraction from motion (Orban, 2011). The common denominator in all these vision tasks appears to be scene segmentation: what is foreground and background, and which visual components belong to the same entity?…”

Section: Ppc Activationsupporting

confidence: 76%

“…Of the few previous studies examining a role of parietal cortex in scene segmentation, almost all either used visual stimuli that differed physically between conditions (Paradis et al, 2000;S. O. Murray et al, 2003;Yokoi and Komatsu, 2009;Zeki and Stutters, 2013), compared different attentional states and tasks (Fink et al, 1996;Mevorach et al, 2006;Romei et al, 2011), or examined a singular specialized stimulus that did not allow for generalization (Zaretskaya et al, 2013;Grassi et al, 2016;Liu et al, 2017).…”

Section: Significance Statementmentioning

confidence: 99%

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A Generic Mechanism for Perceptual Organization in the Parietal Cortex

2018

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Our visual system's ability to group visual elements into meaningful entities and to separate them from others is referred to as scene segmentation. Visual motion often provides a powerful cue for this process as parallax or coherence can inform the visual system about scene or object structure. Here we tested the hypothesis that scene segmentation by motion cues relies on a common neural substrate in the parietal cortex. We used fMRI and a set of three entirely distinct motion stimuli to examine scene segmentation in the human brain. The stimuli covered a wide range of high-level processes, including perceptual grouping, transparent motion, and depth perception. All stimuli were perceptually bistable such that percepts alternated every few seconds while the physical stimulation remained constant. The perceptual states were asymmetric, in that one reflected the default (nonsegmented) interpretation, and the other the non-default (segmented) interpretation. We confirmed behaviorally that upon stimulus presentation, the default percept was always perceived first, before perceptual alternations ensued. Imaging results showed that across all stimulus classes perceptual scene-segmentation was associated with an increase of activity in the posterior parietal cortex together with a decrease of neural signal in the early visual cortex. This pattern of activation is compatible with predictive coding models of visual perception, and suggests that parietal cortex hosts a generic mechanism for scene segmentation. Making sense of cluttered visual scenes is crucial for everyday perception. An important cue to scene segmentation is visual motion: slight movements of scene elements give away which elements belong to the foreground or background or to the same object. We used three distinct stimuli that engage visual scene segmentation mechanisms based on motion. They involved perceptual grouping, transparent motion, and depth perception. Brain activity associated with all three mechanisms converged in the same parietal region with concurrent deactivation of early visual areas. The results suggest that posterior parietal cortex is a hub involved in structuring visual scenes based on different motion cues, and that feedback modulates early cortical processing in accord with predictive coding theory.

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Section: Plaidsupporting

confidence: 91%

Section: Ppc Activationsupporting

confidence: 76%

Section: Significance Statementmentioning

confidence: 99%

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A Generic Mechanism for Perceptual Organization in the Parietal Cortex

2018

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“…This explanation seems unlikely because an inverse V1-LOC relationship has also been established for non-ambiguous shape-like stimuli vs unstructured displays (Murray et al, 2002). Moreover, at least broadly in line with our results, recent studies (Grassi et al, 2016, 2018) found no evidence for the involvement of the LOC when a dynamic, bistable global-local stimulus constantly triggered shape-based interpretations (i.e., moving disks forming large squares or small circles).…”

Section: Discussionsupporting

confidence: 91%

Topographic Signatures of Global Object Perception in Human Visual Cortex

Stoll

Finlayson

Schwarzkopf

2019

Preprint

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Our visual system readily groups dynamic fragmented input into global objects. How the brain represents such perceptual grouping remains however unclear. To address this question, we recorded brain responses using functional magnetic resonance imaging whilst observers perceived a dynamic bistable stimulus that could either be perceived globally (i.e., as a grouped and coherently moving shape) or locally (i.e., as ungrouped and incoherently moving elements). We further estimated population receptive fields and used these to back-project the brain activity during stimulus perception into visual space via a searchlight procedure. Global perception resulted in non-topographic suppression of responses in lower visual cortex accompanied by wide-spread enhancement in higher object-sensitive cortex. However, follow-up experiments indicated that higher object-sensitive cortex is suppressed if global perception lacks shape grouping, and that grouping-related suppression can be diffusely confined to stimulated sites once stimulus size is reduced. These results speak against a rigid between-area response amplitude code acting as a generic grouping mechanism and point to a within-area response amplitude code mediating the perception of figure and ground.

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“…Although the results of the forced-choice task did not indicate differences between the shape assignment task based on stimulus size, eye movement analysis clearly demonstrates that stimuli that are smaller in size are more likely to be attended as grouped together (i.e., the gaze distribution is more likely to be unimodal and directed to the area between the stimuli). A stronger effect on grouping occurs in the case of a smaller stimulus (i.e., a smaller element seems to be easier to group together with the also smaller main object) which is also in line with the results of the studies of Im et al (2016) and Grassi et al (2016).…”

Section: Discussionsupporting

confidence: 87%

Gaze Parameters in the Analysis of Ambiguous Geometric Shapes

Krauze¹,

Ceple

Šķilters

et al. 2021

i-Perception

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This study explores perceptual organisation and shape perception when viewing a tetragon and an additional element (a dot) that is located at varying positions and distances next to the tetragon. The aim of the study is to determine the factors that can alter the interpretation of object configuration and impact whether the presented tetragon is perceived as a diamond or a square. Methods used in this study are a forced-choice task as a subjective measurement and eye tracking as an objective measurement of perceptual processes. Overall, 31 stimuli were presented to the participants: a tetragon in two different sizes with an additional element (a dot) located inside or outside the object at three different positions at three distances. The results indicate significant changes in shape perception, depending on the location of the additional element. The results are complemented with eye movement analysis indicating that as the distance between the elements increases, there is a higher probability of either of the two shape interpretations and the gaze is less likely to be directed to the area between the stimuli. Furthermore, the subjective perception of shape is codetermined by the shape perception when the tetragon is presented without the additional element.

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Parietal cortex mediates perceptual Gestalt grouping independent of stimulus size

Cited by 20 publications

References 91 publications

A Generic Mechanism for Perceptual Organization in the Parietal Cortex

A Generic Mechanism for Perceptual Organization in the Parietal Cortex

Topographic Signatures of Global Object Perception in Human Visual Cortex

Gaze Parameters in the Analysis of Ambiguous Geometric Shapes

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