Spiking Dynamics during Perceptual Grouping in the Laminar Circuits of Visual Cortex

Grouping of collinear boundary contours is a fundamental process during visual perception. Illusory contour completion vividly illustrates how stable perceptual boundaries interpolate between pairs of contour inducers, but do not extrapolate from a single inducer. Neural models have simulated how perceptual grouping occurs in laminar visual cortical circuits. These models predicted the existence of grouping cells that obey a bipole property whereby grouping can occur inwardly between pairs or greater numbers of similarly oriented and co-axial inducers, but not outwardly from individual inducers. These models have not, however, incorporated spiking dynamics. Perceptual grouping is a challenge for spiking cells because its properties of collinear facilitation and analog sensitivity to inducer configurations occur despite irregularities in spike timing across all the interacting cells. Other models have demonstrated spiking dynamics in laminar neocortical circuits, but not how perceptual grouping occurs. The current model begins to unify these two modeling streams by implementing a laminar cortical network of spiking cells whose intracellular temporal dynamics interact with recurrent intercellular spiking interactions to quantitatively simulate data from neurophysiological experiments about perceptual grouping, the structure of non-classical visual receptive fields, and gamma oscillations.

Texture Segregation By Visual Cortex: Perceptual Grouping, Attention, and Learning

A neural model is proposed of how laminar interactions in the visual cortex may learn and recognize object texture and form boundaries. The model brings together five interacting processes: region-based texture classification, contour-based boundary grouping, surface filling-in, spatial attention, and object attention. The model shows how form boundaries can determine regions in which surface filling-in occurs; how surface filling-in interacts with spatial attention to generate a form-fitting distribution of spatial attention, or attentional shroud; how the strongest shroud can inhibit weaker shrouds; and how the winning shroud regulates learning of texture categories, and thus the allocation of object attention. The model can discriminate abutted textures with blurred boundaries and is sensitive to texture boundary attributes like discontinuities in orientation and texture flow curvature as well as to relative orientations of texture elements. The model quantitatively fits a large set of human psychophysical data on orientation-based textures. Object boundar output of the model is compared to computer vision algorithms using a set of human segmented photographic images. The model classifies textures and suppresses noise using a multiple scale oriented filterbank and a distributed Adaptive Resonance Theory (dART) classifier. The matched signal between the bottom-up texture inputs and top-down learned texture categories is utilized by oriented competitive and cooperative grouping processes to generate texture boundaries that control surface filling-in and spatial attention. Topdown modulatory attentional feedback from boundary and surface representations to early filtering stages results in enhanced texture boundaries and more efficient learning of texture within attended surface regions. Surface-based attention also provides a self-supervising training signal for learning new textures. Importance of the surface-based attentional feedback in texture learning and classification is tested using a set of textured images from the Brodatz micro-texture album. Benchmark studies vary from 95.1% to 98.6% with attention, and from 90.6% to 93.2% without attention.

Perceptual grouping and distance estimates in typical and atypical development: comparing performance across perception, drawing and construction tasks

Perceptual grouping is a pre-attentive process which serves to group local elements into global wholes, based on shared properties. One effect of perceptual grouping is to distort the ability to estimate the distance between two elements. In this study, biases in distance estimates, caused by four types of perceptual grouping, were measured across three tasks, a perception, a drawing and a construction task in both typical development (TD: Experiment 1) and in individuals with Williams syndrome (WS: Experiment 2). In Experiment 1, perceptual grouping distorted distance estimates across all three tasks. Interestingly, the effect of grouping by luminance was in the opposite direction to the effects of the remaining grouping types. We relate this to differences in the ability to inhibit perceptual grouping effects on distance estimates. Additive distorting influences were also observed in the drawing and the construction task, which are explained in terms of the points of reference employed in each task. Experiment 2 demonstrated that the above distortion effects are also observed in WS. Given the known deficit in the ability to use perceptual grouping in WS, this suggests a dissociation between the pre-attentive influence of and the attentive deployment of perceptual grouping in WS. The typical distortion in relation to drawing and construction points towards the presence of some typical location coding strategies in WS. The performance of the WS group differed from the TD participants on two counts. First, the pattern of overall distance estimates (averaged across interior and exterior distances) across the four perceptual grouping types, differed between groups. Second, the distorting influence of perceptual grouping was strongest for grouping by shape similarity in WS, which contrasts to a strength in grouping by proximity observed in the TD participants. (c) 2008 Elsevier Inc. All rights reserved.

A longitudinal study of perceptual grouping by proximity, luminance and shape in infants at two, four and six months

Grouping by luminance and shape similarity has previously been demonstrated in neonates and at 4 months, respectively. By contrast, grouping by proximity has hitherto not been investigated in infancy. This is also the first study to chart the developmental emergence of perceptual grouping longitudinally. Sixty-one infants were presented with a matrix of local stimuli grouped horizontally or vertically by luminance, shape or proximity at 2, 4, and 6 months. Infants were exposed to each set of stimuli for three presentation durations. Grouping was demonstrated for luminance similarity at the earliest testing age, 2 months, by shape similarity at 4 months, but was not observed for grouping by proximity. Grouping by shape similarity showed a distinctive pattern of grouping ability across exposure durations, which reflected familiarity preferences followed by novelty preferences. This remained stable across age. No link was found between the emergence of perceptual grouping ability and the exposure duration required to elicit grouping. We conclude by stressing the importance of longitudinal studies of infant development in furthering our understanding of human cognition, rather than relying on assumptions from the adult endstate.

The development of perceptual grouping in infants with Williams syndrome

Perceptual grouping by luminance similarity and by proximity was investigated in infants with Williams syndrome (WS) aged between 6 and 36 months (visit 1, N=29). WS infants who were still under 36 months old, 8 months later, repeated the testing procedure (visit 2, N=15). Performance was compared to typically developing (TD) infants aged from 2 to 20 months (N=63). Consistent with the literature, TD participants showed grouping by luminance at the youngest testing age, 2 months. Grouping by proximity had not previous been charted in typical development: this study showed grouping by proximity at 8 months. Infants with WS could group by luminance. Developmental progression of the WS group showed some similarities to typical development, although further investigation is required to further address this in more depth. In contrast, infants with WS were not able to group by proximity. This pattern of emergence and development of grouping abilities is considered in relation to the pattern of grouping abilities observed in adults with WS.

Perceptual grouping ability in Williams syndrome: evidence for deviant patterns of performance

Williams syndrome (WS) is a rare genetic disorder. At a cognitive level, this population display poor visuo-spatial cognition when compared to verbal ability. Within the visuo-spatial domain, it is now accepted that individuals with WS are able to perceive both local and global aspects of an image, albeit at a low level. The present study examines the manner in which local elements are grouped into a global whole in WS. Fifteen individuals with WS and 15 typically developing controls, matched for non-verbal ability, were presented with a matrix of local elements and asked whether these elements were perceptually grouped horizontally or vertically. The WS group was at the same level as the control group when grouping by luminance, closure, and alignment. However, their ability to group by shape, orientation and proximity was significantly poorer than controls. This unusual profile of grouping abilities in WS suggests that these individuals do not form a global percept in a typical manner. (c) 2004 Published by Elsevier Ltd.

Contour integration and principles of perceptual grouping

Ziel der Arbeit ist die Analyse von Prinzipien der Konturintegration im menschlichen visuellen System. Die perzeptuelle Verbindung benachbarter Teile in einer visuellen Szene zu einem Ganzen wird durch zwei gestalttheoretisch begründete Propositionen gekennzeichnet, die komplementäre lokale Mechanismen der Konturintegration beschreiben. Das erste Prinzip der Konturintegration fordert, dass lokale Ähnlichkeit von Elementen in einem anderen Merkmal als Orientierung nicht hinreicht für die Entdeckung von Konturen, sondern ein zusätzlicher statistischer Merkmalsunterschied von Konturelementen und Umgebung vorliegen muss, um Konturentdeckung zu ermöglichen. Das zweite Prinzip der Konturintegration behauptet, dass eine kollineare Ausrichtung von Konturelementen für Konturintegration hinreicht, und es bei deren Vorliegen zu robuster Konturintegrationsleistung kommt, auch wenn die lokalen merkmalstragenden Elemente in anderen Merkmalen in hohem Maße zufällig variieren und damit keine nachbarschaftliche Ähnlichkeitsbeziehung entlang der Kontur aufweisen. Als empirische Grundlage für die beiden vorgeschlagenen Prinzipien der Konturintegration werden drei Experimente berichtet, die zunächst die untergeordnete Rolle globaler Konturmerkmale wie Geschlossenheit bei der Konturentdeckung aufweisen und daraufhin die Bedeutung lokaler Mechanismen für die Konturintegration anhand der Merkmale Kollinearität, Ortsfrequenz sowie der spezifischen Art der Interaktion zwischen beiden Merkmalen beleuchten. Im ersten Experiment wird das globale Merkmal der Geschlossenheit untersucht und gezeigt, dass geschlossene Konturen nicht effektiver entdeckt werden als offene Konturen. Das zweite Experiment zeigt die Robustheit von über Kollinearität definierten Konturen über die zufällige Variation im Merkmal Ortsfrequenz entlang der Kontur und im Hintergrund, sowie die Unmöglichkeit der Konturintegration bei nachbarschaftlicher Ähnlichkeit der Konturelemente, wenn Ähnlichkeit statt über kollineare Orientierung über gleiche Ortsfrequenzen realisiert ist. Im dritten Experiment wird gezeigt, dass eine redundante Kombination von kollinearer Orientierung mit einem statistischen Unterschied im Merkmal Ortsfrequenz zu erheblichen Sichtbarkeitsgewinnen bei der Konturentdeckung führt. Aufgrund der Stärke der Summationswirkung wird vorgeschlagen, dass durch die Kombination mehrerer Hinweisreize neue kortikale Mechanismen angesprochen werden, die die Konturentdeckung unterstützen. Die Resultate der drei Experimente werden in den Kontext aktueller Forschung zur Objektwahrnehmung gestellt und ihre Bedeutung für die postulierten allgemeinen Prinzipien visueller Gruppierung in der Konturintegration diskutiert. Anhand phänomenologischer Beispiele mit anderen Merkmalen als Orientierung und Ortsfrequenz wird gezeigt, dass die gefundenen Prinzipien Generalisierbarkeit für die Verarbeitung von Konturen im visuellen System beanspruchen können.

Diffusion maps in the Subriemannian motion group and perceptual grouping

Il presente lavoro è motivato dal problema della constituzione di unità percettive a livello della corteccia visiva primaria V1. Si studia dettagliatamente il modello geometrico di Citti-Sarti con particolare attenzione alla modellazione di fenomeni di associazione visiva. Viene studiato nel dettaglio un modello di connettività. Il contributo originale risiede nell'adattamento del metodo delle diffusion maps, recentemente introdotto da Coifman e Lafon, alla geometria subriemanniana della corteccia visiva. Vengono utilizzati strumenti di teoria del potenziale, teoria spettrale, analisi armonica in gruppi di Lie per l'approssimazione delle autofunzioni dell'operatore del calore sul gruppo dei moti rigidi del piano. Le autofunzioni sono utilizzate per l'estrazione di unità percettive nello stimolo visivo. Sono presentate prove sperimentali e originali delle capacità performanti del metodo.

A spatial explanation for synchrony biases in perceptual grouping: Consequences for the temporal-binding hypothesis

If two images are shown in rapid sequential order, they are perceived as a single, fused image. Despite this, recent studies have revealed that fundamental perceptual processes are influenced by extremely brief temporal offsets in stimulus presentation. Some researchers have suggested that this is due to the action of a cortical temporal-binding mechanism, which would serve to keep multiple mental representations of one object distinct from those of other objects. There is now gathering evidence that these studies should be reassessed. This article describes evidence for sensitivity to fixational eye and head movements, which provides a purely spatial explanation for the earlier results. Taken in conjunction with other studies, the work serves to undermine the current body of behavioral evidence for a temporal-binding mechanism.

Axis-alignment affects perceptual grouping: evidence from simultanagnosia

We examined the effect of grouping by the alignment of implicit axes on the perception of multiple shapes, using a patient (GK) who shows simultanagnosia as part of Blint's syndrome. Five experiments demonstrated that: (1) GK was better able to judge the orientation of a global configuration if the constituent local shapes were aligned with their major axes than if they were aligned with their edges; (2) this axis information was used implicitly, since GK was unable to discriminate between configurations of axis-aligned and edge-aligned shapes; (3) GK's sensitivity to axis-alignment persisted even when the orientations of local shapes were kept constant, indicating some form of cooperative effect between the local elements; (4) axis-alignment of shapes also facilitated his ability to discriminate single-item from multi-item configurations; (5) the effect of axis-alignment could be attributed, at least partially, to the degree to which there was matching between the orientations of local shapes and the global configuration. Taken together, the results suggest that axis-based grouping can support the selection of multiple objects.