Border Ownership Research Articles

Face profiles versus non-face shapes: Does meaning influence border ownership assignment in the visual cortex?

Face profiles versus non-face shapes: Does meaning influence border ownership assignment in the visual cortex?

The emergent property of border-ownership and the perception of illusory surfaces in a dynamic hierarchical system

We argued that borderline completion does not explain the completion, that the computation of border-ownership (BOWN) causes illusory signals, and that neurons activated at illusory contours represent BOWN. Although most commentaries show support to our view, they further emphasized the importance of feedback and also pointed out some examples challenging our view. The signal processing in the hierarchy and the classification of neurons are also discussed. In this reply, we explain our position on a dynamic feedback system reflecting the global configuration, and clarify our view on completion, by examining the example figures and neurophysiological data indicated in the commentaries.

Remapping of border ownership in the visual cortex.

We see objects as having continuity although the retinal image changes frequently. How such continuity is achieved is hard to understand, because neurons in the visual cortex have small receptive fields that are fixed on the retina, which means that a different set of neurons is activated every time the eyes move. Neurons in areas V1 and V2 of the visual cortex signal the local features that are currently in their receptive fields and do not show "remapping" when the image moves. However, subsets of neurons in these areas also carry information about global aspects, such as figure-ground organization. Here we performed experiments to find out whether figure-ground organization is remapped. We recorded single neurons in macaque V1 and V2 in which figure-ground organization is represented by assignment of contours to regions (border ownership). We found previously that border-ownership signals persist when a figure edge is switched to an ambiguous edge by removing the context. We now used this paradigm to see whether border ownership transfers when the ambiguous edge is moved across the retina. In the new position, the edge activated a different set of neurons at a different location in cortex. We found that border ownership was transferred to the newly activated neurons. The transfer occurred whether the edge was moved by a saccade or by moving the visual display. Thus, although the contours are coded in retinal coordinates, their assignment to objects is maintained across movements of the retinal image.

Early Visual Cortex Assigns Border Ownership in Natural Scenes According to Image Context

Early Visual Cortex Assigns Border Ownership in Natural Scenes According to Image Context

Memory effects in bi-stable depth-order perception: adaptation and beyond

Kanizsa, G. (1979). Organization in Vision: Essays on Gestalt Perception. New York: Praeger. Kogo, N., Strecha, C., Van Gool, L., & Wagemans, J. (2010). Surface construction by a 2-D differentiation-integration process: A neurocomputational model for perceived border ownership, depth, and lightness in Kanizsa figures. Psychological Review., 117(2), 406–439. Kogo, Naoki, Galli, A., & Wagemans, J. (2011). Switching dynamics of border ownership: A stochastic model for bi-stable perception. Vision Research, 51(18), 2085–2098. Leopold, D. A., Wilke, M., Maier, A., & Logothetis, N. K. (2002). Stable perception of visually ambiguous patterns. Nature Neuroscience, 5(6), 605– 609. van Ee, R. (2009). Stochastic variations in sensory awareness are driven by noisy neuronal adaptation: evidence from serial correlations in perceptual bistability. Journal of the Optical Society of America. A, Optics, image science, and vision, 26(12), 2612–2622. Summary

Perception of Border Ownership by Multiple Gestalt Factors

Gestalt factors such as convexity, closure, and size promote the perception of the direction of figure. Although recent studies have investigated the effects of the individual factors, it has not been clarified how these factors interact with each other, when the features coexist in a local contour. In the present study, we examined psychophysically the interaction of convexity and closure that coexist in a local contour of natural image. First, we established the quantification of convexity and closure (indices to represent the factors) for contours of natural images. By using these quantities, we selected a set of local contours that includes a uniform and wide variation of convexity and closure. Second, we performed a psychophysical experiment to measure the apparent direction of figure for the set of local contours. The result showed that the perceived direction of figure tends to agree with the direction of closure when both convexity and closure coexist in a local contour. The result also showed that while the direction of closure dominates the perception of the direction of figure, the index of closure does not correlate linearly with the perceptual judgment. These results suggest that the perceptual judgment of the direction of figure depends mostly on closure when it coexists with convexity, and that the dependence is dichotomic; two contours with different degrees of closure do not evoke distinct perception. Closure appears to be a dominant and strong cue for the direction of figure.

Two critical periods in early visual cortex during figure-ground segregation.

The ability to distinguish a figure from its background is crucial for visual perception. To date, it remains unresolved where and how in the visual system different stages of figure–ground segregation emerge. Neural correlates of figure border detection have consistently been found in early visual cortex (V1/V2). However, areas V1/V2 have also been frequently associated with later stages of figure–ground segregation (such as border ownership or surface segregation). To causally link activity in early visual cortex to different stages of figure–ground segregation, we briefly disrupted activity in areas V1/V2 at various moments in time using transcranial magnetic stimulation (TMS). Prior to stimulation we presented stimuli that made it possible to differentiate between figure border detection and surface segregation. We concurrently recorded electroencephalographic (EEG) signals to examine how neural correlates of figure–ground segregation were affected by TMS. Results show that disruption of V1/V2 in an early time window (96–119 msec) affected detection of figure stimuli and affected neural correlates of figure border detection, border ownership, and surface segregation. TMS applied in a relatively late time window (236–259 msec) selectively deteriorated performance associated with surface segregation. We conclude that areas V1/V2 are not only essential in an early stage of figure–ground segregation when figure borders are detected, but subsequently causally contribute to more sophisticated stages of figure–ground segregation such as surface segregation.

Local field potentials and border ownership: A conjecture about computation in visual cortex

Border ownership is an intermediate-level visual task: it must integrate (upward flowing) image information about edges with (downward flowing) shape information. This highlights the familiar local-to-global aspect of border formation (linking of edge elements to form contours) with the much less studied global-to-local aspect (which edge elements form part of the same shape). To address this task we show how to incorporate certain high-level notions of distance and geometric arrangement into a form that can influence image-based edge information. The center of the argument is a reaction—diffusion equation that reveals how (global) aspects of the distance map (that is, shape) can be “read out” locally, suggesting a solution to the border ownership problem. Since the reaction—diffusion equation defines a field, a possible information processing role for the local field potential can be defined. We argue that such fields also underlie the Gestalt notion of closure, especially when it is refined using modern experimental techniques. An important implication of this theoretical argument is that, if true, then network modeling must be extended to include the substrate surrounding spiking neurons, including glia.

Consistent and robust determination of border ownership based on asymmetric surrounding contrast

Determination of the figure region in an image is a fundamental step toward surface construction, shape coding, and object representation. Localized, asymmetric surround modulation, reported neurophysiologically in early-to-intermediate-level visual areas, has been proposed as a mechanism for figure-ground segregation. We investigated, computationally, whether such surround modulation is capable of yielding consistent and robust determination of figure side for various stimuli. Our surround modulation model showed a surprisingly high consistency among pseudorandom block stimuli, with greater consistency for stimuli that yielded higher accuracy of, and shorter reaction times in, human perception. Our analyses revealed that the localized, asymmetric organization of surrounds is crucial in the detection of the contrast imbalance that leads to the determination of the direction of figure with respect to the border. The model also exhibited robustness for gray-scaled natural images, with a mean correct rate of 67%, which was similar to that of figure-side determination in human perception through a small window and of machine-vision algorithms based on local processing. These results suggest a crucial role of surround modulation in the local processing of figure-ground segregation.

Image understanding, attention and human early visual cortex

This paper reviews our recent fMRI and psychophysical finding on: 1) perceived size representation in V1; 2) border ownership representation in V2; and 3) neural processing of partially occluded face. These findings demonstrate that the human early visual cortex not only performs local feature analyses, but also contributes significantly to high-level visual computation with assistance of attention-enabled cortical feedback. Moreover, by taking advantage of recent findings on early visual cortex from neuroscience and cognitive science, we build a biologically plausible attention model that can well predict human scanpaths on natural images.

A century of Gestalt psychology in visual perception: I. Perceptual grouping and figure–ground organization.

In 1912, Max Wertheimer published his paper on phi motion, widely recognized as the start of Gestalt psychology. Because of its continued relevance in modern psychology, this centennial anniversary is an excellent opportunity to take stock of what Gestalt psychology has offered and how it has changed since its inception. We first introduce the key findings and ideas in the Berlin school of Gestalt psychology, and then briefly sketch its development, rise, and fall. Next, we discuss its empirical and conceptual problems, and indicate how they are addressed in contemporary research on perceptual grouping and figure-ground organization. In particular, we review the principles of grouping, both classical (e.g., proximity, similarity, common fate, good continuation, closure, symmetry, parallelism) and new (e.g., synchrony, common region, element and uniform connectedness), and their role in contour integration and completion. We then review classic and new image-based principles of figure-ground organization, how it is influenced by past experience and attention, and how it relates to shape and depth perception. After an integrated review of the neural mechanisms involved in contour grouping, border ownership, and figure-ground perception, we conclude by evaluating what modern vision science has offered compared to traditional Gestalt psychology, whether we can speak of a Gestalt revival, and where the remaining limitations and challenges lie. A better integration of this research tradition with the rest of vision science requires further progress regarding the conceptual and theoretical foundations of the Gestalt approach, which is the focus of a second review article.

Public Debt Managers Behaviour: Interactions with Macro Policies

We investigate the evolution of public debt management, the policy behaviour of debt managers, and the impact of debt management on financial stability and monetary policy.The focus is on the euro area. Empirical estimations of a debt management reaction function indicate that the share of short term debt ( i ) responds to the yield curve or the level of interest rates, in line with the objective of cost minimisation; and ( ii ) has been increasing especially since the onset of the economic crisis. The increase in short term debt brings about higher refinancing risks and strengthens the interaction of public debt management with financial stability and monetary policy. The sharp increase in cross border ownership of public debt since the adoption of the euro further amplifies potential spill-over effects. Policy recommendations focus on the need for transparency on the use of derivatives and prudent debt management that reflects broader macroeconomic considerations.

The Influence of Axiality on Figure/Ground Assignment

OF THE THESIS The Influence of Axiality on Figure/Ground Assignment By SEHA KIM Thesis Director: Dr. Jacob Feldman This study investigates the influence of shape on figure/ground assignment. We measure the influence of axiality – a measure of how well a shape is described by a skeletal representation – on border ownership (f/g assignment) by pitting axiality against symmetry, a known figure/ground cue. The axiality is defined via the description length of the maximum a posteriori (MAP) skeleton for a shape. We designed a display in which an axial shape shares a common boundary with a symmetric shape, and used two methods to assess perceived f/g assignment along the common boundary: a local method, the motion probe task, and a global one, an explicit verbal response. Experiment 1, using the motion probe method, found a systematic influence of axiality on border ownership assignment: the shape with stronger axiality tends more often to be perceived as figure, that is, to own the common boundary. The results from Experiment 2 confirm that such effect of axiality was consistent for global f/g assignment as well. We conclude that (a) the axiality has an influence on f/g assignment, so global (from all contour points) and local (only near the motion probe) axialties of shapes predict border ownership, and (b) the contour of the shared boundary is perceptually “owned” by the skeleton that best explains the shape.

Binding and selective attention increase coherence between distant sites in early visual cortex

We have proposed that the border ownership selectivity that is observed in many neurons in early visual cortex is the result of specific network connectivity (Craft et. al., J. Neurophysiol. 97:4310–26, 2007). According to our model, border ownership cells (B-cells) have reciprocal connections with grouping cells (G-cells) in another level of cortex. A G-cell integrates inputs from B-cells and modulates their firing rates. When a pair of neurons is activated by edges that are part of one figure (the contours are bound), the neurons receive reentrant inputs from the same G-cell. When the contours are part of separate figures, the inputs come from different G-cells. Thus the model predicts that coherence will increase between pairs with bound edges in their receptive fields. Specifically, because pairs that both prefer the bound configuration are connected to the same G-cell, they should display enhanced coherence with binding compared to other pairs. In the model, attention is inserted at a G-cell and propagates back to the B-cells, modulating their firing rates for further processing. Thus as with binding, the model predicts that coherence will increase with attention, especially for pairs that both prefer the bound configuration. We tested these predictions by recording local field potentials and single-unit spiking activity from two electrodes separated by long distances (3–10 mm) in macaque areas V1 and V2. We found that binding increases coherence at around 20 Hz, especially for pairs that both prefer the bound configuration. Selective attention also increases coherence in the same range, though the effect is more subtle. As with binding, the increase in coherence with attention is more pronounced for pairs that both prefer the bound configuration. These results support the network connectivity proposed by the model. The coherence difference (although not gamma) may play a role in coding binding and selective attention.

Constraints of surround modulation as a mechanism underlying the selectivity of border ownership

Constraints of surround modulation as a mechanism underlying the selectivity of border ownership

Switching dynamics of border ownership: A stochastic model for bi-stable perception

A model that computes the border-ownership (BOWN) and the depth map of the image (DISC model, Kogo et al., 2010) is applied to investigate the stochastic nature of perception in “face or vase” stimuli. The 2-D integration of BOWN signals determines the figure–ground relationships in the image. In the present application of the model, BOWN signals are made stochastic and feedback connections are established between the higher level depth perception and the lower level BOWN signals. This feedback modifies the BOWN signals to further enhance the figure–ground segregation. Adaptation results in a decay of the response which leads to alternation. This triggers recovery of the adaptation. The alternation rate decreases in response to the increased levels of disambiguation. A detailed examination of the model parameters shows a prolongation of the alternation when the stimulus is presented intermittently in some conditions. In this framework, the adaptation and the recovery processes need to be perception dependent (not physical input dependent) to reproduce human perception.

The speed of context integration in the visual cortex

The observation of figure-ground selectivity in neurons of the visual cortex shows that these neurons can be influenced by the image context far beyond the classical receptive field. To clarify the nature of the context integration mechanism, we studied the latencies of neural edge signals, comparing the emergence of context-dependent definition of border ownership with the onset of local edge definition (contrast polarity; stereoscopic depth order). Single-neuron activity was recorded in areas V1 and V2 of Macaca mulatta under behaviorally induced fixation. Whereas local edge definition emerged immediately (<13 ms) after the edge onset response, the context-dependent signal was delayed by about 30 ms. To see if the context influence was mediated by horizontal fibers within cortex, we measured the latencies of border ownership signals for two conditions in which the relevant context information was located at different distances from the receptive field and compared the latency difference with the difference predicted from horizontal signal propagation. The prediction was based on the increase in cortical distance, computed from the mapping of the test stimuli in the cortex, and the known conduction velocities of horizontal fibers. The measured latencies increased with cortical distance, but much less than predicted by the horizontal propagation hypothesis. Probability calculations showed that an explanation of the context influence by horizontal signal propagation alone is highly unlikely, whereas mechanisms involving back projections from other extrastriate areas are plausible.

Depicting Occlusion in Early Renaissance Art

The artist attempting to give the impression of three-dimensional relationships must convey somehow that one surface is in front of another. There is a large and venerable literature in Psychology on this subject, showing how figure-ground, border ownership and amodal completion and continuation are determined but there is almost no discussion of how artist's have recruited these and other principles to create convincing impressions of occlusion. Even Gombrich (Art & Illusion 1960) only considers the situation in which a figure has to be imagined from very partial cues, not how juxtaposed elements in art are parsed perceptually into occluding and occluded surfaces. In this paper I shall discuss approaches to occlusion present in early Renaissance art and the degree to which the principles now well-known to Psychologists were discovered and used, as artists increasingly depicted naturalistic scenes. Among the preoccupations of these artists, as indicated by their work, were whether and how much to occlude faces (and the related issue of the management of haloes), occlusion of and by architectural features, and the importance or otherwise of transitivity in occlusion relationships within the scene. They also clearly used the ground plane, high viewpoints and arrangements of contour terminations, as well as more conventional figural cues, to disambiguate perceived occlusion or to avoid the confusion of multiple surfaces.

The Interaction between Flanker Phase and Position in Lateral Masking

The visibility of a target pattern can be affected by the presence of an adjacent stimulus (flanker). Here, we showed that such lateral masking effect depends on both the phase and the position of the flanker. The task of the observers was to detect a 4 cy/deg vertical Gabor target with the presence of vertical flankers. The target was in sine phase related to the fixation. The flankers had either the same or the opposite phase as the target and located at either the collinear or the side position from the target. The distance between the target and the flanker varied from 2 to 7.5 wavelengths. We measured the target threshold at 75% correct level. Compared with the no-flanker condition, the same-phase collinear flankers and the opposite-phase side flankers significantly decreased target threshold while the other flankers had little effects. Hence the side flanker has an effect only if the bright region of the target is adjacent to the bight regions of the flanker, and the dark region of the target to the dark region of the flanker. This result is consistent with the notion of border ownership in which facilitation occurs when the target and the flankers signal the same border.

Early Stages of Figure–Ground Segregation during Perception of the Face–Vase

The temporal sequence of neural processes supporting figure-ground perception was investigated by recording ERPs associated with subjects' perceptions of the face-vase figure. In Experiment 1, subjects continuously reported whether they perceived the face or the vase as the foreground figure by pressing one of two buttons. Each button press triggered a probe flash to the face region, the vase region, or the borders between the two. The N170/vertex positive potential (VPP) component of the ERP elicited by probes to the face region was larger when subjects perceived the faces as figure. Preceding the N170/VPP, two additional components were identified. First, when the borders were probed, ERPs differed in amplitude as early as 110 msec after probe onset depending on subjects' figure-ground perceptions. Second, when the face or vase regions were probed, ERPs were more positive (at ∼ 150-200 msec) when that region was perceived as figure versus background. These components likely reflect an early "border ownership" stage, and a subsequent "figure-ground segregation" stage of processing. To explore the influence of attention on these stages of processing, two additional experiments were conducted. In Experiment 2, subjects selectively attended to the face or vase region, and the same early ERP components were again produced. In Experiment 3, subjects performed an identical selective attention task, but on a display lacking distinctive figure-ground borders, and neither of the early components were produced. Results from these experiments suggest sequential stages of processing underlying figure-ground perception, each which are subject to modifications by selective attention.