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Figure-ground (FG) segregation has been considered as a fundamental step towards object recognition. We explored plausible mechanisms that estimate global figure-ground segregation from local image features by investigating the human visual system. Physiological studies have reported border-ownership (BO) selective neurons in V2 which signal the local direction of figure (DOF) along a border; however, how local BO signals contribute to global FG segregation has not been clarified. The BO and FG processing could be independent, dependent on each other, or inseparable. The investigation on the differences and similarities between the BO and FG judgements is important for exploring plausible mechanisms that enable global FG estimation from local clues. We performed psychophysical experiments that included two different tasks each of which focused on the judgement of either BO or FG. The perceptual judgments showed consistency between the BO and FG determination while a longer distance in gaze movement was observed in FG segregation than BO discrimination. These results suggest the involvement of distinct neural mechanism for local BO determination and global FG segregation.

Border ownership (BO) indicates which side of a contour owns a border, and it plays a fundamental role in figure-ground segregation. The majority of neurons in V2 and V4 areas of monkeys exhibit BO selectivity. A physiological work reported that the responses of BO-selective cells show a rapid transition when a presented square is flipped along its classical receptive field (CRF) so that the opposite BO is presented, whereas the transition is significantly slower when a square with a clear BO is replaced by an ambiguous edge, e.g., when the square is enlarged greatly. The rapid transition seemed to reflect the influence of feedforward processing on BO selectivity. Herein, we investigated the role of feedforward signals and cortical interactions for time-courses in BO-selective cells by modeling a visual cortical network comprising V1, V2, and posterior parietal (PP) modules. In our computational model, the recurrent pathways among these modules gradually established the visual progress and the BO assignments. Feedforward inputs mainly determined the activities of these modules. Surrounding suppression/facilitation of early-level areas modulates the activities of V2 cells to provide BO signals. Weak feedback signals from the PP module enhanced the contrast gain extracted in V1, which underlies the attentional modulation of BO signals. Model simulations exhibited time-courses depending on the BO ambiguity, which were caused by the integration delay of V1 and V2 cells and the local inhibition therein given the difference in input stimulus. However, our model did not fully explain the characteristics of crucially slow transition: the responses of BO-selective physiological cells indicated the persistent activation several times longer than that of our model after the replacement with the ambiguous edge. Furthermore, the time-course of BO-selective model cells replicated the attentional modulation of response time in human psychophysical experiments. These attentional modulations for time-courses were induced by selective enhancement of early-level features due to interactions between V1 and PP. Our proposed model suggests fundamental roles of surrounding suppression/facilitation based on feedforward inputs as well as the interactions between early and parietal visual areas with respect to the ambiguity dependence of the neural dynamics in intermediate-level vision.

Many neurons in monkeys' V2 and V4 are selective for border ownership (BO) [H. Zhou, H.S. Friedman, R. von der Heydt, Coding of border ownership in monkey visual cortex, J. Neurosci. 20 (2000) 6594-6611). We have developed a computational model for the BO determination of the neurons based on their contextual modulation. Our model consists of hundreds of model cells with distinct surround suppressive/facilitatory regions that are generated by a linear combination of Gaussians. The simulation results show that many model cells realize the major characteristics of BO selective neurons. Investigating the surrounding regions of the BO selective model cells with perfect consistency, we found that their iso orientation suppression is dominant over the cross orientation facilitation, which agrees quantitatively with physiological reports. These results suggest that the surrounding modulation is a fundamental mechanism for BO selectivity.

A recent physiological finding of neural coding for border ownership (BO) that defines the direction of a figure with respect to the border has provided a possible basis for figure-ground segregation. To explore the underlying neural mechanisms of BO, we investigated stimulus configurations that activate BO circuitry through psychophysical investigation of the BO-dependent tilt aftereffect (BO-TAE). Specifically, we examined robustness of the border ownership signal by determining whether the BO-TAE is observed when gestalt factors are broken. The results showed significant BO-TAEs even when a global shape was not explicitly given due to the ambiguity of the contour, suggesting a contour-independent mechanism for BO coding., This paper was published in Journal of the Optical Society of America. A and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=josaa-24-1-18. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.

Contextual modulation reported in early- to intermediate-level visual areas could be an essential component to signal border ownership (BO) that specifies the direction of figure along a contour. The surrounding regions that evoke significant suppression or facilitation are highly localized and asymmetric with respect to the center of the classical receptive field (CRF). We propose a hypothesis that such surrounding modulation is a basis for BO-selectivity. Although this idea has been discussed for several years, it is uncertain how many of a vast variety of surrounding organizations could signal correctly the direction of ownership, and how many could signal consistently for various stimuli. We carried out computationally a population study of the surrounding effects to investigate how many cells exhibit effective and consistent BO signals. We tested hundreds of various organizations, and found that most of the asymmetric, iso-orientation suppressive regions, regardless of position or size, lead to surprisingly high consistency in the direction of ownership for various stimuli. The combinations of iso-orientation suppression and cross-orientation facilitation indicate both high robustness and consistency in the ownership determination. We constructed a model for BO-selective neurons based on the surrounding effects, and investigated whether the model reproduces major characteristics of the neuronal responses, including a variety in the BO selectivity among neurons, consistency with respect to various stimuli, invariance to stimulus size, and co-selectivity to BO and contrast. The model reproduced successfully the major characteristics of BO-selective neurons.

We have proposed the computational model for border-ownership (BO) determination based on the contrast configurations within a certain range that extends beyond the classical receptive field (CRF). In this study, we adopt two crucial functions of the surrounding modulation reported by the recent physiological studies; (1) changes in functional connection depending on the amplitude of contrast, and (2) a variety of surrounding suppression/facilitation depending on the orientation and retinotopic position of surrounding stimuli relative to the CRF. Simulation results show that the model reproduces the major characteristics of BO selective neurons.

We investigate the neural mechanisms for border-ownership (BO) determination, specifically whether the determination of BO is plausible from the contrast configuration within a certain range that extends beyond the classical receptive fields. The relevance of the contrast is suggested since the majority of BO-selective neurons in V2 and V4 show co-selectivity to the contrast. We hypothesize that the spatial structure of surrounding inhibition/excitation recently revealed in V1, or the similar structure in V2, is a key to integrate surrounding contrast to determine BO. The model reproduces a range of the neuronal activities responding to complex figures including occlusion.

Border Ownership (BO) selective cells show complex behavior in latency, such as a shorter latency for a farther figural element. The complex behavior of latency would give crucial constraints for understanding the neuronal mechanisms underlying BO selectivity. We propose that the delays in the feed-forward mechanisms of surround modulation account for the characteristics of the latency. Specifically, combinations of delays between V1 cells, surround center and BO-selective cells underlie the latency characteristics. To examine the hypothesis, we constructed the V1-V2 feed-forward model and carried out Monte Carlo simulations with a variety of surround regions. The results indicate that physiologically realistic surround regions reproduce the puzzled behavior of latency. The results support the feed-forward mechanism of surround modulation for the neural mechanism underlying the BO selectivity.

The determination of Border-Ownership (BO) that defines the direction of figure along contour is a crucial step toward figure-ground segregation. Recent physiological and computational studies have reported that neurons in V2/V4 are selective to BO [1], and that surround modulation underlies the selectivity [2, 3]. Accurate determination of BO along complex contours in natural images appears difficult for a single BO-selective cell, leading to the hypothesis that multiple cells work simultaneously for BO perception. We studied computationally how many BO cells and what characteristics of the surround modulation are required to achieve accurate determination of BO in natural images. The results indicated that 10 model BO-cells achieve 82% correct while single model cells yield 65%. The results suggest that grouping a small number of BO-selective cells increases effectively the capability for the determination of BO.

The border ownership (BO) that indicates which side of the contour owns the border plays a fundamental role in object perception[1]. The responses of BO-selective cells exhibit rapid transition when a stimulus is fliped along its classical receptive field so that the opposite BO is presented, while the transition is significantly slower when a clear BO is turned into an ambiguous edge such as when a square is enlarged extensively[2]. This phenomenon appears to be a crucial clue for understanding the neural mechanims underlying the credibility of BO. We hypothesize that dynamics of BO-selective cells and networks behind them play a crucial role in the credibility, and that the credibility is related to early visual areas as an appearance of a salient object evokes bottom-up attention. To investigate these hypotheses, we examined the dynamics of BO-selective cells with a computational model that include recurent pathways among V1, V2 and Posterior Parietal (PP) areas[3]. The model cells have been shown to reproduce effects of spatial attention. Simulations of the model exhibited distinct response time depending on the ambiguity of BO, indicating a crucial role of dynamics in the credibility. The recurrent network between PP and V1 appear to play a crucial role for the time course of BO-selective cells that governs simultaneously both credibility of BO and bottom-up attention.

Recent physiological studies have reported Border-Ownership (BO) selective cells that signal the direction of figure along a contour, which appear to be a basis for figure-ground segregation. Surround modulation has been proposed as an underlying neural mechanism of BO determination. The crucial question to the model is its orientation specificity: whether BO could be determined only from iso-orientation (with respect to the preferred orientation of the classical receptive field) that has been reported dominant in the modulation. We investigated computationally the dependence of surround modulation on the orientation characteristics during the determination of BO with natural images. The results showed that, even when modulation was limited to iso-orientation, population responses obtained through integration were unchanged while the responses of individual cells were varied, indicating a dominant role of isoorientation suppression and an effectiveness of population coding in BO determination.

There is little understanding on representation and reconstruction of object shape in the cortex. Physiological studies with macaque suggested that neurons in V1 respond to Medial-Axis (MA). We investigated whether (1) early visual areas could provide basis for MA representation, and (2) we could reconstruct the original shape from its MA, with a physiologically realistic computational model consisting of early- to intermediate-level visual areas. Assuming the synchronization of border-ownership selective cells at stimulus onset, our model was capable of detecting MA, indicating that early visual area could provide basis for MA representation. Furthermore, we propose a physiologically plausible reconstruction algorithm with the summation of distinct gaussians.

We propose a computational model consisting of mutually linked V1, V2, and PP modules. The model reproduces the effect of attention in the determination of border-ownership (BO) that tells which side of the contour owns the border. The V2 module determines BO based on surrounding contrast extracted by the V1 module that could be influenced by top-down spatial attention from the PP module. We carried out the simulations of the model with random-block ambiguous figures to test whether spatial attention alters BO for these meaningless stimuli. To compare quantitatively these results with human perception, we carried out psychophysical experiments corresponding to the simulations. The results of these two showed good agreement in that the perception of BO was flipped when altering the location of spatial attention. These results suggest that spatial attention is a crucial factor for the modulation of figure direction in meaningless figures, and that the effects of spatial attention in early visual area are crucial for the modulation of figure direction.

The representation of object shape in the visual system is one of the most crucial questions in brain science. Although we can perceive figure shape correctly and quickly, without any effort, the underlying cortical mechanism is largely unknown. Physiological experiment with macaque indicated the possibility that the brain represents a surface with Medial Axis (MA) representation. To examine whether early visual areas could provide basis for MA representation, we constructed the physiologically realistic, computational model of the early visual cortex, and examined what constraint is necessary for the representation of MA. Our simulation results showed that simultaneous firing of Border-Ownership (BO) selective cells at the stimulus onset is a crucial constraint for MA representation.

Spatial attention alters contrast gain in early visual areas, which might affect the determination of border ownership (BO)that indicates the direction of figure with respect to the border. We investigated the role of spatial attention applied to earlyvision in the determination of BO with a computational model that consists of V1, V2, and posterior parietal (PP) modules.Attention alters contrast gain in the V1 module so that it enhances local contrast. The V2 module determines BO based onthe surrounding contrast extracted by the V1 module. The simulation results showed that the attention significantlymodulates BO; BO is even flipped in figures with ambiguous BO while BO is stable for unambiguous figures such as asimple square. To evaluate the model quantitatively, we carried out psychophysical experiments to measure the effects ofattention in the perception of BO and compared the results with those from corresponding simulations. The model showedgood agreement with human perception including the determination of BO for ambiguous random-block stimuli. Theseresults indicate that the activity of BO-selective neurons could be modulated significantly by spatial attention that alters localcontrast gain in V1, which may account in part for automatic, bi-stable perception in ambiguous figures.Keywords: attention, border ownership, early vision, computational model, surrounding modulationCitation: Wagatsuma, N., Shimizu, R., & Sakai, K. (2008). Spatial attention in early vision for the perception of borderownership. Journal of Vision, 8(7):22, 1–19, http://journalofvision.org/8/7/22/, doi:10.1167/8.7.22.

Discrimination of a figure from its ground is essential for the perception of surface, which is fundamental for the recognition of shape, spatial structure, and objects. Recent physiological studies have reported that neurons in monkey’s V2 and V4 show activities corresponding to the direction of figure [1–3]. Zhou et al. [1] have distinguished types of neurons that showed selectivity to border ownership and/or contrast, about 80% of which were sensitive to contrast polarity. Figure la illustrates the distribution of the neuronal selectivity in V1, V2, and V4. The selectivity to border ownership and contrast was observed in stimuli with single squares, C-shaped figures, and two overlapping squares, as shown in Fig. lb. However, underlying neural mechanisms for figure determination have not been clarified.