Abstract
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.
Highlights
Neural mechanisms for separating a figural object from the background is a fundamental process necessary for scene perception and object recognition
The interactions between posterior parietal (PP) and V1 modules resulted in these attentional modulations for temporal characteristics of the responses by border ownership (BO)-selective cells. These results suggest that, at least in part, the surrounding suppression/facilitation based on early-level features, as well as cortical interactions between early and parietal visual areas, play important roles in the neural dynamics depending on the ambiguity of direction of figure (DOF) and in the attentional modulation of human perception in figure-ground segregation
We examined the computational model that comprised of V1, V2, and PP modules (Figure 1; Wagatsuma et al, 2008) in order to discuss the dependence of time course on the ambiguity of DOF in BO-selective cells and human response time in the corresponding psychophysics
Summary
Neural mechanisms for separating a figural object from the background is a fundamental process necessary for scene perception and object recognition. A number of psychological studies have clarified the phenomenological characteristics and importance of figure-ground perception from a variety of aspects such as perceptual grouping and organization, attentional selection, three-dimensional (3D) representation, and perception of illusory contours (Sporns et al, 1991; He and Nakayama, 1992; Kimchi et al, 2007; Matsukura et al, 2007; Russell et al, 2014). Spatial characteristics of BO selectivity have been studied extensively from a variety of aspects, including contour groupings, attentional modulation, DOF discrimination, and the representations of shape (Oh and Choe, 2007; Wagatsuma et al, 2008; Mihalas et al, 2011; Grossberg, 2016)
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