Object grouping based on real-world regularities facilitates perception by reducing competitive interactions in visual cortex

In virtually every real-life situation humans are confronted with complex and cluttered visual environments that contain a multitude of objects. Because of the limited capacity of the visual system, objects compete for neural representation and cognitive processing resources. Previous work has shown that such attentional competition is partly object based, such that competition among elements is reduced when these elements perceptually group into an object based on low-level cues. Here, using functional MRI (fMRI) and behavioral measures, we show that the attentional benefit of grouping extends to higher-level grouping based on the relative position of objects as experienced in the real world. An fMRI study designed to measure competitive interactions among objects in human visual cortex revealed reduced neural competition between objects when these were presented in commonly experienced configurations, such as a lamp above a table, relative to the same objects presented in other configurations. In behavioral visual search studies, we then related this reduced neural competition to improved target detection when distracter objects were shown in regular configurations. Control studies showed that low-level grouping could not account for these results. We interpret these findings as reflecting the grouping of objects based on higher-level spatial-relational knowledge acquired through a lifetime of seeing objects in specific configurations. This interobject grouping effectively reduces the number of objects that compete for representation and thereby contributes to the efficiency of real-world perception.In daily life, humans are confronted with complex and cluttered visual environments that contain a large amount of visual information. Because of the limited capacity of the visual system, not all of this information can be processed concurrently. Consequently, elements within a visual scene are competing for neural representation and cognitive processing resources (1, 2). Such competitive interactions can be observed in neural responses when multiple stimuli are presented at the same time. Single-cell recordings in monkey visual cortex revealed that activity evoked by a neuron''s preferred stimulus is suppressed when a nonpreferred stimulus is simultaneously present in the neuron''s receptive field (3–5). Corresponding evidence for mutually suppressive interactions among competing stimuli has been obtained from human visual cortex using functional magnetic resonance imaging (fMRI) (6).According to biased competition theory, these competitive interactions occur between objects rather than between the parts of a single object (1). This idea of object-based competition is supported by behavioral studies showing that judgments on two properties of one object are more accurate than judgments on the same properties distributed over two objects (7). However, the degree of competition among objects is strongly influenced by contextual factors, such as stimulus similarity (8–10), geometric relationships between stimuli (11), and perceptual grouping (12, 13). For example, competitive interactions in human visual cortex are greatly reduced when multiple single stimuli form an illusory contour and hence can be perceptually grouped into a single gestalt (12).Whereas the attentional benefit of grouping based on low-level cues is well established, much less is known about object grouping at more conceptual levels. Many objects in real-world scenes occupy regular and predictable locations relative to other objects. For example, a bathroom sink is typically seen together with a mirror in a highly regular spatial arrangement. When considering highly regular object pairs like these it becomes clear that the world can be carved up at different levels: based on low-level cues such as those specified by gestalt laws, but also based on conceptual knowledge and long-term visual experience; a plate flanked by a fork and a knife is both a dinner plate set and three separate objects.In the present fMRI and behavioral studies, we asked whether grouping based on real-world regularities modulates attentional competition. We hypothesized that objects that appear in frequently experienced configurations are, to some extent, grouped, resulting in reduced competition between these objects. To test this prediction, we presented pairs of common everyday objects either in their typical, regular configuration (e.g., a lamp above a table) or in an irregular configuration (e.g., a lamp below a table). Our findings indicate that grouping of objects based on real-world regularities effectively reduces the number of competing objects, leading to reduced neural competition and more efficient visual perception.