Attention depends on figure-ground organization: figures draw attention, while shapes of the ground tend to be ignored. Recent research has demonstrated mechanisms of figure-ground organization in the visual cortex, but how they relate to the attention process remains unclear. Here we show that the influences of figure-ground organization and volitional (top-down) attention converge in single neurons of area V2. While assignment of border ownership was found for attended as well as for ignored figures, attentional modulation was stronger when the attended figure was located on the neuron's preferred side of border ownership. When the border between two overlapping figures was placed in the receptive field, responses depended on the side of attention, and enhancement was generally found on the neuron's preferred side of border ownership. This correlation suggests that the neural network that creates figure-ground organization also provides the interface for the topdown selection process.Perception tends to segregate visual images into figures and ground, and process the figure regions, but not the ground regions (Fig. 1). 1,2 Apparently, the system is able to group the visible borders at an early stage to configurations that are likely to be objects and process this information with priority. Objects can be selected by spatial filtering when they are separated ('spotlight of attention', Fig. 2a), but such a mechanism fails when objects are partially occluded by others as in everyday images. When trying to select the bottom square in Figure 2b for example, such a mechanism would select contours in the form of an L rather than a square. Observers generally perceive the square-not the L. Apparently, the visual system first subtracts the contours of the occluding object, to use only the remaining contours for further analysis, acknowledging that information is missing (Fig. 2c). Thus, an essential step in the interpretation of images is the correct assignment of the visible borders (contours, edges) to foreground regions. 3,4 Regions of occluded objects are bounded by two types of contour, those that are inherently related to the object (intrinsic contours), and those formed accidentally by interposition of another object (extrinsic contours). 3 Only the intrinsic contours should be processed together for shape recognition; extrinsic contours should be excluded. Single cell recordings from monkey visual cortex have shown that assignment of border ownership occurs at stages as early as areas V1 and V2. 5-7 Neurons in V2 are also influenced by top-down attention. 8-12 How these two processes are related is not clear. Is figure-ground organization the result of selective attention, or is it an independent process? If it is independent, as we shall argue, what is its role in the deployment of attention? Does it enable the attention process to select contours according to border ownership (interface hypothesis), or is attentional modulation determined merely by the distance of a contour from the focus of attentio...

Figure-ground organization is a process by which the visual system identifies some image regions as foreground and others as background, inferring 3D layout from 2D displays. A recent study reported that edge responses of neurons in area V2 are selective for side-of-figure, suggesting that figure-ground organization is encoded in the contour signals (border ownership coding). Here, we show that area V2 combines two strategies of computation, one that exploits binocular stereoscopic information for the definition of local depth order, and another that exploits the global configuration of contours (Gestalt factors). These are combined in single neurons so that the "near" side of the preferred 3D edge generally coincides with the preferred side-of-figure in 2D displays. Thus, area V2 represents the borders of 2D figures as edges of surfaces, as if the figures were objects in 3D space. Even in 3D displays, Gestalt factors influence the responses and can enhance or null the stereoscopic depth information.

Sugihara T, Qiu FT, von der Heydt R. The speed of context integration in the visual cortex.

We tested the binding-by-synchrony hypothesis which proposes that object representations are formed by synchronizing spike activity between neurons that code features of the same object. We studied responses of 32 pairs of neurons recorded with microelectrodes 3 mm apart in the visual cortex of macaques performing a fixation task. Upon mapping the receptive fields of the neurons, a quadrilateral was generated so that two of its sides were centered in the receptive fields at the optimal orientations. This one-figure condition was compared with a two-figure condition in which the neurons were stimulated by two separate figures, keeping the local edges in the receptive fields identical. For each neuron, we also determined its border ownership selectivity (H. Zhou, H. S. Friedman, & R. von der Heydt, 2000). We examined both synchronization and correlation at nonzero time lag. After correcting for effects of the firing rate, we found that synchrony did not depend on the binding condition. However, finding synchrony in a pair of neurons was correlated with finding border-ownership selectivity in both members of the pair. This suggests that the synchrony reflected the connectivity in the network that generates border ownership assignment. Thus, we have not found evidence to support the binding-by-synchrony hypothesis.