Algorithms for region see more filling, on the other hand, require that neurons tuned to similar features excite each other. If the representation of some of the figural image elements is enhanced, the excitatory connections spread the enhanced activity to neurons with a similar feature preference, coding elements of the same figure.

A number of previous studies supported separate mechanisms for FGM at the figure boundary (edge modulation) and figure center (center modulation) (Huang and Paradiso, 2008, Lamme et al., 1998a, Lamme et al., 1999 and Scholte et al., 2008), but other studies disputed the existence of the region-filling process within V1 (Rossi et al., 2001 and Zhaoping, 2003). Another unresolved but possibly related issue is the role of task-driven attention in figure-ground segregation. The Gestalt psychologists (Koffka, 1935, Rubin, 1915 and Wertheimer, 1923) delineated several bottom-up factors for figure-ground organization. They found that small, convex, and symmetric image regions are usually perceived as figures whereas large, concave and asymmetric regions are often perceived as background (Kanizsa and Gerbino, 1976 and Koffka, 1935). But there is also an important influence

of top-down factors (Peterson et al., 1991). For example, if you attend to a region of an ambiguous figure-ground display, this increases Docetaxel mouse the probability that you perceive it as figure (Driver and Baylis, 1996 and Vecera et al., 2004). It is not known how these bottom-up and top-down factors interact with each other (Driver et al., 2001, Qiu et al., 2007 and Scholl, 2001). Does top-down attention act as a spotlight (Posner et al., 1980) and increase neuronal activity at the approximate location of the figure or does it

act in object-based manner (Duncan, 1984) to specifically highlight image elements of the figure, in accordance with a region-filling process (Figure 1A)? Cytidine deaminase It is also not well understood how attention interacts with the boundary-detection process. Attention might enhance neuronal activity in an additive manner (Figure 1B) or selectively boost the representation of figure’s interior (Figure 1C). To address these questions, we investigated neuronal activity in V1 in a texture-segregation task and also recorded simultaneously activity in V4, a higher area that is a source of feedback to V1 and is important for figure-ground segregation (Allen et al., 2009, De Weerd et al., 1994 and Merigan, 1996). To determine the role of attention (Desimone and Duncan, 1995, Reynolds and Chelazzi, 2004 and Treue, 2001), we required the monkeys to either attend the figures or pay attention elsewhere. We report that attention acts in an object-based manner to enhance FGM in V1 and V4.