We determined the timing of the attention Selleck SB431542 effect by subtracting the FGM in the curve-tracing task from that in the figure-detection task (ΔFGM). The effect of attention occurred after 159 ms in V4, which was earlier than the attention effect on center-FGM in V1 with a latency of 204 ms (p < 0.05). We did not obtain a reliable latency measurement for the weak effect of attention on edge-FGM. The effects of attention on the V1 center-FGM and V4 FGM were significantly later than the V1 center-FGM (both Ps < 0.01). Thus, the results show an orderly progression of processing phases in the texture-segregation

task, with visually driven activity preceding FGM, which was modulated by attention at an even later phase of the response ( Figure 8E). Our findings indicate that boundary detection is an early, automatic process whereas the filling in of the figure-center with FGM in V1 depends on attention. These two processes have opposite requirements for the interactions between neurons (Roelfsema et al., 2002), with iso-orientation inhibition for boundary-detection and iso-orientation excitation for region filling. We created a neurodynamical model to test if these connection schemes can be combined in a single, hierarchical neural network

(see Supplemental Information for details). The input into the model was an orientation defined figure on a textured background that is first represented in V1m (“m” stands for model) and was then propagated to V2m and V4m by feedforward connections. Each model area contained two maps, one for each orientation (Figure 9A) Trametinib purchase and higher areas represented the image at a courser resolution. To achieve boundary Cediranib (AZD2171) detection, we implemented local center-surround interactions

for iso-orientation suppression within each of the areas. This suppression is strongest at locations where the orientation is homogeneous and weakest at orientation discontinuities (Figure 9B), as can be seen if the activity of the two orientation maps is summed (third column in Figure 9A). Iso-orientation suppression is also strong at the figure-center in V1m and V2m where the orientation is homogeneous so that the activity is initially similar to that evoked by the background. Area V4m has a lower spatial resolution so that the representation of the edges is more diffuse, causing early FGM across the entire figure representation (Figure 9A). The model uses feedback connections that excite neurons tuned to the same orientation to fill the entire figural region in lower areas with FGM (Figure 9A, fourth column). The figure orientation is represented in area V4 with enhanced activity, and these V4 cells excite neurons in lower areas that represent the same orientation, causing FGM to also fill the interior of the figure (Figure 9B bottom).