Extraction of perceptually salient contours by striate cortical networks

Abstract

We present a cortical-based model for computing the perceptual salience of contours embedded in noisy images. It has been suggested that horizontal intra-cortical connections in primary visual cortex may modulate contrast detection thresholds and pre-attentive "pop-out". In our model, horizontal connections mediate context-dependent facilitatory and inhibitory interactions among oriented cells. Strongly facilitated cells undergo temporal synchronization; and perceptual salience is determined by the level of synchronized activity. The model accounts for a range of reported psychophysical and physiological effects of contour salience. In particular, the model proposes that intrinsic properties of synchronization account for the increased salience of smooth, closed contours. Application of the model to real images is demonstrated.

Computational modeling and exploration of contour integration for visual saliency

“…Two approaches are generally taken when trying to model contour integration. The first is the biological route (Yen and Finkel 1998;Li 1998;Grigorescu et al 2003;Mundhenk and Itti 2003;Choe and Miikkulainen 2004;Ben-Shahar and Zucker 2004). In this method, the idea is to create a model of contour integration that explores how the brain may perform such activities.…”

“…This creates a situation where neural groups that process contour integration need to spread effect throughout the network while at the same time controlling the network and preventing it from losing control. Some biological approaches have included a global normalization gain control and neural synchronization for this effect (Yen and Finkel 1998). We attempt to control our model by taking advantage of the properties of GABAergic interneurons to control local groups of neurons discretely.…”

“…While there is some disagreement to the amount of pop-out from contour closure it is still nonetheless considered significant. This suggests that neurons sensitive to contour integration may perform some sort of linking to each other in a manner conceptually similar to a closed circuit like loop (Li 1998;Yen and Finkel 1998;Braun 1999;Prodöhl et al 2003). That is, neurons that do not directly touch may propagate effect to each other through their neighbors.…”

“…Thus, neurons in V1 and V2 are limited in the scope of their direct effect onto each other and should not cross the entire visual field. For contour closure effects to occur, especially over long contours, there should be some sort of network propagation (Li 1998;Yen and Finkel 1998;Braun 1999).…”

“…Thus, adding to the previous argument, there seems to be some ability for neurons in visual cortex to enhance a contour's perceptibility at locations represented by neurons that they are not directly connected to. Several theories have been advanced to explain how that can happen, for instance neural synchronization (Yen and Finkel 1998;Choe and Miikkulainen 2004), potential propagation (Li 1998) and fast plasticity (Braun 1999;Mundhenk and Itti 2003).…”