No. 20 LAYOUT AND FUNCTION OF THE INTRACORTICAL CONNECTIONS WITHIN THE PRIMARY VISUAL CORTEX

This thesis describes a top-down view of the cat primary visual cortex (area 17), which is faithful to the relevant aspects of the known physiology and anatomy. The centerpiece of this work is an abstract hypercolumn model that is mapped to cat primary visual cortex. This model shows how the recurrent (intracortical) connections can be self-organized and that their presence can explain the emergence of several response properties of the striate cells, such as contrast-invariance of orientation tuning, narrowing of the orientation tuning, response saturation followed by normalization and response facilitation mediated by long-range horizontal connections. The abstract hypercolumn model is in line with other recurrent models by assuming broadly tuned inhibition. It is believed that large basket cells mediate this inhibition. However, the model is unique in that, when mapped to layer 4 it incorporates an additional class of interneurons, which only inhibit excitatory simple cells in their close surroundings. The layout and function of the intracortical connections within a patch of area 17 have been addressed using developmental network models. These models are developed during exposure to visual input using a Bayesian Confidence Propagation Neural Network (BCPNN) with a