In recent years, optical imaging studies gave the comprehensive description of orientation map in primary visual cortex (V1). The optical orientation map contains nonuniform distribution of orientation selectivity, such as pinwheels, fractures and linear zones. This means that each neuron in V1 is placed in different cortical surroundings. Although it is natural to think that different surroundings evoke different functions, little is known about the differences in functions. In the previous study, we have suggested that orientation tuning is sharper and contextual modulation is stronger in the middle of an iso-orientation domain than at the neighborhood of a pinwheel center singularity (Okamoto et al. SFN 2002). In the present study, we examined the localization of orientation tuning and contextual modulation in more detail by simulation of a computational model. The model for layer 2/3 of V1 contains excitatory and inhibitory orientation modules and geometric orientation map. The orientation module is eq...