Figure 3.

Neuronal implementation of D_arg. (a) A cortical hypercolumn. Each circle represents a column, with the bar indicating the preferred direction of cells in this column (i.e. the direction of an input line to which they fire most). Local differentiation of the angle function near angles π and −π would yield a high response, similar to Y_arg. (b) The same hypercolumn, with only positive weights (i.e. angles). (c) Neural implementation of D_arg. Local summation of orientation-dependent cells may detect convexity.