The ASF. a, ASFs are modeled as a difference of two multivariate Gaussian functions. The filter has a positive center (orange) and a negative surround (purple). b, c, Top, View of circular (b) and elliptical (c) filters superimposed on cortical space. The filter sorts contralateral (white pixels) and ipsilateral afferents (black pixels) over the mediolateral (ML) and anteroposterior (AP) axes of cortical space.