Facilitation from collinear flanks is cancelled by non-collinear flanks

Detection of a central Gabor pattern is facilitated by the presence of collinear flanking patterns. We find that this facilitation is greatly reduced when the collinear flanks are combined with non-collinear hanks to form a coherent surround. These results are unlikely to be explained by mechanisms that merely transduce local contrast in a nonlinear fashion. A model wherein the outputs of such mechanisms are combined anisotropically provides a better account for these results. (C) 2000 Elsevier Science Ltd. All rights reserved.