Asymmetries in Visual Texture Discrimination
Rick Gurnsey and Roger A. Browse
Abstract
Recent results have shown that texture discrimination is an asymmetrical process; texture A
within texture B may be much easier to detect than texture B within texture A. Two questions
regarding discrimination asymmetries are addressed: (i) what sorts of textural properties are
associated with discrimination asymmetries; and (ii) what sort of architecture would yield
asymmetries. Two experiments show that discrimination asymmetries are obtained when textures
comprise circles of different sizes (large circles are easier to detect in small than vice versa) and
when circles differ only in the regularity of their placement (irregularly placed circles are easier
to detect in a background of regularly placed circles than vice versa). A plausible account of
texture discrimination would involve the decomposition of images via a set orientation and scale
selective filters, followed by a second layer of filtering to detect energy differences between
adjacent regions in the original convolutions. Discrimination asymmetries provide prima facie
evidence against such a model because it involves only local measurements and comparisons.
We propose that discrimination asymmetries are elegantly explained if it is assumed that the
responses of the orientation and scale selective filters are normalized by the degree to which
similarly tuned operators are responding elsewhere in the image; viz., global normalization of
filter responses. However, there are cases where such global normalization is not required to
explain asymmetrical discrimination.