Texture discrimination with and without abrupt texture gradients.

A common assumption is that effortless, visual texture discrimination relies on the detection of gradients between two textures. This assumption was assessed in two experiments with manipulations that smoothed (Experiment 1) or interrupted (Experiment 2) the gradient between textures comprising L- and X-type micropatterns. Compared to discrimination performance when there was an abrupt discontinuity between juxtaposed textures, performance declined moderately (about 10 percent) when the texture boundary was smoothed. In this case the two textures were asymmetrically discriminated but there was no interaction of this asymmetry with the abruptness of the texture gradient. Abrupt texture gradients, therefore, are not a necessary condition for the asymmetrical discrimination of two textures. A comparison of discrimination performance with juxtaposed textures--having an abrupt gradient--and discrimination performance when the textures were separated into distinct regions--by non-textured areas--yielded very similar results across several texture pairs. Taken together these results indicate that, in certain instances, texture discrimination may involve pattern classification-like processes that are operative in the absence of texture gradients.