Texture contrast attracts overt visual attention in natural scenes

In natural vision, the central nervous system actively selects information for detailed processing through mechanisms of visual attention. It is widely held that simple stimulus features such as color, orientation and intensity contribute to the determination of visual salience and thus can act to guide the selection process in a bottom-up fashion. Contrary to this view, Einhäuser, W. & König, P. (2003) Eur. J. Neurosci., 17, 1089-1097 conclude from their study of human eye movements that luminance contrast does not contribute to the calculation of stimulus salience and that top-down, rather than bottom-up, factors therefore determine attentional allocation in natural scenes. In this article, we dispute their conclusion and argue that the Einhäuser and König study has a number of methodological problems, the most prominent of which is the unintentional introduction of changes in texture contrast. We hypothesize that texture contrast, like luminance contrast, can contribute to the guidance of attention in a bottom-up fashion, and that an appeal to top-down factors is not necessary. To test this hypothesis, we implement a purely bottom-up model of visual selective attention where salience is derived from both luminance and texture contrast. We find that the model can quantitatively account for Einhäuser and König's results and that texture contrast strongly influences attentional guidance in this particular paradigm. The significance of this result for attentional guidance in other paradigms is discussed.