A saliency-based search mechanism for overt and covert shifts of visual attention

Most models of visual search, whether involving overt eye movements or cove rt shifts of attention, are based on the concept of a saliency map, that is , an explicit two-dimensional map that encodes the saliency or conspicuity of objects in the visual environment. Competition among neurons in this map gives rise to a single winning location that corresponds to the next atten ded target. Inhibiting this location automatically allows the system to att end to the next most salient location. We describe a detailed computer impl ementation of such a scheme, focusing on the problem of combining informati on across modalities, here orientation, intensity and color information, in a purely stimulus-driven manner. The model is applied to common psychophys ical stimuli as well as to a very demanding visual search task. Its success ful performance is used to address the extent to which the primate visual s ystem carries out visual search via one or more such saliency maps and how this can be tested. (C) 2000 Elsevier Science Ltd. All rights reserved.