CHAPTER 45 – Visual Saliency and Spike Timing in the Ventral Visual Pathway

I argue against the view that “bottom-up” saliency necessarily recruits the attentional system prior to object recognition. A number of visual processing tasks are clearly performed too fast for such a costly strategy to be employed. Rather, visual attention could simply act by biasing a “saliency-based” object recognition system. At any given level of the ventral pathway, the most activated cells of the neural population simply represent the most salient locations. The notion of saliency itself grows increasingly complex throughout the system, based mostly on luminance contrast until information reaches visual cortex, gradually incorporating information about features such as orientation or color in primary visual cortex and early extrastriate areas, and finally the identity and behavioral relevance of objects in temporal cortex and beyond. Under these conditions, the object that dominates perception, that is, the object yielding not only the strongest, but also the first selective neural response, is by definition the one whose features are most “salient”—without the need for any external saliency map.