The bottom-up contribution to the allocation of exogenous attention is a saliency map, whose neural substrate is hard to identify because of possible contamination by top-down signals. We obviated this possibility using stimuli that observers could not perceive, but that nevertheless, through orientation contrast between foreground and background regions, attracted attention to improve a localized visual discrimination. When orientation contrast increased, so did the degree of attraction, and two physiological measures: the amplitude of the earliest (C1) component of the ERP, which is associated with primary visual cortex, and fMRI BOLD signals in areas V1-V4 (but not the intraparietal sulcus). Significantly, across observers, the degree of attraction correlated with the C1 amplitude and just the V1 BOLD signal. These findings strongly support the proposal that a bottom-up saliency map is created in V1, challenging the dominant view that the saliency map is generated in the parietal cortex.
Furthermore, Zhang and his colleagues measured the attentional effect of the bottom-up saliency map of simple texture stimuli, and found the degree of attention attraction correlated with the amplitude of the earliest component of the ERP as well as the V1 BOLD signal across subjects REF , which also supported the V1 hypothesis.
Neural Activities in V1 Create a Bottom-Up Saliency Map
Neuron
Neuron
Psychology Medicine