Abstract
Salient parts of a visual scene attract longer and earlier fixations of the eyes. Saliency is driven by bottom-up (image dependent) factors and top-down factors such as behavioral relevance, goals, and expertise. It is currently assumed that a saliency map defining eye fixation priorities is stored in neural structures that remain to be determined. Lesion studies support a role for the amygdala in detecting saliency. Here we show that neurons in the amygdala of primates fire differentially when the eyes approach to or fixate behaviorally relevant parts of visual scenes. Ensemble bursting in the amygdala accurately predicts main fixations during the free-viewing of natural images. However, fixation prediction is significantly better for faces—where a bottom-up computational saliency model fails—compared to unfamiliar objects and landscapes. On this basis we propose the amygdala as a locus for a saliency map and ensemble bursting as a saliency coding mechanism.
Highlights
Vision is an active process during which gaze shift to fixate salient locations of the scene
The summary statistics over animals and sessions support the existence of a general mechanism within the amygdala based on the coincidence of bursts across cell ensembles to signal the saliency of targets within a visual scene
The saliency defined by the ensemble bursting appears to be more driven by the goals and experience of the viewers than by low level image features
Summary
Vision is an active process during which gaze shift to fixate salient locations of the scene. The amygdala is in an ideal position to detect visual saliency; it has reciprocal connections with multiple visually responsive areas in the temporal (Desimone and Gross, 1979; Amaral et al, 1992, 2003; Freese and Amaral, 2006) and frontal lobes (Ghashghaei and Barbas, 2002) It is composed by cells with large receptive fields that allow the localization of salient objects outside the foveated area (Rolls et al, 1994) and that show selective responses to faces, facial expressions and gaze direction (Rolls et al, 1994; Gothard et al, 2007; Hoffman et al, 2007; Rutishauser et al, 2011), and to images with inherent or learned emotional significance (Gothard et al, 2007), what permits the amygdala to influence the way in which saliency is dynamically defined by the brain
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