How to Detect the Invisible? Investigating the Role of the Extrageniculate Pathways in the Salience-Based Progression of Attention Using Moving S-Cone Items

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Abstract

Visual attention progresses from the most to the least salient item until a target is found. We explored whether and how the extrageniculate pathways participate in this progression when salience is built on motion signals. Because there is a disynaptic extrageniculate pathway that conveys motion signals to the cortex and because recent studies suggest that motion-related attentional effects rely not on motion per se but on motion-energy (i.e., objectless spatiotemporal changes), we used the S-cone isolation technique to make the search display invisible to the extrageniculate pathways. The search display contained 3 items that moved at different frequencies to assess the hierarchy of salience. It was found that (a) participants were unaware of motion in the S-cone condition but were aware of motion in a control condition. Furthermore, (b) despite the unawareness of motion with S-cone stimulation, a salience-based progression in performance was evidenced and did not differ from the control condition. Overall, conscious perception of motion was not possible in the S-cone condition, and the hierarchical effects observed were independent of any conscious perception of the stimuli that produced them. Salience-based attentional progression can thus occur without awareness of what produces it. Because motion-energy-based nonconscious perception is thought to be mediated by the extrageniculate pathways, we suggest that the observed attentional effects are signs of extrageniculate mediation. The results are also discussed in the light of dominant theories about the establishment and hierarchy of salience.

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