The role of the collicular pathway in the salience-based progression of visual attention

Visual attention has been shown to progress from the most to the least salient item in a given scene. Cognitive and physiological models assume that this orienting of covert attention relies on the collicular pathway, involving the superior colliculus and the pulvinar. Recent studies questioned this statement as they described attentional capture by visual items invisible to the superior colliculus. Electrophysiological studies shown that there is no direct projections from short-wave receptors to the superior colliculus. S-cone stimuli can thus be employed to assess visual processing without the involvement of the collicular pathway. We have attempted to investigate whether this pathway is involved in the salience-based orientation of attention by presenting S-cone stimuli. Volunteers were asked to make a judgment regarding a target among two distractors (all items of unequal sizes). Items' location and size varied randomly, as well as color, randomly black or calibrated for each subject to activate exclusively S-cones. The hierarchical pattern testifying of the salience-based orientation of attention was only found with black stimuli, arguing in favor of an implication of the collicular pathway in salience. In a second experiment, one item was presented at a time in order to test the item-multiplicity effect by comparing experiments. Performance was the most penalized when presenting multiple stimuli in the black condition. Results were interpreted in terms of distinct modes of processing by the collicular and geniculate pathways. The establishment of salience that determines attentional progression appeared to be only possible when the collicular pathway was solicited.