Visual saliency response in the superficial and intermediate superior colliculus and the pupil.

The superior colliculus (SC) is a phylogenetically old midbrain structure that plays a central role in vision, attention, and orienting. The SC has visual representations in the superficial-layers (SCs), and sensorimotor representations linked to the control of eye movements and attention in the intermediate-layers (SCi). Cognitive and computational neuroscience postulates the existence of a visual saliency map that guides visual orienting towards the most visually conspicuous stimuli, and a priority map that combines bottom-up saliency and top-down relevance to allow internal processes such as goals and expectations to also guide behavior. We hypothesize that the SCs embodies the role of a bottom-up saliency map while the SCi embodies the combined priority map. To test this hypothesis, we compared SCs and SCi activity in response to task-irrelevant salient stimuli. In addition, we will measure any pupillary response, as our lab recently showed a transient pupil response upon the presentation of salient stimuli or SCi microstimulation. Monkeys viewed a wide-field arrangement of stimuli (210 radially-arranged items spanning ~40-50deg) extending beyond the classic receptive field (RF). The stimuli were oriented color-bars (~0.4x1.2deg) that formed a perceptual "pop-out" array the monkeys had to ignore; i.e., reward was contingent upon maintaining gaze on central fixation. We compared visual representations in SCs and SCi when 1 to 4 salient pop-out stimuli appeared equally spaced within the array. We also compared this to an array of homogenous items with no pop-out. Consistent with our previous study, only SCs neurons showed a reliable preference for the visually salient but goal irrelevant pop-out stimulus. Also, this representation was the same in the presence of 1 to 4 pop-out items. Interestingly, we found larger pupillary responses when a pop-out stimulus was presented than when a homogenous array was presented, and this pop-out differentiation began approximately 350ms after array onset. Meeting abstract presented at VSS 2016