Saliency and Priority Representation in the Superior Colliculus

Abstract

Animals must combine sensory information about the external world with internal goals and expectations to produce appropriate actions. Saliency maps, indicating areas that stand out from their surroundings, and priority maps, which combine saliency and behavioural relevance information (i.e. internal goals and expectations), are believed to guide visual attention. In this thesis, we looked at how these signals are represented in the midbrain superior colliculus (SC) and reflected in the pupil. In the first study, we investigated how salient, goal-irrelevant visual stimuli were represented in the SC and how that representation was affected by increasing the number of salient stimuli. We recorded neural activity from the SC while monkeys were shown a homogenous array of visual stimuli with 0, 1, 2, or 4 goal-irrelevant oddball stimuli embedded in the array that were a different color and orientation. SC neurons encoded the locations of the salient oddballs, but increasing the number of oddballs had minimal effect. In the second study, we examined priority representation in the SC by giving salient oddballs behavioural relevance and reward information. SC activity was recorded while monkeys were shown an array similar to the first study, but now, the monkeys must make an eye movement to one of the oddballs to receive a reward. The colour of the oddball indicated expected reward magnitude. We demonstrated how a priority signal evolved in the SC throughout the trial to correctly guide behaviour. In the final study, we used the pupil data recorded in the previous two studies to explore how saliency and priority influenced pupil size. Increasing the number of stimuli produced pupil constriction, while increasing reward magnitude produced pupil dilation. Combined with the SC activity patterns observed, these results suggest that how much of the SC is activated is correlated with pupil constriction while the strength of the activation was related to pupil dilation. Together, these studies provide an account of how saliency and priority information in a structured but cluttered scene is represented in the SC, and how these signals may influence pupil size. These data will be important to improve models of visuomotor orienting.