Ocular and neuronal responses to visual stimuli during free exploration of naturalistic videos in rhesus macaques

Under natural conditions, eyes are free to explore the visual scene, and both transient pupil dilations and saccadic movements can be influenced by the salience of visual stimuli. Despite its significance, these aspects of visual exploration and the related neural correlates remain poorly investigated. Here we tackle this topic by studying the patterns of ocular behavior of a macaque monkey watching a naturalistic video while recording the neuronal activity from three areas of the frontal cortex (Prefrontal, Premotor Dorsal rostral, and Premotor Dorsal caudal). Different scenes were assigned to four different categories of stimuli depending on the occurrence in the video, which included natural scenes, conspecifics, non-conspecific predators, and non-conspecific harmless animals. Analysis of pupillometry revealed greater dilation when the monkey was exposed to conspecifics compared to both natural landscapes and non-conspecifics, with a further increase in size if non-conspecifics were predator animals. The frequency of saccades did not differ significantly between the other categories. Notably, neuronal activity in each brain area was higher for scenes eliciting higher pupil dilatation, suggesting their possible involvement in processing stimulus saliency.