Does pupil size track high-level attention?

Higher-level cognitive processes like attention, memory, or mental imagery can produce pupil responses, without any actual difference in luminance of the visual stimulus.Interestingly, the inverse scenario remained untested to date: when a physical luminance difference is perceptually eliminated from awareness, does pupil size still track attention to the stimulus?In this Registered Report, Vilotijevi and Matht (2024) sought to test this experimentally using a perceptual fading phenomenon where two Gaussian patches with different luminances fade from consciousness and are thus perceived as mid-level uniform grey (or at least the subjective difference is much reduced).This fading manipulation, as well as a control condition without perceptual fading, were presented in separate blocks.Participants were instructed to covertly attend one of the patches.