Luminance integration occurs in retinal coordinates during smooth pursuit eye movements

Active vision relies on different forms of eye movements that require the usage of different spatial coordinate systems for successful vision. This is often overlooked in visual psychophysics, when tasks are performed under fixation only, inherently confounding retinal and real-world coordinates. Here we investigated whether the psychophysical principle of luminance integration across time generalizes to smooth pursuit eye movements and in which spatial coordinate system integration operates. In Experiment 1, participants smoothly tracked a moving object, and two brief liminal luminance targets (LTs) were presented with a short interval between them in retinally congruent but incongruent real-world (screen) coordinates. Luminance of the successive LTs was integrated, as reflected in enhanced detectability and perceptual awareness ratings compared to a single LT and to two LTs with an interval exceeding 100 ms. In Experiment 2, we ruled out alternative perceptual accounts through apparent motion and through the percept of a single, spatially extended stimulus. In Experiment 3, we replicated luminance integration in retinal coordinates during smooth-pursuit eye movements but observed no robust evidence for luminance integration operating in real-world coordinates. Our findings confirm the implicit assumption that temporal luminance integration mainly relies on early (e.g., retinal) processes and illustrate the importance of testing alternatives, including active vision, for a full understanding of the principles of visual psychophysics.