The eye's mind
We often think of the eyes as cameras that faithfully capture the world, but this is a misleading metaphor: the eyes do not simply receive the external world—like the brain of which they are an extension, they anticipate it, shaped by what we expect and value. How far does this influence reach? Can what we think, want, or aim actually shape the earliest stages of what we see? In this dissertation, I argue for sensory tuning: the idea that cognition reaches down into the very earliest stages of sensation, optimizing sensory intake based on the demands of the current situation and the immediate future.I first show that attention not only determines what we select in the visual world, but also shapes how visual information is taken in, by dynamically modulating pupil size. I then demonstrate that these attentional effects on pupil size arise specifically from image-forming visual pathways, rather than from non-image-forming visual pathways. Next, I show that attention continues to influence pupil size even when visual stimuli are no longer perceived, indicating that sensory tuning operates both with and without subjective perception. Pushing this idea further, I provide evidence that attention-related influences may extend as far as the retina itself, as reflected in changes in retinal signals, although the precise mechanisms underlying these effects remain unresolved. Finally, I argue that cognitively driven changes in pupil size serve a functional role, helping the visual system balance competing demands such as sensitivity, resolution, and readiness for action, and I integrate these findings into a broader framework that situates sensory tuning as a unifying principle linking cognition and sensation.