 When you look at a landscape and shift your attention from the tree on the left to the mountain range on the right, this implies a change in the determinacy of the perceptually attributed properties: the properties attributed to the tree will be less determinate than before and the properties attributed to the mountain range will be more determinate than before (Yeshurun and Carrasco 1998). Let’s focus on the change in determinacy in the latter case: the extra determinacy of the perceptually attributed properties comes from the sensory input: perceptual attention increases determinacy by means of extracting more information from the sensory input. In the case of mental imagery, in contrast, there is no sensory input to exploit, so when you close your eyes and imagine the same landscape with the tree on the left and the mountain range on the right and you shift your attention from the former to the latter, then the increased determinacy of the properties attributed to the mountain range can’t come from the sensory input. It must come from a top-down source – your beliefs or expectations or memories about mountain ranges (Nanay 2015).