Your internal model has some general idea that you’re in a coffee shop, that there are people to your left, a wall to your right, and that there are several items on the table. When your partner asks, “How many lumps of sugar are left?” your attentional systems interrogate the details of the bowl, assimilating new data into your internal model. Even though the sugar bowl has been in your visual field the entire time, there was no real detail there for your brain. It needed to do extra work to fill in the finer points of the picture.
