The "book cover" can tell us something useful. It's the judging that takes a neural toll.
Scientists are finding that stereotypes are not simply stored and retrieved by the brain, but 'are associated with general regions in the brain involved in memory and goal-planning,' [assistant professor of psychology at New York University] Professor Amodio said, suggesting that 'people recruit stereotypes to kind of help them plan a world that’s consistent with the goal they might have.'
... Research [from Susan Fiske, a professor of psychology and neuroscience at Princeton,] suggests that those in low status register differently in the brain. 'The part of the brain that normally activates when you are thinking about people is surprisingly silent when you’re looking at homeless people,' she said. 'It’s kind of a neural dehumanization. Maybe we can’t bear the horrible situation they are in, or we don’t want to get involved, or we’re afraid we might get contaminated.'
But, she said, the neural response is restored when people are asked to focus on what soup the homeless person might like to eat, something that makes one think about the person as someone with wants or goals.