According to a New York Magazine interview with psychologist Daniel Willingham, two processes take place when you read a book. One is decoding, where your brain translates letters on a page into words that have meaning, and the other is language processing, where you figure out what the words mean together in the context of the story. When it comes to language processing, the mental processes between reading and listening are identical: a 1985 study found that if you read books well, you also listen to them well, and vice versa, and a 1977 study found that college students were able to summarize a story equally well after reading it as after listening to it.

Decoding, for its part, is unique to reading. But this doesn't really matter, since after you've passed a certain reading level—around late elementary school or so—decoding becomes second nature and doesn't require any extra mental power.