The Psychology of Music by Diana Deutsch.
I think this can apply to game design.  One of the things I think is fascinating is how, in Super Mario Bros., the music in World 1-1 is designed to help you figure out what you're supposed to do.  Kondo made it so jump on the high note, land on the down note, and catch the mushroom on the flourish.  This is both an act that makes the player happy because the visual, aural, and tactile senses have all just worked together to achieve a goal, but it teaches people who have never played a video game how to play without them ever realizing it.
I'm trying to figure out a way if that's possible in today's game design.  If those sweeping John Williams-like scores can actually be used to lead the player.  So this book is helping me understand music theory as it pertains to what music makes people feel.