I'd like to see a study, too. Unfortunately, I don't know of any.
I do, however, vaguely recall an ergonomic study finding that it's easier (or at least faster) for humans to read text in variable-width fonts. I'll try to find a reference when I get off work.
That being said, code isn't the same as text. My own experience has been that a missing or wrong character is easier to notice with a fixed-width font (especially narrow characters), and that extraneous or missing spaces are less obvious. Where those things don't matter too much for human readers, they do matter for computer readers. It's obvious to a human that BubleSort is probably supposed to be BubbleSort, but in a more formal setting there is a distinction.
I do, however, vaguely recall an ergonomic study finding that it's easier (or at least faster) for humans to read text in variable-width fonts. I'll try to find a reference when I get off work.
That being said, code isn't the same as text. My own experience has been that a missing or wrong character is easier to notice with a fixed-width font (especially narrow characters), and that extraneous or missing spaces are less obvious. Where those things don't matter too much for human readers, they do matter for computer readers. It's obvious to a human that BubleSort is probably supposed to be BubbleSort, but in a more formal setting there is a distinction.