So to my understanding our brains can't actually do near anything simultaneously, regardless of what it is we all switch attention between tasks-just very, very quickly. Multitasking doesn't exist in the literal sense. 

There are what are called automatic processes that can appear to be done simultaneously as they require little attention and are what you listed above.


In this case it sounds like because people tend to subvocalise it makes it substantially difficult to both listen and read because it's actually using the same part of the brain to listen and read. It's like listening to two people talk at once, both require the same type of attention.