My mind (or specifically, the high-level part of it) is basically split into separate "external" and "internal" sections or "domains" (however, this is actually somewhat of an oversimplification) that are capable of functioning semi-independently, although one usually tends to be dominant (which one depends on the situation). The "external" domain is generally responsible for interacting with the outside world, and the "internal" domain is generally responsible for "internal monologue", visualization, and planning (although it is possible for them to "switch roles" in certain situations). Each of these domains basically mono-processes within itself. It is sometimes possible for me to focus on two things at once, but the functional specialization of my domains limits this to certain situations, and I more or less prefer to do one thing at a time.