I tried thinking about an apple and simultaneously an orange. (I was thinking about its appearance and taste). Despite my best efforts I was not able to do parallel processing to think about the apple and orange at the same time. What I was doing was concurrent processing, thinking about Apple and orange in time division multiplexing.
I noticed that my brain (which is also responsible for thinking) was indeed able to manage my two hands simultaneously, and was able to help me understand sounds comings from multiple sources, so it was helping me to see many things at the same time, in parallel, not concurrently.
I have asked a similar question here which compares processing by the brain with parallel processing by computers.
How exactly we explain these differences of operation by brain in dealing with sensory data (for example touch which can be felt in parallel), and thinking or visualization?