How does the brain process concurrent visual or sensory data? 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?
The tongue is made up of a surface area of about five different types of taste receptor.  They are:


salt
sour
bitter
sweet
unami


These inputs are handled by your gustatory system which can certainly parallel process them.  You may know or have heard of combinations of them.  Sweet n Sour, Sweet and Salty.


  The facial nerve (VII) carries taste sensations from the anterior two
  thirds of the tongue, the glossopharyngeal nerve (IX) carries taste
  sensations from the posterior one third of the tongue while a branch
  of the vagus nerve (X) carries some taste sensations from the back of
  the oral cavity.


From the wiki on the gustatory system

It's more likely that you've just never taste apple and orange at the same time, so you don't have the experience to remember.

But we do have a semantic memory that's specifically focused towards object identification.  This means we put things in little boxes.  You have a box for oranges and a box for apples.  There are neurons in your temporal lobe that Kristoph Koch could find that fire only when you see an apple or even the word apple[1].  There is no such thing as an orpple, so you've never required a box for it.  I don't think imagining it simultaneously is really beyond your imagination though if you worked at it.

(this article is actually somewhat similar idea, competition between two objects in the temporal lobe: here it's pictures of two people)
http://www.klab.caltech.edu/news/Cerf-et-al-10.pdf