I think most of our senses are highly 'customized' by training (with the possible exception of taste, gnarf*).
That means your brain does a lot of filtering/processing, and can totally interfere with your experience/objectivity. Taking a break from the activity is usually the easiest (and legal) way to 'reset' this process. You should also keep in mind that the longer the sessions, the longer the time-out should be.
I don't think there's any magical quick fix, short of debilitating drugs or electro-shocks. These also reset your brain to a certain extent, but rather bluntly, and can influence more than you bargained for.
* (as in: babies probably ALL think bitter is yuck, until you *maybe* get accustomed to it)