Why would you choose internal monologue as the default position and no internal monologue needs to be proved?
It seems the natural position for an unknown would be to assume it is not the case unless there is evidence for it.
I'm not sure why this seems like a problem, or why you have to criticize my default position, but my own personal views on the matter aren't important here.
I did get relatively good scores in reading speed back in primary/middle school when we took such tests, so maybe there's an explanation. At the same time, writing/speaking is a very resource-intensive task for me so I tend to be silent a lot (and then drop a pile of sentences on the unsuspecting people I'm with)