^^indeed, i agree with everything you've said. but don't get me wrong, i wasn't trying to say that all imaginary friends are actually spirits or real voices, more the reason for my post was to put out the possibility of
some, and the more intriguing cases (where the imaginary friend would appear to be real to others, poltergeist activity, children unexplainedly knowing things they shouldn't/couldn't, etc.) could be explained this way. my teacher was just telling us about the research she had read up on, the research is being done right now.

one thing they're thinking of trying is putting the child and a 'medium' in a room together, and seeing if they're both hearing the same 'voices'. there is of course many exceptions to the losing ability to hear certain sounds thing, there are adults who don't lose this ability at all, some, though over 25, can hear the 'Mosquito', along with the irritated teens

this would also explain why some people are 'mediums', but the vast majority of us are not
of course this is all merely theorizing on something we have yet to fully understand...in the meantime, it's interesting to explore the possibilities.

(lol)