I often hear how using how using less mainstream and more difficult to learn (as in requires some mind warping if coming from more mainstream language) languages acts as a filter that will leave more capable programmers to choose from, even if there are less of them.

Does anyone know if there have been studies to back this up? Or studies that back up the above comment.

My experience is that programmers who enjoy warping their minds with something different tend to be more capable, or at the very least, up for a challenge. Would be nice to see something else than anecdotes.