Do capable harmony singers sing in just intonation or tempered tuning?
Given that the human voice is capable of microtonal adjustments to an infinite degree and not limited by the fixed tuning imparted upon an instrument such as a piano - I am wondering if singers who harmonize with the lead vocalist subconsciously adapt and instead of singing a equal tempered third or fifth actually sing something closer to a justly intoned harmonically natural interval. If this does occur, it might help explain why some singers sound so incredible harmonizing together. I have been privileged to hear some performances where the vocal harmonies actually gave me shivers up and down my spine and seemed to touch my soul with their sensual richness. **Have there been any studies (or is there compelling evidence) which attempt to ascertain if trained and capable singers who sing harmony - instinctively gravitate towards pure intonation verses singing the notes they have learned to associate with equal temperament tuned instruments?** In other words if they are singing a fifth above, would the instinctive control center of their brain override their musical training and adaptation and lead them towards singing a perfect natural fifth or would they sing something closer to a equal tempered fifth that a piano would play?