Our choir often practises in sections e.g. the sopranos sing their bit while the rest of us wait their turn. I discovered by accident that as I look at any particular singer, I can very clearly hear their individual voice, even if they are quite quiet and there's a dozen singers. I cannot do it if I don't look at them.
Does this phenomenon have a name? Is it common and why does it work this way? How can I expand on this useful skill?