I think the unique part of this, which may have an effect, is that it's selectively blocking ambient noise, and it's meant to be worn during conversation.
I can't think of anyone today who wears noise-cancelling headphones while trying to hear noise from outside the headphones. Everyone I know takes their headphones off to communicate or listen to specific sounds outside the headset.
Who knows, but my point is that there are two slightly different tests here. We already know that wearing noise-cancelling headphones to block _all_ sound doesn't affect our hearing when they're off. It remains to be seen whether using them to filter some sound effects our ability to filter some sound without them.
