Not quite typing, still insightful. A video from the original paper the article refers to: https://static-content.springer.com/esm/art%3A10.1038%2Fs414...

That's a really cool video, is interesting to experience how much my vision tries to reject the extra finger. Is hard to explain exactly, but every time the hand is held in a way that hides fingers, then my brain goes back to predicting it as a standard hand, then pops back to six digits again when all fingers are visible.