I don't know about this. I mean, to me, the letters 'l' and 'y', and 'r' and 'n' have a very obvious difference. There is another such audio illusion where the word 'oil' sounds the same forwards and backwards, both ways effectively sounding 'oyo'. This is due to the position of the letter 'l' and the sort of elision that happens. However with the laurel thing, I can't imagine it sounding yanny. I could mistake it for wallow but it takes a lot of adjustment to hear yanny. May be I just belong to that 45% or so that always hear laurel.