I’ve just found this fantastic auditory illusion after browsing through Tom’s blog. It’s a YouTube video but the visuals are just text, all you need to do is listen and replay.
It’s like the audio equivalent of a moving spiral. It always seems to be moving up but you realise after a while it can’t possibly be going anywhere. It’s remarkably compelling though.
I’m afraid I don’t know much about how it works, but I suspect it’s a form of Shepard tone.
The Shepard tone link above is a Wikipedia page, and if you scroll down through the page there’s a nice example of a continuous tone which seems to have the same effect.
The article also mentions that the effect has been used in the Muse song ‘Ruled by Secrecy’.
Link to rising tone illusion (via Idiolect).
Link to Wikipedia page on the Shepard tone.
Mind Hacks 
(Note the correct spelling: “Shepard”)
I think it would be called a Shepard scale, since it’s not one single tone, but it’s the same effect. Upper octaves fade out and lower octaves fade in, and we hear them as fused into single tones because they’re at harmonic (1:2) ratios. I usually compare it to an old spinning barbershop pole when I describe it.
Incidentally, some give composer James Tenney more credit for it than Roger Shepard, but I only heard that from a student of Tenney’s. His composition “For Ann (Rising)” is beautiful; it uses a Shepard tone.
JM
Hi JM, thanks for the correction. Now fixed! And thanks for suggesting the track, I shall try and track it down, it sounds great.