In my opinion the most bizarre illusion Professor Deutsch discovered is the "octave illusion".

Be sure to use headphones and prepare to be surprised!

http://philomel.com/musical_illusions/example_octave_illusio...

The mechanisms that give rise to the illusion are not well understood, but it seems to have something to do with hemispheric asymmetry. Individual differences in how the illusion is heard often correlate with handedness (ie whether you're left or right-handed)

I'll forever have the phrase "sometimes behaves so strangely" stuck in my head --

Radiolab interviewed Diana Deutsch on her research a few years back, and it's one of my favorite episodes.

http://www.wnyc.org/shows/radiolab/episodes/2006/04/21/segme...

Hmmm. I pasted the RadioLab link in my description (I just listened to it yesterday) but I guess it didn't show. RadioLab is great! I'm just getting into it and I have 4 years of episodes to catch up on!

This reminds me of Shepard Tones: http://en.wikipedia.org/wiki/Shepard_tone