I'm not sure, but I think an anechoic chamber is a different, more deprived, experience. I've been in the one at NPS in Monterey, and it's a very strange experience. No echos, no external sounds, no vibrations, still body temp air, and no light. In a water tank, you still hear the water, feel the edges of the tank, feel the water move when you move your body, etc, right?
I was also in an anechoic chamber a few times years ago. I remember once, I had been working on a robot for the FIRST competition for about 10 hours straight. I was exhausted, so I thought, 'I'll take a nap in the anechoic chamber'. It was probably the only quiet, dark place around.
I couldn't sleep, and lasted only about 20 minutes in the chamber. I didn't have hallucinations, but I did start feeling paranoid and the lack of sensation was (for lack of a better word) intense. I couldn't stand it. Perhaps I would have started hallucinating if I had stayed longer. Sensory deprivation is a truly bizarre experience.
Interesting. That makes me want to try an anechoic chamber :-). However, the flotation tank also has body temp air and water, no light, good soundproofing (I've also always gone in wearing earplugs). It's true that if I were splash inside, I'd probably hear it some, and that if I floated to the side, I'd feel the edge. But when I went floated, I always lay as still as I could for the whole time, which was pretty still. So I don't really see what would make it all that different, other than maybe the fact that you're lying down instead of sitting.
