Quote Originally Posted by Wikipedia
The ganzfeld effect (from German for “complete field”) or perceptual deprivation, is a phenomenon of perception caused by exposure to an unstructured, uniform stimulation field.[1]
It has been most studied with vision by staring at an undifferentiated and uniform field of colour. The visual effect is described as the loss of vision as the brain cuts off the unchanging signal from the eyes. The result is "seeing black"[2] - apparent blindness. It can also elicit hallucinatory percepts in many people, in addition to an altered state of consciousness.
The Ganzfeld effect is the result of the brain amplifying neural noise in order to look for the missing visual signals. The noise is interpreted in the higher visual cortex, and gives rise to hallucinations.
The ganzfield effect is caused by a prolonged exposure to sensory deprivation. In the experiment, the subject most commonly wears ping pong balls that have been cut in half over the eyes, and headphones playing white noise. From what I've read, people consistently experience hallucinations ranging from simple HI to complex, dream-like imagery.

I stumbled across this last night while researching vision quests and certain psychedelic cacti. Needless to say, I was pretty interested so I constructed my own sensory deprivation mask out of plain printer paper, cotton and an elastic band. I also wore headphones and listened to a random white noise generator. Here are the results from my experiment:
Time+0.00-0.05: I sat in silent meditation for the first 5 or 6 minutes. I wasn't sure anything would happen, but I tried to reserve my judgement.
Time+0.06-0.07: Time is pretty hard to gauge without the use of sensory input to guide you (or a clock), but after what seemed to be about 6-7 minutes I began to see neon purple and green blobs morphing and swirling within my field of vision, much like hypnagogic imagery. This might work after all!
Time+0.10-0.12: Large chunks of my vision started to 'black out'. Instead of seeing actual blackness, it was like my brain was cutting off the input from my eyes. After a few minutes of this I could see nothing but blackness even though I was staring at a blank white field.
Time+0.15-0.17: Nothing else was going on, so I tried blinking rapidly to see if it would have any effect. It temporarily brought my sight back and I saw the white paper in front of my eyes again, but it quickly faded back to darkness.
After about 20 minutes of this blacked out vision, I decided to give up on the hallucinations and go to sleep.

I plan on trying this again tonight and will post my results if anyone cares to see.
Anyone else have any experience on this? Thoughts?