Ganzfeld effect

How it works

Ganzfeld is German for “whole field”. A ganzfeld is a visual field with no edges, no detail, and the same colour everywhere¹. A landscape of nothing but white snow makes a natural one. Arctic explorers who see only featureless snow for a long time report hallucinations¹.

The visual system works by comparing. It reports edges and changes. Give it a field with no differences and it has nothing to report. The brain cuts off the unchanging signal from the eyes. One explanation is that it then amplifies its own neural noise while it looks for the missing signal. The visual cortex turns that noise into images¹.

Sight can seem to fade¹. Some people then see simple percepts, such as flashes of light or patches of colour. With more time, some see complex, dream-like scenes¹³. It is related to prisoner’s cinema, the visions people report after long periods in total darkness¹.

In the 1970s the set-up was used in parapsychology experiments that claimed to test telepathy. Those results are disputed, and no consistent, independent replication exists².

How common it is

Nobody has counted this in a general population. A 2008 review says the flat field produces pseudo-hallucinations in most observers, but it gives no percentage³. That is a lab result, not a share of everybody. The reported effects run from simple specks and colours to complex, dream-like scenes³. A real figure would need a large, mixed group of volunteers, all given the same set-up and questions.

Try it

1. Cut a ping-pong ball in half. Tape one half over each eye.
2. Sit facing a lamp with a plain shade. The light should be even and dim.
3. Put on headphones playing white noise or radio static.
4. Keep your eyes open and relax. Do not try to see anything.
5. After some minutes your sight may seem to fade. Then patterns or images may appear.
6. Stop whenever you like. The images usually stop when you remove the coverings.

Is it a problem?

No. A short session is not known to cause lasting change. The images usually stop when you remove the coverings. It is not evidence of psychic ability, despite the history of the set-up in disputed telepathy research². See a doctor first if you have seizures and plan to use a flickering light, since flicker can trigger them.

History and culture

The psychologist Wolfgang Metzger studied the effect in the 1930s¹. Reports go back to ancient times. Followers of Pythagoras went into pitch-black caves to receive wisdom through visions¹.