In the 1930s, research by psychologist
Wolfgang Metzger established that when subjects gazed into a featureless field of vision they consistently
hallucinated and their
electroencephalograms changed. The ganzfeld effect has been reported since ancient times. The adepts of
Pythagoras retreated to pitch-black caves to receive wisdom through their visions, known as the
prisoner's cinema. Miners trapped by accidents in mines frequently reported hallucinations, visions and seeing ghosts when they were in the pitch dark for days. Arctic explorers seeing nothing but featureless landscape of white snow for a long time also reported hallucinations and an altered state of mind. ==See also==