Ganzfeld is a technique developed in the 1930's to study perception in the absence of visual stimuli. The simplest and most common apparatus used in these experiments, itself known as the ganzfeld, is half a ping pong ball taped over the subject's eye, reducing all illumination to a uniform, textureless field. More involved ganzfeld experiments can make use of further sensory deprivation techniques, such as headphones playing white noise, but it is only the visual component which is properly called "ganzfeld".

Beyond academia, "ganzfeld" commonly refers to two things: parapsychologist Charles Honorton's "Ganzfeld Experiment" technique, in which sensory deprivation is a key element in testing for telepathy; and the host of commercially-available "ganzfeld devices" promoted as aids to meditation. Both rely on the so-called "ganzfeld effect", by which visual deprivation is said to induce transcendent or hallucinatory states of mind.

Suggested reading on use of the ganzfeld: R. N. Haber & M. Hershenson, The Psychology of Visual Perception, 1968 (1st ed).