Ganzfeld

Definition

A ganzfeld (a German word for “whole field”) is obtained when an observer is exposed to an absolutely homogeneous stimulation that covers the entire visual field. Any particular wavelength or intensity can produce the same effect.

History

The ganzfeld was first introduced in 1930 [1], by German Gestalt psychologist Wolfgang Metzger (1899–1979). Metzger was interested in elementary visual phenomena produced by impoverished visual conditions. The ganzfeld contains no luminance border, luminance ramp, or texture, while the light reaching the eyes is equal from all possible directions. Such conditions, called whiteout, can occur naturally during a snowstorm or in an airplane flying through clouds.

Perceptual Experience in the Ganzfeld

The typical visual phenomenology, for a person of normal sight, includes the emergence of “Eigengrau” [2], a uniform gray fog of indeterminate depth. This percept occurs regardless of the physical intensity and wavelength of the ganzfeld. Any color in a ganzfeld will eventually fade to filmy gray. The experience of a bright ganzfeld differs from that of a completely dark ganzfeld. Total darkness implies a lack of visual objects and is somewhat less disorienting. However, disorientation in a bright ganzfeld is fast and compelling.

From the beginning, the observer is unable to fixate any part of the field and becomes conscious of the vitreous opacities and blood vessels within the eye. Perceived luminance gradually decreases, the whole filed slowly decolorizes, turning into a gray fog. This fog sometimes has a barely noticeable washed-out tone complementary to its actual color [3].

Prolonged exposure to a ganzfeld results in more complex percepts. Occasionally even patterns (dots, lines) are reported. Because hallucinations have been reported in extreme cases, the method has been used outside of vision science. Sometimes prolonged exposure (10–20 min) leads to intermittent losses of vision (so-called “blank-out”) and sometimes participants cannot even report if their eyes are open or closed [3].

In traditional studies, phenomenological reports were obtained from observers trained in providing such introspective reports “post hoc” from memory [3]. The extent of this introspection is debatable, especially in the case of complex visual experience. This constitutes a problem for a phenomenon that might involve disorientation and consciousness-altering states. Alternative methods include “on-demand” reports either elicited by the experimenter or volunteered by the observer. This allows a random sample of momentarily experienced states with no involvement of memory [3]. Unfortunately, some of the same criticisms are applicable here, too. This method also requires training in introspection.

Producing an Experimental Ganzfeld

Although a primitive ganzfeld can be achieved by placing a person in complete darkness, creating a proper ganzfeld of the desired brightness is not a trivial challenge.

In the 1930s, observers were placed in front of either a smooth, homogeneous wall (Fig. 1a) or a large sheet of paper [1, 3]. A simple way to create a ganzfeld is to cover each eye with a section of a table tennis ball (Fig. 1c) [3]. These need to be trimmed to fit the shape of the face surrounding the eye, leaving no extra gaps for illumination to leak in, and they can be attached to the face using cosmetic cement. Industrial production does not guarantee an utterly uniform thickness of the plastic, but this is not a problem because the surface is too close to the eye for focus. Another option is placing the head inside a large hemisphere, which is uniformly illuminated from outside (Fig. 1b). A somewhat better solution is the use of translucent contact lenses. This method provides a high degree of homogeneity.

Ganzfeld, Fig. 1

Traditional spatial arrangements of Ganzfeld [3]. (a) Observer in Metzger’s experiments was placed in front of a uniform wall lit from behind. (b) Domes lit from outside. (c) Lenses or table tennis balls placed in front of the eyes functioning as light diffusers

More modern studies tend to use “computer-controlled xenon lamp-based D-ILA projector” creating (usually red) ganzfeld [3, p. 1366].

Finally, any change in luminance or color, including blinking, restores perception. Given that the ganzfeld effect can be achieved fast, this is not necessarily a problem. If prolonged viewing is required, the eyelids can be taped open to prevent blinking, but the eyeballs need to be kept moist. This is easily achieved if the eye is completely covered by the table tennis ball section, as described.

Theoretical Importance

The ganzfeld demonstrates that our senses in general (vision in particular) function to detect change. Invariant stimulation does not produce a sensory response. Framed in Gestalt terminology, an unstructured physical field cannot produce perception due to the lack of perceptual organization.

Observable Characteristics

Brightness. The full ganzfeld phenomenon is achieved on average after 5–7 min [4]. During that time, with no change in stimulation, perceived brightness slowly decreases until it reaches the final value.

If the luminance in a ganzfeld is subjected to subliminal changes over time and space, observers can still detect the correct direction of change [5]. For a completely homogenous ganzfeld (9.1 footlambert), changing 1000-fold per hour at a constant rate, observers detected the direction after 9.7 min.

Wavelength [6]. Although the ganzfeld produces an achromatic, dark gray percept, irrespective of original conditions, the initial wavelength still dictates some characteristics. Longer wavelengths fade faster than short wavelengths. Shorter wavelengths create an additional sensation of field darkening.

Monocular versus binocular ganzfeld. It has been shown that a ganzfeld presented binocularly (i.e., viewed with two eyes) does not show a loss of visual perception (so-called “blank-out”) typical for monocular viewing [7]. However, recent findings show that a gradual loss of brightness and saturation (so-called “fade-out”) is measurable both for monocular and binocular ganzfeld. Fade-out is however determined by the original field intensity and wavelength [8].

Sex differences [9]. Female observers are more responsive to longer wavelengths. They also preserve visual sensation shorter and report a fewer “blank-out” effects than male observers.

Explanation

The patterns that appear during the short ganzfeld exposures, such as zigzag lines or dot fields, are usually explained by early retinal processes [3]. Receptive and other retinal cells exhibit spontaneous activity, oversaturation, and inhibitory reactions. Prolonged exposure elicits complex percepts, which presumably involves the central nervous system. The loss of vision is probably the consequence of brain discarding uninformative visual input about invariant stimulation.

There is a correlation between “blank-outs” and alpha activity in the resting EEG [10]. Alpha activity (8–12 Hz) is otherwise typical for relaxed states with no stimulation and closed eyes.

Related Phenomena

Aftereffects. If the ganzfeld is induced by yellow table tennis balls, after their removal the world will tend to look bluish, due to chromatic adaptation. Also during the initial bleaching of the original ganzfeld color, sometimes the percept does not remain neutral but adopts a pale complementary color.

Artificial scotomata. Eye movements can be counterfeited by fixating a large portion of the visual field to stimulate an identical part of the retina. This leads to “fade-out” and loss of percept within seconds. To maintain normal perception, a constant change of stimulation is necessary and this is achieved by eye movements. The absence of eye movements in large areas of the visual field, known as artificial scotomata, leads to perceptual filling in, creating large uniform surfaces.

Sensory deprivation. Although the ganzfeld is exceptionally impoverished stimulation, the phenomenon represents perceptual but not sensory deprivation. In the former case, we have simply unstructured stimulation, while in the latter, stimulus’ intensity is extremely reduced.

Dark field vision. When observers are placed in total darkness in a relaxed state, with the eyes closed, they often report the appearance of phosphenes, believed to be the consequence of spontaneous firing of the cells [3]. Phosphenes are similar to the percepts in the early stages of ganzfeld exposures.