Successive contrast involving luminance and purity alterations of the Ganzfeld.

Abstract

Os were adapted to a homogeneous visual field by projecting red light (dominant wavelength 648 m/i, luminance .30 ft-L) onto a translucent eye cap. Following chromatic adaptation, homogeneous postadapting fields differing in luminance and/or colorimetric purity were introduced, producing successive contrast. Using an adapting red of purity 1.00 8 of 10 Os adapted chromatically. With an adapting red of purity .50 6 of the 10 Os adapted. For either adapting stimulus, postadapting fields equal to or greater than the colorimetric purity of the red adapting field were perceived as red. Postadapting fields of purity less than that of the adapting field were perceived as complementary blue-green. The luminance of the postadapting field had little effect upon hue. Thus the importance generally attached to luminance parameters in producing chromatic afterimages is not supported.

Vision in the Ganzfeld.

“…The most recent study conducted under empty field conditions (Weintraub, 1964) produced results apparently conflicting with the well-established principle of color conversion (Helson, 1938). Helson's statement of this principle is that in every viewing situation an adaptation level (AL) is established such that objects having reflectances above the AL will be tinged with the hue of the illuminant, objects having reflectances below the AL will be tinged with the hue of the afterimage complement of the illuminant, and objects having reflectances at or near the AL will be either achromatic or weakly saturated and of uncertain hue.…”

“…He maintained that any change in the stimulus distribution that modifies one aspect of experience produces concomitant changes in other phenomenal characteristics of the Ganzfeld. The most recent study of the Ganzfeld (Weintraub, 1964) indicates that Cohen's conclusion is incorrect, and that intensity of stimulation and the colorimetric purity of the Ganzfeld are independent dimensions. Weintraub's results appear to disagree with the well-established principle of color conversion (Helson, 1938), certainly with regard to the chromatic effect of brightness variation.…”

“…Hochberg, Triebel, and Seaman's use of halved table-tennis balls to produce homogeneous stimulation deserves notice. Other investigators have used this technique (e.g., Weintraub, 1964). It is highly likely that this technique produces a different field from that produced by a larger stimulus field at a greater distance from the eyes.…”

Detailed Analyses of Ganzfeld Phenomena as Perceptual Events in Stimulus-Reductive Situations

“…A second event is the desaturation or fade of chromatic visual field that was reported in previous studies (e.g., Cohen, 1958;Hochberg, Triebel, & Seaman, 1951;Weintraub, 1964).…”