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Abstract

Fechner described the phenomenon of inducing illusory colors by means of rotating blackand -white disks. The induced spectral illusions were later termed 'Fechner's colors'. Similar color perceptions can be induced by non-rotating stimuli even on computer screens. We performed an experiment to investigate whether a uniform 'Ganzfeld' formed by means of rhythmically generated, unstructured, monochromatic light (i.e. flicker) is sufficient to induce perceptual phenonemoa analogous with Fechner's colors. Ten human observers participated in the experiment, reporting both color and form illusions despite the absence of particular spectral and spatial variations in the 'Ganzfeld'. Moreover, particular illusions were induced reliably at particular frequencies, which may be taken to indicate that visual experience of different qualities may be subserved by mechanisms with different temporal sensitivities. In conclusion, rhythmic visual stimulation is sufficient to induce form-based illusions and illusions analogous with Fechner's colors, while the qualitative nature of those illusions may necessarily depend upon the frequency of stimulation Fechner (1838) described how color perception can be induced by rotating a black-andwhite disk at a certain velocity. This phenomenon was subsequently referred to as the so-called Fechner's colors. Benham (1985) designed a more complex disk which also induced colors when it was rotated (cf. Fig. 1). Collectively, the color perceptions induced by Fechner's or Benham's disk were termed subjective, illusory or flicker colors and have been widely used in psychophysical experiments (Cohen and Gordon, 1949; Festinger et al., 1971; Jarvis, 1977). Recently, Nieke (1986) demonstrated that the inducing black-and-white stimulus does not have to rotate...