tions to at least 6/6 binocular acuity. All participants are published psychophysicists and highly experienced ob-servers, with prior work in the psychophysics of ''white''and ''colored'' (spectrally nonuniform) spatial noise. Three of the observers were also authors of this study; oneadditional observer (SF) was naı ¨ve to the purpose of the experiment. 2. Apparatus All stimuli were generated and presented on a Silicon Graphics O2 at 30 Hz. The lookup table was modiﬁed tolinearize the display. All stimuli were viewed binocu-larly with natural pupils in a well-lit room (the luminanceof a diffuse reﬂector in the plane of the monitor was 3. 5cd/m 2). Subjects were comfortably ﬁxed in place by a chin rest at a viewing distance of 40 cm from the monitor. 3. Stimuli The stimuli were 70 spatiotemporal, gray-scale, random-phase fractal-like image sequences. For each stimulusimage, the average luminance was constant at 8. 57 cd/m 2 Fig. 1. Appearance map of CIE 1931 color space. Reproduced from Ref. 22 by permission of the Optical Society of America. Billock et al. Vol. 18, No. 10/October 2001/J. Opt. Soc. Am. A 2405