Stimuli were generated using a ViSaGe videographic card (Cambridge Research Systems, Kent, UK) with 14-bit contrast resolution and presented on a Sony Trinitron (GDM 500DIS) monitor (Sony Corporation, Tokyo, Japan) at 120-Hz frame rate and 1024 × 768 spatial resolution. The monitor was gamma corrected using the VSG calibration routine with the OptiCal photometer (Cambridge Research Systems). The spectral emission functions of the red, green, and blue phosphors of the monitor were measured using a Spectra Scan PR-645 spectrophotometer (Photo Research, Inc., Chatsworth, CA, USA). The CIE-1931 chromaticity coordinates of the red, green, and blue phosphors were (x = 0.610, y = 0.333), (x = 0.302, y = 0.591), and (x = 0.153, y = 0.084), respectively. The background was achromatic, with a mean luminance of 51 cd/m2 at the screen center. Stimuli were viewed at a distance of 58 cm in a dimly lit room, with a patch on the nondominant eye (self-reported) for the monocular condition and without it for the binocular condition. Chromatic and achromatic stimuli were controlled independently by lookup tables.