Abstract

We measured sensitivity to sinusoidal modulation of two equally luminant chromatic sources as a function of physical phase difference. The stimuli were presented in a two-channel Maxwellian view system employing red (625-nm) and green (564-nm) LEDs. Radiance was controlled by voltage-to-frequency converters fed by computer-controlled analog multipliers designed to give a linear response up to 1800 cd. The 2.0° stimulus field with a mean luminance of 900 cd was viewed in a dark surround. Using a method of adjustment, threshold modulation was determined for up to forty phases from 0° to 356°, at thirteen frequencies ranging from 1 to 40 Hz. In any given block of trials, frequency was held constant and phase varied from trial to trial. At high (>13-Hz) and low (<2.8-Hz) frequencies the modulation vs phase functions were symmetric ~0°. At intermediate frequencies the point of symmetry occurred at 10-40°, the exact amount differing among the three subjects.

© 1985 Optical Society of America