Laser-Induced Chromatic Adaptation

Detecting a target in a visually noisy back-ground depends on the ability of the observer to discriminate the target from the surrounding terrain. Visible laser irradiation at less than damage levels may act as a masking source by reducing the observer's ability to resolve differences in the visual scene. The experiment reported here specifically investigates the comparability of shuttered CW and Q-switched visible lasers to alter/degrade color discrimination. Visual evoked potentials (VEP's) were used to examine the short time course effects in monkeys of luminance-matched flashes from a 694 nm ruby Q-switched laser and 100 ms shuttered krypton CW laser (676, 568, and 531 nm lines). The test stimulus was a shifting pattern of alternating luminance-matched 510 and 550 nm green bars. With flashes equated to 4.8 log T-s, similar flash effect curves were seen, demonstrating 1.5-s changes in response magnitude. This level of flash did not extinguish the response to the stimulus. The flash effects curve was ''W''-shaped, with an intermediate signal peak occurring at approximately 500 ms after the flash and whose level exceeded the baseline magnitude. The hypothesized mechanism for this result is an induced luminance imbalance caused by a transient shift in the peak color responsiveness of the visual system, which recovers with two different time constants. It is concluded that red and green colored laser flashes shift the color balance transiently in the visual system (yellow flashes to a lesser extent); thus, targets may change both hue and brightness after an observer receives colored flashes.