Readily visible changes in color contrast are insufficient to stimulate accommodation.

In an earlier study (Wolfe & Owens, 1981) it was reported that humans could not accommodate to an insoluminant red-green border. However, recent masking studies (Switkes, Bradley & DeValois, 1988) have shown that, using an appropriately normalized contrast metric, contrast decrements similar to those produced by defocus are equally visible for color or luminance modulated grating patterns. We have compared accommodative responses to 1.75 c/deg gratings that consisted of either isochromatic luminance modulations or isoluminant red-green color modulations. All four observers could accommodate accurately to luminance modulated gratings over a wide range of contrasts. However, no appropriate accommodative responses were obtained even for the highest contrast color modulated gratings. These results show the changes in color contrast are ineffective as stimuli for the human accommodative response even when the changes in chromatic contrast accompanying defocus are readily perceived.