Visual imagery lowers sensitivity to hue-varying, but not to luminance-varying, visual stimuli

Visual sensitivity (d′) is reduced if a subject is instructed to maintain a visual image while the target is presented (the Perky effect; Segal, 1971). This effect, typically .6 d’ units in magnitude for a colored target presented briefly on a uniform white background, is abolished if both target and background are white. (This was found with simple and complex visual images, and with FC and YN signal-detection methods.) It is concluded that visual imagery may lower the sensitivity of a psychophysical chromatic channel, but not that of an achromatic channel.