Brightness changes during book retinoscopy.

Book retinoscopy involves the observation of fundus reflex changes that are said to be related to the reading levels or interpretive levels at which persons are functioning. Recent investigations have shown that increasing the cognitive demand on a person can result in accomodative changes in his eye that increase the luminance of the fundus reflex. Since the ability of observers to distinguish such changes is not known, this experiment was designed to determine the minimum detectable increase in luminance. The experiment involved a 2-alternative forced-choice procedure in which observers were required to indicate during which of 2 designated intervals the reflex from a schematic eye became brighter. The luminance of the reflex had to increase by at least 11% beforeit could be detected. A reduction in the lag of accommodation and dilation of the pupil probably account for the changes observed during book retinoscopy.