Three visual search experiments evaluated the benefits and distracting effects ofusing luminance and flashing to highlight subclasses of symbols coded by shape and color. Each of three general shape/color classes (circular/blue, diamond/red, square/yellow) was divided into three subclasses by presenting the upper half, lower half, or entire symbol. Increasing the luminance of a subclass by a factor of two did not result in a significant improvement in search performance. Flashing a subclass at a rate of 3 Hz resulted in a significantly shorter mean search time (48% improvement). Increasing the luminance of one subclass (by a factor of five) while simultaneously flashing another significantly improved search times by 31 % and 43% respectively, compared with nonhighlighted search conditions. In each experiment, the research times for nonhighlighted target subclasses were not affected by the presence of brighter and flashing targets. The failure of the initial experiment to find a significant performance improvement caused by increasing symbol luminance suggested that a larger luminance increase was necessary for this code to be effective. The overall results suggest that using luminance and flashing to highlight subclasses of
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