[DTK QUALITY INSPECTED S" EXECUTIVE SUMMARY

The increase in the complexity of computer-based graphical information systems has resulted in a requirement for large symbol sets. To ensure that decisions are made with speed and accuracy, it is important for the symbols in such systems to be discriminated consistently and reliably. Studies on symbol discrimination usually find that discrimination is a function of the number and kinds of dimensions along which the symbols vary. However, the critical dimensions often vary from study to study. Some of this variability could be due to the wide range of conditions and methodologies used across studies. If this is the case, it is important to understand how different conditions and tasks influence the perceptibility and discriminability of symbols. The study reported in this paper addressed this problem. It compared the characteristics used in assessing the similarities of a set of symbols in a rating task with those used in picking out symbols in a visual search task. The former task is similar to the process used by a designer in selecting symbols while the latter is an important component of the actual tasks that an user carries out in locating information o