This paper provides rating norms for a set of symbols and icons selected from a wide variety of sources. These ratings enable the effects of symbol characteristics on user performance to be systematically investigated, The symbol characteristics that have been quantified are considered to be of central relevance to symbol usability research and include concreteness, complexity, meaningfulness, familiarity,and semantic distance. The interrelationships between each ofthese dimensions is examined and the importance of using normative ratings for experimental research is discussed.

Because icons, signs, and symbols are now widely used to communicate information, it is essential for system designers to know what makes them easy to use and interpret. The authors report a series of studies that examine characteristics considered central to icon usability. After quantifying the properties of icon concreteness, complexity, and discriminability, the authors assessed each property's effects on user performance when user experience, task demands, and presentation context were systematically varied. Findings indicated that the effects of icon concreteness were primarily associated with the initial grasp of meaning, whereas complexity effects were found to persist longer and to be associated with search efficacy. The effects of icon distinctiveness were complex, but distinctiveness was enhanced by using both semantic and visual contrasts. The implications of these findings for interface design are discussed.

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