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Differences in cellular phones' complexity and their impact on children's performance are under study in this experiment. Twenty children (age 9-14 years) solved tasks on two phones that were simulated according to existing models on a PC with a touch screen, holding constant display size, fonts, and colors. Actions were logged and analyzed regarding execution time, detour steps, and specific errors. Results show that children using the Siemens C35i with 25% higher complexity (with regard to number of required production rules) spent double the time solving tasks and undertook three times as many detour steps as children using the less complex Nokia 3210. A detailed analysis of user actions revealed that the number of production rules to be learned fails to account for most difficulties. Instead, ambiguous naming, poor categorization of functions, and unclear functionality of keys undermined performance. Actual or potential applications of this research include guidelines to improve the usability of all devices with small displays and hierarchical menu structures, such as cellular phones.
INTRODUCTION ]
The number of children possessing cellular phones has increased remarkably within recent years. At least 45% of Germany's 12- to 13-year-olds own such a technical device (CHIP Online, 2003).
The numerous cellular phone models of various brands on the market differ in menu structure as well as number and functionality of keys for navigating through the hierarchical menu. Commonly agreed rules as to which arrangement of functions and keys lead to the best usability have not been defined. Perhaps that is why manufacturers generally allocate few resources to investigating usability issues. Some emphasize "ease and joy of use for complex systems" (e.g., Siemens, as reported in Stanney & Salvendy, 2000), but this may be more of a marketing tool than a focus of research. Even researchers argue that modern phones do not differ much, apart from their shape and color (e.g., Harper, 2001), and the industry may assume that the prevailing small differences in usability of the phones will become less important in the future because of today's children's ability to handle technological Systems easily. Compared with adults, who grew up in a less technological environment, kids are supposed to understand the mode of operation of these devices much faster by virtue of their early contact...