_{Herbert A. Meyer}

Both in Website development and Web-related research, much effort has recently gone into optimizing the structural properties of information systems (e.g. comparing hypertext structures, developing navigation aides). The dynamic, performance-related aspects of human-computer interaction, however, have been widely neglected (arguably for lack of theory and proper metrics in this emerging field). Where performance aspects are considered (e.g. in Web usability, see Nielsen), the computer's system response time (SRT) is usually regarded as annoying waiting- or idle-time for the user. Thus, the technological doctrine 'The Faster, the Better' is applied almost indiscriminately when designing human-computer systems, assuming an inherent cognitive plausibility of this solution. While our own experimental research in this area supports the view that excessive SRT has detrimental cognitive, emotional and motivational effects, there are also reasons for designing the lower end of the SRT scale, in particular between 0.2 and 2 seconds SRT. Here, the user has been found to adopt the computer's speed and to respond faster himself. This unconscious 'pacing' phenomenon seems to induce an agitated, superficial work style, as indicated by deteriorated performance in a succeeding memory test. So far, this effect was investigated using a large picture database, organised as a 'hyper catalogue'. We believe, however, that the pacing effect applies to many of the fast and interactive Web systems currently emerging, as well as to local applications (DVD, CD-ROM) - each with their own temporal characteristics. Thus, the Time Design approach should be entered into the usability development and evaluation process. To extend our previous findings, we are currently collecting field data on the Web from a popular interactive learning application.