Edinburgh Napier University

  Usability is widely recognised to be as important as functionality to the success of interactive computer systems. However, even where usability is considered seriously, the scope of thinking tends to be restricted to the so called 'average' users in typical office situations. Our aim in this chapter is to summarize some of the key findings in the literature on individual differences, exploring their implications for human-computer interaction. A framework comprising the characteristics of accessibility, usability and acceptability is presented to relate the salient factors to existing Human-Computer Interaction concepts. In doing this, the notion of 'user' is elaborated to reveal a much more complex and changing phenomenon than naive novice/expert or frequent/intermittent classifications suggest. In particular, we argue that we are all 'extra-ordinary users' when considered over time, though the term 'extra-ordinary users' is usually applied to disabled people (Edwards, 1994). We believe that the goal of User Interfaces for All is a timely and challenging concept which raises awareness of the inadvertent exclusion that too often results from nomothetic analysis and design. This chapter outlines a number of approaches that designers can take to accommodate individual differences, drawing on current research to illustrate some of the most promising directions being explored.