The notion of task in HCI

Introduction The 1S0 definition of the usability of an interface is “the effectiveness, efficiency, and satisfaction with which specified users can achieve specified goals in a particular environment”. This at first seems pessimistic to many people, as it implies that there may be no generalisation across users or machines or tasks: that measuring how one combination performs may not tell us anything about how others will perform. But is it pessimistic enough? It expresses what many HCI workem assume, that just as it is clear what a “user” is (dMirtct users cart be identified by their bodies — if it is the same person then it is the same user), so a task is the same thing to all people in aU circumstances. This paper points out that this is not me, examines the extent to which this may be a problem, and how it thratens standard practices of both psychologists and designers in HCI.