Twelve users with a range of ages between 20 and 70, were assessed for their cognitive capabilities and degree of experience with microwave cooker features and then trialled with two microwaves, one with a dials interface and the other with a buttons interface. The users were provided with a set of tasks to complete with each microwave. It was hypothesised that all users would perform better with the dials model but that the difference in performance between dials and buttons would become more pronounced as age increased. This was found to be the case in comparing the performance from the trials, with the strongest correlation occurring between the users age and the time taken to complete the tasks.@en

Many products today are laden with a host of features which, for the majority of users, remain unused and often obscure the use of the simple features of use for which the product was devised (Norman in The design of everyday things. Basic Books, 2002; Keates and Clarkson in Countering design exclusion - An introduction to inclusive design. Springer, 2004). Since the cognitive capabilities of the marketed target group are largely not affected by age-related impairment, the intellectual demands of such products are frequently high (Rabbitt in Quart J Exp Psychol 46A(3):385-434, 1993). In addition, the age and technology generation of a product user will colour their expectations of the product interface and affect the range of skills they have available (Docampo in Technology generations handling complex User Interfaces. Ph. D. thesis, 2001). This paper addresses the issue of what features of products make them easy or difficult to learn to use, for the wider population as well as the older user, and whether and in what way individual prior experience affect the learning and use of a product design. To achieve the above, the interactions of users of varying ages and capabilities with two different everyday products were recorded in detail as they performed set tasks. Retrospective verbal protocols were then analysed using a category scheme based on an analysis of types of learning and cognition errors. This data was then compared with users' performance on individual detailed experience questionnaires and a number of tests of general and specific cognitive capabilities. The principal finding was that similarity of prior experience to the usage situation was the main determinant of performance, although there was also some evidence for a gradual, age-related capability decline. Users of all ages adopted a means-end or trial and error interaction when faced with unfamiliar elements of the interaction. There was a strong technology generation effect such that older users were reluctant or unable to complete the required tasks for a digital camera.@en

In a earlier experiment we addressed the extent to which prior experience of a product affect its use as measured by the time taken to complete a set of tasks and by an protocol analysis of the number and type of errors made during interactions. An uncontrolled variable from the previous work was that of the degree of experience of relevant interface elements. Metrics of experience were devised to measure this but depended on self report of amount of experience weighted by product, interface and brand similarity. Hence, we have addressed prior experience directly with a training transfer experiment. A preliminary analysis of the data suggests that learning during the training phase occurred quickly overa few trials. Transfertoa second product with identical functionality and interface sequence but different layout and appearance of controls gave rise to a significant (4 minute) increase in time to complete set tasks. A third product with the same functionality but different controls, layout and appearance roughly doubled the times and errors.@en