C. Stephanidis (Ed.): Universal Access in HCI, Part II, HCII 2011, LNCS 6766, pp. 131���139, 2011. �� Springer-Verlag Berlin Heidelberg 2011 Older User Errors in Handheld Touchscreen Devices: To What Extent Is Prediction Possible? Michael Bradley1,2, Patrick Langdon1, and P. John Clarkson1 1 Engineering Design Centre, Department of Engineering, University of Cambridge, Trumpington Street, Cambridge. CB2 1PZ United Kingdom 2 Product Design and Engineering Department, School of Engineering and Information Sciences, Middlesex University, Snakes Lane, London. N14 4YZ United Kingdom {mdb54,pml24,pjc10}@eng.cam.ac.uk Abstract. Touchscreen technology has been shown to offer advantages to older and novice users of digital products, through the relative ease of learning the in- teraction mechanisms and flexibility of the interface to provide explicit and contextual labelling enabling task sequences to be executed. Interaction prob- lems caused by age related changes in sensory perception, cognition and motor skills are able to be predicted using the Inclusive Design Toolkit, however this technique is unable to predict usage problems caused by lack of prior experience of digital interaction patterns. This paper reports on the ���errors��� that older users made in a pilot study using a tablet touchscreen device in the course of completing tasks such as turning the device on, setting an alarm and sending an email. An initial classification of the problems encountered by the users is made and the potential for prediction of such errors is discussed. Keywords: Touchscreen, errors, older users, usability, prior experience. 1 Introduction People who do not engage in the digital world, the digitally excluded, are more likely to be older, female and from a lower socio economic and educational background grouping [1]. Older users are likely to exhibit perceptual, sensory and motor skill degradations which will affect their interactions with technology devices, and in par- ticular technology devices which are new to them, and/or exhibit unfamiliar interac- tion styles [2]. Differing generations also will have experienced differing interface styles during their impressionable younger years, and this can have an impact on interface expectations and expertise [3]. The proportion of the UK population who are unable to achieve certain interactions due to degradation of perceptual, sensory and motor skill performance can currently be estimated using the Inclusive Design Toolkit���s exclusion calculator, by comparison of task difficulty to data collected by the ONS database [4]. For example, the exclu- sion calculator allows for the effects of a small sized font used on a display to be estimated in terms of the proportion of the population who will be unable to use it due to both age and disability related visual impairment. The calculator is able to predict

132 M. Bradley, P. Langdon, and P.J. Clarkson the proportion of the UK adult population excluded through the visual, hearing, think- ing, dexterity, reach & stretch and locomotion demands of the product. However, it does not take into account the prior technology experience of the users and their consequent expectations and familiarity with the wide variety of digital interaction patterns [5], nor of their fluidity of intelligence which affects their ability to accom- modate to new ways of operating a device [6]. The fragility of learning of newly acquired declarative and procedural knowledge is also not addressed in the calculator. These effects have a very strong impact on the success or otherwise of the interactions that these users have with products with digital interfaces. 1.1 Background Some digitally excluded people complain that technology is not for them, and hence that they don���t want to engage with digital technology [1]. It is hypothesised that for people who don���t have much digital ���prior experience���, this perception is at least partially true: they do not have the pre-requisites to engage with interfaces that are almost always primarily designed for people with a reasonable level of digital tech- nology knowledge. If a legitimate interaction design aim is to make digital technology accessible to people without the digital technology prior experience, it is important to understand their experiences with current technology interfaces, to see where the lack of knowledge and/or training hinders their goal achievement. In studies with older low technology literate people using digital technology, the usual user performance measures such as time to task completion are not as important as the ability for the user to be able to make error-free progress to their goal achieve- ment [7]. Error making can reinforce the negative feelings of confusion and stress, and frequently put the device into a state from which the user is unable to recover. Slow steady progress without error making is therefore preferable to quick error prone interactions which might be preferable for other user groups who are able to learn and recover from the erroneous steps more swiftly. 1.2 Errors A major stumbling block for unfamiliar users using digital technology interfaces is when ���errors��� are made, and the difficulty of recovering from them. These ���errors��� are not the same category of error necessarily as those made by a user who is familiar with an interface or a task, who merely makes a slip in execution of a command. These ���errors��� are perhaps closer in nature to those made during the process of ���trial and error��� providing information to the user about the mental models required to op- erate the interface correctly. Although for some older people the concept of ���trial and error��� as a mechanism for discovering how to use novel device can be at odds with the belief that ���playing with it will break it���, and this can significantly impede the learning process for users holding this belief. Additionally, some errors are not discovered by the users, such as if an email is not sent to the correct address, or an appointment not set on the correct day or time in the schedule which can further disrupt the devel- opment of accurate mental models.