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Design lifecycles and wearable computers for users with disabilities

Helen Petrie[1], Valerie Johnson[1], Stephen Furner[2] and Thomas Strothotte[3]

  1. Sensory Disabilities Research Unit, University of Hertfordshire, Hatfield AL10 9AB, U.K.
  2. British Telecom Laboratories, Human Factors Division, MLB 2/8, Martlesham Heath, Ipswich IP5 7RE, U.K.
  3. Department of Simulation and Graphics, Otto von Guericke University of Magdeburg, Universittsplatz 2, D-39106 Magdeburg, Germany.


Wearable computers have enormous potential to assist people with disabilities. For example, for people with sensory disabilities such as blindness or deafness, they could provide substitute sensory information. Very cumbersome laboratory systems have been developed which provide substitute visual information for blind people by projecting a simple image in tactile form on the back or stomach, and these have been shown to have some utility (Epstein et al, 1989). Such systems would be far more useful as a wearable technology, although the appropriate miniaturization is still in the future. However, it is already possible to provide disabled people with useful information via wearable systems, even if this is not complete sensory substitution. For example, the Low Vision Enhancement System (from Visionics Corp., Minneapolis, MN). is an augmented reality headset which helps the wearer make more effective use of any remaining vision by magnifying images and increasing light/dark contrast.

As with all technological artifacts, wearable computers need to be well-designed if they are going to serve their functions appropriately. We are working towards an appropriate iterative user-centred design lifecycle for the development of wearable computers for disabled and elderly people, taking many ideas from mainstream HCI but adapting them both for the particular characteristics of our user groups and the particular characteristics of wearables. This process has lead us to the conclusion that particular evaluation methodologies need to be developed specific to some of the pecularities of wearables, for both able-bodied and disabled users.

MoBIC: a wearable navigational aid for blind people

One example of our use of the iterative design lifecycle has been in the MoBIC Project, which has developed a wearable navigational aid for blind travelers (Petrie, Johnson, Strothotte et al, 1996; Strothotte, Fritz, Michel et al, 1996). Blind people have two types of problems in moving through their environment, particularly if it is unfamiliar. Firstly, they need to avoid obstacles and to find a clear path to walk in their immediate environment (we have termed this micro-navigation, see Petrie, 1995). This problem can be addressed remarkably well by a long cane or a dog guide, although travel may never be as easy as for sighted people. Secondly, blind people need to orient and navigate through the larger environment, which may require knowing what street they are on, which way they are facing, where to cross a street safely and so on. We have termed this macro-navigation. Without visual information, this macro-navigational problem can be enormously difficult even in familiar environments and impossible in unfamiliar environments.

The MoBIC Outdoor System (MoODS), a wearable system, has been designed to assist in macro-navigation. It combines GPS and dGPS receivers with an on-board GIS which locates the traveler with reasonable accuracy on the digital map. The map contains not only standard information such as the street layout, house numbers and landmarks but also additional information of particular interest to blind travelers.

As MoODS wearers move about, they need to interact with the system, being given appropriate information at appropriate times by a Trip Management System (TMS) to assist them in orientation and navigation. At times information needs to be user-initiated, for example when the user is uncertain of their location. At other times information needs to be system-initiated, for example to give warning.

User Requirements: from paper to cardboard and plastic prototypes

Classic methods of user requirements elicition were initially employed, with interviews and focus groups of potential users of the system and related professionals. However, it quickly became clear that everyone (including the design team) had enormous difficulty in imagining what using a MoODS might be like, both in terms of interaction devices and dialogue. This will be the case in any instance where a wearable is developed to perform a new function rather than simply undertake a known function in new, mobile contexts of use. However, potential users may also have difficulties imagining how they might undertake familiar tasks in new contexts.

In the MoBIC user requirements studies it was clear that participants and the design team were falling back on existing artifacts as metaphors for the use of the MoODS: it would be like a mobile telephone or a Walkman etc. While this can be helpful, it also limits the design space which is explored. In the case of MoODS, neither of these artifacts provided an adequate metaphor for the appropriate interaction. A mobile telephone style MoODS would be carried in a pocket and only interrogated when the user thought they required assistance. However, an important aspect of the functionality which the TMS can offer users is the provision of warnings. Contacting users via a phone call may be too slow to provide this information. A Walkman-style MoODS was a closer approximation to an appropriate metaphor of use, but blind travelers rely on auditory information from the environment, and wearing Walkman-style headphones would mask some sounds. In addition, users need to interact with the system more frequently than with a Walkman, so this metaphor provided no basis for the interaction with the system.

Exploring different metaphors of use and trying to invent new ones proved to be a useful method for potential users and the design team to clarify the MoODS design. A second successful method was the use of cardboard and plastic prototypes, the wearable answer to paper prototypes for 2D interfaces. In the case of input to the MoODS an initial prototype of a wrist worn keypad, similar to a watch, was presented to users along with several cardboard mock-ups representing a number of variations. These variations included different sizes for the keypad and different configurations and sizes of keys. Whilst users were not able to fully interact with these low fidelity prototypes they were able to judge what it would be like to wear them and how easy it would be to identify and operate the keys. A third successful method for establishing the design was the use of simple mobile Wizard of Oz studies. For example, to establish the style for the basic navigational messages, a study was conducted with a short, typical inner city route (which involved turning corners, finding an appropriate point to cross a street and finding certain shops). The route was carefully studied and a suggested set of messages prepared. These messages were tape-recorded and potential users then walked the route with a sighted guide, the pre-recorded instructions guiding them from point to point along the route. At each point, the user paused and listened to the next instruction before acting on the message. Users were then asked to comment on the message structure, content and level of detail. In addition to providing information about how to formulate the navigational messages, this exercise also yielded useful information concerning physical interaction with the MoODS. and what users felt to be important in the design of input and output devices.

Evaluation methodologies

To properly evaluate wearable computers appropriate methodologies are needed. Exactly what tasks should be used and what measures are appropriate depends on the nature of the use of the wearable. Such use can be basically "serial" or "concurrent" in nature. In serial use, the use of the wearable alternates with other tasks, so that only one task is undertaken at any one moment. This is typical of applications such as the mobile desktop and online manuals: the user stops other activities to perform a task with the wearable. The more challenging situation is concurrent use, in which the user wishes to perform two tasks simultaneously, one of which involves the wearable. An increasingly common example of concurrent use of a wearable-like system is people driving cars while talking on a mobile phone (unfortunately, the latter are not usually designed as wearable devices which creates potentially dangerous situations).

In the case of serial use, evaluation needs to cover only the use of the wearable itself in appropriate contexts, and perhaps comparisons with the use of non-wearable equivalents. For example, for a wearable online manual, evaluation would cover the usability and acceptability of the system in situations in which use is proposed, and perhaps comparisons with more traditional situations of consulting a manual for example in an office or library.

In the case of concurrent use, it is necessary to evaluate not only the use of the wearable itself, but also the other task which is being undertaken, to ensure that use of the wearable does not decrease performance on that task. For example, in the MoBIC project the main focus of our evaluations has been on the usability and acceptability of the MoODS system. For this purpose a range of objective measures (e.g. system interrogations, errors) and subjective measures (e.g. rating scales of usability learnability, and satisfaction) have been developed. However, in addition, we have also investigated whether the MoODS system has any adverse effects on the user's concurrent task, that of micro-navigation. For this purpose users are asked to walk specially constructed routes and comparisons are made of their performance with and without the MoODS system.

Finally, it is also important to ensure that concurrent use of a wearable does not put unacceptable stress or excessive workload on the users. In evaluations of the MoODS system we have taken objective and subjective measures of stress. Heartrate was recorded as an objective measure and subjective measures included the Spielberger State Trait Anxiety Inventory (Spielberger,1983). The NASA Task Load Index (TLX) was also included to measure workload. The TLX considers not only overall workload, but also six different contributory factors, three relating to the demands imposed on the participant (Mental, Physical and Temporal Demands) and three to the interaction of the participant with the task.


Appropriate iterative user-centred design lifecycles for wearable technologies need to be developed. These can build on mainstream HCI, but need to consider the particular characteristics of wearables. In the elicitation of user requirements, particular attention needs to be paid to developing appropriate metaphors for the devices, and not relying on existing and possibly inadequate metaphors. In the evaluation of wearables, the different possible types of use of the wearable (serial or concurrent), need to be considered when developing evaluation methodologies and measures.


The MoBIC Project (TP 1148) was supported by the Technological Initiative for Disabled and Elderly (TIDE) Programme of the European Union (DG XIII). The project partners are: BT, U.K.; F.H. Papenmeier GmbH, Schwerte, Germany; Free University of Berlin, Germany; Universitt Magdeburg, Germany; Royal National Institute for the Blind U.K; University of Birmingham U.K.; University of Hertfordshire, U.K.; Uppsala University, Sweden. We would like to thank the MoBIC team and the many people who participated in the MoBIC user studies.


Epstein, W., Hughes, B., Schneider, S.L. and Bach-y-Rita, P. (1989). Perceptual learning in an unfamiliar modality. Journal of Experimental Psychology: Human Perception and Performance, 15, 28 - 44.

Petrie, H. L. (1995). User requirements for a GPS-based travel aid for blind people. In J.M. Gill and H. Petrie (Eds.), Proceedings of the Conference on Orientation and Navigation Systems for Blind Persons. Hatfield: University of Hertfordshire.

Petrie, H., Johnson, V., Strothotte, T. Raab, A., Fritz, S., and Michel, R. (1996). MoBIC: designing a travel aid for blind and elderly people. Journal of Navigation, 49(1), 45 - 52.

Spielberger, C.D. (1983). State-Trait Anxiety Inventory for adults: Sampler set, manual, test and scoring key. Palo Alto, CA: Mind Garden.

Strothotte, T., Fritz, S., Michel, R., Raab, A., Petrie, H., Johnson, V., Reichert, L. and Schalt, A. (1996). Development of dialogue systems for a mobility aid for blind people: initial design and usability testing. Proceedings of ASSETS '96: The Second Annual Conference on Assistive Technology. New York: ACM Press.

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