Human Computer Interaction
ERCIM News No.46, July 2001 [contents]

Enabling Computer Access for Motion-impaired Users

by Simeon Keates, P John Clarkson and Peter Robinson

Conventional computer interfaces and input systems present serious difficulties to users with impaired motion. The Engineering Design Centre of the University of Cambridge, in conjunction with the Computer Laboratory, has been researching methods of enabling computer access for Motion-Impaired Users (CAMIU) for a number of years, and the research is currently funded by both the UK Engineering and Physical Sciences Research Council and Consignia plc.

The primary aim of this research is to enable the design of accessible computer input systems and interfaces for all motion-impaired users.

Current practices in the design of interfaces (both input hardware and software) are often based on user models and descriptions derived almost exclusively from studies of able-bodied users. However, such users are only one point on a wide and varied scale of physical capabilities. Users with a number of different physical impairment conditions have the same desire to use computers as able-bodied people, but cannot cope with most current computer access systems. Such conditions include Cerebral Palsy, Muscular Dystrophy and spinal injuries or disorder. Frequent symptoms include tremor, spasm, restricted movement, and reduced strength. The general population is also growing older. By 2020, almost half the adult population in the United Kingdom will be over 50, with the over 80’s being the most rapidly growing sector. Associated with the ageing process are decreases in physical capability, such as reduced hearing and vision. As computer usage spreads throughout the population, the profile of the user base that must be accommodated is changing.

The issue of how to enable computer access for motion-impaired users is being addressed by a number of key research activities. Central to this research is the idea that an interface needs to attain user acceptability, both socially and practically. To achieve practical acceptability the interface must offer satisfactory functionality (utility), usability and accessibility. Social acceptability requires the user to want to use the system and not feel stigmatised.

Characterising the Users
The first objective of the research is to obtain an understanding of the needs and capabilities of users with motion impairments. Research is being performed to study the impact of each of the principal motion impairment symptoms on computer interaction for both disabled and elderly users. The knowledge gained from this work provides insight to the ways in which computer access may be improved. User modelling techniques, such as the Model Human Processor, are being applied and have helped identify fundamental differences between how able-bodied and motion-impaired users interact with computers. New models and methods of characterising user performance are being developed and calibrated, particularly for cursor control and on-screen selection tasks.

Evaluating Novel Interaction Techniques
Research is being performed to evaluate the acceptability of a number of input systems that have been suggested to offer benefits for motion-impaired users.

For example, gestural input is a popular research area for computer access for motion-impaired users owing to their inherent flexibility and ability to be tailored to particular users. The theoretical justification for using gestural input with motion-impaired users is that the freeform nature of gestures should allow users to select movements that are comfortable and repeatable to make. Gestures are also considered to be natural and intuitive as they constitute a component of everyday interpersonal communication. However, user trials showed that motion-impaired users found gestures to be slow and both physically and cognitively demanding to produce.

Haptic feedback is another input option under investigation. Force feedback, for example implemented as a gravity well enclosing a target, can have a greatly beneficial effect, improving interaction times by up to an order of magnitude under certain conditions. However, haptic feedback must be implemented appropriately. For instance, certain types of vibrotactile feedback such as adding vibration to a target, have been shown to have a detrimental effect on the interaction.

Developing a New User-centred Design Approach
To ensure that users who do not conform to the able-bodied stereotype are not excluded from the use of computers, it is necessary to develop and adopt a methodological design approach for implementing inclusive design of computer interfaces.

There are several existing approaches for designing more inclusive interfaces. However, there are shortcomings of each of these approaches that prevent each of them from being used to provide the definitive design approach that designers can use in all circumstances. The principal weaknesses stem from the targeted nature of the approaches. The existing design approaches are often targeted at specific population groups or impairment types. Alternatively, they may be targeted at specific cultures.

The prescribed ways of application of the existing methods are often vague. For example, Universal Design, with a few notable exceptions, is more of an ethos than a rigorous, systematic design approach. There are very few structured descriptions of the implementation of Universal Design in more detail than broad design objectives. Consequently, while in combination the existing approaches may offer complete coverage of the population needs, individually they do not. Therefore, there is a need for a new approach that draws on the strengths of the existing inclusive design approaches and offers practical and measurable design criteria.

A new design model, the 7-level approach, has been developed as part of the CAMIU project. The approach has been developed to emphasise both aspects of acceptability, the need for practical and social acceptance. The 7-level approach has been successfully applied to a number of case studies, including the design of interfaces for software products, robotics applications and public access kiosks.


Please contact:
Simeon Keates — University of Cambridge, United Kingdom
Tel: +44 1223 766 958