This chapter will start from the viewpoint that it is not easy to separate out the effects of different types of cognitive impairment as they often interact. Many potential users of computer systems, particularly older people, who are a growing proportion of the population, can be affected by multiple impairments which, at a human computer interface level, may interact to produce a handicap which is greater than the effects of the individual impairments. Beyond cognitive impairment per se, similar 'synergistic' interactions can emerge in relation to sensory/perceptual, motor and other impairments that may affect a system user.
With the above caveat, the chapter will consider the various types and levels of cognitive impairment that are relevant to HCI issues. This discussion, will focus on the effects of such impairments on functionality rather than medical causes, but will relate to medical causes where these are relevant to long-term trends in functionality. In addition to long-term trends due to medical pathology there are those generally considered to relate to the 'normal' ageing process. The links between these conceptually distinct areas will again emphasis functionality rather than 'cause'. The chapter will discuss the demography of such impairments, and how they can change with time with particular groups of users.
The problems of designing systems and interfaces for cognitive impairment will be illustrated by examples of computer systems that have been designed to provide both prostheses and training aids for people with cognitive impairment. These will include reading and writing aids for dyslexic people, communication aids for aphasics, and those with other language impairments, systems for people with memory dysfunction and those with dementia. These examples relate to the employment of computer technology to assist people with basic 'day-to-day' tasks, tasks that are otherwise unrelated to 'technology'. Examples will also be given of interface elements known to be beneficial for older people with a range of mild cognitive impairments who need to access various services and other 'day-to-day' tasks increasingly available only through 'computer technology'.
The chapter will consider the important implications of the perception of competence of users, as opposed to their actual competence and how technology can play a part in improving such perceptions as well as supporting the underlying dysfunction. It will also discuss, with appropriate illustrations from research, the dangers of making too many assumptions of what a user with cognitive impairment can and cannot achieve with the help of technology.
The chapter will examine the concept of user centred design and how it needs to be adapted to be sensitive to the needs of users with cognitive dysfunction and the ethical issues involved in researchers and designers interacting with people with moderate to severe cognitive dysfunction.