good example of this is the availability of differing speech rates for text-to-speech on VoiceOver for the iPhone (Figure 1). The fastest rate is not very understandable to people not used to it, but is often preferred by blind users.

Ability-based design. One way to realize universal design is ability-based design as defined by Wobbrock et al. [ 5]. Ability-based design encourages designers to focus on users’ abilities to build into the system efficient ways to make the system adapt to their abilities. The system could adapt automatically, or, more commonly, the system has user-selectable options to make the system work effectively for a user’s abilities. The speaking-rate slider for VoiceOver is a great example. An ability-based designer would know that reading text through speech is intrinsically slower than visually reading text. She would know that speech can be sped up and, with practice, still be understood. A typical designer would likely assume the most usable design for a text-to-speech application is to make the speech as natural as possible and not think about less-natural rapid speech. By contrast, the ability-based designer’s approach yields a design that meets the needs of users who are blind and have abilities the average person does not.

HUMAN-CENTERED DESIGN

Since it is often the case that designers
of technology are not necessarily the
users of that technology, it is important
they engage users in order to achieve
usable designs. This is especially
true for users with disabilities whose
abilities are not well understood by the
designers. User engagement is codified
in the ISO standard ISO 9241-210:2010
Ergonomics of human-system interaction
— Part 210: Human-centered design for
interactive systems, which delineates six
basic principles:
• The design is based upon an explicit
understanding of users, tasks, and
environments.

• Users are involved throughout design and development.

• The design is driven and refined by user-centered evaluation.

• The process is iterative.

• The design addresses the whole user experience.

• The design team includes multidisciplinary skills and perspectives.

These principles are especially
useful when thinking about designing
for people with disabilities using the
universal design approach. Since
typical designers and developers are
not disabled, how are they to practice
human-centered design? The design
cycle typically has four components:
analyzing, designing, prototyping,
and testing. The four-step process is
repeated until a satisfactory result
is obtained. At a minimum, in user-
centered design users are employed
in testing to determine the usability
by users with disabilities [ 6].
Unfortunately, it may be that that the
initial analysis and design is flawed, so
employing users earlier in the process
might be beneficial. In participatory
design (or co-design), users are also part
of the design team, helping to come up
with the requirements and features of
the design [ 7]. Finally, there is design
for user empowerment, where users
participate in all four steps of the
design cycle. User empowerment is a
concept I first introduced in a 2008
article [ 8] but have since refined.
Figure 2 describes these approaches.

DESIGN FOR USER
EMPOWERMENT

The user-centered and participatory design processes have the advantage that the resulting designs from these approaches are more likely to be adopted by users with disabilities.

However, there is still something paternalistic about having these users participate only in the testing and in designing the requirements and features. In design for user empowerment, users develop the project, design the requirements and features, develop the prototypes, test the prototypes, and analyze the results of testing to refine the design.

Naturally, it might not be the same people involved in all these steps. For example, designers and developers should not be testers. The main reason that people with disabilities should be so deeply involved is that they have the biggest stake in the eventual product.

In my view, there are two main human characteristics needed for design for empowerment: self-determination and technical expertise. I will explore each of these in more detail.

Self-determination. Self-determination means that those with disabilities have control of, and are not just passive recipients of,

Figure 2. Basic design cycle, user-centered design, participatory design, and design for user empowerment.

Design for
Empowerment

Test with users

Analyze with
users
Prototype with
users
Design with
users
Participatory
Design
Test with
users
Analyze
Prototype
Design with
users
User-Centered
Design
Test with
users
Analyze
Prototype
Design
Analyze
Prototype
Design
INTERACTIONS.ACM.ORG MARCH–APRIL 2015 INTERACTIONS 27