developers ought to create systems for people with abilities of all kinds and degrees. Likewise, Newell22 referred to “extra-ordinary abilities,” saying, “common sense and observation show us that every human being has . . . abilities, some of which can be described as ‘ordinary’ and some of which are very obviously extra-ordinary.” The focus is not on disability but on the diversity of human ability.

Ability is thus like weight or height— it is positive-valued only. Nobody has dis-weight or dis-height; neither are there disabilities, only abilities. Any experience of disability is not attributable to a person but to a mismatch between a person’s abilities and the ability assumptions of the environment. Like the proverbial water in a glass half full, abilities are only present and “ designed for,” not absent and “filled in.” This view of “design for” rather than “fill in” is not the historical view. Filling in for lost abilities has been the norm. From early human history through World War II and after, the approach has been to restore whatever was lost (such as an arm or a leg). People were expected to adapt themselves to the environment, whether physical or social, as they found it, with little hope that society would meet them halfway.

Although such attitudes have improved, designers and developers still often take a similar stance with interactive computing systems. When users’ abilities fail to match the ability assumptions underlying today’s interactive computing systems, the burden usually falls on the users to make themselves amenable to those systems, and the systems remain oblivious to the users doing it (see Figure 3).

Ability and Situation

The experience of disability applies to us all. With the proliferation of smartphones, tablets, and wearables, we increasingly interact with systems in situations that challenge our abilities.

Consider how the physical envi-
ronment of “the computer user” has
changed from the 1980s to today. A typ-
ical computer user in the 1980s would
have been seated at a stable work sur-
face with ample lighting, controlled
temperatures, quiet surroundings,
and relatively few distractions. Today,
with computing pervading so many as-
disability and accessibility. 7, 22, 27, 33, 38

Sears and Young27 said, “Both the en-
vironment in which an individual is
working and the current context . . . can
contribute to the existence of impair-
ments, disabilities, and handicaps.”
This observation has grown even
more relevant in the 15 years since it
was made. In Stockholm, Sweden, city
officials have erected street signs
alerting drivers to watch out for peo-
ple texting while walking. In Seoul,
South Korea, some sidewalks are di-
vided into two lanes, one for those in-
tent on walking while staring at their
phones, and the other for those who
promise to refrain. In the U.S., the
Utah transit authority imposed a $50

pects of life, “computer users” interact off-the-desktop while adapting to dynamic, distracting environments and their movements through them. 7 An example is how users interact in “ four-second bursts” 24 when walking with smartphones, constantly diverting their attention from and returning to their screens. And yet, with the exception of a few research prototypes (such as in Mariakakis et al. 19), smartphones are oblivious to users’ behaviors, unchanging from the street to the café to the library to the office.

Researchers have identified “ situational impairments” caused by changing situations, contexts, and environments, using the language of

Figure 3. Users adapting themselves to the ability assumptions of their input devices— keyboards and trackballs—which are oblivious to their contortions.

(a)

(b)