Biomedical Engineering Reference
In-Depth Information
When a user interacts with a computer, his/her goal is to perform some tasks that are
specified in the task layer. For example, the user may want to search a file in the file system,
or send an e-mail, or search a page in the Web. The choice of a task triggers activities at the
lower levels of the hierarchy.
At the operation layer, the user has to execute a number of operations. For example, if the
task selected by the user is that of searching the Web, the user's operation consists of writ-
ing the query, submitting the query, browsing the results, and eventually accessing those
web pages he/she is looking for.
Each operation then translates into a set of commands at the command layer. A com-
mand corresponds to an event detected by the program, e.g., the insertion of a character, a
click of the mouse, or the selection of an icon on the screen.
The user sends commands to the computer by performing a suitable number of actions
at the action layer. An action is performed by interacting with the input device and it cor-
responds to simple acts such as pressing a key on the keyboard to write a character or
executing a “double click” by pressing twice the left button of the mouse.
Notice that, for able-bodied people, there is typically a one-to-one correspondence
between the actions and the commands, i.e., each action executed results in a command
sent to the computer. This is not necessarily true for disabled people who use alternative
input devices. For example, typing a single character (the command) using a binary switch
can require operating the switch (the action) several times.
We now use the model of interaction described above to classify existing approaches that
have been proposed in the literature to overcome the digital divide for motion-impaired
people. Depending on the layer of the stack to which these approaches refer, we distin-
guish between action layer approaches and command layer approaches.
Action layer approaches focus on the design and realization of alternative input devices
that allow disabled people to interact with standard software applications. In terms of
the interaction model of Figure 16.1, these approaches allow motion-impaired people to
perform the same set of commands as the able-bodied ones by means of a different set
of actions. For example, an impaired user might move the mouse cursor by means of the
voice or by moving the eyes. Depending on the user's disability and on the actions he/
she can perform, different devices have been considered in this context. Examples include
speech/sound-based interfaces (Manaris et al. 2002; Sporka et al. 2006), eye movement
detection (Fejtová et al. 2006), EMG interfaces (Chin et al. 2006), and a light-spot operated
mouse (Itoh 2006).
The advantage of action layer approaches is that they do not require the software to be
modified, and therefore the impaired people can potentially use any computer application.
Unfortunately, there are some drawbacks to take into account within these approaches.
One disadvantage is that a long training period is required to reach a good level of usabil-
ity. Also, obtaining an alternative input device that can completely replace a keyboard
and mouse can be a difficult result to achieve, especially for individuals with particularly
severe disabilities. Therefore the execution of the commands remains a major bottleneck
for an efficient interaction.
Command layer approaches address the above-mentioned problem by using alternative
input devices, the effectiveness of which is enhanced by means of software adaptation lay-
ers. These software layers act as a bridge between the standard applications and the input
devices. An example of this approach is the use of scanners (Ntoa et al. 2004). Scanners
highlight software controls (e.g., software buttons or menu items) in a predefined order. The
user may choose one of the highlighted controls by using an input device with just two sta-
tuses, such as a BCI or a single button. Another example is the use of force-feedback gravity
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