Biomedical Engineering Reference
In-Depth Information
wells, i.e., attractive basins that pull the cursor to the center of an on-screen target (Hwang
et al. 2003). These techniques are designed to help users who have tremor, spasm, and co-
ordination difficulties to perform “point and click” tasks more quickly and accurately.
Referring to Figure 16.1, command layer approaches allow the user to execute the same
operations as in the standard interaction, but they require him/her to perform a different
set of commands. As an example, consider the operation of sending a query to a search
engine. With standard input devices, the following commands must be executed: “Move
the mouse to the search button” and “Press the button.” The same operation performed
with a scanner consists of the scanner highlighting the search button and the user execut-
ing a single command, namely “Activate the highlighted button.”
The major drawback of command layer approaches is that although the actions to be
performed by the user on the input devices are in general reduced or simplified, the time
needed to execute a single command typically increases. For example, pressing a button
using a scanner requires significantly more time than pressing the same button with a
mouse because of the time needed to scan the whole set of command options. Also, to offer
a seamless integration between the adaptation layer and any application software, the lat-
ter should adhere to precise software design rules that in most cases have not been taken
into account in the design of the application software.
16.2.3 The Information Visualization Approach
The information visualization approach (IVA) aims to overcome the main disadvantages
of the action layer approaches and command layer approaches that have been described
in the previous section. The main characteristic of this approach is to act at the operation
layer of the hierarchical model of Figure 16.1. The idea is to change the set of operations
associated with the execution of a task in such a way that the total number of correspond-
ing commands is reduced. Reducing the number of commands aims at compensating for
the loss of efficiency that a motion-impaired person must pay in executing them because
of the limited number of statuses available in his/her alternative input device.
To achieve this goal, enhanced information visualization technologies can be used.
Visual representations, obtained by using geometric primitives and transformation, col-
ors, and other visual objects, translate data into a visible form that highlights important
features that would be otherwise hardly identifiable or even hidden. It follows that, when
compared with different possible representations of the information space associated with
a task, visual representations are more efficient in conveying information. This is due to
two main reasons. On one hand, visual representations take advantage of the human eye's
broad bandwidth connection into the brain to allow users to see, explore, and understand
large amounts of information at once. On the other hand, the use of visual objects makes
the acquisition of information more intuitive and immediate, and therefore the cognitive
elaboration is reduced.
Thus, IVA makes the end-user interact with a computer in which data are presented in a
nontraditional way by means of sophisticated diagrammatic interfaces. All non-IVA interac-
tion paradigms aim at reducing the discomfort of motion-impaired individuals within the
classical iconic representation of the data offered by traditional operating systems. They do not
try to compensate the reduced expressiveness of the input devices by enlarging the amount of
information that can be visually processed by the end-user in the same time frame.
For example, consider the task of searching a page on the Web. A possible set of opera-
tions is as follows: write the query, submit the query, scan the list of results, and access the
web page. One of the efficiency bottlenecks for the motion impaired would be scanning
