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tem, www.artificialvision.com) perform similar
sensory substitutions by providing some kind of
sound output indicating changes in density in the
environment. However, while these are beginning
to enable visually impaired and blind people to
navigate their environment more independently,
they cannot yet provide instant feedback on im-
portant environmental cues that people need such
as an upcoming curb. Global Positioning Systems
(GPS) are becoming very accurate, but noise can
introduce error margins between one and 10 me-
ters, suggesting that they cannot reliably provide
timely warnings either. The same is true in dense
cityscapes and inside buildings.
Getting a little closer to Weiser's (1991)
original vision of people interacting seamlessly
with multiple computers embedded in their en-
vironment, one could explore the possibility of
tagging objects in the environment with sound,
even speech, capabilities that are activated when
a person carrying the necessary equipment ap-
proaches. We do not know what kinds of objects
should provide such augmented reality, how far in
advance they should identify themselves, whether
such tags would be socially and psychologically
acceptable, or if they would confuse more than to
assist a blind person attempting to navigate their
environment. Alternatively, one could provide
built-in intelligence into the white cane and use
it as a sensory interface to the environment via
vibration, sound, or a mixture of both. This kind of
multimodal research is in its infancy but technolo-
gies are beginning to emerge as discussed below.
The sensing and representation of context is
a very challenging area of research in location-
aware mobile applications. Some early examples
of context-aware mobile systems include several
tour-guides (e.g. Abowd et al., 1997; Feiner et al.,
1997; Cheverst et al., 2000) and mobile games
(Drozd et al., 2006) that combine mobile comput-
ers with various positioning systems, including the
most popular of these, the GPS (see Strachnan et
al., 2009 for a review), introduced already in the
late 1980s. One disadvantage of many of these
systems is that they are limited to outdoor environ-
ments, and that they provide limited contextual
information during navigation. More recently, it
has become possible to use currently available
infrastructure to develop portable, affordable con-
text- aware devices to support high quality, exact
navigation, for example, enabling blind people to
detect the status of traffic lights (Angin, Bhargave
& Helal, 2010). Some of these existing systems
consist of a digital camera and a portable PC that
analyzes video frames captured by the camera
(Charette & Nashahibi, 2009). One drawback of
these is that they are rather cumbersome to use
because of their dependence on hardware for
image- and video processing. To overcome this
drawback, Angin et al. (2010) proposes a two-tier
open, extensible architecture comprising a mobile
Navigation and Awareness Server (mNAS) and a
cloud Navigation and Awareness Server (cNAS).
The mNAS could be any smart phone, and the
cNAS is simply the web services platform. The
mNAS has an integrated GPX receiver; it is
responsible for local navigation, local obstacle
detection and avoidance, and interacting with the
user as well as with the cloud side. It is envisaged
to “provide location data to cNAS, which will
perform the desired location-specific functional-
ity and communicate the desired information as
well as relevant context information and warnings
of potential hazards in contact back to mNAS”
(p. 397). The architecture, which is still in the
conceptualization stage, is described in the paper.
Another approach in this genre of technologies
is by enabling medical implants to interact with
other technologies. Rasmussen and his colleagues
(2009) describe an access control mechanism for
implantable medical devices based on ultrasonic
distance-bounding that enables an implanted medi-
cal device to grant access to its resources only to
those devices that are in its close proximity. They
are investigating the use of the technology to en-
able a treating physician or, in an emergency, a
paramedic access to a patient's pacemaker. The
paper describes how this is done, but for our pur-
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