Biomedical Engineering Reference
In-Depth Information
7.5.2 Issues with Sonar-Based Systems
No visual prostheses are without problems, and all of those here based on sonar discussed
have some shortcomings:
•
With most of the systems, the user must actively scan the environment to detect
obstacles (no scanning is needed with the Sonicguide, but that device doesn't detect
obstacles at floor level). This procedure is time-consuming and requires the user's
constant activity and conscious effort.
•
The user must perform additional measurements when an obstacle is detected to
determine the dimensions of the object. A path must then be planned around the
obstacle. Again, this is a time-consuming, conscious effort that reduces walking
speed.
•
One problem with all blind aids based on acoustic feedback is their interference
(called
masking
) with the blind person's ability to pick up environmental cues
through hearing (Brabyn, 1982; Kay, 1974; Lebedev and Sheiman, 1980). This is a
serious concern, as almost all blind people use acoustic information for situational
awareness, obstacle detection, and navigation.
•
The GuideCane is large and rather unwieldy; it must be lifted up steps and roadside
curbs. The wheels can easily wedge in cracks and holes in the pavement.
7.6
LASER-BASED SYSTEMS
Introduced in 1973 (Benjamin, Ali et al., 1973), the C-5 laser cane, shown in Figure 7-17,
is based on optical triangulation with three laser diodes and three photodiodes as receivers.
It can detect obstacles at head height, drop-offs in front of the user, and obstacles up to a
range of 1.5 or 3.5 m ahead of the user.
7.7
SENSORY SUBSTITUTION
Sensory substitution is defined by Peter Meijer (2006) as “the replacement of one sensory
input (vision, hearing, touch, taste or smell) by another, while preserving some of the
key functions of the original sense.” Due to the astonishing plasticity of the brain, sensory
substitution devices can help the blind regain some sense of sight through touch or hearing
or help a deaf person regain some sense of hearing through vision or touch. It has been
shown experimentally that if the brain is deprived of its main form of input, even for quite
short periods, it will seek out other ways of gaining this information. Sensory substitution
devices are designed to facilitate this process.
FIGURE 7-17
Prototype of the C-5
laser cane.
(Benjamin, Ali et al.,
1973)
