Guidance Systems for Blind People

Human wayfinding involves two different functions: (1) maintaining orientation within the large-scale environment for the purpose of navigating to remote [Page 473]destinations, and (2) sensing of the immediate environment, including paths and obstacles, for the purpose of moving along desired routes. In connection with the training of wayfinding skills in blind people, these functions are referred to as orientation and mobility. Guidance systems have been developed to assist blind people with orientation and mobility. This entry describes a number of these guidance systems.

Visually impaired people are at a disadvantage when it comes to wayfinding. For mobility, sensing of the near environment for obstacles and paths is effortful and error prone, even with a long cane and auditory cues such as sound reflections from surfaces. For orientation, especially within unfamiliar environments, blind people lack much of the information needed for planning routes to destinations, for taking detours while en route, and for keeping track of their movement relative to the destination.

Early research and development of electronic travel aids (ETAs) focused on mobility, the ultimate goal being to supplement or even replace the long cane and the guide dog. The primary concern was obstacle avoidance. Electronic obstacle avoiders used today include devices that detect nearby obstacles using laser and ultrasonic sensing and then inform the user of their locations by way of auditory or vibratory displays. Some useful devices have been developed, but adoption of these devices by the blind population has been limited.

More recently, research and development of ETAs has shifted from mobility to orientation. There are basically two approaches: add electronic location identifiers to the environment or provide the traveler with an electronic device that locates the traveler within the environment. An example of the first approach is the Talking Signs© system of remote signage. Talking Signs are infrared transmitters positioned throughout the environment, such as in shopping centers and public transportation terminals. Infrared signals from the transmitters convey speech information about the identity of the site at which the transmitter is located (e.g., a bus stop). A blind person traveling through an environment picks up signals from the Talking Signs when aiming a small handheld receiver toward any one of them and, consequently, hears speech indicating the identity of the site. An obvious drawback of this approach is the cost of deploying and maintaining so many transmitters.

The second general approach for providing orientation information is best exemplified by guidance systems that use the global positioning system (GPS). A GPS receiver uses signals from satellites to compute its position with an accuracy suitable for pedestrian travel. A limitation of GPS is that positioning is poor indoors and somewhat degraded by tall buildings and dense foliage out of doors. In these situations, GPS guidance systems need to be supplemented by some other means of position tracking, such as Talking Signs or updating the traveler's position using velocity or acceleration sensors that measure the traveler's motion.

A GPS guidance system consists of four components: the GPS receiver for providing current location, the spatial database of streets and environmental sites, the system software for path planning, and the user interface, which displays guidance information using auditory or tactual information and allows user input to control the system. There are now several commercially available GPS guidance systems for blind people, notably Braille Note GPS©, Mobile Geo©, StreetTalk©, and Trekker©. These come equipped with detailed databases of street networks and points of interest (restaurants, museums, businesses, etc.). The effectiveness of these guidance systems in allowing blind people to travel independently through familiar and unfamiliar environments makes these systems one of the true success stories in the field of sensory substitution.

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