7 Navigation AT: Context-aware Computing

Learning objectives

In order to allow visually impaired people the ability to travel freely through the environment, without being constrained to familiar routes and known destinations, this chapter illustrates the need to augment local information acquired from commonly used mobility aids with distant information acquired from context-aware technologies.

When you have read this chapter you should be able to:

•List the types of commonly used mobility aids and explain the limitations of their use.

•Define the concept of cognitive mapping and describe the strategies that are used to acquire spatial information, and the factors influencing how this is acquired.

•Outline technologies that can be used to sense the context of the user, and discuss the technological and human issues that arise.

•Carry out test procedures involving end-users in order to investigate specific human issues affecting the design of context-aware systems.

•Discuss the technological challenges concerned with improving the accuracy and reliability of future positioning technologies.

7.1 Defining the Orientation/Navigation Problem

The ability to orientate and navigate is an important skill that is used to experience and interact with the environment, to make social contact with other people, to undertake daily activities, and, ultimately, to maintain independent mobility. In this section, we will look at:

•What orientation, mobility and navigation mean.

•What types of mobility aids exist and how they are used.

•The limitations of traditional mobility aids.

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7.1.1 Orientation, Mobility and Navigation

‘Orientation’ refers to a person’s awareness of his/her position in space. For instance, a visually impaired person may be aware of their current position due to the sound of a verbal travel announcement when passing a train station. Orientation has been defined as the ‘process of utilising the remaining senses in establishing one’s position and relationship to all other significant objects in one’s environment’ (Hill and Ponder 1976). Orientation is therefore dependent upon the solicitation and interpretation of sensory information, which may be visual, auditory, kinaesthetic (the relative positions and movements of different parts of the body), tactile, thermal, and/or olfactory. Successful interpretation of sensory cues is dependent upon known and predictable environments (LaGrow and Weessies 1994).

Orientation and Mobility (O and M) specialists teach visually impaired travellers to recognise and anticipate the regularities of the environment. However, exceptions to those regularities, such as the smell emanating from a bakery, become more informative than the regularities themselves, and become landmarks that a traveller can use to pinpoint their location in space (Hill and Ponder 1976).

‘Mobility’ refers to the ability of a person to move safely and efficiently from one point to another within the physical environment. It has been defined as the ‘capacity, the readiness, and the facility to move’ (Hill and Ponder 1976). This will involve sensing and negotiating obstacles and hazards, establishing and maintaining a desired course, and recovery from veers and other unintended or unexpected changes in direction. For instance, a visually impaired person may need to negotiate cars parked on the pavement, potholes in the road, temporary road signs, and excavation work.

‘Navigation’ refers to the purposeful process involved in travelling from one place to another, using mobility skills, and orientation in the environment in relation to a desired course. Navigation therefore involves the traveller updating their orientation and position, which can be achieved using three methods classified on the basis of object motion or kinematic order (Loomis et al. 2001):

1.‘Position-based navigation’ depends on external signals within the environment, such as landmarks, indicating the traveller’s position and orientation.

2.‘Velocity-based navigation’ (normally referred to as ‘dead reckoning’) relies on external and internal signals indicating to the traveller their present position by projecting course and speed from a known past location, and predicting a future position by projecting course and speed from a known present position.

3.‘Acceleration-based navigation’ (normally termed ‘inertial navigation’) involves both the traveller’s linear and rotary accelerations to acquire information on displacement and heading change from the origin.

With respect to these three methods, visually impaired people are at a huge disadvantage in unfamiliar routes, as they ‘lack much of the information needed for planning detours around obstacles and hazards, and have little information about distant landmarks, heading and self-velocity’ (Loomis et al. 2001).

7.1.2 Traditional Mobility Aids

Traditional mobility aids have acted as an important and effective tool for helping visually impaired travellers detect objects in the local environment, negotiate narrow spaces, climb and descend stairways, enter and exit buildings, as well as many other mobility tasks. Three widely used traditional aids exist, and are described below.

Human guide. This is where a person with sight serves as a guide to a person who is visually impaired. The human guide is positioned slightly in front in order to ensure safety. At one time or another, most visually impaired travellers use a human guide, either as a primary aid or supplement to other aids.

Long cane. Over the years, various types of canes have been developed for specific user needs and preferences. The long cane (also called the prescription cane or typhlo cane); however, is the most effective and efficient (Farmer 1980). It enables visually impaired travellers to detect obstacles or drop-offs in the path approximately 1 m in front of them. Information regarding the walking surface or texture can also be transmitted, while providing suitable lower-body protection. In the most common technique, the cane is extended and swung back and forth across the body in rhythm with the user’s steps (LaGrow and Weessies 1994).

Dog guide. Trained dogs are used as travel aids by less than 10% of non-visual travellers. The dog responds to commands given by the visually impaired person, such as right, left and forward (commands are only disobeyed to avoid danger, such as refusing to proceed forward due to a car parked on the pavement obstructing their path). The guide dog’s job is not to find the way, but to guide the person around obstacles or stop in front of them. People who use guide dogs must therefore know where they are going and make decisions about the proper time to begin a street crossing.

The requirements and abilities of visually impaired people vary considerable, and so an O and M specialist would advise on a mobility aid (along with techniques and instructional strategies) that reflects the uniqueness of each person. The traveller’s quality of vision, for instance, is a key factor in identifying which mobility aid is most appropriate.

7.1.3 Limitations of Traditional Aids

Long canes and guide dogs have been effective in helping visually impaired people with many mobility tasks, as described in the last section. However, Clark-Carter et al. (1986) state that at least one-third of people with visual impairment or blindness make no independent journeys outside their homes, and most of those who do venture outside independently often travel to known destinations along familiar routes, as exploration is considered stressful and can lead to disorientation. The inability of these aids to facilitate distant (or macro) navigation is considered the main reason for this (Petrie 1995). The visually impaired traveller, for instance, would remain unaware of a supermarket located at the other side of the street. Even for local (or micro) navigation these devices are limited as they only detect