5.2 The Travel Activity

170 5 Mobility: An Overview

Molyneux and the philosopher Locke on this subject. However, it is only relatively recently that empirical studies have been performed and their results used in the design of assistive technology systems for mobility. Research in this area is still continuing. In this section, a study by Ungar (2004) and a model by Brambring (1985) are reviewed to give a flavour of the insight into mobility that can be obtained from empirical and theoretical research. Before discussing these studies, some concepts and definitions used in mobility research will be presented:

1.Near-space and far-space. Near-space is the space immediately around the person’s body (or their body plus a short-range assistive device such as a long cane). This space can be explored by touch and thus it is often called the hapticspace. Far-space is distant geographical space, information about which is required for travel; hence it is also sometimes referred to as the locomotor space. Travelling around a campus or across a city are examples of a far-space or locomotor-space problem. Understanding how mobility mechanisms work in far-space is a key ingredient for travel success.

2.Past experience and new experience. Using past experience involves storing spatial information about a journey and recalling this information when the journey is being repeated. Preparing for new experiences involves applying knowledge from prior experience to new journeys or spatial tasks. In empirical studies it is often important to make a distinction between these two types of situations, one based on memory and the other based on inference.

3.History of visual impairment. Empirical studies, particularly in psychology, frequently involve a variable relating to the onset of visual impairment or blindness. Congenitally or early blind or visually impaired people may have different cognitive approaches and travel strategies from people who became blind or visually impaired later in life. Late blind people have the advantage of familiarity with visual concepts and visual knowledge of a (large) number of routes, but may experience problems developing new travel strategies. Early or congenitally blind people have the advantage of being accustomed to relying on other sources of information than sight. Some of them also have well developed strategies for independent travel as a blind or visually impaired person. Therefore, the existence and extent of prior visual experience can have a significant effect on the performance of mobility tasks in empirical studies. Even more significantly, it can also affect end-user requirements and satisfaction with assistive technology.

4.Body-centred and external referencing strategies. There are two main approaches to fixing the location of an object in (haptic) space. Its location can be referenced either to the body (and/or movements) of the person searching the space or to other objects in the haptic space. The two approaches are called body-centred and/or movement centred and external referencing. The term ego-centred referencing is sometimes used for the first approach.

5.Cognitive maps. A spatial pattern of important locations or way-finding points is often described using a physical map or diagram. A cognitive map is a mental version of this coding or mapping activity. It involves mentally storing the

ordering or relationships between a number of variables that can be physical objects such as way-finding points or abstract objects such as ideas.

The findings of empirical investigations (Ungar 2004) of mobility and its operating mechanisms for visually impaired and blind people included the following two outcomes:

1.Mobility in near-space. In so-called “table-top” experiments where the participants demonstrate mapping abilities for a tableau of objects within arm’s reach, the results indicated that body-centred mapping strategies are used by blind people who are congenitally or early blind. Deeper investigative studies have shown that these strategies are less robust in more demanding tasks that require extrapolation; in these more complex tasks the use of external references was found to be more successful.

2.Mobility in far-space. These studies were performed in a larger environment, typically, school grounds, offices or constructed layouts, and frequently with children of school age. One clear outcome was “that the lack of visual experience does not prevent the acquisition of spatial representation” (Ungar, 2004). However, the studies seemed to show that blind people tend to use body-centred (egocentric) rather than external referencing spatial strategies to record their experiences of far-space and that external referencing strategies can be more robust and successful for the more complicated mobility tasks in far-spaces. Ungar (2004) has also considered the activities that could encourage an improved appreciation of the layout of far-space by visually impaired and blind people. He suggests more specialised mobility training in the use of all the senses from an early age and the use of tactile maps.

Travelling in the real world is considerably more complex than mobility in a limited test environment. A model that is frequently cited is that due to Brambring (1985), as shown in Figure 5.2.

In Brambring’s travel model, the locomotion of a blind person is considered to comprise two types of processes, one concerned with perception and the other with orientation. Perception is interpreted in the most general sense. In this context, it refers to a blind person obtaining information about the environment through any of their senses, whilst orientation is the knowledge of general position on the journey path. With this classification, the two areas of perception and two areas of orientation are refined as follows:

•Perception and obstacle detection. The detection of obstacles means the perception of potentially hazardous objects in the environment ahead of time so they can be avoided. This has always been considered a primary requirement for aided mobility. This is a perception activity in the near portion of locomotor space.

•Perception and the identification of landmarks. Blind travellers have been found to use a greater variety of and different types of landmarks than sighted people in order to determine their location with respect to specific points on a route. The class of landmarks used by blind travellers includes subtle environmental

172 5 Mobility: An Overview

Figure 5.2. Brambring’s decomposition of travel by blind people

clues, such as rises and falls in the path and changes in the texture of the pathway, the presence of walls and hedges, changes in the type and pattern of nearby objects like railings, sound landmarks, including traffic sounds and traffic crossing alerts, as well as odours and temperature changes. Other than intense odours and loud sounds, which can be perceived at a distance, most of the perceptual activity of a profoundly blind person is carried out in the near portion of locomotor space. In addition, a large number of landmarks are required to learn a route. With increasing quality of vision, the class of landmarks approaches the class of landmarks used by sighted people, namely street signs, significant buildings (particularly pubs!) and junctions. In this case, the perception activity moves into the far space. But it should also be noted that there are considerable differences in the type of landmarks used by different sighted people. Differences in the types of landmarks used by different blind people are likely to be a consequence of differences in individual perceptive abilities, rather than differences in cognitive processes or other factors, as in the case of sighted people. This is due to the need for profoundly blind people, in particular, to register as many landmarks as possible and therefore to take note of all the landmarks they can perceive. In some cases, blind (and sighted) people may use several landmarks at a time to confirm location.

•Spatial orientation. This is a near-space activity, and is the ability to maintain a position in the immediate environment of the traveller. Spatial orientation issues include the optimal position on a pavement and the ability to walk without veering from a desired course.

•Geographic orientation. In contrast to spatial orientation, geographic orientation is a far-space activity. It is the ability to determine position in the geographical space of the entire journey. Geographical orientation is dominated by informa-