Electronic Travel Aids New Directions for Research (1986) / Chapter Skim
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4: Perceptual, Cognitive, and Environmental Factors
4: Perceptual, Cognitive, and Environmental Factors
Pages 36-52
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From page 36... ...
Furthermore, the requirements of the task are not usually adequately specified by information acquired from the space in which the task is performed while it is in progress, and the blind pedestrian must supplement this information with information retrieved from memory. PERCEPTUAL, COGNITIVE, AND MOTOR FUNCTIONS Pedestrians acquire some of the information they need for the mobility task directly from the space in which the task is performed while it is in progress, by way of perception.
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From page 37... ...
Perceptual information is distributed over time as well as space, and perception of temporal changes may be as important as perception of stable spatial structure. Physical Features In describing the contents of space, it is customary to mention objects.
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From page 38... ...
Spatial Zones In order to get the spatial information they need, pedestrians must know where in the surrounding space to find it. If blind pedestrians are using mobility aids for that purpose, those aids must be so designed that they can examine the spatial zone or zones in which the information is to be found.
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From page 39... ...
The spatial information that can be acquired by visual perception usually meets these requirements. However 9 because blind pedestrians, using the perceptual processes availab~e to them, acquire less spatial information than sighted pedestrians observing the space in which they are performing the mobility task as they are performing it, they must depend more heavily than sighted pedestrians on information retrieved from memory.
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From page 40... ...
Consequently, the cognitive representations are often syntheses that have been achieved by integrating spatial information resulting from observations made from different positions and at different times. Evidence presented by several investigators (Appleyard, 1970; Beck and Wood, 1976; Lynch, 1960)
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From page 41... ...
Because constructed environments exhibit pervasive reiteration, the cognitive representation incorporates what may be regarded as spatial stereotypes. These stereotypes are the generalizations on which pedestrians can base predictions concerning what they will encounter in spaces not previously experienced.
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From page 42... ...
Recourse to spatial stereotypes is also available to sighted pedestrians, but the perceptual information provided by visual observation is generally sufficient to guide their performance, and they do not have as much need to supplement it with cognitive information. Thus, on first encounter with unfamiliar space, the performance of the blind pedestrians is relatively poor but improves with practice, whereas the initial performance of sighted pedestrians is relatively good and does not improve much with practice (Hollyfield, 1981)
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From page 43... ...
Sighted pedestrians who can gather perceptual information in ample time for the guidance of their locomotor behavior need not rely so heavily on inferences about the environment. What sighted pedestrians can see for themselves, blind pedestrians must often infer, and many if not all of the mobility skills described can be thought of as types of inferential reasoning about what is present in the environment and how one should move as a result.
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From page 44... ...
For example, the unusually sharp curve in a path or the distinctive bump in a sidewalk caused by a tree root underneath may tell blind pedestrians who have traversed the route a number of times exactly where they are. A landmark is most useful when its relationship to other landmarks in the same space is known.
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From page 45... ...
The extent of the space within which the landmarks used by blind pedestrians can be observed is relatively small. They can identify distinctive characteristics of the surface underfoot, they can find things within arm's reach or the reach of the cane or ETA, they can find things a few feet off the path by echo location -- but they are largely unaware of the contents of the spaces bounded by the path segments along which they walk.
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From page 46... ...
There are blind pedestrians who, like gamblers at a casino, seem to enjoy risk and seek the challenge of traveling in unfamiliar situations, but most blind pedestrians, including many apparently skillful travelers, learn routes to the places they must reach with some frequency and avoid unfamiliar situations. They find acceptable the risks they incur when their performance is regulated by both perceptual and cognitive information, but they are reluctant to accept the risks they incur when only perceptual information is available.
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From page 47... ...
It may be that appropriate perceptual experience can provide compensation for these perceptual limitations, but, in the absence of such experience, those who are congenitally blind may exhibit a reduced ability to grasp spatial relationships that persists throughout life. The possibility that early use of mobility aids to serve as environmental sensors (Strelow and Warren, 1985)
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From page 48... ...
Individuals are legally blind for many reasons, and the cause of a visual impairment is an important determinant of the spatial information that can be acquired with the remaining vision. Conclusion The purpose of the discussion has been to make the point that any mobility aid or training effort must be applied in the context of individual differences, and these individual differences may play a major role in determining the effectiveness of the mobility aid or training effort.
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From page 49... ...
It is not the case that the traditional themes of research in perception and cognition are devoid of material bearing on issues of blind mobility; indeed, much of the literature cited in earlier sections of this chapter deals primarily with traditional themes and only secondarily or by implication with issues of visual impairment. To some degree, the theoretical underpinnings of mobility in the blind are weak because there has not been a sustained attack on issues related to blind mobility, and there is no self-sufficient theory of blind mobility.
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From page 50... ...
There are several critical questions in needs of answers from research: Is the use of a natural cue correspondence, such as auditory IAD for azimuth direction in the Sonicguide, superior to a more arbitrary matching of dimensions, such as signal rate for distance in the Mowat Sensor (see Chapter 61? Although the use of natural matches seems intuitively desirable, some evidence (e.g., Strelow and Warren, 1985)
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From page 51... ...
. Some very fundamental questions of human information processing capabilities and perceptual-cognitive function are involved here, and the effective design of future mobility aids will depend more on empirically generated answers than on simple conviction that one approach or the other is best.
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From page 52... ...
. All this must be accomplished in the context of a stimulus environment that goes beyond the user-device interface: natural stimuli also occur that may facilitate performance if they can be effectively attended and processed, and, perhaps just as important, other perceptual-cognitive-motor tasks must be carried on simultaneously that are vital but that have no immediate relevance for the task of mobility RECOMMENDATION: Research should be fostered on the perceptualmotor learning processes that underlie the use of mobility aids.
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