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Chapter 3 THE ASSESSMENT OF MOBILITY The assessment of mobility is a central issue in any discussion of approaches to more effective mobility aids. It is necessary for determining the success or failure of mobility training and the effectiveness of mobility aids and for developing improved techniques and devices for mobility by the visually impaired. In this chapter we review the advances that have been made in the assessment of mobility performance and comment on the further refinements that will be necessary to relate mobility performance measures to the design, development, and use of mobility aids. INDIVIDUAL CHARACTERISTICS An individual's mobility performance is affected, of course, by a multitude of predisposing characteristics. Examples of such factors are listed in Table 4. To provide adequate mobility training to a person in need of it, an instructor must consider psychosocial, sensory/motor, perceptual/cognitive, and environmental factors in the choice of instructional technique, the training procedure, and, inevitably. the outcome of the trainina oroaram. Past studies have examined the differences in assessment and instructional techniques for specific subgroups of the visually impaired population. For the two-thirds or more of the visually impaired population who are 65 or older, travel needs may differ significantly from those of a younger subgroup. Nonetheless, elderly visually impaired persons have received relatively little attention from the rehabilitation community (Allen et al., 1976, 1977; Carney, 1970; Hubbard, 1969; Shaw, 1970~. More attention has been directed to the needs of children (Baird, 1977; Bledsoe, 1963; Ferrell, 1979; Franks and Nolan, 1970, 1971; Goldie, 1977; Hapeman, 1967), the multiply handicapped (Geruschat, 1980; Harley and Merbler, 1980; Primrose, 1981), and the partially sighted (Allen, 1977; Burton, 1976; Cory and Prince, 1976; Hughes, 1967; Quillman, 1977~. 26

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27 TABLE 4 Examples of Predisposing Factors That Affect Mobility Examples of Psychosocial Characteristics Individual expectation Living situation Motivation Demographic profile Sensory/Motor Characteristics Visual capacity Auditory capacity Locomotor capacity Perceptual/Cognitive Characteristics Ability to utilize echoes Spatial awareness Cognitive capacity/processing mode Environmental Characteristics Urban/suburban/rural Weather conditions Time of day Previous training/learning Familiarity Psychosocial Characteristics The psychosocial factors that affect mobility have not received the attention they deserve. Those that have been studied include the dynamics of the student-instructor interaction (Flaharty et al., 1976), client motivation (Murphy, 1965), and self-perception (Schulz, 1972, 1977; Welsh, 1972, 1981~. Among the factors that have not yet been studied systematically are expectations of success prior to mobility training, family relationships, and living conditions. Sensory and Motor Characteristics Sensory and motor capacity are obvious contributors to the eventual success or failure of mobility training. Because most of those who are classified as visually impaired retain some degree of usable vision, efforts have been to determine the residual capacity that characterizes various visual impairments and to determine the capacities of the other senses that either supplement remaining vision or replace lost vision.

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28 Marron and Bailey (1982) have shown that spatial contrast sensitivity and visual fields are better correlates of mobility performance than are standard measures of visual acuity. More research is needed to expand existing knowledge of the relative contributions of residual vision as well as hearing, touch, and gross motor ability to mobility performance. Perceptual and Cognitive Characteristics Considerable attention has been paid to the perceptual and cognitive factors on which mobility depends (Foulke, 1971, 1982b). Barth and Foulke (1979) have pointed out the importance of preview, and others have emphasized the importance of sensory training prior to instruction (Mills and Adamshick, 19691. However, a preponderance of the research relative to mobility has had as its objective a better understanding of the effect of blindness on the ability to acquire and use geographical concepts (Franks and Nolan, 1970, 1971; Lockman et al., 1981; McR-ynolds and Worchel, 1954; Rieser et al., 1980; Worchel, 1951~. There is a need for further study of the ability to acquire and use information contained in echoes {Clark et al., 1975), the interactive functioning of perceptual systems, and the processing mode that is best suited for efficient performance of the mobility task. MEASURES OF MOBILITY PERFORMANCE In the past two decades, significant advances in the assessment of mobility were made by researchers who developed objective measures of overt behavior based on operationally defined criteria and observable responses (Armstrong, 1975~. These methods, described below, have provided rational and scientifically defensible tools for basic research on mobility and for the objective evaluation of mobility aids and training methods. Unfortunately, these objective measures have not been used widely outside the laboratories in which they were developed. In part, this appears to be due to inadequate documentation of the methods and the need for specialized measuring equipment in order to to employ them. Indirect Measures Indirect measures of mobility are those that assess the underlying perceptual and cognitive processes that are responsible for overt behavior. Such methods are used to enhance the sensitivity of measurement by providing indices of stress or the demands placed on mental capacity of the pedestrian performing the mobility task. Heart rate measures obtained during mobility, for example, have provided valuable data concerning the psychological stress experienced by the blind traveler using different aids and performing in various

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29 environments (Heyes et al., 1976; Peake and Leonard, 1971; Tanaka et al., 1981; Wycherley and Nicklin, 1970~. The secondary task technique was used by Shingledecker (1983) to assess the reduction in the informa- tion processing demands of travel as a function of route familiar ity and previewed information. This technique involves having the pedestrian engage in a secondary, unrelated task while negotiating a route; it was also used to perform a performance benefits/mental costs evaluation of mobility aids. Despite the potential of these indirect measures of performance, very little has been done in recent years to further their development. However, several methods, such as analysis of the P300 component of event-related brain potentials (ERP), have proven useful as direct measures of the mental workload demanded by system design tasks and might prove useful in basic mobility research and ETA evaluation as well. A majority of the performance assessment work done by mobility specialists and many applied researchers is accomplished through the use of subjective assessment methods. Unfortunately, these methods have often consisted of informal and global expert judgments. Even when simple rating scales and checklists have been used, examination of subjective approaches has revealed evidence of rater bias and low interjudge reliability (Airasian, 1973; Nye, 1973~. Indirect measures correlate with direct measures of the mobility task. That is, they are influenced by factors other than the com- ponents of the mobility task and may include such measures as a comparison of heart rates during travel in familiar and unfamiliar environments or the personal assessment of confidence under varying circumstances. Indirect measures of mobility may be further divided into subjective and objective measures. Subjective measures include ratings by subjects of their ability to perform a task and to recover from errors and self-reports of mental workload. Objective measures include stride length, secondary task performance, veering tendencies, and the like. Direct Measures Direct measures used to assess mobility performance measure specific aspects of mobility, such as obstacle detection or a mobility specialist's subjective judgment of mobility skills. Examples of direct, objective measures of mobility are found in Table 5. Direct subjective measures include expert judgments (Airasian, 1973), self-reports of the quality of performance, checklists and rating scales (Genensky et al., 1979; Wurzburger, 1965), family reports, and estimates of personal satisfaction (Airasian, 1973; Bailey et al., 1984). The direct observation and measurement of behavior often requires expensive equipment and technical training and may prove impractical in many settings outside the laboratory. A more practical approach in these settings would be the use of instruments that rely on subjective judgments, such as ratings scales, but instruments of this sort require

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30 TABLE 5 Examples of Direct, Objective Measures of Mobility Safety Efficiency Travel Frequency Travel Distance Obstacle contacts Unsafe veering Fail to detect step-down Fail to detect step-up Inner shoreline body contact Walking speed Continuity of travel Navigational errors Veer Route departures Travel Familiarity or Difficulty Device/Sensory System Specific Measures Sign detection Search time Reading time Surface structure/texture determination Drop-off detection Directional determination Distance determination Ratio of Independent to Sighted Guide Travel Object or Landmark Detection psychological scaling before they are suitable for use, and to date little effort has been made to meet psychometric requirements. Outcome Measures of Successful Mobility In addition to objective measures of the performance of the mobility task itself, a thorough assessment of orientation and mobility must include measures of variations that are correlated with performance variables (Darling et al., 1977; Gillman and Simon, 1980; Morrissette et al., 1981~. These correlates are what might be called context van ~ acres. They make up the background against which the mobility task is performed. Included are such factors as social awareness and social skills, perceptual and cognitive strategies, and spatial knowledge. ~ ~ . _ _ -

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31 Personal satisfaction with the quality of life may be the most global and significant correlate of mobility, because mobility is a prerequisite for so many of the activities that give meaning to life (Blasch and Apple, 1975; Weisberger and Hall, 1985~. Few studies have incorporated these issues systematically as design components. ASSESSMENT OF MOBILITY Assessment of Mobility Aids Many of the travel aids that are currently or potentially useful to blind and visually impaired pedestrians are based on the application of electronics and optics technologies. In response to needs expressed by the military service as well as the general public, we can expect both of these technologies, including areas such as the study of artificial intelligence, to make significant contributions to solutions to mobility problems (Deering, 1985; Tou and Adjouadi, 1985~. The high cost of travel aids that make use of new technology, no matter how effective they might be, seriously limits their development. High cost may in part be a consequence of the protection from competition afforded by patents. For example, the Mowat Sensor, and the Sonicguide are both patented inventions that can be produced only by authorized manu- facturers. However, patents expire and other manufacturers may enter the fields and may produce a greater variety of less expensive aids. A recurring criticism of the way in which travel aids have been developed is the lack of communication between their developers and such groups as mobility specialists and specialists in the evaluation of per- formance. The result of this failure of communication is that the conception, development, and production of sensory aids is not guided by full awareness of the needs of those who are expected to use them, by a clear definition of their strengths and weaknesses, or by an adequate understanding of the nature of the training their mastery will require (Brabyn, 1985; Dodds, 1985; Dodds et al., 1983; Spungin, 1985; Warren and Strelow, 1984b, 1985~. A Standardized Method for Assessing Travel Performance The field of mobility assessment is currently in a state of disarray. There is an absence of controlled studies of mobility skills. There is an incomplete understanding of the effects of electronic travel aids, training methods, and other factors on mobility. This situation is due in part to the fact that the field has failed to adopt a standardized method for assessing travel performance. One of the reasons for the lack of a common assessment method rests in the fact that assessments are performed by a variety of individuals to meet diverse goals. The basic research scientist, for example, may use performance measures to test hypotheses about the nature of the perceptual and cognitive processes that underlie travel behavior. The applied research scientist might employ performance measures to evaluate

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32 the efficacy of a particular electronic travel aid. Finally, the mobility specialist may use performance measures to evaluate a student's progress, to formulate training goals, or to develop recommendations for the prescription of a particular aid. The same assessment method does not necessarily suit all situations. It is not really surprising, therefore, that these professionals would select different measures to achieve their particular objectives. The differences among measures--such as those described in Table 5 and elsewhere in this chapter--can be appreciated by considering their theoretical and practical dimensions. Preferred measures are those that would be sensitive to changes in the individual's capabilities, that can be reliably measured, and that validly index the skill being assessed. Performance assessment measures should provide information about overt behavior, such as the quality of the travel skill displayed overtly by the pedestrian. Such measures may be based on expert judgments or on objective performance data that define safe, efficient, and purposeful travel. These goals can be operationally defined in terms of walking speed, obstacle contact, navigational accuracy, and various productivity indices. Ideally, such measures should be "device-free," that is, they should be applicable to an individual's performance regardless of the travel aid used. However, some device- specific measures may be justified if they are used to draw inferences about some objective aspect of travel skill. For example, shoreline cane contacts or efficient sign-reading with a telescope are valid objective indices in an outdoor travel evaluation. Performance assessment measures should also describe covert processes that account for observed travel behavior, such as the psychological cost of mobility under different travel conditions or in the use of various travel aids. Such information may be obtained from subjective reports, behavioral observations, or electrophysiological measurements. Historically, such measures have included rating scales to assess travel ease and confidence, heart rate parameters to assess stress levels, and secondary tasks Performed in conjunction with _ _ _ mon~ty to assess the reserve information-processing capacity of the traveler. An important feature of indirect measurement is its ability to increase the overall sensitivity of the assessment procedure by detecting differences that are not reflected in general measures of overt performance. For example, two travel aids may provide equivalent overt performance but, in one case, the pedestrian is performing at the limits of his or her information-processing capacity. It is important to realize that direct and indirect measures are not mutually exclusive alternatives in the assessment of mobility performance. Finally, an inescapable fact regarding the assessment of mobility is the necessity to isolate the individual components of mobility skill and to synthesize them once more into a global evaluation of total performance. From a practitioner's point of view, the emphasis must be placed on whole-skill measurement.

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33 RECOMMENDATIONS It is clear from the information presented in this chapter that there is a need to develop a framework or theory of mobility that identifies the perceptual and cognitive components of mobility and that makes explicit the extent to which mobility is influenced by such factors as training, travel aids, the nature of the environment in which the mobility task is performed, and social variables. We need to develop consistent techniques and measures of mobility performance so that experiments can be replicated and their results compared. Finally, there is a need for improved experimental designs, which reflect more careful attention to such issues as the use of experimental controls, sample size, statistical analysis, and the generalizability of the results of experiments. In order to attain these goals, we make the recommendations that follow. Standardized Measures of Mobility Performance Accurate and practical assessment of the performance of blind and visually impaired pedestrians is urgently needed. It is not likely that a single scheme that is appropriate to all situations can be developed, but the development of several coordinated methods is a realistic objective. Standardized procedure for evaluating mobility aids and a standardized procedure for assessing and comparing the performances of subjects with different kinds and degrees of visual impairment would be immediately useful to researchers and practitioners alike. Explication of these procedures should include statements of the rationale for all of the instruments involved in assessment, and complete documentation should be provided for each instrument. There is also a need to develop additional indirect measures of mobility performance. These might include measures of the performance of a secondary task, such as the task of conducting a conversation with a companion while traveling on foot independently. Because fluctuations in the performance of a secondary task often permit inferences con- cerning relatively subtle changes in the performance of the primary task, important differences in task performance can be detected only by indirect measures. RECOMMENDATION: Efforts to develop improved methods for measuring performance of the mobility task should be a research priority for federal funding agencies involved in this area. Research should be undertaken immediately on the development of improved objective measures of mobility performance, drawing on past efforts in England, the United States, and New Zealand. Simulation Methods There is a need to develop simulation environments to study mobility performance and its assessment. Such simulations, while

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34 preserving fidelity to the real world in important respects, permit experimental controls that cannot be enforced in the real world. We will not make significant progress in assessing the performance of blind travelers, evaluating training methods and travel aids, and designing improved travel aids until our efforts are guided by a comprehensive theory of mobility that has been confirmed by the results of numerous experiments, and many of these experiments can be conducted more effectively and efficiently in a simulated environment than in any other setting. However, the construction of simulated environments is an expensive undertaking, for which federal assistance is not likely. Simulated spaces must be large enough to permit realistic performance of mobility tasks. Such spaces should also have the physical and acoustical characteristics of the surfaces and space an individual will encounter in the real world (Shingledecker and Foulke, 1978~. RECOMMENDATION: Investigators should more frequently use simulated environments to study mobility performance and its assessment. The private sector could contribute to the development of simulation methods through the development of simulation technology. Improved Field Assessment Techniques Assessment techniques used in the laboratory often require expensive instruments and facilities and technically trained personnel. Conse- quently, their use in field studies is not practical. More subjective techniques such as rating scales, expert judgments, and the like, can be made serviceable if they are validated by the application of psycho- metric methods; this work is yet to be done. RECOMMENDATION: Improved field assessment techniques should be developed through strengthened support for research in which psycho- metric methods are used to develop rating scales and other measuring instruments of that type. Technology Benchmarks As developments in technology continue, new travel aids, which go beyond the current state of technology, will be built. As a necessary step in their development, a rigorous comparison will be needed of the performance facilitated by travel aids now in use. The information yielded by such comparisons is essential in deciding about the actual contribution made by new travel aids to the performance of the mobility taske RECOMMENDATION: Because progress in the development of travel aids and better methods for their assessment will depend in part on making individuals in many different disciplines more aware of the current state of mobility problems, we recommend that communication among such groups as engineers, psychologists, mobility specialists, teachers, and

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35 consumers be facilitated. Federal funding agencies can play a role by actively funding conferences and workshops to further the development of performance comparisons of new and existing technologies. Training Programs It is not sufficient to assess the improvement in performance made possible by the use of a travel aid. We must also do a more effective job of assessing the improvement in performance that is attributed to participation in a training program. Furthermore, we must do a more conscientious job of evaluating the programs in which blind pedestrians are trained and the programs in which mobility specialists are trained. RECOMMENDATION: We recommend that academic departments in which mobility specialists are trained and the federal agencies from which they receive support cooperate in providing more training for students in the assessment of performance.