Showing papers in "Human Factors in 1991"

Improving auditory warning design: relationship between warning sound parameters and perceived urgency.

Abstract: This paper presents an experimental study of the effects of individual sound parameters on perceived (psychoacoustic) urgency. Experimental Series 1 showed that fundamental frequency, harmonic series, amplitude envelope shape, and delayed harmonics all have clear and consistent effects on perceived urgency. Experimental Series 2 showed that temporal and melodic parameters such as speed, rhythm, pitch range, and melodic structure also have clear and consistent effects on perceived urgency. The final experiment tested a set of 13 auditory warnings generated by an application of the earlier experimental findings. The urgency rank ordering of this warning set was predicted, and the correlation between the predicted and the obtained order was highly significant. The results of these experiments have a widespread application in the improvement of existing auditory warning systems and the design of new systems, where the psychoacoustic and psychological appropriateness of warnings could be enhanced.

Psychometric properties of subjective workload measurement techniques: implications for their use in the assessment of perceived mental workload

Abstract: This paper examines fundamental measurement issues that have largely been ignored in scaling techniques for assessing perceived mental workload. It is argued that both theoretical and practical advances in workload assessment have been unnecessarily slowed by a lack of concern for measurement issues. Typical of this impedance are some recently reported “empirical results“ comparing various workload assessment techniques which actually follow directly from some misunderstood statistical properties of the scales. The commonly used subjective workload assessment procedures have distinct psychometric properties that make each procedure sensitive to different kinds of workload measurement. Examination of the properties for the National Aeronautics and Space Administration Task Load Index (NASA TLX) support its potential as a general prediction model for experienced workload and for the Subjective Workload Assessment Technique (SWAT) as a cognitive model sensitive to individual differences.

Work posture, workstation design, and musculoskeletal discomfort in a VDT data entry task

Abstract: Self-report data on musculoskeletal discomfort were collected from several hundred VDT users in two agencies of a state government. Aspects of worker posture and workstation design were objectively assessed for 40 of the VDT users. Multiple regression analyses were used to examine the relationship between these ergonomic variables and musculoskeletal discomfort. Effects of ergonomic factors on musculoskeletal discomfort were clearly evident in the analyses. Regression models explained up to 38% of the variance in discomfort at different body sites. Of special interest was that leg discomfort increased with low, soft seat pans, suggesting that postural constraint is more important than thigh compression as a risk factor for leg discomfort in VDT work. In addition, arm discomfort increased with increases in keyboard height above elbow level, supporting arguments for low placement of the keyboard. Finally, high levels of neck and shoulder girdle discomfort observed in the study population suggest the need for further attention to the control of cervicobrachial pain syndromes in VDT work.

Identifying correlates of accident involvement for the older driver

Abstract: Most older adults rely on the automobile to maintain their mobility and independence, in spite of the fact that age-related behavioral and biomedical changes may make driving more difficult. Indeed, accident and fatality rates begin to rise after age 55. One research goal, therefore, is to identify functional measures that differentiate older adults who drive safely from those who do not. This paper discusses conceptual and methodological issues involved in addressing this question, considers why earlier research has been largely unsuccessful, presents a working model for approaching the problem, and argues the need for large-sample, prospective research in this area.

Visual requirements for safety and mobility of older drivers.

Abstract: Efforts to assess visual deterioration with increasing age, coupled with new mechanisms proposed to limit the exposure of visually impaired drivers to driving risks, have emerged in response to the increase in older drivers. Visual functions discussed in this context include static acuity (photopic, mesopic, and in the presence of glare), dynamic visual acuity, visual field, contrast sensitivity, and motion perception. Exposure control mechanisms discussed include alternative periodic vision testing strategies, visual training, and environmental and vehicular modifications to accommodate the older driver. Finally, relevant research needs are addressed.

The design of electronic map displays

Abstract: This paper presents a cognitive analysis of a pilot's navigation task and describes an experiment comparing a new map display that employs the principle of visual momentum with the two traditional approaches, track-up and north-up. The data show that the advantage of a track-up alignment is its congruence with the egocentered forward view; however, the inconsistency of the rotating display hinders development of a cognitive map. The stability of a north-up alignment aids the acquisition of a cognitive map, but there is a cost associated with the mental rotation of the display to a track-up alignment for tasks involving the ego-centered forward view. The data also show that the visual momentum design captures the benefits and reduces the costs associated with the two traditional approaches.

A three-dimensional motion model of loads on the Lumbar spine: I. model structure

Abstract: Traditionally most biomechanical models that are used to estimate the loading experienced by the spine during work focus on static, two-dimensional representations of the work. However, most work tasks impose loads on the lumbar spine under dynamic, three-dimensional conditions. The objective of this study was to describe the structure and logic of a model that is capable of producing estimates of spine loading under three-dimensional motion conditions. This model is intended for use primarily under laboratory conditions. The model was designed initially for workplace simulation in which the trunk is moving under symmetric and asymmetric constant velocity lifting conditions. Future embellishments may enable the model to be used under free dynamic conditions. The model predicts lumbar spine compression, shear, and torsional forces as well as trunk torque production continuously throughout the exertion. This information may be compared with spine tolerance limits so that the risk of causing a vertebral end-plate microfracture by workplace requirements could be determined.

The older driver.

Abstract: Older drivers constitute the most rapidly growing segment of the driving population in number of drivers licensed, miles driven, and proportion of the driving population. Yet the highway transportation system has not been designed for these drivers. This lack of fit is reflected in the accelerating rate of crashes per mile driven experienced by older drivers beginning around age 55. Furthermore, older persons are more vulnerable to injury once a crash occurs and as a group experience a higher fatality rate. The increasing proportion of our population consisting of older persons, in conjunction with a relative decrease in the young adult population, underscores the need for research to develop a greater understanding of the needs and capabilities of this age group and to develop system improvements that will enable as many older persons as possible to continue to meet their own transportation needs safely.

Attention and driving skills in aging and Alzheimer's disease

Abstract: The number of older drivers with dementia is rising with the aging of the adult population. A public health issue is growing because of concerns about the motor vehicle accident risk posed by drivers with dementia of the Alzheimer's type (DAT) and other progressive, degenerative dementias. However, little is known about the specific perceptual/cognitive deficits contributing to impaired driving in DAT. The present paper proposes, on both theoretical and empirical grounds, that attentional skills in relation to driving should be examined in older adults with and without DAT. Such investigations should focus on normal older adults and those in the mild, early stages of dementia because the latter are the most likely among the dementia population to be still driving. Evidence is presented indicating (1) that motor vehicle accident rates are related to performance on information-processing measures of different components of attention; (2) that this relationship is greatest for measures of the switching of selective attention and less for that of divided and sustained attention (vigilance); and (3) that many of these same attentional functions, and particularly the switching of visual selective attention, are impaired in the early stages of DAT and thus may contribute to increased accident risk. Further studies of cognitive and driving performance in older drivers are necessary to establish that the attentional impairments found in mild DAT contribute to increased accident risk. Implications of these findings for driver assessment, education, and training are discussed.

Three-dimensional motion model of loads on the lumbar spine: II. model validation

Abstract: A three-dimensional motion model has been developed that estimates loads on the lumbar spine under laboratory conditions that simulate manual materials handling conditions. Eleven subjects experienced spinal loading during an experiment in which conditions of trunk velocity, trunk torque output, and trunk asymmetric posture were varied in a series of isokinetic velocity trunk extensions. The electromyographic activity of 10 trunk muscles, subject anthropometry, and trunk kinetics were used as input to a biomechanical simulation model described in Part I of this study. The model calculated estimates of compression, shear, and torsion loading in the lumbar spine, as well as the torque production of the trunk, continuously throughout the exertion. Trunk torque estimates derived from this model were compared with measured trunk torque. The effects of trunk motion, posture, and torque level on spine loading as estimated by the model are discussed. It was concluded that this approach provides a straightforward means of assessing loading of the spine attributable to laboratory simulations of workplace conditions. Language: en

Divided attention in experienced young and older drivers: lane tracking and visual analysis in a dynamic driving simulator.

Abstract: A simulated driving task that required the simultaneous execution of two continuous visual tasks was administered to 12 healthy young (mean age 26.1 years) and 12 healthy older (mean age 64.4 years) experienced and currently active drivers. The first task was a compensatory lane-tracking task involving a three-dimensional road display. The second task was a timed, self-paced visual analysis task involving either a vocal or manual binary response to dot patterns projected within the road display. Using adaptive tasks, single-task difficulty was individually adjusted for each subject. To control for individual differences in attention allocation strategy, the dual task was performed according to three different sets of instructions based on the relative importance of each task. Compared with young adults, older adults showed a significantly decreased ability to divide attention. This effect was apparent in lane tracking and in the accuracy of visual analysis. The impairment of divided attention was less pronounced in the vocal condition than in the manual one. This suggests that difficulty in integrating responses may be an important determinant of poor dual-task performance in old age.

Eyestrain in VDU users: viewing distance and the resting position of ocular muscles

Abstract: Without fixation stimuli--for instance, in darkness--accommodation and convergence of the eyes reach an intermediate state that is relatively stable within a subject but which ranges from about 30 cm to infinity across subjects. This study investigated whether these oculomotor positions in darkness are related to visual strain. During work at a visual display unit (VDU), visual strain at a viewing distance of 50 cm was stronger than at 100 cm (with characters twice as large). The more distant the individual's dark convergence, the greater was the visual strain at the 50-cm viewing distance. When subjects were free to adjust the viewing distance to their comfort level, they chose distances between 51 and 99 cm (mean 74 cm) with characters 5 mm tall.

The development of technology for collective training: SIMNET, a case history

Abstract: SIMNET, an acronym for simulator networking, was initiated in 1983 as a project on large-scale simulator networking by the Defense Advanced Research Projects Agency (DARPA; Order AO 4739, signed Fe...

Strategic behavior, workload, and performance in task scheduling

Abstract: Scheduling theory is proposed as a normative model for strategic behavior when operators are confronted by several tasks, all of which should be completed within a fixed time span, and when they are free to choose the order in which the tasks should be done. Three experiments are described to investigate the effect of knowing the correct scheduling rule on the efficiency of performance, subjective workload, and choice of strategy under different conditions of time pressure. The most potent effects are from time pressure. The reasons for the weak effect of knowing the rules are discussed, and implications for strategic behavior, displays, and decision aids are indicated.

Aurally aided visual search in the central visual field: effects of visual load and visual enhancement of the target

Abstract: Visual search performance was examined in a two-alternative, forced-choice paradigm. The task involved locating and identifying which of two visual targets was present on a trial. The location of the targets varied relative to the subject's initial fixation point from 0 to 14.8 deg. The visual targets were either presented concurrently with a sound located at the same position as the visual target or were presented in silence. Both the number of distractor visual figures (0-63) present in the field during the search (Experiments 1 and 2) and the distinctness of the visual target relative to the distractors (Experiment 2) were considered. Under all conditions, visual search latencies were reduced when spatially correlated sounds were present. Aurally guided search was particularly enhanced when the visual target was located in the peripheral regions of the central visual field and when a larger number of distractor images (63) were present. Similar results were obtained under conditions in which the target was visually enhanced. These results indicate that spatially correlated sounds may have considerable utility in high-information environments (e.g., piloting an aircraft). Language: en

Age-related eye disease, visual impairment, and driving in the elderly.

Abstract: As people age, a number of visual functions such as acuity, visual field, and night vision deteriorate. This decline in vision is associated in part with an increase in vehicular accidents per mile driven by the elderly. Four age-related ocular conditions--cataract, macular degeneration, open-angle glaucoma, and diabetic retinopathy--are primarily responsible for the decline in visual acuity and visual field in the elderly. Few epidemiologic data are available about these diseases, and at present they cannot be prevented. There is need for more information about visual decline and how it affects driving performance and for development of pragmatic approaches for detecting and assessing the elderly driver with functional visual deficits.

An informational perspective on skill transfer in human-machine systems

Abstract: Differentiation of perceptual invariants is proposed as a theoretical approach to explain skill transfer for control at the human-machine interface. I propose that sensitivity to perceptual invaria...

Influence of experience on age differences in cognitive functioning

Abstract: To the extent that adult age differences in measures of cognitive performance have implications for functioning outside the psychological laboratory, the question of the role of experience as a potential moderator of these differences becomes extremely important. Three categories of research relevant to this issue are reviewed, and methodological limitations of each type of research are discussed. Although it is frequently asserted that experience minimizes cognitive differences associated with aging, the evidence currently available does not appear consistent with a strong experiential moderation of age-related effects in cognitive performance. However, the paucity of relevant studies and the methodological weaknesses of those that do exist preclude a definitive conclusion at the present time. Additional research with improved methodology is necessary before strong conclusions can be reached concerning effects of experience on age differences in cognition.

Emergent Features in Visual Display Design for Two Types of Failure Detection Tasks

Abstract: Visual display design for dynamic systems may be helped by exploiting emergent features that allow subjects to easily distinguish different states of the system. Three different types of displays were compared--two object displays and one separated display--each in a version that had a salient emergent feature that distinguished normal and failed states and in a version that did not have such an emergent feature. Subjects monitored for global and local failures simultaneously, which presented demands similar to integrated and separated tasks, respectively. Displays with salient emergent features supported superior global failure detection and may also have helped local failure detection. An object display with a salient emergent feature supported both types of failures better than or at least as well as the other displays. This advantage was attributed to the fact that the display had a salient emergent feature rather than to the fact that it was an object display. This research shows that emergent features can be effectively exploited to support tasks involving both integration of information and attention to individual data sources.

Dementia and the older driver.

Abstract: The association between dementia and driving errors in older adults has been anecdotally noted by clinicians and caregivers. However, until recently, little empirical documentation of this association existed. This paper provides a critical review of available research on dementia and driving and discusses issues that must be considered in attempting to apply this developing body of research to practical problems, such as the relicensing process for selected drivers. This is followed by a discussion of recent research relevant to the development of potential procedures for screening patients with dementing illness--particularly Alzheimer's disease--for probable driving risk.

Using the Subjective Workload Dominance (SWORD) technique for projective workload assessment.

Abstract: The present study examined the utility of the Subjective Workload Dominance (SWORD) technique as a projective workload tool. Two groups predicted the workload associated with using six possible hea...

Comprehension of synthetic speech produced by rule: word monitoring and sentence-by-sentence listening times

Abstract: Previous comprehension studies using postperceptual memory tests have often reported negligible differences in performance between natural speech and several kinds of synthetic speech produced by rule, despite large differences in segmental intelligibility The present experiments investigated the comprehension of natural and synthetic speech using two different on-line tasks: word monitoring and sentence-by-sentence listening On-line task performance was slower and less accurate for passages of synthetic speech than for passages of natural speech Recognition memory performance in both experiments was less accurate following passages of synthetic speech than of natural speech Monitoring performance, sentence listening times, and recognition memory accuracy all showed moderate correlations with intelligibility scores obtained using the Modified Rhyme Test The results suggest that poorer comprehension of passages of synthetic speech is attributable in part to the greater encoding demands of synthetic speech In contrast to earlier studies, the present results demonstrate that on-line tasks can be used to measure differences in comprehension performance between natural and synthetic speech Language: en

Toward an integration of training theory and technique

Abstract: Reviewers of the training literature have generally concluded that training theory and practice are not well integrated, and that research findings are not often translated into useful training methods. In an effort to bridge the gap between training theory and practice, an organizing framework for conceptualizing training research is presented. The purpose of the framework is to highlight the linkages between training-related theory and technique in the areas of training analysis, design, and evaluation. The linkages are described in detail, and illustrated via consideration of research into mental models. We hope that the framework will lead to future research programs that enhance the transition of training research from theory into practice, and integrate more fully these two perspectives

Age-related differences in the maintenance and modification of automatic processes: arithmetic stroop interference

Abstract: This experiment was designed to investigate whether well-learned "automatic" processes remain stable as a function of age, as well as to determine whether the ability to modify these automatic processes is disrupted for older adults. We used an arithmetic Stroop task to measure the stability of an automatic process. Nineteen young (mean age 22) and 19 old (mean age 75) adults participated in three experimental sessions, each of which consisted of 15 blocks of 30 trials. Although the young subjects had faster verification times overall than did the old adults, both young and old subjects showed significant interference effects. For the young adults, there was a decrease in the interference effect with practice, which suggested that they were learning to inhibit the automatic process of performing the arithmetical operation. However, the old adults showed no significant decrease in the associative interference effects. This implies that the older adults were impaired in their ability to inhibit automatic processes, even when those processes interfered with performance. Theoretical and practical training implications are discussed.

A cognitive engineering approach to improving signalized left turn intersections.

Abstract: This research evaluated the effect of providing advanced left turn information to individuals faced with deciding whether or not it is safe to turn at a signalized intersection. Younger (mean age 37 years) and older (mean age 71 years) drivers were tested in simulations of approaching an intersection with and without advanced cueing. Experiment 1 used a featureless background; Experiment 2 used an animated presentation of traffic control displays. In both experiments the subjects had to determine whether or not they had right-of-way to make a left turn. Exaggerated error rates and increased decision latencies for displays conveying unprotected turn status occurred in both studies. Cueing drivers with advanced notice of the decision rule through a redundant upstream posting of sign elements improved both accuracy and latency of younger and older drivers' decisions.

Effects of skill integration and perceptual competition on age-related differences in dual-task performance

Abstract: Age-related differences in dual-task performance may be affected by factors such as skill integration and perceptual competition. Therefore these factors were examined in a dual-task experiment with young and older adults involving two one-dimensional compensatory tracking tasks. Single-task difficulty was individually adjusted for each subject. It was found that differences in pure dual-task performance between young and older subjects increase when the subtasks are coherent such that skills can be integrated. In addition, the degree to which integration reduces the effects of visual competition was larger for the young than for the older subjects. It is concluded that in dual tasks with coherent subtasks, older adults may show an impaired ability to perform the subtasks in an integrated manner.

An ellipsoidal representation of human hand anthropometry

Abstract: Anthropometric data concerning the heometry of the hand's surface are presently modeled as a function of gross external hand measurements; an effort is made to evaluate the accuracy with which ellipsoids describe the geometry of the hand segments. Graphical comparisons indicate that differences between the ellipsoidal approximations and the breadth and depth measurements were greatest near the joints. On the bases of the present data, a set of overlapping ellipsoids could furnish a more accurate representation of hand geometry for adaptation to ellipsoid segment-geometry employing biomechanical models.

Cognitive factors and the use of over-the-counter medication organizers by arthritis patients

Abstract: The present study investigated the ability of 45 arthritis patients, all using three or more prescription medications, to correctly load their medications into three types of over-the-counter medication organizers. The results indicated that use of a seven-day organizer with compartments for different times resulted in fewer errors than did an hour-by-hour wheel organizer or a seven-day organizer with only one compartment for each day. It was concluded that the seven-day organizer with compartments for different times appears to have the potential to improve compliance behaviors, but the usefulness of the other two organizers in promoting compliance is uncertain. Data analyses also indicated that age was not related to comprehension or loading accuracy of the organizers but that individuals using seven or more prescribed medications were particularly likely to make comprehension errors.

Explicit and implicit horizons for simulated landing approaches

Abstract: In a flight simulator experienced pilots flew landing approaches to a representation of an airport scene in which various sources of information had been distorted or removed. Reasonably accurate approaches could be made to a scene that contained only an aimpoint and a horizon. The addition of a runway outline did not enhance accuracy or stability, which lent credence to the hypothesis that the invariant angle between horizon and aimpoint can support glide slope control. Explicit distortion of this angle by simulation of up-sloping or down-sloping terrain beyond the runway had predictable effects on glide slope control. Implicit specification of a veridical horizon with texture lines parallel to the runway centerline weakened the effect of distortions in the explicit horizon. Thus both explicit and implicit specifications of the horizon contribute to perception of the glide slope angle. Implications of these results for the design of visual scenes for flight simulation are discussed.

Recent changes in driving among older adults

Abstract: Driving statistics comparing drivers aged at least 65 years with all drivers are examined for the years 1980 and 1989. In that time older driver fatalities had increased substantially despite a decrease in total driver fatalities. Analyses of size of population, numbers of licensed drivers, estimates of miles driven, and crash rates for these two years imply that the rise in total older driver deaths is related to increasing numbers of older adults who are licensed to drive and an increase in likelihood of fatality following a motor vehicle crash. This latter effect may be associated with a very substantial rise in the numbers of licensed drivers age 70 and older.