Showing papers in "Human Factors in 1993"

The efficiency of instructional conditions: An approach to combine mental-effort and performance measures

Abstract: This article reports on a calculational approach for combining measures of mental workload and task performance that allows one to obtain information on the relative efficiency of instructional conditions. The method is based on the standardization of raw scores for mental effort and task performance to z scores, which are displayed in a cross of axes. Relative condition efficiency is calculated as the perpendicular distance to the line that is assumed to represent an efficiency of zero. We conclude that the method for calculating and representing relative condition efficiency discussed here can be a valuable addition to research on the training and performance of complex cognitive tasks.

Recommendations for Mental Workload Measurement in a Test and Evaluation Environment

Abstract: Research performed during the last decade on estimation of mental workload has resulted in a subset of techniques exhibiting global sensitivity. Other techniques have also been demonstrated to have...

Cockpit checklists - Concepts, design, and use

Abstract: Although the aircraft checklist has long been regarded as a foundation of pilot standardization and cockpit safety, it has escaped the scrutiny of the human factors profession. The improper use, or nonuse, of the normal checklist by flight crews is often cited as a major contributing factor to aircraft accidents. This paper reports the results of a field study of flight deck checklists and examines this seemingly mundane yet critical device from several perspectives: its functions, format, design, length, and usage, and the limitations of the humans who must interact with it. Certain sociotechnical factors, such as the airline 'culture', cockpit resource management, and production pressures that influence the design and use of this device, are also discussed. Finally, a list of design guidelines for normal checklists is provided. Although the focus of this paper is on the air transport industry, most of the principles discussed apply equally well to other high-risk industries, such as maritime transportation, power production, weapons systems, space flight, and medical care.

Modeling Strategic Behavior in Human-Automation Interaction: Why an "Aid" Can (and Should) Go Unused:

Abstract: Task-offload aids (e.g., an autopilot, an 'intelligent' assistant) can be selectively engaged by the human operator to dynamically delegate tasks to automation. Introducing such aids eliminates some task demands but creates new ones associated with programming, engaging, and disengaging the aiding device via an interface. The burdens associated with managing automation can sometimes outweigh the potential benefits of automation to improved system performance. Aid design parameters and features of the overall multitask context combine to determine whether or not a task-offload aid will effectively support the operator. A modeling and sensitivity analysis approach is presented that identifies effective strategies for human-automation interaction as a function of three task-context parameters and three aid design parameters. The analysis and modeling approaches provide resources for predicting how a well-adapted operator will use a given task-offload aid, and for specifying aid design features that ensure that automation will provide effective operator support in a multitask environment.

Improving Auditory Warning Design: Quantifying and Predicting the Effects of Different Warning Parameters on Perceived Urgency

Abstract: The effects of four parameters (speed, fundamental frequency, repetition units, and inharmonicity) on perceived urgency were scaled using an application of Stevens's power law. From the exponents obtained, equal units of urgency change were calculated for three parameters. The units were combined in a set of stimuli, and the order of urgency was predicted. The obtained and predicted orders of urgency were highly correlated. The results also showed that even when equalized by psychophysical techniques, some parameters contribute more to perceived urgency than do others. This may be attributable to the different types of parameters scaled or the proportion of the usable range of each parameter that represents a unit change in urgency. The implication of the work for the design and improvement of auditory warnings is discussed.

Measuring Subjective Workload: When Is One Scale Better Than Many?:

Abstract: The idea that mental workload should be treated as a multidimensional problem is well recognized. Yet the NASA Task Load Index and Subjective Workload Assessment Technique scales incorporate proced...

Head-up auditory displays for traffic collision avoidance system advisories: a preliminary investigation

Abstract: The advantage of a head-up auditory display was evaluated in a preliminary experiment designed to measure and compare the acquisition time for capturing visual targets under two auditory conditions: standard one-earpiece presentation and two-earpiece three-dimensional (3D) audio presentation. Twelve commercial airline crews were tested under full mission simulation conditions at the NASA-Ames Man-Vehicle Systems Research Facility advanced concepts flight simulator. Scenario software generated visual targets corresponding to aircraft that would activate a traffic collision avoidance system (TCAS) aural advisory; the spatial auditory position was linked to the visual position with 3D audio presentation. Results showed that crew members using a 3D auditory display acquired targets approximately 2.2 s faster than did crew members who used one-earpiece headsets, but there was no significant difference in the number of targets acquired.

Effects of Stereoscopic and Rotational Displays in a Three-Dimensional Path- Tracing Task

Abstract: A series of three experiments investigated the effectiveness of stereoscopic and rotational display techniques for the purpose of establishing human factors guidelines for the design of three-dimensional (3D) displays. In the described experiments, depth perception was evaluated by examining accuracy in a 3D path-tracing task, with stimulus displays resembling the structure of cerebral angiograms. The first experiment allowed subjects to control rotation in dynamic displays. The results indicated that performance improved using either technique relative to viewing two-dimensional (2D) displays. However, rotational displays were superior to stereoscopic displays, and performance was best when both techniques were combined. The second experiment compared subject-controlled rotation with observation of continuously rotating displays at different rates of rotation. Performance declined at faster rotation rates; however, there were no advantages of subject-controlled rotation. In the third experiment, performance in rotational displays was no better than that in stereoscopic displays enhanced with multiple static viewing angles. However, performance was always best when both 3D techniques were jointly implemented. The results are discussed in terms of the visual information available using either 3D display technique and are related to the weighted additive model of depth perception. Language: en

Cognitive function at high altitude.

Abstract: The effects of altitude on human performance and cognition were evaluated in a field study performed on Mount Denali in Alaska during the summer of 1990. Climbers performed a series of perceptual, cognitive, and sensory-motor tasks before, during, and after climbing the West Buttress route on Denali. Relative to a matched control group that performed the tasks at sea level, the climbers showed deficits of learning and retention in perceptual and memory tasks. Furthermore, climbers performed more slowly on most tasks than did the control group, suggesting long-term deficits that may be attributed to repeated forays to high altitudes.

Effect of Electronic Performance Monitoring on Job Design and Worker Stress: Review of the Literature and Conceptual Model

Abstract: An approach to electronic performance monitoring is developed that examines job design and worker stress theories and consequently defines the critical job elements of stress response in an electro...

Emergent features and graphical elements: designing more effective configural displays

Abstract: When performing tasks in complex, dynamic domains individuals must consider information regarding both high-level constraints (relationships among several variables, performance goals) and low-level data (the values of individual variables). Previous research has revealed mixed results concerning the effectiveness of configural displays in achieving these dual design goals. Two empirical studies were conducted to investigate these issues using a laboratory analogue of a complex, dynamic task modeled on a real-world domain. Performance with a configural display, which highlighted the low-level data, was compared with performance with a bar graph display. For the extraction of information about high-level constraints in a memory probe task, the configural display significantly increased accuracy with no cost in latency. For low-level data there were no differences in accuracy across the two display conditions, but there was a significant cost in latency with the configural display. However, this cost was de...

Headphone localization of speech

Abstract: Three-dimensional acoustic display systems have recently been developed that synthesize virtual sound sources over headphones based on filtering by head-related transfer functions (HRTFs), the direction-dependent spectral changes caused primarily by the pinnae. In this study, 11 inexperienced subjects judged the apparent spatial location of headphone-presented speech stimuli filtered with nonindividualized HRTFs. About half of the subjects 'pulled' their judgments toward either the median or the lateral-vertical planes, and estimates were almost always elevated. Individual differences were pronounced for the distance judgments; 15 to 46 percent of stimuli were heard inside the head, with the shortest estimates near the median plane. The results suggest that most listeners can obtain useful azimuth information from speech stimuli filtered by nonindividualized HRTFs. Measurements of localization error and reversal rates are comparable with a previous study that used broadband noise stimuli.

Psychophysical determinants of stress in sustained attention.

Abstract: To date, research on the stress of sustained attention tasks has not explored the extent to which such stress is determined by the psychophysical aspects of the monitored display. In the present study, the effects of the sensory modality of signals (audition and vision) and the background event rate (5 and 40 events/min) on task-induced stress were examined in a vigilance situation. Critical signals for detection were slight changes in stimulus duration. Stress was indexed by motor restlessness and subjective reports of fatigue. Restlessness and subjective fatigue increased dramatically across a 50-min watch in all conditions. Stress effects were most notable in the case of visual monitoring but were unrelated to variations in event rate. Hence, from a psychophysical perspective, the stress of sustained attention seems to be identified more specifically with the sensory modality of signals than with the event rate context in which they appear.

Spatial and temporal characteristics of rapid cursor-positioning movements with electromechanical mice in human-computer interaction.

Abstract: This research examines how people make movements with pointing devices during human-computer interaction. It specifically concerns the perceptual-motor processes that mediate the speed and accuracy of cursor positioning with electromechanical mice. In three experiments we investigated the spatial and temporal characteristics of positioning movements made with a mouse, analyzing subjects' speed and accuracy as a function of the types of targets that the movements had to reach. Experiment 1 required rapid and accurate horizontal movements to targets that were vertical ribbons located at various distances from the mouse's starting location. The targets for Experiments 2 and 3, respectively, were vertical lines having various heights and rectangular boxes having various heights and widths. Constraints on movement distance along the primary (that is, horizontal) line of motion had the greatest effects on total positioning times. However, constraints on movement distance along a secondary (vertical) line of motion also affected total positioning times significantly. These effects may be localized in different phases of movements (e.g., movement execution and verification). The duration of movement execution (i.e., physical motion) depends primarily on the target distance, whereas the duration of movement verification (i.e., check for endpoint accuracy) depends primarily on target height and width. A useful account of movement execution is provided by stochastic optimized-submovement models, which have significant implications for designing mice and menu-driven displays.

Experimental evaluation of a model of mental workload

Abstract: This study was designed to test predictions from a model of mental workload. The model predicts that mental workload grows as perceived distance from a task goal increases and the effective time for action decreases. Decreases in workload can be achieved by actions that bring the task goal into the region of acceptable time/distance constraints for successful resolution. We reported an experiment that tested these assertions using the Timepools performance task. Timepools generates a spatial representation of a shrinking temporal target to assess the effects of path length (i.e., the number of sequential targets to be acquired) and shrink rate (i.e., elapsed time during which the circle is halved in area) on reaction time (RT), movement time (MT), error rate, and the subjective perception of workload. Data from the experiment indicated systematic effects for task-related factors across performance and workload measures. Path length and shrink rate had differential effects on both RT and MT, which were also reflected in the components of the individual workload scales. The results support a general form of the workload model which may help researchers and practitioners in the difficult task of workload prediction. Language: en

Further studies of psychophysically determined maximum acceptable weights and forces

Abstract: The effects of lifting boxes without handles, pulling long distances, carrying different size boxes, combining three handling tasks, and lifting with extended horizontal reach were studied using a ...

Pistol Grip Power Tool Handle and Trigger Size Effects on Grip Exertions and Operator Preference

Abstract: Finger and palmar forces were measured during actual pneumatic nutrunner operation using a strain gauge dynamometer. Eighteen student subjects were assigned to one of three categories based on hand length. Two triggers and four handle spans were presented randomly. Handle span affected maximal and submaximal grip force. As span increased from 4 cm to 7 cm, average peak finger force increased 24%, peak palmar force increased 22%, and average finger and palmar tool-holding forces increased 20%. When an extended trigger was used, average peak finger force decreased 9%, peak palmar force decreased 8%, finger tool-holding force decreased 65%, and palmar tool-holding force decreased 48%. Hand size affected grip strength (MVC), grip force, and exertion level (force/MVC). Holding exertion level was maximum for large-handed subjects using a 4-cm handle and for small-handed subjects using a 7-cm handle. Subjective handle span preference increased as hand size increased. A similar experiment was performed using 11 factory workers.

Wayfinding by Newcomers in a Complex Building

Abstract: We conducted several experiments to determine the characteristics of an optimal wayfinding aid for new users of a complex building. In Experiment 1 wayfinders who used signs found their destinations fastest. Those using you-are-here maps were much slower than even those wayfinders given no aids. The main advantage of signs over you-are-here maps results from information-processing differences: Signs provide clear cues about turns and decisions without requiring study time or imposing a high memory load. In Experiment 2 we found that people prefer routes that require the least amount of energy expenditure. Contrary to findings of previous research, we did not find complexity to be an important variable. A third experiment, using artificial floor plans of buildings, confirmed that minimizing energy is much more important than complexity in determining preferred routes. Finally, in Experiment 4, we investigated wayfinders' heuristics and the information necessary to provide unambiguous signs.

Repetitive Motion Disorders: The Design of Optimal Rate-Rest Profiles

Abstract: Repetitive motion disorders of the upper extremities are the primary cause of lost time in hand-intensive industries. Typical remedies include the introduction of job aids and the redesign of the job. An alternative approach is considered here. Procedures are developed that can be used to determine the parameters of a job (e.g., the rate of work and the number and duration of the rest breaks) that minimize repetitive motion disorders and maximize productivity. It is shown that in theory the job parameters can be set so that one can achieve not only a decrease in repetitive motion disorders but also an increase in productivity. The application of the procedures to an actual manufacturing job requiring high-repetitive, high-force hand motions is discussed in detail.

A Task-Analytic Approach to the Temporal and Spatial Placement of Product Warnings

Abstract: The effect of warning placement was investigated using a task-analytic approach to generate alternative warning locations. Within the context of a realistic task, 60 subjects used a consumer produc...

Age and fatal work-related falls

Abstract: In the work environment, an increased risk of fatal injury from falls is seen at ages not normally considered to be old. This study examined fatality data from a National Institute for Occupational Safety and Health death certificate database and from Occupational Safety and Health Administration (OSHA) investigations to analyze the relationship of age to fatal work-related falls. For 1980 to 1986, death certificates reported 43,505 fatal work injuries in men, 4,179 of which were from falls. Fatality rates from falls showed an increase for older workers beginning with the age group of 45-54, whereas fatal injury rates for other work-related causes did not increase until the age group of 55-64. OSHA investigations of 996 fatal work-related falls in 1984-1986 reported that falls from ladders accounted for 20% of fatal falls in workers aged 55 and over, significantly more than the average of 9% of all falls for workers of all ages. OSHA data also showed that fatal falls among older workers were associated with lower energy of impact, which means that the height of fatal falls tends to decrease with increasing age.

Conceptual Graph Analysis: Knowledge Acquisition for Instructional System Design

Abstract: This paper describes the empirical validation of a knowledge acquisition methodology using conceptual graph analysis. Conceptual graphs are a representational medium used to integrate and organize ...

The visibility of symbolic highway signs can be increased among drivers of all ages

Abstract: Visibility and comprehension of standard text, standard symbolic, and improved symbolic highway signs were compared among young, middle-aged, and elderly observers. The average distance at which standard symbolic signs could be identified was about two times that of text signs for all three age groups. The visibility distances of the improved symbolic signs, which were designed using an optical blur (i.e., low-pass) approach in order to avoid higher spatial frequencies, exceeded those of both text and standard symbolic signs. Visibility distance was decreased significantly among older drivers on some signs but not others. There were no significant age differences in the comprehension of symbolic signs. Acuity, a good predictor of visibility distance of both text and standard symbolic signs, was only weakly related to the visibility distance of the improved symbolic signs. These findings demonstrate that low-pass symbolic signs have significant advantages in visibility over their test counterparts for all drivers.

Redundant use of luminance and flashing with shape and color as highlighting codes in symbolic displays

Abstract: Three visual search experiments evaluated the benefits and distracting effects of using luminance and flashing to highlight subclasses of symbols coded by shape and color. Each of three general shape/color classes (circular/blue, diamond/red, square/yellow) was divided into three subclasses by presenting the upper half, lower half, or entire symbol. Increasing the luminance of a subclass by a factor of two did not result in a significant improvement in search performance. Flashing a subclass at a rate of 3 Hz resulted in a significantly shorter mean search time (48% improvement). Increasing the luminance of one subclass (by a factor of five) while simultaneously flashing another significantly improved search times by 31% and 43% respectively, compared with nonhighlighted search conditions. In each experiment, the search times for nonhighlighted target subclasses were not affected by the presence of brighter and flashing targets. The failure of the initial experiment to find a significant performance impro...

Cognitive predictors of vigilance.

Abstract: Three studies are reported of individual differences in performance of high event rate vigilance tasks. In each study, measures of attentional resource availability and elementary cognitive components of sustained attention were correlated with vigilance performance. It was predicted that correlates of vigilance should vary with two parameters of the task: the type of target discrimination required (simultaneous or successive) and the type of stimuli used (sensory or symbolic). Speed and accuracy of controlled, resource-demanding visual search predicted overall perceptual sensitivity on three out of four successive tasks used, but only one out of four simultaneous tasks, partially confirming the hypothesis that successive tasks are more strongly resource-limited than simultaneous tasks. Other correlates of overall level vigilance did not appear to vary systematically with task parameters. Few correlates of temporal decrement in perceptual sensitivity were found, possibly for statistical reasons. The data suggest that measures of controlled search may be useful in predicting vigilance on certain real-world tasks, although a substantial part of the variance of vigilance tasks may not be predictable from short cognitive tasks.

Curvilinear approach to an intersection and visual detection of a collision

Abstract: Visual motion perception plays a fundamental role in vehicle control. Recent studies have shown that the pattern of optical flow resulting from the observer's self-motion through a stable environment is used by the observer to accurately control his or her movements. However, little is known about the perception of another vehicle during self-motion--for instance, when a car driver approaches an intersection with traffic. In a series of experiments using visual simulations of car driving, we show that observers are able to detect the presence of a moving object during self-motion. However, the perception of the other car's trajectory appears to be strongly dependent on environmental factors, such as the presence of a road sign near the intersection or the shape of the road. These results suggest that local and global visual factors determine the perception of a car's trajectory during self-motion. Language: en

An Application of the Analytic Hierarchy Process: A Rank-Ordering of Computer Interfaces:

Abstract: This paper presents the analytic hierarchy process (AHP) as a methodology for developing ratio scales from paired comparison data. The AHP offers several advantages over traditional psychophysical ...

Motion Extrapolation Performance: A Linear Model Approach

Abstract: Researchers have obtained similar results from different visual motion extrapolation experiments despite the large variety of motion stimuli used. With respect to the ability of human subjects to judge the moment at which an occluded moving stimulus arrives at a predetermined position along its motion path, the general conclusion has been that errors increase with the duration of the occluded motion. However, substantial individual differences are often obscured within this statement. We propose a linear model to describe the performance of human observers in motion extrapolation tasks. The results from an experiment on centrifugal and centripetal motion extrapolation are examined in terms of this model. We discuss the restrictions imposed by the model on conclusions drawn after converting estimated arrival times to velocity estimates or accuracy scores. The parameters of the linear regression describing the individual performance in motion extrapolation tasks might be appropriate measures of interindivid...

Control/Display Relationship of the Four-Burner Stove: A Reexamination

Abstract: Several previous studies concerning the arrangement of the control/burner relationship of a four-burner stove showed discrepancy in their results. For this reason, a further analysis of this arrang...

Effects of age and task similarity on dual-task performance

Abstract: When a dual tracking task consisting of two incoherent (uncorrelated) subtasks is partly integrated, such that it is characterized by incompatibility of similarity, or when axis similarity of subtasks is high, it may be difficult to map subtask stimuli to the proper responses. Especially for older adults, an increase in mapping demands may be a source of confusion (cross talk). In the present experiment this issue was addressed with a dual task consisting of two unrelated one-dimensional compensatory tracking tasks with position dynamics. Task performance was measured in terms of root mean square tracking error and cross-axial correlations. Tracking error data were consistent with the hypothesis that older subjects are penalized when there is incompatibility between control and display integration. In general, negative effects of incompatibility of integrality were the greatest when partial integration involved integration of the response component. Both performance measures indicated that with increasing incoherent similarity, task performance of the old subjects was more hampered than was that of their young counterparts.