Teamwork is an essential element in the majority of critical Army lifting tasks. Therefore, an understanding of the relationship between individual and team lifting capacity is of great tactical importance. Twenty-three male and 17 female U.S. Army soldiers were randomly assigned to single- and mixed-gender teams of two, three, and four persons. Individual lifting strength was the one-repetition-maximum (1RM) load lifted from floor to knuckle height using a weight bar. A square-shaped bar was used for two- and four-person lifting, and a triangular-shaped bar was used for three-person lifting. Team lifting strength as a percentage of the sum of individual lifting strength (%sum) did not change with team size. The %sum for teams of men (87.3%) was less than for teams of women (91.1%, p < 0.05). The %sums for both single-gender teams (all men and all women) were greater (p < 0.01) than for mixed-gender teams (80.2%). The number of people lifting a large object was increased to four with no decrease in the effectiveness of the individual lifter beyond that found for two persons. The 1RM loads presented in this paper were lifted under ideal conditions by young soldiers and do not represent norms for an industrial population.
We measured the accuracy with which sounds heard over a binaural, end-fire array could be located when the angular separation of the array's two arms was varied. Each individual arm contained nine cardioid electret microphones, the responses of which were combined to produce a unidirectional, band-limited pattern of sensitivity. We assessed the desirable angular separation of these arms by measuring the accuracy with which listeners could point to the source of a target sound presented against high-level background noise. We employed array separations of 30°, 45°, and 60°, and signal-to-noise ratios of +5, −5, and −15 dB. Pointing accuracy was best for a separation of 60°; this performance was indistinguishable from pointing during unaided listening conditions. In addition, the processing of the array was modeled to depict the information that was available for localization. The model indicates that highly directional binaural arrays can be expected to support accurate localization of sources of sound only near the axis of the array. Wider enhanced listening angles may be possible if the forward coverage of the sensor system is made less directional and more similar to that of human listeners.
This paper addresses theoretical, empirical, and analytical studies pertaining to human use, misuse, disuse, and abuse of automation technology. Use refers to the voluntary activation or disengagement of automation by human operators. Trust, mental workload, and risk can influence automation use, but interactions between factors and large individual differences make prediction of automation use difficult. Misuse refers to overreliance on automation, which can result in failures of monitoring or decision biases. Factors affecting the monitoring of automation include workload, automation reliability and consistency, and the saliency of automation state indicators. Disuse, or the neglect or underutilization of automation, is commonly caused by alarms that activate falsely. This often occurs because the base rate of the condition to be detected is not considered in setting the trade-off between false alarms and omissions. Automation abuse, or the automation of functions by designers and implementation by managers without due regard for the consequences for human performance, tends to define the operator's roles as by-products of the automation. Automation abuse can also promote misuse and disuse of automation by human operators. Understanding the factors associated with each of these aspects of human use of automation can lead to improved system design, effective training methods, and judicious policies and procedures involving automation use.
In two experiments we investigated the role of continuous concurrent visual feedback in the learning of discrete movement tasks. During practice the learner's actions either were or were not displayed on-line during the action; in both conditions the participant received kinematic feedback about errors afterward. Learning was evaluated in retention tests on the following day. We separated (a) errors in the fundamental spatial-temporal pattern controlled by the generalized motor program from (b) errors in scaling controlled by parameterization processes. During practice concurrent feedback improved parameterization but tended to decrease program stability. Based on retention tests, earlier practice with continuous feedback generally interfered with the learning of an accurate motor program and reduced the stability of time parameterization. Continuous feedback during acquisition degrades the learning of not only closed-loop processes in slower movements (as has been found in earlier studies) but also motor programs and their parameterization in more rapid tasks. Implications for feedback in training and simulation are discussed.
Research and operational experience have shown that one of the major problems with pilot-automation interaction is a lack of mode awareness (i.e., the current and future status and behavior of the automation). As a result, pilots sometimes experience so-called automation surprises when the automation takes an unexpected action or fails to behave as anticipated. A lack of mode awareness and automation surprises can be viewed as symptoms of a mismatch between human and machine properties and capabilities. Changes in automation design can therefore be expected to affect the likelihood and nature of problems encountered by pilots. Previous studies have focused exclusively on early generation "glass cockpit" aircraft that were designed based on a similar automation philosophy. To find out whether similar difficulties with maintaining mode awareness are encountered on more advanced aircraft, a corpus of automation surprises was gathered from pilots of the Airbus A-320, an aircraft characterized by high levels of autonomy, authority, and complexity. To understand the underlying reasons for reported breakdowns in human-automation coordination, we also asked pilots about their monitoring strategies and their experiences with and attitude toward the unique design of flight controls on this aircraft.
Three on-road studies were conducted to determine how headway maintenance and collision warning displays influence driver behavior. Visual perspective, visual perspective with a pointer, visual perspective combined with an auditory warning, discrete visual warning, and discrete auditory warning were assessed during both coupled headway and deceleration events. Results indicate that when drivers are provided with salient visual information regarding safe headways, they utilize the information and increase their headway when appropriate. Auditory warnings were less effective than visual warnings for increasing headways but may be helpful for improving reaction time during events that require deceleration. Drivers were some what insensitive to false alarm rates, at least during short-term use. Finally, and most important, driver headway maintenance increased by as much as 0.5 s when the appropriate visual display was used. However, a study to investigate the long-term effects of such displays on behavior is strongly recommended prior to mass marketing of headway maintenance/collision warning devices.
This paper explores the effects of age, system experience, and navigation technique on driving, navigation performance, and safety for drivers who used TravTek, an Advanced Traveler Information System. The first two studies investigated various route guidance configurations on the road in a specially equipped instrumented vehicle with an experimenter present. The third was a naturalistic quasi-experimental field study that collected data unobtrusively from more than 1200 TravTek rental car drivers with no in-vehicle experimenter. The results suggest that with increased experience, drivers become familiar with the system and develop strategies for substantially more efficient and safer use. The results also showed that drivers over age 65 had difficulty driving and navigating concurrently. They compensated by driving slowly and more cautiously. Despite this increased caution, older drivers made more safety-related errors than did younger drivers. The results also showed that older drivers benefited substantially from a well-designed ATIS driver interface.
Participants explored either a real multistory building or a to-scale computer simulation of the same building. Following exploration, we assessed their knowledge of the spatial properties of the environment. Participants in a control group were asked to complete the same assessment tasks without the opportunity to explore either the real building or the computer simulation. Spatial knowledge was assessed using four measures: pointing to objects not directly visible from the test site, Euclidean distance estimates, route distance estimates, and drawings of the building. Transfer of learning from the simulation to the real environment was evident. Pointing to objects not visible from the test site proved to be the most sensitive measure; map-drawing accuracy was very similar to pointing accuracy. However, some other measures did not distinguish the estimates of control participants from the group that explored the real building.
A quantitative description of the human information processor is required for predicting operator workload and performance from the simulated task time line data generated by task network models and related methods. Although many models of workload exist, few appear to be well founded in theory or to provide a satisfactory basis for a quantitative representation of operator load. Adherents of both time- and intensity-based models of operator load individually claim success for their methods, which might suggest that both factors are operating in determining operator workload and performance. This paper describes a study that explicitly investigates the relationship between a time-based factor and an intensity-based factor (amount of information to be processed) within a simulated air traffic control environment. A model is developed that posits that the load on the human information-processing system results directly from the ratio of the time necessary to process the required information to the time allowable for making a decision. This ratio, which can be identified with time pressure, determines subjective estimates of workload as well as operator performance. The model is tested against the data from the air traffic control simulation.
The transfer of tactical aviation technology into automobiles is creating information display requirements that are likely to be met by use of the head-up display (HUD). These developments are based largely on conclusions that the HUD-related safety issues raised in the aviation HUD literature can be dismissed and that the benefits of using HUDs are certain. Such conclusions either neglect relevant research or are supported by a very small amount of evidence, much of which is either irrelevant or generated within a flawed methodological paradigm. This critical review covers the issues of (a) HUD focal distance and its effect on the perception of outside objects and (b) the effects of HUD imagery on visual attention. The issues of focal distance, cognitive capture, and the inherent connection between the two may have a greater impact on safety in the automotive context than they do in aviation.
Two experiments assessed the relative efficiency of line graphs, bar graphs, and tables, applying a multiple-factors approach to study the effects of the type of the required information. the complexity of the data, and the user's familiarity with the display. Information extraction tasks included reading exact values, comparing values, identifying trends, and reading maximum values. Tables led to faster responses for all tasks, and the accuracy for tables was equally high or higher than for graphs. Bar graphs and line graphs differed in their relative efficiency for the different tasks. The complexity of the data also affected the tasks differentially, as did prior familiarity with the display. Performance for most conditions improved with experience. Our findings demonstrate the benefits of a multiple-factors approach to the study of displays. Generalizations about the relative efficiency of displays and computational models of the task performance with displays must consider the various relevant factors if they are to serve as valid design aids.
Three experiments were conducted to determine which of five response bias indices (β, c, B″, B′H′ and B″D) defined by the theory of signal detection provides the most effective measure of the observer's willingness to respond in a vigilance task. The results indicated that the traditional parametric bias index β was an inadequate measure of response bias in every respect, whereas the newer parametric measure c was the most effective of all five indices. When the three nonparametric measures (B″, B′H′ and B″D) were examined separately, B″D emerged as the most effective nonparametric index. We recommend that vigilance researchers use c rather than β to measure bias when a parametric model is involved and B″D instead of B″ and B′H when a nonparametric model is used.
The objectives of this study were (a) to determine errors in wrist angle measurements from a commercially available biaxial electrogoniometer and (b) to develop a calibration routine in order to correct for these errors. Goniometric measurements were collected simultaneously with true angular data using a fixture that allowed wrist movement in one plane while restricting motion in the orthogonal plane. These data were collected in two sets of trials: flexion/extension with radial/ulnar deviation restricted, and radial/ulnar deviation with flexion/extension restricted. During these trials, we studied discrete 30° increments of forearm rotation. The results showed the expected cross talk and zero drift errors during forearm rotation. The application of mathematical equations that describe the effect of goniometer twist resulted in significant error reduction for most forearm rotations. The calibration technique employs both a slope and a displacement transformation to improve the accuracy of angular data. The calibration technique may be used on data collected in the field if forearm rotation is measured simultaneously with the goniometer data.
How reliable must traffic information be for motorists to trust and accept such advice? This study provides data to aid the designer of advanced traveler information systems (ATIS) in selecting an appropriate level of system accuracy. The Battelle Route Guidance Simulator was used to study the effects of information accuracy and familiarity of the driving environment on objective and subjective indices of driver performance and opinion. The simulator provided real-time information and traffic video. Information was 100%, 71%, or 43% accurate. Drivers experienced either Seattle and its environs or an artificial setting that was topologically matched to Seattle. Results showed that 100% accurate information yielded the best driver performance and subjective opinion, information that was 71% accurate was still accepted and used, but information that was 43% accurate produced powerful decrements in performance and opinion. Simulated ATIS information was not used as effectively in the familiar Seattle setting. Driver trust decreased with inaccurate information but recovered—though not always fully—with subsequent accurate information.
This study investigated the effects of flooring on balance during quiet standing in healthy young and older participants. Seven flooring conditions were examined, including a hard tile floor and combinations of low-pile and high-pile carpet with urethane foam and rubber padding. The resulting floors provided a variety of compliant surfaces, ranging from very soft to hard. Participants stood during three separate visual conditions: eyes open, eyes closed, and looking at a moving visual surround. Three measures of postural sway were calculated using center of pressure recordings during the trials. The results showed that the amplitude of sway was higher in the older than in the younger participants, particularly in the moving visual surround condition. Flooring compliance was found to have an effect on sway during moving visual environments, with the largest effects found among the older participants. Softer floors increased the amount of sway in the older participants. These results suggest that floor compliance influences standing postural stability in older people, particularly in destabilizing visual environments.
Experiments were conducted in a fixed-base, high-fidelity simulator to evaluate selected in-vehicle route guidance systems. Drivers navigated a simulated network using five route guidance systems: paper map, head-down turn-by-turn display, head-down electronic route map, head-up turn-by-turn display, and an audio guidance system. The primary measure of driving performance was the reaction time to a scanning task. Other measures included navigation errors, workload, and perception ratings. Censored regression models were developed to study the effect of route guidance type on reaction times. Results indicated that the drivers responded the fastest while using the audio system and the slowest while using the paper map. The head-up turn-by-turn display was associated with lower reaction times compared with an identically designed head-down turn-by-turn display. The head-down electronic map, despite its complexity, performed better than the head-down turn-by-turn display.
In two experiments we examined a number of related factors postulated to influence head-up display (HUD) performance. We addressed the benefit of reduced scanning and the cost of increasing the number of elements in the visual field by comparing a superimposed HUD with an identical display in a head-down position in varying visibility conditions. We explored the extent to which the characteristics of HUD symbology support a division of attention by contrasting conformal symbology (which links elements of the display image to elements of the far domain) with traditional instrument landing system (ILS) symbology. Together the two experiments provide strong evidence that minimizing scanning between flight instruments and the far domain contributes substantially to the observed HUD performance advantage. Experiment 1 provides little evidence for a performance cost attributable to visual clutter. In Experiment 2 the pattern of differences in lateral tracking error between conformal and traditional ILS symbology supports the hypothesis that, to the extent that the symbology forms an object with the far domain, attention may be divided between the superimposed image and its counterpart in the far domain.
A new type of interface, the three-dimensional (3D) audio display, is being developed to enhance cockpit displays in military aircraft. In order to synthesize a sound's location in space, head-related transfer functions are measured for many sound source positions (in space) and incorporated in digital filters, which are then used to synthesize location. However, most military aircraft have communication systems that are band-limited in frequency response, as are most recently designed auditory displays currently used in military applications. The present study investigated the effects of limiting signal bandwidth on sound localization. Results show that broadband signals encompassing frequencies from 0 to (at least) 13 kHz are required in order for listeners to accurately localize signals actually presented from a range of spatial locations. These results have clear implications for the design and implementation of 3D spatial synthesis systems in military aircraft. Communications systems should be capable of carrying broadband signals and acoustic signals used in 3D audio displays should also be broadband in nature.
Although injuries related to postural stability are prevalent, ergonomic job analyses traditionally have not addressed stability issues. In this research functional stability limits are quantified for persons standing in extreme postures under various external load and foot positioning conditions. Participants were asked to lean and displace their center of gravity (COG) as far as possible in eight directions to the sides and front of the body. Stability measures based on these COG displacements were calculated. All controlled variables significantly affected the stability measures. When standing unladen, participants extended their COG to within 99% of their theoretical maximum. Movement was much more restricted when handling a load (89%), especially when holding it with one hand on the shoulder (84%). On average, increased separation of the feet in a particular direction resulted in larger COG displacements in that direction. The results are discussed relative to their effects on balance and stability modeling.
The role of the modern pilot requires a high degree of situational awareness. This involves the ability to search for relevant information, assess opportunities and priorities, and maintain performance under stress. The PC-based WOMBAT™ test has been designed to measure individual aptitude to cope with such demands. In the first experiment performance on the WOMBAT test was compared with performance on a battery of tests of specific underlying abilities. In the second experiment the performance of elite soaring pilots was compared with that of matched pilot and control groups. The results support the theory that the WOMBAT test measures individual ability to maintain situational awareness and that this ability is found in high levels in elite pilots.