John G. Casali

A Validated Rating Scale for Global Mental Workload Measurement Applications

The Cooper-Harper (1969) scale has been extensively used for evaluation of aircraft handling qualities and associated mental workload. The scale is a 10-point scale with a decision tree. A modified version of the scale, called the MCH scale, has been devised for the purpose of assessing workload in systems other than those where the human operator performs motor tasks; namely, where perceptual, mediational, and communications activity is present. The MCH scale has been validated in three different experiments. The scale is recommended for applications in which overall mental workload is to be assessed.

A New Class of Auditory Warning Signals for Complex Systems: Auditory Icons

This simulator-based study examined conventional auditory warnings (tonal, nonverbal sounds) and auditory icons (representational, nonverbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. Brake response times were measured for impending front-to-rear collision scenarios under 6 display configurations, 2 vehicle speeds, and 2 levels of headway. Accident occurrence was measured for impending side collision scenarios under 2 vehicle speeds, 2 levels of visual workload, 2 auditory displays, absence/presence of mirrors, and absence/presence of a dash-mounted iconic visual display. For both front-to-rear and side collision scenarios, auditory icons elicited significantly improved driver performance over conventional auditory warnings. Driver performance improved when collision warning information was presented through multiple modalities. Brake response times were significantly faster for impending front-to-rear collision scenarios using the longer headway condition. The presence of mirrors significantly reduced the number of accidents for impending side collision scenarios. Subjective preference data indicated that participants preferred multimodal displays over single-modality displays. Actual or potential applications for this research include auditory displays and warnings, information presentation, and the development of alternative user interfaces.

Evaluation of 16 measures of mental workload using a simulated flight task emphasizing mediational activity

As aircraft and other systems become more automated, a shift is occurring in human operator participation in these systems. This shift is away from manual control and toward activities that tap the higher mental functioning of human operators. Therefore, an experiment was performed in a moving-base flight simulator to assess mediational (cognitive) workload measurement. Specifically, 16 workload estimation techniques were evaluated as to their sensitivity and intrusion in a flight task emphasizing mediational behavior. Task loading, using navigation problems presented on a display, was treated as an independent variable, and workload-measure values were treated as dependent variables. Results indicate that two mediational task measures, two rating scale measures, time estimation, and two eye behavior measures were reliably sensitive to mediational loading. The time estimation measure did, however, intrude on mediational task performance. Several of the remaining measures were completely insensitive to mediational load.

A comparison of rating scale, secondary-task, physiological, and primary-task workload estimation techniques in a simulated flight task emphasizing communications load

Sixteen potential metrics of pilot mental workload were investigated regarding their sensitivity to communication load and their intrusion on primary-task performance. A moving-base flight simulator was used to present three cross-country flights. The flights varied only in the difficulty of the communications requirements. Rating scale measures were obtained immediately postflight; all others were taken over a 7-min segment of the flight task. The results indicated that both the Modified Cooper-Harper Scale and the workload Multi-descriptor Scale were sensitive to changes in communications load. The secondary-task measure of time estimation and the physiological measure of pupil diameter were also sensitive. As expected, those primary-task measures that were direct measures of communicative performance were also sensitive to load, whereas aircraft control primary-task measures were not, attesting to the task specificity of such measures. Finally, the intrusion analysis revealed no differential interference between workload measures.

Perceived urgency of and response time to multi-tone and frequency-modulated warning signals in broadband noise

Several pulse parameters that were believed to affect the perceived urgency and response time to auditory warning signals were investigated in a factorial experiment. The independent variables included pulse format (sequential, simultaneous, and frequency-modulated pulses), pulse level (65 and 79 dBC), and inter-pulse interval (0, 150 and 300 ms). The applications environments of interest were those having steady-state broadband noise. A probability monitoring task from the Criterion Task Set was used as an operator loading task to impose additional attentional demands during the signal detection and response task. The psychophysical methods of free-modulus magnitude estimation and paired comparison were used to measure subjective perceived urgency. An objective measure of response time to the signal was also obtained. Multivariate statistical analyses indicated that response time decreased significantly as perceived urgency increased. Perceived urgency of the signal increased and response time decreased as pulse level increased. Sequential signals took longer to detect and were rated as less urgent than the other two signal types. Shorter inter-pulse interval was associated with greater perceived signal urgency.

Effects of visual display and motion system delays on operator performance and ueasiness in a driving simulator

The role of visual-motion coupling delays and cuing order on operator performance and uneasiness was assessed in a driving simulator by means of a response surface methodology central-composite design. The most salient finding of the study was that visual delay appears to be more disruptive to an individuals control performance and well-being than motion delay. Empirical mutliple regression models were derived to predict 10 reliable measures of simulator operator driving performance and comfort. Principal components analysis on these 10 models decomposed the dependent measures into two significant models, which were labeled vestibular disruption and degraded performance. Examination of the empirical models revealed that for asynchronous delay conditions, better performance and wellbeing were achieved when the visual system led the motion system. A secondary analysis of the role of subject gender and perceptual style on susceptibility to simulator sickness revealed that neither of these independent variables was a significant source of variance.

Earplug and hearing devices formed in-situ

A custom-molded earplug (18) for swimming protection, hearing protection, and the like, is fabricated in situ by depositing a foaming material (14 or 24) within a persons ear (10 or 42) and allowing the foaming material to form foam (16 or 44). Acoustic and electronic equipment such as a Helmholtz resonator or other tuned device capable of modifying sound waves, a communications transmitter, a communications receiver, a communications transceiver, a hearing aid, an ear microphone, a personal earphone, and a hearing test transducer or probe tube can be fabricated in the ear in a similar fashion. Temperature sensing elements may also be incorporated within or positioned by the foaming material to provide an in the ear thermometer.

On the measurement of pilot perceptual workload: a comparison of assessment techniques addressing sensitivity and intrusion issues

A flight simulator-based study was conducted to examine fourteen distinct mental workload estimation measures, including opinion, secondary task, physiological, and primary task measures. Both the relative sensitivity of the measures to changes in mental workload and the differential intrusion of the changes on primary task performance were assessed. The flight task was varied in difficulty by manipulation of the presentation rate and complexity of a hazard-perception task that required each of 48 licensed pilots to rely heavily on their perceptual abilities. Three rating scales (Modified Cooper-Harper, Multi-descriptor, and Workload-Compensation-Interference/Technical Effectiveness), two secondary task measures (time estimation and tapping regularity), one physiological measure (respiration frequency), and one primary task measure (danger-condition response time) were reliable indicants of workload changes. Recommendations for applying the workload measures are presented.

Driver steering reaction time to abrupt-onset crosswinds, as measured in a moving-base driving simulator.

A moving-base driving simulator was used in three experiments involving driver reaction time (RT) to simulated crosswind disturbances. Analyses were conducted on driver steering reaction time (RT) to the disturbances. Experiment 1 revealed that RT was significantly shorter when physical-motion cues were present. A second variable, vehicle yaw rate rise time, showed no effect. In Experiment 2, design parameters influencing aerodynamic behavior of a vehicle were adjusted. RT increased as the vehicle center of pressure (point of crosslvind application) moved rearward (rom the (ront axle. However, rearward movement of the center of pressure also produced less disturbance of the vehicle itself Changes in understeer and steering sensitivity yielded no significant effect. In Experiment 3, both uninitiated drivers and drivers with time on task were examined. Neither the first exposure to a step gust nor driving time up to 150 mirl caused significant changes in RT when perfurmance was compared with that of practiced, fresh drivers. Interexperiment comparisons using crosswind amplitude and shape as independent variables demonstrated that the amplitude and rise time of the crosswinds were critical determinants of steering RT.

Custom‐fitting earplug formed in situ using foaming action

A custom-fitting earplug (18) for hearing protection or other ear applications, or in-ear communications device mounting (40) is fabricated in situ by depositing a foaming material (14 or 24) within the persons ear (10 or 42, respectively) and allowing the foaming material (14 or 24) to expand therein to form foam (16 or 44, respectively). By applying slight pressure from outside the persons ear (10 or 42) through the stem (13) and/or keeper (11) during expansion, the foam (16 or 44, respectively) will be tightly packed in and conform to the ear canal. An optional sheath (15 or 36) positioned over the foaming material (14 or 24, respectively) serves to provide a smooth outer surface for the earplug (18) or communications device (40) produced and can aid in defining and limiting the expansion of the foam (14 or 24, respectively).