Effect of workload history on task performance

OBJECTIVE: This study investigated the effects of workload history (specifically, sudden shifts in workload) on performance. BACKGROUND: In 1993 the National Research Council identified workload transition as an important concern for human factors researchers. The study of workload history suggests that what an individual has been doing prior to a point in time has an effect on subsequent performance. One trend emerging from workload history studies is that a general decrement in performance is most likely to occur following a decrease in task demand. METHOD: The 198 participants were randomly assigned to a high-to-low or low-to-high condition. Participants performed a version of the Bakan Vigilance Task while correct responses, response times, and total errors were recorded. RESULTS: Results supported previous research suggesting a workload decrease results in a performance decrement. More importantly, this study reports that either a sudden increase or decrease could lead to a loss in accuracy and a slowing of response time in a longer time course. CONCLUSION: An explanation of the decrement is offered in terms of adaptation models. In addition, a follow-up study suggested that the decrement is a result of something inherent in the workload shift rather than an effect of fatigue. APPLICATION: Workload history (more specifically, a workload shift) has significant implications for many work environments. These implications are particularly salient in occupations where individuals are confronted with varying levels of workload demand, especially safety-sensitive occupations.     

Effects of different physical workload parameters on mental workload and performance

The design and evaluation of an occupational task should include an assessment of mental workload, since excessive levels of mental workload can cause errors or delayed information processing. Physically demanding work that is performed concurrently with a cognitive task may impact mental workload by impairing mental processing or decreasing performance. The primary objective of this study was to determine whether there is a differential effect of various types of physical activity on both mental workload and cognitive performance. Objective and subjective assessment tools (heart rate variability and visual analog scale) were used as indicators of mental workload, while correct responses during an arithmetic task reflected levels of performance. Thirty participants (ages 18-24 years) performed a combination of tasks inducing both physical and mental workload. Type of physical effort, frequency of movement, and force exertion level were manipulated to alter the workload associated with the physical activity. Changes in subjective ratings generally corresponded to changes in both performance on the arithmetic task and objective mental workload assessment. Some discrepancies occurred at the highest physical force exertion level as participants perceived an increase in effort to maintain the same level of performance. Further research is needed to determine the force exertion threshold, beyond which the physical effort required interferes with mental workload and/or cognitive performance.

Relevance to industry

Technological advancements have increased the requirement for many workers to execute cognitive tasks concurrently with physical activity. When designing and evaluating such situations it is important to determine the interactive effects of these activities. A simple, uni-dimensional tool is suggested as a screening tool to identify situations requiring excessive or increased mental workload that many degrade performance or place additional stress on the individual.     

The effect of mental workload on the visual field size and shape.

Mental workload is known to reduce the area of one's visual field, but little is known about its effects on the shape of the visual field. Considering this, the visual fields of 13 subjects were measured concurrently under three levels of mental workload using a Goldmann visual perimeter. Tone counting tasks were employed to induce mental workload, avoiding interference with visual performance. Various methods of shape measurement and analysis were used to investigate the variation of the shape of the visual field as a function of mental load. As expected, the mean area of visual fields reduced to 92.2% in the medium workload condition and to 86.41% under heavy workload, compared to light load condition. This tunnelling effect was not uniform, but resulted in statistically significant shape distortion as well, as measured by the majority of the 12 shape indices used here. These results have visual performance implications in many tasks that are susceptible to changes in visual fields and peripheral vision. Knowledge of the dynamics of the visual field as a function of mental workload can offer significant advantages also in mathematical modelling of visual search.     

Multi-modal information processing for visual workload relief

Subjects simultaneously performed two single-dimensional compensatory tracking tasks, one with the left hand and one with the right hand. The tracking performed with the left hand was considered the primary task and was performed with a visual display or a quickened kinaesthetic-tactual(KT) display. The right-handed tracking was considered the secondary task and was carried out only with a visual display. Although the two primary task displays had afforded equivalent performance in a critical tracking task performed alone, in the dual-task situation the quickened KT primary display resulted in superior secondary visual task performance. Comparisons of various combinations of primary and secondary visual displays in integrated or separated formats indicated that the superiority of the quickened KT display was not simply due to the elimination of visual scanning. In an additional condition, a quickened signal obtained from an off-line KT display was used to drive a primary visual display. Performance was equivalent to previous dual visual task situations, indicating that quickening per se also was not the immediate cause of the observed KT superiority. Results are discussed in terms of S-R compatibility differences, competition for modality-dependent processing resources, task discriminability, and the role of sensory buffers in maintaining multi-task frames of reference under conditions of shifting attention.     

Cooling-aware workload placement with performance constraints

Power optimization in data centers requires either to raise the temperature of the cold air supplied by the air conditioner or to reduce the power consumption of the servers by careful workload allocation. Both the approaches must satisfy a number of constraints, mainly temperature at the server intakes, which should not exceed a critical threshold, and capacity and response time requirements. To tackle these issues, we formulate an optimization problem in which the total data center power has to be minimized subject to the constraints imposed by performance requirements and thermal specifications of the servers. At the heart of the optimization problem is an analytical model which takes into account the complex relationship between the performance of servers, the allocation of workloads, the temperature of the air supplied by the conditioning unit and the heat distribution in the server room. For the easy evaluation of this relationship, we adopt a simplified yet accurate heat flow model, which we extensively validate using the data collected in several months of Computational Fluid Dynamics simulations. Extensive tests on 90 randomly generated scenarios suggest that the proposed coupled thermal-performance model can lead to a power saving of 21%. Finally, a case study is presented which is based on 1164 workload traces collected from the data center of a large telco operator. The cooling-aware workload placement suggests a saving of 8% with respect to a performance-only based strategy.     

The effect of performance failure and task demand on the perception of mental workload

An experiment was conducted to investigate the effects of incipient performance failure on subjective workload response. Unknown to the participants, there were two levels of demand embedded in the PC-based flight simulation performance task. These were included to assess whether task-naive subjects could distinguish variations in load in the face of repetitive performance failure. Results confirmed that participants were able to distinguish this change in load level under such circumstances and that failure resulted in higher perceived workload than did successful performance. Within these differences were significant effects dependent upon subject gender. In general, female participants performed more poorly and rated workload higher than their male counterparts. It is concluded that the experience of failure presents a significant source of workload in systems operation.     

Impact of workload on cognitive performance of control room operators

Cognition, Technology & Work - Workload has long been considered as one of the important factors for personal functions and malfunctions, particularly in complex systems. Undertaking operations...     

DQN-based OpenCL workload partition for performance optimization

The Journal of Supercomputing - This paper proposes a deep Q network (DQN)-based method for the workload partition problem in OpenCL. The DQN, a reinforcement learning algorithm, optimizes the...     

The performance of workload rules for order acceptance in batch chemical manufacturing

We investigate the performance of workload rules used to support customer order acceptance decisions in the hierarchical production control structure of a batch chemical plant. Customer order acceptance decisions need to be made at a point in time when no detailed information is available about the actual shop floor status during execution of the order. These decisions need therefore be based on aggregate models of the shop floor, which predict the feasibility of completing the customer order in time. In practice, workload rules are commonly used to estimate the availability of sufficient capacity to complete a set of orders in a given planning period. Actual observations in a batch chemical manufacturing plant show that the set of orders accepted needs to be reconsidered later, because the schedule turns out to be infeasible. Analysis of the planning processes used at the plant shows that workload rules can yields reliable results, however at the expense of a rather low capacity utilization. In practice this is often unacceptable. Since, solving a detailed scheduling problem is not feasible at this stage, this creates a dilemma that only can be solved if we can find more detailed aggregate models than workload rules can provide.     

The visual display of parallel performance data

Several performance visualization tools have demonstrated that helpful insights into parallel performance can be gained through graphical displays. However, much of this work has been experimental, specialized, and ad hoc. Evolving performance visualization into an integral, productive tool for evaluating parallel performance requires a more systematic, formal methodology that relates behavior abstractions to visual representations in a more structured way. We propose a high-level abstract model for the performance visualization process, explain its relationship to the most important concepts and principles of effective visualization practice, and illustrate the relationship between these concepts and our abstract model through specific case studies. We also discuss the relationship of performance visualization to general scientific visualization     

The influence of the instruction of visual design principles on improving pre-service teachers’ visual literacy

This study investigated whether the instruction of visual design principles had an influence on pre-service teachers’ perception and analysis (interpretation) of visual materials. In addition, the relationships between pre-service teachers’ visual intelligence and their perception and analysis (interpretation) of visual materials were also explored. Participants were 86 pre-service teachers who took a one-credit required educational technology course at a mid-western university in the United States. Some participants were absent in the weeks when data were collected, resulting in a total of 59 responses included in data analysis. Findings implied that the instruction of visual design principles could possibly improve pre-service teachers’ visual literacy. Suggestions for future research were discussed.     

Information complexity--mental workload and performance in combat aircraft

The purpose of the present study was to analyse the effects of information complexity on Pilot Mental WorkLoad (PMWL) and Pilot Performance (PP), and to analyse the structure of PMWL. Eighteen pilots performed 72 simulated low level-high speed emissions. The complexity of the Head Down Display (HDD) information varied as a function of the tactical situation. Flight data were recorded continuously. The pilots' eye movements were video taped and psychophysiological activation data, Heart Rate (HR), were obtained. The pilots rated PMWL according to the psychological content of three scales (Bedford Rating Scale, Subjective Workload Assessment Technique, NASA-Task Load indeX) and answered a questionnaire tapping aspects of performance, information load, motivation and mood. It was found that even a moderate complexity of information interfered with the flight task. Altitude and variation in altitude were increased and corrections of altitude errors were delayed, when complexity increased. Changes in information load reached its maximum influence on flight performance (r = 0.60, p < 0.001) after a time delay of 20 to 40 seconds. Performance of the flight task correlated positively (r = 0.59, p <0.001) with the performance of the information handling task (Tactical Situation Awareness, TSA). Durations and frequencies of eye fixations Head Up (HU) versus Head Down (HD) changed as a function of information load. A structural equation model implied that PMWL was affected by mission complexity and that PMWL affected objective and subjective aspects of flight performance and information handling. Heart rate (sortie means) correlated positively with PMWL (r = 0.34, p <0.05) and perceived complexity of mission (r = 0.37, p < 0.01). Heart rate (running means) covaried with variations in information complexity for those pilots who performed well. From spectral analyses of cardiac interval times it was found that the amplitude of the 0.10 Hz component tended to decrease during high as compared to low levels of information load.     

The effects of three blue light filter conditions for smartphones on visual fatigue and visual performance

Although blue light filters have been developed to decrease visual fatigue, the decreased screen brightness and contrast ratios inherent in current filtering techniques should be resolved. To address these issues, we developed a blue light filter, named the Eye Care blue light filter. This study investigated the effects of three blue light filtering techniques (the Eye Care blue light filter, an 80% blue light filter application [app], and a 60% blue light filter app) on visual fatigue and task performance. Thirty‐six healthy adults were recruited. Critical fusion frequency, task performance, and subjective visual fatigue scale were used to assess visual perception and task performance. All subjects played a smartphone game for 40 min in each experimental condition. Task performance was better with the Eye Care blue light filter than with the two filter apps. The value of the Eye Care blue light filter is that it immerses the user in a good task performance environment while reducing blue light exposure per unit of time more than is possible with filter apps.     

Visual evoked potentials as indicators of the workload at visual display terminals

No physiological correlates are known for visual fatigue produced by prolonged viewing of visual display terminals (VDTs). The primary aim of the present study was to find a physiological correlate of a performance measure which is related to fatigue. The assumption was that a change in the state of fatigue expresses itself in fluctuations of accommodation. If indeed variations in accommodation are indicative of fatigue, then visual evoked potentials (VEPs) might be used for the objective estimation of fatigue, because pattern EPs are highly sensitive to the quality of the retinal image.

In a realistic visual task, the VEP to pattern onset and the performance to a binary task are recorded simultaneously. Both indicators of fatigue, the amplitude of the VEP and the reaction time, proved to be sensitive to the workload of the task. If accommodation effort was increased, then reaction time increased and VEP amplitude decreased. Thus, VEPs are an indicator of the workload of a visual task. This allows comparison of the fatiguing effects of various office settings on the basis of the pattern EP of a particular subject. However, because VEP amplitude and reaction time do not have the same relation amongst subjects, the pattern EP cannot be used for inter-individual comparison.     

The influence of virtual human model appearance on visual ergonomics posture evaluation

The objective of this study was to investigate whether the appearance of virtual human models influences observers when judging a working posture. A task in which a manikin is manually assembling a car battery was used in the experiment. In total, 16 different pictures were presented to the subjects. All pictures had the same background, but included a unique posture and manikin appearance combination. 24 subjects consisting of manufacturing managers, simulation engineers and ergonomists were asked to rate and rank the pictures. The results showed that the virtual human model appearance influenced subjects when they rated pictures one by one: a more realistic manikin was rated higher than the identical posture visualized with a less natural appearance. This appearance effect was not seen when subjects ranked the pictures while looking at all of them at the same time. The study demonstrates that the human modelling tool used when showing and visually evaluating results makes a difference. To minimize subjective effects, a combination of visualizations and objective ergonomic assessment methods is recommended.     

Effects of varying the threshold of alarm systems and workload on human performance

The purpose of this research was to investigate the effects of varying the threshold of alarm systems and workload on human response to alarm signals and performance on a complex task. A receiver operating characteristic (ROC) curve was selected to reflect the sensitivity of the alarm system. The threshold of the alarm system was manipulated by changing the value of beta along the ROC curve. A total of 84 students participated in experiment 1 and 48 students participated in experiment 2. Participants performed a compensatory-tracking, a resource management and a monitoring task. As expected, results showed that participants responded significantly faster to true alarm signals when they were using the system with the highest threshold under low-workload conditions. Results also indicated that changing the threshold of the alarm system had a significant effect on overall performance and this effect was greater under high-workload conditions. However, contrary to expectations, the highest level of performance was achieved by setting the threshold at a low level. Results from both experiments revealed that the advantage of faster alarm reaction time as a result of increasing the system's threshold was lost because of its increased probability of missed events.