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.     

Air-to-ground training missions: a psychophysiological workload analysis

Psychophysiological measures are used to assess the workload of F4 Phantom aircraft pilots and weapon systems officers (WSOs) during air-to-ground training missions and during the performance of two levels of difficulty of a laboratory tracking task. The bombing range portion of the missions was associated with the highest pilot workload, while the WSO flying the aircraft was the highest workload segment for the WSOs. The pilots' data were found to have a wider range of values for the physiological measures than were found in the WSO data. The different levels of tracking task difficulty produced significant physiological effects but the range of values found for most of the flight segments were much greater. These data demonstrate that extrapolating laboratory data to the flight environment is risky at best. The various physiological measures were differentially sensitive to the different demands of the various flight segments.     

Techniques of subjective workload assessment: a comparison of SWAT and the NASA-Bipolar methods

Abstract

Assessment of subjective workload is becoming increasingly important in the evaluation of human-machine systems. Two popular methods were compared: (1) the Subjective Workload Assessment Technique (SWAT) that employed a conjoint measurement procedure to confer interval scale properties on the workload ratings, and (2) a technique under development at NASA that used an individually weighted workload score. Both methods were applied in a laboratory experiment that required the rating of a number of single- and dual-tracking and spatial transformation tasks. Both subjective assessment techniques displayed similar sensitivity to the different task manipulations. However, both techniques failed to detect the resource competition effects in the dual-task performance, and were in general insensitive to response execution processing demands. A notable difference between the two techniques was that the NASA-Bipolar ratings consistently had a smaller between-subject variability than the SWAT ratings. Discussion of the results is centred around the issue of the validity of assessment of subjective workload in general, and the construct and concurrent validity of the two techniques in particular.     

A self-analysis of the NASA-TLX workload measure

Computer use and, more specifically, the administration of tests and materials online continue to proliferate. A number of subjective, self-report workload measures exist, but the National Aeronautics and Space Administration-Task Load Index (NASA-TLX) is probably the most well known and used. The aim of this paper is to consider the workload costs associated with the computer-based and paper versions of the NASA-TLX measure. It was found that there is a significant difference between the workload scores for the two media, with the computer version of the NASA-TLX incurring more workload. This has implications for the practical use of the NASA-TLX as well as for other computer-based workload measures.     

Behavioural implications of alarm mistrust as a function of task workload

The research was conducted to investigate the effect of increasing primary task and alarm workload on alarm mistrust as reflected by alarm and primary task performances. A total of 126 undergraduate students performed a complex psychomotor task battery three times, with the number of concurrent tasks increasing each time. During their performance, the students were required to react to an alarm system (including visual and auditory components) of questionable reliability. Depending on the group to which participants were assigned, the alarm presentation rate constituted a low-, medium- or highworkload condition. Alarm response data (times, frequencies, accuracies) and primary task data (tracking error) were analyzed to assess performance differences as a function of primary and secondary task workload levels. Results generally supported the hypotheses: increasing primary task and alarm task workload degraded alarm response performance. Also, response frequencies supported earlier research suggesting that participants ‘probability match’ their response rates to alarm system reliability. The results are discussed with regard to the cry-wolf effect, attention theory and alarm system design.     

Physical,mental, emotional,and subjective workload components in train drivers

This study, using 12 train drivers on a high speed track and 11 drivers on a mountain track, tried to differentiate between the physical, emotional, mental, and subjective workload components imposed on the drivers during work. With the simultaneous recording and on-line analysis of heart rate and physical activity, the emotional component in terms of the so-called additional heart rate was separated from the physical component. Mental workload was calculated by the heart rate variability and by shifts in the T-wave amplitude of the ECG. Speed of the train, mode of driving, and stress of the situation were rated by two observers who accompanied the drivers in the cabin. During speeds up to l00km/h as compared to standstills no heart rate changes occurred, but with speeds from l00km/h up to 200 km/h heart rate decreased indicating a monotony effect. However, heart rate variability, and T-wave amplitude indicated higher mental load during driving in most speed categories. Starting the train and coming to a halt showed greater emotional workload as compared to moving. Observer ratings of stress and subjective ratings of stress by the drivers revealed several discrepancies. Discrepancies were also seen between workload as indicated by the physiological parameters, and corresponding stress ratings by the observers or by the drivers.     

Effect of varying levels of mental workload on startle eyeblink modulation

Previous research using punctuate reaction time and counting tasks has found that the startle eyeblink reflex is sensitive to attentional demands. The present experiment explored whether startle eyeblink is also modulated during a complex continuous task and is sensitive to different levels of mental workload. Participants (N = 14) performed a visual horizontal tracking task either alone (single-task condition) or in combination with a visual gauge monitoring task (multiple-task condition) for three minutes. On some task trials, the startle eyeblink reflex was elicited by a noise burst. Results showed that startle eyeblink was attenuated during both tasks and that the attenuation was greater during the multiple-task condition than during the single-task condition. Subjective ratings, endogenous eyeblink rate, heart period, and heart period variability provided convergent validity of the workload manipulations. The findings suggest that the startle eyeblink is sensitive to the workload demands associated with a continuous visual task. The application of startle eyeblink modulation as a workload metric and the possibility that it may be diagnostic of workload demands in different stimulus modalities is discussed.     

Causes of dissociation between subjective workload measures and performance ; Caveats for the use of subjective assessments

Dissociations between subjective workload assessments and performance were investigated. The difficulty of a Sternberg memory search task was manipulated by varying stimulus presentation rate, stimulus discernibility, value of good performance, and automaticity of performance. All Sternberg task conditions were performed both alone and concurrently with a tracking task. Bipolar subjective workload assessments were collected. Dissociations between workload and performance were found related to automaticity, presentation rate and motivation. The results were interpreted as supporting the hypothesis that the specific cognitive processes responsible for subjective assessments can differ from those responsible for performance. The potential contamination these dissociations could inflict on operational assessments was discussed.     

A complete task analysis to measure the workload associated with operating an agricultural sprayer equipped with a navigation device

The objective of this study was to perform a complete task analysis to measure the workload associated with operating an agricultural sprayer equipped with a navigation device. The task analysis included a written questionnaire and subsequent observation of sprayer operators. The questionnaire revealed that the lightbar was the most important source of guidance information (as opposed to relying on guidance information from external field cues). Observation consisted of recording eye-glance behaviour and heart rate variability while operators were spraying in a field setting. The eye-glance data suggest that external cues are more important than the lightbar for providing the necessary navigation information. Thus, the questionnaire and observation data contradict each other. Based on heart rate variability, operators who used a lightbar navigation device experienced more mental workload than operators who used an auto-steer navigation device.     

Physiological workload evaluation of carrying soft drink beverage boxes on the back

Soft drink manufacturing has become one of the largest food industries in Korea, now competing in a 2.5-billion dollar market, with more than 20,000 people employed. Deliveries of a broad line of soft drink products involve the use of a hand truck and, in many cases, a backpack mode of carriage. Workers usually prefer the backpack mode, because they feel safer by carrying beverage boxes on the back on stairs. In this study, the physiological workload involved in backpack-mode carrying was investigated, especially focusing on the effects of load weight and stairway transport. To measure heart rate and oxygen uptake while carrying on the back, a laboratory experiment was conducted and safety guidelines for such tasks were proposed, based on the experimental results. Eight healthy male subjects performed backpack-mode carrying, weight between 40 and 60 kg: (1) on level ground, (2) upstairs and (3) downstairs. The results showed that stairways involved an increased physiological burden, and that a load of 60 kg entailed a significantly higher physiological cost than carrying a load of 40 kg. Although backpack-mode carrying has some biomechanical advantages, the worker should be advised to carry a load of less than 40 kg, to avoid a high physiological load. During backpack-mode carrying, it is also recommended that a delivery person makes more trips with a light load rather than fewer trips with a heavier load per trip.     

Physiological workload reactions to increasing levels of task difficulty

The sensitivity of physiological measures to mental workload was investigated in a flight simulator. Twelve pilots had to fly through a tunnel with varying levels of difficulty. Additionally, they had to perform a memory task with four levels of difficulty. The easiest memory task was combined with the easiest tunnel task and the most difficult memory task with the most difficult tunnel task. Between the tunnel tasks, subjects had to fly a pursuit task in which a target jet had to be followed. Rest periods before and after the experiment were used as a baseline for the physiological measures. Mental workload was measured with heart period, continuous blood pressure, respiration and eye blinks. Several respiratory parameters, heart rate variability, blood pressure variability and the gain between systolic blood pressure and heart period (modulus) were scored. All measures showed differences between rest and flight, and between the pursuit and the tunnel task. Only heart period was sensitive to difficulty levels in the tunnel task. Heart rate variability increased when respiratory activity around 0.10 Hz increased, which occurred often. The modulus was hardly influenced by respiration and therefore appears to be a better measure than heart rate variability. Among the respiratory parameters, the duration of a respiratory cycle was the most sensitive to changes in workload. The time in between two successive eye blinks (blink interval) increased and the blink duration decreased as more visual information had to be processed. Increasing the difficulty of the memory task led to a decrement in blink interval, probably caused by subvocal activity during rehearsal of target letters. The data show that physiological measures are sensitive to mental effort, whereas rating scales are sensitive to both mental effort and task difficulty.     

Job rotation as a factor in reducing physical workload at a refuse collecting department

The effect of job rotation on the physical workload was investigated for male employees working at a refuse collecting department. Before the introduction of job rotation, an employee worked as a street sweeper, as a refuse collector or as a driver. After the introduction of job rotation, every employee was allowed to alternate between two of the three possible jobs during the day, i.e. refuse collecting/street sweeping, refuse collecting/driving or street sweeping/driving. Two non-rotation groups (i.e. refuse collectors and street sweepers) and two rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers) were mutually compared. The physical workload was determined by measuring the perceived load, energetic load and postural load during a full working day. Job rotation resulted in a significant decrease of the perceived load and energetic load and a slight decrease of the postural load. The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.     

Self-assessed and directly measured occupational physical activities--influence of musculoskeletal complaints, age and gender

This study compares questionnaire assessed physical activity with direct technical measurements among cleaners and office workers, stratified regarding age, gender and self-reported neck/shoulder complaints. During two full working days number of steps was recorded by a pedometer, sitting/standing positions by a posimeter and heart rate by a Sport-Tester. In addition the subjects kept a work task diary for 10 days. There were high intra-individual variations in exposure between the days. Subjects with complaints rated their exposure higher than those without, although they in fact showed lower direct measured exposure. This may imply underestimation of exposure-effect relationships. Rate of perceived exertion showed low correlation with heart rate ratio within the two occupational groups, but high, 0.64 when the two groups were combined. Age and complaints explained 31% of the variance for the cleaners.     

Assessment of pilot performance and mental workload in rotary wing aircraft

This research examined the processing demands imposed upon experienced pilots by two different communication formats, digital and verbal, in a high fidelity simulation of an advanced multi-function helicopter. The mental workload imposed by die type and magnitude of communications was assessed by a battery of subjective, performance, secondary, and physiological measures. The performance data indicated that the pilots had difficulty adhering to the Nap of the Earth altitude criterion with high communication demands, particularly with the digital communication system. This was presumably due to the requirement to spend more time scanning the multi-function displays with the digital than with the verbal communication system. On the other hand, the pilots were less prone to task shedding when they used the digital communication system possibly due to the provision of a permanent list of queries that was unavailable with the verbal system. Measures of heart rate variability and blink rate were larger with the verbal than with the digital system, presumably reflecting increased respiratory demands in the verbal condition as well as increased visual processing demands with the digital format. Finally, the probe evoked P300 component decreased in amplitude as a function of increases in die magnitude of communications. The results are discussed in terms of the structural and capacity demands of the communications systems that were proposed for the advanced multi-function helicopter.     

Time perception as a workload measure in simulated car driving

In experimental studies using flight simulations subjects’ duration estimates have shown to be an effective indicator of cognitive task demands. In this study we wanted to find out whether subjective time perception could serve as a measure of cognitive workload during simulated car driving. Participants drove on a round course of a driving simulator consisting of three different environments with different levels of task demands. Drivers were required to perform a time-production task while driving the vehicle. Electrodermal activity and subjective ratings of mental workload (SWAT) were recorded simultaneously. The length of produced intervals increased significantly in more complex driving situations, as did electrodermal activity and subjective ratings of mental workload. Thus, time production is a valid indicator of cognitive involvement in simulated driving and could become a valid method to measure the current mental workload of car drivers in various traffic situations.     

Development of a mental workload index: A systems approach

The objective of this study is to develop a method for determining the mental workload imposed on train control officers that is objective and quantifiable and can stand up to the tests of validity and reliability. This technical note reports on the methodology used in the development process, as well as the assessment of the criteria considered for the mental workload index (MWLI). The MWLI aims at solving an existing operational shortcoming and could be used as a tool for predicting the mental workload imposed on an operator at a particular train control centre. The method could be applied to manage and improve operational safety in the rail transport environment. A participative approach was followed in the development process. A work group comprising expert users of the system was involved in identifying task factors and assigning weights for task and moderating factors. The newly developed MWLI consists of three task factors and 11 moderating factors, each with a different weight in terms of its contribution to overall mental workload. The work group performed several iterations to reach final consensus and acceptance of the factors and their respective contributions to the MWLI. The criteria and development processes are discussed and the final index with the task and moderating factors is presented.     

An exploratory study: a measure of workload associated with teamwork

Team workload, which is usually described as an index of the ratio of available team resources to task demands, is believed to be critical for optimal human–computer integration. Although research conceptualizing team workload suggests that the measurement of team workload should consider workload unique to the team, the sum/min/max of members’ workload associated with taskwork referring to individual task performance is often used as an indicator of team workload. In order to better assess workload in team performance in which more than two individuals cooperate and conduct a task, it is also necessary to assess members’ workload associated with teamwork that refers to interpersonal interactions among individuals. The present study aims to develop a measure of workload associated with teamwork and discuss its contribution to operationalizing team workload. Results of team experiments indicate that the Teamwork Workload Scale is able to assess workload associated with teamwork and that it is necessary to assess both workload associated with taskwork and teamwork in order to better assess workload in team performance and operationalize team workload. In order to operationalize and measure team workload, it is necessary to investigate workload in team performance using quantitative data.     

A psychophysiological approach to the assessment of work underload

The findings of a laboratory investigation of the relationship between the subjective and physiological components of work underload are reported. The subjective component is described in terms of the subjective work underload checklist, mental effort, and cognitive arousal. The physiological component is defined in terms of heart rate and heart rate variability. Evidence for an increase in work underload with a decrease in heart rate is provided. The relevance of this research to the aerospace environment is discussed and the need to investigate the behavioural component of work underload emphasized.     

A new heart rate variability-based method for the estimation of oxygen consumption without individual laboratory calibration: application example on postal workers

Traditionally, the estimation of oxygen consumption (VO2) at work using heart rate (HR) has required the determination of individual HR/VO2 calibration curves in a separate exercise test in a laboratory (VO2-TRAD). Recently, a new neural network-, and heart rate variability-based method has been developed (Firstbeat PRO heartbeat analysis software) for the estimation of VO2 without individual calibration (VO2-HRV). In the present study, the VO2-values by the VO2-HRV were compared with the values by VO2-TRAD in 22 postal workers. Within individuals the correlation between the two methods was high (range 0.80-0.99). The VO2-TRAD gave higher values of VO2 compared to VO2-HRV (19%) especially during low physical activity work when non-metabolic factors may increase HR. When assessed in different HR categories, the smallest difference (11%), and highest correlations (range 0.83-0.99) in VO2 between the methods were observed at higher HR levels. The results indicate that the VO2-HRV is a potentially useful method to estimate VO2 in the field without laboratory calibration.     

Comparison of physiological and subjective strains of two protective coveralls in two short physically simulated demanding tasks

A total of 15 physically active male students carried out a normalised task (T(N)) and a task of access by ladder and scaffolding (T(L)) in two impermeable protective coveralls and a reference sports wear to compare the physiological and subjective strains. Heart rate (HR) was recorded and sweat loss was checked. Subjective evaluations of comfort parameters, acceptable exposure durations and physical exhaustion were recorded at the end of the tasks. Results show that both protective clothing, compared to the sport wear, increase significantly HR, RPE and CR10 in both tasks. However the strains of both protective clothing are not significantly different except in sweat loss and cumbersomeness.