The effects of whole-body restriction on task performance

Many occupations, particularly involving maintenance operations, require individuals to perform both physical tasks and mental tasks in restricted spaces. Researchers have examined physical task performance under various restrictions; however, little research has investigated the effects of restricted space on cognitive tasks. Cognitive task performance in restricted spaces presents cognitive demands (i.e. the task itself) as well as additional physical demands (e.g. awkward postures), which may adversely affect task performance or operator workload. This research focused on the effects of whole-body restrictions on cognitive task performance. An experiment was conducted that examined 9 levels of restriction created in a laboratory: an unrestricted control, 6 single whole-body restrictions at two severity levels (2 lateral, 2 sagittal and 2 vertical) and 2 multiple restrictions (sagittal/vertical, lateral/sagittal/vertical). An inspection task served as the cognitive task. Behavioural, physiological and psychophysical measures were collected and analysed to measure the operator and performance effects. Operator response differences were found among the various forms of restriction as well as the severity level of similar forms of restriction. Increasing restriction significantly affected the behavioural and physiological operator response as opposed to the cognitive response.     

Vessel motion thresholds for maintaining physical and cognitive performance: a study of naval personnel at sea

Methods and results are reported from a study of ships companies' exposure to low-frequency motions on three vessels of the Royal Navy. The aim of the study was to investigate relationships between deck accelerations and the incidence of problems such as difficulties with physical tasks, cognitive activities, motion sickness, and work effort. Ship motions were recorded continuously during sea patrols of 10-14 days. The data collected from the three vessels comprised 105 days of ship motions over 12 patrols, with 779 associated daily diaries from 78 participants. Problems most strongly associated with vessel motions were related to the difficulties with physical tasks. Some cognitive aspects of task performance and motion sickness were associated with vertical acceleration magnitudes, but the correlations were less strong than with physical tasks. Practitioner Summary: Little is known about the severity of ship motions that degrade physical and mental performance. The paper offers preliminary estimates of the motion threshold values below which the performance will not be degraded by motion.     

Cervicobrachial muscle response to cognitive load in a dual-task scenario

People working in an office environment often have to deal with significant cognitive workload due to the coordination of multiple, simultaneous tasks. The objective of this research was to examine the impact of cognitive load in office-type tasks on physical-stress response, using a dual-task paradigm involving a primary cognitive task and secondary typing task. The central hypothesis of this research was that altering the demands of the cognitive task would lead to a difference in physical stress-level and performance. Cognitive load was manipulated by presenting participants with three different types of cognitive tasks described in taxonomy, including skill-, rule-, and knowledge-based tasks. Dependent variables examined in the study included: (1) electromyographic activity of the upper trapezius (pars descendens) and cervical erector spinae muscles, (2) performance in a secondary typing task, and (3) subjective measures of stress and cognitive workload. The results of this study revealed that the primary task causing the highest level of perceived workload also produced 61% higher muscle activity in the right trapezius, and 6 and 11% higher activity in the left and right cervical erector spinae, respectively, in comparison to muscle activity associated with the cognitive task causing the lowest perceived workload. With respect to performance, a 23% decrease was observed in typing productivity when the rule-based task was completed simultaneously vs. typing in the absence of any additional cognitive task (the baseline condition). This information may be used to better organize work activities in office environments to increase performance and reduce stress.     

Cervicobrachial muscle response to cognitive load in a dual-task scenario

People working in an office environment often have to deal with significant cognitive workload due to the coordination of multiple, simultaneous tasks. The objective of this research was to examine the impact of cognitive load in office-type tasks on physical-stress response, using a dual-task paradigm involving a primary cognitive task and secondary typing task. The central hypothesis of this research was that altering the demands of the cognitive task would lead to a difference in physical stress-level and performance. Cognitive load was manipulated by presenting participants with three different types of cognitive tasks described in Rasmussen's () taxonomy, including skill-, rule-, and knowledge-based tasks. Dependent variables examined in the study included: (1) electromyographic activity of the upper trapezius (pars descendens) and cervical erector spinae muscles, (2) performance in a secondary typing task, and (3) subjective measures of stress and cognitive workload. The results of this study revealed that the primary task causing the highest level of perceived workload also produced 61% higher muscle activity in the right trapezius, and 6 and 11% higher activity in the left and right cervical erector spinae, respectively, in comparison to muscle activity associated with the cognitive task causing the lowest perceived workload. With respect to performance, a 23% decrease was observed in typing productivity when the rule-based task was completed simultaneously vs. typing in the absence of any additional cognitive task (the baseline condition). This information may be used to better organize work activities in office environments to increase performance and reduce stress.     

Effects of physical exertion on task performance in modern manufacturing: a taxonomy,a review,and a model

Modern manufacturing systems have the characteristic of demanding human cognitive task performance in an environment where sudden physical demands are also possible. There is little research addressing the effects of physical work on cognitive task performance and it is not well organized for application to manufacturing systems design. This paper uses an initial three-dimensional taxonomy to review the literature. Some clear findings emerge, but many studies produced contradictory results. While part of this contradiction was due to experimental technique, some was also due to the lack of a detailed structure to guide future research. Such a model is thus proposed, using the concept of limited resources for both the cognitive and physical aspects of tasks. In addition, specific predictions of research needs for modern manufacturing systems arise.     

The influence of seat backrest angle on human performance during whole-body vibration

This study investigated the effects of reclined backrest angles on cognitive and psycho-motor tasks during exposure to vertical whole-body vibration. Twenty participants were each exposed to three test stimuli of vertical vibration: 2-8 Hz; 8-14 Hz and 14-20 Hz, plus a stationary control condition whilst seated on a vibration platform at five backrest angles: 0° (recumbent, supine) to 90° (upright). The vibration magnitude was 2.0 ms(-2) root-mean-square. The participants were seated at one of the backrest angles and exposed to each of the three vibration stimuli while performing a tracking and choice reaction time tasks; then they completed the NASA-TLX workload scales. Apart from 22.5° seat backrest angle for the tracking task, backrest angle did not adversely affect the performance during vibration. However, participants required increased effort to maintain performance during vibration relative to the stationary condition. These results suggest that undertaking tasks in an environment with vibration could increase workload and risk earlier onset of fatigue. PRACTITIONER SUMMARY: Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This paper reports new experimental data systematically investigating the effect of backrest angle on human performance. It demonstrates how workload is elevated with whole-body vibration, without getting affected by backrest angle.     

Investigating the effects of experience on human performance in an object-tracking task: a case study of manual rendezvous and docking

Human involvement with the manual control of object-tracking tasks, such as manual rendezvous and docking, can enhance the flexibility of the task. The operator is required to make decisions as precisely as possible when a chase vehicle is approaching the target vehicle. As the level of mental workload is intensively increased, the operator's perception and decision-making with tracking error-correcting purposes should be properly identified in multiple degrees of freedom (DOFs). The two experimental studies in this paper were conducted for object-based selective attention in six DOFs and object-pointing manipulation under the zero resistance circumstance, which were correlated with human performance when a chaser approached a target spacecraft; the effects of experience level on the two important factors are presented herein. The experimental results demonstrated that some performance details between the novice and experienced groups were different in terms of the attentional priority of multiple DOFs and lateral/vertical movement for deviation error correction, which could provide a certain reference for a cognitive–behavioural model and assist the operator in obtaining proper or even optimal decision-making or operating instructions to improve their adaptation to selective attention and object-pointing manipulation, for preventing accidental manipulation and performance degradation.     

Mechanisms of the effects of vibration frequency,level and duration on continuous manual control performance

This paper describes three experiments, performed to determine the effects of vibration frequency, level and duration on a zero order, pursuit tracking task, and to discover the mechanisms responsible for these effects. The first experiment investigated the effect on tracking performance of vertical, sinusoidal vibration of the control stick in the frequency range 4 to 64 Hz. Control dynamics were either isotonic (displacement), isometric (force) or spring-centred. The second experiment investigated the effect of level of vertical, 4 Hz and 16 Hz whole-body and control vibration on performance with the isotonic and isometric controls. Experiment 3 investigated the effects of duration of continuous, vertical, whole-body vibration at 4 Hz, for durations up to 1 h, on performance with the isotonic and isometric controls. Performance measures included closed-loop transfer functions of the human operator and components of mean-square tracking error correlated with the forcing functions and vibration, and those due to operator-generated noise or remnant.

The results indicated that the primary effects of vibration on the tracking task were increases in remnant and vibration-correlated error. Perceptual and motor sources are suggested for the increased remnant. The effects were largest with 4 Hz vibration and were found to be effectively constant throughout 1 h exposures to continuous 4 Hz whole-body vibration, but after relatively short periods the effect on overall tracking performance was effectively masked by large increases in response lags and suppression of coherent responses, which occurred in both static and vibration conditions as a consequence of diminished levels of arousal.     

Effects of field-of-view restriction on manoeuvring in a 3-D environment

Field-of-view (FOV) restrictions are known to affect human behaviour and to degrade performance for a range of different tasks. However, the relationship between human locomotion performance in complex environments and FOV size is currently not fully known. This paper examined the effects of FOV restrictions on the performance of participants manoeuvring through an obstacle course with horizontal and vertical barriers. All FOV restrictions tested (the horizontal FOV was either 30 degrees , 75 degrees or 120 degrees , while the vertical FOV was always 48 degrees ) significantly reduced performance compared to the unrestricted condition. Both the time and the number of footsteps needed to traverse the entire obstacle course increased with a decreasing FOV size. The relationship between FOV restriction and manoeuvring performance that was determined can be used to formulate requirements for FOV restricting devices that are deployed to perform time-limited human locomotion tasks in complex structured environments, such as night-vision goggles and head-mounted displays used in training and entertainment systems.     

Effects of field-of-view restriction on manoeuvring in a 3-D environment

Field-of-view (FOV) restrictions are known to affect human behaviour and to degrade performance for a range of different tasks. However, the relationship between human locomotion performance in complex environments and FOV size is currently not fully known. This paper examined the effects of FOV restrictions on the performance of participants manoeuvring through an obstacle course with horizontal and vertical barriers. All FOV restrictions tested (the horizontal FOV was either 30°, 75° or 120°, while the vertical FOV was always 48°) significantly reduced performance compared to the unrestricted condition. Both the time and the number of footsteps needed to traverse the entire obstacle course increased with a decreasing FOV size. The relationship between FOV restriction and manoeuvring performance that was determined can be used to formulate requirements for FOV restricting devices that are deployed to perform time-limited human locomotion tasks in complex structured environments, such as night-vision goggles and head-mounted displays used in training and entertainment systems.     

Muscle- and task-dependent responses to concurrent physical and mental workload during intermittent static work

Many workers experience combined physical and mental demands in their jobs, yet the contribution of these demands to the development of musculoskeletal disorders is unclear. The purpose of this study was to investigate muscle- and task-dependent responses to concurrent demands during intermittent static work. Twenty-four participants performed shoulder, wrist, and torso exertions at three levels of physical workload (PWL) in the absence (control) and presence (concurrent) of a mental arithmetic task. Compared to the control, concurrent demand conditions resulted in decreased muscle activity (4–9% decrease), increased cardiovascular load (2–4% increase), and impaired motor co-ordination (9–24% increase in force fluctuation). Furthermore, these outcomes were more prominent at higher PWL levels and within postural (shoulder and torso) muscles. Mental task performance exhibited greater interference with the physical task at low and high PWL levels. Thus, it may be important to consider these muscle- and task-specific interactions of concurrent demands during job design to address worker health and performance issues.

Practitioner Summary: Occupational tasks place both physical and mental demands on workers. These demands can adversely affect physiological responses and performance, and are muscle- and task-dependent. Findings from this research may facilitate the development of ergonomics interventions, such as task redesign and tool/workstation design, that may help reduce risk of workplace injuries.     

Sensitivity of the lane change test as a measure of in-vehicle system demand

The Lane Change Test (LCT) is one of the growing number of methods developed to quantify driving performance degradation brought about by the use of in-vehicle devices. Beyond its validity and reliability, for such a test to be of practical use, it must also be sensitive to the varied demands of individual tasks. The current study evaluated the ability of several recent LCT lateral control and event detection parameters to discriminate between visual-manual and cognitive surrogate In-Vehicle Information System tasks with different levels of demand. Twenty-seven participants (mean age 24.4 years) completed a PC version of the LCT while performing visual search and math problem solving tasks. A number of the lateral control metrics were found to be sensitive to task differences, but the event detection metrics were less able to discriminate between tasks. The mean deviation and lane excursion measures were able to distinguish between the visual and cognitive tasks, but were less sensitive to the different levels of task demand. The other LCT metrics examined were less sensitive to task differences. A major factor influencing the sensitivity of at least some of the LCT metrics could be the type of lane change instructions given to participants. The provision of clear and explicit lane change instructions and further refinement of its metrics will be essential for increasing the utility of the LCT as an evaluation tool.     

The effects of communication modes on performance and discourse organization with an adaptive interface

This paper reports a study of different communication patterns on performance with a simulated adaptive interface that created the impression of a talking and listening computer which would help participants solve problems with a computer. There were four levels of communication modes which differed in the restrictions placed on human-computer communication. Dependent measures included tasks completed per minute as well as participants' utterances, which were assessed for verbosity, disfluencies, and indices of common ground. The largest performance differences were found between the groups that could communicate freely and those where communication was restricted or denied. As restriction increased, performance decreased. Further, as restriction increased, the computer assumed greater control and verbosity decreased. Performance on the simple tasks declined as communication restriction increased, but no differences were observed for complex tasks. The results are discussed with respect to differences between human-human and human-computer communication as well as research on adaptive environments.     

Computer-based task representation: a methodology for improving system design

Task analysis procedures can be used in all stages of system development to examine the nature and severity of performance demands placed upon human operators. Task analyses involve considerable effort in obtaining a detailed set of measurements that represent the behavioural and cognitive tasks performed by the operators; these measures are referred to as task representation. The present article describes a flexible method for incorporating task representation data into an electronic spreadsheet. Such a computer-based procedure has many advantages over the more traditional paper and pencil approaches to task representation and analysis, including greater flexibility in data analysis and the inclusion of both objective and subjective measures of workload. Portions of an illustrative task representation and task analysis are presented along with a discussion of the strengths of computer-based task representation and analysis.     

Effects of respirators on performance of physical, psychomotor and cognitive tasks

Possible work decrements caused by respirator usage were examined. A battery of physical, psychomotor and cognitive tasks was used to investigate the effects of respirator wear on 12 subjects. A repeated measures experimental design was used to study the effects of three types of respirators: a disposable dust mask; an air purifying half-mask; and a full-face airline mask. Performance while wearing a mask was compared to the control condition without a respirator. The results from the physical work task of riding a bicycle ergometer indicated approximately a 10% increase in oxygen consumption when subjects wore half and full-face masks in comparison to when they performed the tasks without a mask. The results indicate that wearing the respirators did not have a significant effect on the performance of cognitive tasks but did affect significantly the performance of psychomotor tasks such as steadiness of work performance and movements requiring accurate control for positioning of objects.     

Driving monotonous routes in a train simulator: the effect of task demand on driving performance and subjective experience

Although monotony is widely recognised as being detrimental to performance, its occurrence and effects are not yet well understood. This is despite the fact that task-related characteristics, such as monotony and low task demand, have been shown to contribute to performance decrements over time. Participants completed one of two simulated train-driving scenarios. Both were highly monotonous and differed only in terms of the level of cognitive demand required (i.e. low demand or high demand). These results highlight the seriously detrimental effects of the combination of monotony and low task demands and clearly show that even a relatively minor increase in cognitive demand can mitigate adverse monotony-related effects on performance for extended periods of time. Monotony is an inherent characteristic of transport industries, including rail, aviation and road transport, which can have adverse impact on safety, reliability and efficiency. This study highlights possible strategies for mitigating these adverse effects. Practitioner Summary: This study provides evidence for the importance of cognitive demand in mitigating monotony-related effects on performance. The results have clear implications for the rapid onset of performance deterioration in low demand monotonous tasks and demonstrate that these detrimental performance effects can be overcome with simple solutions, such as making the task more cognitively engaging.     

Evaluation of reaction time performance and subjective workload during whole-body vibration exposure while seated in upright and twisted postures with and without armrests

There is little knowledge on performance during vibration exposure combined with occupational hazards such as bent or twisted postures. In addition, little information is available on the effective use of armrests during performance-related tasks. This paper investigates the influence of sitting in different working postures on the reaction time and perceived workload of subjects exposed to whole-body vibration. Twenty-one subjects were exposed to 1–20 Hz random vibration in the vertical and fore-and-aft directions. A choice reaction time task was completed while seated in four posture conditions: upright or twisted, with and without armrests. Following the task, participants completed the NASA TLX workload assessment. Posture combined with whole-body vibration exposure had a significant influence on the ability to perform the task. The combined environmental stressors significantly degraded the performance; not only did their reaction times become compromised, the participants’ workload demand also increased. The most severe decrement in performance and workload was experienced while seated in a twisted posture with no armrest support. The inclusion of armrests significantly improved the participants’ ability to complete the task with a lower workload demand.

Relevance to industry

Twisted postures have been observed in a variety of machine operations and it is important to determine their influence on operator workload. Many off-road machines have suspension seats fitted with armrests; this paper demonstrates that armrest support provides additional benefits for off-road machine operators under combined environmental stressors.     

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 impact of knowledge representation on cognitive‐oriented task performance

This research examines the impact of training style and operator individual differences on the task representation developed, automatized task performance, and controlled task performance. Results indicate that performance on relatively straightforward repetitive tasks usually associated with automatization is influenced by training style and the mental task representation held by operators. Also, domain representation is a significant determinant of performance on complex cognitive‐oriented tasks requiring controlled processes. Therefore, the task representation is identified as a high‐level performance determinant for both simple and complex task performance. No effect for training style or individual differences was found. It is concluded that training programs for systems requiring human‐computer interaction must account for this factor in order to facilitate the learning process and enhance task performance.     

Physical fitness and mental performance during and after work

Two groups of subjects who differed in physical fitness (24 well-trained and 24 less well-trained male students) participated in an experiment concerned with mental performance during and after physical work. The physical work was matched between the groups in terms of the percentage of maximal work capacity. Three mental tasks were used: task I involved high information load, placing great demands on continuous concentration and switching of attention as well as on short-term memory; task 2 involved paired associate learning with recall following short and long retention delays; task 3 was a multiplication task with great demands on concentration and on short-term memory. Tasks 1 and 2 were performed during the four different work-load conditions and task 3 after the physical work. As expected, heart rate during physical work was about the same in both groups. No intergroup difference was found in mental performance during physical work. However, recovery rate in terms of heart rate was faster, and mental performance after physical work was significantly better in the fit group than in the unfit group. The results indicate that, even though physical work loads were matched between the groups to make subjective effort equal, the fit subjects were more able to resist the negative after-effects of physical effort.