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Many aspects affect the way humans perform tasks, among others somebody’s personality and current exhaustion level. Under varying conditions the quality of the performance is known to vary as well, for example, due to biases that occur. This paper introduces a cognitive control model addressing these aspects. It has been formally specified, tested in simulations for various scenarios, and formally analyzed. Keywords: modeling; control; biases; task performance.

In our modern society, complex technological systems typically require people to perform several tasks in a limited period of time. In order to be able to optimize such technological systems, the present thesis aims at explicating some difficulties with regard to the fundamentals of multiple-task performance theory - especially in relation to aging- and at providing some basic theoretical improvements. First, the fundamental assumptions of the main recent theories concerning multiple-task performance. In brief, these theories are based on the notion that human performers possess one or a few 'pools' or supplies of central limited-capacity resources. A theoretical analysis shows that these current frameworks offer rather trivial explanations, lack neurobiological support, efficiently account for behavioral plasticity with training. The prevalent conception of attention as 'central supervisory control' does not provide an explanation for what has to be explained, i.e., the control process itself. In this connection, a cognitive neuroscience framework is invoked, which starts with current knowledge concern-ing the basic principles of brain function-ing in combination with the nature of capacity limitations in human performance. According to this framework, the problem of limited behavioral capacity is explained by the way biological systems satisfy two conflicting requirements: massive associative processing power and flexibility against coherent and goal-directed action control. This control conflict is not solved by a mysteri-ous supervisory attentional system. Behavior control basically emerges from elementary, self-regulating, characteris-tics of neuronal information processing. In addition, neurobiology and psychologicanervous system is well-suited for integrated information processing. Hence, atten-tional limitations generally occur when perceptual, cognitive, or motor opera-tions have to be segregated in task performance, whereas the potential efficien-cy of information processing and action increases with the degree to which dual-task elements are related or coherent, such that subtasks can be performed as a whole (skill integration). According to the cognitive neuroscience framework, presented in this thesis, aging-related neuronal de-cline may provide an appropriate, and a neurobio-logi-cally well-founded, basis for explanati-ons for aging-related functional problems. Decreased neuronal connectivity and plasticity may produce several phenomena, such as dealing with emerging task characteristics that affect the integration or segregation of skills (brain programs), to suppress the activation of irrelevant (dominant) routines or to modify these, or to process informa-tion quickly. The second, experimental part, of this thesis reports four experiments aimed at demonstrating that these mecha-nisms may explain dual-task deficits encountered in old age.

In the study maintenance workers were involved in pneumatic wrenching, oxy-gas cutting, and grinding at 5 different heights. Working posture and workers' perceptions were measured. Guidelines on working height were formulated in order to minimize the load on the musculoskeletal system. Data trom the present experiment as weIl as from literature were studied in depth in order to disclose generic mechanisms behind the adoption of working postures during visual-manual operations in relation to workstation adjustment. It was found, for instance, that the working posture was constrained by a strictly followed relationship between gaze inclination and head inclination for-/backwards. Also, the study provided insight into the role of visual interference, viewing distance, manipulation distance, hand grip of the tool, and body support for stability. Concerning evaluation criteria for working postures, it was concluded that neck flexion/extension (i.e., head inclination for-/backwards versus trunk inclination for-/backwards) seems to be the dominant determinant of neck load, as compared to head inclination for-/backwards. Furthermore, the position of the upper arm with respect to the trunk, that is, shoulder flexion/retroflexion in particular, seemed to be a dominant determinant of shoulder and shoulder girdle load, as compared to upper arm elevation.

Dit artikel bevat een overzicht van de 24-uurs experimenten zoals die de laatste jaren in ons lab zijn uitgevoerd. Aangetoond wordt dat vermoeidheidseffecten deels kunnen worden tegengegaan door mensen in een groep als individu aan te spreken.

In this study, effects on task performance and annoyance by aircraft and road traffic noise and attitudes towards these noise sources were addressed in a lab-setting. On day 1 of the study, participants performed a 3-back working memory task in silence and with noise samples played over a headphone at four different loudness levels. On day 2, they filled out questionnaires on aircraft/road traffic-related attitudes and noise sensitivity. We hypothesized that attitudes would only affect task response times for noise samples with recognizable sources. For this reason unrecognizable noise samples were generated from the sound characteristics of an Airbus320 flyover and of a road traffic recording and were used next to the original noise samples. Preliminary results showed no differences of attitudes on annoyance. For participants with negative attitudes towards the noise source, response times were rising with increasing loudness levels during recognizable samples, whereas response times decreased during unrecognizable samples when loudness levels rose. For the group with positive attitudes towards the noise source, reaction times seemed fairly stable across conditions. These results indicate that attitudes towards noise sources may mediate the effect of noise on cognitive tasks.

Een literatuuroverzicht wordt gegeven van de mate waarin beweging van de omgeving (bijv. moving base simulatoren, schepen, vliegtuigen) het werken in die omgeving belemmert.

Shoulder fatigue has been suggested to be a useful risk indicator for shoulder disorders in repetitive, low-force work tasks. In contrast to high-force or purely isometric tasks, it is unclear whether measurable fatigue develops in realistic low-force work. The question addressed in this review was: 'Is there evidence of objective signs of fatigue in the shoulder region in realistic, low-force work tasks?' Studies on objective measures of fatigue applied in realistic low-force work tasks were systematically reviewed, using a task duration of more than 1 h and an intensity level of less than 20% maximum voluntary contraction (MVC) for the median trapezius activation level as inclusion criteria. Thirteen studies were found to fulfil the criteria. All these studies addressed fatigue-related changes in the electromyographic signal in the descending part of the trapezius muscle. Seven did find a combination of frequency decrease and amplitude increase over time, which is generally considered as an objective manifestation of fatigue. Thus, there is evidence of objective signs of fatigue in some of the realistic, low-force tasks. The intensity level appeared to be a main determinant here. In the studies demonstrating signs of fatigue an intensity level of 15%MVC or more was used, while the intensity level in the studies with a negative result was generally lower.

Driving performance deteriorates at high ambient temperatures. Less is known about the effect of low ambient temperatures and the role of subjective aspects like thermal comfort and having control over the ambient temperature. Therefore, an experiment was constructed in which 50 subjects performed a road-tracking task in a cold (5oC), a thermoneutral (20oC) or a warm (35oC) climate. All subjects had a heater/blower (H/B) which generated a .xed amount of heat/wind that could either be controlled or not controlled. In the cold climate, averaged leg skin temperature dropped to 18.5oC and head skin temp 24.9oC; the thermal comfort was rated between ‘cold’ and ‘very cold’. In the warm climate, averaged leg skin temperature rose to 36.6oC and head skin temperature to 30.8oC; the thermal comfort was rated as ‘hot’. Driving performance in the ambient temperature extremes decreased 16% in the cold environment and 13% in the warm situation. Having control over the local head temperature by adjusting a H/B affected neither thermal comfort nor driving performance. In agreement with the literature on priming effects, subjects who started with the no-control condition performed much better in all driving tasks because they were primed to focus on the driving task as such, rather than the complex combination of temperature controls and driving task. It can be concluded that a thermoneutral temperature in a car enhances driving performance and may thus positively affect safety. Using manual climatic controls in hot or cold cars may interfere with the driving task.

In current simulation-based training of knowledgeintensive tasks, human instructors are needed to evaluate a student's task performance. This paper reports a study into the development of a multi-agent-based training system that evaluates student behavior at the result-level (quality of performance) and at the process-level (appropriateness of taken approach). The system uses expert and error modeling as well as plan recognition to evaluate and diagnose the student behavior. Furthermore, it keeps track of this behavior over time and generates feedback on the student's task performance after either one trial or a series of trials. Exploratory results suggest that the system can correctly diagnose the behavior of students. © 2008 IEEE.

Previous studies have shown that identifiability of sound sources influence noise annoyance levels. The aim of the present experiment was to additionally study the effects of actively performing a task versus a less active pastime on noise annoyance. This was done by asking participants to perform a task (task condition) or read a magazine of their choice (no-task condition), while listening to identifiable and unidentifiable samples of transportation noise at varying sound exposure levels (55-85 ASEL). Annoyance was higher for identifiable samples (recordings) than for unidentifiable transformed samples (with equal spectral energy and envelope). Although there was no main effect of activity type on noise annoyance, for the transformed samples, an interaction was found between activity type and sound exposure levels: annoyance started lower in the no-task condition, but rose more steeply with ascending exposure levels than was the case during task performance (large effect). When assessing order effects, it was found that annoyance was higher when the task condition came first, especially for lower sound exposure levels (large effects). It is therefore concluded that the type of activity and the condition order do influence noise annoyance but in interaction with exposure levels, the type of noise and habituation. © 2018 Acoustical Society of America.

The load that is carried in military backpacks has drastically increased over the years. Besides energy expenditure, load carriage increases joint loading which has been associated with an increased risk on injuries, discomfort, and reduced task performance. To support soldiers during load carrying, exoskeletons have been proposed. The use of exoskeletons for load carrying is limited since current active exoskeletons have the disadvantage that their power requirements make them unsuitable for long use and (quasi-)passive exoskeletons have mainly focused on metabolic cost. In this paper we present the Exobuddy exoskeleton. The Exobuddy transfers a part of the load directly to the ground. The Exobuddy mechanism is quasi-passive and thereby eliminates the need for large energy sources associated with active exoskeletons. The Exobuddy was evaluated in indoor and outdoor conditions, each completed by four subjects. Exobuddy unloaded the subjects by transferring on average approximately 30% (130 N) of the load to the ground with a maximum of 53% right after heel strike. The energy drawn from the human body to power the quasi-passive mechanism led only to a small, non-significant, increase in energy expenditure. Although not significant, carrying loads with Exobuddy was perceived less exerted and more comfortable compared to carrying loads with the current backpack. © 2018 IEEE.

Introduction: Exposure to a hypoxic environment has a deleterious effect on physiological and mental functions. We studied the effect of added inspired CO2 during artificially induced hypoxic normobaric hypoxia (oxygen saturation ∼80%) on complex task performance. Methods: In random order, 22 healthy volunteers were exposed to 3 gas mixtures for 50 min each: sham hypoxia (SH, PetO2 103 mmHg without inspired CO2); isocapnic hypoxia (IH, PetO2 ∼40 mmHg, PetCO2 clamped to 0.4 mmHg above resting values); and poikilocapnic hypoxia (PH, PetO2 ∼40 mmHg; no inspired CO2). Brain oxygenation was measured using near infrared spectroscopy. During minutes 25-45 of hypoxia, subjects performed vigilance and task performance tests used in aviation research: the Vigilance and Tracking test and the Multi-Attribute Task battery (MAT-bat). The tests varied in difficulty with the tracking tests considered most difficult. Results: PetCO2 levels differed significantly among groups: IH 42.8 ± 0.7, SH 39.0 ± 0.7, and PH 36.8 ± 0.7 mmHg. Brain oxygenation levels were significantly higher during IH than PH (62.2 ± 1.0 vs. 59.1 ± 1.3%). The results of the performance tests indicated a negative effect of PH vs. SH on most function tests. For the Tracking test of the MAT-bat, performance was worst during PH, but returned to baseline during IH. Discussion: We demonstrate the ability of added inspired CO2 to improve performance during hypoxia by preventing PH-associated hypocapnia-induced vasoconstriction of brain blood vessels. Our results are relevant to aerospace medicine and other circumstances in which complex tasks are performed in a hypoxic environment such as mountain climbing and working in confined spaces. Copyright © by Aerospace Medical Association.

This study investigated the effects of non-obtrusive feedback on continuous lifted hand/finger behaviour, task performance and comfort. In an experiment with 24 participants the effects of two visual and two tactile feedback signals were compared to a no-feedback condition in a computer task. Results from the objective measures showed that all types of feedback were equally effective to reduce lifted hand/finger behaviour (effectiveness) compared to absence of feedback, while task performance was not affected (efficiency). In contrast to objective measures, subjective user experience was significantly different for the four types of feedback signals. Continuous tactile feedback appeared to be the best signal; not only the effectiveness and efficiency were rated reasonable, it also scored best on perceived match between signal and required action. This study shows the importance of including user experiences when investigating usability of feedback signals. Non-obtrusive feedback embedded in products and environments may successfully be used to support office workers to adopt healthy, productive and comfortable working behaviour. © 2011 Elsevier Ltd and The Ergonomics Society.

The effect of the amino acid tyrosine on cognitive task performance were studied on a group of 21 cadets during a demanding military combat training course. In addition, the effects on mood, blood pressure and the norepinephrine metabolite MHPG were determined. Ten subjects received five daily doses of a protein-rich drink containing 2 g tyrosine, and 11 subjects received a carbohydrate-rich drink with the same amount of calories (255 kcal). Assessments were made both immediately prior to the combat course and on the 6th day of the course. The group supplied with the tyrosine-rich drink performed better on a memory and a tracking task than the group supplied with the carbohydrate-rich drink. In addition, the supplementation of tyrosine decreased systolic blood pressure. No effects on mood were found. These findings suggest that supplementation with tyrosine may, under operational circumstances characterized by psychosocial and physical stress, reduce the effects of stress and fatigue on cognitive task performance.

Op basis van een cognitieve taakanalyse is met succes de training verbeterd van WD-onderhoudspersoneel. Technici worden sneller, lossen meer storingen op, terwijl de trainingsduur verkort wordt met 33%.

This paper evaluates a step-by-step participatory approach to better work, applied in reducing the musculoskeletal workload in installation work. To arrive at a reduction in workload, a steering group led the project through the following steps: Introduction: defining the goal and informing all 7000 employees. Analysis: finding major loading tasks. Solution phase: creating solutions in group sessions and prioritise. Testing: promising solutions were tested during real operations. Implementing: spreading the knowledge through the whole company and asking for additional solutions. Evaluation: the effect and process were evaluated.The result was that 138 devices were bought. Seven out of nine devices were used daily. Users reported a good or very good reduction in musculoskeletal loading and were satisfied. The project was cost-effective within 1 year. Adding organizational measures or system solutions could have increased the effect, and more direct participation could have increased the impact. The first steps (introduction, analysis of work, solution generation and user tests) were well organized and contributed to the success. The processes in the last steps were unstructured and the evaluation was not representative. Sixty additional devices were suggested by employees of which 12 were selected. These devices seemed a success, but no data could be obtained on the use and experience with these solutions. © 2002 Elsevier Science Ltd. All rights reserved.

This paper presents an overview of theories concerning the development of RSI (repetitive strain injury), related to muscle disorders. Movement is a noisy process. The level of noise is affected by factors such as fatigue and psychosocial stress. In order for precision movements to be made in such situations, an increased level of muscle activity is required. Positive feedback loops through γ-motoneurones may be responsible for these increases in muscle activity. The Cinderella hypothesis suggests that damage may take place even when muscle activity is of low intensity, due to locally high levels of muscle load. An increase in calcium concentration in muscle cells during long periods of muscle activity may act as a mechanism of this damage. Optimisation of task demands and the prevention of continuous activation of the same groups of muscles appear to be effective measures in the prevention of RSI.

Application of more and more automation in process control shifts the operator’s task from manual to supervisory control. Increasing system autonomy, complexity and information fluctuations make it extremely difficult to develop static support concepts that cover all critical situations after implementing the system. Therefore, support systems in dynamic domains should be dynamic as the domain itself. This paper elaborates on the state information needed from the operator to generate effective mitigation strategies. We describe implications of a real world experiment onboard three frigates of the Royal Netherlands Navy. Although new techniques allow us to measure, combine and gain insight in physiological, subjective and task information, many practical issues need to be solved.

In process control, the ongoing automation and application of new technologies caused a radical change in the position of the operator. Due to this change, increasing manning constraints and the pressure to maximize the operational capability in the Navy, naval operators need personalized and dynamic support which can differ in time: the system should accommodate the user with the right task support at the right time. This paper presents the design and user evaluation of an interface with task allocation support. This kind of support enables the operator to redirect the alarm (system or operator initiated). Evaluation with 34 navy students shows positive results on performance and general usability. Performance increases because the most important problems are solved faster. However, performance on a less important task decreases and can be interpreted as ‘reallocation costs’. Results on questionnaires show an increasing insecurity on the predictability of the system.

Maintenance operations on ITER tokamak components will be largely performed by remote handling. In previous work it was shown that representative maintenance tasks could be performed significantly faster with direct visual feedback than with camera feedback. In post-test interviews, operators indicated that they regarded the lack of 3D perception as the primary factor hindering their performance. This paper discusses various techniques to improve depth perception in teleoperation, including stereo vision, head tracking, virtual camera views and depth gauges. The most promising techniques were tested. Performance metrics included time-to-complete, path analysis and operator work-load. In a first experiment, artificial depth gauges views were tested in a 1:1 scale hardware testbed with mechanical master-slave manipulators handled by experienced operators. Robust real-time image processing was achieved with marker-based objects. The simple depth gauge and graphical overlay did not significantly improve task performance. Operators commented on their view of the task being “obstructed” by the graphical overlay, and the depth gauge was judged not very informative. In a second experiment, real time tracking was combined with VR display including stereo and head tracking. While stereo was found to improve the task performance significantly over the 1 camera (mono) condition, head tracking unexpectedly did not.