Psychological Aspects

Psychological Aspects

Monday, 14 March 2011 19:00

Mental Workload

Mental Versus Physical Workload

The concept of mental workload (MWL) has become increasingly important since modern semi-automated and computerized technologies may impose severe requirements on human mental or information-processing capabilities within both manufacturing and administrative tasks. Thus, especially for the domains of job analysis, evaluation of job requirements and job design, the conceptualization of mental workload has become even more important than that of traditional physical workload.

Definitions of Mental Workload

There is no agreed-upon definition of mental workload. The main reason is that there are at least two theoretically well-based approaches and definitions: (1) MWL as viewed in terms of the task requirements as an independent, external variable with which the working subjects have to cope more or less efficiently, and (2) MWL as defined in terms of an interaction between task requirements and human capabilities or resources (Hancock and Chignell 1986; Welford 1986; Wieland-Eckelmann 1992).

Although arising from different contexts, both approaches offer necessary and well-founded contributions to different problems.

The requirements resources interaction approach was developed within the context of personality-environment fit/misfit theories which try to explain interindividually differing responses to identical physical and psychosocial conditions and requirements. Thus, this approach may explain individual differences in the patterns of subjective responses to loading requirements and conditions, for example, in terms of fatigue, monotony, affective aversion, burnout or diseases (Gopher and Donchin 1986; Hancock and Meshkati 1988).

The task requirements approach was developed within those parts of occupational psychology and ergonomics which are predominantly engaged in task design, especially in the design of new and untried future tasks, or so-called prospective task design. The background here is the stress-strain concept. Task requirements constitute the stress and the working subjects try to adapt to or to cope with the demands much as they would to other forms of stress (Hancock and Chignell 1986). This task requirements approach tries to answer the question of how to design tasks in advance in order to optimize their later impact on the—often still unknown—employees who will accomplish these future tasks.

There are at least a few common characteristics of both conceptualizations of MWL.

MWL mainly describes the input aspects of tasks, that is to say, the requirements and demands made by the tasks on the employees, which might be used in forecasting the task outcome.
The mental aspects of MWL are conceptualized in terms of information processing. Information processing includes cognitive as well as motivational/volitional and emotional aspects, since the persons always will evaluate the demands which they have to cope with and, thus, will self-regulate their effort for processing.
Information-processing integrates mental processes, representations (for example, knowledge, or mental models of a machine) and states (for example, states of consciousness, degrees of activation and, less formally, mood).
MWL is a multidimensional characteristic of task requirements, since every task varies in a couple of interrelated but nevertheless distinct dimensions which separately must be dealt with in task design.
MWL will have a multidimensional impact which at least will determine (a) behaviour, for example, the strategies and the resulting performance, (b) perceived, subjective short-term well-being with consequences for health in the long run, and (c) psycho-physiological processes, for example, alterations of blood pressure at work, which may become long-term effects of a positive kind (promoting, say, fitness improvement) or of a negative kind (involving impairments or ill-health).
From the point of view of task design, MWL should not be minimized—as would be necessary in the case of carcinogenic air pollution—but optimized. The reason is that demanding mental task requirements are inevitable for well-being, health promotion and qualification since they offer the necessary activating impulses, fitness prerequisites and learning/training options. Missing demands on the contrary may result in deactivation, loss of physical fitness, de-qualification and deterioration of so-called intrinsic (task content-dependent) motivation. Findings in this area led to the technique of health and personality promoting task design (Hacker 1986).
MWL therefore, in any case, must be dealt with in task analysis, task requirement evaluation as well as in corrective and prospective task design.

Theoretical Approaches: Requirement-Resources Approaches

From the person-environment fit point of view, MWL and its consequences may be roughly categorized—as is shown in figure 1—into underload, properly fitting load, and overload. This categorization results from the relationships between task requirements and mental capabilities or resources. Task requirements may exceed, fit with or fail to be satisfied by the resources. Both types of misfit may result from quantitative or qualitative modes of misfit and will have qualitatively differing, but in any case negative, consequences (see figure 1).

Figure 1. Types and consequences of requirements-resources relationships

Some theories attempt to define MWL starting from the resource or capacity side of the requirements, namely, resources relationships. These resource theories might be subdivided into resource volume and resource allocation theories (Wieland-Eckelmann 1992). The amount of available capacity may come from a single source (single resource theories) which determines processing. The availability of this resource varies with arousal (Kahneman 1973). Modern multiple resource theories suppose a set of relatively independent processing resources. Thus, performance will depend on the condition whether the same resource or different resources are required simultaneously and concurrently. Different resources are, for example, encoding, processing or responding resources (Gopher and Donchin 1986; Welford 1986). The most critical problem for these types of theories is the reliable identification of one or more well-defined capacities for qualitatively different processing operations.

Resource allocation theories suppose qualitatively changing processing as a function of varying strategies. Depending on the strategies, differing mental processes and representations may be applied for task accomplishment. Thus, not the volume of stable resources but flexible allocation strategies become the key point of interest. Again, however, essential questions—especially concerning the methods of diagnosis of the strategies—remain to be answered.

Assessment of MWL: using requirement-resource approaches

A strict measurement of MWL at present would be impossible since well-defined units of measurement are lacking. But, to be sure, the conceptualization and the instruments for an assessment should meet the general quality criteria of diagnostic approaches, which have objectivity, reliability, validity and usefulness. However, as of now, only a little is known about the overall quality of proposed techniques or instruments.

There are a sizeable number of reasons for the remaining difficulties with assessing MWL according to the requirement-resource approaches (O’Donnell and Eggemeier 1986). An attempt at MWL assessment has to cope with questions like the following: is the task self-intended, following self-set goals, or is it directed with reference to an externally defined order? Which type of capacities (conscious intellectual processing, application of tacit knowledge, etc.) are required, and are they called upon simultaneously or sequentially? Are there different strategies available and, if so, which ones? Which coping mechanisms of a working person might be required?

The most often discussed approaches try to assess MWL in terms of:

required effort (effort assessment) approaches applying—in some versions psychophysiologically validated—scaling procedures such as those offered by Bartenwerfer (1970) or Eilers, Nachreiner and Hänicke (1986), or
occupied or, vice versa, residual mental capacity (mental capacity assessment) approaches applying the traditional dual task techniques as, for example, discussed by O’Donnell and Eggemeier (1986).

Both approaches are heavily dependent on the assumptions of single resource theories and consequently have to struggle with the above-mentioned questions.

Effort assessment. Such effort assessment techniques as, for example, the scaling procedure applied to a perceived correlate of the general central activation, developed and validated by Bartenwerfer (1970), offer verbal scales which may be completed by graphic ones and which grade the unidimensionally varying part of the perceived required effort during task accomplishment. The subjects are requested to describe their perceived effort by means of one of the steps of the scale provided.

The quality criteria mentioned above are met by this technique. Its limitations include the unidimensionality of the scale, covering an essential but questionable part of perceived effort; the limited or absent possibility of forecasting perceived personal task outcomes, for example, in terms of fatigue, boredom or anxiety; and especially the highly abstract or formal character of effort which will identify and explain nearly nothing of the content-dependent aspects of MWL as, for example, any possible useful applications of the qualification or the learning options.

Mental capacity assessment. The mental capacity assessment consists of the dual task techniques and a related data interpretation procedure, called the performance operating characteristic (POC). Dual task techniques cover several procedures. Their common feature is that subjects are requested to perform two tasks simultaneously. The crucial hypothesis is: the less an additional or secondary task in the dual task situation will deteriorate in comparison with the base-line single task situation, the lower the mental capacity requirements of the primary task, and vice versa. The approach is now broadened and various versions of task interference under dual task conditions are investigated. For example, the subjects are instructed to perform two tasks concurrently with graded variations of the priorities of the tasks. The POC curve graphically illustrates the effects of possible dual-task combinations arising from sharing limited resources among the concurrently performed tasks.

The critical assumptions of the approach mainly consist in the suggestions that every task will require a certain share of a stable, limited conscious (versus unconscious, automated, implicit or tacit) processing capacity, in the hypothetical additive relationship of the two capacity requirements, and in the restriction of the approach to performance data only. The latter might be misleading for several reasons. First of all there are substantial differences in the sensitivity of performance data and subjectively perceived data. Perceived load seems to be determined mainly by the amount of required resources, often operationalized in terms of working memory, whereas performance measures seem to be determined predominantly by the efficiency of the sharing of resources, depending on allocation strategies (this is dissociation theory; see Wickens and Yeh 1983). Moreover, individual differences in information processing abilities and personality traits strongly influence the indicators of MWL within the subjective (perceived), performance and psychophysiological areas.

Theoretical Approaches: Task Requirement Approaches

As has been shown, task requirements are multidimensional and, thus, may not be described sufficiently by means of only one dimension, whether it be the perceived effort or the residual conscious mental capacity. A more profound description might be a profile-like one, applying a theoretically selected pattern of graded dimensions of task characteristics. The central issue is thus the conceptualization of “task”, especially in terms of task content, and of “task accomplishment”, especially in terms of the structure and phases of goal-oriented actions. The role of the task is stressed by the fact that even the impact of contextual conditions (like temperature, noise or working hours) on the persons are task-dependent, since they are mediated by the task acting as a gate device (Fisher 1986). Various theoretical approaches sufficiently agree regarding those critical task dimensions, which offer a valid prediction of the task outcome. In any case, task outcome is twofold, since (1) the intended result must be achieved, meeting the performance-outcome criteria, and (2) a number of unintended personal short-term and cumulative long-term side effects will emerge, for example fatigue, boredom (monotony), occupational diseases or improved intrinsic motivation, knowledge or skills.

Assessment of MWL. With task requirement approaches, action-oriented approaches like those of complete versus partialized actions or the motivation potential score (for an elaboration of both see Hacker 1986), propose as indispensable task characteristics for analysis and evaluation at least the following:

temporal and procedural autonomy regarding decisions on self-set goals and, consequently, transparency, predictability and control of the work situation

number and variety of subtasks (especially concerning preparation, organization and checking of the results of implementation) and of actions accomplishing these subtasks (i.e., whether such actions involve cyclical completeness versus fragmentation)

variety (“level”) of action-regulating mental processes and representations. These may be mentally automated or routinized ones, knowledge-based “if-then” ones or intellectual and problem-solving ones. (They may also be characterized by hierarchical completeness as opposed to fragmentation)

required cooperation

long-term learning requirements or options.

The identification of these task characteristics requires the joint procedures of job/task analysis, including document analyses, observations, interviews and group discussions, which must be integrated in a quasi-experimental design (Rudolph, Schönfelder and Hacker 1987). Task analysis instruments which may guide and assist the analysis are available. Some of them assist only the analysis (for example, NASA-TLX Task Load Index, Hart and Staveland, 1988) while others are useful for evaluation and design or redesign. An example here is the TBS-GA (Tätigkeitsbewertungs System für geistige Arbeit [Task Diagnosis Survey—Mental Work]); see Rudolph, Schönfelder and Hacker (1987).

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Vigilance

The concept of vigilance refers to a human observer’s state of alertness in tasks that demand efficient registration and processing of signals. The main characteristics of vigilance tasks are relatively long durations and the requirement to detect infrequent and unpredictable target stimuli (signals) against a background of other stimulus events.

Vigilance Tasks

The prototypical task for vigilance research was that of radar operators. Historically, their apparently unsatisfactory performance during the Second World War has been a major impetus for the extensive study of vigilance. Another major task requiring vigilance is an industrial inspection. More generally, all kinds of monitoring tasks which require the detection of relatively infrequent signals embody the risk of failures to detect and to respond to these critical events.

Vigilance tasks make up a heterogeneous set and vary on several dimensions, in spite of their common characteristics. An obviously important dimension is the overall stimulus rate as well as the rate of target stimuli. It is not always possible to define the stimulus rate unambiguously. This is the case in tasks that require the detection of target events against continuously presented background stimuli, as in detecting critical values on a set of dials in a monitoring task. A less obviously important distinction is that between successive-discrimination tasks and simultaneous-discrimination tasks. In simultaneous-discrimination tasks, both target stimuli and background stimuli are present at the same time, while in successive-discrimination tasks one is presented after the other so that some demands on memory are made. Although most vigilance tasks require the detection of visual stimuli, stimuli in other modalities have also been studied. Stimuli can be confined to a single spatial location, or there can be different sources for target stimuli. Target stimuli can differ from background stimuli by physical characteristics, but also by more conceptual ones (like a certain pattern of meter readings that can differ from other patterns). Of course, the conspicuousness of targets can vary: some can be detected easily, while others may be hard to discriminate from background stimuli. Target stimuli can be unique or there can be sets of target stimuli without well-defined boundaries to set them off from background stimuli, as is the case in many industrial inspection tasks. This list of dimensions on which vigilance tasks differ can be expanded, but even this length of the list suffices to emphasize the heterogeneity of vigilance tasks and thus the risks involved in generalizing certain observations across the full set.

Performance Variations and the Vigilance Decrement

The most frequently used performance measure in vigilance tasks is the proportion of target stimuli, for example, faulty products in industrial inspection, that have been detected; this is an estimate of the probability of so-called hits. Those target stimuli that remain unnoticed are called misses. Although the hit rate is a convenient measure, it is somewhat incomplete. There is a trivial strategy that allows one to achieve 100% hits: one only has to classify all stimuli as targets. However, the hit rate of 100% is then accompanied by a false-alarm rate of 100%, that is, not only the target stimuli are correctly detected, but the background stimuli are incorrectly “detected” as well. This line of reasoning makes it quite clear that whenever there are false alarms at all, it is important to know their proportion in addition to the hit rate. Another measure for performance in a vigilance task is the time needed to respond to target stimuli (response time).

Performance in vigilance tasks exhibits two typical attributes. The first one is the low overall level of vigilance performance. It is low in comparison with an ideal situation for the same stimuli (short observation periods, high readiness of the observer for each discrimination, etc.). The second attribute is the so-called vigilance decrement, the decline of performance in the course of the watch which can start within the first few minutes. Both these observations refer to the proportion of hits, but they have also been reported for response times. Although the vigilance decrement is typical of vigilance tasks, it is not universal.

In investigating the causes of poor overall performance and vigilance decrements, a distinction will be made among concepts that are related to the basic characteristics of the task and concepts that are related to organismic and task-unrelated situational factors. Among the task-related factors strategic and non-strategic ones can be distinguished.

Strategic processes in vigilance tasks

The detection of a signal like a faulty product is partly a matter of the observer’s strategy and partly a matter of the signal’s discriminability. This distinction is based on the theory of signal detection (TSD), and some basics of the theory need to be presented in order to highlight the distinction’s importance. Consider a hypothetical variable, defined as “evidence for the presence of a signal”. Whenever a signal is presented, this variable takes on some value, and whenever a background stimulus is presented, it takes on a value that is lower on the average. The value of the evidence variable is assumed to vary across repeated presentations of the signal. Thus it can be characterized by a so-called probability density function as is illustrated in figure 1. Another density function characterizes the values of the evidence variable upon presentation of a background stimulus. When the signals are similar to the background stimuli, the functions will overlap, so that a certain value of the evidence variable can originate either from a signal or from a background stimulus. The particular shape of the density functions of figure 1 is not essential for the argument.

Figure 1. Thresholds and discriminability

The detection response of the observer is based on the evidence variable. It is assumed that a threshold is set so that a detection response is given whenever the value of the evidence variable is above the threshold. As is illustrated in figure 1, the areas under the density functions to the right of the threshold correspond to the probabilities of hits and false alarms. In practice, estimates of the separation of the two functions and the location of the threshold can be derived. The separation of the two density functions characterizes the discriminability of the target stimuli from the background stimuli, while the location of the threshold characterizes the observer’s strategy. Variation of the threshold produces a joint variation of the proportions of hits and false alarms. With a high threshold, the proportions of hits and false alarms will be small, while with a low threshold the proportions will be large. Thus, the selection of a strategy (placement of the threshold) essentially is the selection of a certain combination of hit rate and false-alarm rate among the combinations that are possible for a certain discriminability.

Two major factors that influence the location of the threshold are payoffs and signal frequency. The threshold will be set to lower values when there is much to gain from a hit and little to lose from a false alarm, and it will be set to higher values when false alarms are costly and the benefits from hits are small. A low threshold setting can also be induced by a high proportion of signals, while a low proportion of signals tends to induce higher threshold settings. The effect of signal frequency on threshold settings is a major factor for the low overall performance in terms of the proportion of hits in vigilance tasks and for the vigilance decrement.

An account of the vigilance decrement in terms of strategic changes (threshold changes) requires that the reduction of the proportion of hits in the course of the watch is accompanied by a reduction of the proportion of false alarms. This is, in fact, the case in many studies, and it is likely that the overall poor performance in vigilance tasks (in comparison with the optimal situation) does also result, at least partly, from a threshold adjustment. In the course of a watch, the relative frequency of detection responses comes to match the relative frequency of targets, and this adjustment implies a high threshold with a relatively small proportion of hits and a relatively small proportion of false alarms as well. Nevertheless, there are vigilance decrements that result from changes in discriminability rather than from changes in threshold settings. These have been observed mainly in successive-discrimination tasks with a relatively high rate of stimulus events.

Nonstrategic processes in vigilance tasks

Although part of the overall poor performance in vigilance tasks and many instances of the vigilance decrement can be accounted for in terms of strategic adjustments of the detection threshold to low signal rates, such an account is not complete. There are changes in the observer during a watch that can reduce the discriminability of stimuli or result in apparent threshold shifts that cannot be considered as an adaptation to the task characteristics. In the more than 40 years of vigilance research, a number of nonstrategic factors that contribute to poor overall performance and to the vigilance decrement have been identified.

A correct response to a target in a vigilance task requires a sufficiently precise sensory registration, an appropriate threshold location, and a link between the perceptual processes and the associated response-related processes. During the watch the observers have to maintain a certain task set, a certain readiness to respond to target stimuli in a certain way. This is a nontrivial requirement because without a particular task set no observer would respond to target stimuli in the way required. Two major sources of failures are thus inaccurate sensory registration and lapses in the readiness to respond to target stimuli. Major hypotheses to account for such failures will be briefly reviewed.

Detection and identification of a stimulus are faster when there is no temporal or spatial uncertainty about its appearance. Temporal and/or spatial uncertainty is likely to reduce vigilance performance. This is the essential prediction of expectancy theory. Optimal preparedness of the observer requires temporal and spatial certainty; obviously vigilance tasks are less than optimal in this respect. Although the major focus of expectancy theory is on the overall low performance, it can also serve to account for parts of the vigilance decrement. With infrequent signals at random intervals, high levels of preparedness might initially exist at times when no signal is presented; in addition, signals will be presented at low levels of preparedness. This discourages occasional high levels of preparedness in general so that whatever benefits accrue from them will vanish in the course of a watch.

Expectancy theory has a close relation to attentional theories. Variants of attentional theories of vigilance, of course, are related to dominant theories of attention in general. Consider a view of attention as “selection for processing” or “selection for action”. According to this view, stimuli are selected from the environment and processed with high efficiency whenever they serve the currently dominant action plan or task set. As already said, the selection will benefit from precise expectations about when and where such stimuli will occur. But stimuli will only be selected if the action plan—the task set—is active. (Drivers of cars, for example, respond to traffic lights, other traffic, etc.; passengers don’t do so normally, although both are in almost the same situation. The critical difference is that between the task sets of the two: only the driver’s task set requires responses to traffic lights.)

The selection of stimuli for processing will suffer when the action plan is temporarily deactivated, that is when the task set is temporarily absent. Vigilance tasks embody a number of features that discourage continuous maintenance of the task set, like short cycle times for processing stimuli, lack of feedback and little motivational challenge by apparent task difficulty. So-called blockings can be observed in almost all simple cognitive tasks with short cycle times like simple mental arithmetic or rapid serial responses to simple signals. Similar blockings occur in the maintenance of the task set in a vigilance task as well. They are not immediately recognizable as delayed responses because responses are infrequent and targets that are presented during a period of absent task set may no longer be there when the absence is over so that a miss will be observed instead of a delayed response. Blockings become more frequent with time spent on the task. This can give rise to the vigilance decrement. There may be additional reasons for temporary lapses in the availability of the appropriate task set, for example, distraction.

Certain stimuli are not selected in the service of the current action plan, but by virtue of their own characteristics. These are stimuli that are intense, novel, moving toward the observer, have an abrupt onset or for any other reason might require immediate action no matter what the current action plan of the observer is. There is little risk of not detecting such stimuli. They attract attention automatically, as is indicated, for example, by the orienting response, which includes a shift of the direction of the gaze toward the stimulus source. However, answering an alarm bell is not normally considered a vigilance task. In addition to stimuli that attract attention by their own characteristics, there are stimuli that are processed automatically as a consequence of the practice. They seem to “pop out” from the environment. This kind of automatic processing requires extended practice with a so-called consistent mapping, that is, a consistent assignment of responses to stimuli. The vigilance decrement is likely to be small or even absent once automatic processing of stimuli has been developed.

Finally, vigilance performance suffers from a lack of arousal. This concept refers in a rather global manner to the intensity of neural activity, ranging from sleep through normal wakefulness to high excitement. One of the factors that is thought to affect arousal is external stimulation, and this is fairly low and uniform in most vigilance tasks. Thus, the intensity of central nervous system activity can decline overall over the course of a watch. An important aspect of arousal theory is that it links vigilance performance to various task-unrelated situational factors and factors related to the organism.

The Influence of Situational and Organismic Factors

Low arousal contributes to poor performance in vigilance tasks. Thus performance can be enhanced by situational factors that tend to enhance arousal, and it can be reduced by all measures that reduce the level of arousal. On balance, this generalization is mostly correct for the overall performance level in vigilance tasks, but the effects on the vigilance decrement are absent or less reliably observed across different kinds of manipulation of arousal.

One way to raise the level of arousal is the introduction of additional noise. However, the vigilance decrement is generally unaffected, and with respect to overall performance the results are inconsistent: enhanced, unchanged and reduced performance levels have all been observed. Perhaps the complex nature of noise is relevant. For example, it can be affectively neutral or annoying; it cannot only be arousing, but also be distracting. More consistent are the effects of sleep deprivation, which is “de-arousing”. It generally reduces vigilance performance and has sometimes been seen to enhance the vigilance decrement. Appropriate changes of vigilance performance have also been observed with depressant drugs like benzodiazepines or alcohol and stimulant drugs like amphetamine, caffeine or nicotine.

Individual differences are a conspicuous feature of performance in vigilance tasks. Although individual differences are not consistent across all sorts of vigilance tasks, they are fairly consistent across similar ones. There is only little or no effect of sex and general intelligence. With respect to age, vigilance performance increases during childhood and tends to decline beyond the age of sixty. In addition there is a good chance that introverts will show better performance than extroverts.

The Enhancement of Vigilance Performance

The existing theories and data suggest some means to enhance vigilance performance. Depending on the amount of specificity of the suggestions, it is not difficult to compile lists of various lengths. Some rather broad suggestions are given below that have to be fitted to specific task requirements. They are related to the ease of perceptual discriminations, the appropriate strategic adjustments, the reduction of uncertainty, the avoidance of the effects of attentional lapses and the maintenance of arousal.

Vigilance tasks require discriminations under non-optimal conditions. Thus one is well advised in making the discriminations as easy as possible, or the signals as conspicuous as possible. Measures related to this general goal can be straightforward (like appropriate lighting or longer inspection times per product) or more sophisticated, including special devices to enhance the conspicuousness of targets. Simultaneous comparisons are easier than successive ones, so the availability of a reference standard can be helpful. By means of technical devices, it is sometimes possible to present the standard and the object to be examined in rapid alternation, so that differences will appear as motions in the display or other changes for which the visual system is particularly sensitive.

To counteract the strategic changes of the threshold that lead to a relatively low proportion of correct detections of targets (and for making the task less boring in terms of the frequency of actions to be taken) the suggestion has been made to introduce fake targets. However, this seems not to be a good recommendation. Fake targets will increase the proportion of hits overall but at the cost of more frequent false alarms. In addition, the proportion of undetected targets among all stimuli that are not responded to (the outgoing faulty material in an industrial inspection task) will not necessarily be reduced. Better suited seems to be explicit knowledge about the relative importance of hits and false alarms and perhaps other measures to obtain an appropriate placement of the threshold for deciding between “good” and “bad”.

Temporal and spatial uncertainty are important determinants of poor vigilance performance. For some tasks, spatial uncertainty can be reduced by way of defining a certain position of the object to be inspected. However, little can be done about temporal uncertainty: the observer would be unnecessary in a vigilance task if the occurrence of a target could be signaled in advance of its presentation. One thing that can be done in principle, however, is to mix objects to be inspected if faults tend to occur in bunches; this serves to avoid very long intervals without targets as well as very short intervals.

There are some obvious suggestions for the reduction of attentional lapses or at least their impact on performance. By proper training, some kind of automatic processing of targets can perhaps be obtained provided that the background and target stimuli are not too variable. The requirement for sustained maintenance of the task set can be avoided by means of frequent short breaks, job rotation, job enlargement or job enrichment. Introduction of variety can be as simple as having the inspector himself or herself getting the material to be inspected from a box or other location. This also introduces self-pacing, which may help in avoiding signal presentations during temporary deactivations of the task set. Sustained maintenance of task set can be supported by means of feedback, indicated interest by supervisors and operator’s awareness of the importance of the task. Of course, accurate feedback of performance level is not possible in typical vigilance tasks; however, even inaccurate or incomplete feedback can be helpful as far as the observer’s motivation is concerned.

There are some measures that can be taken to maintain a sufficient level of arousal. Continuous use of drugs may exist in practice but is never found among recommendations. Some background music can be useful, but can also have an opposite effect. Social isolation during vigilance tasks should mostly be avoided, and during times of day with low levels of arousal like the late hours of the night, supportive measures such as short watches are particularly important.

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Mental Fatigue

Mental strain is a normal consequence of the coping process with mental workload (MWL). Long-term load or a high intensity of job demands can result in short-term consequences of overload (fatigue) and underload (monotony, satiation) and in long-term consequences (e.g., stress symptoms and work-related diseases). The maintenance of the stable regulation of actions while under strain can be realized through changes in one’s action style (by variation of strategies of information-seeking and decision-making), in the lowering of the level of need for achievement (by redefinition of tasks and reduction of quality standards) and by means of a compensatory increase of psychophysiological effort and afterwards a decrease of effort during work time.

This understanding of the process of mental strain can be conceptualized as a transactional process of action regulation during the imposition of loading factors which include not only the negative components of the strain process but also the positive aspects of learning such as accretion, tuning and restructuring and motivation (see figure 2).

Figure 1. Components of the process of strain and its consequences

Mental fatigue can be defined as a process of time-reversible decrement of behavioural stability in performance, mood and activity after prolonged working time. This state is temporarily reversible by changing the work demands, the environmental influences or stimulation and is completely reversible by means of sleep.

Mental fatigue is a consequence of performing tasks with a high level of difficulty that involve predominantly information processing and/or are of protracted duration. In contrast with monotony, the recovery of the decrements is time-consuming and does not occur suddenly after changing task conditions. Symptoms of fatigue are identified on several levels of behavioural regulation: dis-regulation in the biological homeostasis between environment and organism, dis-regulation in the cognitive processes of goal-directed actions and loss of stability in goal-oriented motivation and achievement level.

Symptoms of mental fatigue can be identified in all subsystems of the human information processing system:

perception: reduced eye movements, reduced discrimination of signals, threshold deterioration

information processing: extension of decision time, action slips, decision uncertainty, blockings, “risky strategies” in action sequences, disturbances in sensorimotor coordination of movements

memory functions: prolongation of information in ultrashort-term storages, disturbances in the rehearsal processes in short-term memory, delay in information transmission in long-term memory and in memory searching processes.

Differential Diagnostic of Mental Fatigue

Sufficient criteria exist to differentiate amongst menta fatigue, monotony, mental satiation and stress (in a narrow sense) (table 1).

Table 1. Differentiation among several negative consequences of mental strain

Criteria	Mental fatigue	Monotony	Satiation	Stress
Key condition	Poor fit in terms of overload preconditions	Poor fit in terms of underload preconditions	Loss of perceived sense of tasks	Goals perceived as threatening
Mood	Tiredness without boredom exhaustion	Tiredness with boredom	Irritability	Anxiety, threat aversion
Emotional evaluation	Neutral	Neutral	Increased affective aversion	Increased anxiety
Activation	Continuously decreased	Not continuously decreased	Increased	Increased
Recovery	Time-consuming	Suddenly after task alternation	?	Long-term disturbances in recovery
Prevention	Task design, training, short-break system	Enrichment of job content	Goal-setting programmes and job enrichment	Job redesign, conflict and stress management

Degrees of Mental Fatigue

The well-described phenomenology of mental fatigue (Schmidtke 1965), many valid methods of assessment and the great amount of experimental and field results offer the possibility of an ordinal scaling of degrees of mental fatigue (Hacker and Richter 1994). The scaling is based on the individual’s capacity to cope with behavioural decrements:

Level 1: Optimal and efficient performance: no symptoms of decrement in performance, mood and activation level.

Level 2: Complete compensation characterized by increased peripheral psycho-physiological activation (e.g., as measured by electromyogram of finger muscles), perceived increase of mental effort, increased variability in performance criteria.

Level 3: Labile compensation additional to that described in level 2: action slips, perceived fatigue, increasing (compensatory) psycho-physiological activity in central indicators, heart rate, blood pressure.

Level 4: Reduced efficiency additional to that described in level 3: decrease of performance criteria.

Level 5: Yet further functional disturbances: disturbances in social relationships and cooperation at workplace; symptoms of clinical fatigue like loss of sleep quality and vital exhaustion.

Prevention of Mental Fatigue

The design of task structures, environment, rest periods during working time and sufficient sleep are the ways to reduce symptoms of mental fatigue in order that no clinical consequences will occur:

1. Changes in the structure of tasks. Designing of preconditions for adequate learning and task structuring is not only a means of furthering the development of efficient job structures, but is also essential for the prevention of a misfit in terms of mental overload or underload:

Information processing burdens can be relieved by developing efficient internal task representations and organization of information. The resulting enlargement of cognitive capacity will match information needs and resources more aptly.

Human-centred technologies with high compatibility between the order of information as it is presented and the required task (Norman 1993) will reduce the mental effort necessary for information recoding and, in consequence, relieve symptoms of fatigue and stress.

Well-balanced coordination of different levels of regulations (as they apply to skills, rules and knowledge) may reduce effort and, moreover, increase human reliability (Rasmussen 1983).

Training workers in goal-directed action sequences in advance of actual problems will lighten their sense of mental effort by making their jobs clearer, more predictable and more evidently under their control. Their psychophysiological activation level will be effectively reduced.

2. Introduction of systems of short-term breaks during work. The positive effects of such breaks depend on the observance of some preconditions. More short breaks are more efficient than fewer long breaks; effects depend on a fixed and therefore anticipatable time schedule; and the content of the breaks should have a compensatory function to the physical and mental job demands.

3. Sufficient relaxation and sleep. Special employee-assistant programmes and stress-management techniques may support the ability of relaxation and the prevention of the development of chronicle fatigue (Sethi, Caro and Schuler 1987).

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Ergonomics References

Abeysekera, JDA, H Shahnavaz, and LJ Chapman. 1990. Ergonomics in developing countries. In Advances in Industrial Ergonomics and Safety, edited by B Das. London: Taylor & Francis.

Ahonen, M, M Launis, and T Kuorinka. 1989. Ergonomic Workplace Analysis. Helsinki: Finnish Institute of Occupational Health.

Alvares, C. 1980. Homo Faber: Technology and Culture in India, China and the West from 1500 to Present Day. The Hague: Martinus Nijhoff.

Amalberti, R. 1991. Savoir-faire de l’opérateur: aspects théoriques et pratiques en ergonomie. In Modèle en analyse du travail, edited by R Amalberti, M de Montmollin, and J Thereau. Liège: Mardaga.

Amalberti, R, M Bataille, G Deblon, A Guengant, JM Paquay, C Valot, and JP Menu. 1989. Développement d’aides intelligentes au pilotage: Formalisation psychologique et informatique d’un modèle de comportement du pologage de combat engagé en mission de pènètration. Paris: Rapport CERMA.

Åstrand, I. 1960. Aerobic work capacity in men and women with special reference to age. Acta Physiol Scand 49 Suppl. 169:1-92.

Bainbridge, L. 1981. Le contrôleur de processus. B Psychol XXXIV:813-832.

—. 1986. Asking questions and accessing knowledge. Future Comput Sys 1:143-149.

Baitsch, C. 1985. Kompetenzentwicklung und partizipative Arbeitsgestaltung. Bern: Huber.

Banks, MH and RL Miller. 1984. Reliability and convergent validity of the job component inventory. J Occup Psychol 57:181-184.

Baranson, J. 1969. Industrial Technology for Developing Economies. New York: Praeger.

Bartenwerfer, H. 1970. Psychische Beanspruchung und Erdmüdung. In Handbuch der Psychologie, edited by A Mayer and B Herwig. Göttingen: Hogrefe.

Bartlem, CS and E Locke. 1981. The Coch and French study: A critique and reinterpretation. Hum Relat 34:555-566.

Blumberg, M. 1988. Towards a new theory of job design. In Ergonomics of Hybrid Automated Systems, edited by W Karwowski, HR Parsaei, and MR Wilhelm. Amsterdam: Elsevier.

Bourdon, F and A Weill Fassina. 1994. Réseau et processus de coopération dans la gestion du trafic ferroviaire. Travail Hum. Numéro spécial consacré au travail collectif.

Brehmer, B. 1990. Towards a taxonomy for microworlds. In Taxonomy for an Analysis of Work Domains. Proceedings of the First MOHAWC Workshop, edited by B Brehmer, M de Montmollin and J Leplat. Roskilde: Riso National Laboratory.

Brown DA and R Mitchell. 1986. The Pocket Ergonomist. Sydney: Group Occupational Health Centre.

Bruder. 1993. Entwicklung eines wissensbusierten Systems zur belastungsanalytisch unterscheidbaren Erholungszeit. Düsseldorf: VDI-Verlag.

Caverni, JP. 1988. La verbalisation comme source d’observables pour l’étude du fonctionnnement cognitif. In Psychologie cognitive: Modèles et méthodes, edited by JP
Caverni, C Bastien, P Mendelson, and G Tiberghien. Grenoble: Presses Univ. de Grenoble.

Campion, MA. 1988. Interdisciplinary approaches to job design: A constructive replication with extensions. J Appl Psychol 73:467-481.

Campion, MA and PW Thayer. 1985. Development and field evaluation of an inter-disciplinary measure of job design. J Appl Psychol 70:29-43.

Carter, RC and RJ Biersner. 1987. Job requirements derived from the Position Analysis Questionnaire and validity using military aptitude test scores. J Occup Psychol 60:311-321.

Chaffin, DB. 1969. A computerized biomechanical model-development of and use in studying gross body actions. J Biomech 2:429-441.

Chaffin, DB and G Andersson. 1984. Occupational Biomechanics. New York: Wiley.

Chapanis, A. 1975. Ethnic Variables in Human Factors Engineering. Baltimore: Johns Hopkins University.

Coch, L and JRP French. 1948. Overcoming resistance to change. Hum Relat 1:512-532.

Corlett, EN and RP Bishop. 1976. A technique for assessing postural discomfort. Ergonomics 19:175-182.

Corlett, N. 1988. The investigation and evaluation of work and workplaces. Ergonomics 31:727-734.

Costa, G, G Cesana, K Kogi, and A Wedderburn. 1990. Shiftwork: health, sleep and performance. Frankfurt: Peter Lang.

Cotton, JL, DA Vollrath, KL Froggatt, ML Lengnick-Hall, and KR Jennings. 1988. Employee participation: Diverse forms and different outcomes. Acad Manage Rev 13:8-22.

Cushman, WH and DJ Rosenberg. 1991. Human Factors in Product Design. Amsterdam: Elsevier.

Dachler, HP and B Wilpert. 1978. Conceptual dimensions and boundaries of participation in organizations: A critical evaluation. Adm Sci Q 23:1-39.

Daftuar, CN. 1975. The role of human factors in underdeveloped countries, with special reference to India. In Ethnic Variable in Human Factor Engineering, edited by Chapanis. Baltimore: Johns Hopkins University.

Das, B and RM Grady. 1983a. Industrial workplace layout design. An application of engineering anthropometry. Ergonomics 26:433-447.

—. 1983b. The normal working area in the horizontal plane. A comparative study between Farley’s and Squire’s concepts. Ergonomics 26:449-459.

Deci, EL. 1975. Intrinsic Motivation. New York: Plenum Press.

Decortis, F and PC Cacciabue. 1990. Modèlisation cognitive et analyse de l’activité. In Modèles et pratiques de l’analyse du travail, edited by R Amalberti, M Montmollin, and J Theureau. Brussels: Mardaga.

DeGreve, TB and MM Ayoub. 1987. A workplace design expert system. Int J Ind Erg 2:37-48.

De Keyser, V. 1986. De l’évolution des métiers. In Traité de psychologie du travail, edited by C Levy- Leboyer and JC Sperandio. Paris: Presses Universitaires de France.

—. 1992. Man within the Production Line. Proceedings of the Fourth Brite-EuRam Conference, 25-27 May, Séville, Spain. Brussels: EEC.

De Keyser, V and A Housiaux. 1989. The Nature of Human Expertise. Rapport Intermédiaire Politique Scientifique. Liège: Université de Liège.

De Keyser, V and AS Nyssen. 1993. Les erreurs humaines en anesthésie. Travail Hum 56:243-266.

De Lisi, PS. 1990. Lesson from the steel axe: Culture, technology and organizational change. Sloan Manage Rev 32:83-93.

Dillon, A. 1992. Reading from paper versus screen: A critical review of the empirical literature. Ergonomics 35:1297-1326.

Dinges, DF. 1992. Probing the limits of functional capacity: The effects of sleep loss on short-duration tasks. In Sleep, Arousal, and Performance, edited by RJ Broughton and RD Ogilvie. Boston: Birkhäuser.

Drury, CG. 1987. A biomechanical evaluation of the repetitive motion injury potential of industrial jobs. Sem Occup Med 2:41-49.

Edholm, OG. 1966. The assessment of habitual activity. In Physical Activity in Health and Disease, edited by K Evang and K Lange-Andersen. Oslo: Universitetterlaget.

Eilers, K, F Nachreiner, and K Hänicke. 1986. Entwicklung und Überprüfung einer Skala zur Erfassung subjektiv erlebter Anstrengung. Zeitschrift für Arbeitswissenschaft 40:215-224.

Elias, R. 1978. A medicobiological approach to workload. Note No. 1118-9178 in Cahiers De Notes Documentaires—Sécurité Et Hygiène Du Travail. Paris: INRS.

Elzinga, A and A Jamison. 1981. Cultural Components in the Scientific Attitude to Nature: Eastern and Western Mode. Discussion paper No. 146. Lund: Univ. of Lund, Research Policy Institute.

Emery, FE. 1959. Characteristics of Socio-Technical Systems. Document No. 527. London: Tavistock.

Empson, J. 1993. Sleep and Dreaming. New York: Harvester Wheatsheaf.

Ericson, KA and HA Simon. 1984. Protocol Analysis: Verbal Reports As Data. Cambridge, Mass.: MIT Press.

European Committee for Standardization (CEN). 1990. Ergonomic Principles of the Design of Work Systems. EEC Council Directive 90/269/EEC, The Minimum Health and Safety Requirements for the Manual Handling of Loads. Brussels: CEN.

—. 1991. CEN Catalogue 1991: Catalogue of European Standards. Brussels: CEN.

—. 1994. Safety of Machinery: Ergonomic Design Principles. Part 1: Terminology and General Principles. Brussels: CEN.

Fadier, E. 1990. Fiabilité humaine: méthodes d’analyse et domaines d’application. In Les facteurs humains de la fiabilité dans les systèmes complexes, edited by J Leplat and G De Terssac. Marseilles: Octares.

Falzon, P. 1991. Cooperative dialogues. In Distributed Decision Making. Cognitive Models for Cooperative Works, edited by J Rasmussen, B Brehmer, and J Leplat. Chichester: Wiley.

Faverge, JM. 1972. L’analyse du travail. In Traité de psychologie appliqueé, edited by M Reuchlin. Paris: Presses Universitaires de France.

Fisher, S. 1986. Stress and Strategy. London: Erlbaum.

Flanagan, JL. 1954. The critical incident technique. Psychol Bull 51:327-358.

Fleishman, EA and MK Quaintance. 1984. Toxonomies of Human Performance: The Description of Human Tasks. New York: Academic Press.

Flügel, B, H Greil, and K Sommer. 1986. Anthropologischer Atlas. Grundlagen und Daten. Deutsche Demokratische Republik. Berlin: Verlag tribüne.

Folkard, S and T Akerstedt. 1992. A three-process model of the regulation of alertness sleepiness. In Sleep, Arousal and Performance, edited by RJ Broughton and BD Ogilvie. Boston: Birkhäuser.

Folkard, S and TH Monk. 1985. Hours of work: Temporal factors in work scheduling . Chichester: Wiley.

Folkard, S, TH Monk, and MC Lobban. 1978. Short and long-term adjustment of circadian rhythms in “permanent” night nurses. Ergonomics 21:785-799.

Folkard, S, P Totterdell, D Minors and J Waterhouse. 1993. Dissecting circadian performance rhythms: Implications for shiftwork. Ergonomics 36(1-3):283-88.

Fröberg, JE. 1985. Sleep deprivation and prolonged working hours. In Hours of Work: Temporal Factors in Work Scheduling, edited by S Folkard and TH Monk. Chichester: Wiley.

Fuglesang, A. 1982. About Understanding Ideas and Observations on Cross-Cultural
Communication. Uppsala: Dag Hammarskjöld Foundation.

Geertz, C. 1973. The Interpretation of Cultures. New York: Basic Books.

Gilad, I. 1993. Methodology for functional ergonomic evaluation of repetitive operations. In Advances in Industrial Egonomics and Safety, edited by Nielsen and Jorgensen. London: Taylor & Francis.

Gilad, I and E Messer. 1992. Biomechanics considerations and ergonomic design in diamond polishing. In Advances in Industrial Ergonomics and Safety, edited by Kumar. London: Taylor & Francis.

Glenn, ES and CG Glenn. 1981. Man and Mankind: Conflict and Communication between Cultures. Norwood, NJ: Ablex.

Gopher, D and E Donchin. 1986. Workload—An examination of the concept. In Handbook of Perception and Human Performance, edited by K Boff, L Kaufman, and JP Thomas. New York: Wiley.

Gould, JD. 1988. How to design usable systems. In Handbook of Human Computer Interaction, edited by M Helander. Amsterdam: Elsevier.

Gould, JD and C Lewis. 1985. Designing for usability: Key principles and what designers think. Commun ACM 28:300-311.

Gould, JD, SJ Boies, S Levy, JT Richards, and J Schoonard. 1987. The 1984 Olympic message system: A test of behavioral principles of the design. Commun ACM 30:758-769.

Gowler, D and K Legge. 1978. Participation in context: Towards a synthesis of the theory and practice of organizational change, part I. J Manage Stud 16:150-175.

Grady, JK and J de Vries. 1994. RAM: The Rehabilitation Technology Acceptance Model as a Base for an Integral Product Evaluation. Instituut voor Research, Ontwikkeling en Nascholing in de Gezondheidszorg (IRON) and University Twente, Department of Biomedical Engineering.

Grandjean, E. 1988. Fitting the Task to the Man. London: Taylor & Francis.

Grant, S and T Mayes. 1991. Cognitive task analysis? In Human-Computer Interactionand Complex Systems, edited by GS Weir and J Alty. London: Academic Press.

Greenbaum, J and M Kyng. 1991. Design At Work: Cooperative Design of Computer Systems. Hillsdale, NJ: Lawrence Erlbaum.

Greuter, MA and JA Algera. 1989. Criterion development and job analysis. In Assessment and Selection in Organizations, edited by P Herlot. Chichester: Wiley.

Grote, G. 1994. A participatory approach to the complementary design of highly automated work systems. In Human Factors in Organizational Design and Management, edited by G Bradley and HW Hendrick. Amsterdam: Elsevier.

Guelaud, F, M-N Beauchesne, J Gautrat, and G Roustang. 1977. Pour une analyse des conditions du travail ouvrier dans l’entreprise. Paris: A. Colin.

Guillerm, R, E Radziszewski, and A Reinberg. 1975. Circadian rhythms of six healthy young men over a 4-week period with night-work every 48 h and a 2 per cent Co2 atmosphere. In Experimental Studies of Shiftwork, edited by P Colquhoun, S Folkard, P Knauth, and J Rutenfranz. Opladen: Westdeutscher Werlag.

Hacker, W. 1986. Arbeitspsychologie. In Schriften zur Arbeitpsychologie, edited by E Ulich. Bern: Huber.

Hacker, W and P Richter. 1994. Psychische Fehlbeanspruchung. Ermüdung, Monotonie, Sättigung, Stress. Heidelberg: Springer.

Hackman, JR and GR Oldham. 1975. Development of the job diagnostic survey. J Appl Psychol 60:159-170.

Hancock, PA and MH Chignell. 1986. Toward a Theory of Mental Work Load: Stress and Adaptability in Human-Machine Systems. Proceedings of the IEEE International Conference On Systems, Man, and Cybernetics. New York: IEEE Society.

Hancock, PA and N Meshkati. 1988. Human Mental Workload. Amsterdam: North Holland.

Hanna, A (ed.). 1990. Annual Design Review ID. 37 (4).

Härmä, M. 1993. Individual differences in tolerance to shiftwork: a review. Ergonomics 36:101-109.

Hart, S and LE Staveland. 1988. Development of NASA-TLX (Task Load Index): Results of empirical and theoretical research. In Human Mental Work Load, edited by PA Hancock and N Meshkati. Amsterdam: North Holland.

Hirschheim, R and HK Klein. 1989. Four paradigms of information systems development. Commun ACM 32:1199-1216.

Hoc, JM. 1989. Cognitive approaches to process control. In Advances in Cognitive Science, edited by G Tiberghein. Chichester: Horwood.

Hofstede, G. 1980. Culture’s Consequences: International Differences in Work-Related Values. Beverly Hills, Calif.: Sage Univ. Press.

—. 1983. The cultural relativity of organizational practices and theories. J Int Stud :75-89.

Hornby, P and C Clegg. 1992. User participation in context: A case study in a UK bank. Behav Inf Technol 11:293-307.

Hosni, DE. 1988. The transfer of microelectronics technology to the third world. Tech Manage Pub TM 1:391-3997.

Hsu, S-H and Y Peng. 1993. Control/display relationship of the four-burner stove: A reexamination. Hum Factors 35:745-749.

International Labour Organization (ILO). 1990.The hours we work: new work schedules in policy and practice. Cond Wor Dig 9.

International Organization for Standardization (ISO). 1980. Draft Proposal for Core List of Anthropometric Measurements ISO/TC 159/SC 3 N 28 DP 7250. Geneva: ISO.

—. 1996. ISO/DIS 7250 Basic Human Body Measurements for Technological Design. Geneva: ISO.
Japan Industrial Design Promotion Organization (JIDPO). 1990. Good Design Products 1989. Tokyo: JIDPO.

Jastrzebowski, W. 1857. Rys ergonomiji czyli Nauki o Pracy, opartej naprawdach poczerpnietych z Nauki Przyrody. Przyoda i Przemysl 29:227-231.

Jeanneret, PR. 1980. Equitable job evaluation and classification with the Position Analysis Questionnaire. Compens Rev 1:32-42.

Jürgens, HW, IA Aune, and U Pieper. 1990. International data on anthropometry. Occupational Safety and Health Series. Geneva: ILO.

Kadefors, R. 1993. A model for assessment and design of workplaces for manual welding. In The Ergonomics of Manual Work, edited by WS Marras, W Karwowski, and L Pacholski. London: Taylor & Francis.

Kahneman, D. 1973. Attention and Effort. Englewood Cliffs, NJ: Prentice Hall.

Karhu, O, P Kansi, and I Kuorinka. 1977. Correcting working postures in industry: A practical method for analysis. Appl Ergon 8:199-201.

Karhu, O, R Harkonen, P Sorvali, and P Vepsalainen. 1981. Observing working postures in industry: Examples of OWAS application. Appl Ergon 12:13-17.

Kedia, BL and RS Bhagat. 1988. Cultural constraints on transfer of technology across nations: Implications for research in international and comparative management. Acad Manage Rev 13:559-571.

Keesing, RM. 1974. Theories of culture. Annu Rev Anthropol 3:73-79.

Kepenne, P. 1984. La charge de travail dans une unité de soins de médecine. Mémoire. Liège: Université de Liège.

Kerguelen, A. 1986. L’observation systématique en ergonomie: Élaboration d’un logiciel d’aide au recueil et à l’analyse des données. Diploma in Ergonomics Thesis, Conservatoire National des Arts et Métiers, Paris.

Ketchum, L. 1984. Sociotechnical design in a third world country: The railway maintenance depot at Sennar in Sudan. Hum Relat 37:135-154.

Keyserling, WM. 1986. A computer-aided system to evaluate postural stress in the workplace. Am Ind Hyg Assoc J 47:641-649.

Kingsley, PR. 1983. Technological development: Issues, roles and orientation for social psychology. In Social Psychology and Developing Countries, edited by Blacker. New York: Wiley.

Kinney, JS and BM Huey. 1990. Application Principles for Multicolored Displays. Washington, DC: National Academy Press.

Kivi, P and M Mattila. 1991. Analysis and improvement of work postures in building industry: Application of the computerized OWAS method. Appl Ergon 22:43-48.

Knauth, P, W Rohmert and J Rutenfranz. 1979. Systemic selection of shift plans for continuous production with the aid of work-physiological criteria. Appl Ergon 10(1):9-15.

Knauth, P. and J Rutenfranz. 1981. Duration of sleep related to the type of shift work, in Night and shiftwork: biological and social aspects , edited by A Reinberg, N Vieux, and P Andlauer. Oxford Pergamon Press.

Kogi, K. 1982. Sleep problems in night and shift work. II. Shiftwork: Its practice and improvement . J Hum Ergol:217-231.

—. 1981. Comparison of resting conditions between various shift rotation systems for industrial workers, in Night and shift work. Biological and social aspects , edited by A Reinberg, N Vieux, and P Andlauer. Oxford: Pergamon.

—. 1985. Introduction to the problems of shiftwork. In Hours of Work: Temporal Factors in Work-Scheduling, edited by S Folkard and TH Monk. Chichester: Wiley.

—. 1991. Job content and working time: The scope for joint change. Ergonomics 34:757-773.

Kogi, K and JE Thurman. 1993. Trends in approaches to night and shiftwork and new international standards. Ergonomics 36:3-13.

Köhler, C, M von Behr, H Hirsch-Kreinsen, B Lutz, C Nuber, and R Schultz-Wild. 1989. Alternativen der Gestaltung von Arbeits- und Personalstrukturen bei rechnerintegrierter Fertigung. In Strategische Optionen der Organisations- und Personalentwicklung bei CIM Forschungsbericht KfK-PFT 148, edited by Institut für Sozialwissenschaftliche Forschung. Karlsruhe: Projektträgerschaft Fertigungstechnik.

Koller, M. 1983. Health risks related to shift work. An example of time-contingent effects of long-term stress. Int Arch Occ Env Health 53:59-75.

Konz, S. 1990. Workstation organization and design. Ergonomics 32:795-811.

Kroeber, AL and C Kluckhohn. 1952. Culture, a critical review of concepts and definitions. In Papers of the Peabody Museum. Boston: Harvard Univ.

Kroemer, KHE. 1993. Operation of ternary chorded keys. Int J Hum Comput Interact 5:267-288.

—. 1994a. Locating the computer screen: How high, how far? Ergonomics in Design (January):40.

—. 1994b. Alternative keyboards. In Proceedings of the Fourth International Scientific Conference WWDU ‘94. Milan: Univ. of Milan.

—. 1995. Ergonomics. In Fundamentals of Industrial Hygiene, edited by BA Ploog. Chicago: National Safety Council.

Kroemer, KHE, HB Kroemer, and KE Kroemer-Elbert. 1994. Ergonomics: How to Design for Ease and Efficiency. Englewood Cliffs, NJ: Prentice Hall.

Kwon, KS, SY Lee, and BH Ahn. 1993. An approach to fuzzy expert systems for product colour design. In The Ergonomics of Manual Work, edited by Maras, Karwowski, Smith, and Pacholski. London: Taylor & Francis.

Lacoste, M. 1983. Des situations de parole aux activités interprétives. Psychol Franç 28:231-238.

Landau, K and W Rohmert. 1981. AET-A New Job Analysis Method. Detroit, Mich.: AIIE Annual Conference.

Laurig, W. 1970. Elektromyographie als arbeitswissenschaftliche Untersuchungsmethode zur Beurteilung von statischer Muskelarbeit. Berlin: Beuth.

—. 1974. Beurteilung einseitig dynamischer Muskelarbeit. Berlin: Beuth.

—. 1981. Belastung, Beanspruchung und Erholungszeit bei energetisch-muskulärer Arbeit—Literaturexpertise. In Forschungsbericht Nr. 272 der Bundesanstalt für Arbeitsschutz und Unfallforschung Dortmund. Bremerhaven: Wirtschaftsverlag NW.

—. 1992. Grundzüge der Ergonomie. Erkenntnisse und Prinzipien. Berlin, Köln: Beuth Verlag.

Laurig, W and V Rombach. 1989. Expert systems in ergonomics: Requirements and an approach. Ergonomics 32:795-811.

Leach, ER. 1965. Culture and social cohesion: An anthropologist’s view. In Science and Culture, edited by Holten. Boston: Houghton Mifflin.

Leana, CR, EA Locke, and DM Schweiger. 1990. Fact and fiction in analyzing research on participative decision making: A critique of Cotton, Vollrath, Froggatt, Lengnick-Hall, and Jennings. Acad Manage Rev 15:137-146.

Lewin, K. 1951. Field Theory in Social Science. New York: Harper.

Liker, JK, M Nagamachi, and YR Lifshitz. 1988. A Comparitive Analysis of Participatory Programs in US and Japan Manufacturing Plants. Ann Arbor, Mich.: Univ. of Michigan, Center for Ergonomics, Industrial and Operational Engineering.

Lillrank, B and N Kano. 1989. Continuous Improvement: Quality Control Circles in Japanese Industries. Ann Arbor, Mich.: Univ. of Michigan, Center for Japanese Studies.

Locke, EA and DM Schweiger. 1979. Participation in decision making: One more look. In Research in Organizational Behavior, edited by BM Staw. Greenwich, Conn.: JAI Press.

Louhevaara, V, T Hakola, and H Ollila. 1990. Physical work and strain involved in manual sorting of postal parcels. Ergonomics 33:1115-1130.

Luczak, H. 1982. Belastung, Beanspruchung und Erholungszeit bei informatorisch- mentaler Arbeit — Literaturexpertise. Forschungsbericht der Bundesanstalt für Arbeitsschutz und Unfallforschung Dortmund . Bremerhaven: Wirtschaftsverlag NW.

—. 1983. Ermüdung. In Praktische Arbeitsphysiologie, edited by W Rohmert and J Rutenfranz. Stuttgart: Georg Thieme Verlag.

—. 1993. Arbeitswissenschaft. Berlin: Springer Verlag.

Majchrzak, A. 1988. The Human Side of Factory Automation. San Francisco: Jossey-Bass.

Martin, T, J Kivinen, JE Rijnsdorp, MG Rodd, and WB Rouse. 1991. Appropriate automation-integrating technical, human, organization, economic and cultural factors. Automatica 27:901-917.

Matsumoto, K and M Harada. 1994. The effect of night-time naps on recovery from fatigue following night work. Ergonomics 37:899-907.

Matthews, R. 1982. Divergent conditions in the technological development of India and Japan. Lund Letters on Technology and Culture, No. 4. Lund: Univ. of Lund, Research Policy Institute.

McCormick, EJ. 1979. Job Analysis: Methods and Applications. New York: American Management Association.

McIntosh, DJ. 1994. Integration of VDUs into the US office work environment. In Proceedings of the Fourth International Scientific Conference WWDU ‘94. Milan: Univ. of Milan.

McWhinney. 1990. The Power of Myth in Planning and Organizational Change, 1989 IEEE Technics, Culture and Consequences. Torrence, Calif.: IEEE Los Angeles Council.

Meshkati, N. 1989. An etiological investigation of micro and macroergonomics factors in the Bhopal disaster: Lessons for industries of both industrialized and developing countries. Int J Ind Erg 4:161-175.

Minors, DS and JM Waterhouse. 1981. Anchor sleep as a synchronizer of rhythms on abnormal routines. Int J Chronobiology : 165-188.

Mital, A and W Karwowski. 1991. Advances in Human Factors/Ergonomics. Amsterdam: Elsevier.

Monk, TH. 1991. Sleep, Sleepiness and Performance . Chichester: Wiley.

Moray, N, PM Sanderson, and K Vincente. 1989. Cognitive task analysis for a team in a complex work domain: A case study. Proceedings of the Second European Meeting On Cognitive Science Approaches to Process Control, Siena, Italy.

Morgan, CT, A Chapanis, JS III Cork, and MW Lund. 1963. Human Engineering Guide to Equipment Design. New York: McGraw-Hill.

Mossholder, KW and RD Arvey. 1984. Synthetic validity: A conceptual and comparative review. J Appl Psychol 69:322-333.

Mumford, E and Henshall. 1979. A Participative Approach to Computer Systems Design. London: Associated Business Press.

Nagamachi, M. 1992. Pleasantness and Kansei engineering. In Measurement Standards. Taejon, Korea: Korean Research Institute of Standards and Science Publishing.

National Institute for Occupational Safety and Health (NIOSH). 1981. Work Practices Guide for Manual Lifting. Cincinnati, Ohio: US Department of Health and Human Services.

—. 1990. OSHA Instruction CPL 2.85: Directorate of Compliance Programs: Appendix C, Guidelines Auggested By NIOSH for Videotape Evaluation of Work Station for Upper Extremities Cumulative Trauma Disorders. Washington, DC: US Department of Health and Human Services.

Navarro, C. 1990. Functional communication and problem-solving in a bus traffic-regulation task. Psychol Rep 67:403-409.

Negandhi, ART. 1975. Modern Organizational Behaviour. Kent: Kent Univ..

Nisbett, RE and TD De Camp Wilson. 1977. Telling more than we know. Psychol Rev 84:231-259.

Norman, DA. 1993. Things That Make Us Smart. Reading: Addison-Wesley.

Noro, K and AS Imada. 1991. Participatory Ergonomics. London: Taylor & Francis.

O’Donnell, RD and FT Eggemeier. 1986. Work load assessment methodology. In Handbook of Perception and Human Performance. Cognitive Processes and Performance, edited by K Boff, L Kaufman, and JP Thomas. New York: Wiley.

Pagels, HR. 1984. Computer culture: The scientific, intellectual and social impact of the computer. Ann NY Acad Sci :426.

Persson, J and Å Kilbom. 1983. VIRA—En Enkel Videofilmteknik För Registrering OchAnalys Av Arbetsställningar Och—Rörelser. Solna, Sweden: Undersökningsrapport,Arbetraskyddsstyrelsen.

Pham, DT and HH Onder. 1992. A knowledge-based system for optimizing workplace layouts using a genetic algorithm. Ergonomics 35:1479-1487.

Pheasant, S. 1986. Bodyspace, Anthropometry, Ergonomics and Design. London: Taylor & Francis.

Poole, CJM. 1993. Seamstress’ finger. Brit J Ind Med 50:668-669.

Putz-Anderson, V. 1988. Cumulative Trauma Disorders. A Manual for Musculoskeletal Diseases of the Upper Limbs. London: Taylor & Francis.

Rasmussen, J. 1983. Skills, rules, and knowledge: Sinds, signs, symbols and other distinctions in human performance models. IEEE T Syst Man Cyb 13:257-266.

—. 1986. A framework for cognitive task analysis in systems design. In Intelligent Decision Support in Process Environments, edited by E Hollnagel, G Mancini, and DD Woods. Berlin: Springer.

Rasmussen, J, A Pejtersen, and K Schmidts. 1990. In Taxonomy for Analysis of Work Domains. Proceedings of the First MOHAWC Workshop, edited by B Brehmer, M de Montmollin and J Leplat. Roskilde: Riso National Laboratory.

Reason, J. 1989. Human Error. Cambridge: CUP.

Rebiffé, R, O Zayana, and C Tarrière. 1969. Détermination des zones optimales pour l’emplacement des commandes manuelles dans l’espace de travail. Ergonomics 12:913-924.

Régie nationale des usines Renault (RNUR). 1976. Les profils de poste: Methode d’analyse des conditions de travail. Paris: Masson-Sirtes.

Rogalski, J. 1991. Distributed decision making in emergency management: Using a method as a framework for analysing cooperative work and as a decision aid. In Distributed Decision Making. Cognitive Models for Cooperative Work, edited by J Rasmussen, B Brehmer, and J Leplat. Chichester: Wiley.

Rohmert, W. 1962. Untersuchungen über Muskelermüdung und Arbeitsgestaltung. Bern: Beuth-Vertrieb.

—. 1973. Problems in determining rest allowances. Part I: Use of modern methods to evaluate stress and strain in static muscular work. Appl Ergon 4(2):91-95.

—. 1984. Das Belastungs-Beanspruchungs-Konzept. Z Arb wiss 38:193-200.

Rohmert, W and K Landau. 1985. A New Technique of Job Analysis. London: Taylor & Francis.

Rolland, C. 1986. Introduction à la conception des systèmes d’information et panorama des méthodes disponibles. Génie Logiciel 4:6-11.

Roth, EM and DD Woods. 1988. Aiding human performance. I. Cognitive analysis. Travail Hum 51:39-54.

Rudolph, E, E Schönfelder, and W Hacker. 1987. Tätigkeitsbewertungssystem für geistige arbeit mit und ohne Rechnerunterstützung (TBS-GA). Berlin: Psychodiagnostisches Zentrum der Humboldt-Universität.

Rutenfranz, J. 1982. Occupational health measures for night- and shiftworkers. II. Shiftwork: Its practice and improvement. J Hum Ergol:67-86.

Rutenfranz, J, J Ilmarinen, F Klimmer, and H Kylian. 1990. Work load and demanded physical performance capacity under different industrial working conditions. In Fitness for Aged, Disabled, and Industrial Workers, edited by M Kaneko. Champaign, Ill.: Human Kinetics Books.

Rutenfranz, J, P Knauth, and D Angersbach. 1981. Shift work research issues. In Biological Rhythms, Sleep and Shift Work , edited by LC Johnson, DI Tepas, WP Colquhoun, and MJ Colligan. New York: Spectrum Publications Medical and Scientific Books.

Saito, Y. and K Matsumoto. 1988. Variations of physiological functions and psychological measures and their relationship on delayed shift of sleeping time. Jap J Ind Health 30:196-205.

Sakai, K, A Watanabe, N Onishi, H Shindo, K Kimotsuki, H Saito, and K Kogl. 1984. Conditions of night naps effective to facilitate recovery from night work fatigue. J Sci Lab 60: 451-478.

Savage, CM and D Appleton. 1988. CIM and Fifth Generation Management. Dearborn: CASA/SME Technical Council.

Savoyant, A and J Leplat. 1983. Statut et fonction des communications dans l’activité des équipes de travail. Psychol Franç 28:247-253.

Scarbrough, H and JM Corbett. 1992. Technology and Organization. London: Routledge.

Schmidtke, H. 1965. Die Ermüdung. Bern: Huber.

—. 1971. Untersuchungen über den Erholunggszeitbedarf bei verschiedenen Arten gewerblicher Tätigkeit. Berlin: Beuth-Vertrieb.

Sen, RN. 1984. Application of ergonomics to industrially developing countries. Ergonomics 27:1021-1032.

Sergean, R. 1971. Managing Shiftwork. London: Gower Press.

Sethi, AA, DHJ Caro, and RS Schuler. 1987. Strategic Management of Technostress in an Information Society. Lewiston: Hogrefe.

Shackel, B. 1986. Ergonomics in design for usability. In People and Computer: Design for Usability, edited by MD Harrison and AF Monk. Cambridge: Cambridge Univ. Press.

Shahnavaz, H. 1991. Transfer of Technology to Industrially Developing Countries and Human Factors Consideration TULEÅ 1991: 22, 23024. Luleå Univ., Luleå, Sweden: Center for Ergonomics of Developing Countries.

Shahnavaz, H, J Abeysekera, and A Johansson. 1993. Solving multi-factorial work-environment problems through participatory ergonomics: Case study: VDT operators. In Ergonomics of Manual Work, edited by E Williams, S Marrs, W Karwowski, JL Smith, and L Pacholski. London: Taylor & Francis.

Shaw, JB and JH Riskind. 1983. Predicting job stress using data from the Position Analysis Questionnaire (PAQ). J Appl Psychol 68:253-261.

Shugaar, A. 1990. Ecodesign: New products for a greener culture. Int Herald Trib, 17.

Sinaiko, WH. 1975. Verbal factors in human engineering: Some cultural and psychological data. In Ethnic Variables in Human Factors Engineering, edited by A Chapanis. Baltimore: Johns Hopkins Univ..

Singleton, WT. 1982. The Body At Work. Cambridge: CUP.

Snyder, HL. 1985a. Image quality: Measures and visual performance. In Flat Panel Displays and CRTs, edited by LE Tannas. New York: Van Nostrand Reinhold.

—. 1985b. The visual system: Capabilities and limitations. In Flat Panel Displays and CRTs, edited by LE Tannas. New York: Van Nostrand Reinhold.

Solomon, CM. 1989. The corporate response to work force diversity. Pers J 68:42-53.

Sparke, P. 1987. Modern Japanese Design. New York: EP Dutton.

Sperandio, JC. 1972. Charge de travail et régulation des processus opératoires. Travail Hum 35:85-98.

Sperling, L, S Dahlman, L Wikström, A Kilbom, and R Kadefors. 1993. A cube model for the classification of work with hand tools and the formulation of functional requirements. Appl Ergon 34:203-211.

Spinas, P. 1989. User oriented software development and dialogue design. In Work With Computers: Organizational, Management, Stress and Health Aspects, edited by MJ Smith and G Salvendy. Amsterdam: Elsevier.

Staramler, JH. 1993. The Dictionary of Human Factors Ergonomics. Boca Raton: CRC Press.

Strohm, O, JK Kuark, and A Schilling. 1993. Integrierte Produktion: Arbeitspsychologische Konzepte und empirische Befunde, Schriftenreihe Mensch, Technik, Organisation. In CIM—Herausforderung an Mensch, Technik, Organisation, edited by G Cyranek and E Ulich. Stuttgart, Zürich: Verlag der Fachvereine.

Strohm, O, P Troxler and E Ulich. 1994. Vorschlag für die Restrukturierung eines
Produktionsbetriebes. Zürich: Institut für Arbietspsychologie der ETH.

Sullivan, LP. 1986. Quality function deployment: A system to assure that customer needs drive the product design and production process. Quality Progr :39-50.

Sundin, A, J Laring, J Bäck, G Nengtsson, and R Kadefors. 1994. An Ambulatory Workplace for Manual Welding: Productivity through Ergonomics. Manuscript. Göteborg: Lindholmen Development.

Tardieu, H, D Nanci, and D Pascot. 1985. Conception d’un système d’information. Paris: Editions d’Organisation.

Teiger, C, A Laville, and J Durafourg. 1974. Taches répétitives sous contrainte de temps et charge de travail. Rapport no 39. Laboratoire de physiologie du travail et d’ergonomie du CNAM.

Torsvall, L, T Akerstedt, and M. Gillberg. 1981. Age, sleep and irregular workhours: a field study with EEG recording, catecholamine excretion and self-ratings. Scand J Wor Env Health 7:196-203.

Ulich, E. 1994. Arbeitspsychologie 3. Auflage. Zürich: Verlag der Fachvereine and Schäffer-Poeschel.

Ulich, E, M Rauterberg, T Moll, T Greutmann, and O Strohm. 1991. Task orientation and user-oriented dialogue design. In Int J Human-Computer Interaction 3:117-144.

United Nations Educational, Scientific and Cultural Organization (UNESCO). 1992. Ergonomics Impact of Science on Society. Vol. 165. London: Taylor & Francis.

Van Daele, A. 1988. L’écran de visualisation ou la communication verbale? Analyse comparative de leur utilisation par des opérateurs de salle de contrôle en sidérurgie. Travail Hum 51(1):65-80.

—. 1992. La réduction de la complexité par les opérateurs dans le contrôle de processus continus. contribution à l’étude du contrôle par anticipation et de ses conditions de mise en œuvre. Liège: Université de Liège.

Van der Beek, AJ, LC Van Gaalen, and MHW Frings-Dresen. 1992. Working postures and activities of lorry drivers: A reliability study of on-site observation and recording on a pocket computer. Appl Ergon 23:331-336.

Vleeschdrager, E. 1986. Hardness 10: diamonds . Paris.

Volpert, W. 1987. Psychische Regulation von Arbeitstätigkeiten. In Arbeitspsychologie. Enzklopüdie der Psychologie, edited by U Kleinbeck and J Rutenfranz. Göttingen: Hogrefe.

Wagner, R. 1985. Job analysis at ARBED. Ergonomics 28:255-273.

Wagner, JA and RZ Gooding. 1987. Effects of societal trends on participation research. Adm Sci Q 32:241-262.

Wall, TD and JA Lischeron. 1977. Worker Participation: A Critique of the Literature and Some Fresh Evidence. London: McGraw-Hill.

Wang, WM-Y. 1992. Usability Evaluation for Human-Computer Interaction (HCI). Luleå, Sweden: Luleå Univ. of Technology.

Waters, TR, V Putz-Anderson, A Garg, and LJ Fine. 1993. Revised NIOSH equation for the design and evaluation of manual handling tasks. Ergonomics 36:749-776.

Wedderburn, A. 1991. Guidelines for shiftworkers. Bulletin of European Shiftwork Topics (BEST) No. 3. Dublin: European Foundation for the Improvement of Living and Working Conditions.

Welford, AT. 1986. Mental workload as a function of demand, capacity, strategy and skill. Ergonomics 21:151-176.

White, PA. 1988. Knowing more about what we tell: ‘Introspective access’ and causal report accuracy, 10 years later. Brit J Psychol 79:13-45.

Wickens, C. 1992. Engineering Psychology and Human Performance. New York: Harper Collins.

Wickens, CD and YY Yeh. 1983. The dissociation between subjective work load and performance: A multiple resources approach. In Proceedings of the Human Factors Society 27th Annual Meeting. Santa Monica, Calif.: Human Factors Society.

Wieland-Eckelmann, R. 1992. Kognition, Emotion und Psychische Beanspruchung. Göttingen: Hogrefe.

Wikström.L, S Byström, S Dahlman, C Fransson, R Kadefors, Å Kilbom, E Landervik, L Lieberg, L Sperling, and J Öster. 1991. Criterion for Selection and Development of Hand Tools. Stockholm: National Institute of Occupational Health.

Wilkinson, RT. 1964. Effects of up to 60 hours sleep deprivation on different types of work. Ergonomics 7:63-72.

Williams, R. 1976. Keywords: A Vocabulary of Culture and Society. Glasgow: Fontana.

Wilpert, B. 1989. Mitbestimmung. In Arbeits- und Organisationspsychologie. Internationales Handbuch in Schlüsselbegriffen, edited by S Greif, H Holling, and N Nicholson. Munich: Psychologie Verlags Union.

Wilson, JR. 1991. Participation: A framework and foundation for ergonomics. J Occup Psychol 64:67-80.

Wilson, JR and EN Corlett. 1990. Evaluation of Human Work: A Practical Ergonomics Methodology. London: Taylor & Francis.

Wisner, A. 1983. Ergonomics or anthropology: A limited or wide approach to working condition in technology transfer. In Proceedings of the First International Conference On Ergonomics of Developing Countries, edited by Shahnavaz and Babri. Luleå, Sweden: Luleå Univ. of Technology.

Womack, J, T Jones, and D Roos. 1990. The Machine That Changed the World. New York: Macmillan.

Woodson, WE, B Tillman, and P Tillman. 1991. Human Factors Design Handbook. New York: McGraw-Hill.

Zhang, YK and JS Tyler. 1990. The establishment of a modern telephone cable production facility in a developing country. A case study. In International Wire and Cable Symposium Proceedings. Illinois.

Zinchenko, V and V Munipov. 1989. Fundamentals of Ergonomics. Moscow: Progress.

Mental Workload

Vigilance

Mental Fatigue

Contents

Ergonomics References