Task Demands

The result of this hierarchical process is capability, which reflects the current ability of the driver to respond to task demands. This is not simply the amount of effort a driver has available at any particular moment. Rather it is the amount of effort available plus the knowledge and experience of how to best use and apply this effort, minus any relevant situational factors. 

Task demands sit on the other side of the TCI and reflect the environment in which the driver is currently operating. Task demand is not created in a hierarchical fashion but is rather a combination of environment factors, including the road environment, behaviour of other road users, weather conditions, vehicle characteristics, road position and trajectory of the driver s car, and its travelling speed. 

The environmental factors that make up task demands are both in and outside of the driver s control. For instance, there is little outside of high-level strategic decisions a driver can do to affect the current road environment or weather conditions. However, road position, trajectory and travel speed are mostly under the control of the driver. This means that the speed and trajectory of the driver are also linked to the cjpaWlity of the driver. Fuller (2005) attempted to represent this in an earlier version of TCI where human factors were added to the task dmiand side of the diagram, impacting on speed, road position and trajectory. However, this addition has since distppeaied from TCI. 

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From the traditional HF/E perspective, error is seen as a consequence of a mismatch between the demands of a task and the physical and mental capabilities of an individual or an operating team. An extended version of this perspective was described in Chapter 1, Section 1.7. The basic approach of HF/E is to reduce the likelihood of error by the application of design principles and standards to match human capabilities and task demands. These encompass the physical environment (e.g., heat, lighting, vibration), and the design of the workplace together with display and control elements of the human-machine interface. Examples of the approach are given in Wilson and Corlett (1990) and Salvendy (1987). 

Root cause 2. Incomplete training the incident occurred during the worker s first time alone on the top floor. Training had been given but only in low task demand situations. 

Immiscible solvents like water and oil can be transformed by addition of solubilizers to single-phase solutions. Amphiphilic substances are known as effective solubilizers. Solubilization depends on the HLB of the components that ought to form a single phase and on the kind of solubilizer used. Phosphorus-containing surfactants with their variety of possible molecular structures are solubilizers that can be tailored to the task demanded. 

Anderson, K. and Revelle, W., The interactive effects of caffeine, impulsivity and task demands on visual search task. Personality and Individual Differences 4(2), 127-134, 1983. 

Verbal fMRI/verbal fluency task Interaction of task demand with ketamine was Fu et al. 

Cools R, Barker R, Sahakian BJ, Robbins TW (2001) Enhanced or impaired cognitive function in Parkinson s disease as a function of dopaminergic medication and task demands. Cerebral Cortex 77 1136-1143. 

Domeshek, E., A Case Stndy of Case Indexing Designing Index Feature Sets to Suit Task Demands and Snpport Parallelism, in Advances in Connectionnist and Neural Computation Theory, Vol.2 Analogical Connections, Barenden, J. and Holyoak, K., Eds., Norwood Pnblishing, NJ, 1993. 

If the handling task demands higher accuracy or flexibility, numerically controlled (NC) axes or industrial robots are recommended. Using two or three linear axes allows more complex and precise handling tasks to be performed than with mechanical handling devices. 

Swezey et al. (1994) suggest that in order to complete a team task accurately, four things must happen (1) there must be an exchange of competent information among team members (2) there must be coordination within the team structure of the task requirements (3) periodic adjustments must be made to respond to task demands and (4) a known and agreed-upon organization must exist within the group. 

Research from longitudinal studies of cardiovascular fitness has demonstrated a relationship between perceived job satisfaction and stress and cardiovascular illness. Epidemiologicril studies have shown that particular jobs with specific characteristics such as high demands and low control have a higher incidence of coronary heart disease. Organizational demands and relations, job task demands, social relationships at work, work schedule, work content features, discretionary control and participation, and physical working conditions have all been shown to influence the level of job stress (Smith 1986 Kalimo et al. 1997). 

In the case of Poisson arrivals and exponential service, (7.5) is exact because in this case the network is product-form. In the case of Poisson arrivals but general service, (7.6) is exact as each station becomes an M/G/1 queue, for which the Pollaczek-Khintchine formula (43) holds. We see by comparing (63) and (64) that the flow line has a smaller approximate expected number-in-system if and only if cj s 1/2. This leads us to conclude that low variability favors the flow line. Thus, repetitive tasks are suited to the flow-fine arrangement, whereas tasks demanding cognitive skills may be better grouped. 

The cognitive submodel architecture allows for the development of higher-order functions of cognition. For example, Shiveley et al. 1995 has developed and demonstrated a situation awareness function that combines characteristics of working memory, long-term memory search, and perceptual models to develop an abstraction termed situation, which can then be used to guide behavior or to serve as a measure of adequacy of information in the environment and in the crew s knowledge store to meet task demands. 

In yet another alternative, it is frequently desirable to use values representing demands imposed by tasks (task A) ] as the reference for assessment of performance capacity measures. Demands on performance resources can be envisioned to vary over the time course of a task. In practice, an estimate of the worst-case value (i.e., highest demand) would be used in assessments that incorporate task demands as reference values. In one form, such assessments can produce binary results. For example, availability can be equal to or exceed demand (resource sufficiency), or it can be less than demand (resource insufficiency). These rule-based assessments are useful in identifying limiting factors, that is, those performance resources that inhibit a specified type of task from being performed successfully or that prevent achievement of a higher level of performance in a given type of task. 

An example of an inferential task-analysis approach that is relatively new is nonlinear causal resource analysis (NCRA) [Kondraske, 1998,1999 Kondraske et al., 1997]. This method was motivated by human performance analysis situations where direct analysis is not possible (e.g., determination of the amount of visual information-processing speed required to drive safely on a highway). Quantitative task demands, in terms of performance variables that characterize the involved subsystems, are inferred from a population data set that includes measures of subsystem performance, resource availabilities (e.g., speed, accuracy, etc.), and overall performance on the task in question. This method is based on the simple observation that the individual with the least amount of the given resource (i.e., the lowest performance capacity) who is still able to accomplish a given goal (i.e., achieve a given level of performance in the specified high-level task) provides the key clue. That amount of availability is used to infer the amount of demand imposed by the task. 

Subject s resource availabilities and task demands as percentage of normal population mean availability... 

Overall, the greatest limitation with most endurance-related approaches is that the measures obtained cannot be used to perform task-related assessments. In a workplace assessment, for example, one can determine how long a specific task (defined by the conditions of load, range, and speed) needs to be performed. Endurance-related metrics can be used to reflect changes over time in a subjecfs available endurance capacity however, endurance-related metrics cannot be compared to the demands of the task. Task demands are measured in time or repetitions (e.g., 10 h) with a given rate (e.g., 1/0.5 h) from which total time (e.g., 5 h) can be calculated. A true endurance measure (vs. an endurance-related measure) can serve both purposes. Time reflects changes in endurance as the result of disease, disuse, training, or rehabilitation and also can be Hnked to task demands. 

In modern human-machine systems, task assignments maybe adaptive or blended rather than strictly allocated. The information-processing capabilities of modem machines often includes some form of task knowledge and reasoning capabilities that provide for an adaptive task allocation that shifts the task demands on the basis of contextual variables. Also, in many cases human performance is augmented by (blended with) machine performance to accomplish a given task. 

This technique is useful for analyzing workload, allocating tasks, and determining human and system performance requirements. When the resource requirements for each lower-level task are mapped to the timeline, the result is a dynamic task-demand profile. 

In task analysis, it is common practice to distinguish between stress and strain. However, these terms are sometimes used interchangeably and confusedly. In this chapter, stress refers to a condition that may lead to an adverse effect on the body, whereas strain refers to the effect of stress on the body. For example, working at a computer job in dim lighting often leads to headaches. The dim lighting is considered the stress, and the headache is the strain. The term stressor is also widely used as a synonym for stress. Strain has often been wrongly called stress. These terms must be clearly defined to determine which factors are causative ones (stresses) and which are consequences (strains). Stress is determined by task demands, while strain is determined by the amount of physical resources expended beyond some tolerable level. 

Person-task conflict The situation in which task demands are beyond a person s capacities and the task is unlikely to be performed according to specifications by that person. 

Design strategies for achieving usabiHty follows from an analysis of available and required resources and application of HCI design principles that act to reduce resource task demand on users. For example, usability will tend to increase as the resources required of the user to perform the interaction and appHcation tasks decrease. UsabiHty will tend to increase as interface resource availability of the resources increases. 

Maximal and Submaximal Protocols Static and Dynamic Strength Measurements of Isolated Trunk Muscles Static and Dynamic Trunk Muscle Endurance Lifting Strength Testing Inverse and Direct Dynamics Comparison of Task Demands and Performance Capacity... 

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