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Stress & Workload Chapter 13: 

Stress & Workload Chapter 13 Rebecca W. Boren, Ph.D. IEE 437/547 Introduction to Human Factors Engineering Arizona State University November 20, 2006

What are stressors?: 

What are stressors? Influences on information availability and processing that are not inherent in the content of the information itself.

Examples of physical stressors: noise, vibration, heat or cold, dim lighting. : 

Examples of physical stressors: noise, vibration, heat or cold, dim lighting.

Examples of psychological stressors: anxiety, fatigue, frustration, and anger : 

Examples of psychological stressors: anxiety, fatigue, frustration, and anger

The Effects of Stress: 

The Effects of Stress A psychological experience: usually but not always feelings of frustration or arousal. A change in physiology: e.g., change in heart rate or a change in the output of catecholamine, measured in the urine after periods for flying combat maneuvers. Stressors affect the efficiency of information processing, usually, but not always degrading performance. Stressors may have long-term negative consequences for health.

The Effects of Stress: 

The Effects of Stress

Environmental Stressors -Motion: 

Environmental Stressors -Motion High frequency motion: cyclic motion (aka vibration) – can be specific to a part of the body (handheld power saw) or to the whole body (from a vehicle). Low frequency motion (rocking of a ship) and motion sickness: acts as a distracter making it hard to concentrate. Whole body vibration makes it difficult for the user to input or control the device because of loss of precision. Written information may be blurred.

Environmental Stressors: 

Environmental Stressors Dim Lighting Noise

Remediation for Environmental Stressors: 

Remediation for Environmental Stressors Remediation involves using the midrange of lighting and sound. Remediation for hand vibration involves tool selection and limiting dose exposure. Remediation for whole body vibration involves insulating the user and the interface (input device) from the source of vibration (cushioning).

Thermal Stress : 

Thermal Stress Excessive heat or cold degrades performance and causes health problems. Comfort zone: 73oF to 79oF in the summer; 68oF to 75oF in the winter. Humidity: less humidity is allowed (60%) at the upper temperature limit; more is allowed (85%) at the lower limit.

Thermal Stress : 

Thermal Stress Sources of excessive heat: furnaces or boilers, outside temperatures, ovens, etc. Sources of excessive cold: freezers, outside temperatures, air conditioning

Remediation for Thermal Stress: 

Remediation for Thermal Stress Body temperature is moderated by Clothing (may cause a loss of manual dexterity) Air movement Physical activity Provide ample amounts of fluids in excessive heat.

Poor Air Quality: 

Poor Air Quality Poor ventilation – may not even be aware of carbon monoxide Pollution or smog Lack of oxygen (anoxia) at high altitudes and cold can lead to frostbite as the body tries to provide oxygen to the brain and heart. Negative effects on perceptual, motor, and cognitive performance

Psychological Stressors: 

Psychological Stressors Perceived threat of harm or loss of esteem (embarrassment), or something valued, or of bodily function through injury or death.

Psychological Stressors: 

Psychological Stressors Varies by individual (thrill-seeker versus the novice) Amount of stress is related to the persons understanding or cognitive appraisal of the situation. Varies by person depending on their sense of control. May not appreciate the danger. Research difficult in this area because of ethical issues.

Level of Physiological Arousal Related to Stress: 

Level of Physiological Arousal Related to Stress Documented by changes in heart rate pupil diameter hormonal chemistry

Optimal Level of Arousal: 

Optimal Level of Arousal Performance increases as arousal increases up to a certain point (trying harder). Performance decreases with overarousal (overload).

Performance Degradation with Overarousal.: 

Performance Degradation with Overarousal. Perceptual or attentional narrowing (tunneling) May cause you to focus on the wrong thing. Less ability to use working memory to come up with creative solutions. Long-term memory intact.


Example: Three Mile Island disaster caused by the stress of the auditory alarm indicating a problem when none existed. The stress may have caused the workers to overlook a wider range of correct indicators.

Remediation of Psychological Stress During an Emergency : 

Remediation of Psychological Stress During an Emergency Have written instructions (do not rely on working memory) Practice for emergencies (overlearn). We tend to perform the dominant behavior (turning back from a skid on slippery ice because that’s what we do on dry pavement) Avoid the tendency to “do something now.” Take time to take a deep breath and plan a strategy.

Life Stress: 

Life Stress Stress related to the job or personal life. Poor performance because of lack of attention or motivation. Safety may be compromised because of distraction or diversion of attention.

Remediation is complex. Here are some general suggestions: : 

Remediation is complex. Here are some general suggestions: Address and remove the source of stress within the organization (i.e., low pay, long working hours, etc.) Stress management training Provide counseling


Workload The amount of work assigned to or expected from a worker in a specified time period. Stress may be induced by having too much to do in too little time. Overload can result in forgetting to do some critical task e.g., air traffic controller forgetting that he had already scheduled another aircraft to land on the runway.

Measuring Workload : 

Measuring Workload TR/TA (time required for the task/time available for the task) or time-ratio Determined by task analysis (include “think time”) Allow for spare capacity of about 20% Ratio can be > 1.0 if time-sharing


Question: If you have a report to do that can be completed in 4 hours and is due at exactly 5 PM, what is latest time you can start working on the report in order to avoid stress? Answer:


Question: If you have a report to do that can be completed in 4 hours and is due at exactly 5 PM, what is latest time you can start working on the report in order to avoid stress? Answer: Noon or 12:00

Consequences of Work Overload: 

Consequences of Work Overload More selectivity of input More important sources of information given more weight Decrease in accuracy Decreasing use of mental strategies that require heavy mental computation. Locking onto a single strategy.


Remediation Task redesign or assignment to multiple workers Automate Develop display design that highlights the most important information. Training for high time-stress workload situations. Training of task management skills

Laying out a timeline of what needs to be done and how long it will take.: 

Laying out a timeline of what needs to be done and how long it will take. Identification of task times Provided by observation or experts Scheduling and prioritization Move less critical tasks to a time of less workload. Task resource demands and automaticity Multiple resources Think of the requirements of multitasking.

Mental Workload Measures: 

Mental Workload Measures Primary task measures Secondary task methods Measure the reserve capacity left over after performing the primary task (examples: memory tasks, mental arithmetic) Physiological measures Heart rate Blink rate EEG Pupil diameter Subjective measures Example: NASA Task Load Index

Fatigue : 

Fatigue One effect of continuous work overload is fatigue. Fatigue is a stressor that degrades performance and creates problems in maintaining attention. Fatigue studied in military operations (Desert Storm), long-haul truck drivers, medical workers in hospitals. Fatigue can also result from long periods of doing little.

Vigilance and Underarousal: 

Vigilance and Underarousal An increased number of misses as the vigil progresses (quality control inspectors) Factors that lead to loss of performance Time Event salience (Is event very noticeable?) Signal rate Arousal level Automation may make the problem of underarousal worse.

Vigilance remediations : 

Vigilance remediations Watches should not be too long. Operators should get frequent rest breaks. Signal could be enhanced or increase the payoff for detecting the signal. Introduce false alarms to “keep them on their toes”. Appropriate use of stimulants: caffeine, music, conversation (if not distracting).

Sleep Disruption: 

Sleep Disruption Sleep deprivation (getting less than 7 to 9 hours per night) Being out of sync with our natural circadian rhythms (e.g., early morning work) Disruption of circadian rhythms through jet lag or shift work.

Examples of the effects of fatigue due to sleep disruption: 

Examples of the effects of fatigue due to sleep disruption 60% of class A aircraft mishaps in the Air Force The explosion of the space shuttle Challenger is thought to be due to poor decision making of the launch team who received very little sleep prior to their early morning decision to launch the rocket in excessively cold temperature. Over 200,000 auto accidents per year Medical errors Performance on the battle field.

Sleep deprivation and performance effects: 

Sleep deprivation and performance effects Increased sleepiness causes increased eye blinks, eye closures, and microsleep (nodding off) Tasks that involve judgment are especially sensitive, as are tasks involving learning or storing new material or tasks involving self-initiated cognitive activity like planning. Tasks that are less sensitive are those that involve a lot of motor activity or highly interesting material.

Cognitive Performance: 

Cognitive Performance Loss of cognitive performance occurs within 24 hours of a continuous task (ex: combat). Loss of cognitive performance occurs before loss of performance on physical tasks.

Circadian Rhythms: 

Circadian Rhythms Besides lack of sleep, we can be out of sync with our body’s natural rhythms of temperature and arousal

Circadian Rhythms: 

Circadian Rhythms Most of us perform worse in the early morning hours and better in the late afternoon/early evening. Shift work that requires us to wake earlier than usual is disruptive.

Circadian Disruption : 

Circadian Disruption When one tries to work against the natural circadian rhythm of the body Relevant to jet lag and shift work

Mitigating Jet Lag: 

Mitigating Jet Lag Studies have shown that it takes from 1 to 2.5 days to recover from a trip across the Atlantic.

Jet Lag: 

Jet Lag Eastbound flight is more disruptive than westbound flight Remediations Go on the local time immediately (do not nap to catch up). May need to allow an extra day for recovery after a long trip.

Desynchronization due to shift work: 

Desynchronization due to shift work Shift work - workers can never fully change their rhythm because of exposure to Earth's influences. Rotating shifts fairly frequently - does not work Best plan is to rotate shifts in this manner Rotate slowly (every 14-21 days) Rotate by delaying rather than advancing the shift Longer shifts are problematic (10 to 14 hours) – result in greater fatigue and more errors.

Remediations to sleep disruption : 

Remediations to sleep disruption Get more sleep Build up sleep credits Sleep management What does not work - drugs such as caffeine

Remediations to sleep disruption : 

Remediations to sleep disruption Nap (15 minutes with 10 minutes recovery time) – problem with sleep inertia


Conclusions Concern for potential risk to health and degradation in performance. Human operators are vulnerable to overarousal and underarousal. Humans are vulnerable to overload and underload stress.


Conclusions The continued push for productivity in all domains appears to be increasing the frequency of round-the-clock operations, thereby inviting concerns about night work and sleep disruption.

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