Stress & WorkloadChapter 13

Rebecca W. Boren, Ph.D.IEE 437/547Introduction to Human Factors EngineeringArizona State UniversityDecember 5, 2011

What are stressors?

Textbook: Influences on information availability and processing that are not inherent in the content of the information itself.

What are stressors?

Textbook: Influences on information availability and processing that are not inherent in the content of the information itself.

Dictionary: An agent, condition, or other stimulus that causes stress to an organism.

What are stressors?

Textbook: Influences on information availability and processing that are not inherent in the content of the information itself.

Dictionary: An agent, condition, or other stimulus that causes stress to an organism.

Something that causes physical, mental, or emotional strain or tension.

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

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

The Effects of Stress

A psychological experience: usually, but not always feelings of frustration or arousal.

The Effects of Stress

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.

The Effects of Stress

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

Headache Sleep disturbances Difficulty in

concentrating Short temper Upset stomach Job dissatisfaction Low morale

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.

Environmental Stressors -Motion Low frequency motion (rocking of a ship) and

motion sickness: acts as a distracter making it hard to concentrate.

Environmental Stressors -Motion 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, cont’d

Dim Lighting Noise

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

Excessive heat or cold degrades performance and causes health problems.

Comfort zone: 73oF to 79oF in the summer; 69oF 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

Sources of excessive heat: furnaces or boilers, outside temperatures, ovens, etc.

Sources of excessive cold: freezers, outside temperatures, air conditioning

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 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

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

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

Documented by changes in heart rate pupil diameter hormonal chemistry

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.

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 Have written

instructions (do not rely on working memory)

Remediation of Psychological Stress During an Emergency 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)

Remediation of Psychological Stress During an Emergency Avoid the tendency to “do something now.”

Take time to take a deep breath and plan a strategy.

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: Address and remove the

source of stress within the organization (i.e., low pay, long working hours, etc.)

Stress management training Provide counseling

Human Factors study of Workload

Human Factors Rap Video

Produced by graduate students in Dr. Warm’s laboratory.

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

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% Ideal ratio is 0.8 Ratio can be > 1.0 if time-sharing

Consequences of Work Overload

More selectivity of inputMore 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.

Identification of task times Scheduling and prioritization Task resource demands and automaticity Multiple resources

Mental Workload Measures (1)

Primary task measures

Mental Workload Measures (2)

Secondary task methodsMeasure the reserve

capacity left over after performing the primary task (examples: memory tasks, mental arithmetic)

Mental Workload Measures (3)

Physiological measuresHeart rate Blink rateEEGPupil diameter

Mental Workload Measures (4)

Subjective measures Example: NASA

Task Load Index (TLX)

Ask the workers.

Fatigue One effect of continuous work overload is

fatigue. Fatigue is a stressor that degrades

performance and creates problems in maintaining attention.

Fatigue

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 An increased number of misses as the

vigil progresses (quality control inspectors)

Vigilance and Underarousal

Factors that lead to loss of performanceTimeEvent salience (Is event very

noticeable?)Signal rateArousal level

Vigilance and Underarousal

Automation may make the problem of underarousal worse.

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

(infrequently), music, conversation (if not distracting).

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 60% of class A aircraft mishaps in the Air

Force are due to fatigue 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.

Examples of the effects of fatigue due to sleep disruption Over 200,000 auto

accidents per year Medical errors Performance on the

battle field.

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.

Circadian Rhythms Besides lack of sleep, we

can be out of sync with our body’s natural rhythms of temperature and arousal

Most of us perform worse in the early morning hours and better in the late afternoon/early evening.

Circadian Disruption

When one tries to work against the natural circadian rhythm of the body

Relevant to jet lag and shift work

Jet Lag

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

Traveling east is more stressful than traveling west.

WEST

EAST

Mitigating Jet Lag

Maintain a regular sleep schedule

Exercise and avoid naps Avoid dehydration. Go on local time

immediately.

Desynchronization due to shift work

Shift work - workers can never fully change their rhythm because of exposure to Earth's influences.

Desynchronization due to shift work

Rotating shifts fairly frequently - does not work

Best plan is to rotate shifts in this mannerRotate slowly (every 14 to 21 days)Rotate by delaying rather than

advancing the shift

Desynchronization due to shift work

Longer shifts are problematic (10 to 14 hours) – result in greater fatigue and more errors.

Remediations to sleep disruption

Get more sleep Nap (15 minutes with 10 minutes recovery

time) – problem with sleep inertia Build up sleep credits Sleep management What does not work - drugs such as

caffeine

Cognitive Performance

Loss of cognitive performance occurs within 24 hours of a continuous task

(ex: combat or driving an automobile).

Loss of cognitive performance occurs before loss of performance on physical tasks.

Any Questions?