Stress and Stress and WorkloadWorkload

Human factors Human factors psychologypsychology

Dr. SteveDr. Steve

A Representation of Stress A Representation of Stress EffectsEffects

Experience

HealthDirect (e.g.,vibration)Stressors

Physiological arousal

Direct (e.g., lighting, noise)

InformationProcessing

Input Performance

Indirect

StressStress

StressStress – constraint, pressure, – constraint, pressure, weight, violence (Webster’s weight, violence (Webster’s dictionary)dictionary)

Possible Effects of StressPossible Effects of Stress

1.1. A psychological experience A psychological experience (e.g., (e.g., frustration)frustration)

2.2. A change in physiology A change in physiology (e.g., increased (e.g., increased heart rate)heart rate)

3.3. Reduced efficiency of information Reduced efficiency of information processingprocessing

4.4. Long-term negative consequences for Long-term negative consequences for health health (e.g., heart disease, G-I problems)(e.g., heart disease, G-I problems)

Environmental StressorsEnvironmental Stressors MotionMotion – vibration, G forces & motion sickness – vibration, G forces & motion sickness

Whole body vibration: Whole body vibration: .3-1 Hz – motion sickness, vomiting.3-1 Hz – motion sickness, vomiting 1-4 Hz – blurred vision, difficulty breathing, impaired psychomotor1-4 Hz – blurred vision, difficulty breathing, impaired psychomotor 4-10 Hz – chest pain, rattling jaw4-10 Hz – chest pain, rattling jaw 8-12 Hz – backache8-12 Hz – backache 10-20 Hz – headache, eyestrain, speech disturbance, G-I problems10-20 Hz – headache, eyestrain, speech disturbance, G-I problems

Limb vibration:Limb vibration: 40-300 Hz – pain in arm/wrist, arthritis, bone atrophy, VWF40-300 Hz – pain in arm/wrist, arthritis, bone atrophy, VWF

Thermal stressThermal stress – body temperature, air movement, amount of physical work – body temperature, air movement, amount of physical work Heat – drowsiness, fatigue, heatstroke, dehydration, sweating, vomitingHeat – drowsiness, fatigue, heatstroke, dehydration, sweating, vomiting Cold – restlessness, lower alertness, numbness, shivering, hypothermiaCold – restlessness, lower alertness, numbness, shivering, hypothermia

Air qualityAir quality – anoxia (lack of O – anoxia (lack of O22))

AccelerationAcceleration

High G-force tolerancesHigh G-force tolerances• +/- 2 Gz – pressure on butt, drooping face, noticeable weight +/- 2 Gz – pressure on butt, drooping face, noticeable weight

increaseincrease• +/- 3-4 Gz – Difficult to move, loss of fine motor movements, speech +/- 3-4 Gz – Difficult to move, loss of fine motor movements, speech

affectedaffected• + 5.5 Gz – Negative blood pressure -> GLOC or grayout (passengers + 5.5 Gz – Negative blood pressure -> GLOC or grayout (passengers

may blackout sooner)may blackout sooner)• Higher tolerances (>10) possible in Gx plane (forward acc) – weight Higher tolerances (>10) possible in Gx plane (forward acc) – weight

on chest, difficulty breathingon chest, difficulty breathing

Prevention/ProtectionPrevention/Protection• G-suit – squeezes blood out of extremities – increases tolerance by 2 G-suit – squeezes blood out of extremities – increases tolerance by 2

GG• Active Straining Maneuver (Blue Angels) – Pull head down, slow Active Straining Maneuver (Blue Angels) – Pull head down, slow

forceful breathing, tensing of muscles – increase tolerance by 1.5 Gforceful breathing, tensing of muscles – increase tolerance by 1.5 G

Gz

Gy

Gx

Note: force of gravity ~9.8 m/sec2 or 33 ft/sec2, therefore 5 G would be roughly equivalent to going from 0 to 112 mph in one sec

Heat StressHeat Stress Small fluctuations in body temp greatly impact physical & Small fluctuations in body temp greatly impact physical &

cognitive performancecognitive performance Problems include: Problems include:

+/- 6+/- 6°° C of core body is fatal (normal ~ 37 C of core body is fatal (normal ~ 37°° C) C) Dehydration, heat exhaustion, heat strokeDehydration, heat exhaustion, heat stroke Effects on continuous, low arousal tasks (vigilance)Effects on continuous, low arousal tasks (vigilance) Aggravated by sweating (slippery hands, sweat in eyes, heated metal Aggravated by sweating (slippery hands, sweat in eyes, heated metal

equipment)equipment) May create perceptual difficulties (e.g., mirages, visual distortion, May create perceptual difficulties (e.g., mirages, visual distortion,

optical illusions)optical illusions) Carrying heavy protective gear contributes to heat stress (gloves, Carrying heavy protective gear contributes to heat stress (gloves,

boots, body armor)boots, body armor)

High AltitudeHigh Altitude Altitude SicknessAltitude Sickness

•Loss of aerobic capacity by 10% for every 1000m over 1500 m

•Neurasthenic Syndrome – fatigability, decreased motivation, psychosomatic symptoms + reduced visual ability

•Paranoia, O-C, depression, hostility, decreased cognitive functioning

•Cyclothymic Syndrome – alternating depression, elevated mood

•Acute Organic Brain Syndromes – structural & functional defects in the CNS

7000 m

5000 m

3000 m

Psychological StressorsPsychological Stressors

Resulting from the perceived threat of harm or Resulting from the perceived threat of harm or loss of esteem, something valued, or of bodily loss of esteem, something valued, or of bodily function through injury or death.function through injury or death.

1.1. Cognitive appraisalCognitive appraisal – person’s – person’s understanding / interpretation of the situationunderstanding / interpretation of the situation

2.2. Level of arousalLevel of arousal – heart rate, pupil diameter, – heart rate, pupil diameter, hormonal chemistryhormonal chemistry

3.3. Performance changes with overarousalPerformance changes with overarousal – – e.g., tunnelinge.g., tunneling

4.4. Remediation of psychological stressRemediation of psychological stress – – simplifiers in emergency situationssimplifiers in emergency situations

Yerkes-Dodson LawYerkes-Dodson Law Yerkes-Dodson Law: inverted-U function

• Optimal level of arousal differs for experts/novices and simple/complex tasks.

• Poor performance if too low (low motivation, boredom) or too high (test anxiety)

Effects of Psychological Effects of Psychological Stressors on Information Stressors on Information ProcessingProcessing

Narrowing of attentionNarrowing of attention may be positive or negativemay be positive or negative

Diverted attentionDiverted attention Working Memory LossWorking Memory Loss

Disrupts articulatory loop (subvocal speech)Disrupts articulatory loop (subvocal speech) PerseverationPerseveration

Revert to what people know best – Revert to what people know best – implications for overlearning of emergency implications for overlearning of emergency behaviorsbehaviors

Life StressLife Stress

Causes lack of attention, distraction or Causes lack of attention, distraction or diversiondiversion e.g. Deaths in the family, financial problemse.g. Deaths in the family, financial problems

Related to different aspects of attentionRelated to different aspects of attention

Adapting to StressAdapting to Stress

How do people adapt to stress?How do people adapt to stress? Use more resourcesUse more resources - Try harder - Try harder

Work faster, speed/accuracy tradeoff, avoid Type A Work faster, speed/accuracy tradeoff, avoid Type A behaviorsbehaviors

Remove stressorRemove stressor – leave environment – leave environment Earplugs, coping strategies (relaxation techniques)Earplugs, coping strategies (relaxation techniques)

Change task goalChange task goal – use simpler, stress- – use simpler, stress-resistant strategyresistant strategy Rely on pattern recognition skills, heuristicsRely on pattern recognition skills, heuristics

Do nothingDo nothing – continue until stress takes its toll – continue until stress takes its toll

Moderating Variables of Moderating Variables of StressStress

Interacting effects of multiple stressorsInteracting effects of multiple stressors Noise & sleep loss both decrease performance, but Noise & sleep loss both decrease performance, but

effects not additive effects not additive Noise increases arousal, sleep loss decreases arousalNoise increases arousal, sleep loss decreases arousal

PersonalityPersonality (individual differences) (individual differences) Differences in locus of control, Type A behavior, etc.Differences in locus of control, Type A behavior, etc.

TrainingTraining Experience may reduces negative effects of stress by:Experience may reduces negative effects of stress by:

Reducing anxietyReducing anxiety Increasing repertoire of responsesIncreasing repertoire of responses Increasing knowledge of situation and ability to create Increasing knowledge of situation and ability to create

solutionssolutions

WorkloadWorkload

Task Now Future TaskTIME

Overload

Underload

Overload

Normal

Underload

Fatigue Sleepiness

Circadian Rhythm

Sleep Loss

Work OverloadWork OverloadTime-line ModelTime-line Model

““So much work to do, so little time”So much work to do, so little time” Time-line modelTime-line model

Workload percentage = Time required/Time Workload percentage = Time required/Time availableavailable

Can have over 100% workload and handle it okay Can have over 100% workload and handle it okay or less than 100% and notor less than 100% and not

Moderators of time requirement estimations: Moderators of time requirement estimations: Individual differencesIndividual differences Spare capacitySpare capacity Level of automaticityLevel of automaticity Shared vs. separate resourcesShared vs. separate resources

Work OverloadWork OverloadTime-stress EffectsTime-stress Effects

Under time stress, people tend to:

• restrict tasks to those believed to be more important

• restrict available info sources to those believed to be more importantProblem occurs when subjective evaluation of importance is wrong

e.g., trying to understand one difficult concept for a test, and not studying rest of material

Remediation Remediation Eliminating Stressors at WorkEliminating Stressors at Work

Engineering solutionsEngineering solutions Sound absorbing materials, temperature Sound absorbing materials, temperature

regulation, glare shields, earplugs, vibration regulation, glare shields, earplugs, vibration dampeningdampening

System design solutionsSystem design solutions S-R compatibility, automation, increased cue S-R compatibility, automation, increased cue

saliency, use of command displays (over status), saliency, use of command displays (over status), redundanciesredundancies

TrainingTraining Train task management skills – prioritizing tasks Train task management skills – prioritizing tasks Train important procedures to automaticityTrain important procedures to automaticity Stress exposure or inoculation trainingStress exposure or inoculation training

Effort and WorkloadEffort and Workload

Effort Effort – changes in – changes in workload related to workload related to demands other than timedemands other than time PrecisionPrecision ForceForce DiscriminabilityDiscriminability KSA requirementsKSA requirements Working memory Working memory

requirementsrequirements

FLOWFLOW

Flow occurs when skills are consistent with the Flow occurs when skills are consistent with the level of challenge level of challenge (Csikszentmihalyi)(Csikszentmihalyi)

Skills

Challe

ng

e

boredom

an

xie

ty

apathy

FLOW

Work Overload PredictionWork Overload Prediction When two or more tasks are carried out concurrentlyWhen two or more tasks are carried out concurrently Predictions must account for differences in task Predictions must account for differences in task

automaticity & multiple resource competitionautomaticity & multiple resource competition both of which will influence performanceboth of which will influence performance

Figure shows comparison of predicted to subjective and empirically tested workload

Mental Workload Mental Workload MeasurementMeasurement Primary Task MeasuresPrimary Task Measures

measures of system performance on the task of interestmeasures of system performance on the task of interest Secondary Task MethodsSecondary Task Methods

measures reserve capacity by looking at performance on measures reserve capacity by looking at performance on a secondary or concurrent taska secondary or concurrent task

Physiological MeasuresPhysiological Measures e.g., measuring heart rate variability for mental e.g., measuring heart rate variability for mental

workload & measuring mean heart rate to look at workload & measuring mean heart rate to look at physical workload and stressphysical workload and stress

Subjective MeasuresSubjective Measures done by asking the operator to rate workload on a done by asking the operator to rate workload on a

subjective scale (e.g., NASA TLX)subjective scale (e.g., NASA TLX)

FatigueFatigue

Due to effects of high or even moderate workloadDue to effects of high or even moderate workload Can be mental or physicalCan be mental or physical

e.g., observed during a military combat missione.g., observed during a military combat mission SymptomsSymptoms - Feelings of weariness, faintness, sluggish - Feelings of weariness, faintness, sluggish

thinking, reduced alertness, poor and slow perception, thinking, reduced alertness, poor and slow perception, unwillingness to work, decline in physical and mental unwillingness to work, decline in physical and mental performanceperformance

MeasuresMeasures EEG – increased alpha & theta waves, decreased betaEEG – increased alpha & theta waves, decreased beta Flicker-fusion frequency – lowered with fatigueFlicker-fusion frequency – lowered with fatigue

Vigilance and Vigilance and UnderarousalUnderarousal

VigilanceVigilance – Sustained attention to low – Sustained attention to low stimulus-changing environmentstimulus-changing environment

Low-arousal environments can be just Low-arousal environments can be just as fatiguing as high workload as fatiguing as high workload environments.environments. e.g., seen in low-workload shifts for air traffic e.g., seen in low-workload shifts for air traffic

controller’s and on repetitive assembly line jobscontroller’s and on repetitive assembly line jobs

Vigilance Decrement Vigilance Decrement Causes Causes

1.1. TimeTime – – longer duration of vigilance, longer duration of vigilance, increases chance of missesincreases chance of misses

2.2. Event salienceEvent salience – subtle events increase – subtle events increase chances of errorchances of error

e.g., typesetting errore.g., typesetting error

3.3. Signal rateSignal rate – when signal events occur at – when signal events occur at low rates, likelihood of detection will be low rates, likelihood of detection will be reducedreduced

4.4. Arousal levelArousal level – problems occur when there – problems occur when there is little intrinsic task-related activityis little intrinsic task-related activity

Vigilance RemediationsVigilance Remediations

1.1. Short work shiftsShort work shifts – with frequent breaks– with frequent breaks

2.2. Salient signalsSalient signalse.g., by using signal enhancemente.g., by using signal enhancement

3.3. Use payoffs when miss rates are high or Use payoffs when miss rates are high or change the signal expectancychange the signal expectancye.g., can introduce false signalse.g., can introduce false signals

4.4. Increase/sustain level of arousalIncrease/sustain level of arousale.g., use of caffeine, music, noise, e.g., use of caffeine, music, noise, conversationconversation

BoredomBoredom – the affective reaction to monotony – the affective reaction to monotony Boredom proneness associated with: sensation seeking, job Boredom proneness associated with: sensation seeking, job

dissatisfaction, poor vigilance, ADHD, Type A behavior dissatisfaction, poor vigilance, ADHD, Type A behavior (Vodanovich & (Vodanovich & Kass)Kass)

Boredom proneness Boredom proneness greatestgreatest for for:: People in state of fatiguePeople in state of fatigue Not-adapted night workersNot-adapted night workers People with low motivationPeople with low motivation Highly educated, knowledgeable peopleHighly educated, knowledgeable people Challenge seekersChallenge seekers

Boredom proneness Boredom proneness leastleast for for:: Alert or fresh peopleAlert or fresh people People who are still learningPeople who are still learning People whose jobs suit their abilities People whose jobs suit their abilities (Grandjean)(Grandjean)

BoredomBoredom

Sleep LossSleep Loss

Caused by:Caused by: Purposely staying awake (all-nighter, night shift)Purposely staying awake (all-nighter, night shift) Trying to sleep during the day (against circadian rhythm)Trying to sleep during the day (against circadian rhythm) Stimulants (caffeine)Stimulants (caffeine) StressStress

Aspects of performance that are most Aspects of performance that are most susceptible:susceptible: tasks requiring visual input, tasks involving judgment, tasks requiring visual input, tasks involving judgment,

learning, or storing new materiallearning, or storing new material

Sleepiness blamed for over 200,000 auto accidents per yearSleepiness blamed for over 200,000 auto accidents per year

Remediation to Sleep Remediation to Sleep DisruptionDisruption

Get more sleep!!!Get more sleep!!! – even if it is only 3-4 – even if it is only 3-4 hours per nighthours per night

Build up sleep creditsBuild up sleep credits e.g., gain extra sleep prior to deprivatione.g., gain extra sleep prior to deprivation

Napping helps Napping helps make sure you allow time for full mental make sure you allow time for full mental

recoveryrecovery Sleep managementSleep management

e.g., easier with more controlled jobs – e.g., easier with more controlled jobs – the military the military

DesynchronizationDesynchronization

DesynchronizationDesynchronization - Occurs when the circadian - Occurs when the circadian rhythms are out of synchrony with the level of rhythms are out of synchrony with the level of activity that one is trying to maintainactivity that one is trying to maintain

ShiftworkShiftwork –strategies to deal with the disruption –strategies to deal with the disruption of circadian rhythmsof circadian rhythms e.g., Assignment to permanently different shifts, e.g., Assignment to permanently different shifts,

continuous rotation, alter shift periodscontinuous rotation, alter shift periods Jet LagJet Lag – analogous to shift changes (east-bound – analogous to shift changes (east-bound

more difficult than west-bound)more difficult than west-bound) Remediation – bring the body into the local cycle Remediation – bring the body into the local cycle

rapidly rapidly