wsd2 2013 5c stress & workload

8/10/2019 WSD2 2013 5c Stress & Workload

1/56

Harsh V Bhasin

Stress & Workload


2/56

Representation of Stress Effects

Harsh V Bhasin

InformationProcessing

Input Performance

StressorsExperienceHealth

Direct (e.g. Vibration)

Physiological arousal


3/56

4 Effects of Stressors

1. They produce psychological experience

2. A change in physiology is often observable May be short term change (ex: increased heart

rate) or it might be a more sustained effect (ex:change in the output of catechol-amines)

3. Stressors affect the efficiency of informationprocessing, usually degrading performance

4. Stressors may have long-term negativeconsequences for health

Harsh V Bhasin


4/56

Effects of Stressors

May be direct or indirect

Direct effects influence the quality of

information received by the receptors or

the precision in the response

Indirect effects influence the efficiency of

information processing through

mechanisms that have not yet beendescribed

Harsh V Bhasin


5/56

Environmental Stressors

Motion

Vibration

Vibrating white finger (VWF) syndrome:

enduring loss of sensation to the fingersof a

hand exposed to excessive continuous levels of

high-frequency vibration from sources such as

power tools

Vibration in hand tools disrupt precision ofthe hand operatingthat tool

Harsh V Bhasin


6/56

Vibration

Vibration may disrupt the performance of any eye-

hand coordination task unless hand is stabilized by

external source

Vibration can disrupt the performance of purely

visual tasks through the apparent blurring of the

images perceived

Spatial Frequency Resolution: The smaller the line

or dot that needs to be resolved, the greater will be

the disruptive effect of a given vibration

Harsh V Bhasin


7/56


Motion

Motion Sickness

Effects at much lower frequency

Decoupling between visual and vestibular inputs Motion sickness induced by no true motion, as in full-

screen visual displays

Distractor: the discomfort of sickness is sufficiently

intrusive that it is hard to concentrate on anything else,

including task at hand

Harsh V Bhasin


8/56


Thermal Stress

Both excessive heat & cold can degradeperformance

Comfort Zone defines a region in thespace of temperature & humidity and isone in which most work appears to bemost productive

Effects of heat are indirect, affectingefficiency of info processing

Harsh V Bhasin


9/56

Thermal Stress

3 Key Moderating Variables Body Temperature: moderated by clothing

worn

Air Movement: induced by natural breezes orfans have effect of diminishing the experiencedamount of heat

Physical work can increase experience ofheat

Long term heat exposure can lead todehydration, heat stroke or heatexhaustion

Harsh V Bhasin


10/56

Thermal Stress

Long term exposure to the cold can lead

to frostbite, hypothermia and health

endangerment

Wearing appropriate clothing can trap in

body heat

Value of some clothing (gloves, etc) must be

traded off against some loss in dexterity

Harsh V Bhasin


11/56


Air Quality

Often a result of poor ventilation in closedworking spaces (mines, ships)

Also affects environments polluted bysmog or CO (carbon monoxide)

Can lead to anoxia(lack of oxygen) and

pronounced negative influences onperceptual, motor and cognitiveperformance

Harsh V Bhasin


12/56

Psychological Stressors

Cognitive Appraisal

It is difficult to ascertain for each individual

what may constitute a threat

Amount of stress for a given

circumstance is related to persons

understanding or cognitive appraisal of

the situation

Harsh V Bhasin


13/56

Cognitive Appraisal

Reasons for Different Cognitive Appraisals

Failure to perceive the risk

Failure to understand the risk

Overconfidence in ability to deal with thehazard

If person feels that they are more in control,

they are less likely to experience stress than if

other agents are in control

Harsh V Bhasin


14/56


Level of Arousal Anxiety can produce an increase in

physiological arousal (heart rate, hormonal

chemistry) Inverted U function of performance

Performance first increases up to a point known as theoptimum level of arousal and then subsequentlydecreases as stress-induced arousal increases

Referred to asYerkes-Dodson Law Initial increase due to the threat of loss motivating us to

work harder/perform better

Loss in performance above optimum level of arousalappears to be due to effects of overarousal

Harsh V Bhasin


15/56

Yerkes-Dodson Law

Criticized because it cannot specify

the optimum level of arousal due to

the differences between people inskill and cognitive appraisal

Harsh V Bhasin


16/56

Yerkes-Dodson Law

Poor

Performance

Good

Level of ArousalLow High

Optimum level of Arousal


17/56


Performance Changes with Over-arousal

Perceptual/Attentional Narrowing (Tunneling)

Tendency to restrict the range or breadth of attention to

concentrate very hard on only one thing and to ignore

surrounding information

Cognitive Tunneling

Tendency to focus attention exclusively on one

hypothesis of what is going on and ignore potentially

more creative diagnosis by considering a wider range of

options

Harsh V Bhasin


18/56

Performance Changes with Overarousal

Working Memory Loss Under stress, people appear to be less capable of using

working memory to store or rehearse new material or to

perform computations and other attention demanding

mental activities

Long Term Memory

Will be hampered very little

Tendency under stress to focus on most dominant

thoughts and actions

Problem occurs when appropriate response is not thefrequently encountered one

Harsh V Bhasin


19/56

Performance Changes with Overarousal

Strategic Shifts Taking immediate action

Fast action often sacrifices accuracy throughspeed-accuracy tradeoff

Operators cautioned not to take any action atall for a few seconds until appropriate action isidentified

Harsh V Bhasin


20/56


Remediation of Psychological Stress Depend upon analysis of the likely circumstances

of emergencies and actions that should be taken

Remediation simplifies design of displays, controls

& procedures Training

Extensive training of emergency procedures can makethem more readily available to long-term memory whenneeded

Generic training of emergency stress management canfocus both on guidelines and techniques to reduce thelevel of arousal to a more optimal value

Harsh V Bhasin


21/56

Life Stress

Stressful life events (death, martial

strife, etc) may be associated with

mishaps on the job Poorer performance by those stressed

by job-related factors may be related to

lack of attention, resources, or effort

Harsh V Bhasin


22/56

Life Stress

Greater safety hazards of some who

suffer life stress may be related to

distraction/diversion Maintain awareness of the possibilities

that stress-induced distraction can lead

to breakdowns in safety

Harsh V Bhasin


23/56

Work Overload, Underload &

Sleep Disruption


24/56

Work Overload, Underload &

Sleep Disruption

All have negative consequences on

performance

Over-load: Too much to do in too little time

Under-load: Too little to do

Vigilance Task: Wait and watch for something to

happen

Both work over-load and under-load cancause fatigue

Harsh V Bhasin


25/56

Workload

Time-Line Model

Workload can be described in terms of a

ratio of time required (to do tasks) to timeavailable to do them in

Lay out a timeline of when different tasks

need to be performed and how long they

typically take

Harsh V Bhasin


26/56

Time-Line Model

Harsh V Bhasin


27/56

Time-Line Model

Calculate workload from TR/TA ratio (important to

also consider planning/ think time)

Not accurate to assume that work overload will

occur when TR/TA ratio is greater than 1.0

Time varies from occasion to occasion and from person

to person

Means represented as distributions

Measured TR estimated as 90thor 95thpercentile of the

distribution

Harsh V Bhasin


28/56

Time-Line Model

Spare Capacity Margin of spare time in establishing what an

overload level of TR/TA should be

Necessary to handle the unexpected events

If one or two tasks are learned to a highlevel of automaticity, they may easily sharetime

Workload may be heavily modulated by theextent to which overlapping tasks competefor common vs. separate resources

Harsh V Bhasin


29/56

Workload

Time-Stress Effects

If TR/TA increases, something is likely to suffer

Edland & Svenson found following effects

regarding decision making under time pressure:

More selectivity of input, more important sources of that

info given more weight, decrease in accuracy,

decreasing use of strategies that involve heavy mental

computation, and locking onto a single strategy

Harsh V Bhasin


30/56

Time-Stress Effects


31/56

Time-Stress Effects

People tend to focus on tasks that theybelieve to be most important and will

attend to the information sources that

they believe to be most important People will also focus more on those

info sources that are available

Harsh V Bhasin


32/56

Workload

Remediations

Task redesign by trying to assign certain

time-loading tasks to other operators or to

automation Developing display design such that the

most objectively important sources are

available, interpretable and salient

Training for high time-stress workload

Harsh V Bhasin


33/56

Workload

Effort & Workload Changes in workload that cannot be

uniquely associated with time

Automated vs. non-automated task mayoccupy same space in time line but

automated task requires less effort

More difficult to predict effort demanded by

a task

Harsh V Bhasin


34/56

Workload

Work Overload Prediction

Time-line scales can be used to predict, before a

system is built, the workload that will be imposed

by that system or job environment Prediction relatively easy when TR/TA < 100%

More challenging when TR/TA > 100%

Must take into account task automaticity and multiple

resource competition that will influence performance

Harsh V Bhasin


35/56

Mental Workload Measurement

Primary Task Measures

Measures of system performance on the task of

interest

Not really a workload measure per se, but isinfluenced by workload

There are circumstances in which good primary

task performance is attained but only at a cost of

high workload (no margin of reserve capacity ifunexpected increases in load occur)

Harsh V Bhasin


36/56


Secondary Task Measures Method of measuring reserve capacity

Assumption that performance on primary taskstakes a certain amount of cognitive resources

Secondary task will use whatever resources areleft

The fewer the resources, the more the secondarytasks suffer

Embedded secondary tasks: secondary tasks thatare normally part of a job but have a lower priority

Harsh V Bhasin


37/56


Physiological Measures

Measures of heart rate variability haveproven to be relatively consistent and

reliable measures of mental workload Measures of visual scanning are also

useful to understand the qualitative natureof workload changes

Physiological measures correlate withother measures of workload

Harsh V Bhasin


38/56


Subjective Measures

Simply asking operator to rate workload ona subjective scale

Best scales often anchored by explicitdescriptions of the high and low end of thescale

Easy to obtain but are limited since they

are subjective (peoples reports do notalways coincide with performance)

Harsh V Bhasin


39/56


Workload Dissociations

Most features (subjective, physiological, and

secondary task) generally correlate with each

other in discriminating low vs. high workloadconditions allows user to select technique of

convenience

Multiple measures recommended where possible

Dissociation occurs when workload measures arefound to increase at the same time that primary

task performance is found to improve

Harsh V Bhasin


40/56

Fatigue

While performing a task, performance may

degrade

Effects of high (even moderate) workload are

cumulative in terms of build up of fatigue

Role of fatigue important in predicting

consequences of long-duration, sustained

operations or continuous performance

Harsh V Bhasin


41/56

Vigilance & Underarousal

Causes of Vigilance Decrement Key characteristics of environment that lead to

loss of performance in detecting relevantsignals/events

Time: Longer duration required to maintain vigilance,

greater likelihood that misses will occur Event Salience: Bright, loud, intermittent and other

salient events more easily detected

Signal Rate: When signal events occur at low rate;monitoring for presence more effortful & detectionlikelihood reduced

Arousal Level: Generally little intrinsic task-relatedactivity to maintain info-processing system in state ofalertness or arousal

Harsh V Bhasin


42/56

Vigilance & Underarousal

Vigilance Remediations

Watches/vigils should not be made too

long

Signals should be made more salient

Signal enhancement can be cleverly employed

Harsh V Bhasin


43/56


44/56

Circadian:


45/56

Harsh V Bhasin

Circadian:(circa = approximately; dies = a day)Physiological & biochemical processes in body rise and fall with daily rhythms


46/56

Sleep Loss

Sleep latency test: How long it takes avolunteer to go to sleep in a dark room

on a comfortable bed

Sleep Efficiency: measures how longwe can sleep (greater at night)

Performance fluctuates throughout the

day

Harsh V Bhasin


47/56

Sleep Loss

Performance Loss Due to Sleepiness

Some aspects of performance more susceptible

Sleepiness causes increased blinks, eye closures,

and brief durations of microsleep Tasks depending on visual input particularly sensitive tosleep disruption

Judgment, learning/storing new material and tasks

involving self-initiated cognitive activity are

sensitive to sleep disruption

Harsh V Bhasin


48/56


49/56

Remediation to Sleep Disruption

Sleep Credits Trying to gain extra sleep prior to a mission or

period when sleep deprivation is anticipated

Sleep Management Program

Role of organization to avoid conditions inwhich operators must work long hours in life-

critical jobs, with little sleep

Harsh V Bhasin


50/56

Remediation to Sleep Disruption

Drugs like caffeine can combat sleepinessin the short run

Excessive consumption may be adequate in

short run, but in the long run it disrupts ability to

sleep soundly when sleep time is available

(counterproductive overall)

Avoid working during late night-early

morning hours

Harsh V Bhasin


51/56

Desynchronization

Describes the situation when circadian

rhythms are out of synchrony with the

level of activity that a person is trying to

maintain

Harsh V Bhasin


52/56

Desynchronization

Shift work

Some jobs must be performed round the clock

Strategies for shift work

Assign workers permanently to different shifts, assumingthat circadian rhythms of workers will finally adapt

(although full adaptation never takes place as long as

worker is exposed to some evidence of natural day-night

cycle)

Maintain fairly continuous rotation of shifts Alter shift periods but do so relatively infrequently (14-21

days on one schedule)

Harsh V Bhasin


53/56

Shift Work

Shifts that are delayed are more effectivethan those that are advanced Delayed shift is one in which worker would

move from midnight-8am to an 8am-4pm shift Advanced shift is one in which worker moves

from later to earlier

Shift schedules that adhere to natural

circadian rhythms are preferred byworkers, increase productivity, greaterhealth & reduced turnover

Harsh V Bhasin


54/56

Desynchronization

Jet Lag Desynchronization caused by long-duration east

or west flights

West bound flight is one that makes the day

longer (analogous to a delayed shift) Circadian rhythms adapt more rapidly and sleep

disruption will be less

East bound flights is one that makes the dayshorter (analogous to an advanced shift)

Leads to slow adaptation and greater disruption of sleeppatterns

Harsh V Bhasin


55/56

Jet Lag

Remediations

Waiting until local bedtime to sleep afterone has landed rather than napping during

the day Exposure to intense light prior to departure

at a time that approximates daylight at thedestination

Biochemically, melatonin can help adaptcircadian rhythms

Harsh V Bhasin

J t L


56/56

Jet Lag

wsd2 2013 5c stress & workload

Documents