Transcript 슬라이드 제목 없음
IMEN 368 인간공학II
13. Stress and Workload
stressors
environmental – noise, vibration, heat, light
psychological – anxiety, fatigue, frustration, anger
four effects – direct or indirect (fig 13.1)
1. psychological experience – frustration or arousal
2. change in physiology
3. affect the efficiency of information processing – not always degrading
4. long-term negative consequences for health
ENVIRONMENTAL STRESSORS
Motion
Sustained motion (motion sickness) and cyclic motion (vibration)
High-Frequency Vibration
high frequency; specific limb or whole body
vibrating white finger syndrome – excessive continuous levels of high-frequency vibration
full-body vibration – not well documented; eye-hand coordination, visual task
Low-Frequency Vibration and Motion Sickness
lower frequency
decoupling between the visual and vestibular inputs
Thermal Stress
performance degradation and health problems
고려대학교 산업공학과
IMEN 368 인간공학II
comfort zone
23 - 26°C in summer and 20 - 24°C in winter
skewed -- less humidity is allowed (60%) at the upper temperature limit of 26°C
than lower limit of 20°C (85% humidity allowed)
heat stress – performance degradation on perceptual motor task (tracking and RT);
indirect – the efficiency of information processing not the quality
long-term consequences – dehydration, heat stroke, heat exhaustion
heat (and humidity) influencing variables
clothing worn, air movement, the degree of physical work (metabolic activity)
cold stress – frostbite, hypothermia, health endangerment – disruption of coordinated
motor performance
Air Quality
poor air quality or pollution by smog and carbon monoxide; anoxia
PSYCHOLOGICAL STRESSORS
Cognitive Appraisal
1.
2.
3.
4.
differences in cognitive appraisal
may fail to perceive the circumstances of risk
may fail to understand the risk
relatively more confident or even overconfident
reference in control
고려대학교 산업공학과
IMEN 368 인간공학II
Level of Arousal
anxiety and danger increase in physiological arousal – HR, pupil diameter, hormonal chemistry
inverted U function of performance (Yerkes-Dodson Law)
trying harder, OLA (optimum level of arousal), overarousal
criticized because it never specify exactly where the OLA is (fig 13.2)
Performance Changes with Overarousal
perceptual or attentional narrowing (tunneling) – cognitive tunneling
working memory loss while LTM little hampered, even be enhanced
strategy shifts – “do something now” -- speed-accuracy tradeoff
Remediation of Psychological Stress
simplification – design of displays, controls, procedures
actions should be explicitly instructed; as compatible as possible with conventional, welllearned patterns of actions and compatible mapping of displays to controls – knowledge in the
world
auditory alert and warnings – avoid excessively loud and stressful noise
training
extensive (excessive) training of emergency procedures – LTM
generic training of emergency stress management – guidelines (inhibiting the tendency
to respond immediately), breathing control to reduce the level of arousal
고려대학교 산업공학과
IMEN 368 인간공학II
LIFE STRESS
financial difficulties, labor-management relations, stressful life events
lack of attention (low motivation), distraction or diversion of attention
WORKLOAD OVERLOAD
The Time-Line Model
workload – a ratio of time required to time available (TR/TA) – fig. 13.3
1. predict how much workload a human experiences
2. predict the extent to which performance will suffer because of overload
as the ratio increases, the experience of workload also increases relatively continuously
human performance decrement due to overload occur at or around TR/TA=1 spare
capacity region and overload region – fig. 13 - 4
four challenging factors to workload estimates
1. identification of task times (covert time)
2. scheduling and prioritization
3. task resource demands and automaticity
4. multiple resources
Workload Overload Consequences
important consequences for human performance in the overload region something is
likely to suffer
Edland and Svenson (1993) more selectivity of input, more important sources of
info given more weight, decrease in accuracy, decreasing use of heavy mental
computations, locking onto a single strategy
Remediations
task redesign – automation, display design
training on the component tasks, task management skills, calibration on tasks
고려대학교 산업공학과
IMEN 368 인간공학II
Mental Workload Measurement
mental workload by the ratio of the resources required to the resources available
Primary Task Measures
measures of system performance on the task of interest – the speed and accuracy
Not really a workload measure per se but influenced by workload (reflect workload)
Secondary Task Methods
measures reserve capacity
Available resources – time estimation, memory task, mental arithmetic, etc.
problematic because artificial, intrusive, or both embedded secondary task
Physiological Measures
HR variability – mental workload
Blink rate, pupil diameter, electroencepholography (EEG)
Subjective Measures – NASA Task Load Index (TLX)
Do not always coincide with their performance
Workload Dissociations
multiple measures are recommended
FATIGUE AND SLEEP DISRUPTION
high mental workload performance may degrade
Fatigue – a transition state between alertness and somnolence
A state of muscles and the central nervous system in which prolonged physical activity
or mental processing, in the absence of sufficient rest, leads to insufficient capacity or
energy to maintain the original level of activity and/or processing
Fatigue not only from the accumulated effects of doing too much work, but also from
prolonged periods of doing very little (vigilance)
고려대학교 산업공학과
IMEN 368 인간공학II
Vigilance and Underarousal
Causes of the Vigilance Decrement
Signal detection theory (hits, correct rejections, misses, false alarms) – the increased
number of misses
1. time – the longer , the more misses
2. event salience
3. signal rate – low signal expectancy (more conservative, more misses and fewer false
alarms)
4. arousal level
Vigilance Remediations
frequent rest break
more salient signal (signal enhancement)
payoffs or changing the signal expectancy (false signals)
Sustain a higher level of arousal – frequent rest breaks, external stimulation (music, noise)
Not sleep deprived
Sleep Disruption
major contributor to fatigue – sleep deprivation (loss); circadian rhythm; jet lag or shift work
Sleep Deprivation and Performance Effects
Tasks sensitive to sleep disruption – decision making, innovation and creativity, learning or
storing new material, self-initiated cognitive activity
long-duration missions lasting more than a day (military combat missions or long-haul truck
driving, or an airline pilot’s trip)
the quality of sleep typically less, so a sleep debt built up
less than adequate amount of sleep the night prior to the mission
고려대학교 산업공학과
IMEN 368 인간공학II
Circadian Rhythms
body temperature (fig. 13.5) – min. in the early morning and max in the late afternoon/early
evening
Sleepiness (sleep latency test), sleep duration, performance
Circadian Disruption
Jet Lag
west bound (delayed shift) – adapt more rapidly, less sleep disruption
Shift Work
assign permanently to different shifts – never fully adapted, smaller pool of owls
a fairly continuous rotation of shifts
alter the shift periods but to do so relatively infrequently
delayed shifts are more effective than advanced shifts
Longer shift
Remediation to Sleep Disruption
get more sleep, napping, sleep inertia, sleep credits, sleep management
고려대학교 산업공학과
IMEN 368 인간공학II
14. Safety and Accident Prevention
Product Liability
Injuries or death occurs in the workplace or elsewhere
Product was somehow defective, and the defect caused injuries or death
Design defective (inherently unsafe)
Manufacturing defect
Warning defect
Defective when it “failed to perform safely as an ordinary user would expect when it was
used in an intended or reasonably foreseeable manner, or if the risks inherent in the
design outweighed the benefits of that design
FACTORS THAT CAUSE OR CONTRIBUTE TO ACCIDENTS
Systems approach
accidents occur because of the interaction between system components (fig. 14.1)
task performance -- employee-task-equipment
Social/psychological factors – social norms
Environmental factors – heat, noise (Table 14.1)
Personnel Characteristics (Fig 14.2)
Age and Gender
the most predictive factor is age (15 – 24, peak at 25)
Physical and cognitive abilities – up for the elderly
고려대학교 산업공학과
IMEN 368 인간공학II
Job Experience
70% of accidents within first 3 yrs, peak at about 2 – 3 months
Stress, Fatigue, Drugs, and Alcohol
personality factors – accident prone
Job characteristics
high physical workload, high mental workload, other stress-inducing factors
long work cycles and shift rotation – increase fatigue level
Equipment
Controls and Displays
Electrical Hazards
Mechanical Hazards
Pressure and Toxic Substance Hazards
The Physical Environment
Illumination
Noise and Vibration
Temperature and Humidity
Fire Hazards
Radiation Hazards
Falls
Exits and Emergency Evacuation
고려대학교 산업공학과
IMEN 368 인간공학II
The Social Environment
management practices, social norms, morale, training, incentive
Human Error
Inappropriate human behavior that lowers levels of system effectiveness or safety
Error Classification
errors of commission – does something that should not have been done
errors of omission -- fail to do something that should have been done
Intended error
mistakes – the inappropriate action was intended (Norman, 1981)
Reason (1990) – knowledge-based mistakes and rule-based mistakes
violation – intentionally does something inappropriate – emphasis on productivity
over safety and inadequate safety culture
Unintended error
slip – intention is correct but the execution is incorrect (commission errors)
lapses – nonintentional errors with omission – failure of prospective memory
Errors and System Safety
resident pathogens – an accident waiting to happen – safety culture
hindsight bias or “Monday morning quarterbacking”
Error Remediation
error containment embodied in the design of error-tolerant systems good feedback,
give “a second chance”
고려대학교 산업공학과
IMEN 368 인간공학II
HAZARD IDENTIFICATION AND CONTROL
Hazard Criticality and Risk
criticality – synonymous with risk, combination of the probability and severity
probability – frequent, probable, occasional, remote, improbable
severity – catastrophic (death or loss of a system), critical (severe injury or major
damage), marginal (minor injury or minor system damage), negligible (no injury or
system damage)
Hazard Identification
Preliminary Hazards Analysis
early in the conceptual design phase
a list of the most obvious hazards among task actions, potential users, and environments
cause and effect estimate the likelihood, severity of consequences potential
corrective measures
Failure Modes and Effects Criticality Analysis (FMECA)
an extension of FMEA, the hazards associated with physical components of a system
system subassemblies constituent components failure modes effects on
other components and subassemblies (hazard as well as human error)
Extent to analysis of the human system (operator performance) – table 14.4
Fault Tree Analysis
top down from an accident to possible causes with Boolean AND/OR logic
Powerful method for hazard identification – fig. 14.3
고려대학교 산업공학과
IMEN 368 인간공학II
Hazard Controls
safety analysis -- develop a list of hazard controls
Hazards -- criticality – controls (cost-benefit trade-offs) – relative advantage/disadvantage
column – recommended control column
the best hazard reduction – eliminate it at once (designing out a hazard source,
functionality) providing a barrier or safeguard (path) changing the behavior (warning
and training workers) administrative procedures or legislation (administrative control)
SAFETY MANAGEMENT
Safety Programs
employee involvement makes a significant difference in the effectiveness of a safety
program
Identify Risks
document analysis interviews facility walk-through a list of hazards
Reactive and proactive approach
job safety analysis
the heavy involvement of employees, long-term benefits, efficiency, ergonomic
factors
Implementing Safety Programs
the most effective means after design and guarding methods
participatory approach, training, feedbacks and incentives
Measuring Program Effectiveness
고려대학교 산업공학과
IMEN 368 인간공학II
RISK-TAKING AND WARNINGS
Risk-Taking as a Decision Process
the choice between safe and unsafe behavior is initially knowledge based decision process
to rule based or simply automatic
Diagnosis generation of alternative actions evaluate alternative actions decision
based on simplifying heuristics (satisfying)
three psychological components affecting safe behavior
1. perceived severity of the hazard/injury
2. the novelty of the hazard and whether exposure was voluntary
3. familiarity
Choice to act safely action selection process as involving two cognitive stage
risk perception – availability of risk in memory
action choice -- cost of compliances
Written Warnings and Warning Labels
warnings are the easiest and cheapest means of protecting from product liability suits
signal word (danger, warning, or caution), description of the hazard, consequences
associated with the hazard, behavior needed to avoid the hazard
1. gaining a person’s attention – bright orange
2. legible font size, contrast, short and simple text, easily interpreted pictures and icons
3. compliance by administrative controls and enforcement
고려대학교 산업공학과
IMEN 368 인간공학II
15. Human-Computer Interaction
THE TROUBLE WITH COMPUTERS AND SOFTWARE DESIGN
increased computer technology does not guarantee increased productivity
well-designed software interface impact on learning time, performance speed,
error rate, and user satisfaction
Design Criteria for Usable Software
efficiency, accuracy, learnability, memorability and satisfaction
SOFTWARE DESIGN CYCLE: UNDERSTAND, DESIGN AND EVALUATE (Fig 15.1)
user-centered design, participatory design, iterative design
UNDERSTAND SYSTEM AND USER CHARACTERISTICS
creeping featurism, balance between functionality and ease of use
1. the frequency of task performance using the particular software – efficiency over
memorability
2. mandatory versus discretionary use – ease of use vs. ease of learning and
remembering
3. the knowledge level of the user
novice users – ease of learning, low reliance on memory – “walk up and use”,
GUI (recognition over recall)
knowledgeable intermittent users – reducing the load on memory, adaptive
interface
expert frequent users (efficiency and accuracy)
고려대학교 산업공학과
IMEN 368 인간공학II
DESIGN USING THEORIES AND MODELS
Seven Stages of Action
gulf of execution – the mismatch between the user’s intentions and the actions
supported by the software – good, well-human factored controls
gulf of evaluation – the mismatch between the user’s expectations and the system
state – food, dynamic info in interpretable displays
Models of User Performance for Design: GOMS
1)
2)
3)
goals, operators, methods, selection rules
detailed description of user tasks and specific quantitative predictions
explicitly identify and list user’s goals and subgoals
identify all of the alternative methods that could be used for achieving goal/subgoal
write selection rules
DESIGN TO SUPPORT MENTAL MODELS WITH CONCEPTUAL MODELS
AND METAPHORS
Mental model – a set of expectancies, relatively complete and accurate
conceptual model – the general conceptual framework through which the functionality
is presented
making invisible parts and processes visible to user
providing feedback
building in consistency
presenting functionality through a familiar metaphor
고려대학교 산업공학과
IMEN 368 인간공학II
Metaphors to develop an effective mental model – supports the transfer of knowledge
Overlook powerful capabilities available in the computer (not exist in the real world)
Cause errors or gaps because the differences btn the metaphorical world and the S/W system
DESIGN USING PRINCIPLES AND GUIDELINES
General Usability Guidelines
general usability principles – table 15.1
Basic Screen Design
Mayhew (1992) - general layout, text, numbers, coding techniques, color
Dialog Styles
Menus
pull down or multiple hierarchical menus
should be used as a dialog style with negative attitudes, low motivation, poor typing skills, little
computer or task experience
each menu should be limited to between four and six items – increased by grouping into
categories and separating them with a simple dividing line
‘broader & shallow’ vs. ‘narrow & deep’
Fill-in Forms
negative to neutral attitude, low motivation, little system experience but good typist and be
familiar with the task
Question-Answer
negative attitude, low motivation, little system experience, relatively good typing skills
tasks for low frequency of use, discretionary use, and low importance
고려대학교 산업공학과
IMEN 368 인간공학II
Command Languages
positive attitude, high motivation, medium- to high-level typing skills, high computer literacy,
and high task-application experience
Function Keys
declining; frequent users who want speeds with low-level typing skills
Direct Manipulation
map well onto a user’s mental model, easy to remember, no typing skills
negative to moderate attitude, low motivation, low-level typing skills, moderate to high task
experience
Natural Language
DESIGN OF USER SUPPORT
Software Manuals
should have well-designed, task-oriented, search tools
search words based on their goals and tasks, not on system components or names
standard human factors principles and guidelines (table 15.2)
Online Help Systems
search effectiveness and efficiency is a general difficulty
Egan and colleagues (1989) – 50% longer search time than a hardcopy manual
EVALUATE WITH USABILITY HEURISTICS
less expensive and less time consuming than UT
identifies the most relevant interface design principles and guidelines – 2 to 4 experts
고려대학교 산업공학과
IMEN 368 인간공학II
EVALUATE WITH USABILITY TESTS AND METRICS
Prototypes
1.
2.
3.
low fidelity methods – index cards, stickies, paper and pen drawings, storyboards
faster, easier, can be modified easily during UT
more willing to change or discard ideas
more substantive feedback to the functionality of prototypes
high fidelity methods include fully interactive screens with the look and feel
Usability Metrics
in the conceptual design phase qualitative assessment of general usability and user
satisfaction (low fidelity prototypes)
later stages of UT quantitative measures (table 15.3) fully functioning prototype
think aloud, interviews, observations
what was observed and why such behavior was observed
Number of Users and Data Interpretation
not a research experiment – less concerned with large sample size 5 to 6 (fig 15.3)
Pitfalls of Usability Testing
understanding the users and their tasks
fixation on the laboratory environment
고려대학교 산업공학과
IMEN 368 인간공학II
INFORMATION TECHNOLOGY
Hypertext, Hypermedia, and the Internet
hypertext – linking chunks of information (nodes) in a network
weblication – software delivered as a service over the Web
Information Database Access
four types of search
1. the user knows a precise label for a piece of information to be retrieved
2. the user knows some general characteristics of the desired item but can identify when
he/she sees it
3. the user wants to learn what exists in the database that may be of interest
4. the user simply wants to understand the overall structure of the database
Mediated Retrieval
direct retrieval systems – label the index or keyword terms due to standard conventions
for multiple classes of users – multiple routes to access the same entities keyword
searches are not always satisfactory
1. difficult to specify the queries or combinations of keywords
2. users are not always fully satisfied with the keyword search results
Intelligent Agents
a helper acts as an interface agent between the user and the information database
provide expert assistant to users
고려대학교 산업공학과
IMEN 368 인간공학II
Spatially Organized Databases
rely on spatial representation of the information space to support search processes
navigation or travel through information space rather than direct retrieval spatially
organized databases based on similarity (proximity)
Different kinds of defining proximity (fig 15.4)
benefits
1. layout principles of relatedness and sequence of use
2. better understand the full structure of the database by examining a broad map of its
elements
3. should be allowed an option to “recover”
4. provide a historical record, bookmarks
costs
1. getting lost – (1) consistent with user’s mental model, (2) overall map of the space
2. update rate -- complex graphics, delayed travel time
Virtual and Augmented Reality
1. VR interface for full immersion
2. negative effects of delayed updates
Affective Computing
people with similar personality characteristics will be attracted to each other
the role of trust in Internet-based interactions – “real world feel” (speed of response, listing
a physical address, photos of the organization
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 13.1 A representation of stress effects
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 13.2
The Yerkes-Dodson law showing the relationship between level of arousal (induced by stress)
and performance. The OLA is shown to be higher for less complex tasks.
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 13.3
Timeline analysis. The percentage of workload at each point is computed as the
average number of tasks per unit time, within each window. Shown at the bottom of the
figure is the computed workload value TR/TA.
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 13.5
Graph plotting mean sleep latency (top), circadian rhythms (body temperature), and sleep
duration (Bottom) against time for two day-night cycles. The bars around sleep duration
represent the variability.
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 13.6
Graph showing how performance on four kinds of tasks varies as a function of circadian
rhythms, shown for a one day cycle.
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 14.1
Models of causal factors in occupational injuries.
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 14.5
Fault tree analysis showing the causes of an accident. The unsafe act must be committed at a time when the
system is vulnerable (thus, the and gate). The unsafe might be committed when its safety implications are
understood but dismissed either because the cost of compliance is too high or for other intentional reasons.
Alternatively, the safety implications may not be known, as a result of a series of possible breakdowns in the
effectiveness of warnings, as described in the text .
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
Figure 15.2
Bridging the gulf of execution and gulf of evaluation
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과
IMEN 368 인간공학II
고려대학교 산업공학과