13. Stress and Workload

1
13. Stress and Workload

• stressors
• environmental noise, vibration, heat, light
• psychological anxiety, fatigue, frustration,
  anger
• four effects direct or indirect (figure 13.1)
• psychological experience frustration or arousal
• change in physiology
• affect the efficiency of information processing
  not always degrading
• long-term negative consequences for health
• ENVIRONMENTAL STRESSORS
• Motion
• 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

2

• comfort zone
• 73F to 79F (23 - 26C) in summer and 68F to
  75F (20 - 24C) in winter
• skewed -- less humidity is allowed (60) at the
  upper temperature limit of 79F than lower limit
  of 68F (85 humidity allowed)
• perceptual motor task indirect the efficiency
  of information processing
• the influence of three key moderating variables
• actual body temperature by the clothing worn
• the amount of air movement by natural breeze or
  fans
• the degree of physical work (metabolic activity)
• cold stress frostbite, hypothermia, health
  endangerment disruption of coordinated motor
  performance
• Air Quality
• poor air ventilation anoxia
• PSYCHOLOGICAL STRESSORS
• Cognitive Appraisal
• 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

3

• 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, 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 speed-accuracy tradeoff
• Remediation of Psychological Stress
• simplification emergency instructions easy to
  locate and salient
• little information in WM -- knowledge should be
  in the world
• actions should be explicitly instructed as
  compatible as possible with conventional,
  well-learned patterns of actions and compatible
  mapping of displays to controls
• auditory alert and warnings avoid excessively
  loud and stressful noise
• training
• 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

4

• LIFE STRESS
• financial difficulties, labor-management
  relations, stressful life events
• lack of attention (low motivation), distraction
  or diversion of inattention
• WORKLOAD OVERLOAD
• The Time-Line Model
• workload a ratio of time required to time
  available (TR/TA) fig. 13.3
• how much workload a human experiences
• 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/TA1 ? spare capacity region and
  overload region
• four challenging factors to workload estimates
• identification of task times 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
• Remediations
• task redesign automation, display design
• training on the component tasks, task management
  skills, calibration on tasks

5

• Mental Workload Measurement
• 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 -- TLX
• Workload Dissociations
• multiple measures are recommended
• FATIGUE AND SLEEP DISRUPTION
• Vigilance and Underarousal
• Causes of the Vigilance Decrement
• time the longer , the more misses
• event salience

6

• Vigilance Remediations
• frequent rest break, more salient signal, false
  signals, external stimulation (music, noise)
• Sleep Disruption
• major causes of sleepiness -- deprivation of
  sleep, circadian rhythm
• Sleep Deprivation and Performance Effects
• decision making, innovation and creativity,
  learning or storing new material, self-initiated
  cognitive activity
• long-duration missions military combat missions
  or long-haul truck driving, or an airline pilots
  trip
• the quality of sleep sleep debt less than
  adequate amount of sleep the night prior to the
  mission
• Circadian Rhythms
• body temperature sleepiness, sleep duration,
  performance intentional sleep
• Circadian Disruption
• Jet Lag
• west bound (delayed shift) adapt more rapidly,
  less sleep disruption
• Shiftwork
• 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
• Remediation to Sleep Disruption

7
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
• Personnel Characteristics
• Age and Gender
• the most predictive factor is age (15 24, peak
  at 25)
• Physical and cognitive abilities up for the
  elderly

8

• 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

9

• 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
• Unintended error
• slip intention is correct but the execution is
  incorrect (commission errors)
• lapses nonintentional errors are those of
  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

10

• 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 ?
  estimate the likelihood
• 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

11

• 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) ? providing a barrier or
  safeguard ? changing the behavior (warning and
  training) ? administrative procedures or
  legislation
• 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

12

• RISK-TAKING AND WARNINGS
• Risk-Taking as a Decision Process
• 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
• perceived severity of the hazard/injury
• the novelty of the hazard and whether exposure
  was voluntary
• 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
• gaining a persons attention bright orange
• legible font size, contrast, short and simple
  text, easily interpreted pictures and icons
• compliance by administrative controls and
  enforcement

13
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
• user-centered design, participatory design,
  iterative design
• UNDERSTAND SYSTEM AND USER CHARACTERISTICS
• creeping featurism
• balance between functionality and ease of use
• the frequency of task performance using the
  particular software
• mandatory versus discretionary use
• the knowledge level of the user
• novice users
• knowledgeable intermittent users
• expert frequent users

14

• DESIGN USING THEORIES AND MODELS
• Seven Stages of Action
• gulf of execution the mismatch between the
  users intentions and the actions supported by
  the software good, well-human factored controls
• gulf of evaluation the mismatch between the
  users expectations and the system state food,
  dynamic info in interpretable displays
• Models of User Performance for Design GOMS
• goals, operators, methods, selection rules
• detailed description of user tasks and specific
  quantitative predictions
• explicitly identify and list users 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
• 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

15

• 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

16

• 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 users 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

17

• EVALUATE WITH USABILITY TESTS AND METRICS
• Prototypes
• 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
• Pitfalls of Usability Testing
• understanding the users and their tasks
• fixation on the laboratory environment

18

• 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
• the user knows a precise label for a piece of
  information to be retrieved
• the user knows some general characteristics of
  the desired item but can identify when he/she
  sees it
• the user wants to learn what exists in the
  database that may be of interest
• 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
• difficult to specify the queries or combinations
  of keywords
• 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

19

• 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)
• benefits
• layout principles of relatedness and sequence of
  use
• better understand the full structure of the
  database by examining a broad map of its elements
• should be allowed an option to recover
• provide a historical record, bookmarks
• costs
• getting lost (1) consistent with users mental
  model, (2) overall map of the space
• update rate -- complex graphics, delayed travel
  time
• Virtual and Augmented Reality
• VR interface for full immersion
• 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