Ergonomics 6PS025

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Ergonomics 6PS025

• Module Leader Miles Richardson

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Story so far

• Aim - to ensure knowledge of psychological
  characteristics is brought to bear on practical
  problems of people at work and in leisure.
• Cognitive characteristics info processing etc.
• Psychosocial issues
• groups, attitudes
• applied social
• Stressors
• Individual Differences
• Stages of Change and ergonomics interventions

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On UDEL

• ulib.derby.ac.uk/ecdu/ECDUDigitalResources.html
• Social Psychology of Driver Behaviour. Chapter 8
  of Applied Social Psychology by Semin Fiedler.
• Smith, P (1999) Ch 16 Cognitive Factors In The
  Occupational ergonomics handbook , ed. Karwowski
• Carayon, P. Lim, S (1999) Ch 15 Psychosocial
  work factors In The Occupational ergonomics
  handbook , ed. Karwowski
• In Library - Ch 19 Wickens Intro to HF
  Engineering.

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Today Methods and Ergonomics

• Many the same as Psychology collecting data
  about people....
• Experiments, questionnaires, interviews,
  observation
• Not divided by methods, e.g. discourse v
  experimental
• ...But also about tasks.

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Uses

• Ergonomics methods used to understand human
  behaviour during a task interaction with a task
• Either applied, evaluating user performance with
  a view to improvement, e.g. car design.
• Or theoretical, fundamental understanding of
  behaviour task, e.g. mental models.
• Pure can give results that can be applied.

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Information about People

• Direct Objective Performance Measures -
  Observation - Time, scores, errors using
  checklists, video etc.
• Physiological HR, EEG, eye-movements
• Indirect Subjective Performance Measures
• Knowledge or Attitudes ease of use, feelings,
  perceived effort
• From - Interviews, surveys, questionnaires,
  rating scales.
• In the field or in the lab.
• Ideally objective subjective measures correlate.

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Research Examples

• Qualitative methodology - Hignett (2003) used
  Interviews and snowball sampling to id patient,
  staff and org. issues in NHS. Found lack of
  ergonomics information for female workers.
• Experimental (Filik et al, 2003) PC based study
  to test same/different reaction times. Medication
  errors and the labelling of medicines.
• chlorpromazine v chlorpropamide
• chlorproMAZINE v chlorproPAMIDE
• Coursework wider v focussed, objective v
  subjective etc.

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Exercise

• Research Methods can be applied to
  non-psychological issues
• Design a study to compare forces required to Drag
  Sheep over 5 Surfaces with 2 levels of slope
• DV and IV?
• PPs, trials, design?
• Materials?

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Information about the Task

• Interviews with experts
• Documentation
• Observation
• Data can inform Task Analysis methods
• Environment Light, Noise, Heat subjective and
  objective.
• Bespoke - not psychology methods

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Some Ergonomics Methods

• Checklists predefined list of points
• Expert Appraisal heuristic evaluation
• Co-discovery interview
• Layout analysis
• Workload - NASA-TLX today
• Hierarchical Task Analysis (HTA) - today

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Workload

• Need to quantify how hard a task is
  usability, stress, possibility of error.
• Allows comparisons between tasks/designs
• Definition- Interaction of demands placed on
  individual by the task and the ability to cope.
• Chapter 5 of set text.

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Measuring Workload

• Objective primary task performance methods
• Time taken, errors etc.
• Physiological tests
• heart rate, EEG activity, pupil diameter,
  galvanic skin response, blink rate
• Secondary task performance. RT
• Spare capacity

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Simple Methods

• Time ratio concept - simply Time Required (TR) /
  Time Available (TA).
• Performance suffers when this value is around or
  greater than 1.
• Or - Ratio of resources required to resources
  available.

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Gawron 2000

• Simple task difficulty index
• Familiarity of stimuli Familiar 0 v Unfamiliar
  1
• No. of concurrent tasks Single 0 v Dual 1
• Task Difficulty Memory set lt3 0 v gt4 1
• Resource Competition None 0 v Competition for
  central resources 1

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Gawron 2000

• Workload high when
• Stimuli unfamiliar
• Task performed concurrently
• Load on WM
• Competition for central capacity
• Think of an example?

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Example
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Subjective methods

• Often questionnaires using rating scales for
  responses Attitudes, Ease of use
• Various scales - widely used measure developed by
  NASA - their Task Load Index (NASA-TLX)
• Ideally measures from different methods should
  correlate

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NASA-TLX (Hart Staveland, 1988)

• Rates six aspects of workload
• Mental Demand thinking, deciding memory
• Physical Demand exertion activity.
• Temporal Demand time pressure and pace
• Effort how hard you worked
• Performance success in task
• Frustration stress, irritation, discouragement

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Using NASA-TLX

• Dimensions paired and have to select one that
  contributed most to task
• Did the task require more TEMPORAL DEMAND (time
  pressure) or more MENTAL DEMAND (thinking,
  deciding, remembering etc.)?
• Did the task require more EFFORT (how hard you
  worked) or was the nature of the PERFORMANCE
  (success in accomplishing the task) more of a
  contributor?
• Number of times each dimension selected
  determines its weighting 0 to 5

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Using NASA-TLX

• Task then rated on the six dimensions, low to
  high (0 to 100)
• Score for each dimension equals rating times
  weighting
• Sum divided by 15 for total workload

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E.g. Turner Love
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Turner Love

• Shows increased workload of driving and phone
• Total w/load only just higher than phone alone.
• But relationship of increase to performance?
• Could be primary performance (driving) stays same
  and secondary (phone) reduces.
• Objective measure of driving showed performance
  reduced.

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NASA-TLX Demonstration

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Task Analysis

• TA provides a framework for describing tasks
  such as sending a text
• Sufficient detail to identify individual
  decisions and actions required.
• Task analysis may be specific and meticulous
  method or a guiding framework for neutral
  examination of tasks (Shepherd, 1998).
• Driving 40 major tasks with 1700 subtasks
• Coursework

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Hierarchical Task Analysis (HTA)

• HTA breaks down the overall goal into a series of
  subordinate operations and plans.
• Becomes increasingly detailed as the hierarchy
  progresses through progressive redescription.
• The bottom level will usually be an operation or
  action.
• Operations are observable behaviours or
  activities that accomplish the goals

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Example Generic HTA

• Can now consider psychological issues, e.g.
  Information Processing
• Box 4 A choice or decision, affected by number
  of options

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HTA

• Plans are the unobservable decisions and describe
  how sub-operations combine
• Cognitive task elements being inferred by plans
  that detail the cognitive operations
• Advantages Enlightening process, provides
  framework
• Disadvantages No direct solutions, poor
  reliability, time consuming

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Cognitive Processes

• TA cook food in microwave, each step requires
  cognitive steps.
• Put food in (decide what food to eat)
• Set power level (decide on power level)
• Set timer (decide how long)
• Press start (listen for bell)
• Remove food

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Application of HTA

• Use HTA to inform design, identify issues
• Information required for operation?
• Is information provided to support operation? Are
  there any cues?
• Does operation involve cognition - WM, LTM,
  decision-making?
• Is adequate training provided?
• Identifies operations to be learnt. Aids training
  design.

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Step-by-Step

• Collect data - observation, documentation etc.
• State overall goal
• State subordinate operations plan.
• Redescribe
• Check and revise

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Example - Boiling a Kettle

• State overall goal?
• State subordinate operations plan?
• Redescribe operations?
• Check and revise?
• When to stop? P x C (probability and cost)
  probability of error and cost of error.

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HTA - Exercise

• In groups - perform an HTA of the car park ticket
  machine (complete on your own after session).
• Coursework (On your own) Using the HTA as a
  framework, identify pertinent usability/psychologi
  cal issues related to using the ticket machine.
• Bring HTA to L7 10/3 you will be using it.

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Further Reading

• Shepherd, A. (2000). HTA as a framework for Task
  Analysis. Chapter 2 of Task Analysis by Annett
  and Stanton.
• Theoretical Issues in Ergonomics Science 5, 6,
  November-December 2004 - The role for qualitative
  methodology in ergonomics
• Annett, 2002. A note on the validity and
  reliability of ergonomics methods Theoretical
  Issues in Ergonomics Science 3, 2

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Next Week

• POET - the psychology of how people interact with
  things
• Affordances, causality, visible constraints,
  mapping, transfer effects....
• Then usability evaluation