Ergonomics 6PS025

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Ergonomics 6PS025

• Module Leader Miles Richardson

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Last Week

• What is ergonomics? Why is it needed?
• History shows growth of ergonomics linked to
  growth of technology.
• Systems Ergonomics - people dont operate in a
  vacuum.
• Any questions?

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This Week

• To fit the job to the human need to understand
  the human.
• Psychology students should understand human
  behaviour.
• Important to understand social behaviour as this
  can impact on performance and health e.g.
  motivation, attitudes etc...
• Important to understand cognition, perception,
  information processing and memory.
• Underlies ability to do task affected by social
  issues.

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Human Cognition

• Cognition is a term for the mechanisms we use to
  perceive, think and remember.
• We perceive, process and respond.
• Theory Lab based, not in applied context.
• Tasks that are incompatible with our cognitive
  functions can lead to
• Poor performance
• Stress
• Errors medical errors.
• Disasters 3 mile island.

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Cognitive Factors

• Psychomotor Skills
• Sensory and perceptual skills
• Attention
• Learning and memory
• Language and communication
• Problem solving and decision making
• All relevant to task performance
• Examples?

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Cognitive Characteristics

• Each factor has characteristics
• A person must be able to physically reach the
  controls of a machine
• Technology should not exceed our cognitive
  limits.
• Understanding human cognition can inform task
  design or ability to do task.

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Exercise - Limits

• Think of physical limits that affect task design?
  
• Think of psychological limits how do they
  affect tasks? Are they as clear?

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Understanding Cognition

• Not enough to consider cognitive characteristics
  of user
• Interaction between humans and devices requires
  two-way exchange of information.
• Need model of task or device, ie outputs and
  inputs - Context
• Need model of the users cognitive processes and
  behaviour - Competence
• Can then understand what can and cannot be
  expected of users - Performance

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Considering Human Performance

• Competence (Users Cognitive Characteristics)
• What the person can do
• What the mind can compute
• Performance
• What the person actually does
• What mind computes in a given context
• Context (The workplace, environment etc.)
• How contextual factors affect information
  processing, response selection etc.

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Example

• User may have mental capacity or competence to
  use a mobile phone and drive a car.
• Performance of phone use and driving (the output
  of cognition) can be measured.
• Performance of either task affected by contextual
  factors.
• Context includes weather, time, mood?
• Or phone conversation may be more complicated.
• Or the task more complicated.
• In these situations the task may exceed the
  mental capacities.

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Activity 1

• Examples to illustrate the role of cognitive
  factors in ergonomics.
• 1 Consider the cognitive concerns associated
  with designing a warning sign.

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Activity 2

• Examples to illustrate the role of cognitive
  factors in ergonomics.
• 2 From a psychological perspective consider how
  a person typically refers to a statistics and
  SPSS book when needing help (e.g. on conducting
  an ANOVA).

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Activity 3

• Examples to illustrate the role of cognitive
  factors in ergonomics.
• 3 Consider an industrial task such as visual
  inspection of glass bottles where workers view
  bottles as they move along a conveyor, looking
  for defective items that should be rejected.
  Defects range from bubbles to cracks. What are
  the relevant cognitive factors?

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Information Processing (Wickens, 92)
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Overview

• A useful framework for considering cognition
  during tasks
• Information flows through the system, it is
  sensed, perceived and processed resulting in
  actions that result in feedback leading to
  further processing - consider driving a car.
• A key issue is that we have a limited information
  processing capacity (i.e. attention and STM).
• Chapter 3 set text.

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Sensation Perception

• Sensation - Events in the environment must enter
  the brain.
• Perception involves giving meaning to events
• Perception driven by the senses, termed bottom up
  processing.
• Perception driven by inputs from LTM about
  expected events, termed top down processing.
• Sometimes past experience isnt available,
  meaning we have to rely on bottom up processing.
• Or poor sensory conditions, e.g. fog, means
  relying on top down expectations.

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Perception Characteristics

• Expectancy top-down we sample the world where
  we expect to find information
• Value - how long we attend to the signal depends
  on its value.
• Effort required effort we prefer to scan short
  distances rather than long ones.
• We prefer to avoid head movements to select
  information sources.

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Recognition

• Perception requires sufficient stimuli to reach
  detection identification thresholds -
  physiological thresholds.
• Recognition occurs by matching to stored memory -
  affected by expectations, context and other
  factors.
• E.g. - Pilot in difficult conditions might see a
  series of lights below.
• The pilots expectations, training and external
  factors such as visibility and visual cues will
  affect whether the lights are perceived as lights
  on the runway or streetlights.

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People can be fooled
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Speed Perception

• Characteristics of perception can also be
  exploited.
• Godley et al (2004) investigated Perceptual
  Countermeasures (PCMs).
• Varying the dimensions of centre and roadside
  markings
• PCMs aim to change drivers perception of speed,
  rather than conscious decisions
• Perceptual narrowing, not physical, as narrow
  lanes equal more accidents.

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The Markings

• Best
• lt a
• Good
• lt c
• Poor
• Poor
• Poor

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Why do PCMs work?

• Risk Homeostasis Theory (Wilde 82) gt Narrow lanes
  increase perceived accident risk when perceived
  risk is higher behaviour is modified by
  reducing speed.
• Concept of Safety Margins (Summala 96) gt Drivers
  generally drive to their safety margin narrow
  lane reduces safety margin and therefore speed.
• Mental workload (De Waard et al. 95) gt argue
  lower speed owing to higher mental workload -
  narrow lanes require more mental effort.
• If nearing mental capacity need to switch
  resources from maintaining speed to keeping in
  lane.

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Memory

• WM home of much cognition - therefore limitations
  are important.
• Provide visual echoes or cues to distribute
  cognition and the load on WM.
• Exploit chunking in design, for example post
  codes.
• Order text and instructions in meaningful
  sequences.
• Avoid negatives, use "Do" not "Don't".
• Chapter 3 set text

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LTM Organisation

•         Schema is the entire knowledge structure
  about a particular topic (buildings)
•         Scripts typical sequence of activities
  like getting online or shutting down a piece of
  industrial equipment
•         Conceptual model is the understanding of
  how something works (bicycle, telephone, computer)

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LTM Error

• Actions that are commonly performed will become
  established as unconscious routines.
• When perform an action a group of relevant
  schemas are activated.
• Errors result from
• unintentional activation of inappropriate schemas
• loss of activation through interruption or
  forgotten intention

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LTM implications for Design

• Assist development of conceptual model. Otherwise
  may fail to interact with the system (fault
  diagnosis)
• Standardize
• Carefully design information to be remembered.
  Meaningful to the individual and semantically
  associated with other information.
• Well-organized sets of information (groups)

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Selective or Focussed Attention

• Ability to select information from the vast array
  of stimuli that we are exposed to.
• Quite good at it. Necessary in order to reduce
  overloading senses cognitive processes.
• People limited in their ability to act on
  multiple signals in different channels.
• E.g., concurrent information when flying - visual
  displays, environment outside auditory messages
  via radio.
• Knowledge drives attention where we look
• Chapter 4 6 set text.

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Example

• Try the following task yourself Only read the
  words in capitals
• IT what is IS most QUITE surprising AMAZING is
  that HOW not only PEOPLE can ARE you ABLE focus
  TO attention SELECTIVELY on FOCUS one of THEIR
  the messages ATTENTION but ON you PARTICULAR are
  SOURCES completely OF unaware INFORMATION of AND
  the IGNORE other one OTHERS.

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Divided Attention

• Ability to undertake several tasks at once.
  Affected by number of different things
• Task similarity If the tasks are dissimilar they
  are easier to do together at the same time.
• Task difficulty Two tasks together can lead to
  demands greater than demands of each separate
  task.
• Practice The demands that the task makes may be
  reduced as a function of practice.
• Chapter 5 6 set text.

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Information Processing - Summary

• We have limited information processing capacity.
• Much human information processing occurs without
  conscious effort driving home
• Conscious processing occurs in novel situations
  when decisions have to be made
• Here we may notice the limits of processing
  capacity e.g. driving in a new city at night
  in the rain - while having a complicated
  conversation.

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Cognitive Load

• Cognitive Load Theory (Sweller, 1988) deals with
  the amount of work being done by cognitive
  resources
• Based on the limitations of the human information
  processing system.
• Some causes
• Split Attention integrating sources of
  information
• Redundancy discounting sources of information

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Exercise

• Van driver activity.

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Further Reading

• Chapters 2 to 7 of Matthews, Davies, Westerman
  Stammers (2000). Human Performance Cognition,
  Stress and Individual Differences
• Chapter 9 Expectancy and Control Perceptual
  and Cognitive aspects of the driving task in
  Hancock (1999) Human Performance and Ergonomics
• Wickens, Engineering psychology and human
  performance.
• Chapter 6 Intro to Human Factors Engineering,
  Wickens.