Human Computer Interaction

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Human Computer Interaction

• Jon Ivins
• DMU

2
Overview

• What is HCI?
• Problems faced by designers
• Cognitive issues
• Definitions
• Physical factors
• Some guidelines

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HCI Designers

• 1) try to anticipate as many likely problems as
  possible.
• 2) A prototype design is produced.
• 3) Users are invited to try the prototype and
  comment on the efficiency of the design.
• 4) The feedback is used to amend the initial
  design.
• 5) The process is repeated until the users are
  completely satisfied.

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Problems

• Above is inefficient and expensive
• a) if only a subset of users are involved, they
  can become used to the HCI and not identify
  difficulties that a new user may experience
• b) how does the designer know when to stop the
  iteration?
• Allied to point b) is
• c) how do we measure user satisfaction?

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A Definition and yet more issues

• The engineering process of designing
  interactive computer systems so they are
  efficient, pleasing, easy to use and do what
  people want. Sutcliffe.
• What are the core issues
• Why bother about it anyway?
• Are there any guidelines?

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Core issues

• What are the facets of a person which affects
  HCI?
• How do we analyse what people do with computers
  and their interfaces?
• What are the user needs?
• How do we specify an interface?
• How do we design an interface?
• How do we evaluate an interface?
• What is a good interface?
• How do we ensure good quality for HCI on a
  consistent basis? Can we?

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Why Bother with HCI?

• Less user frustration
• A lower number of errors
• Greater productivity
• Economy
• Health and Safety issues e.g. stress
• Poor HCI System failure and/or inefficiency
• Poor HCI does not sell products

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Human Information Processing

• How is bread made?
• I know that! Alice cried eagerly. You take
  some flour.
• Where do you pick the flower? the White Queen
  asked. In a garden, or in the hedges?
• Well it isnt picked at all, Alice explained,
  its ground.
• How many acres of ground? said the White Queen.
• Lewis Carroll - Through The Looking Glass

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Human Short Term Memory

• short retention time of around 200 ms
• contents can be refreshed within 70 ms
• capacity is 7 items /- 2 items
• capacity can be increased by using tricks
• there are two sub-systems one for language and
  one for visual-spatial data
• STM for language tends to be LIFO based
• Poor retention of visual detail
• Retention best if images/words together.

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HCI and STM

• Minimise distraction during tasks and
  memorisation
• Do not overload STM
• Structure information
• Images need to be accompanied by text.

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Human Long Term memory

• Infinite (?) capacity
• Frequently used information can be retrieved very
  rapidly while less frequent items take longer to
  recall
• Age slows down memory recall
• It appears to be a two-stage process based upon
  recognition (usually started by cues) and recall
  (the actual retrieval).
• It appears that there is a background processor
  to retrieve items as we can do other things while
  recalling information

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• Recalling one item often prompts the recall of
  related items
• It is possible that there are two types of LTM
  associative ( for concepts) and analogue (for
  physical objects)

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Sutcliffe recommends the following HCI guidelines

• )Memorisation is helped by enriching the
  information during learning
• )Reasoning and understanding what is being
  remembered helps retention
• )structuring information helps categorical memory
• )Use techniques like keywords as recall cues
• )Visual images with text aid recall
• )Consistency of association creates better
  contexts for memorisation and recall

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Physical factors 1

• The 5 senses
• Which are important to HCI?
• The Brain
• 15 billion cells, each with 150 connections
• complex
• sensors appear to do pre-processing
• pragmatic approach needed

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Physical factors 2

• The Eyes
• 400-700nm
• optimum performance in middle of range
• brightness is subjective
• contrast is based on luminance
• C(Lmax-Lmin)/(Lmax Lmin)
• Visual acuity (12 point at 0.5 m)
• poor peripheral vision

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• Eyes characteristics lead to
• only one image at a time
• people cannot deal with detail in 2 simultaneous
  windows
• movement alerts peripheral vision and, hence, the
  user
• retina can detect edges easily
• moving images attract attention
• Icons must have clean edges and be simple

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Interaction

• depends upon the computer system being used,
• the software being used and
• the human user
• Norman (1986) argues there are 2 gulfs
• When the user is faced with what to do next - the
  interface should prompt the user
• When the user evaluates an action they have
  performed - the interface should make the effects
  of user action explicit

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Sutcliffe (1995) offers the following principles

• Consistency - reduces learning and increases
  recognition
• Compatibility - how well the HCI design matches
  the users expectations from previous experience
• Predictability - HCI prompts user and suggest
  actions
• Adaptability - The user should be in control and
  computer adapts to pace of work, skill level etc.
• Economy and error prevention - self evident
• User Control - linked to predictability but
  allows the user to backtrack and recover from
  errors e.g. the UNDO command
• Structure - to reduce complexity and give order.
  Only relevant information is shown to the user.

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References

• Many good textbooks available in library
• Best is Jenny Preece et al
• Sutcliffe is also a good text