CS 407 Human Computer Interface

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CS 407 Human Computer Interface

• Class 03
• Monday, August 30, 1999

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Thought for the Day

• Know thy user for (s)he is not thyself!

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Reading Assignment

• http//www.baddesigns.com/examples.html
• Write a 1-2 page summary. Answer these
  questions
• Which ones made you laugh out loud?
• List 3 you have seen personally.
• What do you think are the 3 most important design
  principles you learned? Why?
• Turn in Wednesday, Sept. 1 in class.

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Syllabus

• Who needs a syllabus?
• Prereq sheet?
• Eng CS policies sheet?
• Prerequisites You must have all the
  prerequisites for this course, or you will be
  dropped!

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Quick Review

• How can you tell if a software package is User
  Friendly?
• Note from now on User Friendly is banned in
  this class!
• What did you learn from

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What is User Friendly?

• Time to learn
• Speed of performance
• Error rate
• Retention over time
• Subjective satisfaction
• You can measure each of these!

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Todays Topics

• The Human in HCI
• The Model Human Processor
• Input Channels
• Vision
• Hearing
• Touch
• Movement
• Friday (Finish chapter 1)
• Memory
• Thinking Skill Acquisition
• Implications for HCI

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The Human in HCI

• Humans initiate action, and judge the outcome.
• The Model Human Processor is an
  oversimplification (almost ridiculously!), but it
  gives us a basis to work from.

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Model Human Processor

• Information is received (input) through channels.
• Information is stored in memory.
• Information is processed applied in various
  ways.
• Actions depend on the information.

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The Human Input

• How does a person take in information?
• Channels
• Vision
• Hearing
• Touch
• Movement (Kinesthetic sense)
• Smell
• Smell Taste (not relevant to HCI yet!)

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Vision

• Physical process Reception of stimulus.
• Processing interpretation of stimulus.
• Physical apparatus The Eye
• Anatomy of the eye (Fig 1.1, page 15)
• lens, retina, ganglion cells, rods cones.
• Blind spot.
• Fovea.
• Color brightness sensitivity.

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Interpreting the signal Size and depth

• Visual angle indicates how much of field of view
  object occupies (relates to size and distance
  from eye).
• Visual acuity is ability to perceive fine detail
  (limited).
• Familiar objects perceived as constant size in
  spite of changes in visual anglelaw of size
  constancy.
• Cues like overlapping help perception of size and
  depth.

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Interpreting the signalBrightness

• Subjective reaction to levels of light
• Affected by luminance of object
• Measured by just noticeable difference
• Visual acuity increases with luminance as does
  flicker

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Interpreting the signal Color

• Made up of hue, intensity, saturation
• Cones sensitive to color wavelengths
• Blue acuity is lowest.
• 8 males and 1 females are color blind.

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Interpreting the signal (concluded)

• The visual system compensates for movement and
  changes in luminance.
• Context is used to resolve ambiguity.
• Optical illusions sometimes occur due to over
  compensation.

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Optical Illusions

• Page 21 in your text
• Figure 1 The Ponzo illusion
• Figure 2 The Muller Lyer illusion

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Reading

• Several stages
• visual pattern perceived
• decoded using internal representation of language
  
• interpreted using knowledge of syntax, semantics,
  pragmatics
• Reading involves saccades and fixations.
• Perception occurs during latter.
• Word shape is important to recognition.
• Negative contrast improves reading from computer
  screen.

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Hearing

• Provides information about environment
  distances, directions, objects etc.
• Physical apparatus
• outer ear --- protects inner and amplifies sound
• middle ear --- transmits sound waves as
  vibrations to inner ear
• inner ear --- chemical transmitters are released
  and cause impulses in auditory nerve

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Hearing (2)

• Sound characteristics
• pitch sound frequency
• loudness amplitude
• timbre type or quality

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Hearing (3)

• Humans can hear frequencies from 20Hz to 15kHz
  less accurate distinguishing high frequencies
  than low.
• Auditory system filters sounds can attend to
  sounds over background noise.
• Cocktail party phenomenon.

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Touch

• Provides important feedback about environment.
• May be key sense for someone who is visually
  impaired.
• Stimulus received via receptors in the skin
           thermoreceptors --- heat and cold
           nociceptors --- pain         
  mechanoreceptors --- pressure (some instant, some
  continuous)

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Touch (2)

• Some areas more sensitive than others.
• Fingertips,
• Foreams, back,
• Kinethesis --- awareness of body position
  affecting comfort and performance.

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Movement

• Time taken to respond to stimulus reaction time
  movement time.
• Movement time dependent on age, fitness etc.
  Reaction time dependent on stimulus type
           visual --- 200ms          auditory
  --- 150 ms          pain --- 700ms
• Increasing reaction time decreases accuracy in
  the unskilled operator but not in the skilled
  operator.

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Movement

• Fitts' Law describes the time taken to hit a
  screen target
• Mt a b log 2 (D/S 1)
• where a and b are empirically determined
  constants, Mt is movement time, D is Distance and
  S is Size.
• Guideline Targets in general should be large as
  possible and the distances as small as possible.

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End of Class

• Turn in Prerequisite sheets.
• Turn in green strip, agreeing to abide by the CS
  department policies, and the UA Honor Code.
• If you dont have the prerequisites for this
  class, drop it now, and make room for someone who
  does.