An Overview of the

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An Overview of the H in HCI

• laura leventhal

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Reference

• Chapter 14

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Overview

• This lecture is a whirlwind tour of some of the
  important psychological characteristics of people
  that impacts HCI.

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Psycholgy and UI Design

• Goal of UI design is to improve efficiency and
  effectiveness of user performance
• Improving usability
• Accommodating user characteristics
• Support user tasks

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What Can We Learn (quickly) from Psychology?

• We need a cognitive model of the user that will
  help us predict the way that a user will react to
  an interface or situation
• The model will help us to explain why a user
  reacted the way they did.

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Example

• Psychological Fact
• Humans are limited in their capacity to process
  information
• We say that cognitive resources are limited

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HCI Consequence

• Want to limit resources that users spend on
  operational tasks.
• Want users to focus on functional tasks.

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Simple Model of a Cognition

• Thinking about what we know about (computers) can
  help us organize our model of cognition.
• Computers have structures for and support
• Input and Output
• Memory (storage)
• Processing
• Now can we apply the idea of a computer as an
  analogy to think about humans??

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Our Cognitive Model - Three Aspects

• Physiological structures and processes
• (i/o)
• Cognitive structures
• (storage)
• Cognitive processes
• (data processing)

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A Model of a Human Information Processor
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Sensation/Perception IO Channels

• Input Channels
• Sensors
• eyes, ears, touch, taste, smell, balance
  (proprioceptors)
• Output Channels
• Effectors
• limbs, fingers, eyes(where looking), head, vocal
  system

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Perception is often Parallel, Generation is Serial

• We are often able to take in multiple inputs and
  recognize them.
• Driving, talking on cell phone, recognizing
  instructions from street signs.
• Reading screen and hearing alarm sounds
• Generation of output tends to be more serial.
• Hear alarm, push button
• HCI Consequences
• We take in a number of inputs at once, even when
  some of the inputs are unrelated to the task at
  hand. So when we build an interface with lots of
  "extras", such as sounds and videos, we take
  those in, even as we are taking the task-related
  input in. It is very difficult to selectively
  close out some of these inputs, even if they are
  unrelated to the task. And, just like computer
  inputs, even the input from the "extras" requires
  processing.
• Because generation is more serial, we tend to
  produce (generate) activities more in sequence.

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Sensation/Perception Vision

• Vision is our most important input device.
• Brain structures reflect the importance of vision
  in cognition.
• For example, our brain structures would be
  different if we had monocular vision.
• Humans are drawn to looking at vistas. This
  preference pattern and others are built-in

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Sensation/Perception Vision

• Human visual perception is attuned to movement.
• HCI Consequence.
• Our vision is drawn to moving objects in a user
  interface.

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Sensation/Perception Vision

• Visual system is like a camera, different in some
  critical ways (from simple camera!)
• Eye is in a fixed position and the shape is
  distorted by various muscles.
• Light sensitivity varies across the retina. It
  is best in the center and worst at the edges.
• Two eyes permit depth perception.
• HCI Consequence.
• People can become fatigued when they receive
  visual input from a user interface. When it is
  likely that your user will become fatigued from
  visual input, consider having an alternative
  presentation modality, such as audio.

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Sensation/Perception Vision

• Color is increasingly important in HCI.
• Color perceptions are subject to fatigue.
• We are sensitive to flickering lights

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Sensation/Perception Vision

• Visual Ability Declines with Age
• Vision is an ability that declines with age,
  despite the common belief that most human
  abilities do not decline with age.
• For example, a persons perception of color may
  change. Disorders such as macular degeneration
  and glaucoma severely limit what a person is able
  to see.
• HCI Consequence.
• When designing for users who include persons of
  all ages, be sure to accommodate some of the
  specific changes which come with age

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Sensation/Perception Vision

• Visual processing involves transformation and
  interpretation
• What we "see" is affected by what we know and
  what we expect and the context
• Overhead A

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Sensation/Perception Vision

• Gestalt Principles guide our vision system to
  make images whole
• proximity
• similarity
• continuation
• Closure
• HCI consequence.
• We tend to "fill in" or "finish" a pattern even
  if it is incomplete.

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Sensation/Perception Vision

• Reading
• We see a visual pattern
• whole words or phrases, morphemes, syntax,
  semantics
• Overhead B
• HCI Consequence
• If we disrupt "normal" patterns of words, with
  strange combinations of font types and sizes for
  example, it is difficult to read because we see
  individual characters rather than patterns of
  characters.

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Sensation/Perception Hearing

• We are constantly bombarded with sound
• We use selective attention to filter through the
  sounds.
• Cocktail party phenomena -
• We can hear our name across a room
• HCI Consequence.
• Use alarms sparingly and when appropriate.

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Sensation/PerceptionTouch

• Use touch to provide feedback
• 3 types of touch receptors
• heat/cold
• intense pressure, heat, pain
• Pressure

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A little bit about output

• Next two slides overview the relationship between
  hand movements and performance as predicted by
  Fitts Law

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Fitts Law

• Moving hand is a series of small discrete
  movements and corrections
• Each small movement takes 240 msec
• Time T to move hand to target of size S which is
  distance D away
• T 100 msec log2(D/S .5)
• Time to move hand depends on the relative
  precision needed (D/S)
• Fitts law used to demonstrate for a small number
  of choices (low precision) a pie menu is faster
  than a linear menu.

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