HumanComputer Interaction 6 User Models

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Human-Computer Interaction - 6User Models

• Gary Marsden
• (gaz_at_cs.uct.ac.za)
• July 2002

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Unit Objectives

• We shall cover
• GOMS
• ICS
• Rationale
• We need to reason about what types of tasks users
  are good at and predict the impact of design
  decisions on the user
• User models allow us to do that without building
  prototypes for testing

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What is User Modelling

• Last time we looked at the tasks of the wider
  system
• Now we want to look inside the users head to
  have some idea of how users are likely to
  interact with the system
• We shall look at GOMS ICS

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GOMS

• Stands for Goals, Operators, Methods and
  Selection rules
• Derived from studying humans as information
  processors Model Human Processor
• Comprised of
• Processors, Memories Principles
• Combine to form systems
• Perceptual, cognitive, motor

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MHP Overview
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Back to GOMS

• Goals are what people want to do
• Like tasks in HTA
• Operators are atomic perceptual, motor or
  cognitive acts which are necessary to change
  users mental state or environment
• As such they are the lowest level of a GOMS
  analysis
• Using GOMS a users behavior can be recorded as a
  sequence of operators as operators cant occur
  concurrently.

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Example Operation

• For example, to move a file to a different folder
  the user might perform the following operations
• Move cursor to item
• Hold mouse button down
• Locate destination icon
• Let go of mouse button

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Methods

• Sequence of operators can have sub-methods
• Assumption is that methods are learnt and are
  routine (no processing required)
• For example, a user moving a file to a different
  folder could be described in GOMS as
• Goal move file to a different folder
• Method move file
• Operators - Move cursor to item, Hold mouse
  button down, Locate destination icon, Let go of
  mouse button

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Selection Rules

• Used to select between alternative methods to
  achieve a given goal
• Kind of like a bunch of if..then..else statements
• Goal - print current document
• IF (toolbar visible) THEN click toolbar button
• ELSE type CTRL-P

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Keystroke Level Model

• The lowest level of GOMS is called the KLM
• Used to predict task completion times for skilled
  operators
• Each task described as 5 physical-motor
  operators
• Tk (k)eying how long it takes to press a key
  (including using modifiers such as the shift key)
• Tp (p)ointing how long it takes to move the
  mouse (or other such input device) to a target
• Th (h)oming how long it takes to change
  between input devices e.g. changing between mouse
  and keyboard
• Td (d)rawing how long it takes to draw a line
  using an input such as a mouse
• Tb click (b)utton how long it takes to click
  the mouse button

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Mental operators

• Beside the motor operators there are
• Tm (m)ental operator how long it takes to
  perform the mental processing for the task
• Tr system (r )esponse operator how long the
  system takes to respond
• Consider an example we want to change
• The quick fox jumps over the lazy dog
• To
• The quick brown fox jumps over the lazy dog

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KLM example

• move hand to mouse H (mouse)
• position mouse just after quick P,B
• move hand to keyboard H(keyboard)
• formulate word to insert M
• type brown K (b) K (r) K (o) K (w) K (n) K (
  )
• reposition insertion point at end of sentence
  H (mouse), M, P, B
• Total time is 3Th 2Tp 2Tb 2Tm 6Tk

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Absolute Time

• To calculate a real time, you can observe the
  users
• or use the KLM estimates
• Operators Time (s)
• Tk 0.12
• Tp 1.10
• Th 0.40
• Td 1.06
• Tb 0.20
• Tm 1.35

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GOMS ATMs

• GOAL GET-MONEY
• GOAL USE-ATM
• INSERT-CARD
• ENTER-PIN
• ENTER-AMOUNT
• COLLECT-MONEY
• COLLECT-CARD

• Closure
• Having achieved a task, your brain is satisfied
  and clears up memory for the next task

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GOMS summary

• Designed for expert users performing routine
  tasks
• Gives insight into time to complete task
• Can prove very useful in the correct situation
• Telephone company
• Not a widely applicable tool though

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Interacting Cognitive Sub-systems

• ICS is an elaborate framework which assumes that
  human perception, cognition, and action can be
  analysed in terms of discrete, inter-linked,
  information processing modules
• In contrast to GOMS, ICS is a much richer way of
  modelling human cognition as we shall see in this
  section

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ICS components

• ICS assumes three independent sub-systems
• sensory visual and auditory stimulus
• representational representations of information
• effector body movement
• Each subsystem has
• One input
• One or more outputs
• Memory
• Transformations

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Example - Perception

• Here input (lines) is percieved
• Transformed to a recognised shape
• Shape stored in memory for later use

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Full system

• The real power comes from seeing the cognitive
  load placed on the user completing a task.

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Summary

• We have looked at
• GOMS a system for predicting expert user
  performance
• ICS an example of a more complex user model