Gary MarsdenSlide 1University of Cape Town Human-Computer Interaction - 6 User Models Gary Marsden ( ) July 2002

Gary MarsdenSlide 2University of Cape Town 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

Gary MarsdenSlide 3University of Cape Town What is User Modelling  Last time we looked at the tasks of the wider system  Now we want to look inside the user’s head to have some idea of how users are likely to interact with the system –We shall look at GOMS & ICS

Gary MarsdenSlide 4University of Cape Town 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

Gary MarsdenSlide 5University of Cape Town MHP Overview

Gary MarsdenSlide 6University of Cape Town 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 user’s mental state or environment  As such they are the lowest level of a GOMS analysis –Using GOMS a user’s behavior can be recorded as a sequence of operators as operators can’t occur concurrently.

Gary MarsdenSlide 7University of Cape Town 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

Gary MarsdenSlide 8University of Cape Town 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

Gary MarsdenSlide 9University of Cape Town 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

Gary MarsdenSlide 10University of Cape Town 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

Gary MarsdenSlide 11University of Cape Town 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

Gary MarsdenSlide 12University of Cape Town KLM example 1.move hand to mouse – H (mouse) 2.position mouse just after ‘quick’ – P,B 3.move hand to keyboard – H(keyboard) 4.formulate word to insert – M 5.type ‘brown’ – K (b) K (r) K (o) K (w) K (n) K ( ) 6.reposition insertion point at end of sentence – H (mouse), M, P, B Total time is: 3Th + 2Tp + 2Tb + 2Tm + 6Tk

Gary MarsdenSlide 13University of Cape Town Absolute Time  To calculate a real time, you can observe the users…  … or use the KLM estimates –OperatorsTime (s) –Tk0.12 –Tp1.10 –Th0.40 –Td1.06 –Tb0.20 –Tm1.35

Gary MarsdenSlide 14University of Cape Town GOMS & ATMs –GOAL: GET-MONEY GOAL: USE-ATM –INSERT-CARD –ENTER-PIN –ENTER-AMOUNT –COLLECT-MONEY –COLLECT-CARD Task completed at this point, so users stop  Closure –Having achieved a task, your brain is satisfied and clears up memory for the next task

Gary MarsdenSlide 15University of Cape Town 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

Gary MarsdenSlide 16University of Cape Town 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

Gary MarsdenSlide 17University of Cape Town 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

Gary MarsdenSlide 18University of Cape Town Example - Perception  Here input (lines) is percieved  Transformed to a recognised shape  Shape stored in memory for later use

Gary MarsdenSlide 19University of Cape Town Full system  The real power comes from seeing the cognitive load placed on the user completing a task.

Gary MarsdenSlide 20University of Cape Town Summary  We have looked at –GOMS: a system for predicting expert user performance –ICS: an example of a more complex user model