GOMSKeystroke analysis

When (fine-grained) speed matters

Keystroke analysis

• K - keypress• P - point with mouse• C - click with mouse• H - home hands on new device• M - mentally prepare• R(t) - system response time

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Mental preparation:

• M before K/C or P except• MPMC ... becomes just … • MPC because C “anticipated”– e.g. move mouse to target and click

• MKMKMK ... MKKK for cognitive unit– e.g. type “thanks”

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Example task:The user has been typing “The

cat sat on the mat” using a word processor and they realise that

had intended to type "the cat" in bold.

Based on an example fromNewman and Lamming. Interactive system design. Reading: Addison-Wesley, 1995.

Make "the cat" bold in "the cat sat on the mat”

• GOMS analysis helps a designer think about alternative designs for the interaction for tasks like this.

• Suppose designer is considering 2 methods:1. Mouse-based2. Keyboard only

• Why might these both make sense in general?• Why for expert users?

Make "the cat" bold in "the cat sat on the mat”

• Task analysis:• Subtasks:

1. Get to the part of the text where “the cat” is2. Select “the cat”3. Make it bold

• We will consider a fairly typical word processor interface where subtasks 1 and 2 are common for the mouse-based and key-board shortcut.

Make "the cat" bold in "the cat sat on the mat”

GOMS mapping:Goal - to make "the cat" boldOperations - keystrokes, pointing, clicksMethods

1. mouse/menu based method2. keyboard shortcut

Selection rules– How to chose which method?– Which is faster for expert user?– Under what conditions?

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Subtasks 1 and 2 to select “the cat” • Subtask 1: Get to the part of the text where “the cat” is• H - Reach for mouse • M - mentally prepare• P - Point to the the precise position, just left of "the”• Subtask 2: Select “the cat”• C - Click mouse down and hold• R – see cursor is at the right place• M - mentally prepare• P - Point to the precise position, just right of "cat”• R – see that the “the cat” is highlighted• C - Release mouse• HMP CRMPRC

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Now to subtask 3

Having now selected "the cat”,Make it bold

Method 1 – mouse/menu

M - mentally prepareP - Point to "Format" menuC - Click and holdR - see the menu appearM - mentally prepareP - Point to "Bold" menu itemR - see it is highlightedC - Release mouse to select itR – see the change to bold

MPCRMPRCR

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Method 2 - keyboard shortcut

M - mentally prepareK - Press and hold "Control"K - Press "B"K - Release "Control”R – see the change to bold

MKKKR

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Comparing the two methods• Keystroke analysis• Subtasks 1 and 2 (common)

– HMP CRMPRC• Subtask 3

– Method 1 (Mouse/Menu): MPCRMPRCR– Method 2 (Keyboard shortcut): MKKKR

• Which is faster?• (Often assume R=0 so it is shown in bold so you

can distinguish that)• We now need a way to calculate timing….

Keystroke and GOMS analysis so far

• Key elements:– Given a task, define the methods to be considered– For each method, define the sub-tasks– For each subtask, do the keystroke analysis

• For WIMP interfaces, the available methods are just this small set: – K - keypress– P - point with mouse– C - click with mouse– H - home hands on new device– M - mentally prepare– R(t) - system response time

• So far, we have done only a keystroke analysis…. GOMS timing analysis to come

• Keystroke analysis can be really useful in thinking through design options

Question:Consider the following task:A user is typing an essay on a desktop computer and

realises that they have just typed the word “formation” when they meant to type “information”.

Do a keystroke analysis of the following methods:1. backspace over the letters of “formation” and type the

word “information”2. use the mouse to move to just before the “f” and type

“in”, then move back to the end of “information”3. the vi sequence -- <esc>biin<esc><shift-a>

Preliminary note: the user was typing so we assume their hand are on the keyboard