1 Rensselaer Cognitive Science Keystroke-Level Model: Intro The simplest of all GOMS models: OM...
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Transcript of 1 Rensselaer Cognitive Science Keystroke-Level Model: Intro The simplest of all GOMS models: OM...
1 RensselaerCognitiveScience
Keystroke-Level Model: Intro
The simplest of all GOMS models: OM only!!!
No explicit goals or selection rules
Operators and Methods (in a limited sense) only
“Useful where it is possible to specify the user’s interaction
sequence in detail” (CMN83, p. 259).
Control structure: Flat
Serial or Parallel: Serial
Level of Analysis: Keystroke-level operators
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area code exchange line pin1 2 3 4 5 6 7 8 9 10 11 12 13 14
num 7 0 3 9 9 3 1 3 5 7 1 2 3 4
Keystroke-Level Model: Example
TAO example
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Keystroke-Level Model: Overview
Step 1: Lay out assumptions
Step 2: Write out the basic action sequence (list the keystroke-
level physical operators involved in doing the task)
Step 3: Select the operators and durations that will be used
Step 4: List the times next to the physical operators for the task
Step 4a: If necessary, include system response time operators
for when the user must wait for the system to respond
Step 5: Next add the mental operators and their times
Step 6: Sum the times of the operators
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Keystroke-level Model: Operators
K: Keystroke
T(n): Type a sequence of n characters on a keyboard
P: Point with mouse to a target on a display
B: Press or release mouse button
BB: Click mouse button
H: Home hands to keyboard or mouse
M: Mental act of routine thinking
W(t): Waiting time for system to respond
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Card, Moran, and Newell on “Mentals”
“M operations represent acts of mental preparation for applying
physical operations. Their occurrence does not follow directly
from the physical encoding, but from the specific knowledge
and skill of the user” p. 267
“The rules for placing M’s embody psychological assumptions
about the user and are necessarily heuristic, especially given
the simplicity of the model” p. 267.
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Heuristics for inserting mental operators
Basic psychological principle: physical operations in methods are chunked into submethods.
RULE 0: Insert M’s in front of all K’s or B’s that are not part of argument strings proper (e.g., text or numbers). Place M’s in front of all P’s that select commands (not arguments) or that begin a sequence of direct-manipulation operations belonging to a cognitive unit.
•Pointing to a cell on a spreadsheet is pointing to an argument -- no M•Pointing to a word in a manuscript is pointing to an argument -- no M•Pointing to a icon on a toolbar is pointing to a command -- M•Pointing to the label of a drop-down menu is pointing to a command -- M
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Heuristics for inserting mental operators
Rules 1-4 are heuristics (rules of thumb) for deleting
mentals “A single psychological principle lies behind all the deletion
heuristics . . . physical operations in methods are chunked into
submethods” p. 268
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Heuristics for inserting mental operators
Basic psychological principle: physical operations in methods are chunked into submethods.
RULE 0: Insert M’s in front of all K’s or B’s that are not part of argument strings proper (e.g., text or numbers). Place M’s in front of all P’s that select commands (not arguments) or that begin a sequence of direct-manipulation operations belonging to a cognitive unit.
RULE 1: If an operator following an M is fully anticipated1 in an operator just previous to M, then delete the M (e.g., PMK --> PK or PMBB --> PBB).
•That is, the “M” drops out because the “P” and “BB” belong together in a chunk -- mental unit.•The button press “BB” is fully anticipated as the cursor is being moved to the target.
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Heuristics for inserting mental operators
Basic psychological principle: physical operations in methods are chunked into submethods.
RULE 0: Insert M’s in front of all K’s or B’s that are not part of argument strings proper (e.g., text or numbers). Place M’s in front of all P’s that select commands (not arguments) or that begin a sequence of direct-manipulation operations belonging to a cognitive unit.
RULE 1: If an operator following an M is fully anticipated1 in an operator just previous to M, then delete the M (e.g., PMK --> PK or PMBB --> PBB).
RULE 2: If a string of MK’s or MB’s belongs to a cognitive unit (e.g., the name of a command), then delete all M’s but the first.
•Works with command names -- but what is a command name in a GUI interface?
•Physical actions: P(File)+ B + P(Save) + B•RULE 0: MP + MB + MP + MB•RULE 1: MPB + MPB•Does rule 2 apply to eliminate the middle mental? MPBPB ?
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Heuristics for inserting mental operators
Basic psychological principle: physical operations in methods are chunked into submethods.
RULE 0: Insert M’s in front of all K’s or B’s that are not part of argument strings proper (e.g., text or numbers). Place M’s in front of all P’s that select commands (not arguments) or that begin a sequence of direct-manipulation operations belonging to a cognitive unit.
RULE 1: If an operator following an M is fully anticipated1 in an operator just previous to M, then delete the M (e.g., PMK --> PK or PMBB --> PBB).
RULE 2: If a string of MK’s or MB’s belongs to a cognitive unit (e.g., the name of a command), then delete all M’s but the first
RULE 3: If a K is a redundant terminator (e.g., the terminator of a command immediately following the terminator of its argument), then delete the M in front of it.
•Applies to clicking OKAY in dialog buttons after you select a command; e.g., in Powerpoint, you have selected text, gone to the FORMAT:FONT palette, clicked on bold, and now point and click on OKAY -- pointing to and clicking on OKAY is PBB, not MPBB
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Heuristics for inserting mental operators
Basic psychological principle: physical operations in methods are chunked into submethods.
RULE 0: Insert M’s in front of all K’s or B’s that are not part of argument strings proper (e.g., text or numbers). Place M’s in front of all P’s that select commands (not arguments) or that begin a sequence of direct-manipulation operations belonging to a cognitive unit.
RULE 1: If an operator following an M is fully anticipated1 in an operator just previous to M, then delete the M (e.g., PMK --> PK or PMBB --> PBB).
RULE 2: If a string of MK’s or MB’s belongs to a cognitive unit (e.g., the name of a command), then delete all M’s but the first
RULE 3: If a K is a redundant terminator (e.g., the terminator of a command immediately following the terminator of its argument), then delete the M in front of it.
RULE 4: If a K terminates a constant string (e.g., a command name), then delete the M in front of it; but if the K terminates a variable string (e.g., an argument string), then keep the M in front of it.
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Heuristics for inserting mental operators
The four heuristics do NOT capture the notion of
method chunks precisely -- these are only
approximations
Ambiguities: Is something “fully anticipated” or is
something else a “cognitive unit”?
Much of this ambiguity stems from variations in
expertise of the users we are modeling
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Heuristics for inserting mental operators
Basic psychological principle: physical operations in methods are chunked into submethods.
RULE 0: Insert M’s in front of all K’s or B’s that are not part of argument strings proper (e.g., text or numbers). Place M’s in front of all P’s that select commands (not arguments) or that begin a sequence of direct-manipulation operations belonging to a cognitive unit.
RULE 1: If an operator following an M is fully anticipated1 in an operator just previous to M, then delete the M (e.g., PMK --> PK or PMBB --> PBB).
RULE 2: If a string of MK’s or MB’s belongs to a cognitive unit (e.g., the name of a command), then delete all M’s but the first
RULE 3: If a K is a redundant terminator (e.g., the terminator of a command immediately following the terminator of its argument), then delete the M in front of it.
RULE 4: If a K terminates a constant string (e.g., a command name), then delete the M in front of it; but if the K terminates a variable string (e.g., an argument string), then keep the M in front of it.
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KLM--mentals: example 1.
Example: SET COLUMN WIDTH 5<cr>
List the keystroke level physical operators involved in doing the task
KKKKKKKKKKKKKKKKKKK (19 K’s)
RULE 0
M+KKKK+M+KKKKKKK+M+KKKKKK+K+M+K or
M+4K(set_)+M+7K(column_)+M+6K(width_)+1K(5)+M+1K(<cr>)
RULE 1 no change in this example
RULE 2
M+17K(set_column_width_)+1K(5)+M+1K(<cr>)
RULE 3 No change in this example
Rule 4 No change in this example
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KLM--mentals: example 2
Example: spellcheck “catelog”
List the keystroke level physical operators involved in doing the task P+BBBB+P+BB (where BB is a mousedown + mouseup, and BBBB is a
doubleclick)
RULE 0 P+M+BBBB+M+P+M+BB
RULE 1 P+BBBB+M+PBB
RULE 2 n/a (“catelog” + spellcheck do not form a cognitive unit)
RULE 3 n/a
RULE 4 n/a
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KLM--mentals: example 3
Example: save a file on a Mac using menus
List the keystroke level physical operators involved in doing the
task P+B+P+B
RULE 0 M+P+M+B+M+P+M+B
RULE 1 M+P+B+M+P+B
RULE 2 n/a or M+P+B+P+B ???
Issue: Is this FILE-->SAVE menu selection a single cognitive unit
or two?
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Keystroke-Level Model: m1 current
Step 1: Lay out your assumptions There are several fields on the display, first thing that any error
recovery method must do is to identify the field to be changed.
In this case the field is the calling-card field (CCN).
For purposes of this exercise, we assume the error is made in
the second number of the exchange.
TAO’s hands are on the keyboard
Step 2: Write out the basic action sequence (the
physical operators) ƒkey(ccn) + digit(14) + enterKey
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operator abbrev durationmental M 1200mseckeystroke-<key> K 280msecmouseDown or Up B 100msecclick (mouseD & Up) BB 200msechoming H 400mecpointing w/mouse P 1100msecdoubleClick BBBB 400msec
Keystroke-Level Model: m1 current
Step 3: select the operators and durations that will be
used We will use the ones from Kieras (1993).
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Method 1 of TAO task NUM op type timepress reset function keyfKEY(ccn) 1 K 0.28type digits digit 14 K 3.92outpulse new number to dbaseenter 1 K 0.28
total time 4.48
Keystroke-Level Model: m1 current
Step 4: List the times next to the physical operators
for the task.
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Method 1 of TAO task NUM op type timeM before cmd 1 M 1.20press reset function key fCCN 1 K 0.28type digits digit 14 K 3.92M terminates argument string 1 M 1.20outpulse new number to dbase enter 1 K 0.28
total time 6.88
Keystroke-Level Model: m1 current
Step 5: Next add the mental operators and their times
Step 6: Sum the times of the operators Predicted time for current method is 6.88 sec
(note: this time is the same regardless of “where” the error is
made)
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Keystroke-Level Model: m2 bs/delete
Step 1: Lay out your assumptions
s/a model 1 except;
delete key backs up and deletes each digit
Step 2: Write out the basic action sequence (the physical
operators)
ƒkey(ccn) + delKey(10) + digit(10) + enterKey
Step 3: Same operators as for model 1.
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Keystroke-Level Model: m2 bs/delete
Step 4: List the times next to the physical operators for the task.
Method 2: bs/delete NUM op type timepress reset function key fCCN 1 K 0.28bs/delete to digit delKey 10 K 2.80digits to retype digit 10 K 2.80outpulse new num to dbaseenter 1 K 0.28total time 6.16
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Keystroke-Level Model: m2 bs/delete
Step 5: Next add the mental operators and their times
Step 6: Sum the times of the operators
Method 2: bs/delete NUM op type timeM before cmd 1 M 1.20press reset function key fCCN 1 K 0.28bs/delete to digit delKey 10 K 2.80digits to retype digit 10 K 2.80verify done 1 M 1.20outpulse new num to dbase enter 1 K 0.28total time 8.56
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Keystroke-Level Model:m3 bkup/delete
Step 1: Lay out your assumptions
s/a model 1 except;
backup key backs up without deleting. Delete key backs up and
deletes
Step 2: Write out the basic action sequence (the physical
operators)
ƒkey(ccn) + bkupKey(9) + delKey(1) + digit(1) + enterKey
Step 3: Same operators as for model 1.
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Keystroke-Level Model: m3 bkup/delete
Step 4: List the times next to the physical operators for the task.
Method 3: bkup-delete NUM op type timepress reset function key fCCN 1 K 0.28backup to digit bkup 9 K 2.52delete digit del 1 K 0.28digits to retype digit 1 K 0.28outpulse new num to dbase enter 1 K 0.28total time 3.64
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Keystroke-Level Model: m3 bkup/delete
Step 5: Next add the mental operators and their times (Your turn!!!
Our answer are on the next page, no peeking!!!)
Method 3: bkup-delete NUM op type time
press reset function key fCCN 1 K 0.28
backup to digit bkup 9 K 2.52
delete digit del 1 K 0.28
digits to retype digit 1 K 0.28
outpulse new num to dbase enter 1 K 0.28
total time
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Keystroke-Level Model: m3 bkup/delete
Step 5: KLM w/mentals.
Method 3: bkup-delete NUM op type timeset up workstation to retype number 1 M 1.20press reset function key fCCN 1 K 0.28backup to digit bkup 9 K 2.52delete digit del 1 K 0.28digits to retype digit 1 K 0.28verify done 1 M 1.20outpulse new num to dbase enter 1 K 0.28total time 6.04
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Keystroke-Level Model: m4 zap-gp
Step 1: Lay out your assumptions
s/a model 1 except;
Four separate function keys, zaps (deletes) either area code,
exchange, line, or pin number. Retyping need only retype the
zapped numbers.
Step 2: Write out the basic action sequence (the physical
operators)
ƒkey(ccn) + zapExch(1) + digit(3) + enterKey
Step 3: Same operators as for model 1.
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Keystroke-Level Model: m4 zap-gp
Step 4: List the times next to the physical operators for the task.
Your turn!! (Our answer are on the next page, no peeking!!!)
Method 4: zap-gp NUM op type time
total time
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Keystroke-Level Model: m4 zap-gp
Step 5: Next add the mental operators and their times (Your
turn!!! Our answer are on the next page, no peeking!!!)
Method 4: zap-gp NUM op type time
press reset function key fCCN 1 K 0.28
zap-group zap 1 K 0.28
digits to retype digit 3 K 0.84
outpulse new num to dbase enter 1 K 0.28total time
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Keystroke-Level Model: m4 zap-gp
Step 5: KLM model w/mentals
Method 4: zap-gp NUM op type timeset up workstation to retype number 1 M 1.20press reset function key fCCN 1 K 0.28zap-group zap 1 K 0.28digits to retype digit 3 K 0.84verify done 1 M 1.20outpulse new num to dbase enter 1 K 0.28total time 4.08
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Keystroke-Level Model:
Summary
Of the three new methods, only one seems likely to be fast enough to justify expense of redesign
predicted timeMethod 1: Current 6.88Method 2: bs/delete 8.56Method 3: bkup-delete 6.04Method 4: zap-gp 4.08