1 Rensselaer Cognitive Science 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

2 Rensselaer Cognitive Science Keystroke-Level Model: Example TAO example

3 Rensselaer Cognitive Science 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

4 Rensselaer Cognitive Science 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

5 Rensselaer Cognitive Science 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.

6 Rensselaer Cognitive Science 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

7 Rensselaer Cognitive Science 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

8 Rensselaer Cognitive Science 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 anticipated 1 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.

9 Rensselaer Cognitive Science 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 anticipated 1 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 ?

10 Rensselaer Cognitive Science 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 anticipated 1 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

11 Rensselaer Cognitive Science 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 anticipated 1 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.

12 Rensselaer Cognitive Science 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

13 Rensselaer Cognitive Science 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 anticipated 1 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.

14 Rensselaer Cognitive Science KLM--mentals: example 1. Example: SET COLUMN WIDTH 5 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( ) RULE 1  no change in this example RULE 2  M+17K(set_column_width_)+1K(5)+M+1K( ) RULE 3  No change in this example Rule 4  No change in this example

15 Rensselaer Cognitive Science 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

16 Rensselaer Cognitive Science 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?

17 Rensselaer Cognitive Science 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

18 Rensselaer Cognitive Science Keystroke-Level Model: m1 current Step 3: select the operators and durations that will be used  We will use the ones from Kieras (1993).

19 Rensselaer Cognitive Science Keystroke-Level Model: m1 current Step 4: List the times next to the physical operators for the task.

20 Rensselaer Cognitive Science 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)

21 Rensselaer Cognitive Science 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.

22 Rensselaer Cognitive Science Keystroke-Level Model: m2 bs/delete Step 4: List the times next to the physical operators for the task.

23 Rensselaer Cognitive Science Keystroke-Level Model: m2 bs/delete Step 5: Next add the mental operators and their times Step 6: Sum the times of the operators

24 Rensselaer Cognitive Science 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.

25 Rensselaer Cognitive Science Keystroke-Level Model: m3 bkup/delete Step 4: List the times next to the physical operators for the task.

26 Rensselaer Cognitive Science 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-deleteNUMop typetime press reset function keyfCCN1K0.28 backup to digitbkup9K2.52 delete digitdel1K0.28 digits to retypedigit1K0.28 outpulse new num to dbaseenter1K0.28 total time

27 Rensselaer Cognitive Science Keystroke-Level Model: m3 bkup/delete Step 5: KLM w/mentals.

28 Rensselaer Cognitive Science 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.

29 Rensselaer Cognitive Science 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-gpNUMop typetime total time

30 Rensselaer Cognitive Science 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-gpNUMop typetime press reset function keyfCCN1K0.28 zap-groupzap1K0.28 digits to retypedigit3K0.84 outpulse new num to dbaseenter1K0.28 total time

31 Rensselaer Cognitive Science Keystroke-Level Model: m4 zap-gp Step 5: KLM model w/mentals

32 Rensselaer Cognitive Science Keystroke-Level Model: Summary Of the three new methods, only one seems likely to be fast enough to justify expense of redesign