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  1. This slide contains information in Note View. Switch to note view and print all of these out. • Be sure to set your printer to black and white. • You may need to change fonts if we have used some that you do not have (or if your printer or computer does funny things to our slides)

  2. Cognitive Analysis of Dynamic Performance: Cognitive process analysis and modeling Workshop Presented at the HFES/IEA-2000 Conference in San Diego, CA Wayne D. Gray, Ph.D. Deborah A. Boehm-Davis, Ph.D.

  3. Outline of Workshop • Intro to the GOMS family of models • Keystroke Level GOMS • NGOMSL GOMS • CPM-GOMS REVISED Tutorial Materials may be downloaded from: http://hfac.gmu.edu/~graypubs

  4. Definition of GOMS • Characterization of a task in terms of • The user's Goals • The Operators available to accomplish those goals • Methods (frequently used sequences of operators and sub-goals) to accomplish those goals, and • If there is more than one method to accomplish a goal, the Selection rules used to choose between methods.

  5. What GOMS Is • GOMS is a task analysis technique • Very similar to Hierarchical Task Analysis (Indeed, GOMS is a hierarchical task analysis technique) • Hard part of task analysis is goal-subgoal decomposition • Hard part of GOMS is goal-subgoal decomposition • Different members of the GOMS family provide you with different sets of operators • With established parameters • But set is not complete (extensionable)

  6. Where does GOMS go?(When do you need to do a CTA versus a TA?) • Task analysis versus cognitive task analysis? • What distinguishes GOMS cognitive task analysis from other task analysis techniques? • E.g., Cognitive Task Analysis™

  7. TASK ANALYSIS

  8. Time Scale for GOMS Levels of analysis (based on Newell’s Time Scale of Human Action)

  9. Level 1: Task Analysis: Task  Subtasks  Subtasks 

  10. Levels of analysis (based on Newell’s Time Scale of Human Action)

  11. Level 2: Subtask  Unit Tasks

  12. Levels of analysis (based on Newell’s Time Scale of Human Action)

  13. Classified? Level 3: Cognitive Task Analysis: Unit Tasks  Activities

  14. Levels of analysis (based on Newell’s Time Scale of Human Action)

  15. Level 4: Embodied Cognition: Activity  Microstrategy http://hfac.gmu.edu/~mm

  16. Levels of analysis (based on Newell’s Time Scale of Human Action)

  17. Level 5: Microstrategies  Elements(Where GOMS doesn’t go!) • Production Rules • Declarative memory elements • Internal (created on RHS of production rules) • External (created by shifts of attention in the external environment)

  18. Levels of analysis (based on Newell’s Time Scale of Human Action)

  19. Level 6: Elements  Parameters(GOMS doesn’t go here either!) • w -- amount of attentional capacity • d -- decay rate • s -- fluctuations in the strength of declarative memory elements • rt -- retrieval threshold

  20. KR not KE • GOMS (as with most task analysis methods) focuses on • Knowledge representation, not on • Knowledge elicitation • There are many sources of knowledge elicitation techniques

  21. Task Analysis versus Functionality • A task analysis does not guarantee functionality, see Kieras, D. E. (in press). Task analysis and the design of functionality, CRC Handbook of Computer Science and Engineering.: CRC Press, Inc. for a cogent discussion of this issue

  22. Definition of GOMS • Characterization of a task in terms of • The user's Goals • The Operators available to accomplish those goals • Methods (frequently used sequences of operators and sub-goals) to accomplish those goals, and • If there is more than one method to accomplish a goal, the Selection rules used to choose between methods.

  23. Example of G-O-M-S • To carry out a GOMS analysis of the following task involving a digital clock: • Set the clock • Top level goal: SET CLOCK

  24. Example of G-O-M-S: Goals Goals and subgoals

  25. Example of G-O-M-S: Operators Operators are the most elementary steps in which you choose to analyze the task. • Reach <type> button • Hold <type> button • Release <type> button • ClickOn <type> button • Decide: if <x> then <y> • Verify

  26. Example of G-O-M-S: Methods • Top-level user goals SET-CLOCK • Method for goal: SET-CLOCK Step 1. Hold TIME button Step 2. Accomplish goal: SET-HOUR Step 3. Accomplish goal: SET-MIN Step 4. Release TIME button Step 5. Return with goal accomplished • Method for goal: SET-<digit> Step 1. ClickOn <digit> button Step 2. Decide: If target <digit> = current <digit>, then return with goal accomplished Step 3. Goto 1

  27. Example of G-O-M-S: Selection rules • No selection rules in this example as this clock has only ONE method for accomplishing each goal, but . . . Selection rule for goal: SET-HOUR If target HOUR ≤ 4 hours from current HOUR, then Accomplish Goal: ClickOn HOUR If target HOUR > 4 hours from current HOUR, then Accomplish Goal : Click&Hold HOUR

  28. Applications of GOMS Case 1. Design of mouse-driven text editor Case 2. Directory assistance workstation Case 3. Space operations database system (for orbital objects) Case 4. Bank deposit reconciliation system. Case 5. CAD system for mechanical design. Case 6. Television control system. Case 7. Nuclear power plant operator's associate. Case 8. Intelligent tutoring system. Case 9. Industrial scheduling system. Case 10. CAD system for ergonomic design. Case 11. Telephone operator workstation. List compiled by John & Kieras (1997a).

  29. Where does GOMS go?

  30. Development process without analytic modeling

  31. Development process with analytic modeling

  32. GOMS as Analytic Modeling • GOMS analysis produces a model of behavior • Given a task, the model predicts the methods, or sequences of operators, that a person will perform to accomplish that task • Can look at the GOMS model in different ways to qualitatively and quantitatively assess different types of performance

  33. Scope of GOMS: What it can do • Predict the sequence of operators an expert will perform • Predict performance time of expert users - even in real-world situations • Predict learning time in relatively simple domains • Predict savings due to previous learning • Help design on-line help and manuals

  34. Scope of GOMS: What it can do, con’t • GOMS has been applied to both: • User-driven interaction • “Situated” or event-driven interaction

  35. Scope of GOMS:What it might be able to do • Research has made progress on • Predicting the number of some types of errors • see discussion in: Gray, W. D. (2000). The nature and processing of errors in interactive behavior. Cognitive Science, 24(2), 205-248. • Predicting the effects of display layout on performance time

  36. Scope of GOMS: What it can't do • Predict problem-solving behavior • Predict how GOMS structure grows from user experience • Predict behavior of casual users, individual differences... • Predict the effects of fatigue, user preference, organizational impact...

  37. General Factors to Considerin GOMS Models • When deciding what type of GOMS model you need, you must consider... • what control structure • what level of analysis • whether to approximate behavior with serial or parallel processes • ...different uses of GOMS models lead to different values of these factors • These factors will be a recurring theme

  38. GOMS Family of Analysis Methods Keystroke-Level Model CMN-GOMS NGOMSL CMN-GOMS for Highly Interactive Tasks CPM-GOMS = “worked example” provided in this HFES workshop

  39. Break time

  40. 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

  41. Keystroke-Level Model: Example • TAO example

  42. 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

  43. 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

  44. 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.

  45. 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

  46. 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

  47. 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.

  48. 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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