The Essential Role of Mental Models in HCI: Card, Moran and Newell Papers: Kate Ehrlich, Lorin Hochstein

Introduction Example Three blind men Query : Visualize a horse? Attributes and Operations Horse ( Four legs, people can ride to move from point A to B. Rider has controls to change direction, needs to be fed etc.)

Mental Model An explanation in someone’s thought process for how something works in the real world Internal symbol or representation of external reality Mostly Kids Originated by Kenneth Craik 1943. “The nature of Explanation” Part of Cognition Science

Mental Models & HCI New research based Mental models for computer systems Interface designer started using Mental Model Build computers Mental Model Card, Moran and Newell (1983) – “The Psychology of Human-Computer Interaction” “Our purpose in this book is to help lay a scientific foundation for an applied psychology concerned with the human users of interactive computer systems. Although modern cognitive psychology contains a wealth of knowledge of human behavior, it is not a simple matter to bring this knowledge to bear on the practical problems of design – to build an applied psychology that include theory, data and methodology.”

HCI Metal Model Types Cognitive Science - Metal Models abstract representation HCI - More concrete Types of Models in HCI The actual Model of the System The engineer Model of the System Drives technical design and implementation UI designer’s model of the System The user Model of the system

GOMS In HCI - provide a theory of the user’s representation of the system as well as its construction. According to Card et al - mental model not only be theoretical grounded but also be testable. They came up with Model - GOMS G O M S Goals Operators Methods Selection rules

GOMS - Goals Goals are what the user is trying to accomplish Various levels of abstraction, Very high-level goals (e.g. WRITE-RESEARCH-PAPER) low-level goals (e.g. DELETE-WORD). Higher-level goals are decomposable into sub goals, and are arranged hierarchically

GOMS - Operators Operators are the actions that systems let user to perform. e.g. DOUBLE-CLICK-MOUSE, PRESS-INSERT-KEY, other keyboard commands etc. Used to accomplish the goals Atomic elements in the GOMS model. Operators are not decomposable Assumption - Operator requires a fixed time (e.g. CLICK-MOUSE button takes 0.20 seconds to execute).

GOMS - Methods Sequence of sub-goals and operators to achieve a goal For example Goal - DELETE-WORD MOVE-MOUSE to the beginning of the word, and PRESS-ALT-D-KEY-COMBINATION (the use-mouse-delete-word method). Use arrow keys to reach the beginning of the word (the use-arrows-delete-word method). Algorithm that determines the sequence of sub-goals and operators

GOMS – Selection Rules Goals could have multiple methods Which method should be used? E.g. instead of using mouse to select the text for deletion, the user could use the keyboard arrows. Represent the user's knowledge A conditional statement "if the word to be deleted is less than 3 lines away from the current cursor location, then use the use-arrows-delete-word-method, else use the use-mouse-delete-word method".

Keystroke-Level Model - KLM Simplified version of GOMS (Card & Moran - 1980) Method to predict user performance Estimate execution time by listing the sequence operators and then summing the time of individual operator Aggregates all the perceptual and cognitive function into a single value for entire task, using a heuristic Does not employ selection rules. Six Classes of operators K : Pressing a Key P : Pointing to a location on screen with mouse. H : Moving hands to Home position on the keyboard M : Mentally preparing to perform an action R : System Response

Example - KLM Consider the text editing task of searching a Microsoft Word document for all occurrences of a four-letter word, and replacing it with another four-letter word According to this KLM model, it takes 10.2 seconds to accomplish this task

Example - KLM Description Operation Time (sec) Total 10.2 Reach for mouse H [mouse] 0.40 Move pointer to “Replace” button P [menu item] 1.10 Click on “Replace” command K [mouse] 0.20 Home on keyboard H [keyboard] Specify word to be replaced M4K [word] 2.15 Point to correct field P [field] Click on field H [Keyboard] Type new word Move pointer on Replace-all P [replace-all] Total 10.2

Example 2 - GOMS This example is taken from John & Kieras (1996). It models the task of moving text in a Word processor, in the context of editing a manuscript. Use of sub-goals and selection rules, which do not exist in KLM

Example 2 - GOMS GOAL: EDIT-MANUSCRIPT . GOAL: EDIT-UNIT-TASK ... repeat until no more unit tasks . . GOAL: ACQUIRE UNIT-TASK . . . GOAL: GET-NEXT-PAGE ... if at end of manuscript page . . . GOAL: GET-FROM-MANUSCRIPT . . GOAL: EXECUTE-UNIT-TASK ... if a unit task was found . . . GOAL: MODIFY-TEXT . . . . [select: GOAL: MOVE-TEXT* ...if text is to be moved . . . . GOAL: DELETE-PHRASE ...if a phrase is to be deleted . . . . GOAL: INSERT-WORD] ... if a word is to be inserted . . . . VERIFY-EDIT

* Expansion of MOVE-TEXT goal GOAL: MOVE-TEXT . GOAL: CUT-TEXT . . GOAL: HIGHLIGHT-TEXT . . . [select**: GOAL: HIGHLIGHT-WORD . . . . MOVE-CURSOR-TO-WORD . . . . DOUBLE-CLICK-MOUSE-BUTTON . . . . VERIFY-HIGHLIGHT . . . GOAL: HIGHLIGHT-ARBITRARY-TEXT . . . . MOVE-CURSOR-TO-BEGINNING 1.10 . . . . CLICK-MOUSE-BUTTON 0.20 . . . . MOVE-CURSOR-TO-END 1.10 . . . . SHIFT-CLICK-MOUSE-BUTTON 0.48 . . . . VERIFY-HIGHLIGHT] 1.35 . . GOAL: ISSUE-CUT-COMMAND . . . MOVE-CURSOR-TO-EDIT-MENU 1.10 . . . PRESS-MOUSE-BUTTON 0.10 . . . MOVE-CURSOR-TO-CUT-ITEM 1.10 . . . VERIFY-HIGHLIGHT 1.35 . . . RELEASE-MOUSE-BUTTON 0.10

. GOAL: PASTE-TEXT . . GOAL: POSITION-CURSOR-AT-INSERTION-POINT . . MOVE-CURSOR-TO-INSERTION-POIONT 1.10 . . CLICK-MOUSE-BUTTON 0.20 . . VERIFY-POSITION 1.35 . . GOAL: ISSUE-PASTE-COMMAND . . . MOVE-CURSOR-TO-EDIT-MENU 1.10 . . . PRESS-MOUSE-BUTTON 0.10 . . . MOVE-MOUSE-TO-PASTE-ITEM 1.10 . . . VERIFY-HIGHLIGHT 1.35 . . . RELEASE-MOUSE-BUTTON 0.10 TOTAL TIME PREDICTED (SEC) 14.38 Based on the above GOMS analysis, it should take 14.38 seconds to move text.

Evaluation Theoretical foundation of HCI Force to practice of interface design and usability testing Basic theory of building tools for HCI researcher and practitioners to build models of human behavior UI design standards and design guidelines Look and feel

Limitations Predictions are only valid for expert users Experts user can do mistakes GOMS does not take into account novices No other metric beside execution time GOMS has also been criticized for not being representative of current theories of human cognition. An engineering heuristic, rather than an accurate model of cognitive processes.