1Fall 2004 6.831 UI Design and Implementation 1 Fall 2004 6.831 UI Design and Implementation 2 Suggested by Vikki ChouFall 2004 6.831 UI Design and Implementation 3 Fall 2004 6.831 UI Design and Implementation 4 ! Keystroke-level models GOMS CPM-GOMS2Fall 2004 6.831 UI Design and Implementation 5 Predictive evaluation uses an engineering model of human cognition to predict usability Model is abstract quantitative approximate estimated from user experiments 7 ± 2Fall 2004 6.831 UI Design and Implementation 6"# Don t have to build UI prototype Can compare design alternatives with no implementation whatsoever Don t have to test real live users Theory provides explanations of UI problems So it points to the areas where design can be improved User testing may only reveal problems, not explain themFall 2004 6.831 UI Design and Implementation 7$ %&' ($' ) Keystroke or mouse button press Point with mouse Draw straight line with mouse Home hands between mouse and keyboard Mentally prepareFall 2004 6.831 UI Design and Implementation 8$' " Encode a method as a sequence of physical operators (KPHD) Use heuristic rules to insert mental operators (M) Add up times for each operator to get total time for method3Fall 2004 6.831 UI Design and Implementation 9 *! Keystroke determined by typing speed0.28 s average typist (40 wpm)0.08 s best typist (155 wpm)1.20 s worst typist Pointing determined by Fitts s LawT = a + b log(d/s + 1) = a + b ID0.8 + 0.1 ID [Card 1978]0.1 + 0.4 ID [Epps 1986]-0.1 + 0.2 ID [MacKenzie 1990, mouse selection]0.14 + 0.25 ID [MacKenzie 1990, mouse dragging]ORT ~ 1.1 s for all pointing tasks Drawing determined by steering lawFall 2004 6.831 UI Design and Implementation 10 *! Homing estimated by measurement0.36 s (between keyboard and mouse) Mental preparation estimated by measurement1.35 s [1.08 1.35]Fall 2004 6.831 UI Design and Implementation 11 + #' Basic idea: M before every chunk in the method that must be recalled from long-term memory Insert M s before each K & P K => MK P => MP (if P points at a command, not an argument) Delete M s in typed chunks MK MK MK => M KK .. K if K s form a command name, single text string, or number Delete anticipated M s x M y => x y if x fully anticipates y e.g., point-and-click is a chunk, so PMK => PKFall 2004 6.831 UI Design and Implementation 12, !-#. Shift-click selectionMP [start of word]K [click]MP [end of word]K [shift]K [click]H [to keyboard]MK [Del] Total: 3M + 2P + 4K= 7.37 sec Del key N timesMP [start of word] K [click]MK [Del]x n [length of word] Total: 2M + P + (n+1)K= 4.08 + 0.28n sec4Fall 2004 6.831 UI Design and Implementation 13"!! $' Comparing designs & methods Parametric analysisTnDel n timesShift-clickFall 2004 6.831 UI Design and Implementation 14 $' Only expert users doing routine (well-learned) tasks Only measures efficiency Not learnability, memorability, errors, etc. Ignores errors (methods must be error-free) parallel action (shift-click) mental workload (e.g. attention & WM limits) planning & problem solving (how does user select the method?) fatigueFall 2004 6.831 UI Design and Implementation 15/*' Goals Operators Methods Selection rules GOMS offers a language for task analysis and high-level design description can be abstract or detailed can be qualitative or quantitativeFall 2004 6.831 UI Design and Implementation 16, ! Goal: delete text (n chars long) Select: method 1 if n > 10method 2 if n < 10 Method 1: Goal: highlight text & delete Goal: highlight text Point Click Point Shift Click Method 2: Goal: delete n chars5Fall 2004 6.831 UI Design and Implementation 170/*' Natural GOMS language formal language with restricted English syntax Addresses gaps in KLM modeling learning time measured by the # of NGOMSL statements working memory use modeled by Retain and Recall statements no errors or problem solvingFall 2004 6.831 UI Design and Implementation 180/*' Fall 2004 6.831 UI Design and Implementation 191' &/*' CPM-GOMS models parallel operations e.g. point & shift-click Uses parallel cognitive model each processor is serial different processors run in parallel Fall 2004 6.831 UI Design and Implementation 201 -
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