Cognitive ModelsCS 160, Spring 2004February 18

Why Model Human Performance?To test understandingTo predict influence of new technology

Model Human Processor

What is missing from MHP?Haptic memoryFor touchMoving from sensory memory to WMAttention filters stimuli & passes to WMMoving from WM to LTMRehearsal

MHP BasicsBased on empirical dataYears of basic psychology experiments in the literatureThree interacting subsystemsPerceptual, motor, cognitive

MHP BasicsSometimes serial, sometimes parallelSerial in action & parallel in recognitionPressing key in response to lightDriving, reading signs, & hearing at onceParametersProcessors have cycle time (T) ~ 100-200 msMemories have capacity, decay time, & type

MemoryWorking memory (short term)Small capacity (7 2 chunks)6174591765 vs. (617) 459-1765DECIBMGMC vs. DEC IBM GMCRapid access (~ 70ms) & decay (~200 ms)pass to LTM after a few secondsLong-term memoryHuge (if not unlimited)Slower access time (~100 ms) w/ little decay

MHP Principles of OperationRecognize-Act Cycle of the CPOn each cycle contents in WM initiate actions associatively linked to them in LTMActions modify the contents of WMDiscrimination PrincipleRetrieval is determined by candidates that exist in memory relative to retrieval cuesInterference by strongly activated chunks

The Model Human Processor

Principles of Operation (cont.)Variable Cog. Processor Rate PrincipleCP cycle time Tc is shorter when greater effortInduced by increased task demands/informationDecreases with practice

Principles of Operation (cont.)Fitts LawMoving hand is a series of microcorrections, each correction takes Tp + Tc + Tm = 240 msec Time Tpos to move the hand to target size S which is distance D away is given by: Tpos = a + b log2 (D/S + 1)SummaryTime to move the hand depends only on the relative precision required

Fitts Law ExampleWhich will be faster on average?

Fitts Law ExamplePie menu: bigger targets for a given distance; 6.2 / k vs. 2 / k

Pie MenusPie menus have proven advantages, but you rarely see them (QWERTY phenomenon?).

Examples: Maya (animation tool), and many research systems like DENIM.

Still, open-source code for them exists.

Principles of Operation (cont.)Power Law of PracticeTask time on the nth trial follows a power law Tn = T1 n-a + c, where a = .4, c = limiting constanti.e., you get faster the more times you do it!Applies to skilled behavior (sensory & motor)Does not apply to knowledge acquisition or quality

Power Law of Practice

PerceptionStimuli that occur within one PP cycle fuse into a single conceptFrame rate necessary for movies to look real?time for 1 frame < Tp (100 msec) -> 10 frame/sec.Max. morse code rate can be similarly calculatedPerceptual causalityTwo distinct stimuli can fuse if the first event appears to cause the otherEvents must occur in the same cycle

Perceptual CausalityHow soon must red ball move after cue ball collides with it?

Perceptual CausalityMust move in < Tp (100 msec)

Perceptual CausalityMust move in < Tp (100 msec)

BreakAdministrivia: Midterm is a week from Friday.Material covered up to this Friday.Closed book

In-class quizzes will start this week.

Simple ExperimentVolunteerStart saying colors you see in list of wordsWhen slide comes upAs fast as you canSay done when finishedEveryone else time it

PaperHomeBackSchedulePageChange

Simple ExperimentDo it againSay done when finished

BlueRedBlackWhiteGreenYellow

MemoryInterferenceTwo strong cues in working memoryLink to different chunks in long term memoryWhy learn about memory?Know whats behind many HCI techniquesHelps you understand what users will getLots of people have memory difficulties

Stage TheoryWorking memory is smallTemporary storagedecaydisplacementMaintenance rehearsalRote repetitionNot enough to learn information wellAnswer to problem is organizationFaith Age Cold Idea Value Past LargeIn a show of faith, the cold boy ran past the church

Stage Theory

Elaboration Relate new material to already learned material Recodes informationAttach meaning (make a story)e.g., sentencesVisual imageryOrganize (chunking)Link to existing knowledge, categories

LTM ForgettingCauses for not remembering an item?1) Never stored: encoding failure2) Gone from storage: storage failure3) Cant get out of storage: retrieval failure

LTM ForgettingInterference model of forgettingOne item reduces ability to retrieve anotherProactive interference earlier learning reduces ability to retrieve later info.Retroactive interference later learning reduces the ability to retrieve earlier info.

Recognition over RecallRecallInfo reproduced from memoryRecognitionPresentation of info provides knowledge that info has been seen beforeEasier because of cues to retrievalWe want to design UIs that rely on recognition!

Facilitating Retrieval: CuesAny stimulus that improves retrievalExample: giving hintsOther examples in software?icons, labels, menu names, etc.Anything related toItem or situation where it was learnedCan facilitate memory in any systemWhat are we taking advantage of?Recognition over recall!

SummaryMHP: three interacting subsystemsPerceptual, motor, cognitiveSometimes serial, sometimes parallelWe gave several principles of operationMemory principles:Several types: WM -> LTM progressionInterference causes recognition problemsRecognition over Recall

cut some of the slides on color and memory next year too long for 1 lecture