Human information processing Perception Motor skills Memory Decision making Attention Vision Fall 2004 6 831 UI Design and Implementation 1 Fall 2004 6 831 UI Design and Implementation 2 Attention Memory properties Encoding type of things stored Size number of things stored Decay time how long memory lasts Fall 2004 6 831 UI Design and Implementation 3 Fall 2004 6 831 UI Design and Implementation 4 1 Processors have a cycle time Visual information store Tp 100ms 50 200 ms Tc 70ms 30 100 ms Tm 70ms 25 170 ms encoded as physical image size 17 7 17 letters decay 200 ms 70 1000 ms Auditory information store encoded as physical sound size 5 4 4 6 2 letters decay 1500 ms 900 3500 ms Fall 2004 6 831 UI Design and Implementation Fastman may be 10x faster than Slowman 5 Fall 2004 Two stimuli within the same PP cycle Tp 100ms appear fused Consequences 6 831 UI Design and Implementation 6 Bottom up uses features of stimulus Top down uses context temporal spatial draws on long term memory 1 Tp frames sec is enough to perceive a moving picture 10 fps OK 20 fps smooth Computer response Tp feels instantaneous Causality is strongly influenced by fusion Fall 2004 6 831 UI Design and Implementation 7 Fall 2004 6 831 UI Design and Implementation 8 2 Spotlight metaphor Chunk unit of perception or memory Chunking depends on presentation and what you already know Spotlight moves serially from one input channel to another Visual dominance easier to attend to visual channels than auditory channels All stimuli within spotlighted channel are processed in parallel B M W R C A A O L I B M F B I MWR CAA OLI BMF BIB BMW RCA AOL IBM FBI 3 4 digit chunking is ideal for encoding unrelated digits Fall 2004 6 831 UI Design and Implementation Whether you want to or not 9 Book Pencil Slide Window Car Hat Fall 2004 Fall 2004 6 831 UI Design and Implementation 10 6 831 UI Design and Implementation 12 Green Orange Red Black Pink Blue 6 831 UI Design and Implementation 11 Fall 2004 3 Cognitive processor Reaction time depends on information content of stimulus compares stimuli selects a response Types of decision making RT c d log2 1 Pr stimulus Skill based Rule based Knowledge based Fall 2004 e g for N equiprobable stimuli each requiring a different response RT c d log2 N 6 831 UI Design and Implementation 13 Fall 2004 6 831 UI Design and Implementation 14 Resource metaphor Accuracy varies with reaction time Attention is a resource that can be divided among different tasks simultaneously Can choose any point on curve Can move curve with practice Multitasking performance depends on Task structure Modality visual vs auditory Encoding spatial vs verbal Component perceptual cognitive vs motor vs WM log P correct P error moves up with practice Difficulty Easy or well practiced tasks are easier to share Reaction time Fall 2004 6 831 UI Design and Implementation 15 Fall 2004 6 831 UI Design and Implementation 16 4 Open loop control Fitt s Law Motor processor runs a program by itself cycle time is Tm 70 ms Time T to move your hand to a target of size S at distance D away is Closed loop control T RT MT a b log 2D S Muscle movements or their effect on the world are perceived and compared with desired result cycle time is Tp Tc Tm 240 ms D S Depends only on index of difficulty log 2D S Fall 2004 6 831 UI Design and Implementation 17 6 831 UI Design and Implementation Moving your hand to a target is closedloop control Each cycle covers remaining distance D with error D 18 Targets at screen edge are easy to hit Mac menubar beats Windows menubar Unclickable margins are foolish Hierarchical menus are hard to hit Gimp GTK instantly closes menu Windows 5 s timeout destroys causality Mac does it right triangular zone Velocity Position Fall 2004 Linear popup menus vs pie menus Time Fall 2004 6 831 UI Design and Implementation Time 19 Fall 2004 6 831 UI Design and Implementation 20 5 Time Tn to do a task the nth time is is typically 0 2 0 6 6 831 UI Design and Implementation Small capacity 7 2 chunks Fast decay 7 5 226 sec Maintenance rehearsal fends off decay Interference causes faster decay Tn T1 n Fall 2004 21 Fall 2004 6 831 UI Design and Implementation 22 6 831 UI Design and Implementation 24 Huge capacity Little decay Elaborative rehearsal moves chunks from WM to LTM by making connections with other chunks Fall 2004 6 831 UI Design and Implementation 23 Fall 2004 6 Rods Brightness Only one kind peak response in green wavelengths Sensitive to low light scotopic vision M L rods Multiple nearby rods aggregated into a single nerve signal Red green difference Saturated at moderate light intensity photopic vision L M Cones do most of the vision under photopic conditions Cones Blue yellow difference Operate in brighter light Three kinds S hort M edium L ong S cones are very weak centered in blue wavelengths M and L cones are more powerful overlapping M centered in green L in yellow but called red Fall 2004 6 831 UI Design and Implementation weighted sum of S M L 25 Fall 2004 6 831 UI Design and Implementation 26 Red green color blindness protonopia deuteranopia Different wavelengths focus differently Highly separated wavelengths red blue can t be focused simultaneously 8 of males 0 4 of females Guideline don t use red on blue text Blue yellow color blindness tritanopia It looks fuzzy and hurts to read Far more rare Guideline don t depend solely on color distinctions use redundant signals brightness location shape Fall 2004 6 831 UI Design and Implementation 27 Fall 2004 6 831 UI Design and Implementation 28 7 Fovea has no S cones Rods are more sensitive to dim light In scotopic conditions peripheral vision rod rich is better than foveal vision Can t resolve small blue features unless they have high contrast with background Lens and aqueous humor turn yellow with age Easier to see a dim star if you don t look directly at it Blue wavelengths are filtered out Lens weakens with age Blue is harder to focus Guideline don t use blue against dark backgrounds where small details matter text Fall 2004 6 831 UI Design and Implementation 29 Fall 2004 6 831 UI Design and Implementation 30 8
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