Human Computer Interaction

Human Computer InteractionThe HumanOverviewHumans are limited in their capacity to process information. This has important implications for design.Information i/o visual, auditory, haptic, movementInformation stored in memorysensory, short-term, long-termInformation processed and appliedreasoning, problem solving, skill, errorEmotion influences human capabilitiesEach person is different

VisionTwo stages in vision

physical reception of stimulus

processing and interpretation of stimulusThe Eye - physical receptionMechanism for receiving light and transforming it into electrical energylight reflects from objectsimages are focused upside-down on retinaretina contains rods for low light vision and cones for colour visionSpecial nerve in retina: ganglion cellsX-cell: concentrated in fovea detect pattern Y-cell: distributed in retina movement detect movement

The Eye

The Eye (2)

Interpreting the signalSize and depthvisual angle indicates how much of view object occupies(relates to size and distance from eye)visual acuity is ability to perceive detail (limited)e.g. normal vision can detect a single line if it has a visual angle of 0.5 seconds of arcfamiliar objects perceived as constant size (in spite of changes in visual angle when far away)cues like overlapping help perception of size and depthInterpreting the signal (2)

Interpreting The SignalBrightnesssubjective reaction to levels of lightaffected by luminance of objectmeasured by just noticeable differencevisual acuity increases with luminance as does flicker

Colourmade up of hue, intensity, saturationcones sensitive to colour wavelengthsblue acuity is lowest, blue-sensitive cones: 3-4% 8% males and 1% females colour blind

ColorVisible LightWavelength 400-700nmShortestBlueLongestRed

Interpreting the signal (cont)The visual system compensates for:movementchanges in luminance.

Context is used to resolve ambiguity

Optical illusions sometimes occur due to over compensationAmbigiuous shape?

Ambigiuous shape?

Ambigiuous shape?

Optical Illusionsthe Ponzo illusionthe Muller Lyer illusionMore?Visit:http://www.scientificpsychic.com/graphics/ReadingSeveral stages:visual pattern perceiveddecoded using internal representation of languageinterpreted using knowledge of syntax, semantics, pragmatics

Reading involves saccades and fixationsPerception occurs during fixationsWord shape is important to recognitionNegative contrast improves reading from computer screenInterpretationThe qcuik borwn fox jmup oevr the lzay dog

Read The Color

HearingProvides information about environment:distances, directions, objects etc.Physical apparatus:outer earprotects inner and amplifies soundmiddle eartransmits sound waves asvibrations to inner earinner earchemical transmitters are releasedand cause impulses in auditory nerveSoundpitchsound frequencyloudness amplitudetimbretype or quality

Hearing (cont)Humans can hear frequencies from 20Hz to 15kHzless accurate distinguishing high frequencies than low.

Auditory system filters soundscan attend to sounds over background noise. for example, the cocktail party phenomenon.

TouchProvides important feedback about environment.May be key sense for someone who is visually impaired.Stimulus received via receptors in the skin:thermoreceptors heat and coldnociceptors painmechanoreceptors pressure (some instant, some continuous)Some areas more sensitive than others e.g. fingers.Kinethesis - awareness of body position affects comfort and performance.TouchE-commerce has become very successful in some areas of sales, such as travel services, books and CDs, and food.

However, in some retail areas, such as clothes shopping, e-commercehas been less successful. Why?MovementTime taken to respond to stimulus:reaction time + movement time

Movement time dependent on age, fitness etc.

Reaction time - dependent on stimulus type:visual~ 200 msauditory~ 150 mspain~ 700 ms

Increasing reaction time decreases accuracy in the unskilled operator but not in the skilled operator.MemoryThere are three types of memory function:

Selection of stimuli governed by level of arousal (level of interest or need).

sensory memoryBuffers for stimuli received through sensesiconic memory: visual stimuliechoic memory: aural stimulihaptic memory: tactile stimuliExamplessparkler trailstereo soundContinuously overwrittenShort-term memory (STM)Scratch-pad for temporary recall

rapid access ~ 70ms

rapid decay ~ 200ms

limited capacity - 7 2 chunks

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THE CAT RAN UP THE TREECashing in

Long-term memory (LTM)Repository for all our knowledgeslow access ~ 1/10 secondslow decay, if anyhuge or unlimited capacity

Two typesepisodic serial memory of eventssemantic structured memory of facts, concepts, skills

semantic LTM derived from episodic LTMLong-term memory (cont.)Semantic memory structureprovides access to informationrepresents relationships between bits of informationsupports inference

Model: semantic networkinheritance child nodes inherit properties of parent nodesrelationships between bits of information explicitsupports inference through inheritance

LTM - semantic networkLTM - Storage of informationrehearsalinformation moves from STM to LTM

total time hypothesisamount retained proportional to rehearsal time

distribution of practice effectoptimized by spreading learning over time

structure, meaning and familiarityinformation easier to rememberLTM - Forgettingdecayinformation is lost gradually but very slowly

interferencenew information replaces old: retroactive interferenceold may interfere with new: proactive inhibition

so may not forget at all memory is selective

affected by emotion can subconsciously `choose' to forget

LTM - retrievalrecall information reproduced from memory can be assisted by cues, e.g. categories, imagery

recognitioninformation gives knowledge that it has been seen beforeless complex than recall - information is cue--ThinkingReasoningdeduction, induction, abduction

Problem solvingTheory, Analogyanalogical mapping:novel problems in new domain?use knowledge of similar problem from similar domain analogical mapping difficult if domains are semantically different

Skill acquisitionDeductive ReasoningDeduction:derive logically necessary conclusion from given premises.e.g.If it is Friday then she will go to workIt is FridayTherefore she will go to work.

Logical conclusion not necessarily true:e.g.If it is raining then the ground is dryIt is rainingTherefore the ground is dry

Deduction (cont.)When truth and logical validity clash e.g.Some people are babiesSome babies cryInference - Some people cryCorrect?

People bring world knowledge to bearInductive ReasoningInduction:generalize from cases seen to cases unseene.g.all elephants we have seen have trunkstherefore all elephants have trunks.

Unreliable:can only prove false not true

but useful!

Humans not good at using negative evidencee.g. Wason's cards.

Wason's cardsIs this true?

How many cards do you need to turn over to find out?

. and which cards?If a card has a vowel on one side it has an even number on the other7 E 4 KAbductive reasoningreasoning from event to causee.g.Sam drives fast when drunk.If I see Sam driving fast, assume drunk.

Unreliable:can lead to false explanationsSkill AcquisitionIF cook [type, ingredients, time]THENcook for: timecook[casserole, [chicken,carrots,potatoes], 2 hours]cook[casserole, [beef,dumplings,carrots], 2 hours]cook[cake, [flour,sugar,butter,eggs], 45 mins]

Proceduralized KnowledgeIF type is casseroleAND ingredients are [chicken,carrots,potatoes]THENcook for: 2 hoursIF type is casseroleAND ingredients are [beef,dumplings,carrots]THENcook for: 2 hoursIF type is cakeAND ingredients are [flour,sugar,butter,eggs]THENcook for: 45 mins

Generalized KnowledgeIF type is casseroleAND ingredients are ANYTHINGTHENcook for: 2 hours

EmotionVarious theories of how emotion worksJames-Lange: emotion is our interpretation of a physiological response to a stimuliCannon: emotion is a psychological response to a stimuliSchacter-Singer: emotion is the result of our evaluation of our physiological responses, in the light of the whole situation we are inEmotion clearly involves both cognitive and physical responses to stimuliEmotion (cont.)The biological response to physical stimuli is called affect Affect influences how we respond to situationspositive creative problem solvingnegative narrow thinking

Negative affect can make it harder to do even easy tasks; positive affect can make it easier to do difficult tasks (Donald Norman)

Emotion (cont.)Implications for interface designstress will increase the difficulty of problem solvingrelaxed users will be more forgiving of shortcomings in designaesthetically pleasing and rewarding interfaces will increase positive affectIndividual differenceslong term sex, physical and intellectual abilitiesshort term effect of stress or fatiguechanging age

Ask yourself:will design decision exclude section of user population?