2 the human Information i/o … Information stored in memory visual, auditory, haptic, movementInformation stored in memorysensory, short-term, long-termInformation processed and appliedreasoning, problem solving, skill, errorEmotion influences human capabilitiesEach person is different
3 Vision Two stages in vision • physical reception of stimulus • processing and interpretation of stimulus
4 The Eye - physical reception mechanism 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 visionganglion cells (brain!) detect pattern and movement
5 Interpreting the signal Size 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)familiar objects perceived as constant size (in spite of changes in visual angle when far away)cues like overlapping help perception of size and depth
6 Interpreting the signal (cont) Brightnesssubjective reaction to levels of lightaffected by luminance of objectmeasured by just noticeable differencevisual acuity increases with luminance as does flickerColourmade up of hue, intensity, saturationcones sensitive to colour wavelengthsblue acuity is lowest8% males and 1% females colour blind
7 Interpreting the signal (cont) The visual system compensates for:movementchanges in luminance.Context is used to resolve ambiguityOptical illusions sometimes occur due to over compensation
9 Reading Several stages: Reading involves saccades and fixations visual pattern perceiveddecoded using internal representation of languageinterpreted using knowledge of syntax, semantics, pragmaticsReading involves saccades and fixationsPerception occurs during fixationsWord shape is important to recognitionNegative contrast improves reading from computer screen
10 HearingProvides information about environment: distances, directions, objects etc.Physical apparatus:outer ear – protects inner and amplifies soundmiddle ear – transmits sound waves as vibrations to inner earinner ear – chemical transmitters are released and cause impulses in auditory nerveSoundpitch – sound frequencyloudness – amplitudetimbre – type or quality
11 Hearing (cont) Humans can hear frequencies from 20Hz to 15kHz less accurate distinguishing high frequencies than low.Auditory system filters soundscan attend to sounds over background noise.for example, the cocktail party phenomenon.
12 Touch Provides 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 positionaffects comfort and performance.
13 MovementTime taken to respond to stimulus: reaction time + movement timeMovement time dependent on age, fitness etc.Reaction time - dependent on stimulus type:visual ~ 200msauditory ~ 150 mspain ~ 700msIncreasing reaction time decreases accuracy in the unskilled operator but not in the skilled operator.
14 Movement (cont)Fitts' Law describes the time taken to hit a screen target:Mt = a + b log2(D/S + 1)where: a and b are empirically determined constantsMt is movement timeD is DistanceS is Size of targettargets as large as possible distances as small as possible
15 Memory There are three types of memory function: Sensory memories Short-term memory or working memoryLong-term memorySelection of stimuli governed by level of arousal.AttentionRehearsal
16 sensory memory Buffers for stimuli received through senses Examples iconic memory: visual stimuliechoic memory: aural stimulihaptic memory: tactile stimuliExamples“sparkler” trailstereo soundContinuously overwritten
19 Long-term memory (LTM) Repository for all our knowledgeslow access ~ 1/10 secondslow decay, if anyhuge or unlimited capacityTwo typesepisodic – serial memory of eventssemantic – structured memory of facts,concepts, skillssemantic LTM derived from episodic LTM
20 Long-term memory (cont.) Semantic memory structureprovides access to informationrepresents relationships between bits of informationsupports inferenceModel: semantic networkinheritance – child nodes inherit properties of parent nodesrelationships between bits of information explicitsupports inference through inheritance
22 Models of LTM - Frames Information organized in data structures Slots in structure instantiated with values for instance of dataType–subtype relationshipsDOGFixedlegs: 4Defaultdiet: carniveroussound: barkVariablesize: colourCOLLIEFixedbreed of: DOGtype: sheepdogDefaultsize: 65 cmVariablecolour
23 Script for a visit to the vet Models of LTM - ScriptsModel of stereotypical information required to interpret situationScript has elements that can be instantiated with values for contextScript for a visit to the vetEntry conditions: dog illvet openowner has moneyResult: dog betterowner poorervet richerProps: examination tablemedicineinstrumentsRoles: vet examinesdiagnosestreatsowner brings dog inpaystakes dog outScenes: arriving at receptionwaiting in roomexaminationpayingTracks: dog needs medicinedog needs operation
24 Models of LTM - Production rules Representation of procedural knowledge.Condition/action rulesif condition is matchedthen use rule to determine action.IF dog is wagging tailTHEN pat dogIF dog is growlingTHEN run away
25 LTM - Storage of information rehearsalinformation moves from STM to LTMtotal time hypothesisamount retained proportional to rehearsal timedistribution of practice effectoptimized by spreading learning over timestructure, meaning and familiarityinformation easier to remember
26 LTM - Forgetting decay interference information is lost gradually but very slowlyinterferencenew information replaces old: retroactive interferenceold may interfere with new: proactive inhibitionso may not forget at all memory is selective …… affected by emotion – can subconsciously `choose' to forget
27 LTM - retrieval recall recognition information reproduced from memory can be assisted by cues, e.g. categories, imageryrecognitioninformation gives knowledge that it has been seen beforeless complex than recall - information is cue
29 Deductive Reasoning Deduction: 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
30 Deduction (cont.) When truth and logical validity clash … Correct? e.g. Some people are babiesSome babies cryInference - Some people cryCorrect?People bring world knowledge to bear
31 Inductive Reasoning Induction: Unreliable: … but useful! generalize from cases seen to cases unseene.g. all elephants we have seen have trunks therefore all elephants have trunks.Unreliable:can only prove false not true… but useful!Humans not good at using negative evidencee.g. Wason's cards.
32 How many cards do you need to turn over to find out? Wason's cards7 E 4 KIf a card has a vowel on one side it has an even number on the otherIs this true?How many cards do you need to turn over to find out?…. and which cards?
33 Abductive reasoning reasoning from event to cause Unreliable: e.g. Sam drives fast when drunk.If I see Sam driving fast, assume drunk.Unreliable:can lead to false explanations
34 Problem solvingProcess of finding solution to unfamiliar task using knowledge.Several theories.Gestaltproblem solving both productive and reproductiveproductive draws on insight and restructuring of problemattractive but not enough evidence to explain `insight' etc.move away from behaviourism and led towards information processing theories
35 Problem solving (cont.) Problem space theoryproblem space comprises problem statesproblem solving involves generating states using legal operatorsheuristics may be employed to select operators e.g. means-ends analysisoperates within human information processing system e.g. STM limits etc.largely applied to problem solving in well-defined areas e.g. puzzles rather than knowledge intensive areas
36 Problem solving (cont.) Analogyanalogical mapping:novel problems in new domain?use knowledge of similar problem from similar domainanalogical mapping difficult if domains are semantically differentSkill acquisitionskilled activity characterized by chunkinglot of information is chunked to optimize STMconceptual rather than superficial grouping of problemsinformation is structured more effectively
37 Errors and mental models Types of errorslipsright intention, but failed to do it rightcauses: poor physical skill,inattention etc.change to aspect of skilled behaviour can cause slipmistakeswrong intentioncause: incorrect understandinghumans create mental models to explain behaviour.if wrong (different from actual system) errors can occur
38 Emotion Various theories of how emotion works James-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 stimuli
39 Emotion (cont.)The biological response to physical stimuli is called affectAffect 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)
40 Emotion (cont.) Implications for interface design stress will increase the difficulty of problem solvingrelaxed users will be more forgiving of shortcomings in designaesthetically pleasing and rewarding interfaces will increase positive affect
41 Individual differences long term – sex, physical and intellectual abilitiesshort term – effect of stress or fatiguechanging – ageAsk yourself: will design decision exclude section of user population?
42 Psychology and the Design of Interactive System Some direct applicationse.g. blue acuity is poor blue should not be used for important detailHowever, correct application generally requires understanding of context in psychology, and an understanding of particular experimental conditionsA lot of knowledge has been distilled inguidelines (chap 7)cognitive models (chap 12)experimental and analytic evaluation techniques (chap 9)