Scientific Underpinnings of Usability Engineering

Transcription

1 Scentfc Underpnnngs of Usablty Engneerng Intro Usablty Week 2 1

2 Objectves After ths class you wll be able to (t s my hope!): Descrbe some eye physology Explan how the vsual system works (somewhat) Identfy vsual cues to depth Explan some aspects of the psychology of readng Explan how perceptual and cogntve psychology nfluence HCI desgns Have an excellent memory for VAM Dscuss the mportance of desgnng systems to match the human. 2

3 Desgnng Stuff In Week 1, I asked the queston What would a system look lke f we were desgnng t for dogs? Wouldn t be a lot of text. Wouldn t requre a lot of dexterty. Mght code nformaton n smells and tastes. But we re desgnng systems for humans (usually!). So t wll behoove us to know somethng about how human bengs take n and process nformaton. 3

4 Whole pont... Let s desgn systems to ft people nstead of the other way around. 4

5 Human Informaton Processng How do human bengs take n and process nformaton? Sensory psychology how humans transform physcal energy (e.g., lght and sound waves) nto sensory sgnals to and n the bran. Perceptual psychology how humans nterpret these sensory sgnals as perceptons. Cogntve psychology how humans thnk about these perceptons, and prevous experences, and ther own mental creatons, and... Psycholngustcs The psychology of language -- what goes on between the tme I have a thought and you have the same (or smlar!) thought, whether I say t or wrte t. 5

6 Eye Physology 6

7 Eye Muscles 7

8 Vsual Feld 8

9 Retnal Physology 9

10 Dstrbuton of Rods and Cones 10

11 Vsble Spectrum 11

12 Vsual Senstvty 12

13 Neural Pathways 13

14 Aftereffect 14

15 Ambguous Fgure 15

16 Sensaton/Percepton POINT: Perceptons are made up of more than just a collecton of sensatons! OTHER thngs nfluence our perceptons, e.g., Our experences Our bases The context Our current emotonal state Etc. So, what does that have to say about desgnng human-computer nterfaces??? 16

17 Perceptual Psy Color Vson Color percepton 3 types of cones (RGB) 17

18 Perceptual Psy -- Depth Dfferent vsual cues to depth Oculomotor vs. Vsual Oculomotor Lens accommodaton and extraocular muscle convergence are read by the bran Vsual: Bnocular vs. Monocular Bnocular Stereopss (retnal dsparty) Monocular (next screen)» Statc» Moton parallax 18

19 More Depth Cues Monocular Statc Interposton Sze Perspectve Lnear perspectve Texture gradent Aeral perspectve Shadng Moton parallax 19

20 Monocular Cues -- Interposton 20

21 Monocular Cues -- Sze 21

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24 Monocular Cues Lnear Perspectve 24

25 Monocular Cues Texture Gradent 25

26 Sooooo... The grass really IS greener on the other sde of the fence!!! 26

27 Monocular Cues Aeral Perspectve 27

28 Monocular Cues -- Shadng 28

29 Monocular Cues Moton Parallax 29

30 More vsual percepton Illusons and what they tell us about vson Ponzo lluson Muller-Lyer lluson 30

31 Ponzo Illuson 31

32 Muller-Lyer Illuson 32

33 Psycholngustcs The psychology of language. What goes on from the tme I get an dea untl you have the same dea, Whether I speak my dea (speech producton, audtory scence, speech percepton) Or wrte my dea (motor movements, vsual system, readng) 33

34 The Psychology of Readng Except for farly rare cases of phonetc symbolsm (onomatopoea) words have no nherent meanng. (And rarer cases of orthographc symbolsm!!) So, READING s the nterpretng of words, the acts that go on to mpose meanng, from wthn, on external vsual stmul. 34

35 Some facts about readng Eyes of the mature reader move rhythmcally across the page (from left to rght). Eye movement conssts of fxatons, saccades, regressons, and return sweeps. No nformaton s taken n durng saccades (10-25 msec), regressons (same duraton), or return sweeps (40 msec). Durng fxaton (250 msec) a vsual pattern s reflected onto the retna. Span of percepton = amount of prnt seen durng a sngle fxaton. Span of percepton = 12 letter spaces for good readers, 6 for poor readers. 35

36 More facts Span of recognton 1.21 words for senor hgh, 1.33 words for college readers. So, 7 to 8 fxatons per lne of prnt. As content gets tougher, duraton of fxatons, not number, changes (ncreases). Regressve movements aren t systematc. Used when attenton s falterng. College readers have 1 regressve movement per 3 or 4 lnes of prnt. Immature readers have 3 or 4 regressons per lne. 36

37 Iconc Memory Remember n Week 1 I mentoned a two-stage memory process STM and LTM. A thrd stage, Iconc Memory: The undentfed, pre-categorcal pattern of lnes, curves and angles; formed n about 100 msec. Icon can hold up to 20 letter spaces. Pattern recognton routnes are appled to the lnes, curves. It takes about msec to read each letter out of the conc memory. Neural sgnal takes about 30 msec to go from the retna to the vsual cortex. 37

38 Iconc Memory (cont d.) At some pont, thanks to pattern recognton routnes, letters are read out. Letters are transformed nto abstract phonemc representatons. The abstract phonemes are used to search the mental lexcon. About 300 msec after the eye has fallen upon the page, the frst word s understood,.e., placed n Prmary Memory (STM, Workng Memory). Syntactc and semantc rules are appled to gan the meanng of the sentence. 38

39 How do you know, Randolph? Psycholngusts employ a varety of methods to acqure ths data about human behavor. One queston: Why do we thnk readers routnely transform the vsual representaton nto a phonologcal representaton? Cogntve economy all (healthy) new readers come to the task as sklled hearers. I thought you sad somethng about data? 39

40 Rubensten et al. (1971) Used a lexcal decson task (word/nonword?). Two types of nonwords homophonous (wth real words), lke burd and nonhomophonous lke rolt. Equally wordlke. Longer latences for burd. Smlarly, longer for real homophones lke meat. Ponted to false matches n the mental lexcon. 40

41 More Data McCusker et al. (1977) proofreadng experment Homophonous typos (e.g., furst) went undetected more often than nonhomophonous typos (e.g., farst). Gough and Cosky (1977) used the Stroop task. Nonwords homophonous wth color words (e.g,. bloo) led to more nterference than control words (e.g., blot) or nonwords nonhomophonous wth color words (e.g., blop). I found readers took longer to process words wth rregular spellng-to-sound rules (e.g., pnt) than words wth regular rules (e.g., hnt) (Bas, 1978). 41

42 The Pont The reasons for ths somewhat esoterc dscourse on the psychology of readng are: To communcate the complexty that s human nformaton processng The llustrate the ways scentsts go about answerng questons about nfo processng To senstze you to the sorts of thngs known about human behavor 42

43 In week 1, we were talkng about Percepton and Cognton What do we know about humans? In the physcal realm: Anthropometry. These days we re more nterested n the cogntve realm. Queston: Can you remember a 30-dgt number? I say that you can, rght now, wthout practce, seeng t only once, for 1 second, wth no tme to rehearse. 43

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45 Experment 1 Instead of numbers, I ll present CVC (consonant-vowel-consonant) strngs -- lke NEH. 10 CVCs, one at a tme. Presented vsually. Don t have to remember them n order. Pencls down. Ready? 45

46 BOV NAZ TOL RIJ DIH REN WUK CAQ GOC MEB 46

47 BOV NAZ TOL RIJ DIH REN WUK CAQ GOC MEB 47

48 Experment 2 Now, 10 new CVCs. Same task -- recall them. Ths tme, after we read the 10th tem, we ll all count backwards from 100 by 3s, aloud, together. Then when I say Go, wrte down as many of the 10 CVCs as you can. Pencls down. Ready? 48

49 VAM LUN XOP REH WIV CIT JEG KUC ZOB YAD 49

50 VAM LUN XOP REH WIV CIT JEG KUC ZOB YAD 50

51 Experment 3 Same as Experment 2. Yet 10 more CVCs. Backwards countng. Don t have to recall them n order. Pencls down. Ready? 51

52 GEP TIV WOH LUP MAZ SEX KOL RUC NID BIR 52

53 GEP TIV WOH LUP MAZ SEX KOL RUC NID BIR 53

54 So? So, the answer to Can you remember a 30- dgt number?, s... It depends. On what? Whether you hear or see the number. Whether the number s masked. Whether you have tme to rehearse. Whether you can chunk the numbers. If there are any ntervenng tasks. How meanngful the number s. WHAT the number s. So, what s a usable nterface? It depends. 54

55 SO WHAT? Gven that we re so all-fred complex, what does ths have to say about how we desgn computer nterfaces? Depth cues. Color percepton. Effects of context on percepton. What s easy to read? Recognton vs. recall. 55

56 Break tme! 56

57 People Dffer Some of your users/ vstors may be: Non-natve Englsh speakers Left handed Caprcorns Republcans Heterosexuals Poor vsual processors In a hurry Alabamans In a publc lbrary Blnd Mostly blnd Color blnd Genuses Drunk Vstors to your earler ste Frst-tme web vstors! On a subway Usng an Phone 57

58 Stuatons Dffer Cogntve Set Context nfluences percepton. A seres of events can set a person to perceve thngs a certan way. 58

59 Guess what frequent error was made on ths form, on an IBM Servce ste: Name: Street Address: Cty: State/ZIP: County: 59

60 Desgn of Everyday Thngs It an t rocket scence. You ve already read the book. Let me ht just the hgh ponts from my pont of vew Whle I m presentng ths, see f you can characterze your good and bad desgns that you ve dscovered ths week n Norman s terms. 60

61 Chapter 1 The PsychoPATHOLOGY of everyday thngs Assumpton: We blame ourselves for errors, but the real culprt s faulty desgn. Assumpton: There s nothng specal about computers. They have the same sorts of desgn problems as smpler, everyday thngs. 61

62 Good Desgn Well desgned objects... are easy for the mnd to understand contan vsble cues to ther operaton Poorly desgned objects... provde no clues, or provde false clues. 62

63 Natural Sgnals Natural sgnals lead to natural desgn. A metal plate naturally s to be pushed. Vsble hnges naturally ndcate attachment, and that the other sde swngs open. (And swngs open TOWARD me?) 63

64 Mappng Mappng s a relatonshp between two thngs (e.g., between what you want to do and what appears possble). Good desgn allows for a clear (vsble) mappng between... ntended actons and actual operatons. Now -- thnk of what ths mght mean n a web ste. 64

65 Good Desgn Prncples of good desgn the mportance of vsblty approprate clues feedback of ones actons. Just so you ll know -- others have proposed OTHER prncples of good desgn. Go check out the web ste of Bruce Tognazzn: 65

66 Affordance Affordance s the perceved and actual propertes of a thng. Prmarly those fundamental propertes that determne how a thng could possbly be used. Affords means, bascally, s for. A char affords support, therefore affords sttng. Affordances provde strong clues to thngs operatons. When affordances are taken advantage of, the user knows what to do just by lookng. No label, pcture, or nstructon ( Push ) s requred. - When smple thngs need pctures, labels, or nstructons, the desgn has faled. 66

67 The Paradox of Technology Added functonalty generally comes along at the prce of added complexty. The same technology that smplfes lfe by provdng more functons also complcates lfe by makng the devce harder to learn and use. The Paradox of Technology should never be used as an excuse for poor desgn. Added complexty cannot be avoded when functons are added, but wth clever desgn they can be mnmzed. 67

68 Chapter 2 -- Psy of Everyday Actons Norman s credo on errors -- f an error s possble, someone wll make t. The desgner must desgn so as to: mnmze the chance of errors n the frst place mnmze the effects of an error make errors easy to detect make errors reversble, f possble. 68

69 Models Mental Models = our conceptual models of the way... objects work events take place people behave Mental models result from our tendency to form explanaton of thngs. Models are essental n helpng us... understand our experences predct the outcomes of our actons handle unexpected occurrences. 69

70 Models (cont d.) We base our models on whatever knowledge we have: real or magnary naïve or sophstcated even fragmentary evdence. Everyone forms theores (mental models) to explan what they have observed. In the absence of feedback to the contrary, people are free to let ther magnatons run free. More on models n Chapter 3. 70

71 7 Stages of Acton On p. 47 s a seres of four fgures that llustrate Norman s vew of the structure of acton. Actons have two major aspects: 1. Dong somethng (executon) 2. Checkng (evaluaton) 71

72 Chapter 3 - Knowledge n the Head and n the World Not all knowledge requred for precse behavor must be n the head. It can be dstrbuted: partly n the head partly n the world partly n the constrants of the world. 72

73 Constrants The power of constrants -- the memory for epc poetry s found to be mostly reconstructon, wth the ad of the constrants of rhyme, meter, etc. We use constrants to smplfy what we must remember. For example, puttng mechancal parts together. Some are constraned by what wll and wll not ft together. Also cultural constrants -- screws tghten clockwse. 73

74 Memory... s knowledge n the head. Thnk of all you can remember. Phone numbers, postal codes, passwords, SSN, brthdays, etc., etc. It s tough! So, we put memory n the world. (Daytmers. Smart phones. Address books. Stckes.) 74

75 Tradeoff between nfo n the world and n the head. Knowledge n the world acts as ts own remnder. Knowledge n the head s effcent. (You can travel lght.) Knowledge n the world s easer (no learn tme), but often dffcult to use. Reles heavly on the physcal presence of nfo. See Fg. 3.6, p

76 Ch Knowng what to do When we encounter a novel object, ether We ve dealt wth somethng smlar before, and we transfer old knowledge, or We get nstructon. Thus, nformaton n the head. 76

77 Desgn How can the desgn of an object (NOTE: nfo n the world) sgnal the approprate actons? Natural (physcal) constrants Affordances, that convey messages about the tem s possble uses, actons, and functons The thoughtful uses of affordances and constrants together n desgn lets a user determne readly the proper course of acton even n a novel stuaton. 77

78 Ch. 5 - To err s human Errors come n several forms Slps -- result from automatc behavor, when subconscous actons get waylad en route ( performance errors ) Mstakes -- result from conscous delberatons ( competence errors ) 78

79 Ch The Desgn Challenge Norman talks about what forces work aganst evolutonary, or natural desgn (pp ). The demands of tme (quck product cycles) The pressure to be dstnctve (related to the curse of ndvdualty) 79

80 Ptfalls Three reasons why desgners go astray: 1. Puttng aesthetcs frst 2. Desgners aren t typcal users 3. Desgners clents may not be the users 80

81 Ch. 7 - UCD Chapter 7 s the punch lne of the whole book. User-Centered Desgn Most of the chapter s gven over to descrbng seven prncples for transformng dffcult tasks nto smple ones. 81

82 Etc. He goes on to offer a secton on why you mght want to desgn somethng to be hard to use ON PURPOSE. And he ends wth a few sectons on wrtng, the home of the future, and a concludng secton. 82

83 Now... Let s try to put t n Norman s terms why the good desgns were good and the bad desgns were bad. ( Some mportant feature was, or was not, vsble. ) 83

84 ... your homework Bad web desgns. Good web desgns. Send at least 2 URLs to the TA. Famous quote: No one ever rased a statue to a crtc. Sbelus I want us all to remember that t s easer to crtcze another desgn than t s to desgn somethng. 84

85 For next week Send the TA your whte paper topcs. Due 4 weeks from today. More readng Usablty test plan (for your fnal project) due n 6 weeks. Wll help wth ponters to templates. For next week, come wth one good and one bad example of web usablty. Actually, send em to the TA by Frday noon. 85