COMP 3715 Spring 05

1. COMP 3715 Spring 05

2. Understanding humans • Effective HCI requires we know how human behaves • Two major areas • Physical capabilities: cognition • Mental capabilities: memory

3. Cognition • Interpretation of information from the outside world through senses • Need to interpret • Not just seeing, but looking • Not just hearing, but listening

4. Human senses • Interpretation of information from the outside world through senses • Need to interpret • Not just seeing, but looking • Not just hearing, but listening

5. Human senses • Five senses • Vision • Hearing • Taste • Smell • Touch • Which are useful for HCI?

6. Vision • How does human see? • The eye • Light enter eyes through pupil • Triggers cells at the retina • Focusing of light through muscles • Retina send message to the brain for interpretation • Sometimes, “mis”-interpertation/illusion

7. Vision • Retina • Many receptor layers • Two kinds of cells • Rods – can handle poor light, but no color • Cones – need good lighting, can distinguish color • Cones are at the center, rods are at the side • Implications • Shape can be distinguished in the dark, but not color • Color detect is good at front, but not at the side • Important when developing large screens

8. Visual acuity and visual field • Visual acuity – • Ability to distinguish separate objects • Best at the front, limited at periphery • Visual field • The range discernible to human (in degrees) • Typically without head-moving: 100-120 • Implication • Large screen -> head-movement • Too much head movement: discomfort and dizziness • Too little head movement: stiffness and hurting for eye • Thus -> one must not ask the user to ALWAYS focus on a single point

9. Color • Part of the electromagnetic spectrum • Different wavelength = different color • Three way of classification • Hue • The color; • Chromatic (e.g. red, blue) vs. achromatic (black, white) • Brightness • Subjective, no objective measure • Saturation • How much achromatic color is in the color

10. Color • Contrast • Comparison of light from the object vs. light from the background • Affect the perception of color • Luminance • Light that is reflected from the surface of the object • Increase luminance • increase ability to see detail • More likely for eye to see flicker

11. Contrast -- example

12. Optical illusions • Vision is imperfect • With contrasting brightness, hue etc., optical illusion can occur

13. Hermann Grid See black dots at the intersection of white lines?

14. Poggendorff Illusion

15. Luminance vs Brightness For each block, which is lighter (left or right)?

16. Luminance vs Brightness For each block, which is lighter (left or right)?

17. Color • Color sensitivity • Best at center, poor at periphery • At center of vision • Best for red/green • Poor for blue • Different shades of blue are hard to distinguish • Different shades of red is much easier • Different color require eye to refocus • Extreme colors (red & blue) should not be shown together too often

20. Color • Color sensitivity • At periphery, • best for distinguish blue, • poor for red, green and yellow • Thus, blue makes a good background color for large screens

21. Color • Color-blindness • Fail to distinguish among certain colors • Red-green is the most common • Color representation • Warm colors vs. cold colors • Color connotations in different cultures • Age • Color sensitivity decreases with age (“yellowing”)

22. Color • Implications • Color should be used as reinforcement • Not as a solitary cue • Need care about mixing and matching color

23. Color • Good places to use color to attract attention if: • Information is long and complex • Need to refer to that later • Alerts that do not need user’s immediate attention • The user’s aural system is overburdened (e.g. software is creating a lot of sound; working at a loud environment) • Good illumination

24. Sound • Three attributes of sound (waves) • Amplitude • Wavelength • Frequency • Pitch • Subjective judgment of frequency • Human detect 20-20,000Hz; most sensitive 1,000-4,000Hz • Loudness • Subjective judgment of amplitude • Measured in decibels • Normal: 50-70 decibels • Damage: 140 decibels

25. Sound • Sensitivity • Change of frequency: at least 20 decibels • Location: 45 degrees apart • Hearing impairment • Affect about 10 percent of people • Not taken seriously

26. Sound • Use of sound • As a locator • However, cell phone location is a problem • As an attraction of attention • However, sound can be annoying • One can avoid seeing, but not avoid hearing

27. Sound • Good places to use sound to attract attention if: • Information is short and simple • No need to refer to the message later • Alerts that need user’s immediate attention • The user’s visual system is overburdened (e.g. screen is very busy) • Poor illumination • User is moving around

28. Other senses • Touch • Can be important • E.g. Feel of keyboard, mouse • Smell/Taste • Not used at present

29. Memory • Three types • Sensory memory • Handle input from the senses • Working memory/Short-term memory • Active when conscious • Long term memory • Information is stored “long-term”

30. Short term memory/Working memory • Where immediate processing is done during conscious time • Limited capabilities • 7  2 items (George Miller, 1956)

31. Long term memory • Information stored and retrieve over period of time • Theoretically unlimited • Activation: retrieving from long term memory • Take time • Unclear why certain things are stored over others • Unclear why forgetting happens

32. Sensory memory • Handle information from senses • Seems different from working memory • Can recall/replay such information at will • Can be used for virtual reality

33. Comparing memory • Working memory – needed for calculation and understanding • E.g. you must store the beginning of a sentences while you are reading the rest • Sensory memory – process information through senses • E.g. “Moving pictures” leads to continuous feeling • “Play back” of words/sentences

34. Memory experiments • Digit span • How good your memory is

35. Memory experiments • Working memory = 7  2 items • Thus, password of length 5-9 characters are good for easy remembering • To overcome this: chunking • Grouping similar/related items so to expand on the capability • E.g. 128515284 vs. 128-515-284

36. Example • Remember this • A A B B B C E G G H O U T • Now remember this • B O U G H T C A B B A G E

37. Memory experiments • Primary and recency effects • People remember the first few and last few things from a list, not the middle • Recency effects decay if intervened by other activities • Closure • Relief when you feel a task is finished • Enable memory to function better • Important when designing a system

38. Example • File • Heart • Scarecrow • Stylus • Maggot • Rug • Flea • Ball-pen • Jamboree • Neptune • Magnum • Paper-clip • Typist • Subway • Accident

39. Rescue Gravestone Flower Fountain Statue Fool Aphid Surprise Printer Cenotaph Dog Basket Magnet Lawn Pawn Sandwich 3 + 6 - 4 + 2 - 7 + 15 Example

40. Memory experiments • Memory is affected by • Comfort • relaxed, but not too relaxed • Mood • Happy memories when happy • Sad memories when sad • Environment • Recall easier in same environment • Relevancy • Irrelevant material hinder memorization • Multiple coding • Data coded in many ways are easier to memorize • E.g. : children books – picture with words

41. Implication for interface design • Consistency • Avoid different formats at different part of the interface • Avoid forcing user to learn something out of the norm (unless very necessary) • Cues • Visual and/or audio • Provide comfort and assurance • Consider visual + audio

42. Implication for interface design • Divide workload appropriate • Computer good at memorizing • Human good at analyzing • Let each do its job • Stroop effect • Hard for human to deal with contradicting sources

43. Example Red Green Brown Blue

45. Example Blue Green Brown Red

47. Example Red Brown Blue Green