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Scientific Underpinnings of Usability Engineering

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  1. Scientific Underpinnings of Usability Engineering February 5, 2004

  2. Objectives After this class you will be able to (it is my hope!): • Describe some eye physiology • Explain how the visual system works (somewhat) • Identify visual cues to depth • Explain some aspects of the psychology of reading • Explain how perceptual and cognitive psychology influence HCI designs • Have an excellent memory for “VAM” • Discuss the importance of designing systems to match the human.

  3. Designing Stuff • In Week 1, I asked the question “What would a system look like if we were designing it for dogs?” • Wouldn’t be a lot of text. • Wouldn’t require a lot of dexterity. • Might code information in smells and tastes. • But we’re designing systems for humans (usually!). So it will behoove us to know something about how human beings take in and process information.

  4. Last week . . . • Why were those designs poor? • At a high level, because they didn’t match your understanding, your organization of information. (Your mental model.) • The whole point: Let’s design systems to fit people instead of the other way around.

  5. Human Information Processing • How do human beings take in and process information? • Sensory psychology – how humans transform physical energy (e.g., light and sound waves) into sensory signals to and in the brain. • Perceptual psychology – how humans interpret these sensory signals as perceptions. • Cognitive psychology – how humans think about these perceptions, and previous experiences, and their own mental creations, and . . . • Psycholinguistics – The psychology of language -- what goes on between the time I have a thought and you have the same (or similar!) thought, whether I say it or write it.

  6. Eye Physiology

  7. Eye Muscles

  8. Visual Field

  9. Retinal Physiology

  10. Distribution of Rods and Cones

  11. Visual Sensitivity

  12. Visible Spectrum

  13. Neural Pathways

  14. Aftereffect

  15. Ambiguous Figure

  16. Sensation/Perception • POINT: Perceptions are made up of more than just a collection of sensations! • OTHER things influence our perceptions, e.g., • Our experiences • Our biases • The context • Our current emotional state • Etc. • So, what does that have to say about designing human-computer interfaces???

  17. Perceptual Psy – Color Vision • Color perception – 3 types of cones (RGB)

  18. Perceptual Psy -- Depth • Different visual cues to depth • Oculomotor vs. Visual • Oculomotor – Lens accommodation and extraocular muscle convergence are “read” by the brain • Visual: Binocular vs. Monocular • Binocular – Stereopsis (retinal disparity)

  19. More Depth Cues • Monocular • Static • Interposition • Size • Perspective • Linear perspective • Texture gradient • Aerial perspective • Shading • Motion parallax

  20. Monocular Cues -- Interposition

  21. Monocular Cues -- Size

  22. Monocular Cues – Linear Perspective

  23. Monocular Cues – Texture Gradient

  24. Sooooo . . . The grass really IS greener on the other side of the fence!!!

  25. Monocular Cues – Aerial Perspective

  26. Monocular Cues -- Shading

  27. Monocular Cues – Motion Parallax

  28. More visual perception • Illusions – and what they tell us about vision • Ponzo illusion • Muller-Lyer illusion

  29. Ponzo Illusion

  30. Muller-Lyer Illusion

  31. Psycholinguistics • The psychology of language. • What goes on from the time I get an idea until you have the same idea, • Whether I speak my idea (speech production, auditory science, speech perception) • Or write my idea (motor movements, visual system, reading)

  32. The Psychology of Reading • Except for fairly rare cases of “phonetic symbolism” (onomatopoeia) words have no inherent meaning. • (And rarer cases of “orthographic symbolism”!!) • So, READING is the interpreting of words, the acts that go on to impose meaning, from within, on external visual stimuli.

  33. Some facts about reading • Eyes of the mature reader move rhythmically across the page (from left to right). • Eye movement consists of fixations, saccades, regressions, and return sweeps. • No information is taken in during saccades (10-25 msec), regressions (same duration), or return sweeps (40 msec). • During fixation (250 msec) a visual pattern is reflected onto the retina. • Span of perception = amount of print seen during a single fixation. • Span of perception = 12 letter spaces for good readers, 6 for poor readers.

  34. More facts • Span of recognition – 1.21 words for senior high, 1.33 words for college readers. • So, 7 to 8 fixations per line of print. • As content gets tougher, duration of fixations, not number, changes (increases). • Regressive movements aren’t systematic. Used when attention is faltering. • College readers have 1 regressive movement per 3 or 4 lines of print. Immature readers have 3 or 4 regressions per line.

  35. Iconic Memory • Remember in Week 1 I mentioned a two-stage memory process – STM and LTM. • A third stage, Iconic Memory: The unidentified, “pre-categorical” pattern of lines, curves and angles; formed in about 100 msec. • Icon can hold up to 20 letter spaces. • Pattern recognition routines are applied to the lines, curves. • It takes about 10 – 20 msec to read each letter out of the iconic memory. • Neural signal takes about 30 msec to go from the retina to the visual cortex.

  36. Iconic Memory (cont’d.) • At some point, thanks to pattern recognition routines, letters are read out. • Letters are transformed into abstract phonemic representations. • The abstract phonemes are used to search the mental lexicon. • About 300 msec after the eye has fallen upon the page, the first word is “understood,” i.e., placed in Primary Memory (STM, Working Memory). • Syntactic and semantic rules are applied to gain the meaning of the sentence.

  37. How do you know, Randolph? • Psycholinguists employ a variety of methods to acquire this data about human behavior. • One question: Why do we think readers routinely transform the visual representation into a phonological representation? • Cognitive economy – all (healthy) new readers come to the task as skilled hearers. • “I thought you said something about data?”

  38. Rubenstein et al. (1971) • Used a lexical decision task (word/nonword?). • Two types of words – homophonous (with real words), like burd and nonhomophonous like rolt. Equally “wordlike.” • Longer latencies for burd. • Similarly, longer for real homophones like meat. • Pointed to “false matches” in the mental lexicon.

  39. More Data • McCusker et al. (1977) proofreading experiment • 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 with color words (e.g,. bloo) led to more interference than control words (e.g., blot) or nonwords nonhomophonous with color words (e.g., blop). • I found readers took longer to process words with irregular “spelling-to-sound rules” (e.g., pint) than words with regular rules (e.g., hint) (Bias, 1978).

  40. The Point • The reasons for this somewhat esoteric discourse on the psychology of reading are: • To communicate the complexity that is human information processing • The illustrate the ways scientists go about answering questions about info processing • To sensitize you to the sorts of things known about human behavior

  41. Last week, talking about Perception and Cognition • What do we know about humans? • In the physical realm: Anthropometry. • These days we’re more interested in the cognitive realm. • Question: Can you remember a 30-digit number? • I say that you can, right now, without practice, seeing it only once, for 1 second, with no time to rehearse.

  42. 3333333333333333333333333333333

  43. Experiment 1 Instead of numbers, I’ll present CVC (consonant-vowel-consonant) strings -- like “NEH”. 10 CVCs, one at a time. Presented visually. Don’t have to remember them in order. Pencils down. Ready?



  46. Experiment 2 • Now, 10 new CVCs. • Same task -- recall them. • This time, after we read the 10th item, we’ll all count backwards from 100 by 3s, aloud, together. • Then when I say “Go,” write down as many of the 10 CVCs as you can. • Pencils down. • Ready?