Scientific Underpinnings of Usability Engineering February 16, 2006

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.

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.

Two weeks ago . . . 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.

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.

Eye Physiology

Eye Muscles

Visual Field

Retinal Physiology

Distribution of Rods and Cones

Visual Sensitivity

Visible Spectrum

Neural Pathways

Aftereffect

Ambiguous Figure

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???

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

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) Monocular (next screen) Static Motion parallax

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

Monocular Cues -- Interposition

Monocular Cues -- Size

Monocular Cues – Linear Perspective

Monocular Cues – Texture Gradient

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

Monocular Cues – Aerial Perspective

Monocular Cues -- Shading

Monocular Cues – Motion Parallax

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

Ponzo Illusion

Muller-Lyer Illusion

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)

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.

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.

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.

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.

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.

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?”

Rubenstein et al. (1971) Used a lexical decision task (word/nonword?). Two types of nonwords – 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.

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).

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

In week 1, we were 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.

3333333333333333333333333333333

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?

BOV NAZ TOL RIJ DIH REN WUK CAQ GOC MEB

BOV NAZ TOL RIJ DIH REN WUK CAQ GOC MEB

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?

VAM LUN XOP REH WIV CIT JEG KUC ZOB YAD

VAM LUN XOP REH WIV CIT JEG KUC ZOB YAD

Experiment 3 Same as Experiment 2. Yet 10 more CVCs. Backwards counting. Don’t have to recall them in order. Pencils down. Ready?

GEP TIV WOH LUP MAZ SEX KOL RUC NID BIR

GEP TIV WOH LUP MAZ SEX KOL RUC NID BIR

So? So, the answer to “Can you remember a 30-digit number?”, is . . . It depends. On what? Whether you hear or see the number. Whether the number is masked. Whether you have time to rehearse. Whether you can “chunk” the numbers. If there are any intervening tasks. How meaningful the number is. WHAT the number is. So, what’s a usable interface? It depends.

SO WHAT? Given that we’re so all-fired complex, what does this have to say about how we design computer interfaces? Depth cues. Color perception. Effects of context on perception. What’s easy to read? Recognition vs. recall.

Last week’s homework Good and bad web site designs

Coming Up Next week: Guest Lecture by local usability consultant, Gordon Montgomery Make sure you’ve done the reading!