Scientific Underpinnings of Usability Engineering Intro Usability Week 2

First – something left over from last week. It’s not always a fight!

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.

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.

Ear Physiology

Basilar membrane

Eye Physiology

Eye Muscles

Visual Field

Retinal Physiology

Distribution of Rods and Cones

Visible Spectrum

Visual Sensitivity

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

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.

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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.

Next . . . Let’s take a slightly longer-than-average break. Check out the wiki. Check out the books that have been reviewed. Pick one of these, or some NEWER book that you gotta go buy! You MAY write a second review of a book that has already been reviewed.

The wiki http://courses.ischool.utexas.edu/rbias/wiki/ User ID: seven Pwd: plusorminustwo

Break time!

People Differ Some of your users/visitors may be: In a public library Non-native English speakers Left handed Capricorns Republicans Heterosexuals Poor visual processors In a hurry Alabamans In a public library Blind Mostly blind Color blind Geniuses Drunk Visitors to your earlier site First-time web visitors! On a subway Using a PDA

Situations Differ Cognitive Set Context influences perception. A series of events can “set” a person to perceive things a certain way.

Guess what frequent error was made on this form, on an IBM Service site: Name: ___________________ Street Address: ___________________ City: ___________________ State/ZIP: ___________________ County: ___________________

Design of Everyday Things It ain’t rocket science. You’ve already read the book. Let me hit just the high points from my point of view While I’m presenting this, see if you can characterize your good and bad designs that you’ve discovered this week in Norman’s terms.

Chapter 1 The PsychoPATHOLOGY of everyday things Assumption: We blame ourselves for errors, but the real culprit is faulty design. Assumption: There’s nothing special about computers. They have the same sorts of design problems as simpler, everyday things.

Good Design Well designed objects . . . Poorly designed objects . . . are easy for the mind to understand contain visible cues to their operation Poorly designed objects . . . provide no clues, or provide false clues.

Natural Signals Natural signals lead to natural design. A metal plate “naturally” is to be pushed. Visible hinges “naturally” indicate attachment, and that the other side swings open. (And swings open TOWARD me?)

Mapping Mapping is a relationship between two things (e.g., between what you want to do and what appears possible). Good design allows for a clear (visible) mapping between . . . intended actions and actual operations. Now -- think of what this might mean in a web site.

Good Design Principles of good design the importance of visibility appropriate clues feedback of ones actions. Just so you’ll know -- others have proposed OTHER principles of good design. Go check out the web site of Bruce Tognazzini: http://www.asktog.com/basics/firstPrinciples.html

Affordance Affordance is the perceived and actual properties of a thing. Primarily those fundamental properties that determine how a thing could possibly be used. “Affords” means, basically, “is for.” A chair affords support, therefore affords sitting. Affordances provide strong clues to things’ operations. When affordances are taken advantage of, the user knows what to do just by looking. No label, picture, or instruction (“Push”) is required. When simple things need pictures, labels, or instructions, the design has failed.

The Paradox of Technology Added functionality generally comes along at the price of added complexity. The same technology that simplifies life by providing more functions also complicates life by making the device harder to learn and use. The Paradox of Technology should never be used as an excuse for poor design. Added complexity cannot be avoided when functions are added, but with clever design they can be minimized.

Chapter 2 -- Psy of Everyday Actions Norman’s credo on errors -- if an error is possible, someone will make it. The designer must design so as to: minimize the chance of errors in the first place minimize the effects of an error make errors easy to detect make errors reversible, if possible.

Models objects work events take place people behave Mental Models = our conceptual models of the way . . . objects work events take place people behave Mental models result from our tendency to form explanation of things. Models are essential in helping us . . . understand our experiences predict the outcomes of our actions handle unexpected occurrences.

Models (cont’d.) We base our models on whatever knowledge we have: real or imaginary naïve or sophisticated even fragmentary evidence. Everyone forms theories (mental models) to explain what they have observed. In the absence of feedback to the contrary, people are free to let their imaginations run free. More on models in Chapter 3.

7 Stages of Action On p. 47 is a series of four figures that illustrate Norman’s view of the structure of action. Actions have two major aspects: Doing something (execution) Checking (evaluation)

Chapter 3 - Knowledge in the Head and in the World Not all knowledge required for precise behavior must be in the head. It can be distributed: partly in the head partly in the world partly in the constraints of the world.

Constraints The power of constraints -- the “memory” for epic poetry is found to be mostly reconstruction, with the aid of the constraints of rhyme, meter, etc. We use constraints to simplify what we must remember. For example, putting mechanical parts together. Some are constrained by what will and will not fit together. Also cultural constraints -- screws tighten clockwise.

Memory . . . is knowledge in the head. Think of all you can remember. Phone numbers, postal codes, passwords, SSN, birthdays, etc., etc. It’s tough! So, we put memory in the world. (Daytimers. Smartphones. Address books. Stickies.)

Tradeoff . . . . . . between info in the world and in the head. Knowledge in the world acts as its own reminder. Knowledge in the head is efficient. (You can travel light.) Knowledge in the world is easier (no learn time), but often difficult to use. Relies heavily on the physical presence of info. See Fig. 3.6, p. 79.

Ch. 4 -- Knowing what to do When we encounter a novel object, either We’ve dealt with something similar before, and we transfer old knowledge, or We get instruction. Thus, information in the head.

Design How can the design of an object (NOTE: info in the world) signal the appropriate actions? Natural (physical) constraints Affordances, that convey messages about the item’s possible uses, actions, and functions “The thoughtful uses of affordances and constraints together in design lets a user determine readily the proper course of action even in a novel situation.”

Ch. 5 - To err is human Errors come in several forms Slips -- result from automatic behavior, when subconscious actions get waylaid en route (“performance errors”) Mistakes -- result from conscious deliberations (“competence errors”)

Ch. 6 -- The Design Challenge Norman talks about what forces work against evolutionary, or natural design (pp. 142-143). The demands of time (quick product cycles) The pressure to be distinctive (related to the curse of individuality)

Pitfalls Three reasons why designers go astray: Putting aesthetics first Designers aren’t typical users Designers’ clients may not be the users

Ch. 7 - UCD Chapter 7 is the “punch line” of the whole book. User-Centered Design Most of the chapter is given over to describing “seven principles for transforming difficult tasks into simple ones.”

Etc. He goes on to offer a section on why you might want to design something to be hard to use ON PURPOSE. And he ends with a few sections on writing, the home of the future, and a concluding section.

Now . . . Let’s try to put it in Norman’s terms why the good designs were good and the bad designs were bad. (“Some important feature was, or was not, visible.”)

. . . your homework Bad web designs. Good web designs. Send at least 2 URLs to the TA. Famous quote: “No one ever raised a statue to a critic.” Sibelius I want us all to remember that it is easier to criticize another design than it is to design something.

For next week Book review due in 3 weeks. Send me your white paper topics. Due 5 weeks from today. More reading Usability test plan (for your final project) due in 7 weeks. Will help with pointers to templates. For next week, come with one good and one bad example of web usability. Actually, send ‘em to the TA by Monday noon.