Human Abilities Sensory and cognitive capabilities Typical Person

Human Abilities Sensory and cognitive capabilities

Typical Person l Do we really have limited memory capacity?

Basic Human Capabilities l Do not change very rapidly – Not like Moore’s law! l Have limits, which are important to understand l Why do we care? – – l Better design! Want to improve user performance Universal design – design for everyone, including those with disabilities – We’ll come back to this later in the semester…

Usable Senses The 5 senses (sight, sound, touch, taste and smell) are used by us every day – – each is important on its own together, they provide a fuller interaction with the natural world Computers rarely offer such a rich interaction We can use • sight • sound • touch (sometimes) We cannot (yet) use • taste • smell

Vision (more to come in visual design) l Color – About 9 % of males are red-green colorblind! l – l l See http: //colorlab. wickline. org/colorblind/colorlab/ Color perception is weak in peripheral vision Movement in our peripheral vision is distracting Acuity (the smallest size we can see) – Less for blue and yellow than for red and green

Color Surround Effect l Our perception of a color is affected by the surrounding color

Which is easiest to read and why? What is the time? What is the time? From http: //www. id-book. com

Audition (Hearing) l l Often take for granted how much we rely on it (error beeps, disk whirring) Sounds are transitory – Good for alerts, redundant communication l People become habituated to continuous sounds Some sounds can also be distracting or annoying We are very good at determining source of a sound l Implications ? l l

Attention l Involves audio and/or visual senses l Selecting things to concentrate on from the mass of stimuli around us l Focused and divided attention enables us to be selective but limits our ability to keep track of all events è Structure information to capture users’ attention è perceptual boundaries (windows), color, reverse video, sound and flashing lights From http: //www. id-book. com

Activity: Find the price of a double room at the Holiday Inn in Bradley From http: //www. id-book. com

Activity: Find the price for a double room at the Quality Inn in Columbia From http: //www. id-book. com

Study l Tullis (1987) found that the two screens produced quite different results – – l l 1 st screen - took an average of 5. 5 seconds to search 2 nd screen - took 3. 2 seconds to search Why, since both displays have the same density of information (31%)? Spacing – – In the 1 st screen the information is bunched up together, making it hard to search In the 2 nd screen the characters are grouped into vertical categories of information making it easier From http: //www. id-book. com

Design implications l l Representations of information need to be perceptible and recognizable Make information salient when it needs attending to – Make things stand out with colour, ordering, spacing, underlining, sequencing and animation l Avoid cluttering the interface l Sounds should be audible and distinguishable Speech output should enable users to distinguish between the set of spoken words l From http: //www. id-book. com

Motor System (Our Output System) l Capabilities – l Often cause of errors – – l Wrong button Double-click vs. single click Principles – – l Range of movement, reach, speed, strength, dexterity, accuracy Feedback is important Minimize eye movement See Handbooks for data

What goes on in the mind?

Core cognitive aspects l Attention l Perception and recognition l Memory l Reading, speaking and listening l Problem-solving, planning, reasoning and decisionmaking, learning

The “Model Human Processor” l A true classic - see Card, Moran and Newell, The Psychology of Human-Computer Interaction, Erlbaum, 1983 – – – l Microprocessor-human analogue using results from experimental psychology Provides a view of the human that fits much experimental data But is a partial model Focus is on a single user interacting with some entity (computer, environment, tool) – Neglects effect of other people

Memory l Perceptual “buffers” – l Short-term (working) memory – l Brief impressions Conscious thought, calculations Long-term memory – Permanent, remember everything that ever happened to us

LONG-TERM MEMORY R = Semantic D = Infinite SHORT-TERM (WORKING) MEMORY VISUAL IMAGE STORE R = Visual D = 200 [70 -1000] ms S = 17 [7 -17] letters AUDITORY IMAGE STORE R = Acoustic D = 1. 5 [0. 9 -3. 5] s S = 5 [4. 4 -6. 2] letters R= Acoustic or Visual D (one chunk) = 73 [73 -226] s D (3 chunks) = 7 [5 -34] s S = 7 [5 -9] chunks PERCEPTUAL PROCESSOR COGNITIVE PROCESSOR MOTOR PROCESSOR C = 100 [5 -200] ms C = 70 [27 -170] ms C = 70 [30 -100] MS R = Representation D = Decay Time S = Size C = Cycle Time Eye movement (Saccade) = 230 [70 -700] ms

Sensory Stores l l Very brief, but accurate representation Physically encoded Limited capacity – Iconic: 7 -17 letters – Echoic: 4 -6 – Haptic: ? ? Rapid Decay – Iconic: 70 -1000 ms – Echoic: 0. 9 – 3. 5 sec

Short Term Memory l l Symbolic, nonphysical acoustic or visual coding Somewhat limited capacity – l l 7 +- 2 “chunks” of information Slower decay – 5 -226 sec – rehearsal prevents decay Another task prevents rehearsal - interference

About Chunks l l A chunk is a meaningful grouping of information – allows assistance from LTM 4793619049 vs. 704 687 8376 NSAFBICIANASA vs. NSA FBI CIA NASA My chunk may not be your chunk – User and task dependent

Long-Term Memory l l l Semantic storage Seemingly permanent & unlimited Access is harder, slower – l l -> Activity helps (we have a cache) Retrieval depends on network of associations How information is perceived, understood and encoded determines likelihood of retrieval File system full

LT Memory Structure l Episodic memory – Events & experiences in serial form l l Helps us recall what occurred Semantic memory – Structured record of facts, concepts & skills l l One theory says it’s like a network Another uses frames & scripts (like record structs)

Memory Characteristics l Things move from STM to LTM by rehearsal & practice and by use in context – – l Do we ever lose memory? Or just lose the link? What are effects of lack of use? We forget things due to decay and interference – Similar gets in the way

Processing in memory l Attention filters information into memory and for more processing – – – l The more attention paid to something, And the more it is processed in terms of thinking about it and comparing it with other knowledge, The more likely it is to be remembered Context is important – Difficult to remember things in another context

Activity l l Try to remember the dates of your grandparents’ birthday Try to remember the cover of the last two DVDs or games you bought or rented Which was easiest? Why? People are very good at remembering visual cues about things – l e. g. , the color of items, the location of objects and marks on an object They find it more difficult to learn and remember arbitrary material – e. g. , birthdays and phone numbers From http: //www. id-book. com

Implications? l Which is an implication of 7 +- 2? – – Use about 7 items on a menu Display 7 icons on a task bar No more than 7 tabs on a window 7 bullets in a list ALL WRONG!

Why? l l Inappropriate application of theory People can scan lists of bullets, tabs, menu items till they see the one they want They don’t have to recall them from memory having only briefly heard or seen them Sometimes a small number of items is good design – But it depends on task and available screen, NOT memory From http: //www. id-book. com

Recognition over Recall l We recognize information easier than we can recall information l Examples? Implications? l

Externalizing to reduce memory load l Reminders, calendars, notes, shopping lists, to-do lists - written to remind us of what to do l Post-its, piles, marked emails - where placed indicates priority of what to do l External representations: – – – Remind us that we need to do something (e. g. to buy something for mother’s day) Remind us of what to do (e. g. buy a card) Remind us when to do something (e. g. send a card by a certain date) From http: //www. id-book. com

Memory Summary l l l Involves encoding and then retrieving knowledge We don’t remember everything - involves filtering and processing what is attended to Context is important in affecting our memory (i. e. , where, when) Well known fact that we recognize things much better than being able to recall things Also better at remembering images than words – Why interfaces are largely visual From http: //www. id-book. com

Design implications l l l Don’t overload users’ memories with complicated procedures for carrying out tasks Design interfaces that promote recognition rather than recall Provide users with a variety of ways of encoding digital information to help them remember where they have stored them – e. g. , categories, color, flagging, time stamping From http: //www. id-book. com

Other processes: Learning l Facilitated – – – l By structure & organization By similar knowledge, as in consistency in UI design By analogy If presented in incremental units Repetition Hindered – By previous knowledge l Þ Þ Try moving from Mac to Windows Consider user’s previous knowledge in your interface design Encourage exploration

Other Processes: Problem Solving l l Users focus on getting job done, not learning to effectively use system We are more heuristic than algorithmic – We try a few quick shots rather than plan l l Resources simply not available We often choose suboptimal strategies for low priority problems We learn better strategies with practice Users apply analogy even when it doesn’t apply – Or extend it too far - which is a design problem l Dragging floppy disk icon to Mac’s trash can does NOT erase the disk, it ejects disk!

Implications l l l Help users accomplish main tasks Provide useful analogies Allow flexible shortcuts and multiple ways to accomplish a task – Forcing plans will bore user

People l Good 1. 2. 3. xxx yyy zzz l Bad 1. 2. 3. aaa bbb ccc Fill in the columns what are people good at and what are people bad at?

People l Good – – – Infinite capacity LTM duration & complexity High-learning capability Powerful attention mechanism Powerful pattern recognition Flexible problem solving l Bad – – – Limited capacity STM Limited duration STM Unreliable access to LTM Error-prone processing Slow processing

Example: Passwords l What’s wrong with computer passwords? How do people cope? How to banks, sites, etc. cope? l Suggested improvements: l l – – – Have a tool remember them all How about visual passwords? Eliminate the need – use biometrics

Reminder: Assignment l Task analysis due Monday l And get started on your Project Part 1!