Human Abilities and Models
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Presentation Transcript
Human Abilities and Models Sensory and cognitive abilities and models, models of human performance
Outline • Human capabilities and disabilities • Senses • Motor systems • Memory • Cognitive Processes • Selective attention, learning, problem solving, language • Predictive models • Contextual models
Typical Person • Do we really have limited memory capacity?
Basic Human Capabilities • Do not change very rapidly • Not like Moore’s law! • Have limits, which are important to understand • Why do we care? • Better design! • Want to improve user performance • Universal design – designing for all people, including those with disabilities
But… we’re all disabled sometimes • Environment • Fatigue • Injury • Aging • Changing role of information technology
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 Can we use all the available senses? • ideally, yes • practically – no We can use • sight • sound • touch (sometimes) We cannot (yet) use • taste • smell
Vision Fundamentals • Retina has • 6.5 M cones (color vision), mostly at fovea (1/3)˚ • About 150,000 cones per square millimeter • Fewer blue sensing cones than red and green at fovea • 100 M rods (night vision), spread over retina, none at fovea • Adaptation • Switching between dark and light causes fatigue
Vision implications (more to come in visual design) • Color • Distinguishable hues • optical illusions • Acuity • Determines smallest size we can see • Less for blue and yellow than for red and green
Color/Intensity Discrimination • The 9 hues most people can identify are: ColorWavelength Red 629 Red-Orange 596 Yellow-Orange 582 Green-Yellow 571 Yellow-Green 538 Green 510 Blue-Green 491 Blue 481 Violet-Blue 460
Color Surround Effect • Our perception of a color is affected by the surrounding color
Vision Difficulties • Color blindness • About 9 % of males are red-green colorblind! • See http://colorlab.wickline.org/colorblind/colorlab/ • Low-vision • The vast majority of visually disabled people have some sight • Blindness • Rely on other senses to receive information • Specialized hardware and software • Screen readers • Braille printers, etc.
Myopia and Hypermetropia • Myopia Hypermetropia • (short-sighted) (far-sighted)
Accommodating Partial Sight • Large monitor, high resolution, glare protection • Control of color and contrast • Control of font size everywhere • Keyboard orientation aids
Accommodating Blind Users • Screen Readers • Full-featured • Cursor-tracking, routing • Dialogue focus • View areas • Auditory or tactile output http://www.freedomscientific.com/fs_products/software_jaws.asp http://www.webaim.org/simulations/screenreader
Audition (Hearing) • Capabilities (best-case scenario) • pitch - frequency (20 - 20,000 Hz) • loudness - amplitude (30 - 100dB) • location (5° source & stream separation) • timbre - type of sound (lots of instruments) • Often take for granted how good it is(disk whirring) • Implications ?
Hearing uses • Redundant output • Email beep + icon, IM sound + popup message, etc. • Output when screen not available • Multimedia systems
Hearing problems or deafness • An increasing problem? • Population • Phone interfaces • Various technologies used: • Communication aids • Automated software (speech to text, etc.)
Touch • Three main sensations handled by different types of receptors: • Pressure (normal) • Intense pressure (heat/pain) • Temperature (hot/cold) • Where important? • Mouse, Other I/O, VR, surgery
Motor System • Capabilities • Range of movement, reach, speed,strength, dexterity, accuracy • Workstation design, device design • Often cause of errors • Wrong button • Double-click vs. single click • Principles • Feedback is important • Minimize eye movement • See Handbooks for data
Large Range of Physical Impairments • Complete lack of function • absence of a limb • paralysis – usually due to spinal injury, the higher the damage the greater the degree of paralysis • Lack of strength • Tremor/lack of accuracy • Slowness
Implications • Try to minimize movement and strain • Alternative input devices • Keyboard hardware and software • Speech input • Other input switches for more severe needs • Eye gaze, sip and puff, etc. • Acceleration techniques • Word completion, macros, etc.
The Mind • And now on to memory and cognition…
The “Model Human Processor” • A true classic - see Card, Moran and Newell, The Psychology of Human-Computer Interaction, Erlbaum, 1983 • 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 • Perceptual “buffers” • Brief impressions • Short-term (working) memory • Conscious thought, calculations • Long-term memory • Permanent, remember everything that ever happened to us
LONG-TERM MEMORY R = Semantic D = Infinite S = Infinite SHORT-TERM (WORKING) MEMORY VISUAL IMAGE STORE AUDITORY IMAGE STORE R= Acoustic or Visual D (one chunk) = 73 [73-226] s D (3 chunks) = 7 [5-34] s S = 7 [5-9] chunks R = Visual D = 200 [70-1000] ms S = 17 [7-17] letters R = Acoustic D = 1.5 [0.9-3.5] s S = 5 [4.4-6.2] letters PERCEPTUAL PROCESSOR C = 100 [5-200] ms COGNITIVE PROCESSOR C = 70 [27-170] ms MOTOR PROCESSOR C = 70 [30-100] MS R = Representation D = Decay Time S = Size C = Cycle Time Eye movement (Saccade) = 230 [70-700] ms
Sensory Stores • Very brief, but accurate representation of what was perceived • Physically encoded • Details decay quickly (70 - 1000 ms visual; 0.9 - 3.5 sec auditory) • Limited capacity • Iconic – visual • 7 - 17 letters; 70 - 1000 ms decay • Echoic – auditory • 4 - 6 auditory; 0.9 - 3.5 sec auditory • Haptic - touch • Attention filters information into short term memory and beyond for more processing
Short Term Memory • Symbolic, nonphysical acoustic or visual coding • Decay 5-226 sec, rehearsal prevents decay • Another task prevents rehearsal – interference • Use “chunks”: 7 +- 2 units of information
About Chunks • 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 • Seemingly permanent & unlimited • Access is harder, slower • -> Activity helps (we have a cache) • Retrieval depends on network of associations • How information is perceived, understood and encoded determines likelihood of retrieval • Effected by emotion, previous memory File system full
LT Memory Structure • Episodic memory • Events & experiences in serial form • Helps us recall what occurred • Semantic memory • Structured record of facts, concepts & skills • Semantic network theory • Or theory of frames & scripts (like record structs)
Memory Characteristics • Things move from STM to LTM by rehearsal & practice and by use in context • 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
Recognition over Recall • We recognize information easier than we can recall information • Examples? • Implications?
Processes • Four main processes of cognitive system: • Selective Attention • Learning • Problem Solving • Language
Selective Attention • We can focus on one particular thing • Cocktail party chit-chat • Salient visual cues can facilitate selective attention • Examples?
Learning • Two types: • Procedural – How to do something • Declarative – Facts about something • Involves • Understanding concepts & rules • Memorization • Acquiring motor skills • Automotization • Tennis • Driving to work • Even when don’t want to • Swimming, Bike riding, Typing, Writing
Learning • Facilitated • By structure & organization • By similar knowledge, as in consistency in UI design • By analogy • If presented in incremental units • Repetition • Hindered • By previous knowledge • Try moving from Mac to Windows => Consider user’s previous knowledge in your interface design
Observations • Users focus on getting job done, not learning to effectively use system • Users apply analogy even when it doesn’t apply • Or extend it too far - which is a design problem • Dragging floppy disk icon to Mac’s trash can does NOT erase the disk, it ejects disk!
Problem Solving • Storage in LTM, then application • Reasoning • Deductive - • Inductive - • Abductive - • Goal in UI design - facilitate problem solving! • How?? If A, then B Generalizing from previouscases to learn about new ones Reasons from a fact to theaction or state that caused it
Observations • We are more heuristic than algorithmic • We try a few quick shots rather than plan • Resources simply not available • We often choose suboptimal strategies for low priority problems • We learn better strategies with practice
Good xxx yyy zzz People • Bad • aaa • bbb • ccc Fill in the columns - what are people good at and what are people bad at?
Good Infinite capacity LTM LTM duration & complexity High-learning capability Powerful attention mechanism Powerful pattern recognition People • Bad • Limited capacity STM • Limited duration STM • Unreliable access to LTM • Error-prone processing • Slow processing
Models • Translating empirical evidence into theories and models that influence design. • Performance measures • Quantitative • Time prediction • Working memory constraints • Competence measures • Focus on certain details, others obscured
Fitts’ Law • Models movement times for selection tasks • Paul Fitts: war-time human factors pioneer • Basic idea: Movement time for a well-rehearsed selection task • Increases as the distance to the target increases • Decreases as the size of the target increases
D W STOP START Moving • Move from START to STOP Index of Difficulty: ID = log2 ( 2D/W )(in unitless bits) width of target distance
MT ID Movement Time MT = a + b*ID or MT = a + b log2 (2D/W) • Empirical measurement establishes constants a and b • Different for different devices and different ways the same device is used.
