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Human Abilities

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Basic Human Capabilities

Why do we have to learn this stuff?• Do not change very rapidly

– Not like Moore’s law!

• Have limits, which are important to understand• Our understanding of human capabilities does change

– Cognitive neuroscience– Theories of color perception– Effect of groups and situation on how we act and react

• Have important design considerations

Human Abilities

• Our Senses– How to sense changes/information

• Our Cognition– How we process and interpret input

• Our Motor System– How we can react to input and cognition

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4

Sight, hearing, touch important for the design of current InterfacesSmell, taste, other ???

Abilities and limitations constrain design space

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Sight, hearing, touch important for the design of current InterfacesSmell, taste, balance, pain,

temperature, kinesthetic

Abilities and limitations constrain design space

• Visual angle– Total: 200 degrees– High-res: ~15 degrees

• Rods– 120 million!– B/W– 1000x more sensitive

than cones

• Cones– 6-7 million– 64% red– 32% green– 2% blue

Visual phenomena

• Color perception– 7-8% males cannot distinguish red from green– 0.4% of women

• Peripheral vision– Largely movement oriented

• Stereopsis– Monocular (size, interposition, perspective, paralax)– Binocular (retinal disparity, accommodation)

http://www.michaelbach.de/ot/

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

CS / PSYCH 4750

Touch

• Three main sensations handled by different types of receptors:– Pressure (normal)– Intense pressure (heat/pain)– Temperature (hot/cold)

• Sensitivity, Dexterity, Flexibility, Speed

• Where important?– Mouse, Other I/O, VR, surgery

Key concepts

• Absolute threshold– Lowest detectable signal

• Signal detection– Ability to “tune in” or “tune out” signal

• Just noticeable difference (jnd)• How much change in stimulus is needed before we can sense

difference?• Logarithmic (Webbers Law)

• Sensory adaptation– We react to change– Absence of change leads us to loose sensitivity (psychological

nystagmus)

Color, from 400 to 700 mm

JND

, m

m

Motor System (Our Output 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

COGNITION

Cognitive Processes

• Attention

• Perception and recognition

• Memory

• Learning

• Reading, speaking and listening

• Problem-solving, planning, reasoning and decision-making

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)

Model Human Processor

A simplification/Abstraction of the HumanBrain

Not model of how anyone actually thinksBrain operates, but a useful abstract Model based on real observational data

Useful for reasoning about designDesign guidelines, and the basis forSeveral predictive models of usability

Block Diagram

LONG-TERM MEMORY

SHORT-TERM (WORKING) MEMORY

AUDITORY IMAGESTORE

VISUAL IMAGESTORE

R = SemanticD = InfiniteS = Infinite

R = AcousticD = 1.5 [0.9-3.5] sS = 5 [4.4-6.2] letters

R = VisualD = 200 [70-1000] msS = 17 [7-17] letters

R= Acoustic or VisualD (one chunk) = 73 [73-226] sD (3 chunks) = 7 [5-34] sS = 7 [5-9] chunks

R = RepresentationD = Decay TimeS = SizeC = Cycle Time

PERCEPTUALPROCESSOR

C = 100 [5-200] ms

COGNITIVEPROCESSOR

C = 70 [27-170] ms

MOTORPROCESSOR

C = 70 [30-100] MS

Eye movement (Saccade) = 230 [70-700] ms

Memory

• Perceptual “buffers”– Brief impressions

• Short-term (working) memory– Conscious thought, calculations– Order of seconds

• Long-term memory– Minutes, hours, days, years, decades… – Long term, large storage space

Short Term (Working) Memory

• Working memory– Visuospatial sketchpad, phonological loop, central

control

• Characteristics– Details decay quickly (70 - 1000 ms visual; 0.9 - 3.5

sec auditory)– Limited capacity (7 - 17 letters visual; 4 - 6 auditory)– Rehearsal prevents decay– Chunking to remember more (7+-2)– Interference from LTM & recent items

What about long-term memory?

Long-Term Memory

• Seemingly permanent & unlimited

• Access is harder, slower-> Activity helps (we have a cache)

• Retrieval depends on network of associations

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

• One theory says it’s like a network• Another uses frames & scripts

Different models/theories for decision-making/reasoning

• Production systems– If-then rules

• Connectionism (big idea in IS)– Neural networks– Hidden Markov models– Bayesian networks

• Mediated action– Actions must be interpreted in context– Tools, setting, culture

Conceptual & Mental Models

UserDesigner

Conceptual Model

Mental Model

System model/image

SystemInstantiated in

Mental model of mental model

Invokes existing knowledgeand/or

Affordances guide action

Test hypotheses

Everyday reasoning & mental models

How does the hot water tap work?

How does your AC/Heater work?

Mental models

• User’s understanding (internal rep) of a system– How to use the system (what to do next) (functional

knowledge)– What to do with unfamiliar systems or unexpected

situations (how the system works) (Structural knowledge)

• People make inferences using mental models of how to carry out tasks

• Involves unconscious and conscious processes, where images and analogies are activated

Conceptual Models

Designer’s interpretation of how users should think/reason about the system

Conceptual models based on activities– Instructing: the user instructs the system on what to do next– Conversing: the user and system are dialogue partners; based

on metaphor of human-human conversation– Manipulating and navigating: manipulate objects; navigate

through virtual spaces; based on users’ knowledge of these activites in the real world

– Exploring and browsing: based on people’s experiences with browsing other media, e.g., magazines, radio, TV, libraries

Conceptual Models (2)

Conceptual models based on objects– Books, tools, vehicles

Usually implies a metaphor– Metaphor uses an “unconventional” interpretation of

the relationship between two entities– Analogy is based on the accurate match between two

entities; the closer the match, the better the analogy

In user interface design, we talk about “metaphor”, but we often mean analogy

Building good Mental models

• Leverage existing knowledge and invoke correct associations/assumptions through good cognitive models

• Embed knowledge in the system– Reduce memory load– Computational offloading

• Remember: Physics, devices & environment shape mental models as well

• Allow for transparency to allow users to develop metter models