Human Abilities
1
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
2
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
3
Sight, hearing, touch important for the
design of current Interfaces
Smell, taste, other ???
Abilities and limitations
constrain design space
4
Sight, hearing, touch important for the
design of current Interfaces
Smell, taste, balance, pain,
temperature, kinesthetic
Abilities and limitations
constrain design space
5
• 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
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
CS / PSYCH 4750
Key concepts
• Absolute threshold
– Lowest detectable signal
• Signal detection
– Ability to “tune in” or “tune out” signal
• Just noticeable difference (jnd)
Color, from 400 to 700 mm
• 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)
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
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•
•
•
•
•
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 Human
Brain
Not model of how anyone actually thinks
Brain operates, but a useful abstract
Model based on real observational data
Useful for reasoning about design
Design guidelines, and the basis for
Several predictive models of usability
Block Diagram
LONG-TERM MEMORY
R = Semantic
D = Infinite
S = 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
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
File system full
• Access is harder, slower
-> Activity helps (we have a cache)
• Retrieval depends on network of
associations
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
Conceptua
l Model
Designer
Mental model of
mental model
Test hypotheses
Instantiated in
System
System
model/image
Mental
Model
User
Invokes existing knowledge
and/or
Affordances guide action
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