Transcript Humans as Information Processors CS2352 Lecture 6

Humans as Information Processors
CS2352 Lecture 6
Robert Stevens
http://www.cs.man.ac.uk/~stevensr
http://img.cs.man.ac.uk/stevens
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Introduction
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Humans are intelligent users of tools
They observe the world and its state
The information about state is processed and actions formulated
Actions articulated using tools in the world
The state of the world changes and is observed
Information passes into the human; it is processed and
information passes out into the world
• The Model Human Processor (Card, Moran and Newell)
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The Model Human Processor
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Three sub-systems:
The perceptual system
The motor system
The cognitive system
Each has its own memory and processor
The cognitive system controls the others and is necessarily
more complex
The sensory system gives the state of the world
The motor system articulates actions upon the world
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Capabilities & Limitations
• Senses acquire information and senses have limitations
• Information stored in memory and memory has its limitations
• Reasoning and problem solving applied to stored and observed
information
• …but reasoning and problem solving has its limitations
• Design the UI to work to the limitations and capabilities of the
human system
• GUI rely less on memory and liked by the majority of users
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Five Input Channels
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The perceptual sub-system
Visual system
Auditary system
Haptic (touch) system
Olfactory (smell) system
Taste system
For computers, the first three are important
Important role as input channels to the human processor
Also possible role as output channel, giving information to the
computer
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The Eye
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Capabilities of the Visual System
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Primary source of information
Two stages:
Image acquisition
Processing and interpretation
Rods: Sensitive to light; poor for detail; easily saturated (temporary
blindness on moving into light); dominate peripheral vision
Cones: Colour vision; more detail (concentrated in fovea); less easily
saturated
X-cells nerves in fovea that detect patterns
Y-cells – nerves that help detect movement
Recognition of coherent scenes; Disambiguation of relative distances;
discrimination of colour
All necessary for interaction with the world
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Capabilities of the Visual System
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Visual acuity is the size of the smallest thing we can see
Acuity increases with luminense
High luminense displays afford acuity, but increase flicker
Frequency < 50 Hz gives flicker, but easier to see at higher
luminense and in peripheral vision (larger screens more flicker)
Colour: Hue (wavelength); intensity (brightness) & saturation
(amount of whiteness)
Only 4% fovea has blue cones, so blue less well perceived
150 hues discriminated; varying intensity and saturation mean
7,000,000 colours may be seen
Without training only 10 reliably dscriminated in absolute terms
10 % males and 1% females colour blind
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Vision in Reading
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Eye fixates upon words, during which processing takes place
Jumps from fixation to fixation in saccades (no processing)
Regressions move back to words for re-fixation
Return saccades return to beginning of next line
More complex material, Shorter saccades, longer fixation, more
regression, etc.
Some typefaces easier to recognise than others
10, 11 & 12 point all satisfactory for normal vision
Optimum line length for return saccades
Seriphed typeface has more cues for character recognition
Some words recognised by shape; removing shape cues
decreases reading speed
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The Ear
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Capabilities of the Auditory System
• Viewed as secondary, but large amounts of information, even
excluding speech
• Environmental sound
• Opften cues in vision
• Sound is change in air pressure: Pitch (frequency) loudness
(amplitude) timbre (sound type)
• 15Hz to 20 KHz
• Distinguish changes at 1.5Hz, but less discrimination of high
frequency
• Attention filters out background noise
• Monitoring allows sound to be picked out – the cocktail party
effect
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The Haptic System
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Much environmental information through touch
Feedback about actions taken
“Touch sensitive” buttons often don’t give feeback
Try typing wearing gloves
Touch enhances other senses – picking up a glass without touch
VR environments often lack “reality” because of touch
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Movement
• Kinesthesis gives feedback about movement and position of
limbs
• Touch typists must have awareness of position of fingers etc.
• Memory of “where things are located” through Kinesthetic
memory
• Touch perception that gives impression of comfort – an
important aspect of using computers!
• Hitting a target is a function of target size and distance to be
moved
• Fitt’s law Movement time = a + b log2(distance/size + 1)
• Targets as large as possible and close together as possible
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Human Memory
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Vital to most activities: Short and long term storage of
information; reasoning; protocols or procedures; manipulation of
information
• Memory associated with each part of the model information
processor
1. Sensory memory
2. Working memory
3. Long term memory
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Organisation of Human Memory
Sensory memories
Iconic
Echoic
Haptic
Attention
Short-term memory
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Working memory
Rehearsal
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Long-term memory
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Sensory Memory
• Buffers for stimuli from the physical sensing organs
• Iconic, echoic and haptic sensory memory
• Information short-lived and constantly overwritten (0.5 seconds
for iconic memoory)
• Echoic memory allows some play-back
• Only perceived if moved onward in processing
• Attention (concentration of the mind upon a particular stimulus)
selects stimuli to be passed on
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Working Memory
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for recall and processing of information
A “scratch pad” for information manipulation 42 * 5 (2*5 + 40 *5)
Rapid access (70ms) and rapid decay (200ms)
Limited capacity 7+-2 digits (digit span)
Recency effect means items later in list remembered better
Interference with another task abolishes such an effect – earlier
items in longer storage?
• Visual and auditory tasks interfere less, suggesting visual and
articulatory working memory
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Chunking
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Not just 7 +-2 individual items
7+-2 chunks of information
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Sub-conscious desire to chunk information
Successful formation of a chunk is “closure”
Meaningful chunks better
Useful in organising presentation
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Long Term Memory
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Facts, experience, protocols and procedures – everything we know
Huge, maybe unlimited capacity
Slow access time (0.1 sec)
Long decay time (if at all)
Movement from working to long-term after short time
Allows Inference of new information and generalisations to be made.
Structured, concrete, meaningful & familiar information easier to
remember
Recall easier with cues to “categories” of information
Episodic memory for events & experience in serial form
Semantic memory structured organisation of facts, concepts and skills
A “network” allows associations between items and inheritance of
attributes through the network
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Human Thinking
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Reasoning is the process of using our knowledge to draw conclusions
or infer new knowledge
Deductive reasoning draws the necessary conclusion from the given
premises
On Fridays I go home early: It’s Friday, therefore….
Reasoning not clean, we use our world knowledge & people don’t
reason about UI
Induction is generalisation from cases we have encountered
All elephants I’ve seen have trunks: All elephants have trunks
Again, people will do this with UI
Abduction reasons from a fact to the causative event
When drunk, Robert Slurs: Robert slurs….
Problem solving: Finding a solution to a new task
Of course, Problem solving uses reasoning
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Mental Models and Errors
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Human thinking is impressive, but mistakes are made
Recovery can be easy or difficult, but errors should be minimised
Slips when mental models don’t accommodate deviation
When trying to change a familiar task (attempting to stop at shops on
the way home)
Mis-understanding or poor mental model
Mental models are our view of how the world works
These are partial, often incorrect”, may be irrational and based upon
superstition
Errors occur when the world does not conform to our mental model
Try and give a UI from a good mental model can be derived
Contravening
convention often causes error
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Individual Differences
• There are generalisation about humans, but each human is an
individual
• There are many kinds of user
• Gender, age, disability, culture
• All may lead to different capabilities
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Why is all this Important?
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Humans use computers
They observe the state of the world and articulate actions
Users have a model of the world and its artefacts
Our UI need to either conform to this model or create a good
model
• Capabilities and limitations of the human information processor
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Reading
• Chapter 1: The human
• Dix, Findlay, Abowd and Beale;
• HCI
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