1 humans as information processors cs2352 lecture 6 robert stevens stevensr

1http://img.cs.man.ac.uk/stevens

Humans as Information Processors

CS2352 Lecture 6

Robert Stevens

http://www.cs.man.ac.uk/~stevensr


Introduction

• 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)


The Model Human Processor

• Three sub-systems:

1. The perceptual system

2. The motor system

3. 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


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


Five Input Channels

• The perceptual sub-system

1. Visual system

2. Auditary system

3. Haptic (touch) system

4. Olfactory (smell) system

5. 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


The Eye


Capabilities of the Visual System• Primary source of information• Two stages:1. Image acquisition2. 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


Capabilities of the Visual System (2)

• 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


Vision in Reading• 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


The Ear


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


The Haptic System

• 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


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


Human Memory

• 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


Organisation of Human Memory

Sensory memories Iconic Echoic Haptic

Short-term memoryor

Working memoryLong-term memory

Attention Rehearsal


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


Working Memory

• 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


Chunking

• Not just 7 +-2 individual items• 7+-2 chunks of information• 01412639082 0141 263 9082• Sub-conscious desire to chunk information• Successful formation of a chunk is “closure”• Meaningful chunks better • Useful in organising presentation


Long Term Memory• 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


Human Thinking• 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


Mental Models and Errors

• 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


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


Why is all this Important?

• 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


Reading

• Chapter 1: The human• Dix, Findlay, Abowd and Beale;• HCI

1 humans as information processors cs2352 lecture 6 robert stevens stevensr

Documents

perceptual system

motor system

cognitive system

auditary system

taste system

sensory system

world slide

human system gui