chapter 1

the human
the human

• Information i/o …
– visual, auditory, haptic, movement
• Information stored in memory
– sensory, short-term, long-term
• Information processed and applied
– reasoning, problem solving, skill, error
• Emotion influences human capabilities
• Each person is different
Vision

Two stages in vision

• physical reception of stimulus

• processing and interpretation of

stimulus
Interpreting the signal

• Size and depth

– visual angle indicates how much of view
object occupies
(relates to size and distance from eye)

– visual acuity is ability to perceive detail

(limited)

– familiar objects perceived as constant size

(in spite of changes in visual angle when far away)

– cues like overlapping help perception of

size and depth
Interpreting the signal (cont)

• Brightness
– subjective reaction to levels of light
– affected by luminance of object
– measured by just noticeable difference
– visual acuity increases with luminance as does
flicker

• Colour
– made up of hue, intensity, saturation
– cones sensitive to colour wavelengths
– blue acuity is lowest
– 8% males and 1% females colour blind
Interpreting the signal (cont)

• The visual system compensates for:

– movement
– changes in luminance.

• Context is used to resolve ambiguity

• Optical illusions sometimes occur due to

over compensation
Optical Illusions

the Ponzo illusion the Muller Lyer illusion

Reading

• Several stages:
– visual pattern perceived
– decoded using internal representation of language
– interpreted using knowledge of syntax, semantics,
pragmatics

• Reading involves saccades and fixations

• Perception occurs during fixations
• Word shape is important to recognition
• Negative contrast improves reading from
computer screen
Hearing

• Provides information about environment:

distances, directions, objects etc.
• Physical apparatus:
– outer ear – protects inner and amplifies sound
– middle ear – transmits sound waves as
vibrations to inner ear
– inner ear – chemical transmitters are released
and cause impulses in auditory nerve
• Sound
– pitch – sound frequency
– loudness – amplitude
– timbre – type or quality
Touch

• Provides important feedback about environment.

• May be key sense for someone who is visually impaired.
• Stimulus received via receptors in the skin:
– thermoreceptors – heat and cold
– nociceptors – pain
– mechanoreceptors – pressure
(some instant, some continuous)

• Some areas more sensitive than others e.g. fingers.

• Kinethesis - awareness of body position
– affects comfort and performance.
Movement

• Time taken to respond to stimulus:

reaction time + movement time
• Movement time dependent on age, fitness etc.
• Reaction time - dependent on stimulus type:
– visual ~ 200ms
– auditory ~ 150 ms
– pain ~ 700ms

• Increasing reaction time decreases accuracy in

the unskilled operator but not in the skilled
operator.
Memory
There are three types of memory function:

Sensory memories

Short-term memory or working memory

Long-term memory

Selection of stimuli governed by level of arousal.

sensory memory

• Buffers for stimuli received through

senses
– iconic memory: visual stimuli
– echoic memory: aural stimuli
– haptic memory: tactile stimuli
• Examples
– “sparkler” trail
– stereo sound
• Continuously overwritten
Short-term memory (STM)

• Scratch-pad for temporary recall

– rapid access ~ 70ms

– rapid decay ~ 200ms

– limited capacity - 7± 2 chunks

Examples

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0121 414 2626

HEC ATR ANU PTH ETR EET

Long-term memory (LTM)

• Repository for all our knowledge

– slow access ~ 1/10 second
– slow decay, if any
– huge or unlimited capacity

• Two types
– episodic – serial memory of events
– semantic – structured memory of facts,concepts, skills

semantic LTM derived from episodic LTM

Long-term memory (cont.)

• Semantic memory structure

– provides access to information
– represents relationships between bits of information
– supports inference

• Model: semantic network

– inheritance – child nodes inherit properties of parent
nodes
– relationships between bits of information explicit
– supports inference through inheritance
LTM - semantic network
LTM - Storage of information

• rehearsal
– information moves from STM to LTM

• total time hypothesis

– amount retained proportional to rehearsal time

• distribution of practice effect

– optimized by spreading learning over time

• structure, meaning and familiarity

– information easier to remember
LTM - Forgetting

decay
– information is lost gradually but very slowly

interference
– new information replaces old: retroactive
interference
– old may interfere with new: proactive inhibition

so may not forget at all memory is selective …

… affected by emotion – can subconsciously `choose' to
forget
LTM - retrieval

recall
– information reproduced from memory can be
assisted by cues, e.g. categories, imagery

recognition
– information gives knowledge that it has been seen
before
– less complex than recall - information is cue
 Thinking

Reasoning:is a means of inferring new information

from what is already known

deduction, induction, abduction

Problem solving
Deductive Reasoning

• Deduction:
– derive logically necessary conclusion from given
premises.
e.g. If it is Friday then she will go to work
It is Friday
Therefore she will go to work.

• Logical conclusion not necessarily true:

e.g. If it is raining then the ground is dry
It is raining
Therefore the ground is dry
Deduction (cont.)

• When truth and logical validity clash …

e.g. Some people are babies
Some babies cry
Inference - Some people cry
Correct?
Inductive Reasoning

• Induction:
– generalize from cases seen to cases unseen
e.g. all elephants we have seen have trunks
therefore all elephants have trunks.

• Unreliable:
– can only prove false not true

… but useful!
• Humans not good at using negative evidence
e.g. Wason's cards.
 Wason's cards

7 E 4 K
If a card has a vowel on one side it has an even number on the other

Is this true?

How many cards do you need to turn over to find out?

…. and which cards? E,7

Abductive reasoning

• reasoning from event to cause

e.g. Sam drives fast when angry.
If I see Sam driving fast, assume angry.

• Unreliable:
– can lead to false explanations
Problem solving

• Process of finding solution to unfamiliar task

using knowledge.
• Several theories.
• Gestalt
– problem solving both productive and reproductive
– productive draws on insight and restructuring of problem
– attractive but not enough evidence to explain `insight'
etc.
– move away from behaviourism and led towards
information processing theories
Problem solving (cont.)

Problem space theory

– problem space comprises problem states
– problem solving involves generating states using legal
operators
– heuristics may be employed to select operators
e.g. means-ends analysis
– operates within human information processing system
e.g. STM limits etc.
– largely applied to problem solving in well-defined areas
e.g. puzzles rather than knowledge intensive areas
Problem solving (cont.)

• Analogy
– analogical mapping:
• novel problems in new domain?
• use knowledge of similar problem from similar domain
– analogical mapping difficult if domains are semantically
different

• Skill acquisition
– skilled activity characterized by chunking
• lot of information is chunked to optimize STM
– conceptual rather than superficial grouping of problems
– information is structured more effectively
Errors and mental models

Types of error
• slips
– right intention, but failed to do it right
– causes: poor physical skill,inattention etc.
– change to aspect of skilled behaviour can cause slip

• mistakes
– wrong intention
– cause: incorrect understanding
humans create mental models to explain behaviour.
if wrong (different from actual system) errors can occur
Emotion
• Various theories of how emotion works
– James-Lange: emotion is our interpretation of a
physiological response to a stimuli
– Cannon: emotion is a psychological response to a
stimuli
– Schacter-Singer: emotion is the result of our
evaluation of our physiological responses, in the
light of the whole situation we are in
• Emotion clearly involves both cognitive and
physical responses to stimuli
Emotion (cont.)
• The biological response to physical stimuli is
called affect

• Affect influences how we respond to situations

– positive  creative problem solving
– negative  narrow thinking

“Negative affect can make it harder to do

even easy tasks; positive affect can make
it easier to do difficult tasks”
(Donald Norman)
Emotion (cont.)

• Implications for interface design

– stress will increase the difficulty of problem
solving
– relaxed users will be more forgiving of
shortcomings in design
– aesthetically pleasing and rewarding
interfaces will increase positive affect
Individual differences

• long term
– sex, physical and intellectual abilities
• short term
– effect of stress or fatigue
• changing
– age

Ask yourself:
will design decision exclude section of user
population?