Transcript Lecture 1 File - Makerere University E

The Human
 In order to design something for some one, we need to
understand the capabilities and limitations of that person.
 This chapter covers how humans perceive the world around
them, how they store and process info and solve probs &
how they physically manipulate objects
 Information i/o via
visual
auditory
Haptic-touch
movement channels e.g. fingers
Speech
 Information is stored in memory (short and long term memory)
 Information is processed and applied in problem solving
The Human
Modality: It is a general class of
1. A sense – through which the human can receive the output of
the
computer
2. A Sensor or device through which the computer can receive the input
from the human.
A path of communication between the human and
the computer.
Major modalities: Seeing or vision modality, Hearing or audition modality,
Touch, tactile modality - the sense of pressure
Other Modalities: Taste or gustation modality, Smell or olfaction modality,
thermoception modality – the sense of heat or the cold
Vision
Two stages in vision
•physical reception of stimulus:
•Mechanism for receiving light and transforming it into electrical
energy which in turn reflects (mirrors) object
•processing and interpretation of stimulus
•size and depth
-visual angle indicates how much view object occupies
(relates to size and distance from eye) e.g. view of a tree thru
window different from view when outside
-visual acuity is ability to perceive detail. Size of visual angle
affects acuity
-Familiar objects perceived as constant size (in spite of changes in visual angle
when far away)
Interpreting the signal (cont)
Brightness
subjective reaction to levels of light
affected by luminance (amount of light emitted by an object) of
object measured by just noticeable difference.
Contrast (difference) related to luminance of an object & that of its
background
visual acuity increases with luminance
Color
Perception comprises of hue (shade), intensity (brightness),
saturation (amount of whiteness)
Eye perceives color b’se cones are sensitive to light of different
wavelengths (blue has shortest, green medium & red long)
blue acuity is lowest
8% males and 1% females color blind-can’t distinguish btn green & red
Reading
Concerned with processing text
Stages:
visual pattern perceived e.g. of the word Study
decoded using internal representation of language
(English)
i.e. knowledge of syntax, semantics, pragmatics
(sensible)
During reading, eye moves back and forth-regressions. If text is
complex, there’ll be more regressions
Speed of reading depends on legibility (9-12 points), line spacing &
line length(2.3-5.2 inches)
Reading from comp slower than bk hence fewer words on a page,
dark characters on a light screen (negative contrast) increases acuity
Hearing
Provides information about environment:
distances, directions, objects etc. E.g.
“There is a man behind the house” identify the distance, direction and object components in
this statement?
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
loudness
timbre
- sound frequency
- amplitude
- type or quality
Hearing (cont)
Humans can hear frequencies from 20Hz to 15kHz
less accurate distinguishing high frequencies than low.
Auditory system filters sounds
can attend to sounds over background noise.
e.g. cocktail party phenomenon.
Touch
Provides important feedback about environment.
May be key sense for someone who is visually impaired e.g feeling
button depress is vital.
Stimulus received via receptors in the skin:
thermoreceptors - heat and cold
nociceptors - pain
mechanoreceptors – pressure-what we’re concerned with in
HCI
Some areas more sensitive than others e.g. fingers
Movement e.g using a mouse, hitting a
button
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 (millisecond)
auditory ~ 150 ms
pain ~ 700ms
Memory
There are three types of memory function:
Sensory memories or sensory storage (buffer for stimuli: Holds
info from the eyes (iconic storage) and ears (echoic storage). This
information is stored for a brief time. MUST ENTER WORKING MEMORY OR
BE LOST.
Short-term memory or working memory
Long-term memory
Selection of stimuli governed by level of arousal.
Short-term memory (STM)
Scratch-pad for temporary recall e.g. names of
some people at a party
rapid access ~ 70ms
rapid decay ~ 200ms
limited capacity - 7± 2 chunks
The capacity of short-term memory is small -- info will
disappear within 20 seconds unless it is repeated or practiced.
Chunking: grouping and organizing information to fit into
meaningful units. The size of chunks does affect ability to
remember.
Long-term memory (LTM)
Repository for all our knowledge
slow access ~ 1/10 second
slow decay, if any
huge or unlimited capacity
Once information is transferred to long term memory, it is there forever - the
problem is accessibility or retrieval. - the basic debate is how info is located
and retrieved, and how many long term memory subsystems exist.
Two types
episodic - serial memory of events like memories of key events
in one’s life
semantic - structured memory of facts, concepts, skills
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 (clear)
supports inference through inheritance
Long-term memory - semantic network
Models of LTM - Frames
Information organized in data structures
Slots in structure instantiated with values for instance of data
Type-subtype relationships
DOG
Fixed
legs: 4
Default
diet: carniverous
sound: bark
Variable
size:
colour
COLLIE
Fixed
breed of: DOG
type: sheepdog
Default
size: 65 cm
Variable
colour
Models of LTM - Scripts
Model of stereotypical information required to interpret situation
Script has elements that can be instantiated with values for context
Script for a visit to the vet
Entry conditions: dog ill
vet open
owner has money
Result:
dog better
owner poorer
vet richer
Props:
examination table
medicine
instruments
Roles:
vet examines
diagnoses
treats
owner brings dog in
pays
takes dog out
Scenes:
arriving at reception
waiting in room
examination
paying
Tracks:
dog needs medicine
dog needs operation
Models of LTM - Production rules
Representation of procedural (routine) knowledge.
Condition/action rules
if condition is matched
then use rule to determine action.
IF dog is wagging tail
THEN pat dog
IF dog is growling
THEN run away
Another good example is illness. Most
people can tell when they’ve malaria
LTM - Forgetting
decay
information is lost gradually but very slowly
interference (info gets mixed up with other info)
new information replaces old: retroactive interference
old may interfere with new: proactive interference
affected by emotion - can subconsciously `choose' to forget e.g???
LTM - retrieval
recall
information reproduced from memory
can be assisted by cues e.g. categories
recognition
information given based on what has been seen before
less complex than recall due to cues e.g. metaphors
used in computing .
Thinking: reasoning and problem solving
Reasoning
Deductive: 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 what if she’s sick this friday?
Inductive Reasoning
Inductive: generalize from cases seen to cases unseen
e.g. all elephants we have seen have trunks
therefore all elephants have trunks.
Abductive reasoning
reasoning from event to cause
e.g. Sam drives fast when drunk.
If you see Sam driving fast, assume drunk.
Unreliable: can lead to false explanations.
Problem solving
Process of finding solution to unfamiliar task using knowledge.
Several theories.
Gestalt
problem solving both productive (insight) and reproductive (using
existing knowledge)
Problem solving (cont.)
Problem space theory
problem space comprises problem states (initial state and goal
state ) & p’ple use operators to move from former to latter
heuristics may be employed to select appropriate operators
e.g. means-ends analysis-initial state compared with goal
state & operators chosen to reach goal e.g. moving desk in your
office
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
e.g. containing the ebola outbreak in W. Africa using the experience of
Uganda
analogical mapping difficult if domains are semantically different
Skill acquisition
skilled activity characterized by
chunking - lot of information is chunked to optimize STM
conceptual (meaningful) rather than superficial grouping of
problems e.g. disease diagnosis process by doctors
- information is structured more effectively
Errors and mental models
Types of error
- humans create mental models to explain behaviour.
if wrong (different from actual system) errors can occur.
slips
right intention, but failed to do it right
causes: poor physical skill e.g. car parking, inattention etc.
change to aspect of skilled behavior can cause slip.
They
happen by accident, such as making “typos” by pressing the wrong
key or selecting wrong menu item. The most frequent errors are slips,
especially in well-learned behavior.
mistakes (An incorrect action is taken based on an incorrect decision.)
wrong intention
cause: incorrect understanding
Individual differences
long term - sex, physical and intellectual abilities
short term - effect of stress or fatigue
changing - age
Qestion: will design decision exclude section of user population e.g. for
the mobile money service, URA online tax payment portal?
Cognitive Psychology and Interactive System Design
Some direct applications
e.g. blue acuity is poor
 blue should not be used for important detail.
However, correct application generally requires understanding of
context in psychology
A lot of knowledge has been distilled in
guidelines - see Chapters 4 and 5
experimental and analytic evaluation techniques - see Chapter 11
of main reference for this course
References & Additional Reading
 Alan Dix, Janet Finlay, Gregory Abowd & Russell Beale (2004).
Human-Computer Interaction. Hillsdale, NJ: Prentice Hall, 2004.
ISBN 0-13-458266-7 (hardback); 0-13-437211-5 (paperback) only
outside USA. 1998 (Second Edition) ISBN 0-13-239864-8. Chap. 1
 Revision question
“To design a good system for users it is needed to understand the
capabilities and limitations of those different people.”
a) Explain the term Universality.
b) Explain the following barriers together with the corresponding
personal assistive technologies.
1. Sensory
2. Physical
3. Cognitive and
4. Age Associated Barrier