2. Introduction
• Human–computer interaction (HCI), alternatively
man–machine interaction (MMI) or computer–human
interaction (CHI) is the study of interaction between
people (users) and computers.
• HCI is undoubtedly a multi-disciplinary subject
• HCI involves the design, implementation and
evaluation of interactive systems
3. Introduction
• By user we may mean an individual user, a group of users working
together, or a sequence of users in an organization, each dealing
with some part of the task or process.
• The user is whoever is trying to get the job done using the
technology.
• By computer we mean any technology ranging from the general
desktop computer to a large-scale computer system, a process
control system or an embedded system.
• By interaction we mean any communication between a user and
computer, be it direct or indirect.
– Direct interaction involves a dialog with feedback and control
throughout performance of the task.
– Indirect interaction may involve batch processing or intelligent
sensors controlling the environment
4. WHY HUMAN–COMPUTER INTERACTION?
• this word processor no longer has a delete option in its menu
• Errors such as these, resulting from poor design choices, happen
every day. Perhaps they are not catastrophic:
• when computers are marketed as ‘user friendly’ and ‘easy to use’,
simple mistakes like this can still occur?
• Computers and related devices have to be designed with an
understanding that people with specific tasks in mind will want to
use them in a way that is seamless with respect to their everyday
work.
5.
6. • Involve the users Where possible, the eventual users should be
involved in the design process.
• They have vital knowledge and will soon find flaws.
• A mechanical syringe was once being developed and a prototype was
demonstrated to hospital staff. Happily they quickly noticed the
potentially fatal flaw in its interface
• Automatic syringe: setting the dose to 1372
The doses were entered via a numeric
keypad: an accidental keypress and
the dose could be out by a
factor of 10!
The production version had individual
increment/decrement buttons for each
digit
7. • A basic goal of HCI is
– to improve the interactions between users and
computers
– by making computers more usable and receptive
to the user's needs.
• A long term goal of HCI is
– to design systems that minimize the barrier
between the human's cognitive model of what
they want
– to accomplish and the computer's understanding
of the user's task
8. Introduction
• we introduce the fundamental components of an interactive system: the
human user, the computer system itself and the nature of the interactive
process
• Chapter 1 discusses the psychological and physiological attributes of the
user, providing us with a basic overview of the capabilities and limitations
that affect our ability to use computer systems.
• Chapter 2 - Input and output devices are described and explained and the
effect that their individual characteristics have on the interaction highlighted.
• The computational power and memory of the computer is another important
component
• in Chapter 3, where we look at models of interaction
• In Chapter 4 we take a historical perspective on the evolution of interactive
systems and how they have increased the usability of computers in general
9. the human
• Information is received and responses
given via a number of input and output
channels
– visual, auditory, haptic, movement
• Information is stored in memory
– sensory, short-term, long-term
• Information is processed and applied
– reasoning, problem solving, skill, error
• Emotion influences human capabilities
10. Vision
• It is the primary source of information
for the average person
• Two stages in vision
– physical reception of stimulus from the
outside world
– processing and interpretation of stimulus
• eye as a physical receptor
11. The Eye - physical reception
• mechanism for receiving light and
transforming it into electrical energy
• light reflects from objects
• images are focused upside-down on
retina
• retina contains rods for low light vision
and cones for colour vision
• ganglion cells detect pattern and
movement
13. • The cornea and lens at the front of the eye focus the light into
a sharp image on the back of the eye, the retina.
• The retina is light sensitive and contains two types of
photoreceptor:
– rods and cones
• Rods are highly sensitive to light. they are unable to resolve fine
detail
• There are approximately 120 million rods per eye which are
mainly situated towards the edges of the retina
• Cones are the second type of receptor in the eye. They are less
sensitive to light
• There are three types of cone, each sensitive to a different
wavelength of light. This allows color vision.
• The eye has approximately 6 million cones, mainly
concentrated on the fovea, a small area of the retina on which
images are fixated
14. • retina is mainly covered with photoreceptors there is
one blind spot where the optic nerve enters the eye.
The blind spot has no rods or cones
• retina also has specialized nerve cells called
ganglion cells. There are two types:
– X-cells, which are concentrated in the fovea and
are responsible for the early detection of pattern;
– Y-cells which are more widely distributed in the
retina and are responsible for the early detection
of movement.
15. Interpreting the signal
• Size and depth
– The size of that image is specified as a visual angle
– visual angle indicates how much of view object occupies
(relates to size and distance from eye)
– if two objects are at the same distance, the larger one will have
the larger visual angle.
– if two objects of the same size are placed at different distances
from the eye, the furthest one will have the smaller visual angle
• The visual angle measurement is given in either degrees or minutes
of arc, where 1 degree is equivalent to 60 minutes of arc, and 1
minute of arc to 60 seconds of arc
16. • If we were to draw a line from the top of the object to a central point on
the front of the eye and a second line from the bottom of the object to
the same point, the visual angle of the object is the angle between
these two lines. Visual angle is affected by both the size of the object
and its distance from the eye
17. • Visual acuity is the ability of a person to perceive fine detail
• number of measurements have been established to test visual acuity,
most of which are included in standard eye tests
• our perception of an object’s size remains constant even if its visual
angle changes.
• So a person’s height is perceived as constant even if they move further
from you.
• This is the law of size constancy, and it indicates that our perception of
size relies on factors other than the visual angle
18. Interpreting the signal (cont)
• A second aspect of visual perception is the perception of
brightness.
• Brightness
– subjective reaction to levels of light
– affected by luminance of object
– The luminance of an object is dependent on the
amount of light falling on the object’s surface and its
reflective properties.
– Luminance is a physical characteristic and can be
measured using a photometer.
– Contrast is related to luminance: it is a function of the
luminance of an object and the luminance of its
background
19. • Colour
– made up of hue, intensity, saturation
– Hue is determined by the spectral wavelength of
the light. Blues have short wavelengths, greens
medium and reds long
– Intensity is the brightness of the color
– saturation is the amount of whiteness in the color
– The eye perceives color because the cones are
sensitive to light of different wavelengths.
– There are three different types of cone, each
sensitive to a different color (blue, green and red).
20. limitations of visual processing
• Visual processing involves the
transformation and interpretation of a
complete image, from the light that is
thrown onto the retina.
• our expectations affect the way an image is
perceived.
• For example, if we know that an object is a
particular size,
• we will perceive it as that size no matter
how far it is from us
• The visual system compensates for:
– movement
– changes in luminance.
• Context is used to resolve ambiguity
• Optical illusions sometimes occur due to
over compensation
allows our
expectations to
clearly
disambiguate the
interpretation of
the object, as
either a B or a 13.
21. Optical Illusions
the Muller Lyer illusion
Which line is longer? Most people
when presented with this will say
that the top line is longer than the
bottom. In fact, the two lines are the
same length.
expectations compensating an
image is the proofreading illusion
Most people
reading this rapidly will read it
correctly, although closer inspection
shows that the word ‘the’ is
repeated in the second and third
line.
22. The Ponzo illusion – are these the same size?
Here the top line appears
longer, owing to the distance
effect,
although both lines are the
same length.
These illusions demonstrate that
our perception of size is not
completely reliable.
23. Reading
• Several stages:
– First, the visual pattern of the word on the page is perceived.
– It is then decoded with reference to an internal representation of language.
– The final stages of language processing include syntactic and semantic
analysis and operate on phrases or sentences.
• During reading, the eye makes jerky movements called saccades followed by
fixations.
• Perception occurs during the fixation periods, which account for approximately
94% of the time elapsed.
• The eye moves backwards over the text as well as forwards, in what are known
as regressions.
• If the text is complex there will be more regressions.
• Adults read approximately 250 words a minute
• The speed at which text can be read is a measure of its legibility.
• Experiments have shown that standard font sizes of 9 to 12 points are
equally legible
• there is evidence that reading from a computer screen is slower than
from a book
24. Hearing
• Provides information about environment:
distances, directions, objects etc.
• As I sit at my desk I can hear
– cars passing on the road outside
– machinery working on a site nearby
– the drone of a plane overhead and bird song.
– tell where the sounds are coming from
– estimate how far away they are
– So from the sounds I hear I can tell that a car is passing on a
particular road near my house, and which direction it is traveling
in
25. human ear
• hearing begins with vibrations in the air or sound waves.
• The ear receives these vibrations and transmits them, through various
stages, to the auditory nerves.
• The ear comprises three sections, commonly known as the
– outer ear, middle ear and inner ear.
• outer ear
– has two parts
• the pinna, which is the structure that is attached to the sides of the
head, and the auditory canal, along which sound waves are passed
to the middle ear
• The outer ear serves two purposes.
– protects the sensitive middle ear from damage.
– The auditory canal contains wax which prevents dust, dirt and over-
inquisitive insects reaching the middle ear.
– It also maintains the middle ear at a constant temperature.
– Secondly, the pinna and auditory canal serve to amplify some sounds
26. • The middle ear is a small cavity
– connected to the outer ear by the tympanic membrane, or ear drum,
– connected to the inner ear by the cochlea.
– Within the cavity are the ossicles, the smallest bones in the body.
– Sound waves pass along the auditory canal and vibrate the ear drum which in
turn vibrates the ossicles, which transmit the vibrations to the cochlea, and so
into the inner ear.
– unlike the air-filled outer and middle ears, the inner ear is filled with a denser
cochlean liquid.
– By transmitting sound waves via the ossicles the sound waves are
concentrated and amplified.
• 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
27. Processing sound
• sound is changes or vibrations in air pressure
• Pitch is the frequency of the sound.
• A low frequency produces a low pitch, a high frequency, a high pitch.
• Loudness is proportional to the amplitude of the sound; the frequency remains
constant.
• Timbre relates to the type of the sound
• sounds may have the same pitch and loudness but be made by different
instruments and so vary in timbre.
• The human ear can hear frequencies from about 20 Hz to 15 kHz
• the ear can differentiate quite subtle sound changes and can recognize familiar
sounds without concentrating attention on the sound source.
• It is rarely used to its potential in interface design, usually being confined to
warning sounds and notifications
28. Suggest ideas for an interface which uses the properties of sound
effectively
• Speech sounds can obviously be used to convey information.
– This is useful not only for the visually impaired but also for any
application where the user’s attention has to be divided
• Attention – to attract the user’s attention to a critical situation or to the
end of a process
– Status information – continuous background sounds can be used
to convey status information.
• monitoring the progress of a process
– Confirmation – a sound associated with an action to confirm that
the action has been carried out.
• associating a sound with deleting a file.
– Navigation – using changing sound to indicate where the user is in
a system.
• what about sound to support navigation in hypertext?
29. Touch
• touch or haptic perception.
• Provides important feedback about environment.
– It tells us when we touch something hot or cold, and can therefore act as a warning
• May be key sense for someone who is visually impaired.
• The skin contains three types of sensory receptor
• 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.
30. • There are two kinds of mechanoreceptor, which respond to different
types of pressure.
• Rapidly adapting mechanoreceptors respond to immediate pressure as
the skin is indented.
– These receptors also react more quickly with increased pressure.
– However, they stop responding if continuous pressure is applied.
• Slowly adapting mechanoreceptors respond to continuously applied
pressure
• the whole of the body contains such receptors
• some areas have greater sensitivity or acuity than others.
• It is possible to measure the acuity of different areas of the body using
the two-point threshold test
31. two-point threshold test
• Take two pencils, held so their tips are about 12 mm apart.
• Touch the points to your thumb and see if you can feel two points.
• If you cannot, move the points a little further apart.
• When you can feel two points, measure the distance between them.
• The greater the distance, the lower the sensitivity
32. • haptic perception is kinesthesis
• kinesthesia, is the perception of body movements. It involves being
able to detect changes in body position and movements without relying
on information from the five senses
– awareness of the position of the body and limbs
– This is due to receptors in the joints.
– Again there are three types
• rapidly adapting, which respond when a limb is moved in a
particular direction
• slowly adapting, which respond to both movement and static
position;
• positional receptors, which only respond when a limb is in a
static position.
• perception affects both comfort and performance.
• For example, for a touch typist, awareness of the relative positions of
the fingers and feedback from the keyboard are very important.
33. • E-commerce has become very successful in some areas of sales, such as
travel services, books and CDs, and food. However, in some retail areas,
such as clothes shopping, e-commerce has been less successful. Why?
• With clothes, the experience of shopping is far more important
• We need to be able to handle the goods, feel the texture of the material,
check the weight to test quality.
• demonstration environment called TouchCity allows people to walk around
a virtual shopping mall, pick up products and feel their texture and weight.
• haptic experience requires expensive hardware not yet available to the
average e-shopper
34. Movement
• A simple action such as hitting a button in response to a question involves a number of
processing stages. The stimulus (of the question) is received through the sensory receptors and
transmitted to the brain. The question is processed and a valid response generated. The brain
then tells the appropriate muscles to respond. Each of these stages takes time, which can be
roughly divided into reaction time and movement time.
• Time taken to respond to stimulus:
reaction time + movement time
• Speed and accuracy of movement are important considerations in the design of interactive
systems
• Movement time dependent on age, fitness etc
• Reaction time varies according to the sensory channel through which the
stimulus is received
– visual ~ 200ms
– auditory ~ 150 ms
– pain ~ 700ms
• second measure of motor skill is accuracy. One question that we should
ask is
– whether speed of reaction results in reduced accuracy
35. Movement (cont)
• Fitts' Law describes the time taken to hit a screen
target:
Mt = a + b log2(D/S + 1)
where: a and b are empirically determined constants
Mt is movement time
D is Distance
S is Size of target
• The target may be a button, a menu item or an icon
• The time taken to hit a target is a function of the size of the target and
the distance that has to be moved.
targets as large as possible
distances as small as possible
36. 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.
37. • our memory contains our knowledge
of actions or procedures.
• It allows us to repeat actions, to use
language, and to use new
information received via our senses.
• It also gives us our sense of identity,
by preserving information from our
past experiences
• Memory is the second part of our
model of the human as an
information-processing system.
• three types of memory or memory
function: sensory buffers, short-term
memory or working memory, and
long-term memory
38. sensory memory
• Buffers for stimuli received through senses
• A sensory memory exists for each sensory channel:
– iconic memory: visual stimuli
– echoic memory: aural stimuli
– haptic memory: tactile stimuli
• These memories are constantly overwritten by new information coming in
on these channels
• Information is passed from sensory memory into short-term memory by
attention, thereby filtering the stimuli to only those which are of interest at
a given time
• Attention is the concentration of the mind on one out of a number of
competing stimuli or thoughts
• Information received by sensory memories is quickly passed into a more
permanent memory store, or overwritten and lost.
39. Short-term memory (STM)
• Short-term memory or working memory acts as a ‘scratch-pad’ for
temporary recall of information.
• It is used to store information which is only required fleetingly
• calculate the multiplication 35 * 6 in your head
– To perform calculations such as this we need to store the
intermediate stages for use later
• Reading
– In order to comprehend this sentence you need to hold in your
mind the beginning of the sentence as you read the rest.
• Short-term memory can be accessed rapidly, in the order of 70 ms.
– decays rapidly
• meaning that information can only be held there temporarily,
in the order of 200 ms.
• Short-term memory also has a limited capacity
40. • two basic methods for measuring memory capacity.
• The first involves determining the length of a
sequence which can be remembered in order.
• The second allows items to be freely recalled in any
order.
41. Examples
how many digits could you remember?
212348278493202
the average person can remember 7 + or - 2 digits
Did you recall that more easily? Here the digits are grouped or chunked
0121 414 2626
chunking information can increase the short-term memory capacity
HEC ATR ANU PTH ETR EET
the cat ran up the tree
moving the last character to the first
position
the sequence is easy to recall.
42. • recency effect
– evidence shows that recall of the last words presented is better
than recall of those in the middle
– if the subject is asked to perform another task between
presentation and recall (for example, counting backwards) the
recency effect is eliminated.
• The recall of the other words is unaffected.
• that short-term memory recall is damaged by interference of other
information
43. Long-term memory (LTM)
• long-term memory is our main resource.
• Here we store factual information, experiential knowledge, procedural
rules of behavior
• Repository for all our knowledge
– slow access ~ 1/10 second
– slow decay, if any
– huge or unlimited capacity
• It differs from short-term memory in a number of significant ways.
– First, it has a huge, if not unlimited, capacity.
– Secondly, it has a relatively slow access time of approximately a
tenth of a second.
– Thirdly, forgetting occurs more slowly in long-term memory
44. Long-term memory (cont.)
• Long-term memory structure
• two types of long-term memory
– episodic memory and semantic memory
• Episodic memory represents our memory of events and
experiences in a serial form
• Semantic memory structure
– provides access to information
– represents relationships between bits of information
– supports inference
• representation of knowledge
– semantic network
– Frames
– script
– Representation of procedural knowledge
46. Models of LTM - Frames
• A number of other memory structures have been proposed to explain how we
represent and store different types of knowledge
• Semantic networks represent the associations and relationships between single
items in memory.
• However, they do not allow us to model the representation of more complex
objects or events
– which are perhaps composed of a number of items or activities.
• Structured representations such as frames and scripts organize information into
data structures.
• Slots in these structures allow attribute values to be added.
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
47. Models of LTM - Scripts
Scripts attempt to model the representation of stereotypical knowledge about
situations
John took his dog to the surgery. After seeing the vet, he left.
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
48. • A script comprises a number of elements, which, like slots, can be filled
with appropriate information:
• Entry conditions Conditions that must be satisfied for the script to be
activated.
• Result Conditions that will be true after the script is terminated.
• Props Objects involved in the events described in the script.
• Roles Actions performed by particular participants.
• Scenes The sequences of events that occur.
• Tracks A variation on the general pattern representing an alternative
scenario.
49. Models of LTM - Production rules
Representation of procedural knowledge.
• Condition–action rules are stored in long-term memory.
• Information coming into short-term memory can match a condition in
one of these rules and result in the action being executed
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
50. LTM - Storage of information
• There are three main activities related to long-term memory:
– storage or remembering of information
– forgetting
– information retrieval
• First, how does information get into long-term memory and how can we
improve this process?
• Information from short-term memory is stored in long-term memory by
rehearsal.
• The repeated exposure to a stimulus or the rehearsal of a piece of
information transfers it into long-term memory
51. LTM - Forgetting
• There are two main theories of forgetting:
– decay and interference.
decay
– information is lost gradually but very slowly
interference
• If we acquire new information it causes the loss of old information.
– This is termed retroactive interference.
– you change telephone numbers,
• Sometimes the old memory trace breaks through and interferes with new
information.
– This is called proactive inhibition.
– find yourself driving to your old house rather than your new one
52. LTM - retrieval
• two types of information retrieval, recall and recognition
recall
• In recall the information is reproduced from memory
• recall can be assisted by the provision of retrieval cues, which enable
the subject quickly to access the information in memory
• For example, consider the following list of words:
• child red plane dog friend blood cold tree big angry
• Now make up a story that links the words using as vivid imagery as
possible. Now try to recall as many of the words as you can
recognition
– information gives knowledge that it has been seen before
– less complex than recall - information is cue
54. 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
55. Deduction (cont.)
• When truth and logical validity clash …
e.g. Some people are babies
Some babies cry
Inference - Some people cry
Correct?
• People bring world knowledge to bear
56. 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.
57. Wason's cards
Is this true?
How many cards do you need to turn over to find out?
…. and which cards?
If a card has a vowel on one side it has an even number on the other
7 E 4 K
58. Abductive reasoning
• reasoning from event to cause
e.g. Sam drives fast when drunk.
If I see Sam driving fast, assume drunk.
• Unreliable:
– can lead to false explanations
59. 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
60. 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
61. 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
62. 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
63. 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
64. 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)
65. 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
66. 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?
67. Psychology and the Design of
Interactive System
• 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, and an
understanding of particular experimental conditions
• A lot of knowledge has been distilled in
– guidelines (chap 7)
– cognitive models (chap 12)
– experimental and analytic evaluation techniques (chap 9)
