This document discusses human-computer interaction (HCI) and its key aspects. HCI is defined as a discipline concerned with designing interactive systems that are useful, usable, and used by people. It focuses on understanding user needs and improving user experience. The document outlines various components of HCI including the human, computer, and interaction. It describes how human factors like perception, cognition, memory and movement impact interface design. Designers should understand human capabilities and limitations to create usable systems.

1. Human Computer Interaction
ICT 2402

2. What is HCI?
HCI is a discipline concerned with the design, evaluation
and implementation of interactive computing systems for
human use and with the study of major trends surrounding
them. (The Association for Computing Machinery).
is the study of interaction between people (users) and
computers.
often regarded as the intersection of computer science,
behavioral sciences, design and several other fields of
study.
HCI focuses on the challenges in making computers and
computations useful, usable, and universally accessible to
people.
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.
HCI is a multi-disciplinary field.

3. Cont…
Human
User
Single or a group of users
Important: designers of the system should understand who is
going to use the system.
Computer
Any interactive technology that a user might use to accomplish a
task.
Interaction
Any communication between the user and the computer.
Occurs at the user interface (Hardware & software)
E.g. characters or objects displayed by software on a personal
computer's monitor
E.g. input received from users via hardware peripherals such as
keyboards and mice
Important: interaction design should aim at supporting
user tasks.

4. Some Aspects of HCI
HCI is concerned with all those aspects that
relate to the interaction between users and
computers:
1. Methodologies and processes for designing interfaces
(i.e., given a task and a class of users, design the best
possible interface within given constraints, optimizing for
a desired property such as learning ability or efficiency of
use)
2. Methods for implementing interfaces (e.g. software
toolkits and libraries; efficient algorithms)
3. Techniques for evaluating and comparing interfaces
4. Developing new interfaces and interaction techniques
5. Developing descriptive and predictive models and
theories of interaction

5. Aims of HCI
HCI aims at producing systems that are:
1. Useful or functional
the system should accomplish what it is intended for
or what is required.
2. Usable
the system must allow users to accomplish tasks
easily and naturally.
the system must support user’s tasks
3. Used
The system must make people want to use it.
It should be attractive, engaging, fun etc.
4. safe
The system should not put the health of users at risk.

6. Goals of HCI
The goals of HCI can be explained as follows:
1. Usability:
a key concept in HCI
is concerned with making systems easy to learn and
easy to use.
the system should be easy to remember how to use.
The system should be effective(useful, helpful)
The system should be efficient (good at accomplishing
user task)
The system should be enjoyable
If the system forces the user to adopt
unacceptable mode of work then it is not
usable.

7. Factors that affect Usability
Input format- the format of input should not be difficult.
Feedback- the system should give feedback or result of
the action.
Visibility- the mapping between control and effect. A
control should give proper effect immediately.
Affordance- the operations and manipulations of the
control (command)
Perceived affordance: describes what can be done to a
control just by looking at it.
Users should be able to figure out what can be done to
the control just by looking at it.
User-centred designs aim at putting the system in line
with the user needs and understand user needs.
Tools and techniques are required in order to develop
systems that are usable.

8. Cont…
2. Proper functionality: the program works as it is
expected to, e.g. a word processor is for typing
documents into not playing games on (the things it can
do).
3. Consistency: a control works the same way every
time it is encountered, it's function does not change
inside the program. For example, a user always clicks a
button, they do not click it sometimes and type text into
at other times.
4. Standardization: seeks consistency across
programs so that, for example, a user could learn one
word processor and then be able to use any word
processor available to them, i.e. learn Microsoft Word and
then be able use LibreOffice with a minimum of effort.
5. Reliability: the program works without a flaw, it
does not lock up or crash.

9. Cont…
6. Security and Data Integrity: the program
protects the users' data from unwanted tampering and
alteration.
Hackers and viruses are two of the most common threats
to security and data integrity however flaws in the
programs code (bugs) can also alter and/or destroy users'
data without warning.
7. Integration: seeks to use multiple programs in
conjunction with one another.
e.g. Microsoft Office. In Office, you can type a document
in Word and then insert a spreadsheet into the document
or insert the document into a Power Point presentation.
This is integration.
8. Portability: Portability refers to the ability to use one
program on multiple operating systems without recompiling it
for every system, i.e. be able to install and use Microsoft
Office off the same CD on Macintosh, Linux, and Windows 8
machines.

10. Cont…
Availability: Availability is the principle that if users
cannot find or access a program they will not use it but if
it is readily available, especially if it is more available than
its competition, a user is more likely to use the program.

11. Fields Contributing to HCI
HCI incorporates a range of skills from different
disciplines.
Computer science
provides the technology needed for building systems.
Psychology and cognitive science
provides knowledge of the user’s perceptual, cognitive
and problem solving skills.
Social psychology
provides knowledge of how society affect the use of the
system.
Also how society will be affected by the system.
Helps to understand the wider context of the
interaction.

12. Cont…
Graphics design
To produce an effective interface presentation
Ergonomics
For understanding the user’s physical capabilities to
use the system.
Business
To be able to market the technology
Artificial Intelligence
Technical writing
To produce the manuals
Note: all this is too much for one person. That is why
people tend to specialise in one field.

13. Components of HCI
1.The human
2. Computer
3.Interaction
NYIRENDA M.13

14. The Human
Human aspects for designers
Designers must understand the capabilities and limitations
of the user.
Designers must understand the requirements of the user
since computers are designed to assist the users.
Cognitive psychology
Is concerned with:
1. Perceptual system
how humans perceive the world around them.
Also known as Human Perception.
Designers should be concerned with how the user will acquire
information.
2. Information storage and processing
how humans store and process information and solve problems.
3. How humans physically manipulate objects(Motor
system)

15. The human perceptual system
The user, one whom computers are designed to assist.
Information i/o …
A person’s interaction with the outside world is through
info being received & sent (input & output)
visual, auditory, haptic/touch, movement
In an interaction with a computer, user receives info that is
output by the computer, and responds by providing input
to the computer. The user’s output becomes computer’s
input and vice versa.
Input in human occurs mainly through the senses and
output through the motor control of the effectors.
Major senses
Sight
Hearing
Touch
Taste
Smell

16. Cont…
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

17. Vision
Is the primary source of info for average person
Two stages in vision
• physical reception of stimulus
• processing and interpretation of stimulus

18. Cont…
On one hand the physical properties of the eye
and the visual system mean that there are
certain things that cannot be seen by the
human; on the other hand the interpretive
capabilities of visual processing allow images to
be constructed from incomplete info
Both of the above stages influence what can
and what cannot be perceived visually by a
human being, which in turn directly affects the
way that we design computer systems.

19. 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 (brain!) detect pattern and
movement
NOTE: Students to study the eye as a
physical receptor.

20. Interpreting the signal
Size and depth
Reflected light from the object forms an upside down image
on the retina
visual angle indicates how much of view object occupies
(relates to size and distance from eye)
The visual angle is affected by both the size of the object and
its distance from the eye.
If two objects of the same size are placed at different
distances from the eye, the furthest one will have the smaller
visual angle.
Visual angle is measured in degrees or minutes arc where:
1 degree is equivalent to 60 minutes of arc.
1 minute of arc is equivalent to 60 seconds of arc.
if visual angle of an object is too small we will not be able to
perceive it at all.

21. Cont…
Visual acuity is the ability of a person to perceive
fine detail(limited)
Assuming that we can perceive the object, does its
visual angle affect our perception of its size?
Given that the visual angle of an object is reduced as it
gets further away, we might expect that would expect that
we would perceive the object as smaller.
Perception of size relies on other factors than the visual
angle (The law of size constancy).
These factors are: depth and familiarity
familiar objects perceived as constant size
(in spite of changes in visual angle when far away)
If we expect an object to be of a certain size then we can judge its
distance accordingly.
The size and height of the object in our field of
view provides a cue to its distance.

22. Visual angle and perception of
objects
Objects of the same size at different distances
have different visual angles.
Visual angle

23. Interpreting the signal (cont)
Brightness
is the subjective reaction to levels of light
affected by luminance of object
Luminance the amount of light emitted by an object
Luminance of an object is dependent on the amount of
light falling on the object’s surface and its reflective
properties.
Brightness can be described in terms of luminance that
gives a just noticeable difference in brightness
Visual system compensates for changes in brightness.
In dim light the rods predominate vision.
Since there are fewer rods on the fovea, objects in low
lighting can be seen less easily when fixated upon and
are more visible in peripheral vision.
In normal lighting the cones take over
visual acuity increases with luminance as does flicker
The eye will perceive a light switched on and off rapidly
as constantly on.

24. Interpreting the signal (cont)
Contrast
Related to luminance
Is the difference in luminance between the object and
its background.

25. Interpreting the signal (cont)
Perceiving Colour
made up of hue, intensity and saturation
Hue – determined by spectral wavelength of light
Blues have shorter wavelength, greens medium and reds
long
Intensity – is the brightness of the colour(amount of
light emitted from the colour)
Saturation – the amount of whiteness in the colour
cones sensitive to colour wavelengths
blue acuity is lowest
8% males and 1% females colour blind
Colour vision is best at the fovea and waste at the
periphery where rods predominate.

26. Limitations of visual interfaces
The image is not completely visible but the eye
concentrates in making a complete image
The visual system compensates for:
movement of the image on the retina which occurs as
we move around and as the object we see moves.
changes in luminance.
The ability to interpret and exploit our
expectations can be used to resolve ambiguities
Optical illusions sometimes occur due to over
compensation
Images are interpreted according to what you expect
Leads to creation of wrong interpretations from what is
seen. (Ponzo Illusion)

27. Optical Illusions
the Ponzo illusion
the Muller Lyer illusion
These illusions demonstrate that our perception of size is not
completely reliable.
Similarly colour and brightness are perceived as constant in spite of
changes in luminance.

28. Reading
Several stages:
visual pattern of the word is perceived
decoded using internal representation of language
interpreted using knowledge of syntax, semantics,
pragmatics
Reading involves saccades (jerky movements)
and fixations
Perception occurs during fixations
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
Word shape is important to recognition
This means that removing the word shape clues (for
example, by capitalizing words) is detrimental to
reading speed and accuracy.
The speed at which text can be read is a measure of its
legibility(how easy it is to read a particular text)

29. Reading- cont…
Reading from a computer screen is slower than
from a book.
This is due to the following:
longer line length,
fewer words to a page
Orientation
the familiarity of the medium of the page
Negative contrast improves reading from
computer screen
i.e. Dark characters on a light screen provides higher
luminance and, therefore, increased acuity, than a
positive contrast.
This will in turn increase legibility.

30. Hearing
Provides information about environment:
distances, directions, objects etc.
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.
Physical apparatus (Ear):
outer ear – has two parts:
1. the pinna - attached to the sides of the head
2. the auditory canal – along which sound waves are
passed to the middle ear.
–protects middle ear 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

31. Hearing- Cont…
Sound
sound is changes or vibrations in air pressure.
Characteristics of sound:
pitch – sound frequency
- A low frequency produces a low pitch, a high frequency, a high
pitch.
loudness – amplitude of the sound
timbre – type or quality of the sound
- sounds may have the same pitch and loudness but be made by
different instruments and so vary in timbre

32. Hearing- cont…
Humans can hear frequencies from 20Hz to 15kHz
But less accurate at distinguishing high frequencies than low.
Auditory system filters sounds
allows us to ignore background noise and concentrate on important
information.
can attend to sounds over background noise.
E.g. the cocktail party phenomenon.
- where we can pick out our name spoken across a crowded noisy room.
sound can convey a remarkable amount of information.
It is rarely used to its potential in interface design
confined to warning sounds and notifications in interactive
systems.
exception is multimedia, which may include music, voice
commentary and sound effects.
sound could be used more extensively in interface design, to
convey information about the system state

33. Non-speech sound
Uses of non-speech sounds include the following:
Attention – to attract the user’s attention to a critical
situation or to the end of a process, for example.
Status information – continuous background sounds
can be used to convey status information. For example,
monitoring the progress of a process (without the need for
visual attention).
Confirmation – a sound associated with an action to
confirm that the action has been carried out. For example,
associating a sound with deleting a file.
Navigation – using changing sound to indicate where the
user is in a system. For example, what about sound to
support navigation in hypertext?

34. Touch
Provides important feedback about environment.
Can tell us when we touch something hot or cold & warn us
May be key sense for someone who is visually impaired.
Important in computer systems
Feeling buttons depress is an important part of the task of
pressing the button.
Stimulus received via receptors in the skin:
thermoreceptors – heat and cold
nociceptors – pain
mechanoreceptors – pressure
Rapidly adapting- respond to immediate pressure. The stop if
continuous pressure is applied
Slowly adapting- respond to continuous applied pressure.
Some areas more sensitive than others e.g. fingers.

35. Touch cont…
Kinethesis - awareness of body position and limbs
Due to receptors in the joints.
Affects both comfort and performance.
Types of Kinethesis
Rapidly adapting – respond when a limb is moved in a
particular direction.
Slowly adapting – respond to both movement and static
position.
Position receptors – respond only when a limb is in
static position.

36. 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.

37. 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
⇒targets as large as possible
distances as small as possible

38. Human Memory
Its job is to store and retrieve information
Keeps factual knowledge, procedures undertaken and
actions
This allows humans
to be able to repeat things or actions in future,
To use language
To use new information received via the senses
Gives people the sense of identity by preserving information
from our past experiences.

39. Types of Human 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.
Attention
Rehearsal

40. Sensory memory
Act as buffers for stimuli received through
senses
Eyes: iconic memory- respond to visual stimuli
Ears: echoic memory- respond to aural stimuli
Skin: haptic memory- respond to tactile stimuli
Information on these memories is continuously
overwritten by new information coming in on
these channels.

41. Short-term memory (STM)
Used as a Scratch-pad for temporary recall of
information.
Advantage
rapid access ~ 70ms
Disadvantages
rapid decay ~ 200ms
limited capacity - 7± 2 chunks

42. Measuring memory
Two 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
212348278493202
0121 414 2626
Difficult to remember the sequence of chunks below
HEC ATR ANU PTH ETR EET
Move last character to the first position
becomes “the cat ran up the tree”

43. 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

44. 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

45. LTM - semantic network

46. 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

47. 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

48. Models of LTM - Production
rules
Representation of procedural
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

49. 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

50. 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

51. 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