Human–computer interaction, HCI, is the study
of how people interact with computers.
The Association for Computing Machinery
defines human-computer interaction as "a
discipline concerned with the design, evaluation
and implementation of interactive computing
systems for human use and with the study of
major phenomena surrounding them."
It is often regarded as the intersection of
computer science, behavioral sciences, design
and several other fields of study.
Interaction between users and computers occurs
at the user interface (or simply interface), which
includes both software and hardware
human-computer interaction studies a
human and a machine
On the machine side, techniques in computer
graphics, operating systems, programming
languages, and development environments
are relevant.
• On the human side, communication theory,
graphic and industrial design disciplines,
linguistics, social sciences, cognitive
psychology, and human factors are relevant.
User 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.
computer mean any technology ranging from the
general desktop computer to a large-scale
computer system, a process control system or an
embedded system.
The system may include non-computerized
parts, including other people.
interaction mean any communication between a
user and computer, be 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.
The goals of HCI are to produce usable and safe
systems, as well as functional systems.
computer systems with good usability,
developers must attempt to:
understand the factors that determine how
people use technology,
develop tools and techniques to enable building
suitable systems,
achieve efficient, effective, and safe interaction
put people first.
Usability is one of the key concepts in HCI.
It is concerned with making systems easy to
learn and use.
A usable system is:
• easy to learn
• easy to remember how to use
• effective to use
• efficient to use
• safe to use
• enjoyable to use
1. Methodologies and processes for designing
interfaces
2. Methods for implementing interfaces
(software; 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.
There are a large number of factors which should
be considered in the analysis and design of a
system using HCI principles.
The main factors are:
Organization Factors
Training, job design, politics, roles, work
organization
The User Cognitive processes and capabilities,
satisfaction, personality, experience
User Interface Input devices, output devices,
dialogue structures, use of color.
Task Factors: Easy, complex, novel, task
allocation, monitoring, skills
Constraints : Cost, timescales, budgets, staff.
System Functionality: Hardware, software,
application.
Productivity Factors: Increase output, increase
quality, decrease costs, decrease errors,
increase innovation.
Computer Science
technology
software design, development & maintenance
Cognitive Psychology
information processing
limitations
Social Psychology
social & organizational structures
Ergonomics/Human Factors
hardware design , display readability
Artificial Intelligence intelligent software
Engineering & Design
A person's interaction with the outside world
occurs through information being received and
sent: input and output.
In an interaction with a computer , the user's
output becomes the computer's input and vice
versa
sight may be used primarily in receiving
information from the computer, but it can also be
used to provide information to the computer
There are five major senses: sight, hearing,
touch, taste and smell.
the first three are the most important to HCI.
Taste and smell do not currently play a significant
role in HCI
There are a number of effectors, including the
limbs, fingers, eyes, head and vocal system.
In the interaction with the computer, the fingers
play the primary role, through typing or mouse
control, with some use of voice, and eye, head
and body position.
Imagine using a personal computer (PC) with a
mouse and a keyboard.
Human vision is a highly complex activity
divide visual perception into two stages
the physical reception of the stimulus from the
outside world, and
the processing and interpretation of that
stimulus
Vision begins with light.
The eye is a mechanism for receiving light and
transforming it into electrical energy.
The eye has a number of important components
The cornea and lens at the front of the eye
The retina is light sensitive and contains two
types of photoreceptor: rods and cones.
Rods are highly sensitive to light and therefore
allow us to see under a low level of illumination.
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 than the rods and
can therefore tolerate more light.
The eye has approximately 6 million cones
mainly concentrated on the fovea, a small area of
the retina on which images are fixated.
The retina also has specialized nerve cells called
ganglion cells.
X-cells, which are concentrated in the fovea
and are responsible for the early detection of
pattern; and
Y-cells which are more widely distributed in the
retina and are responsible for the early detection
of movement.
The information received by the visual apparatus
must be filtered and passed to processing
elements.
perceive size and depth, brightness and color,
each of which is crucial to the design of effective
visual interfaces
How does the eye perceive size, depth and
relative distances?
Reflected light from the object forms an upside-
down image on the retina.
The size of that image is specified as a visual
angle.
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.
if two objects are at the same distance, the larger
one will have the larger visual angle
Similarly, 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.
how does an object’s visual angle affect our
perception of its size?
First, if the visual angle of an object is too small
we will be unable to perceive it at all.
Visual acuity is the ability of a person to perceive
fine detail.
A number of measurements have been
established to test visual acuity
For example, a person with normal vision can
detect a single line if it has a visual angle of 0.5
seconds of arc.
Spaces between lines can be detected at 30
seconds to 1 minute of visual arc.
Given that the visual angle of an object is
reduced as it gets further away, we might expect
that we would perceive the object as smaller
our perception of an object’s size remains
constant even if its visual angle changes.
A second aspect of visual perception is the
perception of brightness.
Brightness is in fact a subjective reaction to
levels of light
It is affected by luminance which is the amount
of light emitted by an object.
The luminance of an object is dependent on the
amount of light falling on the objects 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.
A third factor that we need to consider is
perception of color
Color is usually regarded as being made up of
three components: hue, intensity and 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, and
saturation is the amount of whiteness in the
color
