HOW THE HUMAN COMPUTER INTERACT EACH OTHER. ALL ASPECTS REGARDING THE HUMAN COMPUTER INTERACTION

1. 1
Human Factors

2. What is human factors?
Human factors is a branch of science and technology. It includes what is known
and theorized about human behavioral and biological characteristics that can be validly
applied to the specification, design evaluation, operation and maintenance of products
and systems to enhance safe, effective and satisfying use by individual, groups and
organizations.
In the definition of human factors, the importance of the basic human capabilities such
as
• Perceptual abilities
• Attention span
• Memory span
• Physical limitations are embodied.
Figure below shows an abstract version of the human computer system. In this
abstraction the similarity between human and computer system is clear. Both can
be conceptualized in terms of subsystems that are responsible for input
processing and output, respectively.
Environment
Human Machine
Fig. Representation of the Human Machine System.
The Human and Machine are composed of subsystems operating within the large
environment.
In the figure the domains of the design engineer, the human performance researcher and
the human factors specialist is also indicated. The design engineer is interested primarily
in the subsystems of the machine and their interrelations. Similarly the human
performance expect studies the subsystem of the human and their interrelations. Finally
the human factor specialist is most concerned with the relations between the input and
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Cogni
tion
Percept
ion
Action
Displays
Machine
operation
Controls

3. output subsystems of the human and machine components or in other words with the
human machine interface. The final point to note is that the entire human machine
system is embedded within the larger context of work environment.
The psychology of human performance:-
Weber examined people’s ability to tell that two stimuli, such as two weights, differ in
magnitude. Weber’s law can be expressed quantitatively as
ΔI/I=K
Where I is the intensity of a stimulus, ΔI is the amount of change between it and another
stimulus needed to tell that two stimuli differ in magnitude and K is a constant. What
Weber’s law indicate is that the absolute amount of charge needed to perceive a
difference in magnitude increases with intensity, whereas the relative amount remains
constant.
Fehner formalized further and constructed the first scales intended to relate
psychological magnitude (for example loudness) to physical magnitude (for example
amplitude). Fehner assumed that the amount of change needed to perceive a difference
evokes a constant increment in the magnitude of the psychological sensation. He
obtained the psychophysical function,
S=K log (I)
Where S is the magnitude of sensation, I is physical intensity, K is constant. This
function , relating physical intensity to the psychological sensation is called Fehner’s
law. The term psychophysics has been used to describe such research that examines the
basic sensory sensitivities.
One of the Helmhotz’s most important contributions was establishing a method by
which the time for transmission of a nerve impulse could be estimated. His method
involved measuring the different points on the nerve. The measures indicated that the
speed of transmission was approximately 27meter/sec.
Donders reasoned that when performing a speed reaction task, observers must make a
series of judgments. A stimulus is first detected, then identified, subsequently the
stimulus can be discriminated from other stimuli. At this point the observer selects the
appropriate selects the appropriate response to the stimulus. Donders designed several
tasks for humans to perform that differed in terms of the combination of judgment
required for each task. By using a subtractive logic, in which the time to perform one
task was subtracted from the time to perform another task that required one additional
judgment. Donders estimated the time for the respective component judgments.
The importance of the subtractive logic is that it provided the foundation for the notion
that mental processes can be isolated. This notion is the central tenet of Human
Information Processing. This approach assumes that cognition occurs through a series of
operations performed on information originating from the senses. The conception of the
human as the information processing system is invaluable because it meets the
requirement of allowing human and machine performance to be analysed in terms of the
same basic functions.
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4. Fig. Information Processing in Human & Machines.
In a landmark study in the history of human performance psychology, Bryan and Harter
extended the topic of learning and memory to the investigation of skill acquisition. They
proposed that learning proceeds in a series of phases. Another topic for the study of
human performance is that of attention. It is the taking possession by the mind in clear
and vivid form, of one out of what seems several simultaneously possible objects or train
of thought Focalization, concentration, of consciousness are of its essence.
Human Information Processing:
The Human information processing approach characterises the human as a
communication system that receives input from the environment, acts on the information
and then output a response back to the environment. The information processing
approach is used to develop models that depict the flow of information in the human, in
much the same way that system engineers use models to depict information flow in
nonhuman system.
Townsend & Roos (1973) proposed a model to explain human performance in a variety
of tasks in which response are made to visually presented stimuli. The model consists of
a set of distinct subsystems that intervene between the presentation of an array of visual
symbols and the execution of a physical response to the array. The model includes
perceptual subsystem (The visual from system), cognitive subsystem (The long term
memory components, the limited capacity translator, and the acoustic from system), and
the action subsystems (the response-selection and response execution system). The
arrows indicate flow of information through the system.
• A three-stage model:
Fig. Below presents a general model of information processing that distinguishes three-
stages intervening between the presentation of stimulus and the execution of a
subsequent response. Early processes associated with perception and stimulus
identification can be classified as the perceptual stage. Following this stage are
intermediate process involved with decision-making and thought classified as the
cognitive stage. Information from this cognitive stage is used in the final action stage to
select, prepare and control the movements necessary to affect a response.
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Input Information
Reception
Information
Manipulation
Information
Production
Output
Information Storage

5. Stimulus
Fig.: Three-stages of Human Information Processing.
Perceptual-stage:
It includes processes that operate from the stimulation of the sensory organs through the
identification of that stimulation. These processes are involved in the defection,
discrimination and identification of displayed information.
Cognitive-stage:
After enough information has been extracted from a display to allow the identification or
classification of the stimuli, processes being to operate with the goal of determining the
appropriate action or response. These processes can include the retrieval of information
from memory, comparison among displayed items, comparison between these items and
the information in memory, arithmetic operations and decision-making. The cognitive-
stage imposes constraints on performance.
Action-stage:
Following the perceptual-stage and cognitive-stage of processing, an overt response (if
required) needs to be selected, programmed and executed. After a response is selected, it
must then be translated into a set of neuromuscular commands. These commands control
the specific limbs or effectors that are involved, including their direction, and relative
timing.
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Perception Cognition Action

6. An elaborated model of Human Information Processing
Perceptual-stage Cognitive-stage Action-stage
Respo
Feedback
Perspective of User Interface Design:
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S
E
N
S
O
R
Y
Pattern
Organisation
Recognition
Decision
Making
Thou
gh
Response
Selection
Res.
Preparat
ion
Res.
Activatio
n
Shot. Term
Memory
Long-term
Memory
Attenti
on
Res.output

7. Because of the craft like nature of user interface design, the teaching and passing on of
interface-design knowledge is through experience and example more often than books
and lectures
Design of user interface has to be considered from a number of different perspectives,
each of which interacts to affect the quality of the overall design. Three perspectives to
consider are as follows
The functional perspective
The aesthetic perspective
The structural perspective
Functional perspective is concerned with whether or not the design is serviceable for its
intended purpose. This perspective is largely concerned with issues of usability and the
thoroughness of the support for user tasks. Achieving good functional design is difficult
because in the first instance it needs the designs to define for what purposes the design is
intended to be used. In fact there is a tendency for to try to produce systems that users
can then tailor, adapt or extend, so that they can be they can be used to do more and
more things. It is clear that designing a new system a new system will have
unpredictable and unknown effects on the tasks that people can perform. There is a
cyclical relation between designing computer systems for known tasks, which systems,
in turn, allow people to do new tasks. The design of the system should then be
approached in such a way that it can be clearly and easily seen to support those tasks for
which it is intended, and at the same time allow for new uses and hence new tasks to be
performed following Carrol’s design-artifact cycle.
The aesthetic perspective is concerned with whether or not the design is pleasing in its
appearance and conforms to any accepted notions of artistic design. This aspect of the
design is directly concerned with the design of the visual of the appearance of the
interface. The designing of the graphical and textual figures and characters, as well as
their layout on the screen, are of concern. Marcus(1990) has shown how the design of
font styles, color and the general grid layout of the screen can ease confusion and be
more aesthetically pleasing. The aesthetic aspects of design do not stop at the screen.
The size and shape of the input devices and the position, shape, color of buttons and
keys all influence the aesthetic quality of design.
The structural perspective is concerned with whether or not. The design has been built in
a manner that will make it reliable and efficient to use and can be easily maintained and
extended. This is perhaps the area of design with which the software developer is most at
ease. There are many different approaches to providing a good structural perspective to
the overall quality of the design. The essence of the problem is that the design of the
interface should be structured in a way that produces efficient use of software, provides
easy construction, is executable in a reliable and efficient manner allows for the reuse of
software components and the construction of new components out of the existing
components. One solution to the problem has been found in the use of object-oriented
programming languages that support the construction of class hierarchies and have
inheritance mechanisms for sharing properties between members of a class. Through
these properties, object-oriented languages have enabled user-interface design to be
based around sets of primitive objects that each has their own behaviors and connections
to other objects. From these primitive objects(after known as user-interface objects) the
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8. designer can construct newer objects as composites of the primitives(these are often
known as composite-interface objects).
The basic iterative step of Interactive System Design
Fig. The basic iterative step of Interactive System Design & design activities
Problem definition involves the resolution of four basic issues
• Identifying the human activity that proposed interactive system will support
• Identifying the people or user who will perform the activity
• Selling the level of support that the system will provide otherwise known as the
system’s usability.
• Selecting the basic form of solution to the design problem.
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9. Usability: This is a collective term for all aspects of an activity’s performance that can
be affected by the use of technology. The individual aspects are known as usability
factors. Each one provide a measures of a particular aspect of the performance of
activities when supported by the system.
A list of main usability factors are
• The speed of performance of the activity which affect how many are needed to
perform it.
• The incidence of errors while performing the activity.
• User’s ability to recover from errors that occur.
• The magnitude of the user’s task in learning to use the system.
• User’s retention of learned skills.
• User’s ability to customize the system to suit their way of working or situation of
use.
• The ease with which people can reorganize activities supported by the system-
their own activities and other people’s.
• User’s satisfaction with the system.
To define the form of solution means to specify how this support is to be made available.
Provisions of interactive support involves numerous layers of technology and resources
including
• The user interface with which the user interacts directly.
• The application software that supports the user interface.
• The operating system that provides standard services to both the user interface
and its supporting software
• System resources accessed via the user interface and supporting software.
• The hardware that supports all these resources.
In the course of solving the design problem we will specify every layer of the design
in sufficient detail for implementation to be carried out.
Norman’s model of task perfoemance
The design of interactive system involves detailed analysis and prediction of the
performance of tasks, Don Norman (1986) has proposed a model of task perfomance that
identifies seven stages of execution and evaluation of user actions. The model provides a
framework for understanding how user’s actions relate to this goals and to the systems
they use.
The model depicts the stages of mental activity that may be involved in the user’s
achievement of a goal. These consists of
• Establishing the goal to be achieved.
• Forming the intention for action that will achieve the goal
• Specifying the action sequence corresponding to the intention
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10. • Executing the action
• Perceiving the system state
• Interpreting the state as perceived
• Evaluating the system state with respect to the goal & intentions.
Fig. Norman’s seven stage model of interaction.
The model identifies two categories of mental activity concerned respectively with
Execution &Evaluation.
The execution stages lead from the goal to the performance of action and the evaluation
stages lead back from perceiving the resulting state of the system to its evaluation with
respect to goals and intentions.
Norman makes the point that there is a cognitive gulf between the goal physical system
used in achieving the goal and we can design systems to reduce this gulf with positive
effects on the user’s interaction.
A theory of exploratory learning
A theory of exploratory learning explains the organization of a particular kind of activity
namely the way in which someone unfamiliar with a system learns how to use it through
exploration.
The theory can be expressed as a simple functional model with four parts (Polson &
Lewis 1990)
• Goal setting- Users start with a rough description of what they want to
accomplish -a task.
• Exploration- Users explore the system’s interface to discover actions useful in
accomplishing their current task.
• Selection – Users select actions that they think will accomplish their current task,
often based on match between what they are trying to do and the interface’s
descriptions of actions.
• Assessment- Users assess progress by trying to understand system responses,
thus deciding whether the action they have just performed was the correct one to
obtain clues for the next correct action.
Interaction styles represents alternative design strategies for the user interface. Each style
offers its own cohesive way of organizing the systems functionality of managing the
users inputs and of presenting information.
Three categories of style
The main property that sets one interaction style apart from another is the way the
system’s interactive resources are organized – The architecture of the user interface. In
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11. some styles the system’s resources are made available step by step, while in others they
are all made available to the user more or less from the outset and yet others they are
accessed by composing and issuing commands in an appropriate language. The three
categories of interaction styles are
• Key model
• Direct Manipulation
• Linguistic
Key model : The term “key-model” is shorthand way of saying that the user interface
is operated mainly with the aid of function keys or an alphanumeric keyboard and
that it has a number of different modes of behavior. Our common interaction styles
can be considered key-model:
• Menu based interaction
• Question and Answer
• Function key interaction
• Voice based Interaction
Each of these interaction styles depend on shifts of mode key model user interface
are used in almost all systems designed for walk up use, for example , automated
tellers, ticket machine & voice mail systems. One reason why key model interfaces
are so popular for walk up use systems is that they can provide the user user with
step by step instructions. The system always knows what state of the interaction has
been reached and hence what actions are now available to the user so it can
appropriate help.
Direct Manipulation Styles
The user interface can display a no. of objects on the screen and allow the user to
interact with each one independently. With the aid of a pointing device the user can
apply actions directly to the object of interest. This style of user interface is known
as direct manipulation. Two widely used styles of direct manipulations are
• Graphical direct manipulation
• Form fill in
Linguistic styles
Some styles of user interface require all of the user’s inputs to be made on an
alphanumeric keyboard, using a particular set of conventions or language and for this
reason we group them together as linguistic styles. The two principal linguistic styles are
• Command Line Interaction
• Text based natural language
Conceptual Design: The user’s mental model
Conceptual Design is concerned with helping people to accumulate knowledge about the
systems they use. As they gain experience of a particular systems , they acquire
knowledge about the system’s behavior and on this basis they are able to develop
theories about its inner workings. They gradually form a working model of the system
around which they organize their knowledge and theories. This is their mental model of
the system.
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12. Mental model can be formed through many kinds of user experience-through use of the
system, through observation of other users at work, through training, through reading
documentation.
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