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Human Computer Interaction

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As the aim of this lecture is to introduce you the study of Human Computer
Interaction, so that after studying this you will be able to:

. Define interaction

. Discuss interaction styles keeping in view different aspects of HCI
In the previous lectures we have studied the detailed introduction of human side and
computer side. These are two participant of our course Human Computer Interaction.
As the name of the course reveals that both of these complex entities are not in
isolation rather they come in contact with each other. Human communicate with
There are a number of ways in which human can communicate with the system. If we
look at the beginning, batch input system was used, in which the user provides all the
information to the computer in form of batch. Now a day it is the age of virtual reality
and ubiquitous computing. Here user constantly interacts with computers in his
surroundings. Today there is richer interaction.

14.1 The terms of Interaction


A domain defines an area of expertise and knowledge in some real-world activity.
Some examples of domains are graphic design, authoring and process control in a
factory. A domain consists of concepts that highlight its important aspects. In a
graphic design domain, some of the important concepts are geometric shapes, a
drawing surface and a drawing


Task are the operation to manipulate  the concepts of a domain. A goal is the desired output from a performed task. For example, one task within the graphic design domain is the construction of a specific geometric shape with particular attributes on the drawing surface.


A related goal would be to produce a solid red triangle centered on the canvas. So, goal is ultimate result, which you want to achieve after performing some specific tasks.

14.2 Donald Norman’s Model

We have already studied Donald Norman’s Model of interaction. In which user
chooses a goal, formulate a plan of action, which is then executed at the computer
interface. When the plan, or part of the plan has been executed, the user observes the
computer interface to evaluate the result of the execution plan, and to determine
further actions.
The two major parts, execution and evaluation, of interactive cycle are further
subdivided into seven stages, where each stage is an activity of the user. Seven stages
of action are shown in figure. To understand these we see an example, which was also
used by Norman.
Imagine you are sitting reading as evening falls. You decide you need more light; that
is you establish the goal to get lighter. Form there you form an intention to switch on
the desk lamp, and you specify the actions required to reach over and press the lamp
switch. If some one else is closer, the intention may be different-you may ask them to
switch on the light for you. Your goal is the same but the intention and actions are
different. When you have executed the action you perceive the result, either the light
is on or it isn’t and you interpret this, based on your knowledge of the world. For
example, if the light does not come on you may interpret this as indicating he bulb has
blown or the lamp is not plugged into the mains, you will formulate the new state
according to the original goals – is there is now enough light? It so, the cycle is
completed. It not, you may formulate a new intention to switch on the main ceiling
light as well.

Gulf of execution and evaluation

Norman also describes the two gulfs, which represent the problems that are caused by
some interfaces to their users.

Gulf of execution

Gulf of execution is the difference between the user’s formulation of the actions to
reach the goal and the actions allowed by the system. If the action allowed by the
system correspond to those intended by the user, the interaction will effective. The
interface should therefore aim to reduce this gulf of execution.

Gulf of evaluation

The gulf of evaluation is the distance between the physical presentation of the system
state and the expectation of the user. If the user can readily evaluate the presentation
in terms of his goal, the gulf of evaluation is small. The more effort that is required on
the part of the user to interpret the presentation, the less effective the interaction.


14.3 The interaction framework

The interaction framework breaks the system into four main components as shown in
figure. The nodes represent the four major components in an interactive system – the System, the User, the Input and the Output. Each component has its own language. The system and user are each described by means of a language that can express  concepts  relevant in the domain of the application. The system’s language is referred as the core language and the user’s language is referred as the task language. The core language describes computational attributes of the domain relevant to the system state, whereas the task language
describes psychological attributes of the domain relevant to the user state. There are
also languages for both the input and output components. Input and output together
form the interface.
As the interface sits between the user and the system, there are four steps in the
interactive cycle, each corresponding to a translation from one component to another,
as shown by the labeled arcs in figure. The user begins the interactive cycle with the
formulation of a goal and a task o achieves that goal. The only way the user can
manipulate the machine is through the input, and so the task must be articulated
within the input language, the input language is translated into the core language as
operations to be performed by the system. The system then transforms itself as
described by the operations; the execution phase of the cycle is complete and the
evaluation phase now begins. The system is in a new state, which must now be
communicated to the user. The current values of system attributes are rendered as
concepts or features of the output. It is then up to the user to observe the output and
assess the results of the interaction relative to the original goal, ending the evaluation
phase and, hence, the interactive cycle. There are four main translations involved in
the interaction: articulation, performance, presentation and observation. The user’s
formulation of the desired task to achieve some goal needs to be articulated in the
input language. The tasks are responses of the user and they need to be translated to
stimuli for the input. As pointed out above, this articulation is judged in terms of the
coverage from tasks to input and the relative ease with which the translation can be
accomplished. The task is phrased in terms of certain psychological attributes that
highlight the important features of the domain for the user. If these psychological
attributes map clearly onto the input language, then articulation of the task will be
made much simpler.

The ACM SIGCHI Curriculum Development Group presents a framework and uses it
to place different areas that relate to HCI As you can see in the figure, the field of ergonomics addresses issues on the user side of the interface, covering input and output, as well as  the user’s immediate context. Dialog design and  interface styles can be placed particularly along the input branch of the framework, addressing both articulation and performance. However, dialog is most usually associated with the computer and so is biased to that side of the framework. Presentation and screen design relates to the output branch of the framework. The entire framework can be placed within a social and organizational context that also affects the interaction. Each of these areas has important implications for the design of interactive systems and the performance of the user.

Let us first take a brief look.


Ergonomics (or human factors) is traditionally the study of the physical characteristic
of the interaction: how the controls are designed, the physical environment in which
the interaction takes place, and the layout and physical qualities of the screen. A
primary focus is on user performance and how the interface enhances or detracts from
this. In seeking to evaluate these aspects of the interaction, ergonomics will certainly
also touch upon human psychology and system constraints. It is a large and
established field, which is closely related to but distinct from HCI.
Physical aspects of Interface are as follow:

. Arrangement of controls and displays

. The physical environment

. Health issues

. Use of colors

Arrangement of controls and displays

We already have discussed in previous lectures the perceptual and cognitive issues
that affect the way we present information on a screen and provide control
mechanisms to the user. In addition to these cognitive aspects of design, physical
aspects are also important. The user should group sets of controls and parts of the
display logically to allow rapid access. This may not seem so important when we are
considering a single user of a spreadsheet on a PC, but it becomes vital we turn to

safety-critical applications such as plant control, aviation and air traffic control. In
each of these contexts, users are under pressure and are faced with a huge range of
displays and controls. Here it is crucial that the physical layout of these be
appropriate. Indeed, returning to the less critical PC application, inappropriate
placement of controls and displays can lead to inefficiency and frustration.
Industrial Interface
The interfaces to office systems have changed dramatically since the 1980s. However,
some care is needed in transferring the idioms of office-based systems into the
industrial domain. Office information is primarily textual and slow varying, whereas
an industrial interfaces may require the rapid assimilation of multiple numeric
displays; each of which is varying in response to the environment. Furthermore, the
environment conditions may rule out certain interaction styles.
Consequently, industrial interfaces raise some additional design issues rarely
encountered in the office.
Glass interfaces vs. dials and knobs
The traditional machine interface consists of dials and knobs directly wired or piped
to the equipment. Increasingly, some or all of the controls are replaced with a glass
interface, a computer screen through which the equipment is monitored and
controlled. Many of the issues are similar for the two kinds of interface, but glass
interfaces do have some special advantages and problems. For a complex system, a
glass interface can be both cheaper and more flexible, and it is easy to show the same
information in multiple forms.
Indirect manipulation
The phrase ‘direct manipulation,
dominates office system design as
shown in figure (a). there are
arguments about its meaning and
appropriateness even there, but it is certainly dependent on the user being in primary
control of the changes in the interface. The autonomous nature of industrial processes
makes this an inappropriate model. In a direct manipulation system, the user interacts
with an artificial would inside the computer.
In contrast, an industrial interface is merely an intermediary between the operator and
the real world. One implication of this indirectness is that the interface must provide
feedback at two levels as shown in figure (b). at one level, the user must receive
immediate feedback, generated by the interface, that keystrokes and other actions
have been received. In addition, the user’s action will have some effect on the
equipment controlled by the interface and adequate monitoring must be provided for
The indirectness also causes problems with simple monitoring tasks. Delays due to
periodic sampling, slow communication and digital processing often mean that the
data displayed are somewhat out of date. If the operator is not aware of these delays,
diagnoses of system state may be wrong. These problems are compounded if the
interface produces summary information displays. If the data comprising such a
display are of different timeliness the result may be misleading.

The physical environment of the interaction

As well as addressing physical issues in the layout and arrangement of the machine
interface, ergonomics is concerned with the design of the work environment itself.
Where will the system be used? By whom will it be used? Will users be sitting,
standing or moving about? Again, this will depend largely on the domain and will be
more critical in specific control and operational setting s than in general computer use.
However, the physical environment in which the system is used may influence how
will it is accepted and even the health and safety f its users. It should therefore be
considered in all design.

Health issues

Perhaps we do not immediately think of computer use as a hazardous activity but we
should bear in mind possible consequences of our designs on the health and safety of
users. Leaving aside the obvious safety risks of poorly designed safety-critical
systems. There are a number of factors in that may affect the use of more general
computers. Again these are factors in the physical environment that directly affect the
quality of the interaction and the user’s performance:

Physical position

As we discussed earlier users should be able to reach all controls comfortably and see
all displays. Users should not be expected to stand for long periods and, if sitting,
should be provided with back support.


Although most users can adapt to slight changes in temperature without adverse
effect, extremes of hot or cold will affect performance and, in excessive cases, health.


The lighting level will again depend on the work environment. However, adequate
lighting should be provided to allow users to see the computer screen without
discomfort or eyestrain. The light source should also be positioned to avoid glare
affecting the display.


Excessive noise can be harmful to health, causing the user pain, and in acute cases,
loss of hearing. Noise level should be maintained at a comfortable level in the work


The time users spend using the system should also be controlled.

The use of color

Ergonomics has a close relationship to human psychology in that it is also concerned
with the perceptual limitations of humans. For example, the use of color in displays is
an ergonomics issue. The human visual system has some limitations with regard to
color, including the number of colors that are distinguishable and the relatively low
blue acuity. Color used in display should be as distinct as possible and the distinction
should not be affected by changes in contrast. The colors used should also correspond
to common conventions and user expectation. However, we should remember that
color conventions are culturally determined.

14.5 Interaction styles

Interaction is communication between computer and human (user). For a successful
enjoyable communication interface style has its own importance.
There are a number of common interface styles including

. Command line interface

. Menus

. Natural language
Question/answer and query dialog

. Form fills and spreadsheets


. Point and click

. Three-dimensional interfaces.

Command line interface

Command line interface was the first interactive dialog style to be commonly used
and, in spite of the availability of menu-driven interface, it is still widely used. It
provides a means of expressing instructions to the computer directly, using some
function keys, single characters, abbreviations or whole-word commands.
Command line interface are powerful in that they offer direct access to system
functionality, and can be combined to apply a number of tools to the same data. They
are also flexible: the command often has a number of options or parameters that will
vary its behavior in some way, and it can be applied to many objects at once, making
it useful for repetitive


In the menu-driven interface, the set of options available to the user is displayed on the screen and selected using the mouse, or numeric or  alphabetic keys. Since the options are visible they are less demanding of the user, relying on recognition rather than recall. However, menu options still need to be meaningful and logically grouped to aid recognition. Often menus are hierarchically ordered and the option required is not available at the top layer of the hierarchy. The grouping and naming of menu options then provides the only cue for the user to find the required option. Such systems either can be purely text based, with the menu options being presented as numbered choices, or may have a graphical component in which the menu appears within a rectangular box and choices are made, perhaps by typing the initial letter of the desired selection, or by
entering the associated number, or by moving around the menu with the arrow keys. This is restricted form of a full WIMP system.

Natural Language

Perhaps the most attractive means of communicating with computers, at least at first
glance, is by natural language. Users unable to remember a command or lost in a
hierarchy of menus, may long for the computer that is able to understand instructions
expressed in everyday words. Unfortunately, however, the ambiguity of natural
language makes it very difficult for a machine to understand.

Question/answer and query dialog

Question and answer dialog is a simple mechanism for providing input to an
application in
a specific domain. The user is asked a series of questions and so is led through the
interaction step by step. An example would be the wizards as shown in figure.
These interfaces are easy to learn and use, but are limited in functionality and power.
As such, they are appropriate for restricted domains and for novice or casual users.
Query languages, on the other hand, are used to construct queries to retrieve
information from a database. They use natural-language-style phrases, but in fact
require specific syntax, as well as knowledge of database structure. Queries usually
require the user to specify an attribute or attributes for which to search the database,
as well as the attributes of interest to be displayed. This is straightforward where there
is a single attribute, but becomes complex when multiple attributes are involved,
particularly of the user is interested in attribute A or attribute B, or attribute A and not
attribute B, or where values of attributes are to be compared. Most query language do
not provide direct confirmation of what was requested, so that the only validation the
user has is the result of the search. The effective use of query languages therefore
requires some experience.

Form-fills and spreadsheets

Form-filling interfaces are used primarily for data entry but can be useful in data
retrieval applications. The user is presented with a display resembling a paper form,
with slots to fill in as shown in figure. Most form-filling interfaces allow easy
movement around the form and allow some fields to be left blank. They also require
correction facilities, as users may change their minds or make a mistake about the
value that belongs in each field.
Spreadsheets are sophisticated variation of form filling. The spreadsheet comprises a
grid of cells, each of which can contain a value or a formula. The formula can involve

the value of other cells. Now a days MS Excel is used widely. In past VISICALC and
Lotus 123 had been used.

The WIMP Interfaces

Currently many common environments for interactive computing are examples of the
WIMP interface style, often simply called windowing systems. WIMP stands for
windows, icons, menus, and pointers, and is default interface style for the majority of
interactive computer systems in use today, especially in the PC and desktop
workstation arena.

Point and Click interface

In most multimedia systems and in web browsers, virtually all actions take only a
single click of the mouse button. You may point at a city on a map and when you
click a window opens, showing you tourist information about the city. You may point
at a word in some text and when you click you see a definition of the word. You may
point at a recognizable iconic button and when you click some action is performed.

Three-dimensional interfaces

There is an increasing use of three-dimensional effects in user interfaces. The most
obvious example is virtual reality, but VR is only part of a range of 3D techniques
available to the interface designer.
The simplest technique is where ordinary WIMP elements, buttons, scroll bars, etc,,
are given a 3D appearance using shading, giving the appearance of being sculpted out
of stone.

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