CSE3325: Introduction to Interactivity

In the previous lecture:

About Human-Computer Interaction (HCI) and design issues for Multimedia.

In this lecture:

Unusable software :-P

Unusable software is not worth making!

Every aspect of interactive software must be designed and tested for/by the human target audience.

Not just by the software engineers and programmers who wrote the thing!


In the case of websites here are some important issues...

Elements must provide an appropriate mood and operate within a metaphor aimed at the target audience.

A simple rule states... if a user will perform a task

    often, make it fast and easy to perform

    infrequently, it's acceptable that it be slower or slightly more difficult to perform.

For example, if it took three keystrokes to save a word processor file every time, a task which ought to be performed often, a user would rapidly become frustrated. A single key chord (group of keys held down together) such as ALT-S may easily achieve the same task.

The act of setting preferences on the other hand, a task done infrequently, may require the user to navigate several menus and dialogue boxes. This is OK because the user usually only sets preferences for the software every now and again.

What do users do?

Users perform an interaction task or several interaction tasks in sequence – an interaction dialogue.

An interaction task is the entry of a unit of information using a hardware or software device.

Four basic interaction tasks:

  1. Position (input a position)

  2. Text (input a text string)

  3. Select (object identification)

  4. Quantify (input a numeric value)


Interaction techniques are the means of achieving interaction tasks using input devices.

E.g. A selection task may be achieved:


A single input device may be used for more than one kind of interaction task.

E.g. A mouse may be used for:

Interaction Hardware Devices

The most common devices for interaction with computer based multimedia are:

What is the dominant interaction task on the Web? Which hardware device is used the most frequently?

Locator devices (for positioning) may be conveniently categorized

mice track ball
(Common relative locators: mice; trackball)

Direct locators: user points directly at the screen.

Light Pen
(Pen tip and cursor at the same spatial location)
Touch Screen
(Finger tip and cursor at the same spatial location)


Indirect locators: user moves a cursor across the screen using a device separate from the screen.
E.g. mouse, joystick

(Hand on joystick and rocket ship on screen at different spatial locations)


Discrete locators: require repeated operation to achieve a movement in small increments in a given direction.
E.g. buttons, keys

arrow keys
(Cursor control keys)

Continuous locators: require a single smooth operation to achieve a movement in a given direction.
E.g. joystick, mouse, graphics tablet

The C/D ratio is...

The ratio of the speed/distance of hand movement (Control) to the speed/distance of cursor movement (Display) for a continuous device.

A relative device may be set up to change its C/D ratio depending on the velocity of movement.
Should the ratio be high or low for high-velocity movements? Why?

Position Interaction Task

Device movement direction should correspond to movement in screen space. For instance, if the mouse moves left, so should the cursor or selected object!

Key spatial orientation for cursor control should correspond to onscreen movement.

E.g. i- up, m- down, j- left, k- right or properly arranged arrow keys

ijkm keys

Grids may aid spatial positioning tasks by 'snapping' the cursor to specific points in a plane, and not allowing the cursor to locate objects (for example line endpoints in a drawing package) at non-grid points.

This simplifies the task of ensuring neat alignment of objects in a drawing.


Selection Interaction Task

Selection involves choosing an element from a choice set.

Choice sets are either predominantly fixed, or variable.

Choice sets include:

Fixed and variable choice sets may call for different methods of selection...

Menus for selection from fixed sized choice sets may be:

Menus of commands may be grouped functionally and displayed textually,

menu bar

or iconically...

tool bar

Pointing (or naming with auto-completion) for selection from variable sized choice sets.

Naming is preferable where there is insufficient screen space to display all objects for pointing. However, this method assumes some knowledge from the user! (What is it?)

Tips for onscreen location (for mouse selection) - note the contradictory demands

What are the easiest places for a user to position the cursor using a mouse?

Why is this so? How can you use this knowledge to build an effective interface?

Keyboard devices

Selection by Keyboard Shortcut

Text Interaction Task

Quantify Interaction Task

Vital Principles of Interface Design

    1. Be consistent

    2. Provide feedback

    3. Minimize error possibilities

    4. Provide error recovery

    5. Accommodate multiple skill levels

    6. Minimize memorization

This lecture's key point(s):

CSE3325 courseware | CSE3325 lecture notes

©Copyright Alan Dorin 2005