FIT3084: Introduction to Interactivity

In the previous lecture:

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

In this lecture:

• How do users interact with computers?
  
  
• What can be done to improve user interaction with computers?

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...

• Page and site layout
  
  
  • Easy navigation
  • Quick path to outcome
  
  
• Text / Language
  
  
  • Legible and readable
  • Appropriate for target audience
  
  
• Imagery
  
  
  • Clear
  • Relevant
  
  
• Colour
  
  
  • Improve clarity of textual & visual information

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

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.

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

E.g. A selection task may be achieved:

• Point & click with mouse
  
  
• Tab through list, hit enter key
  
  
• Select from a menu
  
  
• Type identifier key / key chord
  
  
• Speak to speech recognition software

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

E.g. A mouse may be used for:

• Selecting
  
  
• Positioning
  
  
• Text & Quantifying
  (Select from an onscreen keyboard or options presented onscreen as 'clickable' objects.)

Interaction Hardware Devices

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

• Mouse (1 button / 3 button / scroll wheel)
  
  
• QWERTY keyboard
  
  
• CRT or LCD screen

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

• absolute / relative
  
  
• direct / indirect
  
  
• discrete / continuous

	Absolute locators: have an origin location and locate in this frame of reference. e.g. touch panel, graphics tablet
	Relative locators: report location relative to their previous location, rather than relative to a fixed origin. e.g. mouse, trackball

(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

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

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

Large ratio - large hand movement : small cursor movement
Good for accurate positioning, poor for long movements.


Small ratio - small hand movement : large curosor movement
Good for rapid movement across long distances, poor for accurate positioning.

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

Linguistic (specify in some coordinate system)

Boxes to quantify position, orientation and scale of an object.
From the UI of Infini-D, a 3D animation package.



Spatial (move cursor to position)

Buttons to change position and orientation of an object by selection.
From the UI of Infini-D, a 3D animation package.

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

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:

• Commands (fixed)
  
  
• Attribute values (fixed)
  
  
• Object classes (fixed)
  
  
• Object instances (variable)

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

Menus for selection from fixed sized choice sets may be:

• Pull down, pop-up, permanent
  
  
• Alphabetically listed
  
  
• Functionally grouped (linear / hierarchical)
  
  
• Iconically represented
  
  
• Conventionally grouped
  
  
• Combinations of these

Menus of commands may be grouped functionally and displayed textually,

or iconically...

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

• Locate frequently selected objects conveniently and consistently.
  
  
• Locate objects together if they are accessed in the same interaction dialogue.
  
  
• Make objects which need to be selected larger than the cursor!
  
  
• Make objects which need to be selected in an interaction dialogue small to minimize mouse movement between them.
  
  
• Make objects small to minimize screen space expenditure.
  
  
• Clearly identify objects which may be selected.
  
  
• Provide feedback when an object is being selected.

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

• Current location (Seems obvious but is frequently forgotten!)
  
  
• Screen corners
  
  
• Screen edges

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

Keyboard devices

• The QWERTY keyboard was designed to slow down typists – to stop mechanical typewriter keys from jamming!
  
  
  
  
• The Dvorak keyboard places frequently used characters under the home position.
  Compare to positioning onscreen objects above.
  
  
• Alpha-numerically organized keyboards have been employed where users are not typists.
  This is becoming more and more rare as the computer becomes more and more common.
  
  
  

Selection by Keyboard Shortcut

• Make shortcuts consistent with convention.
  E.g. ALT-S, ALT-C, ALT-Q, ALT-Z. What tasks do these usually perform?
  
  
• Make non-conventional (and conventional!) shortcuts mnemonic.
  CTRL-I Inverse, CTRL-D Deselect, CTRL-B Brush Tool

Text Interaction Task

• For large amounts of text entry, QWERTY keyboard preferred over simulated keyboard or menu selection of characters.
  
  
• For small amounts of text entry, if the preceding & following stages in an interaction dialogue involve mouse operation, continued mouse operation is preferable to switching devices.
  
  
• Speech input is useful for hands free operation.

Quantify Interaction Task

• Linguistic: value typed on QWERTY keyboard or number pad.
  
  
• Spatial: operate slider, dial, pointer, up/down counter.

• Users perform interaction tasks and dialogues through a user interface.
  
  
• Interaction tasks may be broken down into a few basic kinds.
  
  
• Interaction tasks are performed with hardware and software devices which must be designed so as to enable effective participation of the user in the different kinds of interaction tasks.

Courseware | Lecture notes

©Copyright Alan Dorin 2008