Lecture : Human-Computer Interaction

In the previous lecture:

• What are reference data types?
• What are classes, data members and methods?
• How do you create objects, change their fields and copy them?

In this lecture:

• How do users interact with computers?
• What devices do they use to perform these interactions?

Remember: Unusable software is not worth making!

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 simultaneously) 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.

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:

• 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

Locator devices (for positioning) may be conveniently categorized as 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
Direct locator device: user points directly at the screen Indirect locator device user moves a cursor on the screen using a device separate from the screen.

Track Ball (relative, indirect locator)	Mice (relative, indirect locator)
Light Pen (absolute, direct locator)	Touch Screen (absolute, direct locator)
Joystick (relative, indirect locator)	Graphics tablet (absolute, indirect locator)

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

Continuous locator devices: require a single smooth operation to achieve a movement in a given direction. E.g. joysticks, mice, graphics tablets

Cursor control keys (arrows, ijkm, asdw etc.) (indirect, discrete locator devices)	Joystick (indirect, continuous locator device)
	What type of device is this Nintendo Wii Power Glove?

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

Large ratio - large hand movement / small cursor movement (Good for accurate positioning, poor for long movements)

Small ratio - small hand movement / large cursor movement (Good for rapid movements across long distances, poor for accurate positioning)

A relative device may be set up with a variable C/D ratio depending on the velocity of movement. Should the ratio be high or low for fast 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.

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?

• 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 recommendations for 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.
  
  
  

• 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

• For large amounts of text entry, a hardware keyboard is 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.

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

What guides your choices in designing an interface?

• There are four basic interaction tasks: position, text, select, quantify.
• These may be performed using various hardware and software devices which are themselves categorised according to their properties and potential.
• Be aware of the properties of these devices and understand the benefits and drawbacks of using each in different circumstances.