CHAPTER 6: USABILITY

Usability
*Assesses how easy user interfaces are to use.
*Methods for improving ease-o-use during the design process.
*There are 5 quality component of Usability:

1. Learnability:
How easy is it for users to accomplish basic task the first time they encounter the design?

2. Efficiency:
Once users have learned the design, how quickly can they perform tasks?

3. Memorability:
When users return to the design after a period of not using it, how easily can they reestablish proficiency?

4. Error:
How many errors do users make, how severe are those errors, and how easily can they recover from the errors?

5. Satisfaction:
How pleasant is it to use the design?

Why Usability is important?

• Increased productivity
• Increased sales and revenues
• Decreased training and support costs
• Reduced development time and costs
• Reduced maintenance costs
• Increased customer satisfaction

Affordance
*a property in which physical characteristics of an object or environment influence its function.

Nail clippers are for cutting nails.

Screwdrivers are for rotate the screw.

Constraint
*a method of limiting the actions that can be performed on
a system. 
*there are two types of Constraint:
1.Physical constraints

• limit the range of possible actions by redirecting physical motion in specific ways.
• the three kinds of physical constraints are:

1. Path

This design applied force into linear motion and its useful where the control variable range is small and bounded. 

Volume can be change if it is moved up or down.

2. Axes

This design applied forces into rotary motion and its useful where control real estate is limited, larger or unbounded.

The speed of the ceiling fan can be change when the electronic controller rotated.

3. Barriers

This design applied halting, slowing or directing forces around the barriers. Its useful for denying errant or undesired actions. 

2. Psychological constraints

• limit the range of possible actions by leveraging the way people perceive and think about the world.
• the three kinds of psychological constraints are:

1.Symbols

This symbol convey meaning towards user without state the info. Its able to convey the meaning through symbol communication or precisely its able to influence behavior by communicating meaning through language.

The images and texts works as sign to warn the user about the danger if inserting your hand into the tub while in operation. 

2.Conventions

This design influence behavior based on learned traditions and practices. The symbol allow user to use the button because it design almost the same with the usual one. So, its easier to understand how its going to work. 

3.Mapping

*influence behavior based on learned traditions and practices

Mouse enable user to navigate the cursor

Mapping
*a relationship between controls and their movements or effects.
*good mapping between controls and their effects results in greater ease of use.
*Good mapping is primarily a function of similarity of:

• layout
• behavior
• meaning

In above figure, it is an electronic controller of a ceiling fan. Mapping is defined as the relationship between two things - Controls and their movements and the results in the world. Electronic controller as the controls and ceiling fan produce movements in the world.

Feedback
*sending back to the user information about what action has actually been done.
*there four types of Feedback:
1. auditory
2. visual
3. tactile
4. olfactory(sense of smell)

Feedback is the action which sending back to the user information about what actually been done. It is necessary for the user to know what happened timely when they using user interface.

Visibility
*The usability of a system is improved when its status and methods of use are clearly visible.

Mental Model
*People understand and interact with systems and environments based on mental representations developed from experience.
*there are two basic types of mental models:
1. System Model - how system work.
2. Interaction Model - how people interact with the system

*User Centered Design Approach (UCD)
1. Self-explore
• Reveal design problems
• Fail to reveal problem of interaction
2. Laboratory testing
• Controlled environment - systematic
3. Direct observation

• Costly & impractical for prototype product

*incorporate the following characteristics:
1. Familiarity - use of concepts and techniques that users already understand from their real world experiences
2. Simplicity - well-organized interface
3. Availability - provide visual cues, reminders, lists of choices, and other aids
4. Discoverability - support alternate interaction techniques

Iconic Representation
*The use of pictorial images to improve the recognition and recall of signs and controls.
*there are four type of Icon Representation:
1. Similar

• Visually analogous to an action/concept.
• Representing simple actions, objects or concepts

2. Example

• Images of things that exemplify or are commonly associated with an action, object or concept

3. Symbolic

• Images that represent an action, object or concept at a higher level of abstraction
• Metaphor

4. Arbitrary

• Images that bear little or no relationship to the action, object or concept that has to be learned
• Used for long periods of time (become standard)

*Reduces performance load – knowledge in the world

*Conserves display and control panel

*Signs and control more understandable across cultures

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Electric Stove