Design Analysis Flashcards
Fitts’ law
can be used to determine the size and location of a screen object.
Fitts’ law states that the time it takes to hit a target is a function of the size of the target and the distance to that target
three parts to fitt’s law
ID - Index of Difficulty
* quantifies the difficulty of a task based on width and distance
MT - Movement Time
* quantifies the time it takes to complete a task based on the difficulty of the task (ID) and two empirically derived coefficients that are sensitive to the specific experimental conditions
IP Index of Performance
* based on the relationship between the time it takes to perform a task and the relative difficulty of the task
Fitts’ law - implications
overly elongated objects hold no advantage
objects should be elongated along the most common trajectory path
objects should not be offset from the screen edge
fitts law does not address touch specific problems (e.g. fat fingers)
Hick’s Law
The time T needed to make a decision is proportional to the log number of alternatives given
T= a+bH
H(Entropy) = log2(n+1)
a,b: coefficients, empirically determined from experimental design
requirements: no linear search, no power law of practice, equal probability
Power Law of Practice
Users get better every time they use a system
Time = B*N^-[alpha]
N: Trial Number
B, [alpha]: constants
Mental Models
People use a mental model to have a basic understanding of what is going on
The mental model is often unsharp
Mental models is a method to understand interaction that is both predictive and explanatory
- unscientific
- partial
- unstable
- inconsistent
- personal
Mental Models and Mapping
Mapping can be used to foster understanding and building a correct model - and thus increase usability
Two major principles of design
Mapping
- to a form
- to provide overview
Constraints
- to guide
- for support “affordance”
Mapping
correlation between control element and action
properties for good mapping
- understandable
- consistent
- recognizable or quickly learnable
- natural
Constraints
Constraints lead humans to build correct mental models
Constraints guide the user to the next appropriate action or decision
Constraints also minimize the chance to make errors
- physical constraints
- semantic constraints
- cultural constraints
- logical constraints
Affordance
To build a mental concept of a system we need to interpret symbols and components
This can be seen as the functionality of the device and what we actually want to do - The semantic and articulator Distance
3 principles of affordance
- make usable properties visible
- use natural associations
- give feedback
Norman’s Execution/Evaluation Action Cycle (EEAC)
Goals : we begin with some idea of what we want to happen
* Establish the goal
--> Execution: We must then execute and action * Forming intention * Specifying action * Executing action
–>
World/Action: Manipulate Objects in World
--> Evaluation: Finally, validate our action. compare results with goals * Evaluating Interpretation * Interpreting Perception * Perceiving World State
–> goals
Gulf of Execution
Mismatch between the user’s intentions and the allowable actions
Not enough knowledge about
- concept
- usage
- access to function
Good design minimizes the Gulf of Execution!
- how directly can the actions be accomplished?
- do the actions that can be taken in the system match the actions intended by the person?
