Understandability and Mental Models
Oral Exercise
Purpose:
To analyze the role of understandability in the use of artifacts.
Definitions:
Understandability is the ability of the user to build a logically accurate model of the artifact that she is utilizing to achieve her dynamic goals.
Artifact: an object constructed by people for a particular use; often a machine.
Dynamic goals: Most artifacts are used in an environment which changes in ways that are not under the control of the artifact user. Therefore, even when the overall goal of the artifact user does not change, subgoals do change as the environment changes.
Effector: That part of an artifact used to perform operations directed toward meeting a goal (or subgoal) of its user. The specific object (physical or logical) designed to effect the result desired by the artifact user.
Fractionated mental model: A mental model which is accurate in many specifics but which breaks down at crucial junctures.
Model space: The mental space the user of an artifact builds up and in which he acts. Actions which occur in close proximity in physical space reside in close proximity in model space.
Fracture: A fracture in a mental model occurs when two (or more) interactions which are in close proximity in model space produce wildly divergent results.
Winding staircases
In many old Pennsylvania farmhouses floor space was conserved by using winding staircases in which the steps were triangular in shape. If one ventured too close to the narrow part of a step, a slip or a misstep could plummet one quickly to the bottom of the stairs. The illustration here is of a safe and a dangerous space being in close proximity to each other. This is a physical example of a fractured space.
^x & ^z
In some early editors, where many commands were invoked with control sequences, ^x (control-x) was used to save a file; ^z was used to delete the file. This led to the unfortunate circumstance where a user deleted a file she had meant to save. Right in the middle of what should be a safe space in the mental model is an unsafe area. And this danger zone is hard to avoid because there is no significant conceptual separation between it and the rest of the conceptual space.
Assignment:
Find an example of a fractionated mental model; explain where the fracture in user experience occurs.
Optional Extra Assignment:
1.
Analyze your use of the artifact: automobile. Identify the main goal(s). Identify changes in the usage environment which can effect changes in the current subgoal set. Make a brief list of dynamic subgoals and their associated environmental factors.
2.
Analyze your mental model of this artifact. List a small number (between 5 & 10) of the chief effectors you utilize. Describe your logical understanding of the use of each effector, irrespective of your understanding of its physical operation. What is the role of your mental model in a dynamic environment? In an emergency? What is the role of experience in the construction of your mental model?
3.
If you are not familiar with the term fly by wire with respect to aircraft, look it up. If someone were to apply the fly by wire principle to an automobile, how would that affect your mental model of its use? What would be more important for your ability to successfully operate the fly by wire automobile: your experience with it or your understanding of its physics?
4.
Describe how you handle your car in a skid? What is the most important ingredient in your choice of action to take in that situation?
5.
Briefly analyze your use of two other artifacts: an electric light and a telephone (or a cell phone). What is your mental model? How well do you understand the underlying physics?
6.
Apply the results of your analysis to software design. What role does the user’s mental model play in his use of a software artifact? What design factors promote understandability? Which factors tend to reduce understandability? What is the effect of a logically accurate mental model on productivity? A fractionated mental model?