Previously we reviewed many aspects of user interfaces from the perspective of the behavioral and social sciences. Do you remember the interface metaphors, mental models, and conceptual models? If yes then great, if not just click on the link and have a look at them. In this article, we will show how you can apply such insights, by considering direct manipulation interaction from a cognitive science perspective.
The topics of this article are the Gulf of Execution and the Gulf of Evaluation. These two terms were introduced by Donald Norman in his book, The Psychology of Everyday Things (1988). So Norman developed a framework that characterized directness in terms of two "gulfs" which describe the gap between the users' goals and the system image. The degree of directness in direct manipulation interfaces can be considered as the discrepancy or distance between two gulfs.
The Gulf of Execution
Refers to the distance between the user's goals and the means of achieving them through the system.
The Gulf of Evaluation
Refers to the distance between the system's behavior and the user's goals.
Image from the book The Psychology of Everyday Things (1988)
Both gulfs are related, the concern is finding ways to reduce the discrepancy between the user's goals and the system's physical state and form. By reducing the gap, the mismatch is reduced thereby making it easier for users to carry out their tasks. This is achieved by bridging the two gulfs.
Bridging the gulfs
The users can bridge the gulf of execution by changing the way they currently think and Harry out the task towards the way the system requires it to be done. The designers can bridge the gulf of execution by designing the input characteristic to match the users' psychological capabilities.
The users can bridge the gulf of evaluation by changing their interpretation of the system image and evaluating it with respect to their goals. The designers can bridge the gulf of evaluation by changing the output characteristics of the system.
Image from the book The Psychology of Everyday Things (1988)
Affordances, Constraints, Mapping, and Feedback
In addition to developing a theoretical framework for understanding the principles of direct manipulation, Don Norman in his book The Psychology of Everyday Things (1988) developed the four main design principles of good direct manipulation interface design:
Affordances
When designing interface objects, like buttons, sliders, and files, it is important that the actions meant to be performed on them are obvious.
Constraints
Refers to limit the number of possibilities of what can be done with an object. Norman suggests that there are four main types of constraints: physical, semantic, cultural, and logical.
Mapping
Refers to a design in which the system's controls represent or correspond to the desired outcome. Mappings are said to be good if they appear natural and intuitive to the users.
Feedback
This is a very important and fundamental design concept. Feedback is defined as sending back to the user information about what action has actually been done and what result has been accomplished.
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