Workload capacity

Mental workload is associated with the working memory.

People use their working memory (short-term memory) to evaluate situations and decide what they want to do. The capacity of the working memory is limited. According to research, humans can hold and process only five to nine data items simultaneously. The research is summarized in the classical article by Miller (1971) “The Magical Number Seven, Plus or Minus Two.”

Task demands

When operating an interactive system, the operator has at least two tasks to conduct simultaneously:

• at least one task is related to the controlled system and
• at least one task is related to the interaction.

When the situation requires heavier processing, such as in overloaded screens and in multitasking, human performance decreases significantly.

Attention allocation

To enable multitasking, the five to nine data items are allocated to both the tasks and the task management, implying that in the interaction, only three to seven data items can be manipulated simultaneously.

Effect of practice

With experience, the workload decreases because part of the data required for the processing is stored in the unlimited, long-term memory.

Mental workload issues are relevant to the search style dilemma (page xx). They imply that the visual search is best in routine operation and that interactive search may be better in non-routine procedures.

Related topic

Updated on 29 May 2016.