Textbook of Usability

Cognitive Load Theory (CLT) was developed by John Sweller and colleagues beginning in the 1980s to explain how the demands on working memory affect learning and performance. It has become one of the most influential frameworks in instructional design and interface usability.

The theory distinguishes three types of cognitive load:

• Intrinsic load: arising from the inherent complexity of the material or task. A complex dose calculation is intrinsically loaded regardless of how it's presented.
• Extraneous load: imposed by the design of the interface or presentation rather than the task itself. Poor layouts, unclear terminology, and unnecessary clutter all add extraneous load.
• Germane load: cognitive effort devoted to building mental models and integrating new information with existing knowledge. Unlike extraneous load, germane load is productive — it contributes to learning.

The central design implication is that extraneous load should be minimised so that limited working memory capacity can be devoted to intrinsic and germane load. Every unnecessary element, inconsistency, or navigational detour consumes capacity that could otherwise support task performance.

CLT has produced a body of empirically validated effects: the split-attention effect, the redundancy effect, the modality effect, the expertise reversal effect, and others. These describe specific design patterns that increase or decrease cognitive load for specific user populations.