Capacity Limitations Principle

Overview: The principle of capacity limitations is a concept in cognitive science that states the design of graphics and displays should take account of the limited capacity people have in their working memory and attention to retain and process information. If a message contains excessive information that exceeds people’s capacity to retain and process, it would not to be understood. This principle is commonly used in psychology and other fields to understand and explain why people may struggle with certain tasks or activities. It is based on the idea that people’s abilities are not unlimited and there are limits to what they can do. For example, a person’s working memory has a small and limited capacity, making it difficult to remember a long list of items. Due to the nature of limited capacity in people’s working memory and attention, designs of graphics and displays should contain information that does not exceed the maximum capacity to retain and process. When failing to do so, people will experience cognitive overload and fail to understand the information.

Evidence: The human brain can only hold a limited amount of information at any given time. Graphical or other informational displays should not require the reader to hold more than 4 perceptual groups in mind at once (Kosslyn, 2006). Recent studies about the capacity of working memory have established the capacity at around 4 items (Goldstein, 2010). One experiment by Steven Luck and Edward Vogel (1997) measures the capacity of working memory by flashing two arrays of colored squares separated by a brief delay. The color of one square is changed on trails where the second array is different. The task given to participants was to determine whether the color of the square in the second array is different from the color in the first array. The result of this experiment demonstrates the participants’ performance as close to perfection when 1 to 3 squares are shown in the arrays. However, when there are 4 or more colored squares shown in the arrays, the performance of participants begins to decrease. The decline in participant performance continues as more squares are shown. From the result of this experiment, Luck and Vogel concluded that the short term memory is capable of retaining about 4 items at one time.

Examples Examples of cognitive overload taking place when the design of graphics and informational displays fails to follow The Principle of Capacity Limitations. • The Craigslist. • This image from the article 17 ways to prevent cognitive overload in your students • This image from www.ARNGREN.net

References: 1. Kosslyn, S. M. (2006). Graph design for the eye and mind. https://doi.org/10.1093/acprof:oso/9780195311846.001.0001 2. Luck, S. J., & Vogel, E. K. (1997). The capacity of visual working memory for features and conjunctions. Nature, 390(6657), 279–281. https://doi.org/10.1038/36846