The Magical Mystery Four: How is Working Memory Capacity Limited, and Why?

Abstract

Working memory storage capacity is important because cognitive tasks can be completed only with sufficient ability to hold information as it is processed. The ability to repeat information depends on task demands but can be distinguished from a more constant, underlying mechanism: a central memory store limited to 3 to 5 meaningful items in young adults. I will discuss why this central limit is important, how it can be observed, how it differs among individuals, and why it may occur.

Figure 1

Illustration of the three-part method of Chen and Cowan (in press) using word lists, and the key result. The central capacity limit, which can be observed only if rehearsal is prevented, was about 3 chunks no matter whether these chunks were singletons or learned word pairs.

Figure 2

Illustration of the method of Cowan et al. (in press) using object arrays, and the key result. For simple materials, the capacity limit increased markedly from age 7 to adulthood, whereas the ability to focus on the relevant items and to ignore irrelevant ones stayed rather constant across that time.

Figure 3

Illustration of the method in the fifth and final experiment in Saults and Cowan (2007) using audiovisual arrays, and key results. When sensory memory was eliminated, capacity was about 4 items no matter whether these were all visual objects or were a mixture of visual and auditory items.