The Relation Between Memory Speed and Capacity: A Domain-General Law of Human Cognition?

This study tests an important and appealing hypothesis that has been around in the fields of cognitive psychology and neuroscience for over 40 years, but that lacks a conclusive empirical test. According to this hypothesis, there is a direct relationship between speed and capacity in working memory. Working memory refers to the ability to retain a small amount of information in a highly accessible state for a short period of time. Across different fields, it has been proposed that the limited capacity of working memory can be understood in terms of time instead of space, such that the amount of information that can be actively maintained corresponds to the amount of information through which one can cycle in a constant and relatively short time-window. Here, we present a study that explicitly and directly tests the speed-capacity hypothesis. In particular, we test (1) the speed-capacity hypothesis in verbal working memory, (2) the speed-capacity hypothesis in visuospatial working memory, and most importantly, (3) whether the same speed-capacity relation holds across verbal and visuospatial working memory, reflecting a domain-general, time-based law of human working memory capacity and, as such, of the complexity of human thought. Overall, our results do not provide any evidence for the existence of a domain-general law. However, unexpected findings related to measuring memory speed (i.e., high prevalence of negative search slopes in the Sternberg task) prevent us from drawing firm conclusions.