An empirical test of the independence between declarative and procedural working memory in Oberauer's (2009) theory

It has recently been suggested that working memory could be conceived as two symmetrical subsystems with analogous structure and processing principles: a declarative working memory storing objects of thought available for cognitive operations, and a procedural working memory holding representations of what to do with these objects (Oberauer, Psychology of learning and motivation 51: 45-100, 2009). Within this theoretical framework, the two subsystems are thought to be independent and fueled by their own capacity. The present study tested this hypothesis through two experiments using a complex span task in which participants were asked to maintain consonants for further recall while performing response selection tasks. In line with Oberauer's conception, the load of the procedural working memory was varied by manipulating the number of stimulus-response mappings of the response selection task. Increasing the number of these mappings had a strong detrimental effect on recall performance. Besides contradicting Oberauer's proposal, this finding supports models that assume a resource-sharing between processing and storage in working memory.