The test battery included a test of resistance to interference in working memory. In this task, participants see four probe letters on the screen, followed by a screen displaying a target letter. They are then asked whether the target was among the four probes. On test trials, two of the four letters presented had appeared in the previous trial, providing interference with recall on the present trial. An overall accuracy of working memory score is computed by averaging the number of correct responses across all experimental trials.
Sternberg, S. (1969). The discovery of processing stages: Extensions of Donders’ method. Acta Psychologica, 3, 276-315.