What does Daneman and Carpenter's reading span really measure?

Reading span was assessed in three conditions aiming at varying the processing demands of a reading task. In a Sentence Reading Condition, the participants read aloud lists of sentences and memorize the final word of each sentence as in the original task of Daneman and Carpenter. In two other conditions, each sentence was replaced either by a series of unrelated words (Word Reading Condition) or by a series of meaningless syllables (Syllable Reading Condition); in these two conditions, however, each series ended with the same test words as in the Sentence Reading Condition. There was no significant effect of the condition on the scores for reading span. It is concluded that the typically low scores on reading span are not so much due to the processing demands of the task as to the disruptive effects of the articulatory suppression which characterizes the original task.