Delayed memory for complex visual stimuli does not benefit from distraction during encoding.

Abstract

When subjects are asked to remember stimuli (e.g., words) for an immediate memory test, they usually remember them better when the items are presented without interruption (simple span task), compared to a condition in which a distraction occurs between each item (complex span task). In a delayed memory test, this effect has been shown to be reversed: Memory performance is better after complex span tasks than after simple span tasks. This so-called McCabe effect has not been able to be replicated consistently in the past. Here we investigated five potential boundary conditions of the McCabe effect: (1) Type of Stimuli (doors vs. faces), (2) Type of distractor (pictures vs. math equations), (3) Expectation about task difficulty (mixed vs. blocked lists), (4) Set Size (small vs. large), and (5) Expectation about the LTM test (intentional vs. incidental encoding). Across four experiments, we never found a McCabe effect: delayed memory was either equal between simple, complex and slow span conditions, the order of performance across these conditions from the immediate task transferred to the delayed task (simple > slow > complex), or any benefits on delayed memory performance were equally well explained by the amount of free time in the retention interval (slow span). Our results indicate that the transfer of information from WM to LTM does not seem to be influenced by covert retrieval processes, but rather that a fixed proportion of information encoded into LTM is laid down as a more permanent trace.