Does retrieval require effort? Effects of memory strength on pupil dilation

The current study investigates the relation between retrieval effort and the relative memory strength of mentally stored information. A previous pupillary study by Magliero (1983) showed that encoding effort reacts to the recency effect but no studies have linked effort as measured by pupillary dilation to the frequency effect. In the current study, phasic pupil dilation of 15 participants was measured and analyzed during retrieval tasks while they were learning topographical facts. The facts were studied once and tested during four repetitions in one of two repetition-interval conditions. We hypothesized that retrieval effort will decrease as the relative strength of a memory trace increases. This hypothesis accounts for recency effects as well as for frequency effects. Analysis of the phasic pupil response in the experiment shows a significant main effect for the repetition interval condition. Furthermore an interaction effect between the number of repetitions and repetition interval was found, indicating that the difference in effort between short and long repetition intervals decreased as the number of rehearsals increased. These findings largely confirm our hypotheses and the assumptions of theories that assume that increased retrieval effort increases learning gains.