Abstract
Waugh & Norman's experiment (1965) is among the most influential studies in the field of cognitive psychology. Using a probe digit memory test, they proposed that the proportion of correctly remembered items, digits in this case, depends on the number of interfering items shown between the recall item and the signal, or probe, identifying the recall target. This indicates that interference alone accounts for forgetting in short-term memory. The following study aimed to replicate these results with greater statistical power as the original study used a small sample of 4 participants. In a second study, we used shorter lists to examine potential effects of the relative difficulty of the task. Both studies' results partially support Waugh & Norman's claim, as participants were more likely to recall a digit that was followed by fewer interfering items. Additionally, we observed an interaction involving presentation rate and interference, as participants performed best with a low amount of interfering items presented at 1 item per second. However, lists with a higher number of interfering items (7 and above) had similar correct recall proportion regardless of the presentation rate. These findings further support the prevalence of interference theory over the decay theory but also call for a closer look at the possible interaction between the two. Future studies should examine the latter as well as the possible effect of cognitive fatigue due to the difficulty of the task, underlining the importance of replication studies.