Item Strength Influences Source Confidence and Alters Source Memory zROC Slopes

Increasing the number of study trials creates a crossover pattern in source memory zROC slopes; that is, the slope is either below or above 1 depending on which source receives stronger learning. This pattern can be produced if additional learning affects memory processes such as the relative contribution of recollection and familiarity to source performance. However, the pattern can also be produced by decision processes if participants are more willing to make high-confidence source judgments when they are more confident that the test item was studied. We explored the role of memory and decision processes by comparing performance across 3 conditions: (a) words seen once with a male or female face (no repetition), (b) words seen once with a face after being presented twice with a picture of either a bird or a fish (different-source repetition), and (c) words seen 3 times with the same face (same-source repetition). zROC functions for the male-female decision showed that different-source repetition produced the same crossover effect as same-source repetition. This pattern was predicted by the decision process account, because it assumes that increasing item memory affects source confidence ratings even if source memory is not improved. Also supporting this account, we found a strong positive relationship between recognition confidence and source confidence even when analyses were limited to items that were attributed to the incorrect source or items that were not studied in either source.