Usefulness of a familiarity signal during recognition depends on test format: Neurocognitive evidence for a core assumption of the CLS framework

Familiarity-based discrimination between studied target items and similar foils in yes/no recognition memory tests is relatively poor. According to the complementary learning systems (CLS) framework this is due do a relatively small difference in familiarity strength between these two item classes. The model, however, also predicts that when targets and corresponding similar foils are presented next to each other in a forced-choice corresponding (FCC) test format, familiarity values for targets and foils can be directly compared because in each trial, targets are reliably more familiar than their corresponding foils. In contrast, when forced-choice displays contain non-corresponding foils (FCNC) which are similar to other studied items (but not the target), familiarity should not be diagnostic because familiarity values are not directly comparable (as in yes/no-tasks). We compared ERP old/new effects (ERPs of targets vs. foils) when participants were tested with FCC vs. FCNC displays after having intentionally encoded pictures of objects. As predicted, the mid-frontal old/new effect which is associated with familiarity was significantly larger in FCC compared to FCNC displays. Moreover, the target-foil amplitude difference predicted the accuracy of the recognition judgment in a given trial. This is one of the very few studies which support the assumption of the CLS framework that the test format can influence the diagnosticity of familiarity. Moreover, it implies that the mid-frontal old/new effect does not reflect the mean difference in the familiarity signal itself between studied and non-studied items but reflects the task-adequate assessment of the familiarity signal.