Abstract: People can still have a feel of “I know that”, even though they cannot retrieve the target information. This phenomenon is known as FOK (feeling-of-knowing). Although almost all theories on FOK assume it to be a continuum of subjective feeling from weak to strong, recent neuroimaging studies implied ‘feeling-of-knowing’ (FOK) and ‘feeling-of-not-knowing’ (FOnK) might be sub-served by different cognitive and neural processes (Luo et al., 2002; Luo et al., 2003；Luo et al., 2004). This dual processes hypothesis challenges the traditional view on FOK and provided a new perspective for investigation.
In our previous study, we have examined the effects of level-of-processing (LOP) on FOK and FOnK respectively. The results showed that deep LOP promoted the predictive accuracy of FOK, but not that of FOnK. Moreover, deep LOP deteriorated the predictive accuracy of FOnK. In this study, we attempted to get double dissociation evidence for this dual processes hypothesis of FOK. We compared the predictive accuracy of FOK and FOnK when the cue items were low- or high-frequency words (Experiment 1) or when the materials were “word”-“word” pairs or “word”-“non-word” pairs (Experiment 2).

Method
Sixty paid volunteers participated in the study (30 in each experiment). In the Recall-Judgment-Recognition (RJR) procedure, participants first learned a list of cue-target pairs. They were then provided with the cue items one by one and were asked to retrieve the corresponding target items. If failed, they were asked to make a feeling-of-knowing judgment or a feeling-of-not-knowing (the cued-recall & FOK judgment stage). Finally, participants were given a criterion recognition test to examine if their metamemory prediction was accurate or not (the recognition stage). Based on the performance in the cued-recall & FOK judgment stage and the recognition stage, the items were sorting into five types: SC, PP, NP, PN, and NN:

cue-recall and FOK judgment
Successful cue-recall Failing cue-recall
positive judgment negative judgment
recognize Hint SC PP NP
error report PN NN

The predictive accuracy of FOK (PA-FOK) and that of FOnK (PA-FOnK) were estimated as follows:
PA-FOK ＝ PP / PP+PN
PA-FOnK ＝ NN / NN+NP
Results
The result of Experiment 1 showed, in low-frequency cue words condition, the accuracy of FOK tended to be higher than that of FOnK, whereas in the high-frequency cue words condition, the reverse tendency was observed. However, these differences did not achieve significant level. The result of Experiment 2 showed, in the “word”-“word” condition, the accuracy of FOK was significantly higher than that of FOnK, whereas in the “word”-“non-word” condition, the accuracy of FOK was significantly lower than that of FOnK. This observation showed the double dissociation of FOK and FOnK.
Conclusions
This study suggests that the FOK and FOnK can be doubly dissociated. Some variables can promote the predictive accuracy of FOK but deteriorate that of FOnK, whereas other variables can have the reverse effects: they promote FOnK but deteriorate FOK. Based on these evidences, together with previous neuroimaging studies, we suggested that FOK and FOnK are supported by distinct cognitive brain processes

Key words: feeling-of-knowing (FOK), feeling-of-not-knowing (FOnK), double dissociation