Electrophysiological correlates of the perceptual fluency effect on recognition memory in different fluency contexts

The present study used event-related potentials (ERPs) to investigate the contribution of perceptual fluency to recognition memory in different fluency contexts. In a recognition memory test with a modified remember-know paradigm, we employed conceptually impoverished items (kaleidoscope images) as stimuli and manipulated the perceptual fluency of recognition test cues through masked repetition priming. There were two fluency context conditions. In the random fluency context (RC) condition, primed and unprimed trials were randomly inter-mixed. In the blocked fluency context (BC) condition, primed and unprimed trials were grouped into blocks. Behavioral results showed that priming elevated the incidence of remember hits and the accuracy of remember judgements in the RC condition; no such effects were evident in the BC condition. In addition, priming effects on reaction times were found only for remember hit responses in the RC condition. The ERP results revealed an early100-200 ms effect related to masked repetition priming, which took the form of greater positivity for primed than unprimed trials. This effect was modulated neither by fluency context or response type. The present findings suggest that perceptual fluency induced by masked repetition priming affects recollection-related memory judgments in a specific fluency context and indicate that relative, rather absolute, fluency plays a critical role in influencing recognition memory judgments

What Makes an Image Memorable? Effects of Encoding on the Mechanism of Recognition

Memory is undoubtedly one of the most important processes of human cognition. A long line of research suggests that recognition relies on the assessment of two explicit memory phenomena: familiarity and recollection. Researchers who support the Dual Process Signal Detection (DPSD) model of recognition memory link the FN400 component (a negative ERP deflection peaking around 400 ms at frontal electrodes) with familiarity; however, it is currently unclear whether the FN400 reflects familiarity or implicit memory. Three event-related potentials (ERP) studies were conducted to determine whether implicit memory plays a role in setting up encoding strategies, and how these encoding strategies influence recognition. Experiment 1 consisted of two phases; an encoding/study phase and recognition/test phase. During the encoding phase, participants viewed pictures of common objects and later during a recognition test phase they made remembered/not-remembered judgments about previously seen (old) pictures and new pictures. ERP analysis of the encoding phase compared subsequently-remembered and subsequently-not-remembered stimuli and revealed marginally significant subsequent memory effects for the FN400 and LPC components. Because participants first saw the pictures during the encoding phase, the FN400 effect during this phase suggested that it was driven by conceptual fluency. Additionally, the fluency ERP (a positive ERP deflection during the time window ~200 - 400 ms) during the encoding phase significantly distinguished subsequently-remembered stimuli from subsequently-not-remembered stimuli, indicating that processing during encoding determined the stimuli to-be-remembered during the recognition test. During the recognition test, the FN400 component correlated with the behavioral indicators of recollection and appeared to benefit from repetition. Experiment 2 was similar to Experiment 1 except that participants saw meaningless novel stimuli (fractals). ERP results from recognition indicate that the FN400 effect did not capture repetition-based familiarity, however, the fluency ERP appeared to gain from the repetition of the stimuli. These results suggest that the FN400 potentials were driven by conceptual implicit memory during encoding, whereas during recognition, the behavioural indicators of recognition linked with the perceptual implicit memory, suggesting that explicit memory is not the only source of familiarity and the neural correlates of perceptual (fluency ERP) and conceptual (the FN400 component) implicit memory can influence decisions made by explicit memory. Experiment 3 manipulated perceptual fluency, conceptual fluency, and repetition-driven familiarity. Participants viewed primed and unprimed, blurred and clear images of common objects that were presented once, twice or three times. Based on recognition performance, ERPs were back-sorted into their corresponding conditions. Fluency and FN400 components correlated with the behavioral indicators of recognition. Additionally, a conceptual implicit priming effect was significant over anterior and right frontal electrodes and perceptual implicit priming was significant at the occipital electrodes. Conclusion: Collectively, the behavioural and ERP results add support the idea that the FN400 is “multiply determined” and may reflect familiarity (explicit memory driven) or conceptual fluency (implicit memory) depending on the task and stimulus, revealing that performance on recognition is not explicit memory driven. The Discrepancy Attribution Hypothesis may provide a better understanding of the heuristics of familiarity, however, further research is needed to better examine the processes that underlie recognition

Manipulating letter fluency for words alters electrophysiological correlates of recognition memory. Neuroimage 83, 849–861. doi: 10.1016/j.neuroimage.2013.07.039

The mechanisms that give rise to familiarity memory have received intense research interest. One current topic of debate concerns the extent to which familiarity is driven by the same fluency sources that give rise to certain implicit memory phenomena. Familiarity may be tied to conceptual fluency, given that familiarity and conceptual implicit memory can exhibit similar neurocognitive properties. However, familiarity can also be driven by perceptual factors, and its neural basis under these circumstances has received less attention. Here we recorded brain potentials during recognition testing using a procedure that has previously been shown to encourage a reliance on letter information when assessing familiarity for words. Studied and unstudied words were derived either from two separate letter pools or a single letter pool ("letter-segregated" and "normal" conditions, respectively) in a within-subjects contrast. As predicted, recognition accuracy was higher in the letter-segregated relative to the normal condition. Electrophysiological analyses revealed parietal old-new effects from 500-700 ms in both conditions. In addition, a topographically dissociable occipital old-new effect from 300-700 ms was present in the letter-segregated condition only. In a second experiment, we found that similar occipital brain potentials were associated with confident false recognition of words that shared letters with studied words but were not themselves studied. These findings indicate that familiarity is a multiply determined phenomenon, and that the stimulus dimensions on which familiarity is based can moderate its neural correlates. Conceptual and perceptual contributions to familiarity vary across testing circumstances, and both must be accounted for in theories of recognition memory and its neural basis