Neural pattern similarity across concept exemplars predicts memory after a long delay.

The irregularities of the world ensure that each interaction we have with a concept is unique. In order to generalize across these unique encounters to form a high-level representation of a concept, we must draw on similarities between exemplars to form new conceptual knowledge that is maintained over a long time. Two neural similarity measures - pattern robustness and encoding-retrieval similarity - are particularly important for predicting memory outcomes. In this study, we used fMRI to measure activity patterns while people encoded and retrieved novel pairings between unfamiliar (Dutch) words and visually presented animal species. We address two underexplored questions: 1) whether neural similarity measures can predict memory outcomes, despite perceptual variability between presentations of a concept and 2) if pattern similarity measures can predict subsequent memory over a long delay (i.e., one month). Our findings indicate that pattern robustness during encoding in brain regions that include parietal and medial temporal areas is an important predictor of subsequent memory. In addition, we found significant encoding-retrieval similarity in the left ventrolateral prefrontal cortex after a month's delay. These findings demonstrate that pattern similarity is an important predictor of memory for novel word-animal pairings even when the concept includes multiple exemplars. Importantly, we show that established predictive relationships between pattern similarity and subsequent memory do not require visually identical stimuli (i.e., are not simply due to low-level visual overlap between stimulus presentations) and are maintained over a month.

What psychological process is reflected in the FN400 event-related potential component?

During many recognition contexts, old items elicit a more positive event-related potentials (ERPs) than new items at mid-frontal electrodes about 300-500ms. The psychological processes that are reflected in is ERP component (i.e., the FN400) has been vigorously debated. Some argue that the FN400 reflects familiarity, whereas others argue that it reflects conceptual implicit memory. Three experiments contrasted these two hypotheses by presenting pre-experimentally familiar (i.e., name-brand) products and novel, off-brand products. In addition, some of the off-brand products were conceptually primed by the name-brand product to determine how FN400 amplitude would be affected by conceptually primed, but novel, products. The results provided mixed support for both theoretical views, and it is integrated with a broader theoretical framework to characterize the psychological processes captured by the FN400.

Expertise Moderates Incidentally Learned Associations Between Words and Images.

Individuals with expertise in a domain of knowledge demonstrate superior learning for information in their area of expertise, relative to non-experts. In this study, we investigated whether expertise benefits extend to learning associations between words and images that are encountered incidentally. Sport-knowledge-experts and non-sports-experts encountered previously unknown faces through a basic perceptual task. The faces were incidentally presented as candidates for a position in a sports team (a focus of knowledge for only the sports-experts) or for a job in a business (a focus of knowledge for both the sports-experts and non-sports-experts). Participants later received a series of surprise memory tests that tested: ability to recognize each face as being old, the amount of information recalled about each face, and ability to select a correct face from equally familiar alternatives. Relative to non-sports-experts, participants with superior sports expertise were able to better recall the information associated with each face and could better select associated faces from similarly familiar options for the hypothetical prospective athletes. Hypothetical job candidates were recalled and selected at similar levels of performance in both groups. The groups were similarly familiar with the images (in a yes/no recognition memory test) when the faces were prospective athletes or job candidates. These findings suggest a specific effect of expertise on associative memory between words and images, but not for individual items, supporting a dissociation in how expertise modulates the human memory system for word-image pairings.

Event-related potentials indicate that fluency can be interpreted as familiarity.

Recent evidence suggests that fluency may be capable of supporting recognition independently of familiarity. This hypothesis was further tested in the present study. 29 participants encoded name-brand and off-brand products in an incidental task. Participants then judged whether the product was old or new during two tests with products from one category (i.e., only name-brand or only off-brand products) and a mixed test (where both name-brand and off-brand products were shown). The ERP data elicited by off-brand products varied as a function of test format. During the mixed test, off-brand products were correlated with a FN400 effect, whereas a fluency ERP (old ERPs were more negative than new at parietal electrodes 225-400ms) was observed during the other test. Importantly, no FN400 was detected during this test. The ERP results suggest that viewing the off-brand products during the mixed test produced a familiarity experience; however, fluency supported recognition when viewing off-brand products on the other test. The results are strong evidence that top-down processing of visual features during recognition interprets the information relative to the context. This process results in either fluency or, in other contexts, it is interpreted as familiarity as the Discrepancy-Attribution Hypothesis (Whittlesea and Williams, 2001a, 2001b) contends.