| dc.description.abstract | Pattern separation refers to the process by which individuals form and retrieve distinct memory representations that differentiate similar events. Previous behavioral studies mainly used the Mnemonic Similarity Task (MST) to explore the underlying mechanism of pattern separation. These MSTs typically involve perceptually high similarity but slightly different objects or pictures as stimuli in a recognition memory task, requiring participants to distinguish between previously learned items, referred to as targets, and perceptually similar but novel items, called lures. The performance in this discrimination task is taken as an indicator of pattern separation during memory retrieval.
In this study, Kirwan & Stark′s (2007) object-based recognition memory test was adopted by using similar object images as stimuli for the Perceptual MST. Additionally, we modified the false memory test from Cheng and Rugg (2004), in which semantically related word pairs were used as stimuli for the Conceptual MST. The goal was to investigate whether pattern separation during the retrieval of perceptual versus conceptual memory representations involves shared or distinct mechanisms. In the Perceptual MST, participants were asked to differentiate different images of the same object, meaning the lures and the corresponding old items were conceptually identical yet with only subtle perceptual differences serving as the basis for discrimination. In contrast, the Conceptual MST required participants to distinguish between semantically related word pairs, where the lures and the corresponding old items were perceptually identical but dissimilar in their conceptual composition.
Experiment 1 examined the correlation between perceptual and conceptual pattern separation performance by applying Perceptual MST and Conceptual MST tasks. It also assessed the relationship between pattern separation performance and working memory capacity, using Operation Span Task, Corsi Block-Tapping Task, and Letter-Number Sequncing Task from the Wechsler Memory Scale as indicators of verbal and non-verbal working memory capacity. Pearson correlation analysis revealed a significant, yet weak positive correlation (r = .282) between the pattern separation indices of Perceptual MST and Conceptual MST when the variance in general old/new recognition memory performance were controlled. This suggests that whilst perceptual and conceptual pattern separation involve certain shared mechanisms, each still relies on its distinct processes. Further analyses showed that only conceptual pattern separation performance was significantly correlated with the working memory measures from the Wechsler tests, particularly with Letter-Number Sequncing Task. This result suggests the ability to classify and rearrange varied types of information plays a role in distinguishing conceptually similar items.
Experiment 2 investigated whether pattern separation in perceptual and conceptual memory tasks is mediated by familiarity and recollection processes, using event-related potentials (ERPs) during recognition memory, including the mid-frontal old/new effect and the left parietal old/new effect. ERP amplitude analysis of the Perceptual MST revealed that lures mistakenly recognized as having appeared during the learning phase elicited a larger left parietal old/new effect compared to lures correctly identified as similar but different. This finding suggests that in perceptual memory discrimination, individuals can easily retrieve distinctive memory representations through recollection, leading to the correct rejection of lures. No similar results were observed in the Conceptual MST, indicating that the recollection processes involved in perceptual and conceptual pattern separation may differ.
In summary, the results from both experiments suggest that pattern separation relies on overlapping mechanisms when processing perceptual and conceptual similarity representations. However, these mechanisms differ in their dependence on working memory and exhibit distinct neural activity during memory retrieval. These findings highlight domain-specific characteristics in the operation of pattern separation. | en_US |