Grouping in Working Memory Guides Chunk Formation in Long-Term Memory: Evidence from the Hebb Effect

Abstract

The Hebb effect refers to the improvement in immediate memory performance on a repeated list compared to unrepeated lists. That is, participants create a long-term memory representation over repetitions, on which they can draw in working memory tests. These long-term memory representations are likely formed by chunk acquisition: The whole list becomes integrated into a single unified representation. Previous research suggests that the formation of such chunks is rather inflexible and only occurs when at least the beginning of the list repeats across trials. However, recent work has shown that repetition learning strongly depends on participants recognizing the repeated information. Hence, successful chunk formation may depend on the recognizability of the repeated part of a list, and not on its position in the list. Across six experiments, we compared these two alternatives. We tested immediate serial recall of eight-letter lists, some of which partially repeated across trials. We used different partial-repetition structures, such as repeating only the first half of a list, or only every second item. We manipulated the salience of the repeating structure by spatially grouping and coloring the lists according to the repetition structure. We found that chunk formation is more flexible than previously assumed: Participants learned contiguous repeated sequences regardless of their position within the list, as long as they were able to recognize the repeated structure. Even when the repeated sequence occurred at varying positions over repetitions, learning was preserved when the repeated sequence was made salient by the spatial grouping. These findings suggest that chunk formation requires recognition of which items constitute a repeating group, and demonstrate a close link between grouping of information in working memory, and chunk formation in long-term memory.

Is Repetition Learning Preserved in Old Age? Insights from the Hebb Paradigm

“…It follows that repetition learning in forward serial recall is driven by a mechanism not relying on pairwise associations. An attractive candidate learning mechanism that is consistent with our findings as well as with the previous literature is the acquisition of a chunk representing the entire list (Burgess & Hitch, 2006;Cumming et al, 2003;Fastame et al, 2005;Musfeld et al, 2024;Page & Norris, 2009). Our finding that substantial age difference in repetition learning emerge when participants have to strengthen pairwise associations implies that the process of chunk formation does not rely on first forming representations of pairwise associations in long-term memory before integrating them into a unified chunk representation.…”

“…According to the evidence presented above, successfully forming a chunk of a repeated list in the Hebb paradigm depends on consistent repetition of the whole list, with the exception that appending additional random items at the end does not interfere with chunk formation of the repeated part of the list preceding these items (Fastame et al, 2005;Mızrak & Oberauer, 2022). More recent evidence suggests that the process of chunk formation is more flexible, in that participants can form chunks of the repeated part of the list regardless of its position within the list, in case that the repeated part is presented as a contiguous sequence and that participants recognize which items constitute the repeating sequence (Musfeld et al, 2024).…”