High feature overlap reveals the importance of anterior and medial temporal lobe structures for learning by means of fast mapping

Abstract

Contrary to traditional theories of declarative memory, it has recently been shown that novel, arbitrary associations can be rapidly and directly integrated into cortical memory networks by means of a learning procedure called fast mapping (FM), possibly bypassing time-consuming hippocampal-neocortical consolidation processes. In the typical FM paradigm, a picture of a previously unknown item is presented next to a picture of a previously known item and participants answer a question referring to an unfamiliar label. It is assumed that they thereby incidentally create associations between the unknown item and the label. However, contradictory findings have been reported and factors moderating rapid cortical integration through FM yet need to be identified. In the context of previous behavioral results showing rapid semantic integration through FM especially if the unknown and the known item shared many features, we propose that due to its computational mechanisms during the processing of complex and particularly highly similar objects, the perirhinal cortex might be especially qualified to support the rapid incorporation of these associations into cortical memory networks within the FM paradigm. We therefore expected that a high degree of feature overlap between the unknown and the known item would trigger strong engagement of the perirhinal cortex at encoding, which in turn might enhance rapid cortical integration of the novel picture-label associations. Within an fMRI experiment, we observed stronger activation for subsequent hits than misses during encoding in the perirhinal cortex and an associated anterior temporal network if the items shared many features than if they shared few features, indicating that the perirhinal cortex indeed contributes to the acquisition of novel associations by means of FM if feature overlap is high.

High feature overlap and incidental encoding drive rapid semantic integration in the fast mapping paradigm.

“…Moreover, rapid semantic integration in the FMHO condition was also found to be enhanced compared with an EE condition (Experiment 3) and compared with a condition in which no object discrimination was required at all (incidental encoding, IE; Experiments 3 and 4). This is in line with our assumption that stronger PrC involvement in the FMHO condition fosters rapid integration through FM, which is also further supported by recent fMRI evidence of our own lab (Zaiser et al, 2020), showing stronger PrC activation at encoding and greater PrC contribution to learning in an FMHO condition compared with an FMLO condition. This also corresponds to a study in 18- to 24-month-old children that showed better memory for novel words learned in a fast mapping paradigm when discrimination during learning was more ambiguous, that is, when the known item had been acquired only recently compared with when the known item was highly familiar (Kucker et al, 2020).…”

“…There is an ongoing debate about whether rapid integration of novel associations through fast mapping (FM) is possible as contradictory findings have been reported (see Cooper et al, 2018; and the corresponding commentaries). To resolve these contradictions, we set out to find factors moderating rapid cortical integration through FM from a neurofunctional perspective, suggesting that the functional and representational characteristics of the perirhinal cortex might be especially qualified to contribute to rapid semantic integration through FM (see Zaiser et al, 2019; Zaiser et al, 2020). This research is closely related to previous work by the authors on binding mechanisms in memory which might recruit a similar network (i.e., unitization; e.g., Bader et al, 2010; Bader et al, 2014) and the role of medial temporal lobe structures in semantic processing (e.g., Meyer et al, 2005; Meyer et al, 2010; Meyer et al, 2013).…”

“…1This does not necessarily mean that learning within the FM paradigm is always hippocampus-independent. It has been shown that the hippocampus contributes to learning through FM in healthy young adults (Atir-Sharon et al, 2015; Zaiser et al, 2020) or at least it cannot finally be excluded that it is involved (Merhav et al, 2015). We propose that in patients with severe and selective hippocampal lesions, it is valid to conclude that hippocampal processing cannot have contributed to FM encoding or retrieval.…”