Neural Mechanisms of Learning and Consolidation of Morphologically Derived Words in a Novel Language: Evidence From Hebrew Speakers.

We examined neural mechanisms associated with the learning of novel morphologically derived words in native Hebrew speakers within the Complementary Learning Systems (CLS) framework. Across four sessions, 28 participants were trained on an artificial language, which included two types of morphologically complex words: linear (root + suffix) with a salient structure, and non-linear (root interleaved with template), with a prominent derivational structure in participants' first language (L1). A third simple monomorphemic condition, which served as baseline, was also included. On the first and fourth sessions, training was followed by testing in an fMRI scanner. Our behavioural results showed decomposition of both types of complex words, with the linear structure more easily learned than the non-linear structure. Our fMRI results showed involvement of frontal areas, associated with decomposition, only for the non-linear condition, after just the first session. We also observed training-related increases in activation in temporal areas specifically for the non-linear condition, which was correlated with participants' L1 morphological awareness. These results demonstrate that morphological decomposition of derived words occurs in the very early stages of word learning, is influenced by L1 experience, and can facilitate word learning. However, in contrast to the CLS framework, we found no support for a shift from reliance on hippocampus to reliance on cortical areas in any of our conditions. Instead, our findings align more closely with recent theories showing a positive correlation between changes in hippocampus and cortical areas, suggesting that these representations co-exist and continue to interact with one another beyond initial learning.

Decomposition in early stages of learning novel morphologically derived words: The impact of linear vs. non-linear structure.

We examined whether morphological decomposition takes place in early stages of learning a novel language, and whether morphological structure (linear vs. non-linear) influences decomposition. Across four sessions, 41 native-Hebrew speakers learned morphologically derived words in a novel morpho-lexicon, with two complex conditions: linear and non-linear; and a third simple condition with monomorphemic words. Participants showed faster learning of trained words in the linear condition, and better generalization to untrained words for both complex conditions compared to the simple condition, with better performance for linear than non-linear morphology. Learning the root morpheme, which provides a concrete meaning, was better than learning template/suffix morphemes, which are more abstract. Overall, our results suggest that saliency of discrete units plays an important role in decomposition in early stages of learning derived words, even for speakers highly familiar with the non-linear structure in their L1.