Tracking lexical consolidation with ERPs: Lexical and semantic-priming effects on N400 and LPC responses to newly-learned words

Abstract

a b s t r a c tNovel words can be recalled immediately and after little exposure, but require a post-learning consolidation period to show word-like behaviour such as lexical competition. This pattern is thought to reflect a qualitative shift from episodic to lexical representations. However, several studies have reported immediate effects of meaningful novel words on semantic processing, suggesting that integration of novel word meanings may not require consolidation. The current study synthesises and extends these findings by showing a dissociation between lexical and semantic effects on the electrophysiological (N400, LPC) response to novel words. The difference in N400 amplitude between novel and existing words (a lexical effect) decreased significantly after a 24-h consolidation period, providing novel support for the hypothesis that offline consolidation aids lexicalisation. In contrast, novel words preceded by semantically related primes elicited a more positive LPC response (a semantic-priming effect) both before and after consolidation, indicating that certain semantic effects can be observed even when words have not been fully lexicalised. We propose that novel meanings immediately start to contribute to semantic processing, but that the underlying neural processes may shift from strategic to more automatic with consolidation.

Perturbation of old knowledge precedes integration of new knowledge

“…Previous studies using a semantic relatedness judgment task reported a reduced negativity within N400 and/or LPC time window on new-meaning probes on the day of learning (Bakker et al, 2015; Mestres-Misse et al, 2007; Perfetti et al, 2005). Our contrasting result comes from a paradigm that minimized explicit meaning processing, raising the possibility that semantic priming effects in the previous studies could be attributed to their requirement for explicit meaning retrieval.…”

“…As N400 and LPC were the main focus, we examined specifically the mean amplitudes within 300–500 ms and 500–700 ms at the central midline cluster (i.e., Cz cluster), where meaning effects are robustly observed in word learning studies (Bakker et al, 2015; Batterink & Neville, 2011; Mestres-Misse et al, 2007). For each type of trained words and meaning probes, the mean amplitude within each time window for each participant was extracted using EP Toolkit (Dien, 2010).…”

“…In contrast to the N400, which is interpreted as reflecting automatic meaning processes, the LPC may reflect controlled lexico-semantic processing such as explicit meaning retrieval (Bakker, Takashima, van Hell, Janzen, & McQueen, 2015; Hill, Ott, & Weisbrod, 2005; Hill, Strube, Roesch-Ely, & Weisbrod, 2002; Zachau et al, 2014). Previous studies on novel word learning have shown N400 and/or LPC semantic priming between novel words and existing words on the day of learning in semantic relatedness judgment task (Bakker et al, 2015; Mestres-Misse, Rodriguez-Fornells, & Munte, 2007; Perfetti, Wlotko, & Hart, 2005). However, it remains unclear whether these semantic priming effects rely on explicit retrieval of novel word meanings required to perform the task and whether they would be observable when meaning retrieval is minimized in a task.…”

Language effects in second-language learners: A longitudinal electrophysiological study of spanish classroom learning

“…Several studies have suggested that new L1 words can be lexicalized very quickly after just a few learning encounters and that word-like N400 effects can be obtained from these items (e.g., Borovsky et al, 2010; Mestres-Missé et al, 2007). However, more recently Bakker et al (2015) have reported evidence that the nature of the ERP effects obtained immediately after learning are somewhat different from those where a longer period of consolidation (24 hours in their case) had taken place. Only after consolidation to new word ERPs show effects of lexicalization.…”

“…A parallel (and larger) literature has looked at ERP changes as a function word learning in general – i.e., without telling participants the newly learned items are in a new L2 and/or using items that plausibly could be new L1 words (e.g., Bakker et al, 2015; Borovsky et al, 2010; Borovsky et al, 2012; Mestres-Missé et al, 2007; Perfetti et al, 2005) . One prominent theme in this literature is whether there is a need for a consolidation period after new words are learned in terms of their incorporation into the lexical system.…”