Distinct neural processes for memorizing form and meaning within sentences

Roberto Zamparelli, Matteo Mascelloni, Jutta Mueller, Francesco Vespignani, Thomas Gruber

Abstract:

In order to memorize sentences we use both processes of language comprehension
during encoding and processes of language production during maintenance. While
the former processes are easily testable via controlled presentation of the input,
the latter are more difficult to assess directly as language production is typically
initiated and controlled internally. In the present event-related potential (ERP) study
we track subvocal rehearsal of sentences, with the goal of studying the concomitant
planning processes with the help of a silent cued-production task. Native German
participants read different types of sentences word-by-word, then were prompted by
a visual cue to silently repeat each individual word, in a rehearsal phase. In order
to assess both local and global effects of sentence planning, we presented correct
sentences, syntactically or semantically violated sentences, or random word order
sequences. Semantic violations during reading elicited an N400 effect at the noun
violating the selectional restrictions of the preceding verb. Syntactic violations, induced
by a gender incongruency between determiner and noun, led to a P600 effect at the
same position. Different ERP patterns occurred during the silent production phase.
Here, semantically violated sentences elicited an early fronto-central negativity at the
verb, while syntactically violated sentences elicited a late right-frontal positivity at
the determiner. Random word order was accompanied by long-lasting slow waves
during the production phase. The findings are consistent with models of hierarchical
sentence planning and further indicate that the ongoing working memory processes are
qualitatively distinct from comprehension mechanisms and neurophysiologically specific
for syntactic and lexical-semantic level planning. In conclusion, active working memory
maintenance of sentences is likely to comprise specific stages of sentence production
that are indicated by ERP correlates of syntactic and semantic planning at the phrasal
and clausal level respectively.