Syntactic parsing and working memory: The effects of syntactic complexity, reading span, and concurrent load

Event-related brain potentials (ERPs) and behavioural measures (reaction times and errors) were used to study the potential effects of individual differences in verbal working memory capacity (low vs. high reading span) and a concurrent verbal working memory load (low vs. high load) on the processing of sentences with a local syntactic ambiguity in German. The sentences were disambiguated at the clause-final auxiliary to either a subject relative (SR) clause or to an object relative (OR) clause. The processing difficulty for the OR as compared to the SR clauses was reflected in worse off-line comprehension performance, particularly for low span readers. Moreover, ERPs time-locked to the disambiguating auxiliary showed an early posterior positivity between 200–350 ms for OR clauses as compared to SR clauses for high span readers. Low span readers, in contrast, showed a late frontal positivity between 500 and 800 ms. While the early positivity for high span readers was independent of the concurrent load, the late positivity varied as a function of concurrent load, being delayed in the high load condition. These results indicate that syntactic processes in language comprehension are related to individual differences in parsing strategies.