Information similarity in working memory and the processing of syntactically complex sentences

An important syntactic property of natural languages is recursion. It allows the addition of an embedded clause into another clause. However, a sentence with double center-embedded relative clauses is very difficult to understand. This difficulty could reflect the restricted computing capacity involved in sentence processing. To check whether this restriction is related to the limitation of human working memory; we conducted two experiments where participants had to maintain words while processing double-embedded relative clauses. We manipulated a factor known as influencing working memory capacity:. the similarity between the maintained information and the processed words. For sentences with two embedding clauses, the memory load composed of similar words was less recalled than a memory load containing different words. This similarity effect was not significant when the sentence structure was easier to process. This result was replicated in a second experiment where the duration of the load retention was controlled. These results are consistent with the crucial role of working memory in processing syntactically complex sentences.