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Difficulty of Certain Sentence Constructions in Comprehension

Native speakers of a language find some sentences more difficult to understand than others. The sources of difficulty vary: some are lexical (e.g., the use of unknown words), some are due to the lack of contextual information (e.g., no shared knowledge), and some are due to structural complexity. Here we will focus on the difficulties caused by one kind of structural complexity, center embeddings. The defining property of these structures is that a clause X appears within another clause Y, with material from Y surrounding X, i.e., the configuration [Y ...X... ].