Parallelism and Competition in Syntactic Ambiguity Resolution

A central issue in sentence-processing research is whether the parser entertains multiple analyses of syntactically ambiguous input in parallel, and whether these analyses compete for selection. In this article, we review theoretical positions for and against such competitive parallelism. We then review empirical evidence, primarily drawing on reading time studies, bearing on the prediction made by parallel competitive models that some cost ought to be associated with processing syntactically ambiguous material. We argue that this prediction is not confirmed by the data, and we discuss recent claims that the models in question do not actually make this prediction. We also emphasize the contrast with lexical ambiguity, where there is clearly a processing cost associated with competition between alternate meanings. Finally, we review a different kind of recent evidence suggesting that two syntactic analyses may indeed coexist under specific circumstances. The question of how readers and listeners resolve ambiguities of the sort found in (1)–(3) has been a central topic for psycholinguistic research for the last three decades, because of the light it can shed on how people recognize words and put them together into sentence meanings. (1) The specialist examined the organ very carefully. (2) Someone shot the servant of the actress who was on the balcony. (3) While the men hunted the deer ran through the woods. Sentence (1) contains a lexical ambiguity: organ has two unrelated meanings. In sentence (2), the relative clause who was on the balcony could be interpreted as modifying either servant or actress. Speakers of English tend to prefer the analysis on which the relative clause modifies the most recent noun (in this case, actress), but this preference is not universal across speakers or across individual sentences (Corley 1995; Gilboy et al. 1995). The syntactic ambiguity in sentence (3) is only temporary: at the point of reading the deer, this noun phrase could be either the object of the first clause (i.e. the thing that the men hunted) or the subject of the second clause. There is very clear evidence that readers and listeners initially