Language comprehension

Sentence processing takes place whenever a reader or listener processes a language utterance, either in isolation or in the context of a conversation or a text.

Many studies of the human language comprehension process have focused on reading of single utterances (sentences) without context. Extensive research has shown, however, that language comprehension is affected also by context preceding a given utterance, as well as many other factors.

Sentence comprehension has to deal with ambiguity in spoken and written utterances, for example lexical, structural, and semantic ambiguities. Ambiguity is ubiquitous, but people usually resolve it so effortlessly that they do not even notice it. For example, the sentence Time flies like an arrow has (at least) the interpretations Time moves as quickly as an arrow, A special kind of fly, called time fly, likes arrows and Measure the speed of flies like you would measure the speed of an arrow. Usually, readers will be aware of only the first interpretation.

Instances of ambiguity can be classified as local or global ambiguities. A sentence is globally ambiguous if it has two distinct interpretations. Examples are sentences like Someone shot the servant of the actress who was on the balcony (was it the servant or the actress who was on the balcony?) or The cop chased the criminal with a fast car (did the cop or the criminal have a fast car?). Comprehenders may have a preferential interpretation for either of these cases, but syntactically and semantically, neither of the possible interpretations can be ruled out.

Local ambiguities persist only for a short amount of time as an utterance is heard or written and are resolved during the course of the utterance so the complete utterance has only one interpretation. Examples include sentences like The critic wrote the book was enlightening, which is ambiguous when The critic wrote the book has been encountered, but was enlightening remains to be processed. Then, the sentence could end, stating that the critic is the author of the book, or it could go on to clarify that the critic wrote something about a book. The ambiguity ends at was enlightening, which determines that the second alternative is correct.

When readers process a local ambiguity, they settle on one of the possible interpretations immediately without waiting to hear or read more words that might help decide which interpretation is correct (the behaviour is called incremental processing). If readers are surprised by the turn the sentence really takes, processing is slowed and is visible for example in reading times. Locally-ambiguous sentences have, therefore, been used as test cases to investigate the influence of a number of different factors on human sentence processing. If a factor helps readers to avoid difficulty, it is clear that the factor plays a factor in sentence processing.

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