Sentence processing is a branch of psycholinguistics that studies how the mind understands relationships among words in a sentence and derives meaning from utterances. Approaches to sentence processing differ based on their understanding of the role of general cognitive functions, as opposed to specialized linguistic functions, in using language. They may also vary in whether their primary concern is with syntax or with the broader context of a sentence.
A large source of controversy in the field of psycholinguistics is the debate over to what extent various aspects of cognition are involved in language use. Some linguists go so far as to postulate a "black box" in the mind that is responsible for all linguistic knowledge and skills, separate from any other type of thinking. Others, such as proponents of cognitive semantics, see language as more closely related to general cognitive functions, especially memory.
In the area of sentence processing in particular, researchers tend to be divided between these two camps. Some will tend to focus on extralinguistic properties of cognition, such as verbal working memory, to explain sentence processing. These researchers may also deal with factors external to the mind altogether. They may, for instance, theorize that the difficulty of understanding a sentence corresponds to how similar the sentence is in syntax or content to other sentences that the person has previously encountered.
Natural language theorists, on the other hand, believe that there are particular areas of the brain specifically devoted to understanding the syntax of sentences that the hearer has never encountered before. Much of the research in sentence processing done by these theorists involves studying how the mind makes adjustments while reading a sentence to make sense out of its syntactic and semantic content, especially if there is some sort of ambiguity. According to this theory, sentence processing is not likely to be directly tied to memories of deciphering similar sentences in the past, but it will draw on the mind's innate ability to understand syntax.
One influential theory in natural language is known as minimal processing, which states that the mind automatically assumes that the sentence will follow the simplest structure possible until something in the sentence proves otherwise. For example, the two sentences "I saw the elephant" and "I saw the elephant was dancing" begin in the same way. The first sentence follows a very basic subject-verb-direct object structure, but the second uses a clause in place of a direct object. A person reading or hearing the second sentence would assume that it follows the simpler pattern until coming to the phrase "was dancing," which would cause him or her to evaluate the sentence structure. This person would not, however, encounter the first sentence and assume that it would have a separate clause as its direct object because such a structure is more complex.
A different but related theory, the theory of late closure, states that rather than assuming a simple structure to begin with, the mind does not make any assumptions about the syntax of the sentence until after the whole sentence has been read. Given the example sentences above, for example, this theory postulates that the reader would not come to any conclusions about whether "the elephant" is a direct object or anything else until the end of the sentence. This would eliminate the need to re-evaluate the sentence midway through.