Language Structure And Processing

Human language can be viewed as a code that links linguistic representations to aspects of meaning. The basic types of representations of language (or language levels) are simple words (the lexical level), words with internal structure (the morphological level), sentences, and discourse. The lexical level of language makes contact with the categorial structure of the world. Lexical items (simple words) designate concrete objects, abstract concepts, actions, properties, and logical connectives. The basic form of a simple lexical item consists of a phonological representation that specifies the segmental elements (phonemes) of the word and their organization into metrical structures (e.g., syllables). The form of a word can also be represented orthographically. Words are associated with syntactic categories (e.g., noun and verb). The morphological level of language allows the meaning associated with a simple lexical item to be used as a different syntactic category (e.g., noun formation with the suffix -tion allows the semantic values associated with a verb to be used as a noun, as in the word "destruction" derived from "destroy") and thus avoids the need for an enormous number of elementary lexical items in an individual's vocabulary. The sentential level of language makes use of the syntactic categories of lexical items to build hierarchically organized syntactic structures (e.g., noun phrase, verb phrase, and sentence) that define relationships between words relevant

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to the propositional content of a sentence. The propositional content of a sentence expresses aspects of meaning, such as thematic roles (who did what to whom), attribution of modification (which adjectives go with which nouns), the reference of pronouns, and other referentially dependent categories. Propositional meanings make assertions that can be entered into logical and planning processes and that can serve as a means for updating an individual's knowledge of the world. The discourse level of language includes information about the general topic under discussion, the focus of a speaker's attention, the novelty of the information in a given sentence, the temporal order of events, causation, and so on. Information conveyed by the discourse level of language also serves as a basis for updating an individual's knowledge of the world and for reasoning and planning action.

The forms of language and their associated meanings are activated in the usual tasks of language use—speaking, auditory comprehension, reading, and writing. There is wide agreement among linguists, psychologists, and computer scientists that these different forms are activated by different "components" of a "language processing system." Components of the cognitive processing system are devices that accept as input a certain type of representation and operate on these inputs to activate another type of representation, where at least one of these representations is part of the language code. For instance, a component of the language processing system might accept as input the semantic representation (meaning) activated by the presentation of a picture and produce as output a representation of the sound pattern of the word that corresponds to that meaning.

The operations of the components of the language processing system are obligatory and largely unconscious. The obligatory nature of language processing can be appreciated intuitively by considering that we are generally unable to inhibit the performance of many language processing tasks once the system is engaged by an appropriate, attended input. For instance, we must perceive a spoken word as a word, not just as a nonlinguistic percept. The unconscious nature of most of language processing can be appreciated by considering that when we listen to a lecture, converse with an interlocutor, read a novel, or engage in some other language processing task, we usually have the subjective impression that we are extracting another person's meaning and producing linguistic forms appropriate to our intentions without paying attention to the details of the sounds of words, sentence structure, etc.

In general, cognitive processes that are automatic and unconscious are thought to require relatively little allocation of mental resources. However, many experimental results indicate that language processing does require the allocation of attention and/or processing resources. The efficiency of each of the components of the language processing system is thought to be a function of the resources available to that component, up to the maximum level of resource utilization of which the component is capable. Components of the system are remarkably efficient. For instance, it has been estimated on the basis of many different psycholinguistic experimental techniques that spoken words are usually recognized less than 125msec after their onset (i.e., while they are still being uttered). Similarly, normal word production in speech requires searching through a mental word production "dictionary" of over 20,000 items, but it still occurs at the rate of about three words per second with an error rate of about one word misselected per 1 thousand and another one word mispronounced per 1 thousand. The efficiency of the language processing system as a whole reflects the efficiency of each of its components but also is achieved because of the massively parallel computational architecture of the system, in which many components of the system are simultaneously active.

Functional communication involving the language code occurs when people use these processors to undertake language-related tasks to accomplish specific goals—to inform others, to ask for information, to get things done, etc. The language code is remarkably powerful with respect to the semantic meanings it can encode and convey, and psycholin-guistic processors are astonishingly fast and accurate. The ability to use this code quickly and accurately is critical to human success, both as a species and as individuals.

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