This target article discusses the verbal working memory system used in sentence comprehension. We review the concept of working memory as a short-duration system in which small amounts of information are simultaneously stored and manipulated in the service of accomplishing a task. We summarize the argument that syntactic processing in sentence comprehension requires such a storage and computational system. We then ask whether the working memory system used in syntactic processing is the same as that used in verbally mediated tasks that involve conscious controlled processing. Evidence is brought to bear from various sources: the relationship between individual differences in working memory and individual differences in the efficiency of syntactic processing; the effect of concurrent verbal memory load on syntactic processing; and syntactic processing in patients with poor short-term memory, patients with poor working memory, and patients with aphasia. Experimental results from these normal subjects and patients with various brain lesions converge on the conclusion that there is a specialization in the verbal working memory system for assigning the syntactic structure of a sentence and using that structure in determining sentence meaning that is separate from the working memory system underlying the use of sentence meaning to accomplish other functions. We present a theory of the divisions of the verbal working memory system and suggestions regarding its neural basis.

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The context in which a word occurs could influence either the actual decoding of the word or a postrecognition judgment of the relatedness of word and context. In this research, we investigated the loci of contextual effects that occur in lexical priming, when prime and target words are related along different dimensions. Both lexical decision and naming tasks were used because previous research had suggested that they are differentially sensitive to postlexical processing. Semantic and associative priming occurred with both tasks. Other facilitative contextual effects, due to syntactic relations between words, backward associations, or changes in the proportion of related items, occurred only with the lexical decision task. The results indicate that only associative and semantic priming facilitate the decoding of a target; the other effects are postlexical. The results are related to the different demands of the naming and lexical decision tasks, and to current models of word recognition.A basic question in psycholinguistic research concerns the manner in which contextual information influences lexical processing. Does contextual information enter into the processes by which a word is recognized, or does it influence processes that occur after recognition is achieved? Some models (e.g., Marslen-Wilson & Tyler, 1980;Rumelhart, 1977) emphasize that the bottom-up analysis of a word is supplemented by nonlexical (i.e., syntactic, semantic, or pragmatic) information provided by the context, facilitating recognition. An alternate proposal (Forster, 1979; Gough, Alford, & HolleyWilcox, 1981) is that contextual information does not affect the identification of a word per se; rather, it influences post recognition comprehension processes involved in the integration of words into meaningful representations (e.g., propositions). According to Forster (I979), skilled word recognition is functionally autonomous because the bottom-up decoding of the input allows recognition to occur without contextual support.

In these studies, we examined predictions of the time-course model of word recognition (Seidenberg, 1985b;Seidenberg, Waters, Barnes, & Tanenhaus, 1984). The model suggests that effects of irregular spelling or pronunciation should be specific to more slowly recognized words, such as lower frequency items, as shown in previous studies and replicated here. The model also explains why effects of irregular pronunciation are more robust in naming than in lexical decisions: Only the effects in lexical decisions depend on subjects' response criteria. We show that these criteria are affected by the composition of the stimuli in an experiment (i.e., whether irregularly spelled words are present) and by pressure to respond quickly. In contrast to the dual-route model of word recognition, the time-course model accounts for these task differences without assuming that subjects strategically control access to phonology.Although reading does not logically require the use of phonological information, research dating at least from Huey (1908Huey ( /1968) has attempted to determine whether this information is utilized nonetheless. Much of this research has centered on whether recognition of visually presented words is "phonologically mediated." Some researchers (e.g., Coltheart, 1978;Gough, 1972;Rubenstein, Lewis, & Rubenstein, 1971) have suggested that recognition is based on phonological information derived on the basis of knowledge of how an alphabetic orthography represents sound (grapheme-phoneme correspondence rules). Other researchers (e.g., Baron, 1973;Bower, 1970;Kolers, 1970) have argued that readers recognize words on a visual basis, without reference to phonology. A reconciliation of these two views is provided by dual-route models of word recognition (e.g., Coltheart, Davelaar, Jonasson, & Besner, 1977;Meyer, Schvaneveldt, & Ruddy, 1974), in which words can be recognized either on the basis of visual information, or through the use of phonology. These two routes are thought to operate in parallel, with a race between the two processes determining whether phonological mediation occurs.The dual-route model is consistent with the finding that word recognition is not necessarily phonologically mediated. However, it is not necessary to assume the existence of two recognition processes operating in parallel in order to account for this finding. In several papers, we have developed a time-course model of word recognition (Seidenberg, 1985a(Seidenberg, , 1985bSeidenberg, Waters, Barnes, & Tanenhaus, 1984;Waters, Seidenberg, & Bruck, 1984), based on the work of Glushko (1979), Kay and Marcel (1981), McClelland and Rumelhart (1981), and others. Rather than postulating separate orthographic and phonological processes operating in parallel, as in the dual-route model, the time-course model emphasizes a single interactive process with differences in the availability of orthographic and phonological information over time.In the time-course model, recognition is initiated with the extraction of visual information from the input. ...

Positron emission tomography (PET) was used to determine regional cerebral blood flow (rCBF) as a function of the syntactic form and propositional density of sentences. rCBF increased in the left pars opercularis, part of Broca's area, when subjects processed syntactically more complex sentences. There were no differences in rCBF in the perisylvian association cortex traditionally associated with language processing when subjects made plausibility judgments about sentences with two propositions as compared to sentences with one proposition, but rCBF increased in infero-posterior brain regions. These results suggest that there is a specialization of neural tissue in Broca's area for constructing aspects of the syntactic form of sentences to determine sentence meaning. They also suggest that this specialization is separate from the brain systems that are involved in utilizing the meaning of a sentence that has been understood to accomplish a task.