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An interactive 2-step theory of lexical retrieval was applied to the picture-naming error patterns of aphasic and nonaphasic speakers. The theory uses spreading activation in a lexical network to accomplish the mapping between the conceptual representation of an object and the phonological form of the word naming the object. A model developed from the theory was parameterized to fit normal error patterns. It was then "lesioned " by globally altering its connection weight, decay rates, or both to provide fits to the error patterns of 21 fluent aphasic patients. These fits were then used to derive predictions about the influence of syntactic categories on patient errors, the effect of phonology on semantic errors, error patterns after recovery, and patient performance on a single-word repetition task. The predictions were confirmed. It is argued that simple quantitative alterations to a normal processing model can explain much of the variety among patient patterns in naming. Difficulty in word retrieval is the most pervasive symptom of language breakdown in aphasia. As with other symptoms of brain damage, word retrieval is subject to graceful degradation (Marr, 1982; Rumelhart & McClelland, 1986): Unsuccessful attempts at retrieval generally resemble the target, either in

The patterns of semantic errors in speaking and writing are used to constrain claims about the structure of lexical access mechanisms in speech and written language production. It is argued that it is not necessary to postulate a modality-neutral level of lexical representation (lemma) that is intermediate between lexical-semantic representations and modality-specific lexical representations. A dual-stage access model is proposed in which the first stage involves the selection of semantically and syntactically specified, modality-specific lexical forms, and the second stage involves the selection of specific phonological (orthographic) content for the selected lexemes.

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Lexical access in object naming involves the activation of a set oflexical candidates, the selection of the appropriate (or target) item, and the phonological encoding of that item. Two views of lexical access in naming are compared. From one view, the 2-stage theory, phonological activation follows selection of the target item and is restricted to that item. From the other view, which is most explicit in activation-spreading theories, all activated lexical candidates are phonologically activated to some extent. A series of experiments is reported in which subjects performed acoustic lexical decision during object naming at different stimulus-onset asynchronies. The experiments show semantic activation of lexical candidates and phonological activation of the target item, but no phonological activation of other semantically activated items. This supports the 2-stage view. More-over, a mathematical model embodying the 2-stage view is fully compatible with the lexical deci-sion data obtained at different stimulus-onset asynchronies. One of a speaker's core skills is to lexicalize the concepts intended for expression. Lexicalization proceeds at a rate of two to three words per second in normal spontaneous speech, but doubling this rate is possible and not exceptional. The skill of

In 7 experiments the authors investigated the locus of word frequency effects in speech production. Experiment 1 demonstrated a frequency effect in picture naming that was robust over repetitions. Experiments 2, 3, and 7 excluded contributions from object identification and initiation of articulation. Experiments 4 and 5 investigated whether the effect arises in accessing the syntactic word (lemma) by using a grammatical gender decision task. Although a frequency effect was found, it dissipated under repeated access to a word's gender. Experiment 6 tested whether the robust frequency effect arises in accessing the phonological form (lexeme) by having Ss translate words that produced homophones. Low-frequent homophones behaved like high-frequent controls, inheriting the accessing speed of their high-frequent homophone twins. Because homophones share the lexeme, not the lemma, this suggests a lexeme-level origin of the robust effect. The word frequency effect in speech production was discovered by Oldfield and Wingfield (1965). In a picture-naming task, they found that pictures with low-frequency (LF) names (such as syringe) took longer to name than pictures with high-frequency (HF) names (such as basket). Wingfield (1968)

Current research in natural language generation is situated in a computational linguistics tradition that was founded several decades ago. We critically analyse some of the architectural assumptions underlying existing systems and point out some problems in the domains of text planning and lexicalization. Guided by the identification of major generation challenges viewed from the angles of knowledge-based systems and cognitive psychology, we sketch some new directions for future research.

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Most of us would like to believe that the different patterns of language breakdown observed in aphasic patients reflect the way that the human mind and brain are organized for language. However, because so much modern research on aphasia has been carried out in English, it is difficult to separate universal mechanisms from language-specific content. Crosslinguistic com-parisons permit us to disentangle these confounds, while we address one of the most important issues in cognitive neurobiology, the issue of behavioral and neural plasticity: How many different forms can the language processor take under a range of normal and abnormal conditions? We must have an answer to this question if we want to understand what the neural mechanisms responsible for language

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