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.

The ability to combine words into novel sentences has been used to argue that humans have symbolic language production abilities. Critiques of connectionist models of language often center on the inability of these models to generalize symbolically (Fodor & Pylyshyn, 1988; Marcus, 1998). To address these issues, a connectionist model of sentence production was developed. The model had variables (role-concept bindings) that were inspired by spatial representations (Landau & Jackendoff, 1993). In order to take advantage of these variables, a novel dual-pathway architecture with event semantics is proposed and shown to be better at symbolic generalization than several variants. This architecture has one pathway for mapping message content to words and a separate pathway that enforces sequencing constraints. Analysis of the model’s hidden units demonstrated that the model learned different types of information in each pathway, and that the model’s compositional behavior arose from the combination of these two pathways. The model’s ability to balance symbolic and statistical behavior in syntax acquisition and to model aphasic double dissociations provided independent support for the dual-pathway architecture.

We present the performances of thirteen aphasic patients on a picturenaming task, and attempt to model these data using computer simulations. We systematically manipulate the assumptions underlying several interactive, two-step, spreading-activation models, including the proposals of Dell, Schwartz, Martin, Saffran, and Gagnon (1997), Foygel and Dell (1999), and Rapp and Goldrick (in press). Using a numerical regression procedure and multiple views of each model's possible output, we find that peripheral pragmatic assumptions play a role equal to that of theoretically more central model components. None of the models we consider can account for all of the patients, leading us to conclude that one or more of the assumptions underlying each model is flawed. We argue that there are strong limitations on the conclusions that can legitimately be drawn from such simulation studies, but that close analysis of individual patients can allow sound testing of potentially more accurat...

Representations of linguistic information and the neural substrates that underlie them are incredibly complex. This chapter illustrates how connectionist modeling has furthered our understanding of normal and impaired processing in three related domains – semantic memory, knowledge of grammatical class, and word reading – and how the

In principle, a specific deficit in processing verbs relative to nouns might arise as a result of damage to any of several mechanisms involved in speech planning and lexical production. Here we describe a fluent aphasic patient HG who is much worse at retrieving verbs relative to nouns in picture naming and sentence generation, but who retains the ability to produce verbal morphology and even to generate novel verbs productively from nominal roots when she is unable to retrieve appropriate action words (e.g., looming for weaving). Moreover, the results of single-word and sentence comprehension tasks suggest that her ability to access lexical forms of verbs is sensitive to their thematic properties. When contrasted with patients who have specific deficits in processing morphosyntactic properties of verbs (Tsapkini, Jarema, & Kehayia, in press), HGs pattern of performance can be seen as evidence that grammatical properties are functionally distinct from other aspects of lexical representation. We discuss the implications of this dissociation, and of HGs performance specifically, in light of various models of lexical access. 3

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Neuropsychological studies have demonstrated that the production of nouns and verbs can be dissociated in aphasia. These reports have been taken as evidence for separate representations of nouns and verbs in the human brain. We used whole-head magnetoencephalography to record cortical dynamics of action and object naming in 10 healthy adults and in 1 anomic patient with superior naming of verbs compared with nouns due to a left posterior parietal lesion. A single set of 100 line drawings was used for both action and object naming. In normal subjects, the activation sequences in action and object naming were essentially identical, advancing from the occipital to posterior temporoparietal and further to the left frontal cortex, without consistent involvement of the classical left inferior frontal (Broca) and temporal (Wernicke) language areas. In the anomic patient, pronounced differences between action and object naming emerged in the left hemisphere. The activation sequence was disrupted at the level of the damaged parietal cortex and did not reach the left frontal cortex even in the relatively easier action naming. The more severely impaired object naming was associated with exceptionally strong and early activation of the left inferior frontal cortex (Broca) and subsequent pronounced activation of the left middle temporal cortex, silent in action naming. Verb and noun retrieval thus utilized a spatiotemporally similar neuronal network in healthy individuals. A clear dissociation in cortical correlates of verb and noun retrieval only became evident in our anomic patient, in whom damage to the language network has resulted in disproportionately worse performance in object than action naming.

Introduction 1 1.1. Two plans for a brain A central question in the study of cognition concerns the way conceptual information is represented and organized in the mind/brain. If we presuppose, as most experimental scientists do, that cognitive processes are computational processes, it becomes self-evident that the presumably enormous amount of information over which these processes operate must be structured in some way in order to be accessible and useful. Given these two minimal criteria (accessibility and usefulness), along with the straightforward assumption of computational efficiency, we can reject as doubtful a host of potential models of organization---e.g., Borges' Chinese encyclopedia, the Boston telephone directory, the Internet, etc. The task of the cognitive scientist is then to sort through the remaining options and divine which has in fact been preferred in the course of neural evolution. In practice, of course, this undertaking is informed as much by em

picture-word interference paradigm:

The idea that concepts are embodied by our motor and sensory systems is popular in current theorizing about cognition. Embodied cognition accounts come in di¤erent versions and are often contrasted with a purely symbolic amodal view of cognition. Simulation, or the hypothesis that concepts simulate the sensory and motor experience of real world encounters with instances of those concepts, has been prominent in psychology and cognitive neuroscience. Here, with a focus on spatial thought and language, I review some of the evidence cited in support of simulation versions of embodied cognition accounts. While these data are extremely interesting and many of the experiments are elegant, knowing how to best interpret the results is often far from clear. I point out that a quick acceptance of embodied accounts runs the danger of ignoring alternate hypotheses and not scrutinizing neuroscience data critically. I also review recent work from my lab that raises questions about the nature of sensory motor grounding in spatial