Rita Sloan Berndt

The quantitative analysis of agrammatic production: procedure and data.

Despite the long-standing interest in structural aspects of aphasic production, no method has emerged for the systematic analysis of aphasic speech. This paper attempts to address that need by outlining a procedure for the quantitative assessment of narrative speech which yields measures for both morphological and structural characteristics of aphasic production. In addition to complete instructions for carrying out this analysis, data for three groups of subjects are presented: agrammatic aphasics, aphasics who are similarly nonfluent but not clinically judged as agrammatic, and normal controls. While the agrammatics were distinguishable from the nonagrammatic patients on most measures, both nonfluent groups showed comparable reductions in the structural complexity of their propositional utterances. Other findings include indications from individual patient data that aspects of grammatical morphology may dissociate in agrammatism.

Retrieval of nouns and verbs in agrammatism and anomia

The ability of five agrammatic and five anomic aphasic patients to produce nouns and verbs was assessed in four tasks. Target words were form class unambiguous, frequency and length matched nouns and verbs, elicited as single words in picture naming and naming-to-definition tasks. The same unambiguous verbs were targets in an action description task. Narrative speech was obtained from each patient using a story elicitation procedure. Agrammatic aphasics produced significantly fewer verbs than nouns, relative to other groups, in all tasks. Anomic aphasics reliably produced more verbs than nouns in naming to definition. These results replicate previous findings for Italian-speaking patient groups, and for several individual cases. In addition, these results extend the relative verb deficit among agrammatic patients to connected speech tasks. Results are interpreted in light of current models of lexical and sentence production.

Working memory retention systems: A state of activated long-term memory

High temporal resolution event-related brain potential and electroencephalographic coherence studies of the neural substrate of short-term storage in working memory indicate that the sustained coactivation of both prefrontal cortex and the posterior cortical systems that participate in the initial perception and comprehension of the retained information are involved in its storage. These studies further show that short-term storage mechanisms involve an increase in neural synchrony between prefrontal cortex and posterior cortex and the enhanced activation of long-term memory representations of material held in short-term memory. This activation begins during the encoding/comprehension phase and evidently is prolonged into the retention phase by attentional drive from prefrontal cortex control systems. A parsimonious interpretation of these findings is that the long-term memory systems associated with the posterior cortical processors provide the necessary representational basis for working memory, with the property of short-term memory decay being primarily due to the posterior system. In this view, there is no reason to posit specialized neural systems whose functions are limited to those of short-term storage buffers. Prefrontal cortex provides the attentional pointer system for maintaining activation in the appropriate posterior processing systems. Short-term memory capacity and phenomena such as displacement of information in short-term memory are determined by limitations on the number of pointers that can be sustained by the prefrontal control systems.

Verb Retrieval in Aphasia. 1. Characterizing Single Word Impairments

The ability of aphasic patients to produce words from the grammatical classes of nouns and verbs was investigated in tasks that elicited these types of words in isolation. Eleven chronic aphasic patients produced nouns and verbs in picture naming, videotaped scene naming, sentence completion, naming from definition, and oral reading. Comprehension of the meanings of nouns and verbs was tested in word/picture and word/video scene matching, and appreciation of noun/verb grammatical class differences was tested with two metalinguistic tasks. Five patients demonstrated significantly more difficulty producing verbs than nouns, two patients were significantly more impaired producing nouns than verbs, and the remaining four patients showed no difference between the two classes. There was no improvement in verb production when naming actions presented on videotape, suggesting that selective verb impairments are not attributable to conceptual difficulty in identifying actions in static pictures. Selective noun impairments occurred in the context of severe anomia, as reported in previous studies. Selective verb impairments were demonstrated for both agrammatic and fluent (Wernicke) patients, indicating that such deficits are not necessarily associated with the nonfluent and morphologically impoverished production that is characteristic of agrammatism. There was no indication that single word comprehension was affected in these patients in a manner consonant with their production impairments. Results are interpreted in light of current models of lexical organization and processing.

A redefinition of the syndrome of Broca's aphasia: Implications for a neuropsychological model of language

A neuropsychological theory is offered to account for the syndrome of Brocas aphasia. A critical review of the literature, with emphasis on recent research, provides the basis for a redefinition of the syndrome that considerably broadens its classical description. The argument is advanced that the focus of neuropsychological explanation should be on theoretically separable psychological mechanisms that might be disrupted in relative isolation from other components in conditions of focal brain damage, rather than on isolated units of aphasic performance. The symptoms that characterize Brocas aphasia are explained as predictable behavioral manifestations of a central disruption of the syntactic parsing component of the language System, coupled with a (theoretically independent) articulatory deficit that affects only the speech output System. The neuroanatomical implications of this argument are considered within the framework of the classical “strong localizationist” hypothesis.

Semantic and syntactic processes in aphasia: a review of the literature.

Recent investigations of lexical and syntactic aspects of language comprehension in aphasia are reviewed. It is argued that these studies support theoretical assumptions concerning the functional independence of various components of normal language processing. Studies of the structure of the lexicon in aphasia provide support for componential theories of lexical semantics in that different types of features of meaning can be selectively disrupted under conditions of brain damage. Studies of sentence comprehension support the existence of a syntactic mechanism that is independent of lexically based heuristic strategies for assigning meaning. There is evidence that these independent elements of language are subserved by different portions of the dominant hemisphere of the brain. Focal brain damage can thus cause selective disruption of components, allowing the separation of elements that are highly integrated in the normal adult. Studies of aphasic language, therefore, provide a valuable source of constraints on theories of normal language processing.

Grammatical class and context effects in a case of pure anomia: Implications for models of language production

Abstract Numerous variables have been used in previous attempts to account for the performance of aphasic patients on naming tasks. These include lexical/semantic factors such as frequency, and contextual factors such as whether the target is produced as a single word or in a sentence. This paper reports the case of a pure anomic patient (HY) who was strongly affected by both lexical and contextual factors in his naming. Beyond a strong frequency effect, a marked grammatical class difference was noted. Verb production was far superior to noun production in single word naming. Production of nouns was highly facilitated by provision of a semantically relevant sentence frame. These two findings were related to current models of single word and sentence production; a functional locus for HYs naming deficit is proposed.

The Selective Impairment of Phonological Processing: A Case Study

A case study is reported of an aphasic patient with fluent speech and markedly superior comprehension of written vs. spoken words. Results of extensive testing supported the hypothesis that the patient suffers from a phonological processing deficit that affects performance in all tasks that require the generation of a phonological code. This selective deficit is interpreted as the underlying cause of diverse symptoms such as asyntactic comprehension of written sentences, the commission of spelling errors in writing, and the production of literal paraphasias and neologisms in spontaneous speech. Alternative possibilities for the classification of this patient are discussed.

Quantitative Analysis of Aphasic Sentence Production: Further Development and New Data

The narrative production of patients with Brocas aphasia and age-and education-matched control subjects was analyzed using the Quantitative Production Analysis (Saffran et al., 1989), a procedure designed to provide measures of morphological and structural characteristics of aphasic production. In addition to providing data for a larger number of subjects than in the original study, we provide data on interrater and test-retest reliability. The data were also submitted to factor and cluster analyses. Two factors characterized the data and the cluster analysis yielded four sets of patients who performed differently on these factors. In particular, there is evidence that agrammatic patients can differ in their production of free and bound grammatical morphemes, substantiating earlier claims in the literature.

Empirically derived probabilities for grapheme-to-phoneme correspondences in english

Prior probabilities of graphemes and conditional probabilities for their pronunciation as specific phonemes are given based on a corpus of 17,310 English words. Phonemes are as given in recent editions ofWebster’s New Collegiate Dictionary, with minor revisions; graphemes are defined as letters or letter clusters corresponding to single phonemes. Grapheme-phoneme probabilities were derived from a revised table of frequency of occurrence of phoneme-to-grapheme correspondences generated in a study of spelling regularities (P. R. Hanna, J. S. Hanna, Hodges, & Rudorf, 1966). This quantitative descriptive information provides an index of the strength of particular grapheme-phoneme associations in English. Suggestions are made for the utilization of these probabilities as estimates of spelling/sound predictability in reading research.