Gabriele Miceli

On the Basis for the Agrammatic's Difficulty in Producing Main Verbs

Current theories of agrammatism do not provide a clear explanation for the co-occurrence of omission of grammatical markers and main verbs in this disorder. This study tested the hypothesis that the two symptom features have distinct underlying causes. Specifically, that the omission of main verbs in agrammatic speech is caused, at least in part, by a lexical (as opposed to a syntactic) deficit. Agrammatic and anomic aphasics and normal controls were given an object and action naming test. Agrammatic patients showed a marked impairment in naming actions in contrast to anomic aphasics and normal controls who named actions better than objects. The action naming impairment in agrammatic patients was interpreted as evidence for the lexical deficit hypothesis of verb omission in the speech of these patients and as a demonstration that agrammatism is a heterogeneous disorder that implicates damage to both lexical and syntactic mechanisms.

The structure of graphemic representations

The analysis of the spelling performance of a brain-damaged dysgraphic subject is reported. The subjects spelling performance was affected by various graphotactic factors, such as the distinction between consonant and vowel and graphosyllabic structure. For example, while the subject produced many consonant and vowel deletion errors when these were part of consonant and vowel clusters, respectively (e.g., sfondo----sondo; giunta----gunta), deletions were virtually never produced for single consonants flanked by two vowels (e.g., onesto----oesto) or for single vowels flanked by two consonants (e.g., tirare----trare). The demonstration that graphosyllabic factors affect spelling performance disconfirms the hypothesis that graphemic representations consist simply of linearly ordered sets of graphemes. It is concluded that graphemic representations are multidimensional structures: one dimension specifies the grapheme identities that comprise the spelling of a word; a second dimension specifies the consonant/vowel status of the graphemes; a third dimension represents the graphosyllabic structure of the grapheme string; and, a fourth dimension provides information about geminate features.

The Role of the Graphemic Buffer in Spelling: Evidence from a Case of Acquired Dysgraphia

Information processing models of spelling assume that an abstract graphemic representation of the to-be-written word must be generated at some point in the spelling process. This representation specifies the orthographic structure-the sequence of letters-that must be produced. How these graphemic representations are generated in the course of spelling is currently a much debated issue. One class of models assumes that the graphemic representations of familiar and novel words are generated by a single processing mechanism (e.g. Campbell, 1983). Another class of models assumes that the graphemic representations of familiar words are addressed directly in a graphemic lexicon whereas the graphemic representations for novel words (or nonwords) are computed through the application of a Phoneme-Grapheme Conversion Mechanism (e.g., Patterson, in press; Caramazza, Miceli, & Villa, 1986). However, independently of the class of model one adopts for the generation of graphemic representations, there is the issue of how these representations are processed further in the course of spelling. That is, we must specify the types of processes that transform an abstract graphemic representation into a form that is suitable for guiding motor output processes (see Margolin, 1984). Thus, we can consider the spelling process as consisting of two stages: First, those processes involved in the generation of a graphemic representation and, second, those processes involved in using the computed graphemic representation to generate the proper graphomotor processes for oral and written spelling.

Contrasting cases of Italian agrammatic aphasia without comprehension disorder

Two patients with agrammatic speech and unimpaired comprehension are presented and contrasted. Case 1 had an infarction involving precentral gyrus, subjacent white matter, and posterior and superior aspects of the insula, largely sparing Brocas area. His speech was slow and dysarthric, consisting of short disconnected phrases with some omission of lexical verbs. Case 2 had an unusual transient aphasia of acute onset without hemiplegia; speech rate, articulation, and sentence length and complexity appeared normal. Both patients tended to omit function words and finite verb inflections, but Case 2 did so much more than did Case 1. Neither patient showed impairment in any other area of language performance. Tentatively, Case 2 is described as being more morphologically impaired but less syntactically impaired than Case 1, while neither has damage to a central language processor.

Dissociation of inflectional and derivational morphology

A patient is described who makes morphological errors in spontaneous sentence production and in repetition of single words. The great majority of these errors were substitutions of inflectional affixes. The patient did make some derivational errors in repeating derived words but almost never made such errors for nonderived words. The inflectional errors for adjectives and nouns occurred mostly on the plural forms for nouns and adjectives and on the feminine form for adjectives. For verbs, inflectional errors were produced for all tense, aspect, and mood forms. There were no indications that these latter verb features constrained the form of inflectional errors produced. The results are interpreted as support for the thesis that morphological processes are located in the lexicon but that inflectional and derivational processes constitute autonomous subcomponents of the lexicon.

Variation in the Pattern of Omissions and Substitutions of Grammatical Morphemes in the Spontaneous Speech of So-Called Agrammatic Patients

We describe the patterns of omissions (and substitutions) of freestanding grammatical morphemes and the patterns of substitutions of bound grammatical morphemes in 20 so-called agrammatic patients. Extreme variation was observed in the patterns of omissions and substitutions of grammatical morphemes, both in terms of the distribution of errors for different grammatical morphemes as well as in terms of the distribution of omissions versus substitutions. Results are discussed in the context of current debates concerning the possibility of a theoretically motivated distinction between the clinical categories of agrammatism and paragrammatism and, more generally, concerning the theoretical usefulness of any clinical category. The conclusion is reached that the observed heterogeneity in the production of grammatical morphemes among putatively agrammatic patients renders the clinical category of agrammatism, and by extension all other clinical categories from the classical classification scheme (e.g., Brocas aphasia, Wernickes aphasia, and so forth) to more recent classificatory attempts (e.g., surface dyslexia, deep dysgraphia, and so forth), theoretically useless.

The dissociation of color from form and function knowledge

We report on two brain-damaged subjects who exhibit the uncommon pattern of loss of object color knowledge, but spared color perception and naming. The subject P.C.O., as in previously reported patients, is also impaired in processing other perceptual and functional properties of objects. I.O.C., in contrast, is the first subject on record to have impaired object color knowledge, but spared knowledge of object form, size and function. This pattern of performance is consistent with the view that semantic information about color and other perceptual properties of objects is grounded in modality-specific systems. Lesion analysis suggests that such grounding requires the integrity of the mesial temporal regions of the left hemisphere.

Neuropsychological correlates of localized cerebral lesions in non-aphasic brain-damaged patients

A neuropsychological test battery made up of verbal, visual-spatial, and intelligence tests was administered to 82 right and 67 on-aphasic left brain-damaged patients with localized cerebral lesions, in order to draw impairment profiles of the various subgroups. Separate analyses were undertaken on patients with unilobar and multilobar lesions. As for hemisphere effects, LH patients performed worse than RH subjects on verbal tests, while the reverse was true for visual-spatial tasks. As for lobe effects, patients with frontal lobe damage fared worse than other subgroups on word fluency, independent of the side of the lesion. RH patients with multilobar posterior lesions were significantly more impaired than other RH subgroups on the test of Copying Drawings with Landmarks, probably owing to the detrimental effect of unilateral spatial neglect on tasks requiring an accurate visual-spatial analysis.

Separable processing of consonants and vowels

There are two views about the nature of consonants and vowels. One view holds that they are categorically distinct objects that play a fundamental role in the construction of syllables in speech production. The other view is that they are convenient labels for distinguishing between peak (vowel) and non-peak (consonant) parts of a continuous stream of sound that varies in sonority (roughly the degree of openness of the vocal apparatus during speech), or that they are summary labels for bundles of feature segments. Taking the latter view, consonants and vowels do not have an independent status in language processing. Here we provide evidence for the possible categorical distinction between consonants and vowels in the brain. We report the performance of two Italian-speaking aphasics who show contrasting, selective difficulties in producing vowels and consonants. Their performance in producing individual consonants is independent of the sonority value and feature properties of the consonants. This pattern of results suggests that consonants and vowels are processed by distinct neural mechanisms, thereby providing evidence for their independent status in language production.

Reading Mechanisms and The Organisation of the Lexicon Evidence from Acquired Dyslexia

The study of patients with acquired reading disorders has contributed significantly to the formulation and development of models of the normal reading process (e.g., Coltheart, 1981; Patterson, 1981; Saffran, in press; Shallice, 1981; Martin & Caramazza, in press). Various forms of acquired dyslexia have been described providing a rich source of constraints on the structure and organisation of the lexicon and of the cognitive mechanisms implicated in the reading process. The explanation within a single, coherent framework of such diverse symptoms as the production of semantic (e.g., reading “table” as “chair”) or morphological (e.g., reading “walked” as “walking”) paralexias or the ability to read some types of words (e.g., nouns or regularly spelled words) but not other types (e.g., function words or irregularly spelled words), and so forth, severely reduces our options in formulating a model of normal reading which when appropriately lesioned produces the various symptoms and symptom complexes observed.