Claudio Luzzatti

Unilateral Neglect of Representational Space

Two patients showing left unilateral neglect were asked to describe imagined perspectives of familiar surroundings. Left-sided details were largely omitted in the descriptions. Some theoretical implications of the occurrence of unilateral neglect in representational space are briefly considered.

Brain and conscious representation of outside reality

Abstract Right brain-damaged patients with contralateral neglect proved unable to describe accurately the left half of recollected images. Analogical brain processes seem therefore to underlie these representations. It is suggested that the left half of the spatial framework of visual representations is impaired in these patients. The alternative explanation based on the unilateral involvement of a hypothetical scanning of inner images is criticized.

Verb–Noun Double Dissociation in Aphasic Lexical Impairments: The Role of Word Frequency and Imageability

Neurolinguistic studies have provided important evidence regarding the organization of lexical representations and the structure of underlying conceptual knowledge; in particular, it has been shown that the retrieval of verbs and nouns can be damaged selectively. Dissociated lexical damage is proof of an independent mental organization of lexical representations and/or of the underlying processes. The aim of the present study is to estimate the rate of dissociated impairments for nouns and verbs on a large sample of mild to moderate aphasic patients and to investigate the mechanisms underlying such phenomena. In addition, the authors wished to verify to what degree the impairment for nouns and verbs is related to a specific type of language disorder. A confrontation naming task for verbs and nouns was administered to 58 aphasic patients. The major lexical (word frequency and age of acquisition) and semantic variables (familiarity and imageability of the underlying concept) were considered for each noun and verb used in the task. Verbs were distinguished by major functional classes (transitive, intransitive, and ergative verbs). The data collected from this task were analyzed twice: (i) as a group study comparison of major aphasic subgroups and (ii) as a multiple single case study to evaluate the differences on the naming of verbs and nouns and the effect of the lexical semantic variables on each individual patient. The results confirm the existence of dissociated naming impairments of verbs and nouns. Selective impairment of verbs is more frequent (34%) than that of nouns (10%). In many cases, the dissociated pattern of naming impairment disappeared when the effect of the concomitant variables (word frequency and imageability) was removed, but in approximately one-fifth of the cases the noun or verb superiority was preserved. Noun superiority emerged in five of six agrammatic patients. Both the naming of verbs (n = 9) or of nouns (n = 6) could be impaired selectively in fluent aphasic patients. The results lend support to the hypothesis of an independent mental organization of nouns and verbs, but a substantial effect of imageability and word frequency suggests an interaction of the naming impairment with underlying lexical and semantic aspects.

A place for nouns and a place for verbs? A critical review of neurocognitive data on grammatical-class effects

It is generally held that noun processing is specifically sub-served by temporal areas, while the neural underpinnings of verb processing are located in the frontal lobe. However, this view is now challenged by a significant body of evidence accumulated over the years. Moreover, the results obtained so far on the neural implementation of noun and verb processing appear to be quite inconsistent. The present review briefly describes and critically re-considers the anatomo-correlative, neuroimaging, MEG, TMS and cortical stimulation studies on nouns and verbs with the aim of assessing the consistency of their results, particularly within techniques. The paper also addresses the question as to whether the inconsistency of the data could be due to the variety of the tasks used. However, it emerged that neither the different investigation techniques used nor the different cognitive tasks employed fully explain the variability of the data. In the final section we thus suggest that the main reason for the emergence of inconsistent data in this field is that the cerebral circuits underlying noun and verb processing are not spatially segregated, at least for the spatial resolution currently used in most neuroimaging studies.

LOSS OF MENTAL IMAGERY: A CASE STUDY

Abstract A case of loss of mental imagery following a vascular lesion of the left occipital lobe is described and discussed. The findings support a twofold (analogue and propositional) theory of neural representations of the external world. It is argued that sense-specific representations may be preserved in spite of the reported loss of imagery in the corresponding modality. the possibility that this disorder may reflect a functional disconnection between brain centres is discussed.

Does the hemisphere stimulated play a specific role in delayed recognition of complex abstract patterns? A tachistoscopic study.

Abstract Abstract visual patterns were projected tachistoscopically to the left and right striate cortex of 50 undergraduates. After a delay of 0, 5, 15, 30 and 60 sec the recognition of the target was checked without time constraints on a six-alternatives set. The result was that stimuli projected to the left striate area at a 15 sec retention interval were better recognized than those projected to the right, whereas the opposite was true when the stimuli were recognized at a 60 sec delay.

Nouns and verbs in the brain: grammatical class and task specific effects as revealed by fMRI.

The wide variety of techniques and tasks used to study the neural correlates of noun and verb processing has resulted in a body of inconsistent evidence. We performed a functional magnetic resonance imaging (fMRI) experiment to detect grammatical class effects that generalize across tasks. A total of 12 participants undertook a grammatical-class switching task (GCST), in which they were presented with a noun (or a verb) and were asked to retrieve the corresponding verb (or noun), and a classical picture naming task (PNT) widely used in the previous aphasiological and imaging literature. The GCST was explicitly designed to ensure control over confounding variables, such as stimulus complexity or imageability. Conjunction analyses of the haemodynamic responses measured in the two tasks indicated a shared verb-related activation of a dorsal premotor and posterior parietal network, pointing to a strong relationship between verb representation and action-oriented (visuo-)spatial knowledge. On the other hand, no brain area was consistently associated with nouns in both tasks. Moreover, there were task-dependent differences between noun and verb retrieval both at behavioural and at physiological level; the grammatical class that elicited the longest reaction times in both tasks (i.e., verbs in the PNT and nouns in the GCST) triggered a greater activation of the left inferior frontal gyrus. Therefore, we suggest that this area reflects a general increase in task demand rather than verb processing per se.

Morphological processing in Italian agrammatic speakers : Eight experiments in lexical morphology

Agrammatic speech production has often been characterized as amorphology. This study of two Italian agrammatic patients shows that, with respect to inflectional morphology of simple and derived nouns, the morphological features of gender and number are almost fully preserved for one patient (MG) and only mildly disturbed in the other patient (DR). Like inflection, the use of derivational suffixation as a means of word-building is only mildly disturbed in both patients. However, they show a severe disturbance with respect to inflectional morphology of lexical compounds, which requires syntactic analysis at the word level. Moreover, they are severely impaired in the choice of the function word for the construction of prepositional compounds, syntactically generated phrases which have the status of a word. Apart from such syntax-dependent morphological and word-building operations, neither inflectional nor derivational morphology are seriously disturbed in our patients. The apparent amorphology in their spontaneous speech can thus not be explained by a disorder of morphological representations in the lexicon system perse. In another study (De Bleser and Luzzatti, 1994) we were able to show that the patients had severe problems with the implementation of morphology in specific syntactic contexts, thus pointing to a problem in morphosyntactic rather than morpholexical processing as a factor contributing to agrammatic speech production.

Characteristics of Writing Disorders in Italian Dyslexic Children

Objective:This study characterizes the spelling impairment of Italian dyslexic children and evaluates the relationship between reading and spelling disorders. Background:Developmental spelling deficits are much less investigated than reading deficits. Based on the dual-model approach, studies of English-speaking subjects describe a surface and a phonological dysgraphia. In languages with shallow orthographies, there is evidence of surface and phonological dyslexia, but no data are available for dysgraphia. Methods:Eighteen dyslexic children were studied. Writing was investigated by means of a spelling test that included regular words with one-sound-to-one-letter correspondence, regular words requiring syllabic conversion rules, words with unpredictable transcription, and nonwords with one-sound-to-one-letter correspondence. The dyslexics’ spelling errors were compared with those of 30 age-matched proficient readers. Results:The dyslexic participants were very slow readers. Their errors were compatible with the hypothesis of a prevalent use of the sublexical reading procedure (i.e., surface dyslexia). They were also generally impaired with respect to the control children in all subsections of the spelling test. However, multivariate and single case analyses as well as qualitative analysis of errors indicated that their major problem was writing words with unpredictable transcription. This failure was consistent with the view of prevalent subword level processing in writing. Conclusion:The pattern of the spelling impairment mirrors the children’s reading impairment, with most children suffering from surface dysgraphia.

Morphological representation of compound nouns: A study on Italian aphasic patients

Abstract Two experiments are reported whereby naming tasks for compound and monomorphemic nouns were administered to Italian aphasics. The results suggest that patients who are unable to retrieve compound nouns may still be able to retain morphological knowledge about target compound nouns in absence of the ability to retrieve its phonological form. These findings confirm previous observations in German speaking aphasics: an identical result in Italian was not easily predictable, given the differences of the Italian compounding system. Another important result came from the performance of Brocas aphasics who are known, as a group, to have difficulty in naming actions. They tended to omit the verb component of noun compounds with a verb-noun structure. This finding provides a strong indication that compound words are parsed into their component parts in the course of lexical retrieval.