Rita Capasso

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.

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.

The Treatment of Anomia Resulting from Output Lexical Damage: Analysis of Two Cases

This study describes a treatment project, carried out with two anomic subjects, RBO and GMA failed to name pictures correctly as a consequence of damage to phonological lexical forms; their ability to process word meaning was unimpaired. Words that were consistently comprehended correctly, but produced incorrectly by each subject, were identified. Some words were treated, whereas some served as the control set. A significant improvement was observed in both subjects. As predicted by the model of lexical-semantic processing used as the theoretical background for the study, improvement was restricted to treated items and did not generalize to untreated words, not even to words that were semantically related to those administered during treatment. Improvement was long-lasting, as shown by the fact that 17 months post-therapy GMAs performance on treated words was still significantly better than before treatment. These results are discussed in relation to the claim that cognitive models can be profitably used in the treatment of language disorders.

SELECTIVE DEFICIT FOR PEOPLE’S NAMES FOLLOWING LEFT TEMPORAL DAMAGE: AN IMPAIRMENT OF DOMAIN-SPECIFIC CONCEPTUAL KNOWLEDGE

As a consequence of a head trauma, APA presented with selective anomia for the names of familiar people, in the absence of comparable disorders for common names and other proper names. Face recognition was normal; and naming performance was unaffected by stimulus and response types. Selective proper name anomia was not due to effects of frequency of usage or of age of acquisition, or to selective memory/learning deficits for the names of people. Even though APA was able to provide at least some information on many celebrities whom she failed to name, she was clearly impaired in all tasks that required full conceptual information on the same people (but she performed flawlessly in similar tasks that involved common names). This pattern of performance indicates that in our subject the inability to name familiar persons results from damage to conceptual information. It is argued that detailed analyses of conceptual knowledge are necessary before it is concluded that a subject with proper name anomia suffers from a purely output disorder, as opposed to a conceptual disorder. The behaviour observed in APA is consistent with the domain-specific hypothesis of conceptual organisation (Caramazza & Shelton, 1998), and in this framework can be explained by assuming selective damage to knowledge of conspecifics. The anatomo-clinical correlates of our subjects disorder are discussed with reference to recent hypotheses on the neural structures representing knowledge of familiar people.

The Neural Correlates of Grammatical Gender: An fMRI Investigation

In an fMRI experiment, subjects saw a written noun and made three distinct decisions in separate sessions: Is its grammatical gender masculine or feminine (grammatical feature task)? Is it an animal or an artifact (semantic task)? Does it contain a /tch/ or a /k/ sound (phonological task)? Relative to the other experimental conditions, the grammatical feature task activated areas of the left middle and inferior frontal gyrus and of the left middle and inferior temporal gyrus. These activations fit in well with neuropsychological studies that document the correlation between left frontal lesions and damage to morphological processes in agrammatism, and the correlation between left temporal lesions and failure to access lexical representations in anomia. Taken together, these data suggest that grammatical gender is processed in a left fronto-temporal network. In addition, the observation that the grammatical feature task and the phonology task activated neighboring but distinct regions of the left frontal lobe provides a plausible neuroanatomical basis for the systematic occurrence of phonological errors in aphasic subjects with morphological deficits.

The interaction of lexical and sublexical processes in reading, writing and repetition

It has recently been proposed that in the course of repetition, reading aloud and writing to dictation, lexical representations are activated and selected for output by the joint operation of the semantic system and of sublexical conversion mechanisms--the Summation Hypothesis [Hillis and Caramazza, Brain Lang. 40, 106-144, 1991]. The hypothesis predicts that semantic errors in oral reading and in writing to dictation should only occur when both the semantic system and the sublexical component involved in that task (orthography to phonology and phonology to orthography conversion, respectively) are damaged. The performance of Italian patient E.C.A. indicates damage to the semantic system, and to sublexical phonology to phonology and phonology to orthography conversion mechanisms, but with substantial sparing of sublexical orthography to phonology conversion processes. In agreement with expectations derived from the Summation Hypothesis, E.C.A. produced semantic errors in repetition and in writing to dictation, but not in reading aloud. The paucity of semantic errors in speakers of languages with relatively transparent orthographies is discussed in the context of the Summation Hypothesis.

Spelling and dysgraphia.

Early cognitive models of spelling assumed that orthographic word representations are linear, ordered sequences of abstract letter identities (graphemes), activated only by word meaning information, and in some cases proposed that activating phonological information is a necessary stage of the spelling process. Over the past 20 years, studies on dysgraphia have shown that orthographic representations are autonomous from phonological representations and, just like the latter, are directly activated from semantics. The selection of an orthographic form for output relies on the convergence of activation from lexical-semantic information and from sublexical phoneme–grapheme conversion procedures. In addition, it is increasingly clear that orthographic representations are multidimensional objects that separately represent the graphosyllabic structure (or perhaps the nucleus/non-nucleus positions) of the target, and the identity, the CV status, and the quantity (doubling) of each grapheme. In spelling, the structure of orthographic knowledge and the mechanisms involved in processing serial order interact in complex ways and constrain performance accuracy. Further research is needed to clarify some critical issues: We need to specify in greater detail the mechanisms involved in the interaction between meaning and sublexical information; we must consider the possibility that orthographic representations have texture, in addition to structure; we must provide explicit hypotheses on the mechanisms that process orthographic knowledge; and we must gain a better understanding of the interaction between structure and serial order.

The Categorical Distinction of Vowel and Consonant Representations: Evidence from Dysgraphia

Subject GSI presents with a graphemic buffer deficit following a massive left fronto-parietal lesion. His errors involved essentially only consonants (98.2%). However, he always spelled correctly the first consonant in a string, and produced steadily increasing numbers of errors on the following consonants, while always spelling all the vowels in the target correctly. The pattern of performance observed in this subject provides strong evidence for the separate (categorical) representation of consonants and vowels, and suggests that working memory interacts with independent consonant and vowel representations in spelling.

Word-centred Neglect Dyslexia: Evidence from a New Case

Neglect dyslexia resulting from damage to word-centred representations is extremely rare. We report on a new case. A left-handed subject, SVE, presented with aphasia and neglect dyslexia/dysgraphia following a right hemisphere stroke. In tachistoscopic reading tasks, some of his errors resulted from retina-centred neglect, as he responded more accurately to words flashed in the left visual field than to words flashed in the right visual field. However, the critical aspects of his reading performance indicated word-centred neglect. SVE incorrectly produced the initial elements of four-letter words, regardless of stimulus location (to the left and to the right of fixation, or at fixation), and orientation (horizontal and vertical presentation). A similar distribution of errors was demonstrated in writing (very inaccurate performance on initial letters). This pattern of performance suggests damage to an letter string representation defined by spatial coordinates, rather than to an ordering mechanism. It is most naturally accommodated by models of word recognition which assume a word-centred level of representation, and cannot be explained by models which do not include such a representational level. Consideration of our subject in the light of other similar reports prompts hypotheses on the neural mechanisms involved in computing word-centred representations.

Interactivity and continuity in normal and aphasic language production.

Current research in cognitive modelling has assumed that the interactive nature of processing during language production has been supported by fits to the behaviour of brain-damaged patients. In this paper, several previously proposed theories of word production, all based on the interactive spreading-activation theory of Dell (1986), are evaluated in the context of picture naming. Using a new corpus of data from 50 Italian aphasic patients, we find that patient patterns do not seem to demand an interactive theory. We also explore the corollary ideas of continuity between normal and random performance, and global damage in aphasia, and we find that they are incompatible with our data. We argue that it is very difficult for a modelling study to yield strong constraints on cognitive theory. Although valuable, such efforts currently do not contribute evidence for interactive processing in language production.