11/41. Right hemisphere reading mechanisms in a global alexic patient.We investigated the implicit, or covert, reading ability of a global alexic patient (EA) to help determine the contribution of the right hemisphere to reading. Previous studies of alexic patients with left hemisphere damage have suggested that the ability to derive meaning from printed words that cannot be read out loud may reflect right hemisphere reading mechanisms. Other investigators have argued that residual left hemisphere abilities are sufficient to account for implicit reading and moreover do not require the postulation of a right hemisphere system that has no role in normal reading processes. However, few studies have assessed covert reading in patients with lesions as extensive as the one in EA, which affected left medial, inferior temporal-occipital cortex, hippocampus, splenium, and dorsal white matter. EA was presented with lexical decision, semantic categorization, phonemic categorization, and letter matching tasks. Although EA was unable to access phonology and could not overtly name words or letters, she was nevertheless capable of making lexical and semantic decisions at above chance levels, with an advantage for concrete versus abstract words. Her oral and written spelling were relatively intact, suggesting that orthographic knowledge is retained, although inaccessible through the visual modality. Based on her ability to access lexical and semantic information without contacting phonological representations, we propose that EA's implicit reading emerges from, and is supported, by the right hemisphere. Finally, we conclude that her spelling and writing abilities are supported by left hemisphere mechanisms.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
12/41. Actors but not scripts: the dissociation of people and events in retrograde amnesia.We describe our further investigations of the retrograde amnesia in a single case. R.F.R. became globally amnesic following an attack of herpes simplex encephalitis. He could generate and recognize superordinate level information about the vast majority of proper names including the names of people but he was very impaired at giving information about what had "happened" to these same individuals. He could also provide detailed information about family friends but he could not recall salient major personal episodes in which these same individuals had been involved. knowledge of people appears to be represented in a different way to that of events, even when a singular event has provided the main or only opportunity for learning about the individual.- - - - - - - - - - ranking = 3keywords = information (Clic here for more details about this article) |
13/41. Modality-specific naming deficit: cognitive and neural mechanisms implicated in naming to definition.We report the case of an anomic patient who had a significantly greater impairment in naming to definition than in picture naming. His difficulty did not depend on the number of semantic attributes (two vs. four) or type of information (visual vs. non-visual) carried in the definition. When asked to visualize the perceptual characteristics of the stimulus by means of drawing, his performance on the naming to definition task improved significantly. We first discuss this performance pattern in terms of the debate between the modality access deficit hypothesis and the multiple semantics position. The patient's more severe impairment in naming to definition suggests that his dissociation may be due to a more selective involvement of verbal semantics. In line with recent PET findings indicating that top-down semantic-to-visual sensory neural feedback improves the retrieval of semantic information in naming to definition tasks, we hypothesize that the patient's difficulty in retrieving the name was due to his inability to automatically activate this pathway. Picture drawing facilitated his naming because it activated the visual system directly (through the structure description level), implementing the retrieval of semantic information.- - - - - - - - - - ranking = 3keywords = information (Clic here for more details about this article) |
14/41. What does recovery from anomia tell us about the underlying impairment: the case of similar anomic patterns and different recovery.Although word-finding difficulties have been largely studied from a theoretical and a rehabilitation point of view, recovery mechanisms and especially the fact that patients with similar anomic patterns may exhibit different recovery, are still not fully understood. In the first part of the present study we investigated the word retrieval curve during therapy and the psycholinguistic variables affecting word-finding recovery patterns in three anomic subjects (PG, AH and TM). Despite the fact that all patients had similar anomia at baseline, they presented different recovery patterns during an identical therapy program. The progress during therapy and the number of sessions necessary to reach satisfactory improvement was similar in two patients (AH and TM), but differed in the third patient (PG), who needed more treatment sessions. Moreover, these two different patterns were affected by different psycholinguistic variables: words age of acquisition predicted improvement in AH and TM, whereas phonological neighbourhood predicted improvement in PG. Following the observation that phonological neighbourhood density affected the slower progress during therapy, in the second study we analysed whether this variable also predicts pseudo-word learning in healthy controls and in anomic subjects. Indeed, phonological neighbourhood predicted pseudo-word learning speed in controls and in some anomic patients. We suggest that the analysis of progress during therapy for anomia and the comparison of the variables affecting learning and recovery may provide information about the underlying nature of the anomic deficit that is not available through the simple assessment of performance.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
15/41. Levels of processing for visual stimuli in an "extinguished" field.Volpe et al. (nature 282, 722, 1979 [19]) described an experimental study of four patients with parietal tumours who were able to judge whether two simultaneous stimuli were identical or different, even when they were unable to name the stimulus contralateral to their brain injury. We report the case of another patient, E.M., in whom we have investigated this phenomenon further. E.M. had undergone a right temporal lobectomy to prevent recurrent seizures. She could correctly name photographs of objects presented in isolation to either the left or right visual field, at 150 msec exposure (although she was impaired for single objects on the left at 10 msec exposures). She was able to judge correctly whether two simultaneous objects on the left and right had the same or different names, even though she was often unable to name the object on the left. These judgements remained above chance when same-name pairs of stimuli showed the same object but seen from two different viewpoints, or even when they showed visually dissimilar exemplars of the same name category. This implies that the patient based her same-different judgements on categorical information about the pair of objects, even though she was often unable to name the contralateral object.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
16/41. Preservation of propositional speech in a pure anomic: the importance of an abstract vocabulary.We describe a detailed quantitative analysis of the propositional speech of a patient, FAV, who became severely anomic following a left occipito-temporal infarction. FAV showed a selective noun retrieval deficit in naming to confrontation and from verbal description. Nonetheless, his propositional speech was fluent and content-rich. To quantify this observation, three picture description-based tasks were designed to elicit spontaneous speech. These were pictures of professional occupations, real world scenes and stylised object scenes. FAV's performance was compared and contrasted with that of 5 age- and sex-matched control subjects on a number of variables including speech production rate, volume of output, pause frequency and duration, word frequency, word concreteness and diversity of vocabulary used. FAV's propositional speech fell within the range of normal control performance on the majority of measurements of quality, quantity and fluency. Only in the narrative tasks which relied more heavily upon a concrete vocabulary, did FAV become less voluble and resort to summarising the scenes in an manner. This dissociation between virtually intact propositional speech and a severe naming deficit represents the purest case of anomia currently on record. We attribute this dissociation in part to the preservation of his ability to retrieve his abstract word vocabulary. Our account demonstrates that poor performance on standard naming tasks may be indicative of only a narrowly defined word retrieval deficit. However, we also propose the existence of a feedback circuit which guides sentence construction by providing information regarding lexical availability.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
17/41. Mechanisms for accessing lexical representations for output: evidence from a category-specific semantic deficit.We report the performance of a neurologically impaired patient, JJ, whose oral reading of words exceeded his naming and comprehension performance for the same words--a pattern of performance that has been previously presented as evidence for "direct, nonsemantic, lexical" routes to output in reading. However, detailed analyses of JJ's reading and comprehension revealed two results that do not follow directly from the "direct route" hypothesis: (1) He accurately read aloud all orthophonologically regular words and just those irregular words for which he demonstrated some comprehension (as indicated by correct responses or within-category semantic errors in naming and comprehension tasks); and (2) his reading errors on words that were not comprehended at all (but were recognized as words) were phonologically plausible (e.g., soot read as "suit"). We account for these results by proposing that preserved sublexical mechanisms for converting print to sound, together with partially preserved semantic information, serve to mediate the activation of representations in the phonological output lexicon in the task of reading aloud. We present similar arguments for postulating an interaction between sublexical mechanisms and lexical output components of the spelling process.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
18/41. Dysnomia in dementia and in stroke patients: different underlying cognitive deficits.The performance of 11 Alzheimer's (DAT) and 8 anomic aphasic stroke patients is contrasted with that of 32 normal elderly subjects on both the boston Naming Test (BNT) and the Controlled Oral Word association Test (COW), a letter-category verbal-fluency test. While both tests require phonological processing, only the BNT requires semantic processing (object recognition). Both DAT and anomic aphasic stroke patients were significantly impaired on the BNT, with mean z scores (based on the performance of the normals) of -4.08 and -2.57, respectively; the DAT patients were significantly farther from normal than were the anomic aphasics. Their relative levels of impairment on the COW were reversed: The anomic aphasics' performance (z = 1.79) was worse than that of the DATs (z = -0.66). This pattern of performance on the two tests is consistent with the hypothesis that impaired word finding reflects impaired processing mainly of semantic information for the DAT subjects, mainly of lexical-phonological information for the anomic aphasic subjects.- - - - - - - - - - ranking = 2keywords = information (Clic here for more details about this article) |
19/41. Repetition and verbal STM in transcortical sensory aphasia: a case study.The repetition performance of a patient (S.T.) with transcortical sensory aphasia is examined in four experiments with particular emphasis on the STM capacities underlying her performance. S.T.'s repetition of word strings exceeding her span (two words) is characterized by good recall of the final items and a strong tendency to lose the initial items in the input string. This pattern contrasts with the serial position effects observed in a phonologically based STM impairment, and it is suggested that a lexical-semantic impairment, also evident in S.T.'s naming and lexical comprehension, contributes to her inability to retain the primacy portions of the input string. Lexical effects obtained in her reproduction of words and nonwords, as well as word strings (Experiments 1 and 2), indicate that under conditions of impaired semantics S.T. is relying on lexical phonological information to repeat. Priming by repeated exposure (Experiment 3) failed to improve her repetition performance, indicating that access to lexical information is brief and dependent on recent phonological input. In Experiment 4, the role of syntactic structure in S.T.'s sentence repetition was examined, and it was shown that syntactic structure affects the recall of order information, but not the number of items recalled. The repetition and verbal STM abilities of this patient, in light of her total language profile, are then evaluated in the context of a language-based view of verbal STM.- - - - - - - - - - ranking = 3keywords = information (Clic here for more details about this article) |
20/41. Unilateral visual neglect overcome by cues implicit in stimulus arrays.The case of a man with a right hemisphere lesion and with evidence of left-sided visuospatial neglect is reported. On a variety of verbal and nonverbal tasks his performance was significantly modified by information implicit in stimulus configurations. Neglect deficits were present on tests involving spatially distinct or meaningless stimulus arrays but almost absent when stimuli were continuous or meaningfully integrated.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
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