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PubMed2002

Preserved semantic learning in an amnesic patient.

A case study is reported of an amnesic patient (KN), who displayed an ability to learn a substantial body of new visual and verbal semantic concepts, despite having a severe deficit in episodic memory. In two experiments, using an errorless learning paradigm, he was able to perform at a level close to that of his wife, who served as a control subject. When recall of material was retested after a delay of several months, during which time there were no further learning sessions, his retention was at least as good as, if not better, than that of his wife. This is taken as further evidence for the dissociation of semantic and episodic processes in amnesia. It also provides further evidence for the role of "errorless learning" in efficient acquisition of new facts in amnesia.

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PubMed1997

Dissociations between reading responses and semantic priming effects in a dyslexic patient.

We report a patient (Y.Y.) with senile dementia of the Alzheimer's type. The patient read aloud some words composed of two or three kanji characters with errors applying typical pronunciations of each character and defined them in keeping with the mispronunciation if the pronunciation represented another real word. The results of single-word semantic priming in a lexical decision task, however, suggested normal recognition processes for these kanji-words, despite the patient's reading errors. We consider her reading to represent surface dyslexia in Japanese. We discuss these dissociations between reading responses and priming effects in the context of dual-route models of human reading, and conclude that the "visual route" (direct access from orthography to semantics and phonology) was not completely disrupted, but partially preserved and functioning in automatic access.

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PubMed1999

Naming people ignoring semantics in a patient with left frontal damage.

Studies about proper name anomia generally assume that persons' names are harder to recall than other semantic information one knows about them and that name retrieval is not possible without biographical knowledge. We describe a patient, SB, who, after a left frontal haemorrhage, was unable to recall any biographical information about people she could name. Moreover, she had a normal score in an Object Picture Naming Test, but gave confabulatory answers in a Semantic Questionnaire involving the same items. The role of frontal function in producing this pattern of impairment is discussed, together with the possible existence of a direct route from visual perception to proper name retrieval.

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PubMed1999

Visual paralexias in a Spanish-speaking patient with acquired dyslexia: a consequence of visual and semantic impairments?

We report the case of a Spanish patient SC who misread 55 per cent of the single words shown to her. SC's reading accuracy was affected by word imageability and frequency. Nonword reading was very poor. The majority of SC's errors to real-word targets bore a close visual similarity to the items that elicited them, but there was no indication of an effect of serial position on the probability that a letter from a target word would be incorporated into the error made to that word. SC made some visual errors in object naming and also showed evidence of a general semantic impairment. We consider the similarity between SC and patient AB reported by Lambon Ralph and Ellis (1997), and suggest that the very high levels of visual errors shown by these two patients may reflect a combination of visual and semantic impairments.

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PubMed2005

A pet study of visual and semantic knowledge about objects.

The distinctiveness of temporal lobe regions activated during the retrieval of knowledge regarding structural, colour and associative (encyclopaedic) aspects of familiar objects was investigated using PET. These three types of knowledge were contrasted using well matched tasks requiring the detection, in a series of coloured-in line drawings, of occasional anomalous objects (in the three conditions: structurally incorrect chimeras composed of parts of real objects; inappropriately coloured objects; familiar objects that do not exist in the modern world). Relative to a resting baseline condition, all semantic retrieval tasks yielded extensive bilateral activations in occipital and temporal areas, extending anteriorly on the ventral surface of the brain, plus an area in the right superior parietal lobe. In direct semantic-task comparisons focussing on the temporal lobe: (i) structural relative to associative decisions activated the right posterior middle/inferior temporal gyrus; (ii) colour decisions relative to structural judgements were associated with a region in the right superior temporal gyrus; (iii) the associative decision task selectively activated the left anterior middle/superior temporal gyrus and temporal pole relative to both object structure and colour, and also the homologous right temporal pole relative to colour only. These results indicate that each type of stored knowledge involves at least partially distinct cortical areas, and suggest that both anterior/posterior and left/right temporal regions have specialised roles.

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PubMed1992

Categorical-semantic and spatial-imagery judgements of non-verbal stimuli in the cerebral hemispheres.

A divided visual field task was given to two groups of normal subjects to investigate hemisphere differences in the processing of standardised pictorial stimuli. There were two conditions: subjects were asked to decide whether an entity represented by a picture was living or non-living, a task involving a categorical judgement based on semantic information, or, in the second condition, whether these depictions represented entities which were bigger or smaller than a cat. This latter task, it is suggested, requires visual imagery to compare spatial dimensions. The first, categorical task produced an LH advantage in reaction time. The second, imagery task, produced an RH advantage provided the comparison involved items whose sizes were relatively close to that of a cat. Furthermore, the size difference was inversely related to reaction time, only when items were presented to the RH. The data obtained are consistent with the notion that there are at least two systems for processing visual information, one specializing in categorical and semantic distinctions related to LH functions, and the other, specialized in spatial coordinates, an aspect of visual imagery, related to the RH.

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PubMed1983

Event-related potentials and reaction times as measures of hemispheric differences for physical and semantic Kanji matching.

Hemispheric differences associated with Physical Identity Matching and Semantic Classification of Japanese characters (Kanji) were examined using visual event-related potentials and behavioural measures. Event-related potentials to the Kanji during matching tasks revealed hemispheric differences in the later components. Right hemisphere responses were larger than those or the left. The interaction of Types of Matches by Hemispheres was not significant. This interaction however was significant with the behavioural measure. On Semantic Classification Matching reaction times for right-visual-field Kanji were faster than those of the left field while no visual field difference was found for Physical Identity Matching. The sensitivity of both measures as indicators of laterality is discussed from the point of view of levels of processing.

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PubMed1989

Selective preservation of oral spelling without semantics in a case of multi-infarct dementia.

A 70 year old retired van driver, with a diagnosis of multi-infarct dementia, showed features associated with transcortical sensory aphasia, with excellent repetition, a severe anomia, poor semantic comprehension and fluent speech. He was able to spell orally words which he did not understand, as well as nonwords; he wrote to dictation only after first spelling the words orally. Some of his spellings provided evidence for a dissociation between semantics and the graphemic output lexicon, the application of sub-word rules and partial lexical knowledge. These findings are interpreted in terms of a cognitive neuropsychological model.

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PubMed1996

Modality specific semantic knowledge loss for unique items.

We report the case of a man who, following a major myocardial infarction, suffered anoxia followed by significant event memory impairment. Investigations indicated that his semantic memory for word concepts and object meanings was well preserved. However, he had great difficulty in identifying in the visual (but not verbal) modality historically known people, such as Queen Elizabeth I and Napoleon, and well known world and London landmarks, such as the Parthenon and Buckingham Palace. This selective impairment could not be accounted for in terms of prosopagnosia or high level visual perceptual deficits and we interpret it as a modality specific semantic memory loss for unique objects.

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PubMed2001

The effects of left- versus right-hemisphere lesions on the sensitivity to intra- and interconceptual semantic relationships.

Studies on split-brain, normal and brain-damaged subjects suggest differences in the processing of semantic relationships by the two hemispheres. Various authors have conceived of this distinction in terms of the paradigmatic/syntagmatic dissociation, and the connotative and denotative meanings of words, and as reflecting different types of links between words. Drews has suggested that a left-hemisphere lesion would affect the processing of intraconceptual relationships, while a right-hemisphere lesion would impair the processing of interconceptual relationships. The goal of this study was to test this hypothesis, using a number of intra- and interconceptual semantic relationships. Pairs of common words were submitted to left-hemisphere brain-damaged and right-hemisphere brain-damaged subjects. The task required subjects to indicate whether or not there was any relationship between the words. The results only partially support the hypothesis. The right/left opposition applied to only one of three types of intraconceptual relationships (whole-part relation) and to one of two types of interconceptual relationship (same location relation). This partially unexpected result is discussed in reference to other studies.

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PubMed2001

Deficits in irregular past-tense verb morphology associated with degraded semantic knowledge.

Two distinct mechanisms are often considered necessary to account for generation of the past-tense of English verbs: a lexical associative process for irregular forms like speak-->spoke, and a rule-governed process ("add -ed") for regular and novel forms like talk-->talked and wug-->wugged. An alternative account based on a parallel-distributed processing approach proposes that one complex procedure processes all past-tense types. In this alternative view, neuropsychological dissociations are explained by reduced input from word meaning that plays a greater role in successful generation of the past-tense for lower frequency irregular verbs, and by phonological deficits that disproportionately affect regular and novel forms. Only limited evidence has been available concerning the relationship between knowledge of word meaning and verb-tense processing. The study reported here evaluated the past-tense verb abilities of 11 patients with semantic dementia, a neurodegenerative condition characterised by degraded semantic knowledge. We predicted and confirmed that the patients would have essentially normal ability to generate and recognise regular (and novel) past-tense forms, but a marked and frequency-modulated deficit on irregular verbs. Across the set of 11 patients, the degree of impairment for the irregular past-tense was significantly correlated with the degree of comprehension impairment as measured by verb synonym judgements. These results, plus other features of the data such as the nature of the errors to irregular verbs, are discussed in relation to currently developing theories of the language system.

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PubMed2001

Spared numerical abilities in a case of semantic dementia.

We report a case study of a patient (IH) with a progressive impairment of semantic memory affecting all categories of knowledge apart from numbers. Pictorial material was better understood than words, but was still severely impaired. The selective preservation of nearly all aspects of numerical knowledge suggested that this domain might have different neuropsychological status from other aspects of semantic memory.

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PubMed2002

Hemispheric semantic priming in the single word presentation task.

Functional brain asymmetries in semantic activation were studied by presenting categorically related (e.g. TABLE-BED) or unrelated primes and targets to the left visual field (LVF)/right hemisphere or to the right visual field (RVF)/left hemisphere in the single word presentation lexical decision task. The results showed that the primes in the RVF/left hemisphere primed lexical decisions to the targets both in the RVF and in the LVF. However, the primes in the LVF/right hemisphere did not induce any priming in the LVF or RVF. These results suggest that the left hemisphere automatically activates categorically related meanings in both hemispheres. The role of the right hemisphere in automatic semantic processing may be very limited.

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PubMed2002

Electrophysiological estimates of the time course of semantic and phonological encoding during listening and naming.

Current psycholinguistic models suggest that we know what we want to say before we decide how we are going to say it: in other words, for speaking, word meaning is activated prior to information about syntax and phonology. Listening likely involves the reverse order of processes: phonological processing before meaning activation. We examined the relative time courses of phonological and semantic processing during language production and comprehension using event-related brain potentials (ERPs). Participants viewed a series of pictures (with the instruction to covertly name the depicted item), or heard a series of words, and made dual choice Go/noGo decisions based on each item's conceptual (whether the item was an animal or an object) and phonological features (whether the item's German name started with a vowel or a consonant). During picture naming, the N200 component (related to response inhibition) indicated that conceptual processing preceded phonological processing by about 170ms. During auditory word processing, on the other hand, the brain activity related to these two aspects of comprehension indicated some temporal overlap with the N200 to phonological processing preceding that to semantic processing by only about 85ms. In sum, the data are compatible with current psycholinguistic models of speech production and comprehension and argue for serial or widely spaced cascaded processing during production but more parallel processing of information during comprehension.

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PubMed2002

Category-specific naming deficits for objects and actions: semantic attribute and grammatical role hypotheses.

Research on category-specific naming deficits and on noun and verb naming has raised questions about how organization of knowledge in the brain impacts word retrieval. The semantic attribute hypothesis posits that lexical access is mediated by brain systems that process the most definitive attributes of specific concepts. For example, it has been suggested that the most definitive attribute of living things is their visual form, whereas the most definitive attribute of non-living things is their function. The competing grammatical role hypothesis posits that access to a word depends on the grammatical role it plays in a sentence. Since nouns and verbs have different roles, it is assumed that the brain uses different systems to process them. These two hypotheses were tested in experimental subjects who had undergone left anterior temporal lobectomy (LATL) or right anterior temporal lobectomy (RATL) by assessing confrontation naming of living things, tools/implements, non-human actions, and human actions. The names of living things and implements are nouns and the names of actions are verbs. Within each grammatical class, items were characterized either predominantly by visual attributes (living things and non-human actions) or by attributes related to human activity (implements and human actions). Our results support the semantic attribute hypothesis. Patients with LATL were worse at naming tools/implements and human actions than RATL patients. Dysfunction in or removal of the left anterior temporal lobe disrupts fronto-temporal connections from the uncinate fasciculus. These connections may mediate activation of action-related information (i.e. movement plan and/or motor use) that facilitates the retrieval of names for tools/implements and human actions.

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PubMed2003

Priming of strong semantic relations in the left and right visual fields: a time-course investigation.

Prior time-course investigations of cerebral asymmetries in word processing have sometimes reported hemisphere differences in the onset and duration of semantic priming. In the current study, very strongly related word pairs (categorical associates such as arm-leg) were employed in a low relatedness proportion lexical decision priming paradigm. A range of prime-target stimulus onset asynchronies (SOAs: 150-800 ms) was included. Only very weak evidence was obtained for a LVF priming lag at the briefest SOA, while priming was bilateral at moderately long SOAs. We consider these data in the context of previous time-course studies and suggest that, when highly semantically similar word pairs are used, a right hemisphere priming lag is, at best, a very small effect.

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PubMed2003

Nonconscious formation and reactivation of semantic associations by way of the medial temporal lobe.

A successful strategy to memorize unrelated items is to associate them semantically. This learning method is typical for declarative memory and depends on the medial temporal lobe (MTL). Yet, only a small fraction of perceived items emerge into conscious awareness and receive the status of representations in declarative memory. This functional magnetic resonance imaging (fMRI) study tackled the mnemonic fate of unrelated item pairs processed without conscious awareness. Stimuli consisted of a face and a written profession (experimental condition) or of a face (control condition) exposed very briefly between pattern masks. Although the participants were unaware of the stimuli, activity in the hippocampus and perirhinal cortex was changed in the experimental versus the control condition; perirhinal activity changes correlated with the reaction time measure of the later nonconscious retrieval. For retrieval, the previously presented faces were shown again, this time for conscious inspection. The task was to guess the professional category of each face. This task was to induce a nonconscious retrieval of previously formed face-profession associations. Remarkably, activity in the hippocampus and perirhinal cortex was enhanced when subjects were confronted with faces from the experimental versus the control condition. The degree of hippocampal and perirhinal activation changes correlated with the reaction time measure of nonconscious retrieval. Together, our findings suggest that new semantic associations can be formed and retrieved by way of the medial temporal lobe without awareness of the associations or its components at encoding or any awareness that one is remembering at retrieval.

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PubMed1997

Time course of semantic activation in the cerebral hemispheres.

Recent visual half-field studies using relatively long stimulus onset asynchronies (SOAs) and non-associated category members (e.g. deer-pony) as word pair stimuli have indicated that with a low proportion of related stimuli, automatic priming of non-associated category information is larger in the right than in the left hemisphere [Chiarello and co-workers]. The present study examined semantic priming of non-associated category members, with a low proportion of related stimuli in the visual fields/hemispheres across SOAs of 165, 250, 500, and 750 msec. Eighty normal, right-handed subjects were tested (20 subjects/SOA). The results revealed a left hemisphere advantage in priming at the 165 msec SOA, whereas the right hemisphere advantage reported in earlier studies was observed at the longest 750 msec SOA only. The results challenge the view that a larger range of related meanings is activated in the right than in the left hemisphere. Rather, the time course of semantic activation may be different in the hemispheres.

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