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PubMed2002

Relearning of verbal labels in semantic dementia.

Semantic dementia is a degenerative disorder of temporal neocortex characterised by loss of word and object concepts. There is limited evidence that temporary relearning of lost vocabulary may be possible, attributed to sparing of hippocampal structures. However, learning is variable across patients and factors underlying learning success are poorly understood. The study investigated relearning of object names in two severely anomic semantic dementia patients. Following memory models that assume that hippocampal memories require some neocortical representation to underpin them it was predicted that relearning would be influenced by patients' residual semantic information about stimuli. Experiment 1 confirmed that residual knowledge influenced learning success. On the assumption that neocortical knowledge encompasses concepts of space and time, as well as words and objects, it was predicted that learning would be affected by the availability of contextual (temporo-spatial) information. Experiment 2 demonstrated effective learning of object names, attributed to the patient's use of temporal order and spatial position knowledge. Retention of object names over months was linked to the patient's capacity for autobiographical experiential (temporo-spatial contextual) association. The findings indicate that relearning of lost vocabulary is possible in semantic dementia, indicating a role of the medial temporal lobes in the acquisition of semantic information. Effective learning does not imply reinstatement of lost concepts, but, it is argued, does involve some reacquisition of meaning. The findings challenge the traditional semantic-episodic memory dichotomy and are consistent with a "levels of meaning" account of semantic memory.

Anomia↗

PubMed1996

Identification of famous faces and famous names in early Alzheimer's disease. Relationship to anterograde episodic and general semantic memory.

We assessed remote memory in 33 patients with dementia of Alzheimer's type (DAT) with Mini-Mental State Examination (MMSE) scores between 17 and 30, and 30 matched controls using a Famous Faces Test and Famous Names Test designed to assess face recognition, identification and naming, and name recognition and identification, respectively, together with a range of anterograde episodic and semantic memory tests. Patients with DAT were impaired on all components of the remote memory tests, i.e. famous face recognition, identification and naming, and famous name recognition and identification. There was also evidence of a modest temporal gradient, with relatively greater impairment of more recent memory, which may be artefactual resulting from the very insidious onset of their anterograde amnesia. In contrast to the uniform impairment of anterograde memory, there was considerable heterogeneity in performance on remote memory. Although the DAT patient group's performance on remote memory measures was impaired with respect to controls, some patients had significant impairment on all measures, whereas others had intact remote memory. Overall, there was only a weak correlation between dementia severity and remote memory, and no correlation between performance on the Faces and Names tests and measures of anterograde memory. At a cognitive level, the deficit in face and name processing in DAT involved recognition, identification and naming. This would suggest that so called 'face and name recognition units', semantic knowledge of famous persons and post-semantic processing are all affected by the disease. There was also supporting evidence for the concept that recognition of famous faces and names both draw on common sources. Similar results were found for face and name identification. This suggests that face and name recognition units are closely linked, and that identification of a face or name accesses the same central pool of semantic knowledge regarding the famous person. Performance on famous names tests correlated, to a limited degree, with that on general semantic tests, suggesting that knowledge of famous people, at least as accessed by names, is associated with general semantic memory. By contrast, no correlation was found between performance on the famous faces and on other general semantic tasks.

Aged↗

PubMed1999

Disrupted temporal lobe connections in semantic dementia.

Semantic dementia refers to the variant of frontotemporal dementia in which there is progressive semantic deterioration and anomia in the face of relative preservation of other language and cognitive functions. Structural imaging and SPECT studies of such patients have suggested that the site of damage, and by inference the region critical to semantic processing, is the anterolateral temporal lobe, especially on the left. Recent functional imaging studies of normal participants have revealed a network of areas involved in semantic tasks. The present study used PET to examine the consequences of focal damage to the anterolateral temporal cortex for the operation of this semantic network. We measured PET activation associated with a semantic decision task relative to a visual decision task in four patients with semantic dementia compared with six age-matched normal controls. Normals activated a network of regions consistent with previous studies. The patients activated some areas consistently with the normals, including some regions of significant atrophy, but showed substantially reduced activity particularly in the left posterior inferior temporal gyrus (iTG) (Brodmann area 37/19). Voxel-based morphometry, used to identify the regions of structural deficit, revealed significant anterolateral temporal atrophy (especially on the left), but no significant structural damage to the posterior inferior temporal lobe. Other evidence suggests that the left posterior iTG is critically involved in lexical-phonological retrieval: the lack of activation here is consistent with the observation that these patients are all anomic. We conclude that changes in activity in regions distant from the patients' structural damage support the argument that their prominent anomia is due to disrupted temporal lobe connections.

Anomia↗

PubMed2002

Differential age effects in semantic and episodic memory.

Results from 4 experimental tasks and 8 data sets (the 4 tasks involved either multiple sessions or different stimuli) as well as a vocabulary test conducted on the same 80 participants (40 younger and 40 older adults) are reported. The authors employed 2 semantic memory tasks (lexical decision and multiplication verification) using data from 2 sessions (for a total of 4 semantic data sets) and 2 episodic memory tasks (hybrid visual search and memory search with digits and with words as stimuli). Factor analyses using slope and intercept data from the 8 experimental data sets indicated the presence of 3 latent factors: a single intercept factor for both episodic and semantic tasks and separate slope factors for episodic and semantic tasks. A structural equation model with paths from age to 3 different 1st-order latent factors (episodic central processes, semantic central processes, and combined episodic and semantic peripheral processes) fit better than general factor models. These data are consistent with a theoretical framework in which there are age-related dissociations between peripheral and central processes across semantic and episodic memory.

Adolescent↗

PubMed2001

Episodic memory: insights from semantic dementia.

Semantic dementia, also known as the temporal lobe variant of fronto-temporal dementia, results in a progressive yet relatively pure loss of semantic knowledge about words, objects and people, and is associated with asymmetric, focal atrophy of the antero-lateral temporal lobes. Semantic dementia provides a unique opportunity to study the organization of long-term memory particularly since initial observations suggested sparing of episodic memory. Recent studies reveal, however, a more complex but theoretically revealing pattern. On tests of autobiographical memory, patients with semantic dementia show a 'reverse step function' with sparing of recall of events from the most recent 2 to 5 years but impairment on more distant life periods. Anterograde recognition memory for visual materials is extremely well preserved, except in the most deteriorated cases, although performance is heavily reliant upon perceptual information about the studied stimuli, particularly for items that are no longer known by the subjects. On tests of verbal anterograde memory such as word learning, performance is typically poor even for words which are 'known' to the patients. A source discrimination experiment, designed to evaluate familiarity and recollection-based anterograde memory processes, found that patients with semantic dementia showed good item detection, although recollection of source was sometimes impaired. Semantic knowledge about studied items and measures of item detection and source discrimination were largely independent. The implications of these findings for models of long-term memory are discussed. The results support the concept that episodic memory, or at least the recall of temporally specific autobiographical experiences, draws upon a number of separable memory processes, some of which can function independently of semantic knowledge.

Dementia↗

PubMed1995

Event-related potential and behavioral correlates of semantic processing in Alzheimer's patients and normal controls.

In normal young adults, N400 amplitude varies inversely with the extent to which a word has been primed by its preceding semantic context. Based on a series of behavioral studies, it appears that in Probable Alzheimer's patients (PAD) the organization of semantic memory is disrupted such that specific items within a category lose their distinction, although superordinate information remains relatively intact. The present study examined whether the N400 gradient which has been found with normal young adults would also reflect this loss of discriminability among semantically related items in PAD patients. Ten normal young adults, 10 normal elderly, and 6 "mild" PAD patients made speeded (but accurate) sense/nonsense decisions to the terminal words of a series of highly constrained sentence contexts. The terminal words belonged to one of four stimulus types which varied as a function of relatedness to a highly expected word. Counter to our predictions, N400 amplitude was identically responsive to semantic relatedness in the young normal and PAD groups, but was characterized differently in the normal elderly. Given the significantly greater number of errors committed by PAD patients, we concluded that their disruption in semantic processing occurs at some point between the elicitation of N400 and the generation of the reaction time response. The anomalous N400 pattern in the normal elderly appeared to be strategy related and superimposed upon an otherwise normal semantic network.

Adult↗

PubMed1998

Semantic transparency in the processing of compounds: consequences for representation, processing, and impairment.

The role of semantic transparency in morphological processing in general and in compound processing in particular is examined. It is argued that the notion of semantic transparency is crucial to an account of how compounds are represented and processed in the mind. A sketch of a model is proposed in which compound processing is described in terms of stimulus properties, lexical properties, and conceptual properties. The model represents the notion of semantic transparency in terms of a four-way classification of the semantic relationship between a compound's constituents and the corresponding independent morphemes. It also distinguishes between semantically componential and noncomponential compounds. It is proposed that the model offers a framework within which experimental psycholinguistic findings can be understood and within which aphasic deficits associated with compound processing can be characterized. As an example of this, the paper presents a reanalysis of an aphasic patient who exhibits the tendency to interpret semantically opaque compounds as though they were transparent and to interpret opaque compounds in terms of a blend of constituent and whole-word meaning. It is argued that the underlying deficit in this patient is the failure for inhibition to result from the competition among stimuli at the conceptual level of representation.

Aphasia↗

PubMed1999

Convergent cortical representation of semantic processing in bilinguals.

This study examined whether semantic processes in two languages (English and Spanish) are mediated by a common neural system in fluent bilinguals who acquired their second language years after acquiring their first language. Functional magnetic resonance imaging was performed while bilingual participants made semantic and nonsemantic decisions about words in Spanish and English. There was greater activation for semantic relative to nonsemantic decisions in left and right frontal regions, with greater left frontal activation. The locations of activations were similar for both languages, and no differences were found when semantic decisions for English and Spanish words were compared directly. These results demonstrate a shared frontal lobe system for semantic analysis of the languages and are consistent with cognitive research on bilingualism indicating that the two languages of a bilingual person access a common semantic system.

Adult↗

PubMed2000

When does a deep dyslexic make a semantic error? The roles of age-of-acquisition, concreteness, and frequency.

Semantic reading errors are the central and defining feature of deep dyslexia. This study compared the words the deep dyslexic patient LW read correctly with those she omitted and those to which she produced semantic errors in terms of their concreteness, age-of-acquisition, frequency, and length. Semantic errors were made to less concrete, later-acquired, and shorter words than were read correctly; there was no reliable effect of word frequency. More importantly, the actual semantic errors produced were later-acquired than the stimulus words, but they were not more concrete or reliably more frequent. These results implicate age-of-acquisition in the process that produces semantic errors. It is proposed that concreteness determines the specificity of the semantic system to activate a set of candidate responses and that age-of-acquisition biases the ease with which certain words can be selected from this set to be produced as reading responses.

Age Factors↗

PubMed1993

Phonologic and semantic processing in reading-disabled and nondisabled males at two age levels.

The purpose of the following study was to replicate the confusability paradigm of Byrne and Shea (1979) by examining phonologic and semantic performances of good and poor readers. This study added an older age group and a phonological awareness task to examine other aspects of phonological processing across age. The confusability tasks included a pseudoword recognition task with only phonological information available for coding and a word recognition task with both phonetic and semantic information available for coding. Forty poor readers and 40 good readers were divided into two separate age groups (8-10 years, 14-16 years). Rhyming, semantic, control, and general errors were recorded. On the pseudoword task poor readers' rhyming versus control errors increased whereas good readers' rhyming versus control errors decreased with age. On the word task poor readers made more errors on semantic than rhyming trials while good readers made more rhyming than semantic errors. Poor readers made significantly more errors on the phonological awareness task than good readers. The combined results suggest, as did Byrne and Shea, that poor readers have a weak-functioning phonological system which they rely upon less when semantic information is available for coding.

Adolescent↗

PubMed1998

Mapping neural interactivity onto regional activity: an analysis of semantic processing and response mode interactions.

Neuroimaging studies of cognition have typically been designed to identify brain regions that are active during a cognitive process. However, identifying how brain regions interact may be equally important. In a recent study we found that the pattern of activation associated with a semantic task differed depending on how subjects made a response, suggesting that there was an interaction between the neural systems underlying response mode and semantic processing (J. M. Jennings et al., 1997, NeuroImage 5, 229-239). This result raises two important questions, which we examined here: (1) How did the regions underlying semantic performance influence one another, or interact, to produce a different pattern of activation in each case? (2) What can be learned about the neurobiology of semantic processing when different regions are identified as a function of response? We addressed these questions using structural equation modeling. This technique produced functional network models representing the effect of different regions on each other during the semantic task for each response. A common network of regions associated with semantic processing was observed and included the left inferior frontal and left superior temporal cortices, with other regions brought into that network depending on response (e.g., right middle frontal). Moreover, changes in the influences among these regions across response condition predicted the pattern of activation found previously. These results show how an arbitrary response can affect the neural pathways associated with a cognitive process, likely due to the parallel and reentrant organization of the brain, and emphasize the importance of examining functional connections when studying cognition.

Adult↗

PubMed1991

On the semantic content of subcategorization frames.

This paper investigates relations between the meanings of verbs and the syntactic structures in which they appear. This investigation is motivated by the enigmas as to how children discover verb meanings. Well-known problems with unconstrained induction of word meanings from observation of world circumstances suggest that additional constraints or sources of information are required. If there exist strong and reliable parallels between the structural and semantic properties of verbs, then an additional source of information about verb meanings is reliably present in each verb's linguistic context. Five experiments are presented which investigate the following hypothesis regarding the scope of these relations: The closer any two verbs in their semantic structure, the greater the overlap should be in their licensed syntactic structures. To investigate this hypothesis, data of two kinds were collected from different groups of subjects: (a) One group of subjects was asked to judge the semantic relatedness of verbs by selecting the semantic outlier in triads presented to them. (b) A second group of subjects was asked to judge the grammaticality of these same verbs in a large range of syntactic environments. These two types of data were then compared to assess the degree of correspondence in the two partitionings (syntactic and semantic) of the verb set. The findings, overall, support the view that the syntax of verbs is a quite regular, although complex, projection from their semantics. In conclusion, we discuss the kinds of features that are formally marked in syntactic structure and relate these to the problem of verb-vocabulary acquisition in young children.

Concept Formation↗

PubMed1994

Word retrieval to letter and semantic cues: a double dissociation in normal subjects using interference tasks.

Recent evidence suggests that letter and semantic category verbal fluency tasks may use different component processes of a distributed word retrieval system. We hypothesized that the retrieval of words that begin with the same letter places greater demands on frontal lobe mediated strategic search processes than on temporal lobe mediated semantic knowledge. Conversely, generation of words from the same semantic category places greater demands on semantic knowledge than on strategic search. This hypothesis was tested by requiring subjects to generate lists of words to letter and semantic cues alone and while performing an interference task. A motor sequencing task (developed by Moscovitch, Neuropsychology of Memory, pp. 5-22, 1992) was used to activate frontal regions and an object decision task was used to activate posterior temporal cortex. In support of the hypothesis, letter fluency was reduced to a greater extent by concurrent performance of the motor sequencing task than by the object decision task. The opposite interference pattern was found for semantic category fluency.

Adult↗

PubMed1989

Priming and semantic memory loss in Alzheimer's disease.

Semantic memory (SM) was investigated in six patients with probable Alzheimer's disease (AD) by on-line measurement of semantic priming in a lexical decision task, and off-line tests of comprehension. Detailed assessment was carried out on naming, name comprehension, and probes of semantic knowledge with a battery of 150 items. The patients performed normally on perceptual tests and displayed an item-specific loss of knowledge on the semantic tests. In a primed lexical decision task, greater semantic priming was found relative to age-matched normals. The priming was substantially greater for items with "degraded" representations as determined by the off-line tests. Lexical decision was also performed more slowly on these items. These unexpected results demand a reevaluation of the concepts of the lexicon and semantic memory structure and their possible alteration in dementia.

Aged↗

PubMed1990

Automatic and volitional semantic processing in aphasia.

The present study investigated the status of semantic information in aphasia by comparing the performances of aphasic and nonaphasic subjects on two tasks: an automatic semantic facilitation task and a volitional task of relatedness judgment. Both the aphasic and nonaphasic groups evidenced a semantic facilitation effect, in an on-line task of semantic processing. However, those aphasics with severe comprehension and naming disturbances (termed low comprehension aphasics) demonstrated considerable difficulty in judging the relatedness between a pictured object and members of that object's semantic field, the severity of the impairment being greater for those pictures that the low comprehension aphasics were unable to name. The pattern of results can best be explained by supposing the structural integrity of the store of semantic information in aphasia, and in particular in low comprehension aphasia: information that is retrieved and manipulated in judgment-mediated tasks with considerable difficulty.

Adult↗

PubMed1991

Hemispheric specialization for semantic and syntactic components of language in simultaneous interpreters.

Hemispheric specializations for semantic and syntactic components in Italian (L1) and English (L2) were studied with a dichotic listening test, simulating simultaneous interpretation tasks in 24 right-handed female interpretation students at the Scuola Superiore di Lingue Moderne per Interpreti e Traduttori (SSLM) of the University of Trieste and in 12 right-handed female professional interpreters at the European Communities (EEC). The test involved the recognition of correct translations, translations with semantic errors, and translations with syntactic errors from L1 to L2 and vice versa. As an overall result, both students and interpreters gave significantly more correct answers when sentences in L2 as the target language were sent to the left ear. Students recognized significantly more sentences containing syntactic errors than did professional interpreters, while professional interpreters recognized significantly more sentences with semantic errors than did interpreting students. In regard to hemispheric specialization in interpreting students, no significant asymmetries were revealed in the recognition of semantic and syntactic errors. Professional interpreters showed a significant right-ear superiority in recognizing semantic errors in L1 and a significant left-ear superiority in recognizing semantic errors in L2. In the recognition of syntactic errors, professional interpreters showed significant left-ear superiority for L1 and significant right-ear superiority for L2. The prolonged practice in simultaneous interpreting strategies in EEC professional interpreters may account for some of their peculiar hemispheric specializations for languages revealed by this study.

Adult↗

PubMed1996

Impairment of the semantic network in schizophrenia.

It is well established that patients with schizophrenia display a variety of language impairments. Despite considerable research, however, the underlying mechanisms of the language deficits in schizophrenia remain unclear. Representations of semantic networks of 56 patients with schizophrenia and 28 normal comparison (NC) subjects of similar ages and educational levels were generated by multidimensional scaling and Pathfinder analyses of their responses on the Animal Fluency Test. On the basis of traditional scoring techniques (i.e., total number of correct animal names generated in 60 s), all patients performed significantly worse than the NC subjects. More detailed analyses of the underlying semantic networks revealed that performance in the patients varied according to age of onset and subtype of schizophrenia. The semantic network of patients with late-onset schizophrenia (i.e., with onset after age 45) was virtually identical to that of the NC group. In contrast, the semantic network of patients with a younger age of onset was disorganized and differed significantly from that of the NC subjects. Findings demonstrated that patients with nonparanoid subtypes displayed greater disorganization in their semantic networks than patients with a paranoid subtype. Although general fluency impairments (e.g., difficulties in initiation, retrieval, and search mechanisms) may be sensitive to schizophrenia, per se, specific deficits in the structure of semantic knowledge may be associated with certain characteristics of individual patients with schizophrenia, such as an earlier age of onset and nonparanoid subtype.

Adult↗

PubMed1988

Semantic, episodic, and autobiographical memory in a postmeningitic amnesic patient.

This study is concerned with the semantic and episodic memory performance of a highly intelligent and intellectually unimpaired patient, K.J., who became amnesic following meningitis. Although densely amnesic he showed unimpaired performance on tests of vocabulary and verbal fluency, while both speed and accuracy on semantic category judgment and sentence verification tests are unimpaired. It is concluded that semantic memory performance may be intact despite dense amnesia. However, this does not necessarily imply separate semantic and episodic memory systems. K.J. showed an impaired capacity for registering new material in semantic memory, and apparently normal autobiographical memory for events occurring well before his illness. The simplest interpretation of our results would therefore appear to be in terms of the sparing of old and overlearned memories rather than the specific preservation of semantic memory.

Amnesia↗