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PubMed1996

Reading lexically without semantics: evidence from patients with probable Alzheimer's disease.

Recent modifications of the lexical model of oral reading make the prediction that under conditions where sublexical reading processes alone cannot achieve the target pronunciation (i.e., when words have exceptional spellings or when sublexical processes are impaired), patients with severe semantic impairment should have more difficulty reading aloud semantically impaired words than semantically retained words. In a battery of lexical-semantic and reading tasks, two neurologically normal control subjects and two subjects with probable Alzheimer's disease (AD) and only moderate semantic impairment read aloud all words accurately. One AD subject with severe semantic impairment was impaired in word reading but demonstrated no difference in reading words with regular and exceptional spellings. Another AD subject with severe semantic impairment read aloud without error virtually all regular and exception words. Neither severely impaired AD subject demonstrated any relationship between oral reading accuracy and semantic knowledge of exception words. These findings support a model of word reading incorporating lexical, nonsemantic processes by which lexical orthographic input representations directly activate lexical phonological output representations without the necessity of semantic mediation.

Aged↗

PubMed1997

Conjoint and dissociable effects of syntactic and semantic context.

Manipulating the semantic relatedness of noun and verb targets in contexts where they are grammatically appropriate or inappropriate allows for simultaneous examination of syntactic and semantic context effects. A lexical-decision experiment showed both a syntactic context effect and a semantic relatedness effect that was stronger in syntactically appropriate conditions. Thus, latencies appeared to be conjointly determined by syntactic and semantic context. In contrast, naming experiments also showed both semantic and syntactic effects, but the syntactic context effect was independent of semantic relatedness and was observed in the virtual absence of sensitivity to semantic anomaly. Thus, syntactic and semantic processing are largely dissociable in the naming task. In conjunction with other findings in the literature, this suggests the existence of an isolable level of syntactic assignment that precedes semantic integration of content words in sentence comprehension.

Decision Making↗

PubMed2001

Encoding specificity revisited: the role of semantics.

Three experiments examined the effects of semantic characteristics of word pairs on memory using the encoding specificity paradigm. The paradigm involved four phases: (a) an encoding phase to relate cues and targets, (b) a phase in which words were generated to new cues, (c) a phase for recognition of generated targets, and (d) a cued-recall phase using the original encoding cues. Encoding pairs were classified a priori as either semantically similar (e.g., alluring-PRETTY), semantically contrasting (e.g., drab-PRETTY), or semantically unrelated (e.g., sore-PRETTY). Generation pairs were classified a priori as either semantically similar (e.g., beautiful-PRETTY) or semantically contrasting (e.g., ugly-PRETTY). For recall, the results showed that both the semantic relations between the encoding cue and target and the reprovision of the encoding cue at retrieval were important factors. In the case of recognition, however, both the semantic congruence between the encoding and generation contexts and the amount of semantic elaboration provided by the encoding context were important factors.

Analysis of Variance↗

PubMed2003

Effects of visual deprivation on the organization of the semantic system.

Early onset blindness provides a lesion model to investigate whether experience-dependent mechanisms subtend the functional anatomy of semantic retrieval. In particular, visual deprivation might alter the neural systems underlying retrieval of semantic information that is acquired via visual experience. Using functional MRI, we demonstrate that both early blind and sighted subjects activate a left-lateralized fronto-temporal 'core' semantic retrieval system and show common effects for retrieval of visually experienced semantic information. However, irrespective of the type of semantics, blind subjects activate additional extrastriate regions, which are coupled with frontal and temporal semantic regions. The resilience of semantic retrieval responses to visual deprivation suggests a considerable degree of innate and epigenetic specification of the semantic system. In contrast, the exuberant functional connectivity between extrastriate and 'core' semantic retrieval regions might be explained by abnormal pruning processes during early neurodevelopment.

Adult↗

PubMed2005

New insights into the anatomo-functional connectivity of the semantic system: a study using cortico-subcortical electrostimulations.

Despite a better understanding of the organization of the cortical network underlying the semantic system, very few data are currently available regarding its anatomo-functional connectivity. Here, we report on a series of 17 patients operated on under local anaesthesia for a cerebral low-grade glioma located within the dominant hemisphere. Prior to and during resection, intraoperative electrical stimulation was used to map sensorimotor and language structures so that permanent neurological deficits could be avoided. In a number of cases, cortical and subcortical stimulation caused semantic paraphasias. Using postoperative MRI, we correlated these functional findings with the anatomical locations of the sites where semantic errors were elicited by stimulation, especially at the subcortical level, with the aim of studying the connectivity underlying the semantic system. In temporal gliomas, cortical sites involved in semantic processing were found around the posterior part of the superior temporal sulcus, with subcortical pathways reproducibly located under the depth of this sulcus. In insular gliomas, although stimulation elicited no semantic disturbances at the cortical level, such semantic paraphasias were generated at the level of the anterior floor of the external capsule. In frontal tumours, cortical regions implicated in semantics were detected in the lateral orbitofrontal region and dorsolateral prefrontal cortex, with subcortical fibres located under the inferior frontal sulcus. All these eloquent structures were systematically preserved, thereby avoiding permanent postoperative deficits. Our results provide arguments in favour of the existence of a main ventral subcortical pathway underlying the semantic system, within the dominant hemisphere, joining the two essential cortical epicentres of this network: the posterior and superior temporal areas, and the orbitofrontal and dorsolateral prefontal regions. Such a ventral stream might anatomically partly correspond to the inferior fronto-occipital fasciculus.

Adolescent↗

PubMed2002

Hippocampal and brain stem activation during word retrieval after repeated and semantic encoding.

Repeated word presentation during learning and the use of a semantic encoding task both increase the accuracy of subsequent word retrieval. Previous neuroimaging studies have shown that successful word retrieval depends on the recruitment of the hippocampus, whereas the effort of retrieval is linked to activation of prefrontal cortex modules. We studied the effects of repetition (4x versus 1x presentation) and encoding task (semantic versus perceptual) on hippocampal and prefrontal cortex activation during word-stem cued recall using positron emission tomography. Repeated and semantic encoding resulted in increased recall accuracy, with word repetition showing a greater effect when using a semantic encoding task. The more successful retrieval of words presented repeatedly compared with words presented once was associated with activation of the left anterior hippocampus. The more successful retrieval of words encoded using a semantic compared with a perceptual task was associated with activation of the right posterior and, less significantly, the left anterior hippocampus. The greater benefit of repeated learning when using the semantic task was linked to activation of the right brainstem, in the region of the ventral tegmentum. Our results suggest that word repetition and semantic encoding increase recall accuracy during subsequent word retrieval via distinct hippocampal mechanisms and that ventral tegmentum activation is relevant for word retrieval after semantic encoding. These findings confirm the importance of hippocampal recruitment during word retrieval and provide novel evidence for a role of brainstem neurons in word retrieval after semantic encoding.

Adult↗

PubMed2006

The semantic pathfinder: using an authoring metaphor for generic multimedia indexing.

This paper presents the semantic pathfinder architecture for generic indexing of multimedia archives. The semantic pathfinder extracts semantic concepts from video by exploring different paths through three consecutive analysis steps, which we derive from the observation that produced video is the result of an authoring-driven process. We exploit this authoring metaphor for machine-driven understanding. The pathfinder starts with the content analysis step. In this analysis step, we follow a data-driven approach of indexing semantics. The style analysis step is the second analysis step. Here, we tackle the indexing problem by viewing a video from the perspective of production. Finally, in the context analysis step, we view semantics in context. The virtue of the semantic pathfinder is its ability to learn the best path of analysis steps on a per-concept basis. To show the generality of this novel indexing approach, we develop detectors for a lexicon of 32 concepts and we evaluate the semantic pathfinder against the 2004 NIST TRECVID video retrieval benchmark, using a news archive of 64 hours. Top ranking performance in the semantic concept detection task indicates the merit of the semantic pathfinder for generic indexing of multimedia archives.

Abstracting and Indexing↗

PubMed2006

Word-stem completion task to investigate semantic network in patients with Alzheimer's disease.

Semantic impairment in patients with Alzheimer's disease (AD) is revealed by tasks of verbal naming, verbal fluency, and semantic knowledge. Causes of the deficit remain unclear in spite of many studies to investigate whether AD patients suffer from the inability to have voluntary access to an almost intact semantic store or from its break down. Word-stem completion (WSC) tasks have been utilized in healthy subjects in order to study semantic memory and network by exploiting the possibility of the involuntary access to them. Available conflicting data refer to the presence of semantic prime in AD patients. To explore the semantic network in AD, patients were requested to complete with the first word that sprang to their mind a stem submitted immediately after presentation of the word prime, as a WSC task. Stems consisted of the three beginning letters of words that were semantically related to primes. We compared data obtained with this task from patients with mild to moderate AD with those from normal controls (NC). AD patients completed less stems (P<0.001) with the expected words than NC, suggesting a break down of the semantic network rather than a deficit in the access to the semantic store.

Aged↗

PubMed1997

Constraints on the cerebral basis for semantic processing from neuroimaging studies of Alzheimer's disease.

OBJECTIVE: Functional activation studies of semantic processing in healthy adults have yielded conflicting results. The purpose was to evaluate the relative role of the brain regions implicated in semantic processing with converging evidence from imaging studies of patients with impaired semantic processing. METHODS: Semantic memory was assessed in patients with Alzheimer's disease using two measures, and these performance patterns were related to profiles of reduced cerebral functioning obtained with high resolution single photon emission computed tomography (SPECT). Patients with frontotemporal degeneration were similarly evaluated as a control group. RESULTS: Reduced relative cerebral perfusion was seen in parietal and posterior temporal brain regions of patients with Alzheimer's disease but not patients with frontotemporal degeneration. Impairments on semantically guided category membership decision tasks were also seen in patients with Alzheimer's disease but not those with frontotemporal degeneration. Performance on the semantic measures correlated with relative cerebral perfusion in inferior parietal and superior temporal regions of the left hemisphere only in Alzheimer's disease. Relative perfusion was significantly lower in these regions in patients with Alzheimer's disease with semantic difficulty compared with patients with Alzheimer's disease with relatively preserved semantic processing. CONCLUSION: These findings provide converging evidence to support the contribution of superior temporal and inferior parietal regions of the left hemisphere to semantic processing.

Aged↗

PubMed2001

Differing patterns of temporal atrophy in Alzheimer's disease and semantic dementia.

OBJECTIVE: To characterize and quantify the patterns of temporal lobe atrophy in AD vs semantic dementia and to relate the findings to the cognitive profiles. Medial temporal lobe atrophy is well described in AD. In temporal variant frontotemporal dementia (semantic dementia), clinical studies suggest polar and inferolateral temporal atrophy with hippocampal sparing, but quantification is largely lacking. METHODS: A volumetric method for quantifying multiple temporal structures was applied to 26 patients with probable AD, 18 patients with semantic dementia, and 21 matched control subjects. RESULTS: The authors confirmed the expected bilateral hippocampal atrophy in AD relative to controls, with involvement of the amygdala bilaterally and the right parahippocampal gyrus. Contrary to expectations, patients with semantic dementia had asymmetric hippocampal atrophy, more extensive than AD on the left. As predicted, the semantic dementia group showed more severe involvement of the temporal pole bilaterally and the left amygdala, parahippocampal gyrus (including the entorhinal cortex), fusiform gyrus, and the inferior and middle temporal gyri. Performance on semantic association tasks correlated with the size of the left fusiform gyrus, whereas naming appeared to depend upon a wider left temporal network. Episodic memory measures, with the exception of recognition memory for faces, did not correlate with temporal measures. CONCLUSIONS: Hippocampal atrophy is not specific for AD but is also seen in semantic dementia. Distinguishing the patients with semantic dementia was the severe global but asymmetric (left > right) atrophy of the amygdala, temporal pole, and fusiform and inferolateral temporal gyri. These findings have implications for diagnosis and understanding of the cognitive deficits in AD and semantic dementia.

Aged↗

PubMed2002

Knowledge of the human body: a distinct semantic domain.

BACKGROUND: Patients with selective deficits in the naming and comprehension of animals, plants, and artifacts have been reported. These descriptions of specific semantic category deficits have contributed substantially to the understanding of the architecture of semantic representations. OBJECTIVE: This study sought to further understanding of the organization of the semantic system by demonstrating that another semantic category, knowledge of the human body, may be selectively preserved. METHODS: The performance of a patient with semantic dementia was compared with the performance of healthy controls on a variety of tasks assessing distinct types of body representations, including the body schema, body image, and body structural description. RESULTS: Despite substantial deficits on tasks involving language and knowledge of the world generally, the patient performed normally on all tests of body knowledge except body part naming; even in this naming task, however, her performance with body parts was significantly better than on artifacts. CONCLUSIONS: The demonstration that body knowledge may be preserved despite substantial semantic deficits involving other types of semantic information argues that body knowledge is a distinct and dissociable semantic category. These data are interpreted as support for a model of semantics that proposes that knowledge is distributed across different cortical regions reflecting the manner in which the information was acquired.

Atrophy↗

PubMed2004

Semantic distance norms computed from an electronic dictionary (WordNet).

WordNet, an electronic dictionary (or lexical database), is a valuable resource for computational and cognitive scientists. Recent work on the computing of semantic distances among nodes (synsets) in WordNet has made it possible to build a large database of semantic distances for use in selecting word pairs for psychological research. The database now contains nearly 50,000 pairs of words that have values for semantic distance, associative strength, and similarity based on co-occurrence. Semantic distance was found to correlate weakly with these other measures but to correlate more strongly with another measure of semantic relatedness, featural similarity. Hierarchical clustering analysis suggested that the knowledge structure underlying semantic distance is similar in gross form to that underlying featural similarity. In experiments in which semantic similarity ratings were used, human participants were able to discriminate semantic distance. Thus, semantic distance as derived from WordNet appears distinct from other measures of word pair relatedness and is psychologically functional. This database may be downloaded from www.psychonomic.org/archive/.

Cognitive Science↗

PubMed1997

Long-term semantic priming: a computational account and empirical evidence.

Semantic priming is traditionally viewed as an effect that rapidly decays. A new view of long-term word priming in attractor neural networks is proposed. The model predicts long-term semantic priming under certain conditions. That is, the task must engage semantic-level processing to a sufficient degree. The predictions were confirmed in computer simulations and in 3 experiments. Experiment 1 showed that when target words are each preceded by multiple semantically related primes, there is long-lag priming on a semantic-decision task but not on a lexical-decision task. Experiment 2 replicated the long-term semantic priming effect for semantic decisions with only one prime per target. Experiment 3 demonstrated semantic priming with much longer word lists at lags of 0, 4, and 8 items. These are the first experiments to demonstrate a semantic priming effect spanning many intervening items and lasting much longer than a few seconds.

Adult↗

PubMed1976

[Elementary logic and semantic fields in aphasia].

Modern linguistics, like genetic psychology, postulate a non-linguistic basis for the structurisation of the semantic fields. If such is the case, it should be possible to observe in aphasia, where semantic deficiency predominates, a related disturbance in the semantic fields and logic. Paraxodically, such disturbances have been observed both in Broca's aphasia and in the predominantly semantic aphasia of Wernicke. A qualitative analysis shows that quantitatively identical results in the semantic aphasias of Broca and Wernicke are the result of phenomenological convergence. The related disturbance in the semantic fields and logic appears characteristic of the semantic deficiency which, in aphasic semiology, is marked by the substitution of one word for another. These finding support the theory of the relative autonomy of phonemic and semantic disorders in Wernicke's aphasia. They confirm the linguistic and genetic theory that the structure of vocabulatory is based on extralinguistic factors. They do not however provide an explantation for semantic disorders in aphasia. Further research is required to discover on what functional system articulation of the symbolic function and general operative capacity is based.

Adolescent↗

PubMed2002

Memory consolidation and the hippocampus: further evidence from studies of autobiographical memory in semantic dementia and frontal variant frontotemporal dementia.

Studies of autobiographical memory in semantic dementia have found relative preservation of memories for recent rather than remote events. As semantic dementia is associated with progressive atrophy to temporal neocortex, with early asymmetric sparing of the hippocampus, this neuropsychological pattern suggests that the hippocampal complex plays a role in the acquisition and retrieval of recent memories, but is not necessary for the recall of older episodic events. In an alternative view of memory consolidation, however, the hippocampus plays a role in the retrieval of all autobiographical memories, regardless of the age of the memory [Curr. Opin. Neurobiol. 7(1997)217]. This 'multiple trace theory' predicts that patients with semantic dementia should show no effects of time in their autobiographical recall. In this article, we ask whether it is possible to reconcile the data from semantic dementia with the multiple trace theory by investigating whether the time-dependent pattern of autobiographical retrieval seen in the disease is due to (i) patients showing this effect being exceptional in their presentation; and/or (ii) patients with semantic dementia exhibiting impaired strategic retrieval from concomitant frontal damage. A series of experiments in patients with semantic dementia, the frontal variant of frontotemporal dementia and Alzheimer's disease clearly demonstrates that neither of these two factors can explain the documented effect of time seen in semantic dementia. Nonetheless, we discuss how damage to semantic knowledge could result in an autobiographical memory deficit and suggest that data from semantic dementia may be consistent with both views of hippocampal involvement in long-term memory.

Aged↗

PubMed2001

Semantic dementia: relevance to connectionist models of long-term memory.

Semantic dementia is a recently documented syndrome associated with non-Alzheimer degenerative pathology of the polar and inferolateral temporal neocortex, with relative sparing (at least in the early stages) of the hippocampal complex. Patients typically show a progressive deterioration in their semantic knowledge about people, objects, facts and the meanings of words. Yet, at least clinically, they seem to possess relatively preserved day-to-day (episodic) memory. Neuropsychological investigations of semantic dementia provide, therefore, a unique opportunity to investigate the organization of human long-term memory and, more specifically, to determine the relationship between semantic memory and other cognitive systems, such as episodic memory. In this review, we summarize recent empirical findings from patients with semantic dementia and discuss whether the neuropsychological phenomena of the disease are consistent with current cognitive and computational models of human long-term memory and amnesia. Six specific issues are addressed: (i) the relative preservation of category-level (superordinate) compared with fine-graded (subordinate) semantic knowledge as the disease progresses; (ii) the better recall of recent autobiographical and semantic memories compared with those in the distant past; (iii) the preservation of new learning, as measured by recognition memory, early in the disease; (iv) the interaction between autobiographical experience and semantic knowledge in the current, but not the distant, time-period; (v) increased long-term forgetting of newly learned material; and (vi) impaired implicit memory. It is concluded that recent findings from semantic dementia offer strong support for the view that memory consolidation in humans is dependent upon interactions between the hippocampal complex and neocortex. Furthermore, these investigations have provided computational modellers of human memory with a novel set of neuropsychological data to be simulated and tested.

Amnesia↗

PubMed1998

Evoked potential correlates of semantic meaning--A brain mapping study.

According to the 'semantic differential technique' the affective meaning of words can be quantified in statistically defined, independent dimensions where every word is uniquely located on the three dimensions evaluation ('good-bad'), potency ('strong-weak'), and activity ('active-passive'). Two experiments were performed on a total of 52 adults: first, 162 nouns were rated by 30 subjects. All words had a comparable number of letters and frequency of occurrence in the German language. A factor analysis followed by varimax rotation on the ratings yielded three semantic dimensions, and for each dimension up to 20 words were selected which scored highly positive or highly negative on one of the three dimensions, and had small scores on the others. This resulted in six semantic word classes which were then used in electrophysiological experiments performed on another group of 22 healthy right-handed adults. Stimuli were presented sequentially on a computer monitor in a randomized order, and the EEG was recorded in 30 channels and continuously stored on hard disk. A checkerboard reversal stimulus was used in a control condition. Evoked potentials were computed off-line for each semantic class. Comparison of the factor structure revealed highly similar semantic dimensions and classification of all words used. In the electrophysiological data, specific brain activity occurred that was related to semantic processing. These components, however, showed distinctive differences to brain activity elicited by contrast reversing checkerboard patterns as was evident from significant differences in component latency, amplitude, and scalp topography. Significant differences in scalp topography, latency and field strength between semantic word classes were not restricted to late 'cognitive' components, but brain activity at small latencies was affected by semantic meaning of the stimuli. Our data show how visually evoked brain activity is modulated by the meaning of the stimuli at early processing stages without reflecting hemispheric differences.

Adult↗

PubMed1995

The effects of phonological and semantic features of sentence-ending words on visual event-related brain potentials.

Event-related brain potentials (ERPs) were recorded to terminal words of visually presented sentences that were identical to those used in an auditory modality study examining the effects of phonological and semantic characteristics of words on ERPs (Connolly and Phillips, 1994). Phonological and/or semantic characteristics of terminal words were manipulated in 4 conditions in which: (1) the terminal word was the highest cloze probability ending for the sentence and was thus phonologically and semantically appropriate to the sentence context (e.g., Ray fell down and skinned his knee(s).; (2) the terminal word had the initial phonemic sound of the highest cloze probability sentence-ending word but was semantically anomalous to the context of the sentence (e.g., They sat together without saying a single worm. [word]); (3) the initial phoneme of the terminal word was phonologically unexpected but the word was semantically correct (e.g., The dough was put in the hot pan. [oven]); or (4) the initial phoneme of the terminal word was phonologically unexpected and the word was semantically inappropriate to the sentence context (e.g., Bill jumped into the lake and made a big farm. [splash]). A left fronto-temporally distributed negative peak was observed in the 250-300 msec range to varying degrees in all conditions but was largest in the condition in which terminal words were both phonologically unexpected and semantically inappropriate. A second, parietally distributed, symmetrical negativity (the N400) was found which peaked around 365 msec and was largest in the two conditions involving semantically anomalous terminal words. Results are discussed in terms of modality factors in ERP manifestations of receptive language functions and the implications of ERP modality differences for theories of word recognition.

Adult↗