Towards a distributed account of conceptual knowledge

doi:10.1016/S1364-6613(00)01651-X

Trends in Cognitive Sciences

Volume 5, Issue 6, 1 June 2001, Pages 244-252

https://doi.org/10.1016/S1364-6613(00)01651-X Get rights and content

Abstract

How is conceptual knowledge organized and represented? Are domains (such as living things) and categories (such as tools, fruit) represented explicitly or can domain and category structure emerge out of a distributed system? Taken at face value, evidence from brain-damaged patients and neuroimaging studies suggests that conceptual knowledge is explicitly structured in independent content-based stores. However, recent analyses of the fine-grained details of semantic impairments, combined with research using connectionist modelling, suggest a different picture – one in which concepts are represented as patterns of activation over multiple semantic properties within a unitary distributed system. Within this context, category-specific deficits emerge as a result of differences in the structure and content of concepts rather than from explicit divisions of conceptual knowledge in separate stores.

Section snippets

Domain/category-specific deficits

Patients with category-specific semantic deficits show poorer performance for items in the impaired domain/category on a range of semantic tasks, including picture naming, word-picture matching, and generation of definitions. Various category-specific semantic dissociations have been reported including deficits for concrete words compared to abstract words 6, 7 and vice versa ⁸, deficits for body parts 9, 10, and colour names ¹¹. Our major focus here is, however, the contrast between the

Evidence from neuroimaging

Neuroimaging studies, looking for evidence of neural specialization corresponding to categories or domains of knowledge, do not clearly support either the domain-specific or sensory–functional accounts. These studies typically test healthy subjects and use a variety of different tasks (silent naming, word-picture matching, category fluency) and materials (pictures, silhouettes, words). Although regions of activation specific to living or non-living things have been identified, these regions are

The internal structure of categories and concepts

Explaining category-specific deficits in terms of damage to distinct conceptual stores does not in itself elucidate the structure and content of the concepts within those stores, and therefore cannot provide an adequate explanation for the detailed pattern of semantic deficits observed in patients. Brain damage does not selectively impair a specific type of knowledge or property in an all-or-none manner. Categories within domains are not always equally impaired – for example, musical

Organization of semantic space

None of the major models of conceptual knowledge (domain-specific, sensory–functional and conceptual structure) can currently account for all of the neuropsychological data. The strength of connectionist models is that they have the potential to account for seemingly complex patterns of impaired and preserved features which result in category-specific deficits, although they are not yet sufficiently well-formulated to account for all of the data. For example, our current model predicts that

Conclusions

Understanding the functional and neural architecture of the conceptual system remains a huge, but important, challenge. However, distributed, feature-based accounts of conceptual knowledge provide a promising way forward in terms of explaining the complex patterns of behavioural deficits that arise following brain damage. Moreover, this general approach provides a theoretical context within which integrated accounts of the functional and neural properties of conceptual knowledge can be

Questions for future research

•
Can existing theories of conceptual knowledge go beyond the representation of concrete nouns (carrots, cats, corkscrews) to other word categories (e.g. abstract nouns, verbs, adjectives)? Are concrete nouns a special case?
•
Connectionist accounts of concept representation have incorporated a relatively small number of factors: feature overlap, sparsity, correlation and distinctiveness. Can we identify other important determinants of conceptual structure and model them successfully in a

Acknowledgements

This work was supported by an MRC programme grant to L.K. Tyler and W.D. Marslen-Wilson, and a Wellcome Trust Fellowship to H.E. Moss. We thank Rebekah Anokhina, Mike Greer, and William Marslen-Wilson for their contributions.

Glossary

Category:: Refers to individual semantic categories at the superordinate level; for example, animals, tools, fruit.
Category-specific semantic deficit:: following Caramazza ²⁹ we use this term to refer to deficits that are genuinely semantic in nature – that is, they affect the ability to access conceptual knowledge from all modalities of input, and under all output requirements. This review does not extend to patients whose deficits are restricted to a particular output route (e.g. spoken naming)

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Refined grounded cognition accounts propose that abstract concepts might be grounded in brain circuits involved in mentalizing. In the present event-related potential (ERP) study, we compared the time course of neural processing in response to semantically predefined abstract mental states and verbal association concepts during a lexical decision task. In addition to scalp ERPs, source estimates of underlying volume brain activity were determined to reveal spatio-temporal clusters of greater electrical brain activity to abstract mental state vs. verbal association concepts, and vice versa. Source estimates suggested early (onset 194 ms), but short-lived enhanced activity (offset 210 ms) to verbal association concepts in left occipital regions. Increased occipital activity might reflect retrieval of visual word form or access to visual conceptual features of associated words. Increased estimated source activity to mental state concepts was obtained in visuo-motor (superior parietal, pre- and postcentral areas) and mentalizing networks (lateral and medial prefrontal areas, insula, precuneus, temporo-parietal junction) with an onset of 212 ms, which extended to later time windows. The time course data indicated two processing phases: An initial conceptual access phase, in which linguistic and modal brain circuits rapidly process features depending on their relevance, and a later conceptual elaboration phase, in which elaborative processing within feature-specific networks further refines the concept. This study confirms the proposal that abstract concepts are based on representations in distinct neural circuits depending on their semantic feature content. The present research also highlights the importance of investigating sets of abstract concepts with a defined semantic content.
Impaired semantic categorization during transcranial direct current stimulation of the left and right inferior parietal lobule: Impaired semantic categorization
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We investigated whether semantic knowledge is organized according to domain- or feature-dimensions during a semantic categorization task. In addition, using transcranial direct current stimulation (tDCS), we assessed whether the left or right inferior parietal lobule is differentially engaged based on these dimensions. To this end, four different tDCS electrode montage groups were employed (anodal left, cathodal left, anodal right, cathodal right). Reaction times and accuracy were recorded in response to visually presented words (living and non-living concepts with a high or low number of features). In line with our expectations, living concepts elicited faster reaction times compared with non-living concepts and concepts with a high number of features elicited faster reaction times compared with concepts with a low number of features. In addition, a general, regionally and polarity-unspecific, deteriorating effect of tDCS emerged, with stimulation slowing down reaction times compared with sham. The results are discussed in the frameworks of major theories on the organization of semantic knowledge, including the Distributed Domain-Specific Hypothesis.
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Concepts held in long-term memory are the basic building blocks of cognition because they constitute the meaning of objects, events, and abstract ideas. Embodied cognition theories assume that concepts are essentially constituted by reinstatements of experiences related to perception and introspection as well as to bodily actions. In this article, we provide a comprehensive overview of the latest research on embodied cognition in the domains of memory for concrete, abstract and number concepts as well as for reading and writing. Reviewed evidence indicates that even the most complex and abstract thoughts are grounded in modal systems and are not abstract-symbolic.
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Citation Excerpt :
This intercorrelation theory states that concepts are represented as patterns of activation over multiple semantic properties within a unitary distributed system. This intercorrelation theory is appealing in that it does not rely on damage to specific subtypes of attribute (visual, associative, motor) to produce category-specific deficits (Caramazza et al., 1990; Caramazza and Shelton, 1998; Tyler and Moss, 2001). Still another account holds that living items contain a larger number of structurally similar exemplars (e.g. many different types of trees), requiring a more fine-grained visual analysis for successful recognition (Sartori et al., 1993).
Object and scene recognition both require mapping of incoming sensory information to existing conceptual knowledge about the world. A notable finding in brain-damaged patients is that they may show differentially impaired performance for specific categories, such as for “living exemplars”. While numerous patients with category-specific impairments have been reported, the explanations for these deficits remain controversial. In the current study, we investigate the ability of a brain injured patient with a well-established category-specific impairment of semantic memory to perform two categorization experiments: ‘natural’ vs. ‘manmade’ scenes (experiment 1) and objects (experiment 2). Our findings show that the pattern of categorical impairment does not respect the natural versus manmade distinction. This suggests that the impairments may be better explained by differences in visual features, rather than by category membership. Using Deep Convolutional Neural Networks (DCNNs) as ‘artificial animal models’ we further explored this idea. Results indicated that DCNNs with ‘lesions’ in higher order layers showed similar response patterns, with decreased relative performance for manmade scenes (experiment 1) and natural objects (experiment 2), even though they have no semantic category knowledge, apart from a mapping between pictures and labels. Collectively, these results suggest that the direction of category-effects to a large extent depends, at least in MS′ case, on the degree of perceptual differentiation called for, and not semantic knowledge.
Category-specific activations depend on imaging mode, task demand, and stimuli modality: An ALE meta-analysis
2021, Neuropsychologia
The cortical organization of the semantic network has been examined extensively in neuropsychological and neuroimaging studies; however, after decades of research, several issues remain controversial. A comprehensive and systematic investigation is needed to characterize the consistent patterns of category-specific activations as well as to examine factors that contribute to the varying findings across numerous neuroimaging studies. In this study, we reviewed 113 published papers that reported category-specific activations for living or nonliving concepts from the past two decades. Using the Activation Likelihood Estimate (ALE) method, we characterized the brain regions associated with living and nonliving concepts and revealed how the observed patterns were heavily influenced by methodological factors including imaging mode, task demand, and stimuli modality. Our findings provided the most comprehensive summary of category-specific activations for living and nonliving concepts and critically revealed that these activation patterns are highly contextually dependent. This work advanced our knowledge about the organization of the cortical semantic network and provided important insights into theoretical accounts and future research directions.

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Trends in Cognitive Sciences

ReviewTowards a distributed account of conceptual knowledge

Abstract

Section snippets

Domain/category-specific deficits

Evidence from neuroimaging

The internal structure of categories and concepts

Organization of semantic space

Conclusions

Questions for future research

Acknowledgements

Glossary

Brain

Psychonomic Bull. Rev.

Brain Lang.

Brain Lang.

Cognit Neuropsychol.

Cognit. Neuropsychol.

Neuropsychologia

Cognit. Neuropsychol

Neurocase

Brain

Proc. R. Soc. London Ser. B

Nature

Domain-specific knowledge systems in the brain: the animate–inanimate distinction

J. Cogn. Neurosci.

Reversal of the concreteness effect in a patient with semantic dementia

Cognit. Neuropsychol.

Concrete word dyslexia

Br. J. Psychol.

Abstract word deficits in aphasia: evidence from semantic priming

Neuropsychology

Dissociated naming and locating of body parts after left anterior temporal lobe resection: an experimental case study

Brain Lang.

Category-specific comprehension deficit restricted to body parts

Neurocase

Category-specific versus modality-specific aphasia for colours: a review of the pioneer case studies

Int. J. Neurosci.

Progressive language impairment without dementia: a case with isolated category specific semantic impairment

J. Neurol. Neurosurg. Psychiatry

Category-specific deficits: the role of familiarity re-examined

Neuropsychology

Are semantic systems separately represented in the brain? The case of living category impairment

Cortex

Neural subsystems for knowledge

Nature

Category-specific naming and comprehension impairment: a double dissociation

Brain Lang.

Semantic category dissociations: a longitudinal study of two cases

Cortex

Category specific semantic impairments

Brain

Category-specific naming deficit following cerebral infarct

Nature

Review
Towards a distributed account of conceptual knowledge