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David C. Plaut - One of the best experts on this subject based on the ideXlab platform.

  • Published In JOURNAL OF COGNITIVE NEUROSCIENCE, 7. Systematicity and Specialization in Semantics: A Computational Account of Optic Aphasia
    2016
    Co-Authors: Sean Mcguire, David C. Plaut
    Abstract:

    AbstractOptic aphasic patients are selectively impaired at naming visu-ally presented objects but demonstrate relative intact compre-hension of those objects (e.g., by gesturing or categorization) and are able to name them when presented in other modalities (e.g., via tactile input). This and other modality-specific nam-ing deficits have been taken as evidence that semantics is or-ganized into distinct modality-specific subsystems. We adopt an alternative view in which semantics is a set of learned, in-ternal representations within a parallel distributed processing system that maps between multiple input and output modal-ities. We account for the critical aspects of Optic Aphasia in terms of the effects of damage to such a system, despite its lack of modality-specific specialization. We show that the ro-bustness of a task in such a system depends critically on its systematicity, and that modality-specific naming deficits can arise because naming is an unsystematic task

  • Systematicity and Specialization
    2007
    Co-Authors: In Semantics David, David C. Plaut
    Abstract:

    Most models of cognitive processing assume a considerable amount of built-in structure in the cognitive system, such as modality-specific semantic systems. Such structural distinctions are thought to be necessary to account for various neuropsychological dissociations, including the selective impairment of visual object naming with spared tactile naming and visual gesturing, known as Optic Aphasia. A distributed connectionist simulation is presented in which Optic Aphasia occurs following damage as a result of more graded representational specialization. This specialization emerges through learning under the combined influence of two general factors: the relative systematicity of mappings between input and output modalities, and a topographic bias favoring short connections. The results raise the possibility that much of the structure of the lexical/semantic system can be derived from general learning principles and need not assumed a priori

  • Systematicity and Specialization in Semantics: A Computational Account of Optic Aphasia
    Erlbaum, 1997
    Co-Authors: Sean Mcguire, David C. Plaut
    Abstract:

    Optic aphasic patients are selectively impaired at naming visually presented objects but demonstrate relative intact comprehension of those objects (e.g., by gesturing or categorization) and are able to name them when presented in other modalities (e.g., via tactile input). This and other modality-specific naming deficits have been taken as evidence that semantics is organized into distinct modality-specific subsystems. We adopt an alternative view in which semantics is a set of learned, internal representations within a parallel distributed processing system that maps between multiple input and output modalities. We account for the critical aspects of Optic Aphasia in terms of the effects of damage to such a system, despite its lack of modality-specific specialization. We show that the robustness of a task in such a system depends critically on its systematicity, and that modality-specific naming deficits can arise because naming is an unsystematic task. Introduction The lexical sema..

  • Systematicity and Specialization in Semantics: A Computational Account of Optic Aphasia
    1996
    Co-Authors: Sean Mcguire, David C. Plaut
    Abstract:

    Modality-specific naming deficits, such as Optic Aphasia, have been taken as evidence that semantics is organized into distinct modality-specific subsystems. We adopt an alternative view in which semantics is a learned, internal representation within a parallel distributed processing system that maps between multiple input and output modalities. We show that the robustness of a task to damage depends critically on its systematicity, and that modality-specific naming deficits can arise because naming is an unsystematic task. 2 Background What is the organization of semantic knowledge of objects? Standard view: A single, amodal semantic system (Caramazza et al., 1990; Hillis & Caramazza, 1995; Riddoch et al., 1988) Visual Input Verbal Input Tactile Input Action (Gesturing) Phonology (Naming) Semantics Challenge: Performance of brain-damaged patients with modality-specific naming disorders (e.g., Optic Aphasia) (Gil et al., 1985; Lhermitte & Beauvois, 1973; Riddoch & Humphreys, 1987)..

  • systematicity and specialization in semantics a computational account of Optic Aphasia
    1996
    Co-Authors: Sean Mcguire, David C. Plaut
    Abstract:

    Optic aphasic patients are selectively impaired at naming visually presented objects but demonstrate relative intact comprehension of those objects (e.g., by gesturing or categorization) and are able to name them when presented in other modalities (e.g., via tactile input). This and other modality-specific naming deficits have been taken as evidence that semantics is organized into distinct modality-specific subsystems. We adopt an alternative view in which semantics is a set of learned, internal representations within a parallel distributed processing system that maps between multiple input and output modalities. We account for the critical aspects of Optic Aphasia in terms of the effects of damage to such a system, despite its lack of modality-specific specialization. We show that the robustness of a task in such a system depends critically on its systematicity, and that modality-specific naming deficits can arise because naming is an unsystematic task.

M Poncet - One of the best experts on this subject based on the ideXlab platform.

  • Optic Aphasia with pure alexia a mild form of visual associative agnosia a case study
    Cortex, 1998
    Co-Authors: V Chanoine, Teixeira C Ferreira, Jeanfrancois Demonet, J L Nespoulous, M Poncet
    Abstract:

    Abstract A single-case study is reported of a naming disorder selective to the visual modality. The patient showed intact access to structural knowledge of objects and letters, but impaired access to complete semantic knowledge of objects and alphabetical knowledge of letters from visual input. The impairment was most striking when the patient had to discriminate between semantically similar objects or within a given symbolic repertoire, i.e. letters. The co-occurrence of a partial deficit of visual recognition for objects and for letters indicated features of Optic Aphasia and pure alesia. This symmetric performance between object and letter processing may also constitute a mild form of visual associative agnosia.

  • Optic Aphasia evidence of the contribution of different neural systems to object and action naming
    Cortex, 1997
    Co-Authors: Carla Teixeira Ferreira, Bernard Giusiano, Mathieu Ceccaldi, M Poncet
    Abstract:

    Visual stimulus naming was studied in a 66-year-old male patient with Optic Aphasia subsequent to left occipito-temporal infarction. While having difficulty in naming objects perceived visually, he was able to name objects by viewing gestures illustrating their use, and to name actions shown in pictures. These results suggest that naming performance depends on the kind of stimulus that is visually presented (object vs. action). The present findings lend support to congnitive models which postulate the existence of visual and functional semantic systems.

Morihiro Sugishita - One of the best experts on this subject based on the ideXlab platform.

  • modality specific naming and gesture disturbances a case with Optic Aphasia bilateral tactile Aphasia Optic apraxia and tactile apraxia
    Cortex, 1996
    Co-Authors: Kunihiko Endo, Hideo Makishita, Nobuo Yanagisawa, Morihiro Sugishita
    Abstract:

    This study reports a patient who manifested Optic Aphasia, tactile Aphasia, Optic apraxia, and tactile apraxia following an operation for epidural left parietal haematoma. He could neither name nor pantomime the use of objects presented visually or tactually, but correctly performed semantic association tasks, thus demonstrating preserved recognition. He could name and pantomime the use of auditorily presented objects. Experimental results disproved that pantomime disorders were secondary to naming disorders, and suggested that modality specific Aphasia and modality specific apraxia are independent clinical syndromes. CT scans showed injury to the posterior callosal radiations, the white matter of the angular gyrus, and the medial portion of the occipital lobe in the left hemisphere. We suggest that modality specific Aphasia and modality specific apraxia can be explained by assuming a common semantic memory store.

Martha J Farah - One of the best experts on this subject based on the ideXlab platform.

  • superadditive effects of multiple lesions in a connectionist architecture implications for the neuropsychology of Optic Aphasia
    Psychological Review, 2000
    Co-Authors: Mark Sitton, Michael C Mozer, Martha J Farah
    Abstract:

    Traditional accounts of neuropsychological disorders have been based on the assumption that brain damage results in a single focal lesion of the cognitive architecture. Although this strategy has been productive for neuropsychology, some syndromes defy explanation in this way, resulting in an unparsimonious architecture with many specialized components or connections. Optic Aphasia is one such syndrome. Patients with Optic Aphasia have difficulty naming visually presented objects. However, the deficit is not in visual recognition per se because patients can pantomime the appropriate use of objects, and the deficit is not in naming per se because they can name objects from auditory cues. To explain Optic Aphasia, past accounts have hypothesized multiple semantic systems or multiple functional pathways to visual naming. Farah (1990) instead sketched an account based on lesions to multiple pathways—one that maps visual input to semantics, and the other that maps semantics to naming responses. This account supposes that the effects of the two lesions are superadditive, meaning that a task requiring both damaged pathways (e.g., naming a visually presented object) would manifest a much higher error rate than expected based on the sum of error rates on two tasks requiring just one pathway or the other (e.g., gesturing the appropriate use of a visually presented object, and naming from auditory cues). We have explored this hypothesis by modeling superadditive effects of damage in a connectionist architecture. The resulting model explains other phenomena associated with Optic Aphasia, including the tendencies of patients to: produce a large number of naming errors that are semantically related to the target but few visually related errors, show response perseveration from one trial to the next, “home in” on the correct response over time, and make fewer errors on naming from a verbal description than on gesturing the use of an object from a visual presentation. More broadly, superadditive effects of damage provide a novel class of explanations for neuropsychological deficits that might previously have seemed to imply the existence of highly specialized processing components.

  • a superadditive impairment theory of Optic Aphasia
    Neural Information Processing Systems, 1997
    Co-Authors: Michael C Mozer, Mark Sitton, Martha J Farah
    Abstract:

    Accounts of neurological disorders often posit damage to a specific functional pathway of the brain. Farah (1990) has proposed an alternative class of explanations involving partial damage to multiple pathways. We explore this explanation for Optic Aphasia, a disorder in which severe performance deficits are observed when patients are asked to name visually presented objects, but surprisingly, performance is relatively normal on naming objects from auditory cues and on gesturing the appropriate use of visually presented objects. We model this highly specific deficit through partial damage to two pathways-one that maps visual input to semantics, and the other that maps semantics to naming responses. The effect of this damage is superadditive, meaning that tasks which require one pathway or the other show little or no performance deficit, but the damage is manifested when a task requires both pathways (i.e., naming visually presented objects). Our model explains other phenomena associated with Optic Aphasia, and makes testable experimental predictions.

Tim Shallice - One of the best experts on this subject based on the ideXlab platform.

  • perseverative and semantic influences on visual object naming errors in Optic Aphasia a connectionist account
    Journal of Cognitive Neuroscience, 1993
    Co-Authors: David C. Plaut, Tim Shallice
    Abstract:

    Although perseveration---the inappropriate repetition of previous responses---is quite common among patients with neurological damage, relatively few detailed computational accounts of its various forms have been put forth. A particularly well-documented variety involves the pattern of errors made by “Optic aphasic” patients, who have a selective deficit in naming visually presented objects. Based on our previous work in modeling impaired reading via meaning in deep dyslexia, we develop a connectionist simulation of visual object naming. The major extension in the present work is the incorporation of short-term correlational weights that bias the network towards reproducing patterns of activity that have occurred on recently preceding trials. Under damage, the network replicates the complex semantic and perseverative effects found in the Optic aphasic error pattern. Further analysis reveals that the perseverative effects are strongest when the lesions are near or within semantics, and are relatively mild when the preceding object evokes no response. Like Optic aphasics, the network produces predominantly semantic rather than visual errors because, in contrast to reading, there is some structure in the mapping from visual to semantic representations for objects. Viewed together with the dyslexia simulations, the replication of complex empirical phenomena concerning impaired visual comprehension based on a small set of general connectionist principles strongly suggests that these principles provide important insights into the nature of semantic processing of visual information and its breakdown following brain damage.

  • Perseverative and Semantic Influences on Visual Object Naming Errors in Optic Aphasia: A Connectionist Account
    1992
    Co-Authors: Cognitive Neuroscience, David C. Plaut, Connectionist A Account, Tim Shallice
    Abstract:

    A recurrent back-propagation network is trained to generate semantic representations of objects from high-level visual representations. In addition to the standard weights, the network has correlational weights useful for implementing short-term associative memory. Under damage, the network exhibits the complex semantic and perseverative effects of patients with a visual naming disorder known as "Optic Aphasia," in which previously presented objects influence the response to the current object. Like Optic aphasics, the network produces predominantly semantic rather than visual errors because, in contrast to reading, there is some structure in the mapping from visual to semantic representations for objects. Most of the research presented in this paper was carried out while the authors were visiting scientists in the Departments of Psychology and Computer Science at the University of Toronto under the generous support and guidance of Geoff Hinton. We also wish to thank Marlene Behrmann..