Category-specific Impairment Research Articles

A Spurious Category-Specific Visual Agnosia for Living Things in Normal Human and Nonhuman Primates

Abstract Patients with visual associative agnosia have a particular difficulty in identifying visually presented living things (plants and animals) as opposed to nonliving things. It has been claimed that this effect cannot be explained by differences in the inherent visual discriminability of living and nonliving things. To test this claim further, we performed two experiments with normal subjects. In Experiment 1 normal human observers were asked to identify objects in tachistoscopically presented line drawings. They made more errors with living things than with nonliving things. In Experiment 2 normal monkeys learned to discriminate among the same line drawings for food reward. They made many more errors in discriminating among living things than nonliving things. Agnosic patients' responses to the same line drawings were made available to us for correlative analysis with the subjects' responses to these drawings in Experiments 1 and 2. We conclude that a category-specific visual agnosia for living things can arise as a consequence of a modality-specific but not category-specific impairment in visual representation, since living things are more similar to each other visually than nonliving things are.

Calling a squirrel a squirrel but a canoe a wigwam: a category-specific deficit for artefactual objects and body parts

Abstract A single-case study is reported of a patient, CW, with a category-specific deficit for naming artefactual objects and body parts along with good naming of natural objects. Tests using matching rather than naming techniques further suggested that CW had some difficulty in distinguishing between close semantic co-ordinates of artefactual objects. The case provides a double dissociation relative to patients with selective problems in identifying natural objects. Possible reasons for CW's category-specific impairment are discussed.

A computational model of semantic memory impairment: Modality specificity and emergent category specificity.

It is demonstrated how a modality-specific semantic memory system can account for category-specific impairments after brain damage. In Experiment 1, the hypothesis that visual and functional knowledge play different roles in the representation of living things and nonliving things is tested and confirmed. A parallel distributed processing model of semantic memory in which knowledge is subdivided by modality into visual and functional components is described. In Experiment 2, the model is lesioned, and it is confirmed that damage to visual semantics primarily impairs knowledge of living things, and damage to functional semantics primarily impairs knowledge of nonliving things. In Experiment 3, it is demonstrated that the model accounts naturally for a finding that had appeared problematic for a modality-specific architecture, namely, impaired retrieval of functional knowledge about living things. Finally, in Experiment 4, it is shown how the model can account for a recent observation of impaired knowledge of living things only when knowledge is probed verbally.

A computational model of semantic memory impairment: Modality specificity and emergent category specificity.

It is demonstrated how a modality-specific semantic memory system can account for category-specific impairments after brain damage. In Experiment 1, the hypothesis that visual and functional knowledge play different roles in the representation of living things and nonliving things is tested and confirmed. A parallel distributed processing model of semantic memory in which knowledge is subdivided by modality into visual and functional components is described. In Experiment 2, the model is lesioned, and it is confirmed that damage to visual semantics primarily impairs knowledge of living things, and damage to functional semantics primarily impairs knowledge of nonliving things. In Experiment 3, it is demonstrated that the model accounts naturally for a finding that had appeared problematic for a modality-specific architecture, namely, impaired retrieval of functional knowledge about living things. Finally, in Experiment 4, it is shown how the model can account for a recent observation of impaired knowledge of living things only when knowledge is probed verbally.

Interaction between vision and language in category-specific semantic impairment

Abstract A category-specific semantic disorder, selectively affecting Living things and food and sparing inanimate objects, was observed in a patient (LA) who had made a partial recovery from herpes simplex encephalitis. This impairment was observed to have similar characteristics both with verbal and pictorial material, and a significant degree of consistency was observed between repeated presentations and across various modalities of administration of the same stimuli. In order to study the possible role of interactions between verbal-semantic and visual-semantic impairment, we constructed a test of “naming animals by definitions”, in which two sorts of definitions were contrasted: (1) those stressing visual perceptual features; and (2) those using verbal metaphorical expressions, or a description of the function accomplished by that animal for man, to allow identification. LA performed much better in the second than in the first condition. On the grounds of these results, the following hypotheses were ...