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Biomedical subjects

J Davidoff

Publications and source records attributed to J Davidoff.

27 records · Page 2Linked to original sources
PubMed1990

Recognition of unfamiliar faces in prosopagnosia.

Prosopagnosia is clinically defined as a specific and extreme inability to recognize familiar faces. However, doubts have been expressed concerning prosopagnosics' preserved ability to recognize unfamiliar faces and to make other within category discriminations. The present study pursues these doubts. If recognition of unfamiliar faces and objects is intact, then prosopagnosics should demonstrate normal processing for all tasks that depend on the possession of intact stored visual descriptions at the category level. In particular, they should show normal face and object superiority effects. A detailed investigation was carried out on a well documented prosopagnosic (KD) and less extensively on three other (RB, AH and OA) well attested cases. Experiments 1 and 2 considered whether face and object superiority effects were observed in these patients. No difference in the pattern of recognition performance was found between normal and unusual arrangements of faces and objects. Their pattern of performance differed both from unilateral brain-damaged patients and normal controls. The results suggest both that these prosopagnosic patients were impaired on the recognition of unfamiliar faces and that their problem is not specific to faces. Experiment 3 showed that KD was impaired on a face/non-face decision task but appeared to benefit by the stimulus being presented in the normal orientation. For normal controls, mental rotation of a face appeared to be a separate process from face categorization. Experiment 4 found that KD, AH and OA were impaired, compared to normal controls, in their ability to recognize emotional expressions but not more than brain-damaged controls. The impairment of the prosopagnosics tested in the present study is placed at the interaction between stored object descriptions and the structural encoding stage of Bruce and Young. Consideration is given to an elaboration of the structural encoding stage in which boundary (category defining) information is separately processed from surface (detailed texture) information.

Agnosia↗
PubMed1987

Quantitation of T cell antigen-binding molecules (TABM) in the sera of nonimmunized, immunized, and desensitized mice.

Heterologous antibodies to non-MHC-restricted T cell antigen-binding molecules (TABM) were used in an ELISA to detect and quantitate TABM levels in the sera of nonimmune mice and in mice immunized and/or desensitized to methylated bovine serum albumin (MBSA). TABM were detected at low levels in sera from nonimmune and immune mice. Amounts of TABM rose 300-fold in MBSA-immune mice within 12 hr of a desensitizing injection of MBSA, and rapidly returned to pre-desensitization levels. Serum TABM were purified by precipitation with 50% (NH4)2SO4 and chromatography in carboxymethylcellulose. The purified TABM were Mr 30,000 to 37,000 reduced, 72,000 nonreduced, and had a pI range of 5.5 to 7.1. A portion of the elevated TABM in desensitized mice bound MBSA specifically, whereas TABM from the sera of nonimmune/nondesensitized mice did not bind MBSA. The timing of the appearance of TABM early in desensitization suggests the possibility that they may play a role in the subsequent appearance of suppressor cells in later stages of this phenomenon. In addition, the results presented here raise the possibility that fluctuations in TABM levels might prove to be a sensitive indicator of immunoregulatory status in general.

Animals↗
PubMed1985

A case of visual agnosia showing a disorder of pre-semantic visual classification.

A case (J.R.) of associative visual agnosia (loss of meaning for visually presented objects without any serious sensory disorder) is reported. When asked to match a given name to sample the patient made both visual and semantic errors. Whereas semantic errors were reduced by priming, visual errors were intractable. It is argued that there is a disorder at the stage of pre-semantic abstraction, similar to that postulated elsewhere for some cases of deep dyslexia, contributing to the agnosia.

Adult↗
PubMedDate not supplied

Selective impairments of object knowledge in a case of acquired cortical blindness.

A patient (N.B.) is described, who displays distinct deficits of object knowledge related to knowledge type (Functional/Associative vs Visual) and also to knowledge category (Animate vs Inanimate). The patient was first given an orally presented forced-choice test devised to assess orthogonal combinations of knowledge type and knowledge category. In the production of this test it was found that normals took longer to respond to Visual questions than to Functional/Associative questions; therefore, sets of questions were compiled that were matched for both accuracy and latency. There were two main findings concerning N.B.'s semantic memory. First, with careful matching of difficulty level, the patient showed selective preservation of Functional/Associative knowledge of Animate objects compared with Visual knowledge of Animate objects and also compared with Functional/Associative knowledge of Inanimate objects. Second, there was a qualitative difference in patterns of knowledge retrieval for Visual compared with Functional/Associative knowledge. Retrieval of Visual knowledge, both Animate and Inanimate, was inconsistent and, in a word-pair recall test, a high degree of connection of a Visual property to an object did not promote paired-associate learning. In contrast, retrieval of Functional/Associative knowledge (both Animate and Inanimate) was consistent and paired-associate learning was influenced by connection strength. This study provides strong evidence to support the validity of both "knowledge type" and "category" based accounts of the organisation of semantic memory.

Adult↗