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Biomedical subjects

J Davidoff

Publications and source records attributed to J Davidoff.

9 recordsLinked to original sources
PubMed1990

Object superiority: a comparison of complete and part probes.

Previous research on object superiority effects has shown that certain contexts enhance the recognition of an object part. However, those contexts would not normally be called objects. The present study discusses object superiority within more general issues of object recognition. By using what we call 'complete' probes, superiority effects were extended to exposure durations much longer than those used in previous research. Experiments 1 and 2 found that complete probes gave stable superiorities at 250 msec and even 2-sec stimulus exposures. These object superiority effects were found for both objects (faces and chairs) investigated. Experiment 3 showed that object superiorities established with complete probes were not necessarily greater than those for part probes. The experiments stress the role of spatial arrangement of object parts in accessing stored information. It is argued that a successful match of a structural description to a representation in long-term memory influences stimulus processing by allowing the formation of higher level features.

Adult↗
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↗