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Biomedical subjects

A Pollock

Publications and source records attributed to A Pollock.

At least 19 recordsLinked to original sources
PubMed1992

Public health heresy.

Explore the source record for details and available documents.

Public Health Administration↗
PubMed1992

Semantic additivity and semantic inhibition: dissociable processes in the cerebral hemispheres?

We report the results of two visual half-field semantic priming experiments using a high proportion of related trials to examine hemisphere asymmetries for semantic processes beyond those attributable to automatic meaning activation. Contrary to previous investigations, we obtained inhibition for unrelated trials in both visual fields. However, priming was additive (being greater for words related via category membership and association than for either single dimension) only when words were presented to the RVF/left hemisphere. A third experiment, using centrally presented stimuli, implied that semantic additivity should be attributed to post-access meaning comparisons and inhibition to the generation of semantic expectancies. These results suggest (1) that inhibition and additivity are potentially dissociable "controlled" semantic processes and (2) that the left hemisphere predominates for meaning integration across successively presented words. The availability of finely tuned meaning integration processes in the left hemisphere may contribute to its superiority in language processing, despite right hemisphere competence for some semantic operations.

Adult↗
PubMed1992

Radioimmunoassay that measures serum vitamin B12.

AIMS: To develop a specific radioimmunoassay for the routine determination of serum vitamin B12. METHODS: Antisera were raised in rabbits by immunisation with the monocarboxylic acid derivative of cyanocobalamin coupled to human serum albumin. Antibody titres and affinities were determined and the antiserum giving the highest binding affinity constant, Ka, was used to develop the assay protocol. Donkey-anti-rabbit gamma globulin-coated magnetisable particles were used to separate the bound from free vitamin B12. The considerable cobalamin binding capacity of human serum was destroyed by autoclaving in acetate-cyanide buffer. Sixty samples were assayed by the radioimmunoassay (RIA) and the Lactobacillus leichmannii assay. Recovery and cross-reactivity experiments were performed. RESULTS: Final rabbit antibody titres varied from 1/20,000 to 1/188,000. Scatchard plots did not correlate with the antibody titres. The Ka values varied from 2.6 to 6.7 x 10(10) litres/mol. For maximum sensitivity the highest Ka (titre 1/66,000) was chosen. A tracer concentration of 22 pmol/l, an antiserum dilution of 1/100,000, and a sample volume of 0.1 ml were used. At an antiserum dilution of 1 in 100,000 the cyanocobalamin binding of the rabbit serum was diluted out. The assay showed excellent correlation with the microbiological assay, with 100% recovery of added vitamin B12. Levels of cross-reactivity for dicyanide cobinamide and hydroxocobalamin were 9.8 and 8.1%, respectively. CONCLUSIONS: The development of this immunoassay permits the measurement of serum vitamin B12 without important interference from cobalamin analogues, related corrinoids, and non-specific binders.

Animals↗
PubMed1992

Use of technicon H*1 technology in routine thalassaemia screening.

In a retrospective study of 36 cases of alpha-thalassaemia trait, 43 cases of beta-thalassaemia trait and 45 cases of iron deficiency, we have assessed the performance of the Technicon H*1 erythrogram, the hypochromia minus microcytosis (H-M) index, and the discriminant function (DF). The diagnostic accuracy of the erythrogram pattern was 83.3% for alpha-thalassaemia trait and 95.3% for beta-thalassaemia trait. The diagnostic accuracy for the H-M index was 19.4% for alpha-thalassaemia trait, 72.1% for beta-thalassaemia trait and 91.1% for iron deficiency. By comparison, the DF gave a diagnostic accuracy of 75.0% for alpha-thalassaemia trait, 81.4% for beta-thalassaemia trait and 88.9% for iron deficiency when using a locally derived value for the constant (k) = 19.2. Our study shows that the H*1 erythrogram pattern, the H-M index and the DF are useful predictive indicators in routine laboratory screening for thalassaemia.

Discriminant Analysis↗
PubMed1992

The significance of neopterin and biopterin concentrations at presentation in haematological malignancies.

Urinary neopterin and biopterin concentrations were measured in 32 healthy controls and 53 patients with newly diagnosed haematological malignancies classified and staged by accepted criteria. The neopterin concentrations were only significantly raised in chronic lymphocytic leukaemia at stages III-IV. Total biopterin concentrations after oxidation with iodine at acid pH were decreased in chronic lymphocytic leukaemia stages O-II, multiple myeloma, and acute myeloid leukaemia but not in chronic lymphocytic leukaemia stages III-IV. Although of research interest, neopterin concentrations proved of little prognostic value at presentation, but taken with the biopterin concentration they may be useful for the assessment of tumour activity.

Biomarkers, Tumor↗
PubMed1990

Semantic and associative priming in the cerebral hemispheres: some words do, some words don't ... sometimes, some places.

This study investigated spreading activation for words presented to the left and right hemispheres using an automatic semantic priming paradigm. Three types of semantic relations were used: similar-only (Deer-Pony), associated-only (Bee-Honey), and similar + associated (Doctor-Nurse). Priming of lexical decisions was symmetrical over visual fields for all semantic relations when prime words were centrally presented. However, when primes and targets were lateralized to the same visual field, similar-only priming was greater in the LVF than in the RVF, no priming was obtained for associated-only words, and priming was equivalent over visual fields for similar + associated words. Similar results were found using a naming task. These findings suggest that it is important to lateralize both prime and target information to assess hemisphere-specific spreading activation processes. Further, while spreading activation occurs in either hemisphere for the most highly related words (those related by category membership and association), our findings suggest that automatic access to semantic category relatedness occurs primarily in the right cerebral hemisphere. These results imply a unique role for the right hemisphere in the processing of word meanings. We relate our results to our previous proposal (Burgess & Simpson, 1988a; Chiarello, 1988c) that there is rapid selection of one meaning and suppression of other candidates in the left hemisphere, while activation spreads more diffusely in the right hemisphere. We also outline a new proposal that activation spreads in a different manner for associated words than for words related by semantic similarity.

Adult↗
PubMed1990

Basal serum dehydroepiandrosterone sulphate concentration does not predict the cortisol response to provocative testing.

The concentration of dehydroepiandrosterone sulphate (DHEAS) was measured in the plasma of 104 patients aged 16-78 years (48 men) undergoing routine assessment of anterior pituitary reserve. A fasting plasma sample was collected at 0900 h on the same day that either an insulin tolerance test or a glucagon stimulation test was performed. Serum cortisol, DHEAS and prolactin were measured by radioimmunoassay. DHEAS levels between 0.5 and 14 nmol/L were significantly but negatively correlated with age but there was no significant correlation with basal cortisol, maximum stimulated cortisol, the increment in cortisol or basal prolactin. The correlation of DHEAS with age was also observed when results for women were analysed separately but this did not hold for men. For male and female results separately, there was again no correlation of basal DHEAS with basal cortisol, maximum stimulated cortisol, increment of cortisol or basal prolactin. The age and sex related reference range and other factors affecting basal DHEAS concentration make it a cumbersome and unreliable measure of hypothalamic-pituitary-adrenal axis reserve.

Adolescent↗
PubMed1989

Advantages of IRMA over RIA in the measurement of ACTH.

A technically simple and rapid two-site immunoradiometric assay (IRMA) for human ACTH, based on monoclonal antibodies (MAbs), was compared with a clinically validated ACTH radioimmunoassay (RIA). Both methods measure ACTH 1-39 in unextracted plasma and cross-react less than 0.5% with ACTH fragments. ACTH levels were assessed in 103 patient samples: for concentrations in the range 5.3-1000 ng/L, results by the two methods were significantly correlated (r = 0.82, n = 86, P less than 0.001). The IRMA was more sensitive and had a wider working range than the RIA (detection limits 5.3 ng/L (IRMA) vs 11 ng/L (RIA); CV less than 10% between 19 and 1000 ng/L (IRMA) and CV less than 15% between 30 and 400 ng/L (RIA). In two patients for whom discrepant results were obtained, measurement of ACTH by bioassay and ACTH precursors by direct IRMA demonstrated the greater accuracy of the ACTH IRMA result. The improved performance of the IRMA combined with its many practical advantages compared to RIA, make it ideal for use in detailed clinical and physiological studies which have previously been hampered by the poor reliability of ACTH measurement.

Adrenocorticotropic Hormone↗
PubMed1988

Lexical decision and naming asymmetries: influence of response selection and response bias.

Signal detection measures were used to evaluate the effects of several response variables (manual vs. vocal, Go-NoGo vs. Yes-No) on lexical decision asymmetries. An unvarying right visual field advantage in discriminability (d') was observed in each condition. However, response criteria (beta) varied over visual fields and conditions. Naming and lexical decision were shown to have equivalent asymmetries when the effects of response bias are removed. The results indicate that postaccess decision processes make important contributions to lexical decision asymmetries.

Adult↗