Showing papers by "Medical Research Council published in 1986"

Attention to action: willed and automatic control of behavior

Abstract: Much effort has been made to understand the role of attention in perception; much less effort has been placed on the role attention plays in the control of action Our goal in this chapter is to account for the role of attention in action, both when performance is automatic and when it is under deliberate conscious control We propose a theoretical framework structured around the notion of a set of active schemas, organized according to the particular action sequences of which they are a part, awaiting the appropriate set of conditions so that they can become selected to control action The analysis is therefore centered around actions, primarily external actions, but the same principles apply to internal actions—actions that involve only the cognitive processing mechanisms One major emphasis in the study of attentional processes is the distinction between controlled and automatic processing of perceptual inputs (eg, Shiffrin & Schneider, 1977) Our work here can be seen as complementary to the distinction between controlled and automatic processes: we examine action rather than perception; we emphasize the situations in which deliberate, conscious control of activity is desired rather than those that are automatic

Mental models: towards a cognitive science of language, inference, and consciousness

Abstract: Mental Models offers nothing less than a unified theory of the major properties of mind: comprehension, inference, and consciousness. In spirited and graceful prose, Johnson-Laird argues that we apprehend the world by building inner mental replicas of the relations among objects and events that concern us. The mind is essentially a model-building device that can itself be modeled on a digital computer. This book provides both a blueprint for building such a model and numerous important illustrations of how to do it. In several key areas of cognition, Johnson-Laird shows how an explanation based on mental modeling is clearly superior to previous theory. For example, he argues compellingly that deductive reasoning does not take place by tacitly applying the rules of logic, but by mentally manipulating models of the states of affairs from which inferences are drawn. Similarly, linguistic comprehension is best understood not as a matter of applying inference rules to propositions derived from sentences, but rather as the mind's effort to construct and update a model of the situation described by a text or a discourse. Most provocative, perhaps, is Johnson-Laird's theory of consciousness: the mind's necessarily incomplete model of itself allows only a partial control over the many unconscious and parallel processes of cognition. This an extraordinarily rich book, providing a coherent account of much recent experimental work in cognitive psychology, along with lucid explanations of relevant theory in linguistics, computer science, and philosophy Not since Miller, Galanter, and Pribram's classic Plans and the Structure of Behavior has a book in cognitive science combined such sweep, style, and good sense. Like its distinguished predecessor, Mental Models may well serve to fix a point of view for a generation. (http://books.google.fr/books?id=FS3zSKAfLGMC&printsec=frontcover&hl=fr#v=onepage&q&f=false)

Antigens induced on erythrocytes by P. falciparum: expression of diverse and conserved determinants

Abstract: Red blood cells that are infected with the malaria parasite Plasmodium falciparum express new antigens on their surface. In a study of these antigens in the erythrocytes of naturally infected children in the Gambia, an antibody-mediated agglutination assay revealed an extreme degree of antigenic diversity. Serum samples from each of ten children in the convalescent stage of malaria infection reacted with infected cells from the same child but generally not with infected cells from the other children. The Gambian children's erythrocytes also expressed shared determinants: sera from Gambian adults often reacted with the surface of infected cells from all of the children and were shown by adsorption and elution experiments to contain antibodies that recognized several isolates. Conserved determinants exposed on infected erythrocytes may be important for development of antimalarial immunity either naturally or through vaccination.

A developmental framework for developmental dyslexia.

Abstract: There are surprisingly few theories of the normal development of literacy that take into account the different cognitive processes underlying reading and spelling skills. The present framework suggests three phases, corresponding to the acquisition of logographic, alphabetic, and, finally, orthographic skills. At each phase, a new skill is introduced with either reading (input processes) or writing (output processes) acting as pacemaker. This stepwise progress is driven by a certain opposition between reading and writing processes. At any of the critical points where a new step has to be taken, breakdown can occur. This will result in different types of literacy disorder. However, the disorder will not only be characterized by the deficiency in a particular skill, but also by compensatory skills which will inevitably develop. Only by using models of this type will we be able to achieve a properly developmental perspective for developmental dyslexia.

Starch utilization by the human large intestinal microflora

Abstract: High levels (2-565 units/g) of amylase activity were observed in human faeces. Over 92% of amylase activity in faeces obtained from healthy persons was extracellular, whereas only about 9% of activity was associated with particulate material and washed cells. Bacterial cell-bound amylases were considerably more efficient in breaking down starch, however, than were the soluble enzymes which occurred in cell-free faecal supernatant fluids. Cell population densities of anaerobic starch-hydrolysing bacteria in the stools of ten persons ranged from 1.1 X 10(10) to 3.3 X 10(12)/g of faeces. Identification of 120 starch-hydrolysing colonies isolated from the stools of six subjects showed that the predominant amylolytic bacteria belonged to the genera Bifidobacterium, Bacteroides, Fusobacterium and Butyrivibrio. Mixed populations of gut bacteria rapidly fermented starch with the production of volatile fatty acids and organic acids. Lactate was observed to be a major, though transient intermediate during starch fermentation by these cultures. Approximately 60% of starch utilized was converted to volatile fatty acids, which in the human colon would be potentially available for absorption.

The rDNA of C. elegans: sequence and structure

Abstract: We have sequenced one complete rDNA tandem repeat from the nematode C. elegans. By comparative analysis we derive secondary structures for the 18s, 5.8s, and 26s rRNA molecules, and comment on other important features of the sequence. We also present the sequence of a junction between the rDNA and non-ribosomal DNA. Finally, we use our data to quantify the evolutionary relationships among several organisms currently studied in developmental biology.

Subjective Memory Assessment and Test Performance in Elderly Adults

Abstract: The everyday memory of a group of elderly adults was assessed using techniques developed for use with younger head-injured people (Sunderland et al., 1983). The participants completed a memory questionnaire and a daily checklist; their spouses gave their assessment using a separate questionnaire. These subjective methods showed only moderate agreement, and the questionnaire had low test-retest reliability. It appears that these methods of subjective memory assessment have little validity when used with normal elderly adults. Two positive findings did emerge: As in previous studies, a story recall test was the strongest predictor of reported memory performance; and despite a universal belief among elderly adults that their memory had deteriorated with age, very few of them felt that they were at all handicapped by forgetfulness in everyday life.

Forbear is a homophone: Lexical prosody does not constrain lexical access

Abstract: Because stress can occur in any position within an English word, lexical prosody could serve as a minimal distinguishing feature between pairs of words. However, most pairs of English words with stress pattern opposition also differ vocalically: OBject and obJECT, CONtent and conTENT have different vowels in their first syllables as well as different stress patterns. To test whether prosodic information is made use of in auditory word recognition independently of segmental phonetic information, it is necessary to examine pairs like FORbear - forBEAR or TRUSty - trusTEE, semantically unrelated words which exhibit stress pattern opposition but no segmental difference. In a cross-modal priming task, such words produce the priming effects characteristic of homophones, indicating that lexical prosody is not used in the same way as segmental structure to constrain lexical access.

Suppression of visually evoked postural responses.

Abstract: Normal subjects standing on an earth-fixed force platform inside a movable room displaced at velocities comparable to those accompanying spontaneous body sway, exhibit a visually evoked postural response (VEPR) some 600 ms after the start of the room movement. It consists of a displacement of the centre of force of the body in the direction of the stimulus (primary component), followed shortly by a corrective displacement in the opposite (secondary component). On second presentation of the stimulus VEPR is markedly reduced, but only if full proprioceptive information from the lower limbs is available to the subjects. A patient deprived of this information showed much enhanced VEPR which he was unable to suppress, in contrast to a patient with absent vestibular function who presented normal VEPR. The results show that in the presence of conflict between different sensory clues, vision is initially dominant in sway control, although adaptive processes can quickly rearrange this hierarchy.

Cell division and death in the mouse blastocyst before implantation.

Abstract: The numbers of cells in the trophectoderm (TE) and inner cell mass (ICM) of mouse blastocysts were counted by differentially labelling their nuclei with two polynucleotide-specific fluorochromes. Blastocysts recovered from the uterus at intervals between their formation early on Day 4 to the initial stages of implantation on day 5 were analysed. TE cell number increase was initially rapid, indicating some synchronisation of the sixth division, but slowed down progressively and plateaued on Day 5, possibly due to the onset of primary giant cell formation. ICM cell number increase was slower than the corresponding TE cells. As a result, TE cell number more than quadrupled, whereas ICM cell number only doubled over this period. Although the mitotic index of both populations of cells fell steadily, there was no significant difference between them. The decline in the proportion of ICM cells, therefore, is likely to be due to cell death, first detected in early blastocysts and predominantly located in the ICM. In addition, however, a contribution of ICM cells to the overlying polar TE cannot be excluded.

Ethinyl estradiol and norethindrone in the treatment of primary hyperparathyroidism in postmenopausal women.

Abstract: Treatment with ethinyl estradiol or norethindrone reduces the bone-turnover rate and plasma calcium levels in normal postmenopausal women, without affecting the secretion of calcium-regulating hormones. To assess the effect of these sex steroids in patients with primary hyperparathyroidism, we treated postmenopausal women who had hyperparathyroidism with either ethinyl estradiol (n = 6) or norethindrone (n = 11). After three weeks of treatment, the bone-turnover rate declined and plasma calcium fell from a mean (±1 SE) of 2.77±0.07 mmol per liter (11.1±0.3 mg per deciliter) to 2.58+0.05 mmol per liter (10.3±0.2 mg per deciliter; P<0.01) in the group treated with ethinyl estradiol, and from 2.93±0.08 mmol per liter (11.7±0.3 mg per deciliter) to 2.84±0.08 mmol per liter (11.4±0.3 per deciliter; P<0.05) in the patients who received norethindrone. No significant changes in the plasma levels of parathyroid hormone, calcitonin, or calcitriol were observed after the estrogen-induced increases in vitami...

Associated postural adjustments in Parkinson's disease.

Abstract: Postural activity in muscles of the back and legs associated with voluntary forward elevation of the arm at the shoulder with the subject standing was examined in 14 patients with Parkinson's disease and nine normal individuals. The time of onset of EMG activity in each of the postural muscles, relative to the onset of activity in the prime mover, was the same for both patient and normal groups and did not depend on load. The amplitude of the EMG bursts and their frequency of occurrence, was less in patients off drug treatment and immobile, than when mobile on therapy. We conclude that the timing of associated postural adjustments is normal in Parkinson's disease, although their size may be decreased.

Immunological identification of the genes encoding the four myosin heavy chain isoforms of Caenorhabditis elegans.

Abstract: The nematode Caenorhabditis elegans produces four distinct myosin heavy chain (MHC) isoforms, A, B, C, and D. The MHC A and MHC B proteins are coordinately expressed in the body wall muscle and are incorporated into different regions of a single kind of thick filament. MHC C and MHC D are exclusively produced in the pharyngeal muscle. Previous studies of mutations that affect MHC B have shown that this isoform is encoded by the unc-54 gene. Three other MHC genes, myo-1, myo-2, and myo-3, were isolated from a C. elegans genomic library by hybridization with fragments of the unc-54 gene. We have now established the MHC isoform encoded by each gene. Restriction fragments from each of these genes were cloned in the plasmid expression vector pUR288, producing fusion proteins between Escherichia coli beta-galactosidase and portions of the MHC rod domains of each gene. The hybrid proteins were screened with a panel of 18 isoform-specific monoclonal antibodies. The results demonstrate that myo-1 encodes MHC D, myo-2 encodes MHC C, and myo-3 encodes MHC A.

Identification of isolate-specific proteins on sorbitol-enriched Plasmodium falciparum infected erythrocytes from Gambian patients.

Abstract: We have compared the surface radio-iodinated proteins of uninfected and Plasmodium falciparum-infected erythrocytes from natural infections of human patients. Cryopreserved infected blood from Gambian children with falciparum malaria was thawed, cultured to the middle trophozoite stage, and surface radio-iodinated. Trophozoite-infected cells were enriched about 10-fold on a Percoll gradient newly designed to separate cells based on their differential permeability to sorbitol. Infected blood was radio-iodinated and erythrocyes from the fraction enriched in parasitized cells and uninfected erythrocytes from the same sample obtained from the gradient and compared by SDS–PAGE and autoradiography. In each sample, parasitized erythrocytes contained one or more polypeptides of very high molecular weight (Mr 250000–300000) that were not found on uninfected erythrocytes from the same patient. These proteins were isolate-specific in size and number, suggesting that natural isolates contain a variable number of different P. falciparum phenotypes for this surface protein. In addition, these radio-iodinated surface proteins could not be extracted from the host cell membrane by the non-ionic detergent Triton X-100, but were extracted by SDS. The properties of these proteins suggest they are the equivalent for natural infections of the strain-dependent antigen previously described (Leech, Barnwell, Miller & Howard, 1984) on the surface of P. falciparum-infected Aotus erythrocytes. In addition, we observed a second parasite-dependent modification of labelled proteins on infected erythrocytes with the appearance of a new band of Mr 30000. There were also variations in the pattern of radio-isotope labelled proteins on uninfected erythrocytes from different patients.