Showing papers by "University of Aberdeen published in 1968"

Phenomenal simultaneity and the perceptual moment hypothesis

Abstract: Successive brief visual stimuli falling within a critical time interval are phenomenally simultaneous. This paper examines two models of perceptual sampling which purport to account for phenomenal simultaneity. The first is Stroud's (1955) theory that the sensory input is quantized into successive, discrete summation periods or ‘moments’ (the Discrete Moment Hypothesis). An alternative model which has not generally been considered represents the ‘moment’ as a continuous, running sample of the input (the Travelling Moment Hypothesis). Two experiments on phenomenal simultaneity are reported which provide a critical test between these two hypotheses. The results were entirely incompatible with the discrete moment model, which is therefore rejected. The travelling moment model accounted well for the results. These also suggest a possible relation between the limits of phenomenal simultaneity and the critical duration of brightness summation.

Biochemical studies on the production of marine zooplankton.

Abstract: Summary 1 Phytoplanktonic algae vary in their value as food for zooplankton and no single algal food can meet the full nutritional needs of zooplanktonic animals Perhaps this is because optimal amounts of essential micronutrients are not all present in any one alga The dietary requirements of planktonic Crustacea, as far as they are known, bear some resemblance to those of vertebrates 2 The proteins of phytoplankton are similar in amino acid composition to those of zooplankton This circumstance should favour efficient synthesis of protein by the animal, for assuming amino acids are all released in the gut and absorbed at approximately the same rate, they will be presented to the tissues in roughly the right relative amounts for protein formation 3 Zooplankton are able to alter the characteristics of the fatty acids present in their diet by elongating the carbon chain length and by increasing the degree of unsaturation 4 Measurements of phosphorus and nitrogen excretion indicate that zooplankton are metabolically very active Some of the very high rates of phosphorus excretion are questioned and it is suggested that some portion of the phosphorus compounds liberated by zooplankton have passed straight through the gut without being assimilated It is unlikely that all forms of organically bound phosphorus are equally rapidly assimilated and turned over by zooplankton 5 Estimates of the rate of ammonia excretion by zooplankton differ markedly This may be a matter of size/surface area of the animals concerned—smaller animals excreting more rapidly than larger animals It has been claimed that a-amino nitrogen is released in considerable quantities by zooplankton but the evidence is not yet compelling 6 There is considerable disagreement on the efficiency of food assimilation and conversion by zooplankton One view is that irrespective of the quantity of phyto-plankton ingested assimilation is uniformly high The opposing view holds that when rapid ingestion of phytoplankton occurs the percentage assimilated falls More information on the feeding behaviour of zooplankton and on the physiology of their digestive processes is required before this controversy can be satisfactorily resolved

Visual Thresholds and Spectral Sensitivity of Herring Larvae

Abstract: 1. Herring larvae are characterized by eyes with no rods and no retinomotor responses, though both are present in the adult. 2. By observing the extinction of phototactic behaviour and feeding in herring larvae of different ages held at low intensities of white and coloured light, it was possible to obtain a measure of both threshold light intensities and spectral sensitivity for a pure-cone eye. 3. The phototaxis was positive at higher intensities, the threshold being 10 0 to 10 -1 m.c. Below this threshold a negative phototaxis was observed which disappeared at a much lower threshold, about 10 -5 to 10 -6 m.c. The threshold for feeding varied with age and the type of food organism, lying between 10 -1 and 10 -2 m.c. 4. The high sensitivity for negative phototaxis was probably a visual response and not one mediated by a dermal light sense. 5. Spectral sensitivity varied depending on age and behavioural criteria. Using feeding and positive phototaxis the action spectrum was broad and plateau-like with a maximum in the yellow-green and would appear to be similar to other photopic curves. The action spectra for negative phototaxis showed a number of peaks. At hatching three peaks at 450, 520 and 600 m µ might represent three types of cone as postulated by the Young-Helmholtz theory of colour vision.

Cortical synapses and reinforcement: a hypothesis.

Abstract: MOST theories of learning assume some change in the synaptic conductivity of cortical pathways1,2. Facilitation by use alone, however, will not account for the most characteristic feature of learning—that what is learned are those motor responses which lead to a satisfactory or adaptive state of affairs for the organism3–5.

Rearing herring larvae to metamorphosis and beyond

Abstract: The use of natural plankton and other foods, and of transfer techniques during phases of mortality before metamorphosis, has made it possible for substantial numbers of herring larvae to be reared beyond this stage, thus supplying requirements for experimental work. A survival to and beyond metamorphosis of over 10% of larvae passing the yolk-sac stage (3–4% of hatched larvae) has been obtained.

On better-quasi-ordering transfinite sequences

Abstract: Let Q be a quasi-ordered set, i.e. a set on which a reflexive and transitive relation ≤ is defined. If, for every finite sequence q1, q2, … of elements of Q, there exist i and j such that i < j and qi ≤ qj then we call Q well-quasi-ordered. For any ordinal number α the set of all ordinal numbers less than α is called an initial set. A function from an initial set into Q is called a transfinite sequence on Q. If ƒ: I1 → Q, g: I2 → Q are transfinite sequences on Q, the statement ƒ ≤ g means that there is a one-to-one order-preserving function o:I1 → I2 such that f(α) ≤ g(o(α)) for every α ∈ I1. Milner has conjectured in (3) that, if Q is well ordered, then any set of transfinite sequences on Q is well-quasi-ordered under the quasi-ordering just defined. In this paper, we define so-called ‘better-quasi-ordered sets’, which are well-quasi-ordered sets of a particularly ‘well-behaved’ kind, and we prove that any set of transfinite sequences on a better-quasi-ordered set is better-quasi-ordered. Milner's conjecture follows a fortiori, since every well ordered set is better-quasi-ordered and every better-quasi-ordered set is well-quasi-ordered.

The form and function of the sieve tube: a problem in reconciliation.

Abstract: Publisher Summary This chapter focuses on one aspect of phloem transport alone: the structure of the sieve tube in relation to possible mechanisms of transport. Although structure and function represent different ways of looking at one and the same organism or part of an organism their study all too often develops along independent, even divergent lines. This is true of the study of transport in the phloem and in this particular case it is aggravated by the fact that the sieve tubes which are the conducting elements are dispersed among other cells of different function and are easily damaged. The structure of the functioning sieve tube has been difficult to discover first because of its possibly delicate nature combined with its state of high turgor pressure, second because its contents become more tenuous during ontogeny, and it is not known whether this marks increasing or decreasing translocatory function. The cytological evidence suggests that any of the five patterns of structure may exist. These have been examined from the standpoint of the rate of translocation.

Free perforation in regional enteritis.

Abstract: 1. Free perforation is a not infrequent complication of regional enteritis; 95 cases have now been recorded. It can occur in any age group and at any stage in the disease.

Mode of Action of Morphine-like Drugs on Autonomic Neuro-effectors

Abstract: MORPHINE-like drugs depress transmission across certain neuro-effector junctions1–7 ; this effect is more marked at low than at high frequencies of stimulation3,5,6 and is caused by depression of transmitter release3,5–11. Fig. 1 shows the reduction in the release of acetylcholine caused by morphine when the innervated longitudinal muscle strip of the guinea-pig ileum is stimulated transmurally. These observations confirm and extend the findings of Paton and Zar11 that in the presence of morphine the spontaneous output of acetylcholine of the unstimulated preparation is reduced and that the evoked output per volley is low and almost constant at frequencies between 0.1 and 10/s, whereas without morphine the output per volley is usually much higher at low frequencies of stimulation and falls with increasing rates of excitation.

Biolaser Endothelial Trauma as a Means of Quantifying Platelet Activity in vivo

Abstract: ALTHOUGH several methods of studying platelet behaviour in vitro have been described, there has not been a simple and precise technique for making quantitative studies. Useful measurements have been obtained by counting the platelet microemboli formed in response to injury caused by pinching exposed rabbit pial vessels with ophthalmic forceps1. This method has been used in preliminary studies of drugs claimed to affect platelet adhesiveness2,3. The degree of trauma, however, cannot be reproducibly controlled and, in addition, the animals must be anaesthetized. Trauma is inflicted during exposure of the pial vessels before the experiment, and afterwards the animal has to be killed. A more precise method involves the use of a microelectrode applied to the wall of a blood vessel in the cheek pouch of the hamster and the measurement in mA of the minimal stimulus required to induce a platelet thrombus4,5. But reproducible application of the microelectrode is difficult and as with the pial vessel method the animals are anaesthetized, subjected to preliminary trauma and later killed.

Academic motivation and school attainment

Abstract: Summary. A twenty-four item self-rating inventory was constructed to assess academic motivation. Scores on the inventory were compared with teachers' ratings to give evidence of concurrent validity. A test-retest reliability coefficient of + 0.83 was obtained with an interval of 2 1/2 months. The inventory was given to 2,707 Aberdeen 13-year-olds who had previously been given various intellectual tests. School attainment was measured from teachers' estimates scaled against a verbal reasoning test. The scores on the inventory were found to correlate more closely with school attainment than with reasoning ability. Academic motivation scores also distinguished between groups of children who had improved their academic performance after transfer and those who had deteriorated. This distinction could not be attributed simply to social class differences. Even within social class, ‘improvers' had significantly higher scores on the inventory than ‘deteriorators' which suggests that ‘academic motivation’ is not closely related to social class.

Natural selection and the de Finetti diagram.

Abstract: SUMMARY The properties of the de Finetti diagram for the case of two alleles at a locus are described in terms of homogeneous co-ordinates.

Neuroticism and school attainment—a linear relationship?

Abstract: Summary. In a follow-up study 2,995 Aberdeen children aged about 13 years were given the Junior Eysenck Personality Inventory. School attainment was measured by teachers' average rank order in class, scaled on a verbal reasoning test. The relationships between attainment and the personality dimensions of neuroticism and extraversion were examined. Evidence is presented which suggests that the relationship between neuroticism and attainment is linear; high attainment in this age-group was associated with stability. The results for extraversion showed a sex difference, which may explain earlier conflicting findings. Girls who were stable extraverts and boys who were stable introverts formed superior groups. These relationships were also present among the brightest children.

Structure of Tin(II) “Hydroxide” and Lead(II) “Hydroxide”

Abstract: Donaldson and Moser1 have shown that there is only one stable solid tin(II) hydroxide, a unique crystalline phase quite distinct from other tin(II) oxides, which can be described as a hydrous oxide or oxy-hydroxide. The formula of the finely divided material was determined analytically as 5SnO.2H2O, but analytical results on a fine powder of large surface area cannot distinguish between this formula and the alternative 3SnO.H2O, which differs by only one molecule of water per fifteen formula units of tin(II) oxide.

Conductance or Resistance

Abstract: IN circulatory physiology, there may be difficulty in expressing quantitatively the response of a vascular bed in which blood flow has altered. If change of flow is used to express the response, then a large change in arterial pressure may be overlooked. For this reason it has been customary to express responses as changes of resistance, vascular resistance being the pressure difference across the vascular bed divided by the flow through it.

Crystal Structure of Ettringite

Abstract: ETTRINGITE (Ca6[Al(OH)6]2(SO4)3.26H2O) occurs as a natural mineral, and is technically important as a hydration product of Portland and supersulphated cements and in its use, as satin white, for coating paper. It forms hexagonal, prismatic crystals which in synthetic material are often highly elongated. Bannister, Hey and Bernal1 obtained unit-cell data (hexagonal: a 11.26, c 21.48 A, space group P63/mmc, Z = 2). No crystal structure determination based on single crystal evidence has been reported, but Welin2 determined the structure of a related mineral, thaumasite (Ca6H4(SiO4)2(SO4)2(CO3)2.26H2O), which he found to be based on chains of Ca2+ and SiO44− ions with the remaining ions and water molecules in between.

Microfilaments in pores between frozen-etched sieve elements.

Abstract: Sieve tubes were frozen before being cut from plants and were prepared for electron microscopy by freeze-etching. Structures that may be interpreted as filaments appeared in and near pores through sieve plates. Their presence suggests that filaments seen in sieve-pores prepared chemically may be there normally. Filaments appeared more numerous and compacted in sieve pores between sieve elements that had been pre-treated with glycerol than in those that had merely been frozen. A sieve element treated with glycerol appeared plasmolysed. No evidence was found for membrane-bound transcellular strands through pores in sieve plates even though membrane-bound transvacuolar strands of cytoplasm appeared clearly in nearby parenchyma cells.

The effect of certain growth substances on asymbiotic germination and development of orchis purpurella

Abstract: Summary The effect of some growth substances on gernnination and development of Orchis (Dactylorchis) purpurella seeds was studied in an attempt to simulate the developmental pattern observed in symbiotic cultures. Gibberellic acid enhanced protocorm survival and caused abnormal elongation of the emergent shoot but did not influence the growth and overall size of the protocorms. Indoleacetic acid impeded germination and caused some elongation of the protocorms. Kinetin, both alone and in conjunction with indoleacetic acid, had a pronounced effect on growth and development and the results suggested that the auxin/cytokinin ratio is important in controlling root and shoot initiation. Adenine appeared to have little effect. The growth factor mixtures used did not have as beneficial an effect on protocorm development as did the presence of either symbiotic fungi or undefined fractions such as potato extract and coconut milk, suggesting that symbiotic fungi also provide other growth substances.

Experiments with Mixtures: A Generalization of the Simplex‐Lattice Design

Abstract: The purpose of these designs is the empirical prediction of the response to any mixture of the components when the response depends only on the proportions of the components present, but not on the total amount of the mixture. Gorman and Hinman (1962) applied and extended the simplex-lattice design. There may be problems in practice in which the n components with proportions (1.1) are mixtures of several other components with proportions

Characterization and biosynthesis of cytochrome b5 in rat liver microsomes

Abstract: 1. Cytochrome b 5 is released from rat liver microsomes by both proteolytic enzymes and by treatments that disrupt phospholipids. Cytochrome P -420 is only released to a marked extent by treatments that disrupt phospholipids. 2. Cytochrome b 5 was isolated in a pure state from both the rough and smooth fractions of rat liver microsomes after treatment with trypsin, and was shown to contain two cytochrome components with identical spectral properties. 3. Amino acid analyses of the two components are presented, together with peptide ‘fingerprint’ patterns of tryptic digests of the two components. 4. Studies based on the direct isolation of cytochrome b 5 after administration of a single dose of radioactive amino acid to rats demonstrate that the cytochrome is synthesized initially in the rough fraction of microsomes and only subsequently appears in the smooth fraction. 5. Isolated rat liver microsomes are capable of incorporating radioactive amino acids into cytochrome b 5 under standard conditions. 6. Under these conditions the amino acid is incorporated into peptide linkage in the cytochrome.