Showing papers by "University of York published in 1981"

Publication recommendations for electrodermal measurements.

Abstract: This committee was appointed by the SPR Board to provide recommendations for publishing data on electrodermal activity (EDA). They are intended to be a stand-alone source for newcomers and experienced users. A short outline of principles for electrodermal measurement is given, and recommendations from an earlier report (Fowles et al., ) are incorporated. Three fundamental techniques of EDA recording are described: (1) endosomatic recording without the application of an external current, (2) exosomatic recording with direct current (the most widely applied methodology), and (3) exosomatic recording with alternating current-to date infrequently used but a promising future methodology. In addition to EDA recording in laboratories, ambulatory recording has become an emerging technique. Specific problems that come with this recording of EDA in the field are discussed, as are those emerging from recording EDA within a magnetic field (e.g., fMRI). Recommendations for the details that should be mentioned in publications of EDA methods and results are provided.

Asymmetrical competition in insects

Abstract: It is widely believed that when populations of two species of animals compete, each has an adverse effect on the other1,2. In other words, each zero growth isocline (dNi/dt = 0 where Ni is the population density of species i) is assumed to be some negative function of the population density of the other species. Cases where one species has a marked effect on the other, but there is no detectable reciprocal effect are sometimes distinguished as ‘amensalism’2,3. This is regarded as unusual. Standard textbooks of ecology either do not mention it1,4–6, define it but do not discuss it2, or occasionally give a brief account3. Ricklefs7 states that “competition can manifest itself by reducing the numbers of one or both competing species” without saying which is the more usual. Here we show that for insects in natural conditions, strongly asymmetrical competition (amensalism or near amensalism) is the norm rather than the exception by a ratio of at least 2:1.

Time left: linear versus logarithmic subjective time.

Abstract: In two experiments, subjects were given a choice between a standard fixed interval to reinforcement and the time left to reinforcement in an elapsing comparison interval. In Experiment 1, rats were trained to respond on a comparison 60-sec fixed-interval schedule on one lever and a standard 30-sec fixed-interval schedule on a second lever. Then combined trials were given that began with the entry of the comparison 60-sec lever, followed by the standard 30-sec lever after 15, 30, or 45 sec. Rats preferred to respond on the standard lever when it entered early (at 15 sec), they preferred to respond on the comparison lever when the standard entered late (at 45 sec), and they were approximately indifferent between the two levers when the standard entered halfway through the comparison interval so that the remaining time to food was equal on both levers. In Experiment 2, pigeons were trained to choose between the time left to food in an elapsing comparison interval (C sec long) and a standard fixed interval one half as long (S = C/2) in a concurrent-chains paradigm. Birds came to choose the standard early and the comparison late in the trial interval. The indifference point was linearly related to the midpoint of the elapsing C interval at a variety of S,C pairs. The results of both experiments are consistent with a Scalar Timing theory in which subjective time is linear in real time and memory variance is scalar, and they are inconsistent with a logarithmic time scale.

Social Support, Social Networks, and Schizophrenia

Abstract: This article considers the meaning of "social support" and its relationship to social networks, and discusses a structural approach to analysis of social connections in the study of schizophrenia. The concept of social supports is seen as methodologically more problematic and less strategic than the more structurally oriented concepts of social networks and social connections. It is argued that in terms of research strategy, if social connections are studied structurally as they change and develop over time, the impact of the specifically social processes can be better separated from that of the personal characteristics of the focal individual than seems possible with other approaches. Analysis of the properties of the networks around the focal individual, independently of that individual's own social behavior, can help to disentangle the interwoven complex of causes, characteristics, and consequences of schizophrenia.

Modelling ecological succession, with particular reference to Markovian models

Abstract: There is a brief review of models of succession: these are classified as verbal or descriptive, simulation, population dynamic, and Markovian. Many facets of the latter class of models are discussed, demonstrating that there are far more disadvantages to their use than apparent advantages. However, Markovian models do appear to have predictive ability, and it is also considered that the patterns of probabilities in Markovian matrices may have a role to play in interpreting opposing views on the mechanisms of succession. Data from the Breckland grasslands (Watt, 1960b) are used as an example.

Energy is Required for Maturation of Exported Proteins in Escherichia coli

Abstract: It has been established in numerous cases that proteins which are exported from Escherichia coli are synthesized on membrane-bound polysomes in precursor forms which are proteolytically cleaved to generate the mature species. Here we present evidence that at least one step in the export of proteins requires energy. Energy requirements for processing of the precursors of both the M13 coat protein [Date, T., Zwizinski, C., Ludmerer, S., and Wickner, W. (1980) Proc. Natl Acad. Sci. USA, 77, 827-831; Date, T., Goodman, J. M., and Wickner, W. T. (1980) Proc. Natl Acad. Sci. USA, 77, 4669-4673] and the B subunit of heat-labile enterotoxin [Palva, T., Hirst, T. R., Hardy, S. J. S., Holmgren, J., and Randall, L. L. (1981) J. Bacteriol. in the press] have been demonstrated previously. An energy requirement for the proteolytic processing of an additional five exported proteins is reported here. Studies utilizing an uncA mutant suggest that the form of energy required is proton-motive force. Thus an energized membrane is probably essential for export of most periplasmic and outer membrane proteins.

Unemployment and the efficiency wage hypothesis

Abstract: There has been much recent discussion of the reasons why prices in certain markets, and in particular in labour markets, may not adjust to eliminate excess supply. The absence of speedy adjustment of prices is an essential feature of the recent models of disequilibrium macroeconomics but, for the most part, no explanation for this absence is provided from within those models. One explanation that has been around in the literature for some time and has been receiving increasing attention recently is the efficiency wage hypothesis. Initially applied to developing economies (see Leibenstein, I957), it has more recently been adapted to developed economies by Weiss (i 980) and used in the context of a Keynesian macroeconomic model by Hart (i 980). Similar concepts have been applied to the credit market by Stiglitz and Weiss (I98I). The purpose of the present paper is to explore further the conditions under which the notion of an efficiency wage is applicable and can provide an explanation of involuntary unemployment. The essential feature of the efficiency wage hypothesis is that the productivity of a firm's employees increases as their wage is increased, at least over an economically relevant part of its range. If the wage paid by the firm is denoted by w, the number of employees by L, and the productivity of each employee by p(w) where p'(w) > o, then the effective labour force of the firm, E, can be represented by

Testing Linear and Log-Linear Regressions for Functional Form

Abstract: It is often a problem to know what functional form to choose when specifying an econometric model since economic theory does not usually provide a very precise guide. The choice of functional form may, however, have important implications for subsequent statistical tests, for forecasts and for policy analysis, e.g. see Hall (1978)and Mizon (1977). Due to their simplicity, the specifications most commonly used are the linear and log-linear models. Sometimes the estimates of these two variants are compared with a view to choosing one of them as the "correct" representation. Although this comparison may be of interest in certain cases, in others it may be more appropriate to test linearity or log-linearity against a more general functional form rather than against each other. In this paper, we discuss two approaches to testing the adequacy of the linear and log-linear specifications against the more general alternative of the extended Box-Cox (1964) regression model considered by Savin and White (1978). The first of these procedures is based on the Lagrange multiplier approach discussed by Breusch and Pagan (1980) and by Godfrey and Wickens (1980), while the second is derived from work by Andrews (1971) on the selection of data transformations.1 Both approaches lead to tests which are easy to compute and which can reject both models as well as being capable of selecting one form rather than the other. The paper is set out as follows. In Section 2 we compare some existing procedures for testing the functional form of linear and log-linear models. In Section 3 we derive new large sample tests which are based on the Lagrange multiplier approach. The possibility of using small sample tests is discussed in Section 4 and a numerical example to illustrate the use of our new tests is given in Section 5.

Multiple late positive potentials in two visual discrimination tasks.

Abstract: Event-related potentials (ERPs) were recorded from 30 adolescents during two versions of the continuous performance test (CPT). Task B involved more complex processing than Task A, because subjects were required to store and compare successive stimuli to determine if a target had occurred, while Task A required a simple match-mismatch decision. This was corroborated behaviorally, with Task B producing greater error rate, longer reaction times, and greater reaction time variance than Task A. Principal Components Analysis (PCA) with Varimax rotation was performed separately on the signal (SIG) and non-signal (NSIG) ERPs from each task to objectively verify the presence of multiple positive peaks which had been visually identified in the individual and grand mean waveforms. These PCAs yielded factor structures and “components” whose shapes, time courses and factor score topographies were similar across ERP subsets, suggesting that each might represent activity within the same brain region. Differences in these factors across data sets were also evident. To assess these, ANOVAs of the factor scores from the PCA performed on the ERPs pooled across stimuli and tasks were performed. Consistent between-task effects were shown by P450, P550 and slow wave, potentials which appear to reflect processes related to the discriminative outcome. These data conclusively demonstrate the presence of multiple late positive components within the latency range of the classical P300 wave.

Domestic Homicide in early modern England

Abstract: One of the most striking features of recent writing on early modern social history has been the emergence of the family as a subject of central concern. As befits an historical area being subjected to new scrutiny, much of this concern has expressed itself in the form of specialized, and often narrowly-focused articles or essays.1 To these have been added a number of more general works intended to examine the broader developments in and implications of family life in the past.2 Several themes within family history have already received considerable attention: the structure of the family, for example, a topic already rendered familiar by earlier work on historical demography; the concomitant topic of sexual practices and attitudes; and the economic role of the family, especially in its capacity as a unit of production. These are, of course, important matters, and the research carried out on them has revealed much of interest and consequence to the social historian; this should not, however, obscure the existence of a number of other significant dimensions of family life in the past which await thorough investigation.

Cortical Augmenting‐Reducing — Modality Specific?

Abstract: The assumption that cortical augmenting-reducing is independent of stimulus modality was tested by presenting both auditory and visual stimuli to 42 subjects. Cross-modal correlations for P1N1 and N1P2 slope measures were negligible and nonsignificant. They remained insignificant using a measure independent of overall responsivity, after exclusion of “inconsistent” slope values, after equating for relative stimulus intensity, and after data transformations. No evidence was found for overall reducing in the auditory modality, although “paradoxical” reducing was observed over low intensity levels. Slopes derived from this reducing range did not correlate with visual slopes. Visual reducing was not found to be an artifact of selective EP latency jitter or scatter of the data points, but was found to correlate with confidence ratings of peak-trough identification. These results suggest that cortical reducing is modality-specific and is not mediated by a generalized, central inhibitory mechanism but by independent, sensory-specific pathways. Implications were drawn for both the neuroanatomical basis of cortical augmenting-reducing and its application in psychopathology.

Observations on the mechanism of chloroplast division in higher plants

Abstract: SUMMARY The sequence of changes in membranes that occur during the division of young green chloroplasts is described from observations in the electron microscope of thin sections of leaf tissue of Triticitm aestivum var. Maris Dove, Atriplex semibaccata R.Br. and Sesamum indicum var. glauca. Comparative observations of the morphological forms of dividing chloroplasts present in suspensions from young wheat leaves were made using phase contrast and Nomarski interference optics and from thin sections. The isthmus region of the dividing chloroplasts has a similar form in all three species and fuzzy plaques of electron opaque material and some invaginations in the isthmus were frequently observed. The significance of these fuzzy plaques is discussed and a possible mechanism for chloroplast division suggested.

Clozapine: plasma levels and prolactin response.

Abstract: Serial plasma clozapine levels and serum prolactin levels were determined in two schizophrenic patients receiving clozapine, a novel antipsychotic drug. Despite marked therapeutic response and substantial clozapine blood levels, prolactin levels obtained 11–12 h after the last oral dose were unaffected or only minimally elevated. This confirms previous evidence of clozapine's unusal characteristics.

Properties of a traffic control policy which ensure the existence of a traffic equilibrium consistent with the policy

Abstract: The paper considers the traffic assignment problem when there are junctions controlled by traffic signals, and the traffic capacity of each junction is limited. We give certain properties of a control policy. If a particular policy possesses these properties then (under natural conditions) any feasible assignment problem has a solution consistent with that policy. In the mathematical model, traffic flows at one junction do not affect costs at others; this is the most important restriction on the work presented here.

Are optimal search rules reasonable? and vice versa? (And does it matter anyway?)

Abstract: The Economics of Search has made rapid progress in recent years and its results have contributed siginificantly to economic knowledge. Recent work has been particularly marked for the steadily increasing realism of the assumptions describing the environment surrounding the searcher. However, concomitant with this improvement has been a steady growth in the technical complexity of the problem supposedly solved by the searcher. Indeed, many of the recent models are so complicated that their solutions are beyond the capacity of even modern-day computers. After elaborating on this impracticability of optimal search rules, the paper goes on to consider two more realistic and practical alternatives — the adoption of either ‘suboptimal’ or ‘reasonable’ rules. Paradoxically, reasonable rules may, in some circumstances, be better than ‘optimal’ rules. The paper contains a preliminary discussion of what might be meant by ‘reasonable’ behaviour, and shows that a minimal set of criteria for reasonableness leads to the major qualitative conclusions at a market level of optimal search theory.

One Thing Behind Another: problems of representation in children's drawings

Abstract: A series of five studies was designed to investigate children's representation of a depth‐relationship on a two‐dimensional surface. Subjects ranged from 4 to 10 years and also included adult samples. It was found that if a model is present and their attention is specifically drawn to it, young children do attempt to draw one object behind another. When simple objects are used, their technique is to place the two elements vertically, but separate, on the page. The ‘adult’ strategy of partial occlusion did not emerge until at least age 8. The tendency to separate the elements was not a function of a drawing task; ‘separate’ arrangements were also chosen in a selection task. Neither was it connected with a reluctance to represent a partially occluded whole object with an incomplete shape; a disc task also led to separation in the same way as the drawing and selection tasks. Finally, a task in which the idea of one object being partially hidden by the nearer was inherent to the task itself produced ...

Localization of DNA in Mature and Young Wheat Chloroplasts Using the Fluorescent Probe 4′-6-Diamidino-2-phenylindole

Abstract: The spatial organization of chloroplast DNA in developing and dividing wheat chloroplasts was studied in the light microscope using the fluorescent probe 4′-6-diamidino-2-phenylindole, which binds specifically to DNA. The DNA of wheat chloroplasts was localized at the periphery of the plastid, frequently in a discrete band. No relocalization of the DNA was observed during plastid replication. This peripheral location of the DNA was shown to differ from the central random location of DNA in tobacco and spinach chloroplasts.