The effect of interstimulus interval on sequential effects in absolute identification

In absolute identification experiments, the participant is asked to identify stimuli drawn from a small set of items which differ on a single physical dimension (e.g., 10 tones which vary in frequency). Responses in these tasks show a striking pattern of sequential dependencies: The current response assimilates towards the immediately preceding stimulus but contrasts with the stimuli further back in the sequence. This pattern has been variously interpreted as resulting from confusion of items in memory, shifts in response criteria, or the action of selective attention, and these interpretations have been incorporated into competing formal models of absolute identification performance. In two experiments, we demonstrate that lengthening the time between trials increases contrast to both the previous stimulus and the stimulus two trials back. This surprising pattern of results is difficult to reconcile with the idea that sequential dependencies result from memory confusion or from criterion shifts, but is consistent with an account that emphasizes selective attention. </jats:p

The effect of stimulus range on two-interval frequency discrimination

It has traditionally been thought that performance in two-interval frequency discrimination tasks decreases as the range over which the standard tone varies is increased. Recent empirical evidence and a reexamination of previous results suggest that this may not be the case. The present experiment found that performance was significantly better when the standard roved over a wide range (1500 Hz) than a narrow range (30 Hz). This pattern cannot readily be accommodated by traditional models of frequency discrimination based on memory or attention, but may be explicable in terms of neural plasticity and the formation of perceptual anchors

Psychophysics and the judgment of price: judging complex objects on a non-physical dimension elicits sequential effects like those in perceptual tasks

When participants in psychophysical experiments are asked to estimate or identify stimuli which differ on a single physical dimension, their judgments are influenced by the local experimental context — the item presented and judgment made on the previous trial. It has been suggested that similar sequential effects occur in more naturalistic, real-world judgments. In three experiments we asked participants to judge the prices of a sequence of items. In Experiment 1, judgments were biased towards the previous response (assimilation) but away from the true value of the previous item (contrast), a pattern which matches that found in psychophysical research. In Experiments 2A and 2B, we manipulated the provision of feedback and the expertise of the participants, and found that feedback reduced the effect of the previous judgment and shifted the effect of the previous item’s true price from contrast to assimilation. Finally, in all three experiments we found that judgments were biased towards the centre of the range, a phenomenon known as the “regression effect” in psychophysics. These results suggest that the most recently-presented item is a point of reference for the current judgment. The findings inform our understanding of the judgment process, constrain the explanations for local context effects put forward by psychophysicists, and carry practical importance for real-world situations in which contextual bias may degrade the accuracy of judgments

Formulation of boundary conditions for the multigrid acceleration of the Euler and Navier Stokes equations

An explicit, Multigrid algorithm was written to solve the Euler and Navier-Stokes equations with special consideration given to the coarse mesh boundary conditions. These are formulated in a manner consistent with the interior solution, utilizing forcing terms to prevent coarse-mesh truncation error from affecting the fine-mesh solution. A 4-Stage Hybrid Runge-Kutta Scheme is used to advance the solution in time, and Multigrid convergence is further enhanced by using local time-stepping and implicit residual smoothing. Details of the algorithm are presented along with a description of Jameson's standard Multigrid method and a new approach to formulating the Multigrid equations

ORTHOPEDIC LEG BRACE

Knee braces generally have been rigid in both the knee bending direction and in the knee straightening direction unless a manually operated release is incorporated in them to allow the knee to bend. Desirably a braced knee joint should effectively duplicate the compound, complex, actions of a normal knee. The key to knee braces is the knee joint housing. The housing herein carries a number of cam action pawls. with teeth adapted to engage the internal teeth of a ratchet ring mounted in the housing. Cam action return springs and the shape of the cam action pawl teeth allow rotation of the ratchet ring in a leg straightening direction while still supporting a load. The leg can then be extended during walking while at the same time being prevented by the cam action pawls from buckling in the knee bending direction

Determination of the permeability parameters of bagasse pulp from two different sugar extraction methods

The permeability, the specific surface area and the swelling factor have been determined for Australian bagasse pulp derived from bagasse from two different sugar extraction processes. The sugar extraction process was not found to affect the permeability of the pulp. The results for bagasse pulp are compared to those of eucalypt pulp, which is widely used in Australia for paper manufacture. The fibre length distribution showed a high fraction of small fibres in all of the bagasse pulp samples. Surprisingly, the permeability properties of the bagasse pulp samples were better than that that of eucalypt. It is presumed that this is due to the relatively large fraction of longer fibres in the bagasse pulp compared to the eucalypt pulp

Importance of organic phosphate hydrolyzed in stalks of the lotic diatom Didymosphenia geminata and the possible impact of atmospheric and climatic changes

The aquatic colonial stalked diatom, Didymosphenia geminata, has acquired notoriety in recent years because of huge increases in many rivers of temperate regions. However, in some streams in northern England it has probably or, in the case of the R. Coquet (Northumberland), certainly been abundant for many decades. The paper describes the nutrient environment and phosphatase activities of Didymosphenia in Stony Gill (N. Yorkshire), a fast-flowing stream draining an upland catchment with peaty soils overlying limestone. Organic phosphate formed 85% of the filtrable phosphate in the water during the study (January–August 2000), with a maximum in April. Colonies were most abundant in June, but had disappeared by August. Surface phosphomonoesterase (PMEase) and phosphodiesterase activities assayed from March to July showed low PMEase activity in early March, but otherwise both were high throughout the period and especially so in June and July. Use of BCIP-NBT staining procedure showed that PMEase activity occurred in the stalks. A more detailed study of colony structure and staining with material from the R. Coquet in June 2006 also showed marked PMEase activity, with staining localized in the upper part of the stalks and the cells remaining unstained. It is suggested that organic phosphate is hydrolyzed in the stalk and the inorganic phosphate passes to the cell via a central tube in the stalk. It seems likely that organic phosphate as a major P source is a key factor favouring the success of Didymosphenia. The possible impact of environmental changes in the catchment such as climatic warming, C loss from peat and atmospheric N deposition is discussed