Nonmonotonic Extrapolation in Function Learning.

This article reports the results of an experiment addressing extrapolation in function learning, in particular the issue of whether participants can extrapolate in a nonmonotonic manner. Existing models of function learning, including the extrapolation association model of function learning (EXAM; E. L. DeLosh, J. R. Busemeyer, & M. A. McDaniel, 1997), cannot account for this type of extrapolation pattern. We present the results of an experiment in which participants were shown a series of paired stimulus-response magnitudes where the relationship between these 2 dimensions conformed to a cyclic function. Participants were shown to extrapolate from these training data in a nonmonotonic way, contrary to predictions from EXAM. A new model of function learning is presented, which predicts responses more accurately than EXAM. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual processes in matching and recognition of complex pictures.

The role of perceptual feature sampling in speeded matching and recognition was explored in 4 experiments. Experiments 1-3 involved a perceptual matching task with pictures of various objects and scenes. In Experiments 2 and 3, same-different judgments were given under time pressure. The main objective of the matching task was to obtain measures of the perceptual processing rates of different object features. Experiment 4 was an old-new recognition experiment, in which the same stimuli as those in the matching task were used. Response signals were used to limit processing time in the recognition task. The results demonstrated that it is possible to predict speeded recognition performance from performance in perceptual matching. A simple stochastic feature-sampling model provides a unified account of the data from the 4 experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An evaluation of the total similarity principle: Effects of similarity on frequency judgments.

Memory models that embody the total similarity principle (e.g., G. Gillund and R. Shiffrin, see PA, Vol 71:8340; D. Hintzman, see PA, Vol 76:10832; B. Murdock, see PA, Vol 69:4936; and R. Ratcliff, see PA, Vol 77:18992) assume that frequency judgments reflect the total similarity of a test item to stimuli that have been studied. In 4 experiments, Ss estimated the frequencies of target words that had been presented in the context of varying numbers of semantically similar words. In a 5th experiment, Ss made forced-choice relative frequency judgments. The results of these experiments supported 1 prediction of total similarity models: Presenting similar words will increase rather than decrease frequency judgments of target words. However, a 2nd prediction of these models was not supported. In particular, similar-word presentations had no effect on the judged frequencies of target words that had not been shown. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Low molecular weight heparin: a critical analysis of clinical trials

LMWHs are an important new class of antithrombotic agents. They differ from UFH in having relatively more anti-Xa activity, greater bioavailability at low doses, longer half-life, and more predictable anticoagulant response when administered in fixed doses. These properties allow LMWHs to be administered QD or at most BID and without laboratory monitoring. The incidence of heparin-induced thrombocytopenia also appears to be lower with an LMWH than with heparin. Given their favorable pharmacological profile, it was of interest to critically appraise clinical trials of thromboprophylaxis and treatment with these new agents. In orthopedic trials, it was noted that LMWH provided safe and effective thromboprophylaxis for patients undergoing major orthopedic surgery of the lower limb. In those having hip arthroplasty, LMWH was as effective as low-intensity warfarin therapy, but its use was associated with more wound hematomas. In those having total knee arthroplasty, LMWH was more effective than warfarin and did not increase bleeding. However, the prevalence of DVTs complicating this procedure as well as acute hip fracture remains unacceptably high, and additional studies of LMWH in combination with other prophylactic methods, such as external pneumatic compression, are needed. Only one adequately designed trial found less bleeding resulted from LMWH prophylaxis administered at an equivalent antithrombotic dose to UFH. In general medical patients, LMWH appeared to be as effective as UFH and had the advantages of less frequent injections and fewer injection site hematomas. In general surgical patients, there was a lower risk of thromboembolism but a trend toward an increase in bleeding events. Subjects with strokes and spinal cord injuries benefited from fewer thrombotic events, and the latter had fewer bleeding complications. Other potential indications for LMWH, such as cardiopulmonary bypass, hemodialysis, and preservation of graft patency, are presently under study. Perhaps the most impressive benefits of LMWH will be realized when it is used for the treatment of venous thromboembolism. The meta-analysis presented in this review showed a trend toward greater efficacy with LMWH and fewer major bleeding events in comparison with adjusted-dose intravenous UFH. Also, during the months following the thrombotic event, there was significantly less mortality in patients receiving LMWH. A further advantage was the subcutaneous route of administration and lack of requirement for laboratory monitoring. Additional treatment trials are presently in progress and may establish LMWH as the treatment of choice for patients with thromboembolic disorders.     

Modeling the Effects of Prior Knowledge on Learning Incongruent Features of Category Members.

The authors conducted 3 experiments addressing the issue of how observations and multiple sources of prior knowledge are put together in category learning. In Experiments 1 and 2, learning was faster for critical features, which were predictable on the basis of prior knowledge, than for filler features, and this advantage increased as more observations were made. In addition, learning was fastest for incongruent features that could only be predicted using knowledge from other domains. In Experiment 3, presenting contradictory features that violated prior knowledge led to rote learning rather than use of prior knowledge. The results were simulated with the Baywatch model, which addresses how observations of category members lead to recruitment and selection of sources of prior knowledge. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature-sampling and random-walk models of individual-stimulus recognition.

Traditional process models of old-new recognition have not addressed differences in accuracy and response time between individual stimuli. Two new process models of recognition are presented and applied to response time and accuracy data from 3 old-new recognition experiments. The 1st model is derived from a feature-sampling account of the time course of categorization, whereas the 2nd model is a generalization of a random-walk model of categorization. In the experiments, a new technique was used, which yielded reliable individual-stimulus data through repeated presentation of structurally equivalent items. The results from the experiments showed reliable differences in accuracy and response times between stimuli. The random-walk model provided the better account of the results from the 3 experiments. The implications of the results for process models of recognition are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Issues in OTEC commercialization

The commercialization of a new capital intensive technology requires coordination between government and industry. Government regulation of the energy industry can hinder its commercial development. On the other hand, government financial incentive is essential to induce industry to invest in a new technology such as OTEC. Incentives will be necessary in the early phases of development both for the manufacturers of OTEC systems and components and for the owner/operators of OTEC power plants. The various incentives are analyzed and their impact on manufacturers of, investors in, and users of OTEC technology is discussed. Analysis shows that OTEC is technically and economically ready to enter the electric utility market in tropical islands. For the larger U.S. mainland market, economies of scale are expected to reduce the capital cost to a low enough level where OTEC can be competitive.     

Predicting reasoning from memory.

In an effort to assess the relations between reasoning and memory, in 8 experiments, the authors examined how well responses on an inductive reasoning task are predicted from responses on a recognition memory task for the same picture stimuli. Across several experimental manipulations, such as varying study time, presentation frequency, and the presence of stimuli from other categories, there was a high correlation between reasoning and memory responses (average r = .87), and these manipulations showed similar effects on the 2 tasks. The results point to common mechanisms underlying inductive reasoning and recognition memory abilities. A mathematical model, GEN-EX (generalization from examples), derived from exemplar models of categorization, is presented, which predicts both reasoning and memory responses from pairwise similarities among the stimuli, allowing for additional influences of subtyping and deterministic responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retina simulation using cellular automata and GPU programming

This article shows how the architectural modelization of biological retina allows real-time performances, on standard widespread computing systems. First, we describe the biological retina with regard to its pipeline architecture, detailing its layer behaviours and properties. Then we propose a corresponding pipelined model of artificial retina based on cellular automata. In this work, the main innovation is the computing method based on the programming of a personal computer graphical card using OpenGL shading language. The last section demonstrates the efficiency of our model through numerical and graphical results. We lay particular emphasis on the fact that our direct implementation of the Graphical Processor Unit (GPU) provides computation power about 20 times as fast as conventional programming.