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PubMed2001

Uncertainty of measurement. Twenty years afterwards.

The application of the concept "uncertainty" causes considerable difficulties. In this paper an analysis of the intrinsic contradictions of the concept itself and its relationship with the statements of metrology is given with the aim of establishing possible reasons for these difficulties. As a result of this analysis several examples are presented to demonstrate the conflicts of the concept and its several statements in the general fundamental notions of metrology.

Journal Article↗
PubMed2003

Motor planning: effect of directional uncertainty with discrete spatial cues.

We investigated the effect of spatial uncertainty on motor planning by using the cueing method in a reaching task (experiment 1). Discrete spatial cues indicated the different locations in which the target could be presented. The number of cues as well as their direction changed from trial to trial. We tested the adequacy of two models of motor planning to account for the data. The switching model assumes that only one motor response can be planned at a time, whereas the capacity-sharing model assumes that multiple motor responses can be planned in parallel. Both models predict the same relation between average reaction time (RT) and number of cues, but they differ in their prediction of the shape of the distribution of the reaction time. The results showed that RT increased with the number of cues independently from their spatial dispersion. This relation was well described by the function predicted by both models, whereas it was poorly described by the Hick-Hyman law. In addition, the distribution of RT conformed to the prediction of the capacity-sharing model and not to that of the switching model. We investigated the role that the requirement of a spatially directed motor response might have had on this pattern of results by testing subjects in a simple RT task (experiment 2) with the same cueing presentation as in experiment 1. The results contrasted with those in experiment 1 and showed that RT was dependent on the spatial dispersion of the cues and not on their number. The results of the two experiments suggest that the mode of processing of potential targets is dependent on the spatial constraints of the task. The processing resources can be either divided relative to the spatial distribution of possible targets or across multiple independent discrete representations of these targets.

Adult↗
PubMed2003

Motor planning: effect of directional uncertainty with continuous spatial cues.

We have investigated the effect of directional uncertainty on the planning of reaching movements. For this purpose, we have used sections of annuli as spatial cues to indicate the directional range within which the target would be presented. The results showed that the reaction time of the reaching response increased with cue range and with the angle between the center of the cue and the target. In addition, the initial direction of movement was biased toward the center of the cue. These results conformed to the predictions of the capacity-sharing model. This model assumes that the processing resources used for motor planning are limited and distributed as a function of the range of directions indicated by the cue, and that when the target appears, these resources are reallocated to represent the response to be executed.

Adult↗
PubMed2006

Temporal uncertainty does not affect response latencies of movements produced during startle reactions.

Previous research has shown that a startle 'go' stimulus, presented at a constant latency with respect to a warning stimulus, is capable of eliciting an intended voluntary movement in a simple reaction time (RT) task at very short latencies without involvement of the cerebral cortex (Carlsen et al. in Exp Brain Res 152:510-518, 2003; J Motor Behav 36:253-264, 2004a; Exp Brain Res 159:301-309 2004b; Valls-Solé et al. in J Physiol 516:931-938, 1999). The purpose of the present experiment was to determine the effect of temporal uncertainty on response latency during an RT task that comprised a startle stimulus. Participants were required to perform an active 20 degrees wrist extension movement in response to an auditory tone that was presented 2,500 to 5,500 ms after a warning stimulus, in 1,000 ms increments. On certain trials the control auditory stimulus (80 dB) was unexpectedly replaced by the startle stimulus (124 dB). When participants were startled the intended voluntary movement was initiated at approximately 70 ms, regardless of foreperiod duration. The magnitude and invariance of response latencies to the startle stimulus suggest that the intended movement had indeed been prepared prior to the arrival of the imperative go stimulus, within 2.5 s of the warning stimulus. Furthermore, there was no evidence that the prepared movement decayed over a period of at least 3 s.

Acoustic Stimulation↗
PubMed2000

Implications of fluctuations in substitution rates: impact on the uncertainty of branch lengths and on relative-rate tests.

Many tests of the lineage dependence of substitution rates, computations of the error of evolutionary distances, and simulations of molecular evolution assume that the rate of evolution is constant in time within each lineage descended from a common ancestor. However, estimates of the index of dispersion of numbers of mammalian substitutions suggest that the rate has time-dependent variations consistent with a fractal-Gaussian-rate Poisson process, which assumes common descent without assuming rate constancy. While this model does not affect certain relative-rate tests, it substantially increases the uncertainty of branch lengths. Thus, fluctuations in the rate of substitution cannot be neglected in calculations that rely on evolutionary distances, such as the confidence intervals of divergence times and certain phylogenetic reconstructions. The fractal-Gaussian-rate Poisson process is compared and contrasted with previous models of molecular evolution, including other Poisson processes, the fractal renewal process, a Lévy-stable process, a fractional-difference process, and a log-Brownian process. The fractal models are more compatible with mammalian data than the nonfractal models considered, and they may also be better supported by Darwinian theory. Although the fractal-Gaussian-rate Poisson process has not been proven to have better agreement with data or theory than the other fractal models, its Gaussian nature simplifies the exploration of its impact on evolutionary distance errors and relative-rate tests.

Amino Acid Substitution↗
PubMed2003

Choice of model and uncertainties of the gamma-ray and neutron dosimetry in relation to the chromosome aberrations data in Hiroshima and Nagasaki.

Chromosome data pertaining to blood samples from 1,703 survivors of the Hiroshima and Nagasaki A-bombs, were utilized and different models for chromosome aberration dose response investigated. Models applied included those linear or linear-quadratic in equivalent dose. Models in which neutron and gamma doses were treated separately (LQ-L model) were also used, which included either the use of a low-dose limiting value for the relative biological effectiveness (RBE) of neutrons of R(0)=70+/-10 or an RBE value of R(1)=15+/-5 at 1 Gy. The use of R(1) incorporates the assumption that it is much better known than R(0), with much less associated uncertainty. In addition, error-reducing transformations were included which were found to result in a 50% reduction of the standard error associated with one of the model fit parameters which is associated with the proportion of cells with at least one aberration, at 1 Gy gamma dose. Several justifiable modifications to the DS86 doses according to recent nuclear retrospective dosimetry measurements were also investigated. Gamma-dose modifications were based on published thermoluminescence measurements of quartz samples from Hiroshima and on a tentative reduction for Nagasaki factory worker candidates by a factor of 0.6. Neutron doses in Hiroshima were modified to become consistent with recent fast neutron activation data based on copper samples. The applied dose modifications result in an increase in non-linearity of the dose-response curve for Hiroshima, and a corresponding decrease in that for Nagasaki, an effect found to be most pronounced for the LQ-L models investigated. As a result the difference in the dose-response curves observed for both cities based on DS86 doses, is somewhat reduced but cannot be entirely explained by the dose modifications applied. The extent to which the neutrons contribute to chromosome aberration induction in Hiroshima depends significantly on the model used. The LQ-L model including an R(1) value of 15 at 1 Gy which is recommended here, would predict between 10% and 20% of the observed chromosome aberrations to be due to neutrons, at all doses. Because of the good agreement between DS86 predictions and the results of retrospective gamma and neutron dosimetry, the modifications applied here to DS86 doses are relatively small. Consequently, the choices of model and RBE values were found to be the major factors dominating the interpretation of the chromosome data for Hiroshima and Nagasaki, with the dose modifications resulting in a smaller influence.

Bone Marrow↗
PubMed1997

Measurement of resuspended aerosol in the Chernobyl area. I. Discussion of instrumentation and estimation of measurement uncertainty.

Results of measurements of the resuspended radioactive aerosols in the Chernobyl area are presented which were obtained soon after the Chernobyl reactor accident and in a European project in 1992-1993. The measurements were carried out with the intention of obtaining a data base for dose assessment of resuspended radioactive particles. Potential significant dose contributions may result from inhalation and secondary contamination due to resuspended radionuclides. In this first article of a series of three papers, the instrumentation and the measurement uncertainties are discussed. An effort was made to sample quantitatively giant aerosol particles (particles larger than 10 microns aerodynamic diameter) as well. The comparison of the samplers shows, in general, an agreement of concentration measurements of 137Cs and 7Be within a factor of two. One sampler was identified with larger discrepancies and needs additional investigation of its sampling characteristics; for another device, the recalibration of the analysing system is recommended. Ordinary integrating samplers have a loss of about 30% in 137Cs activity compared to an isokinetic sampler collecting giant particles as well. The mean ratio of 137Cs activity concentration between an instrument sampling only particles larger than 10 microns and an ordinary integrating sampler is 0.39 +/- 0.15 during anthropogenic-enhanced resuspension. These findings demonstrate the significant contribution of giant particles to resuspended airborne radioactivity. The results of this study concerning integral measurements during wind-driven resuspension proved to be in good agreement with previously published data on resuspension.

Aerosols↗
PubMed2000

The politics of certainty: conceptions of science in an age of uncertainty.

The prestige of science, derived from its claims to certainty, has adversely affected the humanities. There is, in fact, a "politics of certainty". Our ability to predict events in a limited sphere has been idealized, engendering dangerous illusions about our power to control nature and eliminate time. In addition, the perception and propagation of science as a bearer of certainty has served to legitimate harmful forms of social, sexual, and political power. Yet, as Ilya Prigogine has argued, renewed attention to the irreducible reality of time has brought us to "the end of certainty". As we enter the age of uncertainty, there is disagreement about how science should be understood and communicated. Some scientists cling to the ideal of certainty, while others emphasize the creative potential of spontaneity, novelty, and surprise.

Cultural Diversity↗
PubMed2001

Learning from the law to address uncertainty in the precautionary principle.

Environmentalists have advocated the Precautionary Principle (PP) to help guide public and private decisions about the environment. By contrast, industry and its spokesmen have opposed this. There is not one principle, but many that have been recommendedfor this purpose. Despite the attractiveness of a core idea in all versions of the principle--that decision-makers should take some precautionary steps to ensure that threats of serious and irreversible damage to the environment and public health do not materialize into harm--even one of the most widely endorsed principles needs considerable specification and refinement before it can be used. Moreover, the PP is an approach or guide to utilizing scientific evidence in social or legal decision-making contexts. In this it does not differ in kind from other approaches to using factual information such as in the law. The law provides some models for different strategies to guide decision-making under uncertainty when factual issues cannot be resolved with certainty. These in turn can help guide the formulation of different versions of PP and help clarify some presuppositions of the principle. Once some plausible versions of PP are articulated, I suggest some applications to existing environmental problems.

Decision Making↗
PubMed1996

Uncertainty and processing routes in the selection of a response: an S-R compatibility study.

Stimulus-response (S-R) pairs are usually processed faster when-they are presented in a series that consists entirely of compatible relations rather than incompatible relations. A mixture of the two pairs in a series, which induces uncertainty, increases processing speed for both pairs, but more so for compatible S-R pairs. The results of three choice reaction time (RT) tasks showed that presentation of a precue that only indicated either compatible or incompatible S-R pairs reduced the detrimental effect of mixing pairs more for the former than for the latter pairs. A similar asymmetric reduction was observed in the third experiment when either pair was preceded by the same pair or the same class of pairing. Analyses of RT bins revealed that decreases in RT for the mixed compatible S-R pairs occurred only for the faster responses. It was shown further that errors consisted primarily of a correct application of an incorrect S-R transformation rule. The results are interpreted within the framework of the dimensional overlap model of Kornblum et al. (1990) suggesting two sources of the S-R compatibility effect; interference of primed responses and the need to suppress response priming.

Adolescent↗
PubMed1991

Controlling system uncertainty in sport and work.

An applied psychological framework for coping with performance uncertainty in sport and work systems is presented. The theme of personal control serves to integrate ideas prevalent in industrial and organisational psychology, the stress literature and labour process theory. These commonly focus on the promotion of tacit knowledge and learned resourcefulness in individual performers. Finally, data from an empirical evaluation of a development training programme to facilitate self-regulation skills in professional athletes are briefly highlighted.

Journal Article↗
PubMed1990

Uncertainties in structural determinations of oligosaccharide conformation, using measurements of nuclear Overhauser effects.

A fundamental problem in the determination of molecular structure by n.m.r. spectroscopy is insufficient experimental constraints. This problem is particularly marked for oligosaccharides, where few constraints are available across glycosidic linkages. By calculating distances as a function of dihedral angle, it is shown that, in general, two n.O.e. constraints result in two possible conformations for each glycosidic linkage, one of which can usually be discarded on the basis of model building or energy calculations. Using these calculations, an estimate of the uncertainty in the structure can be obtained.

Carbohydrate Conformation↗
PubMedDate not supplied

Uncertainty and the difficulty of thinking through disjunctions.

This paper considers the relationship between decision under uncertainty and thinking through disjunctions. Decision situations that lead to violations of Savage's sure-thing principle are examined, and a variety of simple reasoning problems that often generate confusion and error are reviewed. The common difficulty is attributed to people's reluctance to think through disjunctions. Instead of hypothetically traveling through the branches of a decision tree, it is suggested, people suspend judgement and remain at the node. This interpretation is applied to instances of decision making, information search, deductive and inductive reasoning, probabilistic judgement, games, puzzles and paradoxes. Some implications of the reluctance to think through disjunctions, as well as potential corrective procedures, are discussed.

Decision Making↗
PubMed1992

Thinking through uncertainty: nonconsequential reasoning and choice.

When thinking under uncertainty, people often do not consider appropriately each of the relevant branches of a decision tree, as required by consequentialism. As a result they sometimes violate Savage's sure-thing principle. In the Prisoner's Dilemma game, for example, many subjects compete when they know that the opponent has competed and when they know that the opponent has cooperated, but cooperate when they do not know the opponent's response. Newcomb's Problem and Wason's selection task are also interpreted as manifestations of nonconsequential decision making and reasoning. The causes and implications of such behavior, and the notion of quasi-magical thinking, are discussed.

Choice Behavior↗
PubMed1987

Spatial information and uncertainty in anisometropic amblyopia.

Anisometropic amblyopes were found to have a reduced sensitivity for shape discrimination. The introduction of positional jitter in the elements of the display had a profound effect on the performance of the normal eye, but not on that of the amblyopic eye. On the other hand the introduction of gaussian blur affects the performance of both eyes to the same degree. We conclude that raised spatial uncertainty due to metrical scrambling is a suitable model for anisometropic amblyopia.

Adult↗
PubMed1993

Express saccades: the effects of spatial and temporal uncertainty.

Once trained to make express saccades, monkeys continue to make express saccades when there is a high level of uncertainty about both the location and the time of onset of a peripheral target. Providing additional information about the location and the time of onset of a peripheral target does not increase the frequency of occurrence of short latency saccades. Furthermore, the metrics of saccades with express latencies are typical of visually-guided saccades, rather than anticipatory movements or saccades to the remembered location of a target. Finally, practice on the gap paradigm restricted to one target location always viewed from the same initial eye position does not increase the probability of producing express saccades to the same target from other initial eye positions. Instead, the practice effect is specific to targets that have the same relative location, regardless of initial eye position.

Animals↗
PubMed1987

Uncertainty, inequalities in health and the demand for health.

As it has become increasingly recognized that inequalities in health stem more from inequalities in wealth, rather than from inequalities in access to medical care, economists have begun to suggest that Michael Grossman's model of the demand for health may be a useful analytical framework for investigating the issue. Ironically, the more popular of Grossman's two submodels--the 'pure-investment' model--provides little by way of insights into the relationship between inequalities in wealth and inequalities in health. In common with other pure investment models of human capital formation, Grossman's model predicts that an individual's health investment decisions at each stage in the lifecycle will be independent of his initial wealth. This paper shows that if uncertainty is introduced into the model, this result no longer holds. It also shows that if individuals display decreasing absolute risk aversion, wealthier individuals will invest more in health capital than individuals who start life with relatively small stocks of financial capital.

Health Services Needs and Demand↗