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PubMed1990

Strategy knowledge and strategy change in skilled performance: a study of the game Othello.

Skill and skill development in playing the game Othello were investigated. In particular, we studied the role of strategies and strategy change, rather than focusing on knowledge of particular board patterns. The history of the development of the game suggests a shift from positional to mobility strategies, a change which also is reproduced in the development of individual players. The first two studies used historical analysis of tournament transcripts to study strategy change. The third study investigated one possible basis for the greater accessibility or ease of positional versus mobility strategy, namely differential encoding and memorability of typical board patterns. Study 3 demonstrated that completely naive as well as positional players remember positional games and moves more easily than mobility games and moves. The easier mastery of positional strategy may be caused in part by the greater ease of encoding typical positional patterns. We suggest that strategic change and conceptual reorganization may be particularly important for domains where the naive encoding of events is not the most apt. We also suggest that similarities exist between strategy change in Othello and other domains.

Attention↗
PubMed1990

[Comparative pathophysiology of the atrioventricular node].

The apparent mismatch between size and electrical function of the mammalian heart can be exemplified by the relation between ventricular rate during atrial fibrillation in dog, human, and horse, and bodyweight. The same is true for the relation between atrioventricular transmission time and heart size. While heart size may increase with a factor of 10(8), PR interval (on the surface ECG) will only increase with a factor 30. The curve of the PR interval versus the third root of heart weight has an S-shape. This form of relation cannot easily be explained on the basis of current electrophysiological theories. The contribution of the AV nodal delay to AV transmission time probably diminishes with increasing heart size. The mechanism of AV nodal delay is therefore not clear. Right ventricular pacing with intervals twice as long as the shortest PR-intervals in patients with atrial fibrillation results in complete block of anterograde conduction. The AV node as an unprotected pacemaker, entrained during sinus rhythm and electrotonically modulated during atrial fibrillation, rather than a cable with conduction properties, may offer an explanation for the non-linear and non-conductive behaviour of the AV node. This may well have consequences for the treatment of patients with atrial fibrillation.

Animals↗
PubMed1986

Uterine fluid volume. Cyclic variations and possible extrauterine contributions.

Uterine fluid (UF) was obtained from 12 women at midcycle and in the midluteal phase using a standardized sampling technique allowing comparison of samples by volume. Much greater volumes were encountered at midcycle (83-180 microL) than in the midluteal phase (5-35 microL). Six of the women who had previously been sterilized by laparoscopic coagulation of the fallopian tubes had lower midcycle volumes (83-127 microL) than had the women in the nonsterilized group (113-180 microL), indicating that UF is probably supplemented by fluid from the tubes at midcycle. Support for the theory that at least some of this additional fluid may be of peritoneal origin comes from observations on the concentrations of estradiol and progesterone in the peritoneal, tubal and uterine fluids.

Adult↗
PubMed1985

Morphological differences in cutaneous and skeletal muscle vasculature during compensatory and decompensatory hemorrhagic hypotension.

PURPOSE: to determine if morphological differences exist between vasculature shown to decompensate, ie, skeletal muscle (SM) and vasculature that maintains the compensatory effort, ie, cutaneous (C). METHODS: dogs were anesthetized and subjected to a Wiggers hemorrhagic shock protocol. SM and C flows were monitored using electromagnetic flowmeters. Gracilis (SM) and saphenous (C) arterial segments were removed during: prehemorrhage control, compensation, and decompensation. Segments were fixed at in vivo intraluminal pressures. Both light and EM sections were made from each sample. RESULTS: During the compensatory phase, both SM and C showed signs of strong vasoconstriction. Even though the amount of endothelial folding was comparable, the C did and the SM did not sustain the vasoconstriction. Vascular diameters of the SM but not C increased during decompensation. Ultrastructural changes consisted of extreme folding of the internal elastic lamina (IEL) during compensation and subsequent flattening out of the IEL during decompensation in the SM but not the C tissues. Cell deformation, damage, and exfoliation were seen in both SM and C tissues. CONCLUSION: The data are consistent with the theory that SM vasculature, specifically endothelium, synthesizes an inhibitor of NE release, probably prostaglandins.

Animals↗
PubMed1995

[Traumatic myositis ossificans. Posttraumatic non-neoplastic heterotopic ossification].

Myositis ossificans traumatica (MOT) is a nonneoplastic, heterotopic ossification of soft tissues i.e. skeletal muscle, tendons, aponeuroses and fascia. It is often encountered in young male athletes participating in contact sports as a result of a single or repeated contusion. MOT tends to be solitary, localized and well circumscribed with a self-limited growth potential that may culminate in regression. The pathogenesis of MOT is still enigmatic. Recent animal experiments have led to a theory that mesenchymal connective tissue cells, undergo metaplasia induced by trauma and probably osteogenic proteins, to fibroblasts and osteoblasts. These cells deposit and structure osteoid centripetally in the lesion. As the lesion matures, cancellous bone develops into mature, lamellar bone in the periphery of the lesion. In its earlier stages MOT is easily cytologically and radiologically confused with osteogenic sarcoma. The management of MOT is largely conservative and the principles are of considerable value to physicians and physiotherapists engaged in the treatment of sports injuries. This article reviews the various forms of myositis ossificans as well as the pathology, diagnosis and treatment options.

Adolescent↗
PubMedDate not supplied

Experience of risk for pregnant black women.

This qualitative study explores how risk is determined by black women during pregnancy. A total of 17 women were assessed for risk; 7 were at risk for preterm birth, and 10 were not at risk. These women were interviewed by using an open-ended interview guide. The transcribed interviews were analyzed by using grounded theory. Risk was defined by the provider's assessment of a mathematical probability of the occurrence of preterm labor according to the risk screening tool developed by Creasy. Risk was also defined by black women on the basis of their experience of problematic change, on the counsel of other black women, and on the assessment of the provider. All of the women perceived their pregnancy as a normal process. For some, that perception never changed; for others, it did change. The change was precipitated by the occurrence of an unexpected event, indicated in this study as a critical moment. The critical moment is a dynamic interplay among biophysical changes, patterns of social interaction, and intersubjective reflection. These findings emphasize the black woman's reliance on herself in problematic situations and the significant role of sharing between black women in perpetuating their culture's normative expectations concerning pregnancy.

Black or African American↗
PubMed1997

Classification and acute management of thoracolumbar fractures.

Successful management of traumatic injuries of the thoracolumbar spine requires understanding of the concepts of spinal stability and instability. There are numerous classifications of injury patterns based on fracture type and the probable forces involved. This article focuses on Denis's three-column theory of spinal stability and its utility in categorizing five injury patterns and the forces involved: specifically, wedge compression fractures, burst fractures, flexion distraction injuries, fracture dislocations, and miscellaneous injuries. The authors also highlight the acute management and evaluation of patients suspected to have these types of injuries.

Acute Disease↗
PubMed1998

On the application of information theory to neural spike trains.

The nervous system represents time-dependent signals in sequences of discrete action potentials or spikes are identical so that information is carried only in the spike arrival times. We show how to quantify this information, in bits, free from any assumptions about which features of the spike train or input waveform are most important. We apply this approach to the analysis of experiments on a variety of systems, including some where we confront severe sampling problems, and discuss some to the results obtained and hopes for future extensions.

Animals↗
PubMed1990

Choice behavior in transition: development of preference for the higher probability of reinforcement.

Ten acquisition curves were obtained from each of 4 pigeons in a two-choice discrete-trial procedure. In each of these 10 conditions, the two response keys initially had equal probabilities of reinforcement, and subjects' choice responses were about equally divided between the two keys. Then the reinforcement probabilities were changed so that one key had a higher probability of reinforcement (the left key in half of the conditions and the right key in the other half), and in nearly every case the subjects developed a preference for this key. The rate of acquisition of preference for this key was faster when the ratio of the two reinforcement probabilities was higher. For instance, acquisition of preference was faster in conditions with reinforcement probabilities of .12 and .02 than in conditions with reinforcement probabilities of .40 and .30, even though the pairs of probabilities differed by .10 in both cases. These results were used to evaluate the predictions of some theories of transitional behavior in choice situations. A trial-by-trial analysis of individual responses and reinforcers suggested that reinforcement had both short-term and long-term effects on choice. The short-term effect was an increased probability of returning to the same key on the one or two trials following a reinforcer. The long-term effect was a gradual increase in the proportion of responses on the key with the higher probability of reinforcement, an increase that usually continued for several hundred trials.

Animals↗
PubMed2001

Endodontic retreatment. Aspects of decision making and clinical outcome.

Epidemiological surveys have reported that 25%-35% of root filled teeth are associated with periapical radiolucencies. Descriptive studies have demonstrated that clinicians' decision making regarding such teeth are subject to substantial variation. A coherent model to explain the observed variation has not been produced. In the present thesis a "Praxis Concept theory" was proposed. The theory suggests that dentists perceive periapical lesions of varying sizes as different stages on a continuous health scale. Interindividual variations can then be regarded as the result of the choice of different cut-off points on the continuum for prescribing retreatment. In the present study experiments among novice and expert decision makers gave evidence in favour of the theory. Data also suggested that the choice of retreatment criterion is affected by values, costs of retreatment and technical quality of original treatment. From a prescriptive point of view, the presence of a persistent periapical radiolucency has often been used as a criterion of endodontic "failure" and as an indication for endodontic retreatment. As an alternative decision strategy, the use of decision analysis has been proposed. Logical display of decision alternatives, values of probabilities, utility values (U-values) of the different outcomes and calculation of optimal decision strategy are features of this theory. The implementation of this approach is impeded by the uncertainty of outcome probabilities and lack of investigations concerning U-values. U-values of two periapical health states in root filled teeth (with and without a periapical lesion respectively) were investigated in a group of 82 dental students and among 16 Swedish endodontists. Two methods were used to elicit U-values: Standard gamble and Visual Analogue Scale. Large interindividual variation for both health states were recorded. The difference in U-values between the two health states was found to be statistically significant regardless of assessment method. Compared with Standard gamble Visual Analogue Scale systematically produced lower ratings. U-values were found to change considerably in both the short and long-term. Any significant correlation between endodontists' U-values and retreatment prescriptions could not be demonstrated. Surgical and nonsurgical retreatment were randomly assigned to 95 "failed" root filled teeth in 92 patients. Cases were followed clinically and radiographically for four years postoperatively. At the 12-month recall a statistically significant higher healing rate was observed for teeth retreated surgically. At the final 48-month recall no systematic difference was detected. Patients were found to be more subject to postoperative discomfort when teeth were retreated surgically compared with nonsurgically. Consequently, surgical retreatment tended to be associated with higher indirect costs than a nonsurgically approach. In the final part of the thesis it is argued that retreatment decision making in everyday clinical practice normally should be based on simple principles. It is suggested that in order to achieve the best overall consequence a periapical lesion in a root filled tooth that is not expected to heal should be retreated. Arguments to withhold retreatment should be based on (i) respect for patient autonomy, (ii) retreatment risks or (iii) retreatment costs.

Decision Making↗
PubMed2005

Survival probability of diffusion with trapping in cellular neurobiology.

The problem of diffusion with absorption and trapping sites arises in the theory of molecular signaling inside and on the membranes of biological cells. In particular, this problem arises in the case of spine-dendrite communication, where the number of calcium ions, modeled as random particles, is regulated across the spine microstructure by pumps, which play the role of killing sites, while the end of the dendritic shaft is an absorbing boundary. We develop a general mathematical framework for diffusion in the presence of absorption and killing sites and apply it to the computation of the time-dependent survival probability of ions. We also compute the ratio of the number of absorbed particles at a specific location to the number of killed particles. We show that the ratio depends on the distribution of killing sites. The biological consequence is that the position of the pumps regulates the fraction of calcium ions that reach the dendrite.

Animals↗
PubMedDate not supplied

Probabilistic analysis of decision trees using symbolic algebra.

Uncertainty in medical decision making techniques occurs in the specification of both decision tree probabilities and utilities. Using a computer-based algebraic approach, methods for modeling this uncertainty have been formulated. This analytic procedure allows an exact calculation of the statistical variance at the final decision node using automated symbolic manipulation. Confidence and conditional confidence levels for the preferred decision are derived from gaussian theory, and the mutual information index that identifies probabilistically important tree variables is provided. The computer-based algebraic method is illustrated for a problem previously analyzed by Monte Carlo simulation. This methodology provides the decision analyst with a procedure to evaluate the outcome of specification uncertainty, in many decision problems, without resorting to Monte Carlo analysis.

Adult↗
PubMed1996

Measurement of pulsatile flow using MRI and a Bayesian technique of probability analysis.

This work shows that complete spatial information of periodic pulsatile fluid flows can be rapidly obtained by Bayesian probability analysis of flow encoded magnetic resonance imaging data. These data were acquired as a set of two-dimensional images (complete two-dimensional sampling of k-space or reciprocal position space) but with a sparse (six point) and nonuniform sampling of q-space or reciprocal displacement space. This approach enables more precise calculation of fluid velocity to be achieved than by conventional two q-sample phase encoding of velocities, without the significant time disadvantage associated with the complete flow measurement required for Fourier velocity imaging. For experimental comparison with the Bayesian analysis applied to nonuniformly sampled q-space data, a Fourier velocity imaging technique was used with one-dimensional spatial encoding within a selected slice and a uniform sampling of q-space using 64 values of the pulsed gradients to encode fluid flow. Because the pulsatile flows were axially symmetric within the resolution of the experiment, the radial variation of fluid velocity, in the direction of the pulsed gradients, was reconstructed from one-dimensional spatial projections of the velocity by exploiting the central slice theorem. Data were analysed for internal consistency using linearised flow theories. The results show that nonuniform q-space sampling followed by Bayesian probability analysis is at least as accurate as the combined uniform q-space sampling with Fourier velocity imaging and projection reconstruction method. Both techniques give smaller errors than a two-point sampling of q-space (the conventional flow encoding experiment).

Bayes Theorem↗