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Biomedical subjects

R A Carlson

Publications and source records attributed to R A Carlson.

17 recordsLinked to original sources
PubMed1996

Cognitive sequence knowledge: what is learned?

In 4 experiments, participants performed running-arithmetic tasks. These tasks involved a sequential ordering of individual operations and a structure of subgoals that defined how calculations fit together in purpose. Consistent transitions between adjacent steps facilitated performance only when subgoal structures were relatively simple. When subgoal structures were more complex, consistent mapping of operations to serial locations produced a slight benefit. Consistency of subgoal structure produced a substantial benefit in both speed and accuracy, and some knowledge of subgoal structure integrated with knowledge of the sequence of operations. Apparently, a task's subgoal structure imposes demands that either facilitate or obscure benefits of sequence consistencies. The benefits are attributed to increased efficiency in using working memory.

Adult↗
PubMed1993

Coordinating information from perception and working memory.

Individuals must often coordinate information in working memory with information from perception. The demands of coordination have been analyzed in terms of the cost to switch attention. Coordination is considered in terms of the organization of control processes. Ss in 4 experiments performed list-processing tasks that sometimes required alternation between sets of items that were held in working memory or were currently displayed. Experiment 1 demonstrated that performance was slower and more error-prone when alternating between sets than when reporting a single set. On alternation tasks, latency varied with serial position, indicating that Ss paused between pairs of responses. In Experiment 2, this serial position function was observed for tasks requiring alternation between sets of information in the same modality (memory or perception). Experiments 3 and 4 demonstrate that this effect depends on the requirement to generate a new sequence of responses. A model of control processes for coordination is developed and tested.

Adult↗
PubMed1992

Strategy guidance and memory aiding in learning a problem-solving skill.

Guidance can help learners overcome the difficulties of getting started in a novel domain, but it is often ineffective in promoting learning and transfer. This article examines two aspects of guidance--communicating solution strategies for a problem domain and providing working memory support--in learning a novel problem-solving skill. Subjects in two experiments learned to troubleshoot simulated information networks. The learning environment varied in type of guidance provided--none, variable template, fixed template, and procedural instruction--and in availability of memory aiding. Variable-template guidance was effective when memory aiding was provided, and procedural instructions produced effective learning with or without memory aiding. However, fixed-template guidance was not effective, and there was no consistent effect of memory aiding in unguided, discovery learning conditions. The results have theoretical implications for the locus of guided-learning effects and suggest practical guidelines for the design of guided-learning environments.

Computer Communication Networks↗
PubMed1989

Acquisition context and the use of causal rules.

Judgmental asymmetries in using causal knowledge (e.g., for prediction or diagnosis) have been attributed to the inherent directionality of causal knowledge. The present study examines the effect of acquisition context--representations used for initial instruction, and the type of judgement required during acquisition--on judgments using causal rules. In contrast to traditional concept formation research, this paradigm examined the development of procedures for using rules, rather than rule induction. College-student subjects learned to use causal rules describing digital logic gates, receiving instruction with either verbal rules or truth tables, and practicing either predicting or verifying logic-gate outputs. After 200 trials of practice with each rule, subjects were transferred to the untrained judgment task. Transfer was strongly asymmetrical. Subjects trained to make prediction judgments were slowed substantially by transfer to the verification task, while subjects trained to make verification judgments had little difficulty with transfer to the prediction task. Truth-table representations resulted in superior performance, especially for verification judgments. Contrary to prediction, verification judgments always required more time. The results demonstrate that acquisition context may be partly responsible for judgmental asymmetries, and imply that examining conditions of acquisition is important for understanding how causal knowledge is used.

Humans↗
PubMed1985

Budd-Chiari syndrome presenting as sudden infant death.

Budd-Chiari syndrome rarely occurs in infants. We report a case of a 1-month-old female infant who presented as a sudden infant death and was found at autopsy to have thrombi occluding both hepatic veins. Microscopically the liver showed perivenular fibrosis extending into the lobule and central venous congestion consistent with Budd-Chiari syndrome.

Budd-Chiari Syndrome↗
PubMed1980

Characterization of a unique population of unfilled estrogen-binding sites associated with the nuclear fraction of immature rat uteri.

Studies were initiated to determine whether resident nuclear estrogen receptors with unfilled binding sites existed in the nuclear fraction of uteri from untreated immature rats. These studies revealed a small population (mean +/- SEM, 0.087 +/- 0.017 pmol/uterus) of unfilled estrogen-binding sites in the uterine nuclear fraction from untreated immature rats, which bound [3H]estradiol in the absence of added cytoplasmic receptor. These nuclear estrogen-binding sites occurred in addition to the 0.60--1.2 pmol estrogen-binding activity/uterus in the uterine cytoplasmic fraction of these animals. [3H]Estradiol bound reversibly with high affinity (apparent Kd = 1.4 x 10(-10)M to these binding sites, and only estrogenic compounds competed for this binding. Binding studies done at a variety of temperatures (0--37 C) showed that there were no estradiol-filled receptor sites associated with the nuclear fraction. In addition, these unfilled nuclear estrogen-binding sites remained unfilled 15 min after injections of either 1.0 or 0.1 micrograms estradiol/rat. Extraction of these sites was achieved with 0.4 M KCl, and when this extract was centrifuged on a 5--20% linear 0.010 M Tris-HCl, 0.0015 M Na2EDTA, and 0.40, M KCl sucrose gradient, the binding activity exhibited a sedimentation coefficient of 3.6S. These unfilled nuclear estrogen-binding sites did not appear to have arisen as a contaminant from the estrogen-binding proteins present in either uterine cytoplasm or serum during tissue homogenization. The existence of these unfilled nuclear estrogen-binding sites does not represent a major exception to the classical two-step theory of estrogen action; instead, they seem to be novel forms of the estrogen receptor whose physiological role has not been determined.

Animals↗
PubMed1976

Pulmonary involvement by histiocytosis X in the pediatric age group.

The lungs may be involved by histiocytosis X either as part of a generalized disease or as a separate entity, primary pulmonary histiocytosis X. The former is much more frequent in the pediatric age group, and although it occurs primarily in those who are quite sick with widely disseminated disease, the lung involvement rarely caused symptoms and almost invariably clears. By contrast, primary pulmonary histiocytosis X is mainly seen in young adult males and frequently leads to severe disability. Twelve patients less than 20 years old with lung involvement by histiocytosis X are presented.

Adolescent↗
PubMedDate not supplied

Retrorectal cyst-hamartomas: CT diagnosis.

Retrorectal cyst-hamartomas (RRCH) are congenital lesions characterized by the presence of cysts lined by multiple types of epithelium, often predominantly mucin-secreting. Three cases of RRCH are presented with their associated histologic and CT findings. The lesion requires complete surgical excision to prevent complications of recurrence, infection, or metastasis.

Adult↗
PubMedDate not supplied

Dose comparisons for mammographic systems.

Dose estimates were made for Kodak Min-R screens combined with Kodak Min-R film and Kodak Ortho M film, both with and without a 5:1 Bucky grid; for standard xeroradiographic techniques in negative development mode; and for the new, higher sensitivity xeroradiographic process of the Xerox 175 System. The estimates were derived from exposure versus depth measurements in phantoms made of BR12 breast simulation material using thermoluminescent detectors. A molybdenum target source with molybdenum filtration, at a half-value layer of 0.37-mm Al, was used for the screen-film measurements. All xeroradiographic measurements were made with a tungsten target source with aluminum filtration at half-value layers of 1.5 to 1.56 mm Al. Mean glandular dose estimates for the Min-R screen/Ortho M film combination with Bucky grid and for the new xeroradiographic process were found to be similar. Dose reduction with the new xeroradiographic system was achieved through a more sensitive photoreceptor and more sensitive development, which also improved the unique imaging characteristics of xeroradiography.

Biophysical Phenomena↗