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At least 631 records · Page 35Linked to original sources
PubMed1995

Why is 9 + 7 harder than 2 + 3? Strength and interference as explanations of the problem-size effect.

In four experiments, the problem-size effect was investigated, using an alphabet-arithmetic task in which subjects verified such problems as A + 2 = C. Problem size was manipulated by varying the magnitude of the digit addend (e.g., A + 2, A + 3, and A + 4). The frequency and similarity of problems was also manipulated to determine the contribution of strength and interference, respectively. Experiment 1 manipulated frequency at low levels of practice and found that strength could account for the problem-size effect. Experiment 2 manipulated frequency at higher levels of practice, and found that strength alone could not account for the problem-size effect at asymptote. Experiment 3 manipulated frequency and similarity and found a substantial problem-size effect at asymptote, suggesting that both strength and interference contribute to the problem-size effect. Experiment 4 manipulated similarity, keeping frequency constant, and found no problem-size effect at asymptote, suggesting that interference alone is not responsible for the problem-size effect. The results are related to findings with number arithmetic.

Adult↗
PubMed1998

From algorithmic computing to direct retrieval: evidence from number and alphabetic arithmetic in children and adults.

A number of theories of mental arithmetic suggest that the ability to solve simple addition and subtraction problems develops from an algorithmic strategy toward a strategy based on the direct retrieval of the result from memory. In the experiment presented here, 2nd and 12th graders were asked to solve two tasks of number and alphabet arithmetic. The subjects transformed series of 1 to 4 numbers or letters (item span) by adding or subtracting an operand varying from 1 to 4 (operation span). Although both the item and operation span were associated with major and identical effects in the case of both numbers and letters at 2nd grade, such effects were clearly observable only in the case of letters for the adult subjects. This suggests the use of an algorithmic strategy for both types of material in the case of the children and for the letters only in the case of the adults, who retrieved numerical results directly from memory.

Adolescent↗
PubMed1999

Bars and lines: a study of graphic communication.

Interpretations of graphs seem to be rooted in principles of cognitive naturalness and information processing rather than arbitrary correspondences. These predict that people should more readily associate bars with discrete comparisons between data points because bars are discrete entities and facilitate point estimates. They should more readily associate lines with trends because lines connect discrete entities and directly represent slope. The predictions were supported in three experiments--two examining comprehension and one production. The correspondence does not seem to depend on explicit knowledge of rules. Instead, it may reflect the influence of the communicative situation as well as the perceptual properties of graphs.

Adult↗
PubMed1999

Mental multiplication: nothing but the facts?

Current models of adult arithmetic performance assume that representation includes only facts and procedures. However, other kinds of representations such as an analog scale or sets of number multiples might be useful in a variety of multiplication-related tasks. Introducing the practice transfer paradigm, we demonstrate that associations between distinct representational structures can be detected via cross-task transfer, provided that initial performance is retrieval based. Results support the predictions of the integrated-structures model of multiplication knowledge. Implications for well-established item differences such as the problem-size effect are addressed, and the question of how integration occurs is considered.

Adolescent↗
PubMed1998

Lead toxicokinetics. Development of a biokinetic model to understand and predict the outcome of treatment.

Quite often physicians contact the Dutch Poisons Control Centre for information on patients with increased lead exposure. The most important questions raised by physicians dealing with these patients are how to estimate the lead exposure and the total lead body burden, how to interpret blood lead concentrations and whether the patient needs treatment. In order to answer these questions we need knowledge of the toxicokinetics of lead in the human body. To achieve insight and to make this knowledge accessible to physicians a biokinetic model for lead metabolism in the human body was developed. A four-compartment model with first-order kinetics, based on the concept of Kneip, was used. A biokinetic model uses a mathematical approach to translate the complex biological and kinetic behaviour of lead. In order to develop this biokinetic model two computer programmes were used. At the moment the model is tested with clinical data from patient treated at the medical toxicology outpatient clinic of the Utrecht University Hospital (this department cooperates very closely with the National Poisons Control Centre). Especially with regard to chelation therapy for elevated blood lead levels due to chronic exposure, the model is very helpful in visualising the toxicokinetics of lead in the human body. Toxicokinetic model might help improve knowledge of lead toxicokinetics, leading to well-considered guidelines for treatment of lead intoxications.

Absorption↗
PubMed1985

Development of linear measurement in five- and six-year-old children.

This study sought to identify the higher level knowledge (e.g., conservation of number) necessary for a child to understand linear measurement and to chart the growth of linear measurement in terms of the development of its components. To assess the presence of these components, a battery of 34 number, length, and distance tasks was developed and administered to 100 children between the ages of 63 and 78 months from kindergarten and Grade 1. Results indicate that there is a substantial delay between acquisition of the necessary components and emergence of a mature grasp of linear measurement. The collection of components for the number and length domains form scaled sets; within each domain, however, the pattern of development is marked by discontinuities. These discontinuities are interpreted as being associated with the need to reorganize number and length concepts. Most elements of the observed sequences of development are predicted by Piagetian theory, although others, such as asynchronies between conservation and transitive inferences of nonequivalence, are more consistent with Gagne's (1968) model of development.

Child↗
PubMed1979

Developmental relations between notational counting and number conservation.

The 2 studies of this report sought to determine the developmental relationship between the child's use of counting as a notational symbol system to extract, compare, and reproduce numerical information and the development of number conservation. In study 1, children between 4 and 6 years of age were administered notational-counting and number-conservation tasks. Analysis of children's profiles across tasks indicated that children develop quantitative counting strategies (but do not necessarily count accurately) before they develop number-conservation concepts. In study 2, the generality of this sequence was tested. A population of 7- to 9-year-old "learning-disabled" children who reportedly were developing atypical counting skills were administered notational-counting and number-conservation tasks. All of these children who conserved number also used quantitative counting strategies, although some of these children frequently counted arrays inaccurately. The significance of these findings is discussed with respect to existing models of counting/number-conservation relations, and an alternative formulation is suggested based upon the new findings.

Child↗
PubMed1984

Long-term effects of four preschool programs: ninth- and tenth-grade results.

Follow-up of achievement test and IQ data on low-income black youths who had participated for 1 year in Bereiter-Engelmann, DARCEE, Montessori, or Traditional prekindergarten was continued through ninth and tenth grades. Stable trends persisted. Montessori males and DARCEE females were high; Montessori males were performing at about grade level on reading and math; IQs parallelled achievement test results. Additional tests of fluid intelligence, task persistence, self-esteem, divergent thinking, task approach, and aspirations and expectations were administered in ninth and tenth grades. Results from program comparisons and factor analyses were consistent with those on IQ and school achievement. The possibility of relationships between techniques used in the different preschool programs and sex differences in children's developmental level was discussed.

Achievement↗
PubMed1978

Stability of direct and transfer effects of number-conservation training with mentally retarded adults.

Twenty nonconserving retarded adults were assigned to equated training and control groups (n = 10 in each group). Training-group subjects were given multiple-strategy training for number conservation consisting of: demonstrating effects of addition-subtraction; negation of addition-subtraction by inverse operations; and addition-subtraction combined with perceptually induced cognitive conflict, reversibility, and verbal-rule instruction. Analyses of variance and critical difference multiple comparisons showed significant direct-training effects immediately after training and after 8 monhts. Significant short-term transfer was obtained on other types of conservation (discontinuous quantity, substance, liquid quantity, length, and weight), but long-term transfer was much weaker and less consistent. Transfer resulted primarily from gains in correct conservation judgements, with a majority of trained subjects failing to give any acceptable conservation explanations.

Adult↗
PubMed1985

Mathematical models of central pattern generators in locomotion: I. Current problems.

As a background for subsequent studies of mathematical models of central pattern generators in locomotion (Stafford & Barnwell, 1985a, b) relevant aspects of the literature on locomotion are reviewed, concepts of locomotion discussed, and extant models considered. Advantages and disadvantages of present models are discussed, and the need for mathematical models is emphasized. It is shown that realistic models of pattern generation in locomotion must take numerous factors into account, including phases of step cycle, muscle sequencing, gait and interlimb coordination, initiation and cessation of locomotion, and many aspects of neuromuscular control and function.

Journal Article↗
PubMed2006

Platform technologies to support brain-computer interfaces.

There is a lack of adequate and cost-effective treatment options for many neurodegenerative diseases. The number of affected patients is in the millions, and this number will only increase as the population ages. The developing areas of neuromimetics and stimulative implants provide hope for treatment, as evidenced by the currently available, but limited, implants. New technologies are emerging that are leading to the development of highly intelligent, implantable sensors, activators, and mobile robots that will provide in vivo diagnosis, therapeutic interventions, and functional replacement. Two key platform technologies that are required to facilitate the development of these neuromimetic and stimulative implants are data communication channels and the devices' power supplies. In the research reported in this paper, investigators have examined the use of novel concepts that address these two needs. These concepts are based on ionic volume conduction (VC) to provide a natural communication channel to support the functioning of these devices, and on biofuel cells to provide a continuously rechargeable power supply that obtains electrons from the natural metabolic pathways. The fundamental principles of the VC communication channels, including novel antenna design, are demonstrated. These principles include the basic mechanisms, device sensitivity, bidirectionality of communication, and signal recovery. The demonstrations are conducted using mathematical and finite element analysis, physical experiments, and animal experiments. The fundamental concepts of the biofuel cells are presented, and three versions of the cells that have been studied are discussed, including bacteria-based cells and two white cell-based experiments. In this paper the authors summarize the proof or principal experiments for both a biomimetic data channel communication method and a biofuel cell approach, which promise to provide innovative platform technologies to support complex devices that will be ready for implantation in the human nervous system in the next decade.

Animals↗
PubMed2005

Modelling skin disease: lessons from the worlds of mathematics, physics and computer science.

Theoretical biology is a field that attempts to understand the complex phenomena of life in terms of mathematical and physical principles. Likewise, theoretical medicine employs mathematical arguments and models as a methodology in approaching the complexities of human disease. Naturally, these concepts can be applied to dermatology. There are many possible methods available in the theoretical investigation of skin disease. A number of examples are presented briefly. These include the mathematical modelling of pattern formation in congenital naevi and erythema gyratum repens, an information-theoretic approach to the analysis of genetic networks in autoimmunity, and computer simulations of early melanoma growth. To conclude, an analogy is drawn between the behaviour of well-known physical processes, such as earthquakes, and the spatio-temporal evolution of skin disease. Creating models in skin disease can lead to predictions that can be investigated experimentally or by observation and offer the prospect of unexpected or important insights into pathogenesis.

Humans↗