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PubMed1977

Influence of population on the classification of ECG-VCG's using linear regression techniques.

This paper describes the influence of different populations on statistical multivariate classification rules and classification results where the word "population" refers only to the frequency of diagnoses to be expected, the so-called prior probabilities. Using linear regression as a multivariate classification technique and six groups consisting of five pathological conditions and normals as test data, it has been shown: (a) That the population influences to a great extent the selection of the best ECG-VCG measurements for the classification rule. (b) That a mismatch of the populations in the learning and test sets can considerably decrease the number of correct classifications. (c) That a certain correction of the mismatch can be achieved when the prior probabilities in the learning and test sets are known, Further, the paper discusses the change of prior probabilities over the years at the Variety Club Heart Hospital in the University of Minnesota and its effect on the performance of the classification algorithm which has been used.

Electrocardiography↗
PubMed2004

Mechanisms of theory formation in young children.

Research suggests that by the age of five, children have extensive causal knowledge, in the form of intuitive theories. The crucial question for developmental cognitive science is how young children are able to learn causal structure from evidence. Recently, researchers in computer science and statistics have developed representations (causal Bayes nets) and learning algorithms to infer causal structure from evidence. Here we explore evidence suggesting that infants and children have the prerequisites for making causal inferences consistent with causal Bayes net learning algorithms. Specifically, we look at infants and children's ability to learn from evidence in the form of conditional probabilities, interventions and combinations of the two.

Bayes Theorem↗
PubMed1994

Both non-NMDA and NMDA glutamate receptors are necessary for memory consolidation in the day-old chick.

Day-old chicks (black Australorp-white Leghorn) trained to avoid an aversive stimulus will usually retain memory for this event indefinitely. The passive avoidance task used involves a period of pretraining where chicks peck freely at two differently colored glass beads, a single training trial where one of the beads is coated in a chemical aversant eliciting typical disgust reactions from the chicks, and a test trial where both beads are presented dry, and discrimination memory is demonstrated by avoidance of the previously aversive bead with continued pecking of the nonaversive bead. Intracranial administration of a N-methyl-D-aspartate glutamate receptor antagonist (50 microM 2-amino-5-phosphopentanoate) immediately after or prior to learning, or a non-N-methyl-D-aspartate glutamate receptor antagonist (100 microM 6,7-dinitro-quinoxaline-2,3-dione) between 10 and 25 min after learning, resulted in amnesia for this task at 80 to 90 min post-training. These data indicate that processes dependent on N-methyl-D-aspartate and non-N-methyl-D-aspartate glutamate receptor activation are necessary for memory consolidation of a passive avoidance task in the day-old chick. Since these agents must be administered during the earlier stages of memory formation to cause amnesia, the receptors are probably activated close to the time of learning. The delayed effect of these antagonists, however, suggests that memory is independent of these receptors until quite late in the memory consolidation process.

2-Amino-5-phosphonovalerate↗
PubMed2005

Competition between simultaneous stimuli modulated by location probability in hemispatial neglect.

Many aspects of spatial neglect can be explained as arising from competition for attentional selection, with salient ipsilesional stimuli emerging as the winner more often than contralesional stimuli. The outcome of the competition, however, can be affected both by bottom-up perceptual factors such as the gestalt properties of the display and by top-down factors such as expectancy or stimulus blocking. This study examines whether the competition for attentional selection can be modulated by manipulating the probability of the target's location in hemispatial neglect. Five patients with left-sided hemispatial neglect and a group of control participants performed a visual target discrimination task. In equal probability blocks, the target appeared randomly in any of six possible horizontal locations (three left, three right) whereas in biased blocks, the target appeared in the mid-location on the left on 50% of the trials and in each of the other locations on 10% of the trials. The target appeared either alone or was accompanied by a distractor on the opposite side. The results showed that the spatial bias facilitated detection of all left-sided targets in the neglect group, but was more spatially specific in the control group. Furthermore, while distractors on either side interfered with target processing in both groups, the patterns differed across the visual field. Finally, the magnitude of facilitation due to the bias was greatest in the condition with the most inhibition, i.e. a left-sided target accompanied by a right-sided distractor in the neglect group. These data underscore the competitive push-pull relationship between different bottom-up and top-down attentional factors, particularly within neglect patients, in whom a strong ipsilesional attentional bias already exists.

Aged↗
PubMed1998

Acute exposure to a 60 Hz magnetic field affects rats' water-maze performance.

Rats were trained in six sessions to locate a submerged platform in a circular water-maze. They were exposed to a 1 mT, 60 Hz magnetic field for one hour in a Helmholtz coil system immediately before each training session. In addition, one hour after the last training session, they were tested in a probe trial during which the platform was removed and the time spent in the quadrant of the maze in which the platform was located during the training sessions was scored. Control animals were sham-exposed using the exposure system operating with the coils activated in an anti-parallel direction to cancel the fields. A group of "non-exposed" control animals was also included in the study. There was no significant difference between the magnetic field-exposed and control animals in learning to locate the platform. However, swim speed of the magnetic field-exposed rats was significantly slower than that of the controls. During the probe trial, magnetic field-exposed animals spent significantly less time in the quadrant that contained the platform, and their swim patterns were different from those of the controls. These results indicate that magnetic field exposure causes a deficit in spatial "reference" memory in the rat. Rats subjected to magnetic field exposure probably used a different behavioral strategy in learning the maze.

Animals↗
PubMed2000

Hippocampal mossy fibers and swimming navigation learning in two vole species occupying different habitats.

We showed previously for mice that size differences of the infrapyramidal hippocampal mossy fiber projection (IIP-MF) correlate with spatial learning abilities. In order to clarify the role of the IIP-MF in a natural environment, we studied the bank vole (Clethrionomys glareolus), adapted to a wide range of different habitats, and the root vole (Microtus oeconomus), living in homogenous grassland habitats with small home ranges. Morphometry on Timm-stained horizontal brain sections of six C. glareolus and six M. oeconomus revealed that the size of the entire mossy fiber projection was 42% larger in C. glareolus than M. oeconomus. C. glareolus had also an IIP-MF projection about 230% larger than that of the root vole. A sample of captured animals was then transferred to the laboratory (C. glareolus, n = 23; M. oeconomus, n = 15) and underwent testing for swimming navigation according to a standardized protocol used to assess water maze learning in about 2,000 normal and transgenic mice. Both species learned faster than laboratory mice. Overall escape times showed no differences, but path length was significantly reduced in C. glareolus, which also showed superior performance in a variety of scores assessing spatial search patterns. On the other hand, M. oeconomus showed faster swimming speed, and strong thigmotaxis combined with circular swimming. M. oeconomus also scored at chance levels during the probe trial, about as poorly as mutant knockout mice considered to be deficient in spatial memory. These differences probably reflect differential styles of water maze learning rather than spatial memory deficits: C. glareolus appears to be superior in inhibiting behavior interfering with proper spatial search behavior, while M. oeconomus succeeds in escaping by using rapid circular swimming. We assume that size variations of the IIP-MF correspond to a mechanism stabilizing hippocampal processing during spatial learning or complex activities. This corresponds to the ecological lifestyle of the two species and is in line with previous observations on the role of the IIP-MF.

Animals↗
PubMed2001

Effects of binge ethanol administration on the behavioral outcome of rats after lateral fluid percussion brain injury.

This study examined the effects of 4 weeks of binge ethanol administration (BEAn) on the behavioral outcome in rats after lateral fluid percussion (FP) brain injury. Rats were intragastrically given 7.5 mL/kg of either 40% ethanol in 5% glucose solution (3 g ethanol/kg; binge ethanol group), or 5% glucose solution (vehicle group), twice on Thursday and Friday of 3 consecutive weeks. Then rats from both groups were subjected to either lateral FP brain injury of moderate severity (1.8 atm) or to sham operation. Postinjury behavioral measurements revealed that brain injury caused significant spatial learning disability in both groups. There were no significant differences in mean search latencies in the sham animals between the vehicle and binge ethanol groups. On the other hand, the mean search latency of the binge ethanol group was significantly higher than that of the vehicle group in trial blocks 2 and 4. There were no significant differences in the target visits (expressed as mean zone difference [MZD]) during the probe trial between the injured animals of binge ethanol and vehicle groups. However, there was only a minor trend towards worsened MZD score in the binge-injured animals. Histologic analysis of injured animals from both injured ethanol and vehicle groups revealed similar extents of ipsilateral cortical and observable hippocampal damage. These results suggest that 4 weeks of binge ethanol treatment followed by ethanol intoxication at the time of injury worsens some aspects of the spatial learning ability of rats. This worsening is probably caused by subtle, undetectable morphologic damage by binge ethanol administration.

Animals↗
PubMed2005

Probability matching in the right hemisphere.

Previously it has been shown that the left hemisphere, but not the right, of split-brain patients tends to match the frequency of previous occurrences in probability-guessing paradigms (Wolford, Miller, & Gazzaniga, 2000). This phenomenon has been attributed to an "interpreter," a mechanism for making interpretations and forming hypotheses, thought to reside exclusively in the left hemisphere. In this study with a split-brain patient, we had him guess one of two types of faces, stimuli known to be preferentially processed in the right hemisphere of this patient. Unlike previous studies using other kinds of stimuli, the right hemisphere matched the frequency of the previous occurrences of a face-type, but the left hemisphere did not.

Adult↗
PubMed2003

Monitoring cell cycle distributions in living cells by videomicrofluorometry and discriminant factorial analysis.

BACKGROUND: The study of the cell cycle of living cells is often based on quantification of nuclear DNA. These studies may be improved by multifactorial analysis evaluating several parameters for each cell. METHODS: Single lymphoblastoid living cells were labeled with three fluorescent markers: Hoechst 33342 for nuclear DNA, Rhodamine 123 for mitochondria, and Nile Red for plasma membrane. Numerical image analysis allowed us to obtain, for each cell, morphological parameters (e.g., cell size, nuclear size, and shape) and functional information (e.g., nuclear DNA content, level of mitochondria energetic state, and the amount and properties of the plasma membrane) by fluorescence intensity. These parameters were used in a typological analysis that separated control cells into four groups. RESULTS: A discriminant factorial analysis (DFA) confirmed the four groups: G0-G1, S, G2+M, and polyploid cells called Gn. These groups were significantly different, with a classification probability of 0.9999; these control cells defined a learning population. Different populations of untreated and adriamycin-treated cells were analyzed as additional individuals within a DFA and were classified into the G0-G1, S, G2+M, and Gn groups by their probability of belonging to each of the groups. CONCLUSIONS: This approach is particularly efficient when it is used to determine variations in cellular properties and to objectively study cellular populations.

Cell Cycle↗
PubMed1995

Learned irrelevance is not the sum of exposure to CS and US.

In three experiments hungry rats received appetitive conditioning trials with a light that signalled the delivery of sucrose solution. In Experiment 1, prior exposure to uncorrelated presentations of the conditioned stimulus (CS) and unconditioned stimulus (US) retarded conditioning significantly more than did prior exposure to the CS alone. In Experiments 2 and 3, groups exposed to uncorrelated presentations of the CS and US within the same session conditioned significantly more slowly than groups given separate sessions of exposure to the CS followed by sessions of exposure to the US (or vice versa). Some part of the learned irrelevance effect depends on exposure to a zero correlation between the CS and US, perhaps because this promotes learning that the CS predicts no change in the probability of the US.

Animals↗
PubMed2002

A network representation of response probability in the striatum.

The striatum of the basal ganglia is considered a key structure in the learning circuitry of the brain. To analyze neural signals that underlie striatal plasticity, we recorded from an identifiable class of striatal interneurons as macaque monkeys underwent training in a range of conditioning and non-associative learning paradigms, and recorded eyeblink electromyographs as the measure of behavioral response. We found that the responses of these striatal interneurons were modifiable under all training conditions and that their population responses were tightly correlated with the probability that a given stimulus would evoke a behavioral response. Such a network signal, proportional to current response probability, could be crucial to the learning and decision functions of the basal ganglia.

Animals↗
PubMed1999

Learning abilities, NGF and BDNF brain levels in two lines of TNF-alpha transgenic mice, one characterized by neurological disorders, the other phenotypically normal.

In this study we used two lines of transgenic mice overexpressing tumor necrosis factor alpha (TNF-alpha) in the central nervous system (CNS), one characterized by reactive gliosis, inflammatory demyelination and neurological deficits (Tg6074) the other showing no neurological or phenotypical alterations (TgK3) to investigate the effect of TNF-alpha on brain nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) levels and learning abilities. The results showed that the amount of NGF in the brain of Tg6074 and TgK3 transgenic mice is low in the hippocampus and in the spinal cord, increases in the hypothalamus of Tg6074 and showed no significant changes in the cortex. BDNF levels were low in the hippocampus and spinal cord of TgK3. BDNF increased in the hypothalamus of TgK3 and Tg6074 while in the cortex, BDNF increased only in Tg6074 mice. Transgenic mice also had memory impairments as revealed by the Morris Water Maze test. These findings indicate that TNF-alpha significantly influences BDNF and NGF synthesis, most probably in a dose-dependent manner. Learning abilities were also differently affected by overexpression of TNF-alpha, but were not associated with inflammatory activity. The possible functional implications of our findings are discussed.

Animals↗
PubMed2002

Implementation of nutrition education and rehabilitation programs (NERPs) in Viet Nam.

Rigorous assessments of program quality are uncommon in developing countries. We evaluated the quality of the two-week, volunteer-facilitated, caregiver-child rehabilitation "hearth," or nutrition education and rehabilitation program (NERP), sessions in Save the Children's integrated nutrition program in Viet Nam. Field workers observed attendance, food contribution, food preparation, meal consumption, health message delivery, hygiene, and weighing at 240 NERP days at 59 NERP centers during seven months of implementation. Participation in cooking NERP meals (75.8%), washing mothers' and children's hands (75.7% and 81.6%, respectively), and weighing (74.5% on days 1 and 12) were high, but attendance rates (50.3%), food contributions (20.3%), and health message delivery (20.0%) were lower than expected, all with wide variation among communes, ecology, NERP day, and NERP round. Contrary to protocol, food was often delivered to malnourished children who stayed at home to accommodate caregivers' workloads and other constraints. While home-delivery of food prevented caregivers from learning from each other in a group, it did bring "tangible messages" (i.e., a large serving size of a new food) to the doorstep. Health volunteers were wise to stress active learning over repetitive message delivery. In summary, these NERPs were probably typical of previous NERPs although comparable quality measures are lacking. Despite imperfect implementation, the NERP's active-learning and local problem-solving helped achieve measurable impact on growth, diet, morbidity, and empowerment despite uncommon program challenges, such as uncharacteristically low baseline levels of malnutrition and high population dispersion. Regular quality monitoring may enhance impact even further.

Adult↗
PubMed1989

Learning problems in neurofibromatosis patients.

Learning problems in patients with neurofibromatosis (NF) are probably the most frequent characteristics after those that define the disorder. They are not secondary to the physical problems. A recent survey that compared children who have NF with their siblings revealed a 37% greater incidence of learning disabilities in the children with NF. Intelligence quotient (IQ) data from several studies indicate that almost all patients with NF have a normal IQ, but there is a progression from low normal to normal as these patients reach adulthood. The most common psychoeducational problems include visual-perceptual-motor delay, spelling and arithmetic disabilities, and a cluster of weaknesses related to cortical organization, similar to those seen in children with attention-deficit disorders. A type of learning disability unique to patients with NF has not been identified, and the diagnosis and treatment of the learning problems are generally the same as for children without NF.

Adolescent↗
PubMed2005

The asymptotic equipartition property in reinforcement learning and its relation to return maximization.

We discuss an important property called the asymptotic equipartition property on empirical sequences in reinforcement learning. This states that the typical set of empirical sequences has probability nearly one, that all elements in the typical set are nearly equi-probable, and that the number of elements in the typical set is an exponential function of the sum of conditional entropies if the number of time steps is sufficiently large. The sum is referred to as stochastic complexity. Using the property we elucidate the fact that the return maximization depends on two factors, the stochastic complexity and a quantity depending on the parameters of environment. Here, the return maximization means that the best sequences in terms of expected return have probability one. We also examine the sensitivity of stochastic complexity, which is a qualitative guide in tuning the parameters of action-selection strategy, and show a sufficient condition for return maximization in probability.

Algorithms↗
PubMed2002

Differential involvement of the hippocampus and temporal lobe cortices in rapid and slow learning of new semantic information.

The present study examined the rapid and slow acquisition of new semantic information by two patients with differing brain pathology. A partial double dissociation was found between the patterns of new learning shown by these two patients. Rapid acquisition was impaired in a patient (YR) who had relatively selective hippocampal damage, but it was unimpaired in another patient (JL) who, according to structural MRI, had an intact hippocampus but damage to anterolateral temporal cortex accompanied by epileptic seizures. Slow acquisition was impaired in both patients, but was impaired to a much greater extent in JL. The dissociation suggests that the mechanisms underlying rapid and slow acquisition of new semantic information are at least partially separable. The findings indicate that rapid acquisition of semantic, as well as episodic information, is critically dependent on the hippocampus. However, they suggest that hippocampal processing is less important for the gradual acquisition of semantic information through repeated exposure, although it is probably necessary for normal levels of such learning to be achieved.

Adult↗
PubMed2005

Learning artificial phonotactic constraints: time course, durability, and relationship to natural constraints.

G. S. Dell, K. D. Reed, D. R. Adams, and A. S. Meyer (2000) proposed a "breadth-of-constraint" continuum on phoneme errors, using artificial experiment-wide constraints to investigate a putative middle ground between local and language-wide constraints. The authors report 5 experiments that test the idea of the continuum and the location of the experiment-wide constraints within it. Experiments 1 and 2 replicated the findings of Dell et al. on the experiment-wide constraints but showed only chance adherence to the local positional constraints. Experiment 3 showed that the latter constraints are uniquely affected by the form of practice used. Experiments 4 and 5 investigated the time course and robustness of the experimental constraints by reversing them during testing. This caused no difficulty when occurring between blocks (Experiment 4) but caused short-lived disruption when occurring within block (Experiment 5). The authors propose that the results do not support the idea of a continuum, but that the experiment-wide constraints reflect a local biasing of language-wide constraints, probably related to the need for rapid learning.

Humans↗