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PubMed1999

Independent component analysis using an extended infomax algorithm for mixed subgaussian and supergaussian sources.

An extension of the infomax algorithm of Bell and Sejnowski (1995) is presented that is able blindly to separate mixed signals with sub- and supergaussian source distributions. This was achieved by using a simple type of learning rule first derived by Girolami (1997) by choosing negentropy as a projection pursuit index. Parameterized probability distributions that have sub- and supergaussian regimes were used to derive a general learning rule that preserves the simple architecture proposed by Bell and Sejnowski (1995), is optimized using the natural gradient by Amari (1998), and uses the stability analysis of Cardoso and Laheld (1996) to switch between sub- and supergaussian regimes. We demonstrate that the extended infomax algorithm is able to separate 20 sources with a variety of source distributions easily. Applied to high-dimensional data from electroencephalographic recordings, it is effective at separating artifacts such as eye blinks and line noise from weaker electrical signals that arise from sources in the brain.

Algorithms↗
PubMed1992

Quantitative effects of cerebral infarction on spatial learning in rats.

Outcome following stroke is difficult to measure because the behavioral response to infarction is variable. We hypothesized that cognitive function, such as spatial learning, may be a reproducible and sensitive outcome variable. We developed an animal model of multifocal cerebral ischemia in order to study the effects of infarction on learning. To cause ischemia, several hundred microspheres were injected into the internal carotid arteries of rats. After ischemia, behavior was measured using a global rating and a Morris water maze. Postmortem serial brain sections were stained and the size of the infarctions was measured. We found that intracerebral microspheres caused cortical infarction and an impairment of spatial learning. This impairment was not due to occlusion of the internal carotid artery and was not found in animals who received a sham injection of saline. The degree of learning impairment was not correlated with the volume density of the infarctions or with the volume density of the remaining cerebral hemisphere. The learning impairment clearly differentiated normal from lesioned animals, and the impairment was probably due to a delay in acquisition of spatial information rather than a defect in retention or retrieval. Measurement of learning deficit after cerebral ischemia is an efficient and sensitive method for evaluating new stroke treatments and possibly for exploring structure function relationships.

Animals↗
PubMed2001

Mechanism of action of flibanserin in the learned helplessness paradigm in rats.

The mechanism of action of flibanserin, a 5-HT(1A) receptor agonist and a 5-HT(2A) receptor antagonist, was investigated in learned helplessness in rats. The effect of flibanserin (32 mg/kg, i.p. 30 min before testing) on learned helplessness was not antagonized by the (a) 5-HT synthesis inhibitor parachlorophenylalanine (pCPA; 150 mg/kg p.o.x3 times), which reduced brain 5-HT by 89%; (b) 5-HT(1A) receptor antagonists (+/-)-N-tert-butyl-3-4-(2-ethoxyphenyl)piperazin-1yl-2-phenyl propionamide [WAY100135; 10 mg/kg, i.p. 30 min before flibanserin, or 40 mg/kg, s.c. 15 min before flibanserin] and tertatolol (2.5 and 5 mg/kg, i.p. 30 min before flibanserin); and (c) 5-HT(2) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI; 3 mg/kg, s.c. simultaneously with flibanserin). The effect of flibanserin on learned helplessness was antagonized by the dopamine D(1) receptor antagonist [R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390; 0.1 mg/kg, i.p. 30 min before flibanserin) and by the opioid receptor antagonist naloxone (3 mg/kg, s.c. 15 min before flibanserin). Flibanserin (32 and 64 mg/kg) did not induce conditioned place preference. In conclusion, flibanserin improved rats' performance in the learned helplessness paradigm, by stimulating dopamine D1 and opioid receptors, probably indirectly, since flibanserin has a low affinity for these receptors.

Animals↗
PubMed2005

Data classification with radial basis function networks based on a novel kernel density estimation algorithm.

This paper presents a novel learning algorithm for efficient construction of the radial basis function (RBF) networks that can deliver the same level of accuracy as the support vector machines (SVMs) in data classification applications. The proposed learning algorithm works by constructing one RBF subnetwork to approximate the probability density function of each class of objects in the training data set. With respect to algorithm design, the main distinction of the proposed learning algorithm is the novel kernel density estimation algorithm that features an average time complexity of O(n log n), where n is the number of samples in the training data set. One important advantage of the proposed learning algorithm, in comparison with the SVM, is that the proposed learning algorithm generally takes far less time to construct a data classifier with an optimized parameter setting. This feature is of significance for many contemporary applications, in particular, for those applications in which new objects are continuously added into an already large database. Another desirable feature of the proposed learning algorithm is that the RBF networks constructed are capable of carrying out data classification with more than two classes of objects in one single run. In other words, unlike with the SVM, there is no need to resort to mechanisms such as one-against-one or one-against-all for handling datasets with more than two classes of objects. The comparison with SVM is of particular interest, because it has been shown in a number of recent studies that SVM generally are able to deliver higher classification accuracy than the other existing data classification algorithms. As the proposed learning algorithm is instance-based, the data reduction issue is also addressed in this paper. One interesting observation in this regard is that, for all three data sets used in data reduction experiments, the number of training samples remaining after a naive data reduction mechanism is applied is quite close to the number of support vectors identified by the SVM software. This paper also compares the performance of the RBF networks constructed with the proposed learning algorithm and those constructed with a conventional cluster-based learning algorithm. The most interesting observation learned is that, with respect to data classification, the distributions of training samples near the boundaries between different classes of objects carry more crucial information than the distributions of samples in the inner parts of the clusters.

Algorithms↗
PubMed2004

The emerging lexicon of children with phonological delays: phonotactic constraints and probability in acquisition.

The effects of phonotactic constraints (i.e., the status of a sound as correctly or incorrectly articulated) and phonotactic probability (i.e., the likelihood of a sound sequence) on lexical acquisition have been investigated independently. This study investigated the interactive influence of phonotactic constraints and phonotactic probability on lexical acquisition in 3 groups of children: children with functional phonological delays (PD), phonology-matched, younger, typically developing children (PM), and age-/vocabulary-matched typically developing peers (AVM). Sixty-eight children participated in a multitrial word-learning task involving nonwords varying in phonotactic constraints (IN vs. OUT) and phonotactic probability (common vs. rare). Correct and error responses were analyzed. Results indicated that OUT sound sequences were learned more rapidly than IN sound sequences. This suggests that OUT sounds may be salient because they represent only a small subset of the child's sound system. The effect of phonotactic probability varied across groups: Children with PD showed a common sound sequence disadvantage, younger PM children showed a common sound sequence advantage, and AVM children showed no effect. Moreover, error analyses indicated that children with PD had particular difficulty creating lexical representations and associations between lexical and semantic representations when learning common sound sequences. Children with PD may rely more heavily on lexical representations to learn new words or may have difficulty learning common sound sequences because of the high degree of similarity between these sequences and other known words. Finally, the effect of phonotactic probability was consistent across IN and OUT sound sequences, suggesting that the lexical representation of both correctly articulated and misarticulated words is based on the adult-target pronunciation.

Articulation Disorders↗
PubMed1985

Uncertainty explains many aspects of visual contrast detection and discrimination.

More than 20 years ago, Tanner [Ann. N.Y. Acad. Sci. 89, 752 (1961)] noted that observers asked to detect a signal act as though they are uncertain about the physical characteristics of the signal to be detected. The popular assumptions of probability summation and decision variable, taken together, imply this uncertainty. This paper defines and uncertainty model of visual detection that assumes that the observer is uncertain among many signals and chooses the likeliest. With only four parameters, the uncertainty model explains why d' is approximately a power function of contrast ("nonlinear transduction") and accurately predicts effects of summation, facilitation, noise, subjective criterion, and task for near-threshold contrast. Thus the uncertainty model offers a synthesis of much of our current understanding of visual contrast detection and discrimination.

Attention↗
PubMed2000

Human cerebellar activity reflecting an acquired internal model of a new tool.

Theories of motor control postulate that the brain uses internal models of the body to control movements accurately. Internal models are neural representations of how, for instance, the arm would respond to a neural command, given its current position and velocity. Previous studies have shown that the cerebellar cortex can acquire internal models through motor learning. Because the human cerebellum is involved in higher cognitive function as well as in motor control, we propose a coherent computational theory in which the phylogenetically newer part of the cerebellum similarly acquires internal models of objects in the external world. While human subjects learned to use a new tool (a computer mouse with a novel rotational transformation), cerebellar activity was measured by functional magnetic resonance imaging. As predicted by our theory, two types of activity were observed. One was spread over wide areas of the cerebellum and was precisely proportional to the error signal that guides the acquisition of internal models during learning. The other was confined to the area near the posterior superior fissure and remained even after learning, when the error levels had been equalized, thus probably reflecting an acquired internal model of the new tool.

Adult↗
PubMed1976

A six-year controlled trial of prevention of children's behavior disorders.

Preschool interviews between a clinician and mothers were studied to determine their influence upon the behavioral patterns and learning abilities of the mother's children. After six years, 124 children of this experimental group were compared with 122 control children; the results indicated that a significant number of experimental children had fewer fears, sleep disorders, eating problems, loud modes of speech, and aggression toward others and fewer of the girls distorted events to their advantage or demanded their parents to share in joint play. A larger proportion of the experimental children had positive feelings, and to a lesser degree negative feelings, toward their mothers, but a greater number were late for school, with more of the boys being excitable and hard to control. The greater benefits, which were more apparent in the girls than in the boys, were consistent with an effectiveness of more firmly expressed views about the girls, whereas the confidence of the boys' mothers may well have been affected by too cautious an approach to discipline problems. The interviews probably had no influence on the children's learning capacities.

Adult↗
PubMed2006

What do we know about cognitive and motivational effects of small group tutorials in problem-based learning?

Students collaborating in small groups is a characteristic of problem-based learning (PBL) that is receiving increased consideration in the literature. In this paper findings from studies in this area are synthesized and discussed. A distinction is made between studies focusing on cognitive effects of group learning and studies focusing on motivational effects of group learning. Studies concentrating on the cognitive effects of small-group PBL seem to demonstrate that activation of prior knowledge, recall of information, causal reasoning or theory building, cognitive conflicts leading to conceptual change and collaborative learning construction take place in the tutorial group. Studies focusing on the motivational effects of PBL demonstrate that group discussion positively influences students' intrinsic interest in the subject matter under discussion. The studies also demonstrate that a haphazard discussion in the tutorial group or a discussion that just scratches the surface, probably caused by students being less motivated, inhibits student learning. Several studies are reported providing suggestions on how to optimize group work in PBL. Although the studies demonstrate that group learning in PBL may have positive effects, much more research is needed to obtain more evidence and deeper insight in the cognitive and emotional effects of small group learning in PBL.

Cognition↗
PubMed1993

A decade of studies of human exposure: what have we learned?

All four TEAM Studies operated on the basis concepts of probability sampling and direct measurement of exposure. These concepts made possible the discovery that, for nearly all of the 50 or so targeted pollutants, personal exposures exceeded outdoor levels by large margins. The conclusion, corroborated in part by other studies around the world, is that the major sources of exposure are personal activities and consumer products. This result is at odds with most existing environmental legislation, which generally does not deal with products or with indoor air in homes, in favor of regulating "major" stationary and mobile sources. These sources, however, provide only between 2-25% of personal exposure to most of the two dozen or so toxic and carcinogenic VOCs and pesticides included in the TEAM Studies. Several official publications have accepted this point, finding that funding priorities are skewed, with lower-risk problems receiving more funding than higher-risk problems such as indoor air pollution. However, just as exposures are due to small nearby sources, control of exposures can often be instituted by small individual actions. Among these are stopping smoking, reducing or eliminating the use of moth balls and bathroom deodorizers containing p-dichlorobenzene, reducing or eliminating the use of dry-cleaned clothes or airing them out for a day, and maintaining dust-free homes.

Air Pollutants↗
PubMed2006

Neural mechanisms of birdsong memory.

The process through which young male songbirds learn the characteristics of the songs of an adult male of their own species has strong similarities with speech acquisition in human infants. Both involve two phases: a period of auditory memorization followed by a period during which the individual develops its own vocalizations. The avian 'song system', a network of brain nuclei, is the probable neural substrate for the second phase of sensorimotor learning. By contrast, the neural representation of song memory acquired in the first phase is localized outside the song system, in different regions of the avian equivalent of the human auditory association cortex.

Animals↗
PubMed2001

Stimulus probability directs spatial attention: an enhancement of sensitivity in humans and monkeys.

We examined whether improvements in sensory processing, defined as changes in sensitivity, could be elicited in a simple luminance discrimination task without eliciting concomitant changes in decision processing. To this end we developed a task, for use in both humans and monkeys, in which prior knowledge about where a discriminative stimulus was likely to appear (1) offered no decisional advantage in solving our task and (2) could be parametrically varied to yield a psychometric function. We found that if we parametrically varied the quality of prior knowledge, by increasing the probability, and thus the certainty, that a discriminative stimulus would appear at a particular location under these conditions, luminance discrimination improved for both human and monkey subjects. This improvement was correlated with an enhancement in sensory processing, but not with any systematic changes in decisional processing, as assessed by signal detection theory. These results suggest that (1) sensory processing and decision processing can be separated by task design and (2) systematic changes in prior knowledge about where a stimulus may appear can lead to systematic changes in sensitivity; providing a psychometric function for the influence of prior knowledge on perceptual sensitivity. Importantly, these results were obtained from both human and monkey subjects. Similar task designs could be used in physiological studies attempting to generate linking hypotheses between psychometric and neurometric functions, ultimately allowing changes in perceptual sensitivity to be linked to changes in an underlying neural substrate.

Adult↗
PubMed1987

[Effect of intracisternal administration of antisera against neurospecific enolase (protein 14-3-2) on avoidance behavior in rats].

The antisera to three isoenzymes (alpha alpha, alpha gamma, and gamma gamma) of the rat neurospecific enolase were studied. gamma gamma-antiserum administered into the brain cistern (8 microliters) prior to learning, in contrast to two other antisera, impaired the retrieval of passive avoidance response within 1-28 days after learning. Maximal amnestic effect occurred in the first 3 days. Probable mechanisms of the neurospecific enolase participation in the formation of memory traces, are discussed.

Animals↗
PubMed2006

The influence of averaging and noisy decision strategies on the recognition memory ROC.

Many single- and dual-process models of recognition memory predict that the ratings and remember-know receiver operating characteristics (ROCs) are the same, but Rotello, Macmillan, and Reeder (2004) reported that the slopes of the remember-know and ratings z-transformed ROCs (zROCs) are different The authors show that averaging introduces nonlinearities to the form of the zROC and that ratings and remember-know zROCs are indistinguishable when constructed in a conventional manner. The authors show, further, that some nonoptimal decision strategies have a distinctive, nonlinear effect on the form of the single-process continuous-state zROC. The conclusion is that many factors having nothing to do with the nature of recognition memory can affect the shape of zROCs, and that therefore, the shape of the zROC does not, alone, characterize different memory models.

Association Learning↗
PubMedDate not supplied

Exposure to lead and specific attentional problems in schoolchildren.

A pilot study was carried out to investigate the relationship between exposure to lead and attention in children. The participants were 43 boys, 8 to 12 years of age, attending special schools for children with educational and/or learning problems (so called LOM schools). Children with probable causes of attentional or memory problems other than lead contamination were excluded from the study. Various aspects of attention were measured using neuropsychological tests. As an assessment of body lead burden, lead concentration in the boys' hair was measured by means of the Synchrotron Radiation-Induced X-ray Fluorescence technique (SXRF). Information was collected about variables that possibly could influence attention and/or body lead burden (confounding factors). A multiple regression analysis was used to determine the contribution of lead to variance in performance, after correction for confounding factors. The results showed that children with relatively high concentrations of lead in their hair reacted significantly slower in a simple reaction-time task than did children with relatively low concentrations of lead in their hair. In addition, the former were significantly less flexible in changing their focus of attention, even after correction for the influence of their delayed reaction time.

Attention Deficit Disorder with Hyperactivity↗
PubMed2006

Involvement of the CA3-CA1 synapse in the acquisition of associative learning in behaving mice.

One of the brain sites more directly related with learning and memory processes is the hippocampus. We recorded, in conscious mice, the activity-dependent changes taking place at the hippocampal CA3-CA1 synapse during the acquisition, extinction, recall, and reconditioning of an associative task. Mice were classically conditioned to evoke eyelid responses using a trace [conditioned stimuli (CS), tone; unconditioned stimuli (US), shock] paradigm. A single electrical pulse presented to the Schaffer collateral-commissural pathway during the CS-US interval evoked a monosynaptic field EPSP (fEPSP) at ipsilateral CA1 pyramidal cells. The slope of evoked fEPSPs increased across conditioning sessions and decreased during extinction, being linearly related to learning evolution. In contrast, fEPSPs were not modified when evoked in control mice in the absence of a conditioning protocol. Long-term potentiation (LTP) evoked by high-frequency stimulation of Schaffer collaterals prevented acquisition, extinction, recall, or reconditioning, depending on the moment when it was triggered. Learning and memory impairments evoked by LTP induction resulted probably from the functional saturation of the CA3-CA1 synapse, although an additional disturbance of the subsequent information transfer toward postsynaptic circuits cannot be discarded. CGP 39551 [(E)-(+/-)-2-amino-4-methyl-5-phosphono-3-pentenoic acid ethyl ester] (an NMDA antagonist) prevented LTP induction in behaving mice, as well as the acquisition of an eyelid learned response, and the synaptic changes taking place at the CA3-CA1 synapse across conditioning. In conclusion, the responsivity of the CA3-CA1 synapse seems to be modulated during associative learning, and both processes are prevented by experimental LTP or NMDA-receptor inactivation. Our results provide evidence of a relationship between activity-dependent synaptic plasticity and associative learning in behaving mice.

2-Amino-5-phosphonovalerate↗