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PubMed2004

Fatal outbreak of chickenpox (varicella-zoster virus infection) among institutionalised adults with learning difficulties.

Most adults are not susceptible to chickenpox. We present a report of an outbreak of chickenpox among institutionalised adults with learning difficulties. An inventory of exposed and possible affected residents was done after three adult males were diagnosed with chickenpox following a case of zoster. Individuals with a recent history of chickenpox rash or herpes zoster were included as cases. Medical files were used to derive background information. Serum samples of the first two patients were tested for IgM varicella-zoster virus (VZV) antibodies. Eventually ten cases of chickenpox (eight residents and one group leader and her partner) and two residents with herpes zoster were registered over a period of four months in 2001. The first two patients tested positive in serum. One resident with chickenpox died. This outbreak suggests a higher risk from chickenpox for institutionalised adults with learning difficulties in comparison with the general Dutch population, probably due to limited contacts with the general population. Further research into varicella-zoster seroprevalence, preferably with low-invasive diagnostic methods, is necessary to determine if this potential risk is present elsewhere, since the risk of life-threatening chickenpox in adults could be reduced by the now available live attenuated VZV vaccine.

Adult↗
PubMed1987

Butoctamide hydrogen succinate and intensive learning sessions: effects on night sleep of Down's syndrome patients.

Mentally retarded children present a reduction in percentage of REM sleep and of oculomotor frequencies. These sleep patterns are probably relevant for their cognitive activities. The effects of butoctamide hydrogen succinate and intensive learning sessions on the night sleep of five Down's syndrome patients was studied by the authors. They found an increase in percentage of REM sleep after pharmacological treatment and an increase in oculomotor frequencies after learning sessions. The authors' hypotheses of REM sleep as a neurophysiological indicator of cerebral "plasticity" and of oculomotor frequencies as an indicator of "organization" abilities are discussed in this article. Pedagogical implications and therapeutical perspectives are also outlined.

Amides↗
PubMed2004

FloatBoost learning and statistical face detection.

A novel learning procedure, called FloatBoost, is proposed for learning a boosted classifier for achieving the minimum error rate. FloatBoost learning uses a backtrack mechanism after each iteration of AdaBoost learning to minimize the error rate directly, rather than minimizing an exponential function of the margin as in the traditional AdaBoost algorithms. A second contribution of the paper is a novel statistical model for learning best weak classifiers using a stagewise approximation of the posterior probability. These novel techniques lead to a classifier which requires fewer weak classifiers than AdaBoost yet achieves lower error rates in both training and testing, as demonstrated by extensive experiments. Applied to face detection, the FloatBoost learning method, together with a proposed detector pyramid architecture, leads to the first real-time multiview face detection system reported.

Algorithms↗
PubMed2000

Does the type of judgement required modulate cue competition?

According to the comparator process hypothesis (Matute, Arcediano, & Miller, 1996), cue competition in the learning of between-events relationships arises if the judgement required involves a comparison between the probability of the outcome given the target cue and the probability of the outcome given the competing cue. Alternatively, other associative accounts (the Rescorla-Wagner model: Rescorla & Wagner, 1972) conceive cue competition as a learning deficit affecting the target cue-outcome association. Consequently, the comparator process hypothesis predicts that cue competition occurs in inference judgements but not in contiguity ones, for only the first type of judgement implicitly involves such a comparison. On the other hand, the Rescorla-Wagner model predicts cue competition in both inference and contiguity judgements, because it establishes no relevant role for the type of judgement in producing cue competition. In Experiments 1 and 2 we manipulated the relative validity of cues and the type of question (inference vs. contiguity) in a predictive learning task. In both experiments we found a cue competition effect, but no interaction between the relative validity of cues and the type of question, suggesting that the Rescorla-Wagner theory suffices to explain cue competition.

Adult↗
PubMed2001

[The effects of ZMS on learning and memory ability and brain choline acetyltransferase in scopolamine-induced mouse model].

OBJECTIVE: To observe the effects of ZMS on learning and memory ability and on brain choline acetyltransferase activity. METHODS: A single intraperitoneal injection of scopolamine was used to establish a dementia mouse model. The learning and memory ability was detected by step-through and sted-down tests. And the choline acetyltransferase activity in brain was determined by 3H-acetyl-CoA incorporation analysis. RESULTS: ZMS could significantly reduce wrongness frequences, prolong incubation period of scopolamine-induced dementia mice in step-through and step-down tests (P < 0.01). ZMS could also significantly improve the activity of brain choline acetyltransferase (ChAT) (P < 0.01). CONCLUSION: ZMS could improve the learning and memory ability and the activity of brain ChAT in scopolamine-induced dementia mice. However, ZMS had no significant dose-response effect on improving the activity of brain ChAT, and the effect of Tacrine was similar to that of ZMS, it seemed unlikely that ZMS had a direct action on the ChAT. More probably, ZMS exerted its effect on ChAT activity and on learning and memory ability via elevating brain M receptor density.

Animals↗
PubMed2001

Knowledge of results for motor learning: relationship between error estimation and knowledge of results frequency.

The authors of the present study investigated the apparent contradiction between early and more recent views of knowledge of results (KR), the idea that how one is engaged before receiving KR may not be independent of how one uses that KR. In a 2 &times: 2 factorial design, participants (N = 64) practiced a simple force-production task and (a) were required, or not required, to estimate error about their previous response and (b) were provided KR either after every response (100%) or after every 5th response (20%) during acquisition. A no-KR retention test revealed an interaction between acquisition error estimation and KR frequencies. The group that received 100% KR and was required to error estimate during acquisition performed the best during retention. The 2 groups that received 20% KR performed less well. Finally, the group that received 100% KR and was not required to error estimate during acquisition performed the poorest during retention. One general interpretation of that pattern of results is that motor learning is an increasing function of the degree to which participants use KR to test response hypotheses (J. A. Adams, 1971; R. A. Schmidt, 1975). Practicing simple responses coupled with error estimation may embody response hypotheses that can be tested with KR, thus benefiting motor learning most under a 100% KR condition. Practicing simple responses without error estimation is less likely to embody response hypothesis, however, which may increase the probability that participants will use KR to guide upcoming responses, thus attenuating motor learning under a 100% KR condition. The authors conclude, therefore, that how one is engaged before receiving KR may not be independent of how one uses KR.

Adult↗
PubMed1997

Food safety training needs exist for staff and consumers in a variety of community-based homes for people with developmental disabilities.

OBJECTIVE: To determine staff and consumer-focused food safety training needs in community-based homes for people with developmental disabilities as well as dietitians' perceptions of food-handling practices in these homes. DESIGN: Direct-care staff and dietitians were surveyed according to a modified Dillman method using a mailed, self-administered questionnaire. Main outcome measures included food-handling knowledge, attitudes, and practices of staff and consumers as reported by staff and dietitians; critical control points in safe food preparation in the homes based on the Hazard Analysis and Critical Control Point system; and learning preferences of staff and consumers. SUBJECTS: A 10% probability sample of direct-care staff in homes for people with developmental disabilities in western Massachusetts and a nonprobability sample of dietitians who work with this population were surveyed. Results are reported from 132 and 18 respondents, respectively. STATISTICAL ANALYSES PERFORMED: Descriptive statistics, chi 2 statistic, and the Fisher's exact test. RESULTS: Staff knowledge of safe food preparation is lacking in several areas, including storage and handling procedures. Although staff and consumers do not always follow safe food-handling practices, the staff reported that they follow recommended food-handling practices more often than the dietitians reported they do. Most staff and dietitians reported that staff and consumers had never attended a food safety training program, but that all of the critical control points surveyed would be somewhat helpful if they were included in a food safety workshop. APPLICATIONS: A food safety training program would be beneficial for staff and consumers. Programs should be geared to staff and include ideas and materials for consumers. Consumer modules could then be adapted to individual learning levels by direct-care staff in the homes. The Safe Food at Home workshop was developed on the basis of the results of this study and incorporates the approaches described in this article.

Adult↗
PubMed1990

Oxiracetam prevents mecamylamine-induced impairment of active, but not passive, avoidance learning in mice.

The nicotinic antagonist mecamylamine (2.5 and 5 mg/kg/IP) depressed both active (shuttle-box) and passive (step-through) avoidance learning in mice of the DBA/2 strain. The nootropic drug oxiracetam (50 and 100 mg/kg/IP) improved acquisition in the multitrial active avoidance test, but had no effect on one-trial passive avoidance learning. When the two drugs were combined, oxiracetam did not counteract mecamylamine-induced impairment of passive avoidance learning, even if it maintained a facilitating action on shuttle-box avoidance acquisition in mice receiving the nicotinic receptor blocker. Prevention of mecamylamine-induced shuttle-box avoidance depression by oxiracetam indicates that central nicotinic mechanisms are probably involved in the improving effects exerted by nootropic drugs on learning.

Animals↗
PubMed2002

Partial ablations of the flocculus and ventral paraflocculus in monkeys cause linked deficits in smooth pursuit eye movements and adaptive modification of the VOR.

The vestibuloocular reflex (VOR) generates compensatory eye movements to stabilize visual images on the retina during head movements. The amplitude of the reflex is calibrated continuously throughout life and undergoes adaptation, also called motor learning, when head movements are persistently associated with image motion. Although the floccular-complex of the cerebellum is necessary for VOR adaptation, it is not known whether this function is localized in its anterior or posterior portions, which comprise the ventral paraflocculus and flocculus, respectively. The present paper reports the effects of partial lesions of the floccular-complex in five macaque monkeys, made either surgically or with stereotaxic injection of 3-nitropropionic acid (3-NP). Before and after the lesions, smooth pursuit eye movements were tested during sinusoidal and step-ramp target motion. Cancellation of the VOR was tested by moving a target exactly with the monkey during sinusoidal head rotation. The control VOR was tested during sinusoidal head rotation in the dark and during 30 degrees/s pulses of head velocity. VOR adaptation was studied by having the monkeys wear x2 or x0.25 optics for 4-7 days. In two monkeys, bilateral lesions removed all of the flocculus except for parts of folia 1 and 2 but did not produce any deficits in smooth pursuit, VOR adaptation, or VOR cancellation. We conclude that the flocculus alone probably is not necessary for either pursuit or VOR learning. In two monkeys, unilateral lesions including a large fraction of the ventral paraflocculus produced small deficits in horizontal and vertical smooth pursuit, and mild impairments of VOR adaptation and VOR cancellation. We conclude that the ventral paraflocculus contributes to both behaviors. In one monkey, a bilateral lesion of the flocculus and ventral paraflocculus produced severe deficits smooth pursuit and VOR cancellation, and a complete loss of VOR adaptation. Considering all five cases together, there was a strong correlation between the size of the deficits in VOR learning and pursuit. We found the strongest correlation between the behavior deficits and the size of the lesion of the ventral paraflocculus, a weaker but significant correlation for the full floccular complex, and no correlation with the size of the lesion of the flocculus. We conclude that 1) lesions of the floccular complex cause linked deficits in smooth pursuit and VOR adaptation, and 2) the relevant portions of the structure are primarily in the ventral paraflocculus, although the flocculus may participate.

Adaptation, Physiological↗
PubMed2003

In-phase implies large likelihood for independent codon model: distinguishing coding from non-coding sequences.

It is proven that under the independent codon model, the likelihood of a DNA coding sequence read according to the correct frame is asymptotically larger than that read with an incorrect frame. Based on this proposition, a single set of probabilities of the codon usage is enough for discriminating the six frames of coding sequences under the independent codon model. The direct coding sequence of Escherichia coli genome is taken as an example to examine the codon independency by using the mutual information and chi2 analysis. The contrast between the coding frame and the two offset frames is evident. A self-learning approach for generating training set is proposed to estimate probability parameters.

Codon↗
PubMed1988

Dose-specific effects of trimethyltin poisoning on learning and hippocampal corticosterone binding.

The organometal neurotoxin trimethyltin (TMT) damages limbic forebrain, and impairs acquisition of lever-directed behaviors in an autoshaping task, in which a lever is presented according to a random time schedule, and rats learn to associate its presentation/retraction with food delivery (Cohen et al., 1987). This impairment is evident only if a sufficiently long delay of reinforcement is interposed between lever retraction (which occurs either automatically after 15 sec, or immediately upon a touch response) and food pellet delivery. Paradoxically, rats given a higher (7.5 mg/kg) dose show a smaller acquisition impairment, perhaps because they are generally more reactive to the lever than controls. These rats sustain a larger hippocampal lesion (measured by wet weight of the structure). The experiment reported here was done to investigate (1) an autoshaping deficit related to hippocampal weight loss, and (2) biochemical changes in hippocampus which might be related to behavioral impairments. Rats were treated with water vehicle or TMT four weeks before autoshaping using a 6 sec reinforcement delay. In addition to lever touching, touches of the food trough were measured. The timing of trough-touching behaviors within a trial was used as an indication of the strength of the association formed between the lever and the site of food delivery. Following autoshaping rats were adrenalectomized and killed for measurement of cytosolic [3H]corticosterone binding in hippocampus. As before, rats treated with 6.0 mg TMT/kg showed a deficit in acquisition of lever-directed behaviors. Also, as hypothesized, the proportion of total trough-directed behaviors made during the 6 sec reinforcement delay intervals (when reinforcement probability was high) diverged significantly from control values as learning progressed. These rats also showed a reduction in hippocampal weight compared with controls, but significant decreases in hippocampal steroid binding were observed only in groups given the low and median dose of TMT. Further, steroid binding was correlated with lever-directed behaviors. It thus appears that lever and trough behaviors can be used to simultaneously assess different aspects of impairment in associative learning which are accompanied by differential cell loss and biochemical deficit.

Animals↗
PubMed2004

Fast adaptation of the internal model of gravity for manual interceptions: evidence for event-dependent learning.

We studied how subjects learn to deal with two conflicting sensory environments as a function of the probability of each environment and the temporal distance between repeated events. Subjects were asked to intercept a visual target moving downward on a screen with randomized laws of motion. We compared five protocols that differed in the probability of constant speed (0g) targets and accelerated (1g) targets. Probability ranged from 9 to 100%, and the time interval between consecutive repetitions of the same target ranged from about 1 to 20 min. We found that subjects systematically timed their responses consistent with the assumption of gravity effects, for both 1 and 0g trials. With training, subjects rapidly adapted to 0g targets by shifting the time of motor activation. Surprisingly, the adaptation rate was independent of both the probability of 0g targets and their temporal distance. Very few 0g trials sporadically interspersed as catch trials during immersive practice with 1g trials were sufficient for learning and consolidation in long-term memory, as verified by retesting after 24 h. We argue that the memory store for adapted states of the internal gravity model is triggered by individual events and can be sustained for prolonged periods of time separating sporadic repetitions. This form of event-related learning could depend on multiple-stage memory, with exponential rise and decay in the initial stages followed by a sample-and-hold module.

Adaptation, Physiological↗
PubMed1997

Anosognosia and procedural learning in Alzheimer's disease.

Awareness of cognitive deficits may rely on the implicit learning of intellectual limitations, and anosognosia in Alzheimer's disease (AD) may result from deficits in implicit learning. To examine this hypothesis, a consecutive series of 55 patients with probable AD were divided into groups with mild (n = 13), severe (n = 12), or no anosognosia (n = 30) and were assessed with a neuropsychological battery that included tests of declarative and procedural learning. Whereas there were no significant between-group differences in tests of declarative learning (the Buschke Selective Reminding Test and the Benton Visual Retention Test), patients with severe anosognosia showed a significantly worse performance on procedural learning (as measured with the Maze Learning Test) and a test assessing set shifting abilities (the Wisconsin Card Sorting Test) than AD patients without anosognosia. The authors' results suggest that deficits in procedural learning and anosognosia in AD may result from dysfunction in habit-learning systems.

Aged↗
PubMed2001

A fast and convergent stochastic MLP learning algorithm.

We propose a stochastic learning algorithm for multilayer perceptrons of linear-threshold function units, which theoretically converges with probability one and experimentally exhibits 100% convergence rate and remarkable speed on parity and classification problems with typical generalization accuracy. For learning the n bit parity function with n hidden units, the algorithm converged on all the trials we tested (n=2 to 12) after 5.8 x 4.1(n) presentations for 0.23 x 4.0(n-6) seconds on a 533MHz Alpha 21164A chip on average, which is five to ten times faster than Levenberg-Marquardt algorithm with restarts. For a medium size classification problem known as Thyroid in UCI repository, the algorithm is faster in speed and comparative in generalization accuracy than the standard backpropagation and Levenberg-Marquardt algorithms.

Algorithms↗
PubMed2004

Local estimation of posterior class probabilities to minimize classification errors.

Decision theory shows that the optimal decision is a function of the posterior class probabilities. More specifically, in binary classification, the optimal decision is based on the comparison of the posterior probabilities with some threshold. Therefore, the most accurate estimates of the posterior probabilities are required near these decision thresholds. This paper discusses the design of objective functions that provide more accurate estimates of the probability values, taking into account the characteristics of each decision problem. We propose learning algorithms based on the stochastic gradient minimization of these loss functions. We show that the performance of the classifier is improved when these algorithms behave like sample selectors: samples near the decision boundary are the most relevant during learning.

Probability↗
PubMed1990

The learning needs in diabetes of general practitioners.

The aim of the study was to determine the learning needs of General Practitioners (GPs) in diabetes. A postal questionnaire was sent to all GPs in South East Thames Region (England). The level of interest in continuing professional education in diabetes is sufficient to merit production of tailored learning materials and opportunities. Eighty-three percent of GPs would definitely or probably avail themselves of the opportunity even if they did have to pay. This percentage represents a figure of over 780 GPs. They are most keen to learn the clinical and other skills associated with diabetes and its management. A large number, 71%, requested education on retinal examination and adjustment of insulin, 56% on adjustment of tablet therapy, and 51% on the management of children with diabetes. Individual study materials, backed up by small group meetings and video material would be the most appreciated format. A course of study divided into half-hourly periods adding up to a total of about 5 h might be the most widely acceptable format. GPs would most like to study with other GPs from local practices and with hospital staff. Group work might best be designed to incorporate both an experienced GP, if one were available, and a consultant. The materials themselves might also best be designed and written by such a partnership.

Diabetes Mellitus↗
PubMed2000

Machine learning for survival analysis: a case study on recurrence of prostate cancer.

Machine learning techniques have recently received considerable attention, especially when used for the construction of prediction models from data. Despite their potential advantages over standard statistical methods, like their ability to model non-linear relationships and construct symbolic and interpretable models, their applications to survival analysis are at best rare, primarily because of the difficulty to appropriately handle censored data. In this paper we propose a schema that enables the use of classification methods--including machine learning classifiers--for survival analysis. To appropriately consider the follow-up time and censoring, we propose a technique that, for the patients for which the event did not occur and have short follow-up times, estimates their probability of event and assigns them a distribution of outcome accordingly. Since most machine learning techniques do not deal with outcome distributions, the schema is implemented using weighted examples. To show the utility of the proposed technique, we investigate a particular problem of building prognostic models for prostate cancer recurrence, where the sole prediction of the probability of event (and not its probability dependency on time) is of interest. A case study on preoperative and postoperative prostate cancer recurrence prediction shows that by incorporating this weighting technique the machine learning tools stand beside modern statistical methods and may, by inducing symbolic recurrence models, provide further insight to relationships within the modeled data.

Artificial Intelligence↗