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PubMed1998

Detecting simulated memory impairment with the Rey Auditory Verbal Learning Test: implications of base rates and study generalizability.

The accuracy of the Rey Auditory Verbal Learning Test (RAVLT) for detecting simulated neuropsychological impairment was investigated using discriminant function analyses and cross-validation procedures. In Study 1, a discriminant function analysis, using six RAVLT variables, correctly classified 80% of 50 simulating and 50 non-simulating participants. Base rates were changed and this discriminant function was tested in Study 2 with a 33% base rate of simulation. The discriminant function correctly classified 75% of 20 simulators and 90% of 40 non-simulators, yielding an overall classification rate of 85%. To determine the generalizability of this discriminant function to a clinical sample, Study 3 compared the RAVLT performance of 20 simulating participants to that of 40 motor vehicle accident (MVA) patients. The discriminant function from Study 1 incorrectly classified 60% of the MVA patients and yielded an overall correct classification rate of 48%. The limitations associated with generalizing from analog research and the implications of varying base rates on classification accuracy are discussed.

Adult↗
PubMed2004

Neural foundations of emerging route knowledge in complex spatial environments.

Behavioral evidence suggests that spatial knowledge derived from ground-level navigation can consist of both route and survey knowledge. Neuroimaging and lesion studies aiming to identify the neural structures responsible for topographical learning in humans have yielded partially inconsistent results, probably due to the lack of an effective behavioral parameter allowing for a reliable distinction between different representations. Therefore, we employed a novel virtual reality environment that provides accuracy and reaction time measures precisely indicating the emergence of route vs. survey knowledge. Functional magnetic resonance imaging (fMRI) was used to localize brain regions involved in the acquisition of pure route knowledge in the form of associations between consecutive landmark views and the direction of intermediate movements. Participants were scanned during repeated encoding of the complex environment from a first-person, ground-level perspective. Behavioral data revealed emerging route knowledge in 11 out of 14 subjects. Overall comparisons between encoding and control conditions identified activation in medial frontal gyrus, retrosplenial cortex and posterior inferior parietal cortex. Most importantly, only posterior inferior parietal regions showed increasing activation across sessions, thus paralleling behavioral measures of route expertise. Given the established role of the posterior parietal cortex in spatial processing, this area is thought to provide the pivotal spatial link between two landmarks encountered in immediate temporal succession.

Adult↗
PubMed1998

Self-organization property of Kohonen's map with general type of stimuli distribution.

Here the self-organization property of one-dimensional Kohonen's algorithm in its 2k-neighbor setting with a general type of stimuli distribution and non-increasing learning rate is considered. A new definition of the winner is given, which coincides with the usual definition in implementations of the algorithm. We prove that the probability of self-organization for all initial weights of neurons is uniformly positive. For the special case of a constant learning rate, it implies that the algorithm self-organizes with probability one. The conditions imposed on the neighborhood function, stimuli distribution and learning rate are quite general.

Journal Article↗
PubMed1995

alpha-Helix region prediction with stochastic rule learning.

We propose a new method, based on the theory of stochastic rule learning, for predicting alpha-helix regions in a given protein sequence. Our method (hereafter referred to as the SR method) produces stochastic rules, each of which assigns, to any region in an amino acid sequence, the probability that it is an alpha-helix region. When learning a stochastic rule from a particular alpha-helix region, our method makes use of positive training examples obtained from a number of regions that are homologous to that region. Each stochastic rule is optimized using the minimum description length (MDL) principle, and such optimized stochastic rules are used to predict alpha-helix regions of any given protein sequence. In our experiments, using 25 proteins selected from the HSSP database as training examples, we applied the SR method to the problem of predicting alpha-helix regions in test examples, which consisted of > 5000 residues with 38% alpha-helix content. Each of these test examples possesses < 25% homology to any proteins in the training and other test examples. Our method achieved 81% average prediction accuracy for the test examples; this compares favorably to Qian and Sejnowski's method, which attains no more than 75% average accuracy, and further which compares to Rost and Sander's method which has proven to be one of the best secondary structure prediction methods.

Amino Acid Sequence↗
PubMed1989

[Variable cycle avoidance program: systematic variation of the probability of a programmed noxious stimulus].

Six albino rats were exposed in three groups to different values of T (a repetitive time cycle at the end of which an electric shock occurs with a specified probability in absence of a first response), (V.g.: P(E-/R) = .75 and .10) on different weeks. When occurs at least one response on each T cycle it has a probability to delete the shock equal to P(E-/R) that changed on different weeks from .50 to .10. In this way, as the Bayesian probability system indicate for exclusive events, Pk = P(E-/R) - [P(E-/R) x P(E-/R)] was the effective probability of shocks when at least one response occur on each T cycle and Pm = P(E-/R) - [P(E-/R) x P(E-/R) x P(1rst Response)] is the modulated probability of shocks when a first response occur on some T cycles. The results indicated that T/Pk (the mean interval between shocks before the experimental session) nor T/Pm (The mean interval between shocks after the experimental session when the subject responds), or its inverse, are reductional continua that explains monotonically ordered changes of the response rate or the mean total number of responses. As a consequence T and P must be dissociated. On the other hand, corrected response rate (Total responses minus Total first responses/minute) is a direct and monotonically increased function of Pk and of 1/T. In this sense is the increased probability with which noxious stimuli impinge on the behavior stream and the time reduction between stimuli, that separated, sustain responding.

Animals↗
PubMed2006

Parameter learning from stochastic teachers and stochastic compulsive liars.

This paper considers a general learning problem akin to the field of learning automata (LA) in which the learning mechanism attempts to learn from a stochastic teacher or a stochastic compulsive liar. More specifically, unlike the traditional LA model in which LA attempts to learn the optimal action offered by the Environment (also here called the "Oracle"), this paper considers the problem of the learning mechanism (robot, an LA, or in general, an algorithm) attempting to learn a "parameter" within a closed interval. The problem is modeled as follows: The learning mechanism is trying to locate an unknown point on a real interval by interacting with a stochastic Environment through a series of informed guesses. For each guess, the Environment essentially informs the mechanism, possibly erroneously (i.e., with probability p), which way it should move to reach the unknown point. When the probability of a correct response is p > 0.5, the Environment is said to be informative, and thus the case of learning from a stochastic teacher. When this probability p < 0.5, the Environment is deemed deceptive, and is called a stochastic compulsive liar. This paper describes a novel learning strategy by which the unknown parameter can be learned in both environments. These results are the first reported results, which are applicable to the latter scenario. The most significant contribution of this paper is that the proposed scheme is shown to operate equally well, even when the learning mechanism is unaware of whether the Environment ("Oracle") is informative or deceptive. The learning strategy proposed herein, called CPL-AdS, partitions the search interval into d subintervals, evaluates the location of the unknown point with respect to these subintervals using fast-converging E-optimal LRI LA, and prunes the search space in each iteration by eliminating at least one partition. The CPL-AdS algorithm is shown to provably converge to the unknown point with an arbitrary degree of accuracy with probability as close to unity as desired. Comprehensive experimental results confirm the fast and accurate convergence of the search for a wide range of values for the Environment's feedback accuracy parameter p, and thus has numerous potential applications.

Algorithms↗
PubMed1998

Use of public performance reports: a survey of patients undergoing cardiac surgery.

CONTEXT: Publicly released performance reports ("report cards") are expected to foster competition on the basis of quality. Proponents frequently cite the need to inform patient choice of physicians and hospitals as a central element of this strategy. OBJECTIVE: To examine the awareness and use of a statewide consumer guide that provides risk-adjusted, in-hospital mortality ratings of hospitals that provide cardiac surgery. DESIGN: Telephone survey conducted in 1996. SETTING: Pennsylvania, where since 1992, the Pennsylvania Consumer Guide to Coronary Artery Bypass Graft [CABG] Surgery has provided risk-adjusted mortality ratings of all cardiac surgeons and hospitals in the state. PARTICIPANTS: A total of 474 (70%) of 673 eligible patients who had undergone CABG surgery during the previous year at 1 of 4 hospitals listed in the Consumer Guide as having average mortality rates between 1% and 5% were successfully contacted. MAIN OUTCOME MEASURES: Patients' awareness of the Consumer Guide, their knowledge of its ratings, their degree of interest in the report, and barriers to its use. RESULTS: Ninety-three patients (20%) were aware of the Consumer Guide, but only 56 (12%) knew about it before surgery. Among these 56 patients, 18 reported knowing the hospital rating and 7 reported knowing the surgeon rating, 11 said hospital and/or surgeon ratings had a moderate or major impact on their decision making, but only 4 were able to specify either or both correctly. When the Consumer Guide was described to all patients, 264 (56%) were "very" or "somewhat" interested in seeing a copy, and 273 (58%) reported that they probably or definitely would change surgeons if they learned that their surgeon had a higher than expected mortality rate in the previous year. A short time window for decision making and a limited awareness of alternative hospitals within a reasonable distance of home were identified as important barriers to use. CONCLUSIONS: Only 12% of patients surveyed reported awareness of a prominent report on cardiac surgery mortality before undergoing cardiac surgery. Fewer than 1% knew the correct rating of their surgeon or hospital and reported that it had a moderate or major impact on their selection of provider. Efforts to aid patient decision making with performance reports are unlikely to succeed without a tailored and intensive program for dissemination and patient education.

Adult↗
PubMed2000

Striatum forever, despite sequence learning variability: a random effect analysis of PET data.

This PET study is concerned with the what, where, and how of implicit sequence learning. In contrast with previous studies imaging the serial reaction time (SRT) task, the sequence of successive locations was determined by a probabilistic finite-state grammar. The implicit acquisition of statistical relationships between serially ordered elements (i.e., what) was studied scan by scan, aiming to evidence the brain areas (i.e., where) specifically involved in the implicit processing of this core component of sequential higher-order knowledge. As behavioural results demonstrate between- and within-subjects variability in the implicit acquisition of sequential knowledge through practice, functional PET data were modelled using a random-effect model analysis (i.e., how) to account for both sources of behavioural variability. First, two mean condition images were created per subject depending on the presence or not of implicit sequential knowledge at the time of each of the 12 scans. Next, direct comparison of these mean condition images provided the brain areas involved in sequential knowledge processing. Using this approach, we have shown that the striatum is involved in more than simple pairwise associations and that it has the capacity to process higher-order knowledge. We suggest that the striatum is not only involved in the implicit automatization of serial information through prefrontal cortex-caudate nucleus networks, but also that it plays a significant role for the selection of the most appropriate responses in the context created by both the current and previous stimuli, thus contributing to better efficiency and faster response preparation in the SRT task.

Adult↗
PubMed1990

Lay understanding of low-frequency electric and magnetic fields.

People do not start with a blank slate when they hear risk-communication messages. All such messages are processed through existing knowledge structures and understanding. Hence, to design effective and reliable risk-communication materials one must understand the state of people's knowledge--correct and incorrect--about an issue. We developed a simple "mental model" of what people minimally need to know to make informed decisions about field-related issues. Then we performed studies to explore how and to what extent respondents of various groups understood physical properties of 60-Hz electric and magnetic fields. Actual knowledge of respondents was then compared with the predicates of the model. Electrical engineering juniors and semi-technical employees of utilities displayed a good command of most of the concepts in the simple model, but little awareness of the limits to their knowledge. Lay respondents correctly knew only a few of the simplest elements of the model, but they displayed a much greater awareness of the limits to their knowledge. Both lay and semi-technical respondents were found to share several misconceptions. On average, they correctly rank-ordered some common field-exposure conditions by field strength, but they could not differentiate between electric and magnetic fields and could not differentiate among field strengths associated with different appliances. Most respondents dramatically underestimated the range of actual field strengths. Many respondents understood that field strength decreases with distance from a source, but they underestimated the rate of decrease. In contrast to X-rays and microwaves, which respondents appeared to think about in rather similar terms, 60-Hz fields were not thought of as being highly similar to any other agent, although the closest parallels were found with ultrasound. Changes in mood, thought, and behavior, and the existence of an "electrical aura," were all seen as plausible results of exposure to a 60-Hz field. Although lay respondents displayed a variety of incomplete and confusing ideas, most of these ideas probably do not pose significant obstacles to the learning of a correct, simple, mental model.

Communication Barriers↗
PubMed1996

Effects of posttraining administration of glucose on retention of a habituation response in mice: participation of a central cholinergic mechanism.

Male Swiss mice were allowed to explore a novel environment, provided by an open-field activity chamber, for 10 min. The procedure was repeated twice with a 24-h interval. The difference in the exploratory activity between the first (training) and the second (testing) exposures to the chamber was taken as an index of retention of this habituation task. Posttraining intraperitoneal administration of glucose (10-300 mg/kg) enhanced retention in a dose-related manner, although only the dose of 30 mg/kg of glucose produced significant effects. Thus, the dose-response curve adopted an inverted U-shaped form. Glucose (30 mg/kg) given to untrained mice did not modify their exploratory performance when recorded 24 h later. The effects of glucose on retention were time-dependent, suggesting an action on memory storage. The memory-improving actions of glucose were prevented by the simultaneous administration of both the central acting muscarinic cholinergic antagonist atropine (0.5 mg/kg) and by the central acting nicotinic cholinergic antagonist mecamylamine (5 mg/kg). In contrast, neither methylatropine (0.5 mg/kg), a peripherally acting muscarinic receptor blocker, nor hexamethonium (5 mg/kg), a peripherally acting nicotinic receptor blocker, prevented the effects of glucose on retention. Low subeffective doses of glucose (10 mg/kg) and the central anticholinesterase physostigmine (35 microg/kg), but not neostigmine (35 microg/kg), given together, act synergistically and facilitated retention. We suggest that glucose modulates memory storage of one form of learning elicited by stimuli repeatedly presented without reinforcement, probably through an enhancement of brain acetylcholine synthesis and/or its release.

Animals↗
PubMed1999

Effects of posttraining administration of insulin on retention of a habituation response in mice: participation of a central cholinergic mechanism.

Male Swiss mice were allowed to explore a novel environment, provided by an open-field activity chamber for a 10-min period. The procedure was repeated twice within a 24-h interval. The difference in the exploratory activity between the first (training) and the second exposure (testing) to the chamber was taken as an index of retention of this habituation task. Posttraining intraperitoneal administration of insulin (8, 20, or 80 IU/kg) impaired retention in a dose-related manner, although only the dose of 20 IU/kg of insulin produced significant effects. Thus, the dose-response curve adopted a U-shaped form. Insulin (20 IU/kg) given to untrained mice did not modify their exploratory performance when recorded 24 h later. The effects of insulin on retention were time dependent, suggesting an action on memory storage. An ineffective dose (8 IU/kg) of insulin given together with an ineffective dose of a central acting muscarinic cholinergic antagonist atropine (0.5 mg/kg) or with a central acting nicotinic cholinergic antagonist mecamylamine (5 mg/kg) interacted to impair retention. In contrast, neither methylatropine (0.5 mg/kg), a peripherally acting muscarinic receptor blocker, nor hexamethonium (5 mg/kg), a peripherally acting nicotinic receptor blocker, interacted with the subeffective dose of insulin on retention. The impairing effects of insulin (20 IU/kg) on retention were reversed by the simultaneous administration of physostigmine (70 microg/kg) but not neostigmine (70 microg/kg). We suggest that insulin impairs memory storage of one form of learning elicited by stimuli repeatedly presented without reinforcement, probably through a decrement of brain acetylcholine synthesis.

Animals↗
PubMed1994

Psychometric testing in rats during normal ageing. Procedures and results.

Examples are given for assessing parameters for motor activity learning and memory. By using the method of the open field the authors could verify that motor activity decreases with age and that it underlies obviously endogenous rhythms which undergo age dependent alterations (e.g. diminution of the amplitude). From the results of an investigation on the influence of ageing and stress on learning ability and memory of the rat the authors draw the following conclusions: Learning ability declines with advancing age. The effect of ageing on memory could not be clearly shown. The effect of the stressors used (crowding and noise) seems to depend on the season of the year (circannual biorhythm).

Aging↗
PubMed1997

Fine-Needle Aspiration in the Evaluation of Thyroid Neoplasms.

Fine-needle aspiration (FNA) is a safe, rapid, and accurate diagnostic tool. Although it continues to gain acceptance, the pace is slow. Probably, if more pathologists master the basics (i.e., learn how to obtain a good sample), this simple technique could be utilized to its fullest advantage. If the sample is not adequate or representative of the lesion, the diagnosis will not be correct. Based on personal experience, we believe that suction should be minimal when obtaining thyroid aspirates. Cytologic diagnostic criteria for the most common neoplasms of the thyroid gland are provided.

Journal Article↗
PubMed2000

The role of attention shifts in the categorization of continuous dimensioned stimuli.

Results of human category learning experiments, using stimulus dimensions with binary values, have implicated a rapidly acting mechanism of attention shifts. Theories of categorization desire that stimuli with binary, discrete and continuous valued dimensions should all be treated similarly. Theoretical analyses of attention shifting, however, have up to now only been developed for shifts between features, or shifts between entire dimensions, not shifts within dimensions. Here we present a model of how people learn to discriminate categories made up of stimuli with continuous-valued dimensions. The model uses rapid shifts in attention within stimulus dimensions to reduce errors during learning; the model generalizes J. K. Kruschke's (Psychological Review, 99, 22-44, 1992) ADIT model. In an experiment in category learning, subjects were trained to discriminate four bivariate normal distributions that are presented with differential base rates. The base-rate manipulation produces several qualitative effects, for which the model accounts very well. With attention shifting turned off, the model fails to account for some aspects of the data, suggesting that attentions shifts are an important mechanism in the model.

Association↗