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Results for “Predictive Learning Models”

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PubMed2002

Fruits and vegetables categorized: an application of the generalized context model.

In the study reported in this paper, we investigated the categorization of well-known and novel food items in the categories fruits and vegetables. Predictions based on Nosofsky's (1984,1986) generalized context model (GCM), on a multiplicative-similarity prototype model, and on an instantiation model as applied in Storms, De Boeck, and Ruts (2001) were compared. Despite suggestions in the literature that prototype models predict categorization from large categories better than exemplar models do, our results showed that the exemplar-based GCM yielded clearly better predictions than did a (multiplicative-similarity) prototype model.

Adult↗

PubMed1990

The perceptual buildup of three-dimensional structure from motion.

We present a set of psychophysical experiments that measure the accuracy of perceived three-dimensional (3-D) structure derived from relative motion in the changing two-dimensional image. The experiments are motivated in part by a computational model proposed by Ullman (1984), called the incremental rigidity scheme, in which an accurate 3-D structure is built up incrementally, by considering images of moving objects over an extended time period. Our main conclusions are: First, the human visual system can derive an accurate model of the relative depths of moving points, even in the presence of noise in their image positions; second, the accuracy of the 3-D model improves with time, eventually reaching a plateau; and third, the 3-D structure currently perceived appears to depend on previous 3-D models. Through computer simulations, we relate the results of our psychophysical experiments with the predictions of Ullman's model.

Adult↗

PubMed2003

The case for an internal dynamics model versus equilibrium point control in human movement.

The equilibrium point hypothesis (EPH) was conceived as a means whereby the central nervous system could control limb movements by a relatively simple shift in equilibrium position without the need to explicitly compensate for task dynamics. Many recent studies have questioned this view with results that suggest the formation of an internal dynamics model of the specific task. However, supporters of the EPH have argued that these results are not incompatible with the EPH and that there is no reason to abandon it. In this study, we have tested one of the fundamental predictions of the EPH, namely, equifinality. Subjects learned to perform goal-directed wrist flexion movements while a motor provided assistance in proportion to the instantaneous velocity. It was found that the subjects stopped short of the target on the trials where the magnitude of the assistance was randomly decreased, compared to the preceding control trials (P = 0.003), i.e. equifinality was not achieved. This is contrary to the EPH, which predicts that final position should not be affected by external loads that depend purely on velocity. However, such effects are entirely consistent with predictions based on the formation of an internal dynamics model.

Adult↗

PubMed2006

Remembering source evidence from associatively related items: explanations from a global matching model.

The authors tested source memory across three conditions, one in which 3 strongly associated primes of a target word were presented in the same source as the target, one in which primes were presented in a different source than the target, and one in which no associates of targets were encoded. In the first 2 experiments, target source memory increased in the same-prime condition and decreased in the different-prime condition relative to the no-prime condition. In Experiment 3, the different-prime condition created the illusion that target words had been presented in both sources at encoding. The MINERVA 2 model (D. L. Hintzman, 1988) was able to predict these effects by basing source decisions on the global match of source-specific retrieval probes to all of the items in the memory set.

Adolescent↗

PubMedDate not supplied

Isometric pinch force control and learning in older adults.

The learning of a dynamic isometric pinch force task was investigated in young adults (aged 19 to 29 years) and older adults (aged 64 to 75 years) through use of a visuo-motor tracking paradigm. Both groups significantly improved performance over trials, retained what was learned 1 week later, successfully transferred to a new target, and demonstrated interlimb transfer of training effects, reflecting a strong central component to this task that is apparently intact in older adults. However, performance differences between the two groups remained throughout the trials. Although it appeared that older adults were able to utilize a model-based strategy to predict the target path, as evidenced by minimal response lag, their absolute performance was inferior to that of young adults relative to an overall root mean square error score, a correlation coefficient, and their increased use of high-frequency components in the tracking signal. The age-related performance differences may be attributable to a peripheral decrement in tactile sensibility and/or muscle reorganization as well as a slowness in processing afferent information.

Adult↗

PubMed1999

Interactions between the foot and the head patterning systems in Hydra vulgaris.

The Cnidarian, hydra, is an appealing model system for studying the basic processes underlying pattern formation. Classical studies have elucidated much basic information regarding the role of development gradients, and theoretical models have been quite successful at describing experimental results. However, most experiments and computer simulations have dealt with isolated patterning events such as the dynamics of head regeneration. More global events such as interactions among the head, bud, and foot patterning systems have not been extensively addressed. The characterization of monoclonal antibodies with position-specific labeling patterns and the recent cloning and characterization of genes expressed in position-specific manners now provide the tools for investigating global interactions between patterning systems. In particular, changes in the axial positional value gradient may be monitored in response to experimental perturbation. Rather than studying isolated patterning events, this approach allows us to study patterning over the entire animal. The studies reported here focus on interactions between the foot and the head patterning systems in Hydra vulgaris following induction of a foot in close proximity to a head, axial grafting of a foot closer to the head, or doubling the amount of basal tissue by lateral grafting of an additional peduncle-foot onto host animals. Resulting positional value changes as monitored by antigen (TS19) and gene (ks1 and CnNK-2) expression were assessed in the foot, head, and intervening tissue. The results of the experiments indicate that positional values changed rapidly, in a matter of hours, and that there were reciprocal interactions between the foot and the head patterning systems. Theoretical interpretations of the results in the form of computer simulations based on the reaction-diffusion model are presented and predict many, but not all, of the experimental observations. Since the lateral grafting experiment cannot, at present, be simulated, it is discussed in light of what has been learned from the axial grafting experiments and their simulations.

Animals↗

PubMedDate not supplied

Lessons learned from validation of in vitro toxicity test: from failure to acceptance into regulatory practice.

As no scientific approach or regulatory guidelines existed for the experimental validation of in vitro toxicity tests, in 1990 a US/European validation workshop agreed in Amden (Switzerland) on a simple definition of the validation process. Several international validation studies failed, although they were conducted according to these recommendations. Taking into account the lessons learned from this experience, a second validation workshop was held by ECVAM in Amden in 1994 to develop a more precisely defined validation concept. Prevalidation and the development of biostatistically defined prediction models were added as essential elements to the validation process. In 1995/1996 the ECVAM validation procedure was officially accepted by EU member countries and at the international level by the US regulatory agencies and the OECD. The improved validation concept was immediately introduced into ongoing validation studies. In 1996 the ECVAM/COLIPA validation study of the in vitro phototoxicity test, which was conducted according to the ECVAM/OECD validation concept, was finished successfully and in 1998 a supporting study on UV-filter chemicals was undertaken. In 1998 the 3T3 NRU PT in vitro phototoxicity test was the first experimentally validated in vitro toxicity test that was recommended for regulatory purposes by ESAC, the ECVAM Scientific Advisory Committee, and by the DG ENV of the EU Commission. Meanwhile, two in vitro skin corrosivity tests have successfully been validated by ECVAM. Finally, in June 2000 the three experimentally validated tests were accepted by EU member states for regulatory purposes as the first in vitro toxicity tests. In addition, ECVAM has funded a successful validation study of three in vitro embryotoxicity tests, which was conducted in 12 European laboratories and finished in July 2000. The three tests validated in this study were the whole embryo culture (WEC) test applied to rat embryos, the micromass (MM) test employing primary cultures of dissociated mouse limb bud cells and the mouse embryonic stem cell test (EST). Examples will be given of successful validation studies during the past decade with particular reference to in vitro toxicity tests that were evaluated for regulatory purposes either by the US validation centre ICCVAM or ECVAM in the fields of sensitisation, phototoxicity and embryotoxicity

Animal Testing Alternatives↗

PubMed2000

Kinesthetic and visual image in modeling closed motor skills: the example of the tennis serve.

It was assumed that kinesthetic modeling has more beneficial effects on learning the tennis serve than visual modeling because the spatial anchor points used to reach targets within the vicinity of the body are mainly defined with respect to the body. Also, we predicted that the efficiency of modeling is also affected by the way the representations are activated mentally. Thirty two participants were assigned to kinesthetic or visual modeling with or without mental practice. Analyses showed the primacy of kinesthetic representation over visual representation in terms of speed scores and form performances but only if the learner had the opportunity to rehearse the model mentally. The results support the contention that the motor system can program closed skills more easily when one can represent efficiently the kinesthetic image of its later execution.

Achievement↗

PubMed2005

Deriving the expected utility of a predictive model when the utilities are uncertain.

Predictive models are often constructed from clinical databases with the goal of eventually helping make better clinical decisions. Evaluating models using decision theory is therefore natural. When constructing a model using statistical and machine learning methods, however, we are often uncertain about precisely how the model will be used. Thus, decision-independent measures of classification performance, such as the area under an ROC curve, are popular. As a complementary method of evaluation, we investigate techniques for deriving the expected utility of a model under uncertainty about the model's utilities. We demonstrate an example of the application of this approach to the evaluation of two models that diagnose coronary artery disease.

Artificial Intelligence↗

PubMed2003

Probabilistic methods in BCI research.

This paper suggests a probabilistic treatment of the signal processing part of a brain-computer interface (BCI). We suggest two improvements for BCIs that cannot be obtained easily with other data driven approaches. Simply by using one large joint distribution as a model of the entire signal processing part of the BCI, we can obtain predictions that implicitly weight information according to its certainty. Offline experiments reveal that this results in statistically significant higher bit rates. Probabilistic methods are also very useful to obtain adaptive learning algorithms that can cope with nonstationary problems. An experimental evaluation shows that an adaptive BCI outperforms the equivalent static implementations, even when using only a moderate number of trials. This suggests that adaptive translation algorithms might help in cases where brain dynamics change due to learning effects or fatigue.

Algorithms↗

PubMed2003

Complex dynamic processes in sign tracking with an omission contingency (negative automaintenance).

Hungry pigeons received food periodically, signaled by the onset of a keylight. Key pecks aborted the feeding. Subjects responded for thousands of trials, despite the contingent nonreinforcement, with varying probability as the intertrial interval was varied. Hazard functions showed the dominant tendency to be perseveration in responding and not responding. Once perseveration was accounted for, a linear operator model of associative conditioning further improved predictions. Response rates during trials were correlated with the prior probabilities of a response. Rescaled range analyses showed that the behavioral trajectories were a kind of fractional Brownian motion.

Animals↗

PubMed2003

The role of working memory in motor learning and performance.

Three experiments explore the role of working memory in motor skill acquisition and performance. Traditional theories postulate that skill acquisition proceeds through stages of knowing, which are initially declarative but later procedural. The reported experiments challenge that view and support an independent, parallel processing model, which predicts that procedural and declarative knowledge can be acquired separately and that the former does not depend on the availability of working memory, whereas, the latter does. The behaviour of these two processes was manipulated by providing or withholding visual (and auditory) appraisal of outcome feedback. Withholding feedback was predicted to inhibit the use of working memory to appraise success and, thus, prevent the formation of declarative knowledge without affecting the accumulation of procedural knowledge. While the first experiment failed to support these predictions, the second and third experiments demonstrated that procedural and declarative knowledge can be acquired independently. It is suggested that the availability of working memory is crucial to motor performance only when the learner has come to rely on its use.

Adult↗

PubMed2002

Functional integration and inference in the brain.

Self-supervised models of how the brain represents and categorises the causes of its sensory input can be divided into two classes: those that minimise the mutual information (i.e. redundancy) among evoked responses and those that minimise the prediction error. Although these models have similar goals, the way they are attained, and the functional architectures employed, can be fundamentally different. This review describes the two classes of models and their implications for the functional anatomy of sensory cortical hierarchies in the brain. We then consider how empirical evidence can be used to disambiguate between architectures that are sufficient for perceptual learning and synthesis. Most models of representational learning require prior assumptions about the distribution of sensory causes. Using the notion of empirical Bayes, we show that these assumptions are not necessary and that priors can be learned in a hierarchical context. Furthermore, we try to show that learning can be implemented in a biologically plausible way. The main point made in this review is that backward connections, mediating internal or generative models of how sensory inputs are caused, are essential if the process generating inputs cannot be inverted. Because these processes are dynamical in nature, sensory inputs correspond to a non-invertible nonlinear convolution of causes. This enforces an explicit parameterisation of generative models (i.e. backward connections) to enable approximate recognition and suggests that feedforward architectures, on their own, are not sufficient. Moreover, nonlinearities in generative models, that induce a dependence on backward connections, require these connections to be modulatory; so that estimated causes in higher cortical levels can interact to predict responses in lower levels. This is important in relation to functional asymmetries in forward and backward connections that have been demonstrated empirically. To ascertain whether backward influences are expressed functionally requires measurements of functional integration among brain systems. This review summarises approaches to integration in terms of effective connectivity and proceeds to address the question posed by the theoretical considerations above. In short, it will be shown that functional neuroimaging can be used to test for interactions between bottom-up and top-down inputs to an area. The conclusion of these studies points toward the prevalence of top-down influences and the plausibility of generative models of sensory brain function.

Animals↗

PubMed2006

Parameter selection for and implementation of a web-based decision-support tool to predict extubation outcome in premature infants.

BACKGROUND: Approximately 30% of intubated preterm infants with respiratory distress syndrome (RDS) will fail attempted extubation, requiring reintubation and mechanical ventilation. Although ventilator technology and monitoring of premature infants have improved over time, optimal extubation remains challenging. Furthermore, extubation decisions for premature infants require complex informational processing, techniques implicitly learned through clinical practice. Computer-aided decision-support tools would benefit inexperienced clinicians, especially during peak neonatal intensive care unit (NICU) census. METHODS: A five-step procedure was developed to identify predictive variables. Clinical expert (CE) thought processes comprised one model. Variables from that model were used to develop two mathematical models for the decision-support tool: an artificial neural network (ANN) and a multivariate logistic regression model (MLR). The ranking of the variables in the three models was compared using the Wilcoxon Signed Rank Test. The best performing model was used in a web-based decision-support tool with a user interface implemented in Hypertext Markup Language (HTML) and the mathematical model employing the ANN. RESULTS: CEs identified 51 potentially predictive variables for extubation decisions for an infant on mechanical ventilation. Comparisons of the three models showed a significant difference between the ANN and the CE (p = 0.0006). Of the original 51 potentially predictive variables, the 13 most predictive variables were used to develop an ANN as a web-based decision-tool. The ANN processes user-provided data and returns the prediction 0-1 score and a novelty index. The user then selects the most appropriate threshold for categorizing the prediction as a success or failure. Furthermore, the novelty index, indicating the similarity of the test case to the training case, allows the user to assess the confidence level of the prediction with regard to how much the new data differ from the data originally used for the development of the prediction tool. CONCLUSION: State-of-the-art, machine-learning methods can be employed for the development of sophisticated tools to aid clinicians' decisions. We identified numerous variables considered relevant for extubation decisions for mechanically ventilated premature infants with RDS. We then developed a web-based decision-support tool for clinicians which can be made widely available and potentially improve patient care world wide.

Birth Weight↗

PubMed2005

Punishment prediction by dopaminergic neurons in Drosophila.

The temporal pairing of a neutral stimulus with a reinforcer (reward or punishment) can lead to classical conditioning, a simple form of learning in which the animal assigns a value (positive or negative) to the formerly neutral stimulus. Olfactory classical conditioning in Drosophila is a prime model for the analysis of the molecular and neuronal substrate of this type of learning and memory. Neuronal correlates of associative plasticity have been identified in several regions of the insect brain. In particular, the mushroom bodies have been shown to be necessary for aversive olfactory memory formation. However, little is known about which neurons mediate the reinforcing stimulus. Using functional optical imaging, we now show that dopaminergic projections to the mushroom-body lobes are weakly activated by odor stimuli but respond strongly to electric shocks. However, after one of two odors is paired several times with an electric shock, odor-evoked activity is significantly prolonged only for the "punished" odor. Whereas dopaminergic neurons mediate rewarding reinforcement in mammals, our data suggest a role for aversive reinforcement in Drosophila. However, the dopaminergic neurons' capability of mediating and predicting a reinforcing stimulus appears to be conserved between Drosophila and mammals.

Animals↗

PubMed2005

Generalized Bienenstock-Cooper-Munro rule for spiking neurons that maximizes information transmission.

Maximization of information transmission by a spiking-neuron model predicts changes of synaptic connections that depend on timing of pre- and postsynaptic spikes and on the postsynaptic membrane potential. Under the assumption of Poisson firing statistics, the synaptic update rule exhibits all of the features of the Bienenstock-Cooper-Munro rule, in particular, regimes of synaptic potentiation and depression separated by a sliding threshold. Moreover, the learning rule is also applicable to the more realistic case of neuron models with refractoriness, and is sensitive to correlations between input spikes, even in the absence of presynaptic rate modulation. The learning rule is found by maximizing the mutual information between presynaptic and postsynaptic spike trains under the constraint that the postsynaptic firing rate stays close to some target firing rate. An interpretation of the synaptic update rule in terms of homeostatic synaptic processes and spike-timing-dependent plasticity is discussed.

Action Potentials↗

PubMed1988

[The status of life events in causal analytic considerations in child and adolescent psychiatry: model development trials with LISREL (linear structural relationship analysis)].

An epidemiological longitudinal child psychiatric study with 334 eight- and thirteen-year-olds tried to put life events in an optimal order within a model of causal interrelations. The causal connections were tested by a Linear Structural Relationship Analysis (LISREL), which in addition to life events included child psychiatric disorders, adverse family factors and learning disabilities. By testing different models it could be demonstrated, that adverse family factors do not directly influence the number of life events of 8 to 13-year-old children. Adverse family factors influence life events as well as psychiatric disorders at age 13 predominantly by way of early psychiatric disorders. Psychiatric disorders at age 13 are best predicted by psychiatric disorders at age 8 and to a smaller degree by life events and learning disabilities.

Adolescent↗

PubMed1999

How well do elderly people cope with uncertainty in a learning task?

The relation between age, task complexity and learning performance in a Multiple Cue Probability Learning task was studied by systematically varying the level of uncertainty present in the task, keeping constant the direction of relationships. Four age groups were constituted: young adults (mean age = 21), middle-aged adults (45), elderly people (69) and very elderly people (81). Five uncertainty levels were considered: predictability = 0.96, 0.80, 0.64, 0.48, and 0.32. All relationships involved were direct ones. A strong effect of uncertainty on 'control', a measure of the subject's consistency with respect to a linear model, was found. This effect was essentially a linear one. To each decrement in predictability of the task corresponded an equal decrement in participants' level of control. This level of decrement was the same, regardless of the age of the participant. It can be concluded that elderly people cope with uncertainty in probability learning tasks as well as young adults.

Adaptation, Psychological↗