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PubMed2001

Category discriminability, base-rate, and payoff effects in perceptual categorization.

The optimality of perceptual categorization performance under manipulations of category discriminability (i.e., d' level), base rates, and payoffs was examined. Base-rate and payoff manipulations across two category discriminabilities allowed a test of the hypothesis that the steepness of the objective reward function affects performance (i.e., the flat-maxima hypothesis), as well as the hypothesis that observers combine base-rate and payoff information independently. Performance was (1) closer to optimal for the steeper objective reward function, in line with the flat-maxima hypothesis, (2) closer to optimal in base-rate conditions than in payoff conditions, and (3) in partial support of the hypothesis that base-rate and payoff knowledge is combined independently. Implications for current theories of base-rate and payoff learning are discussed.

Adult↗
PubMed2003

Decision making in adolescents with behavior disorders and adults with substance abuse.

OBJECTIVE: The study assessed the validity of the Gambling Task as a test of decision-making ability in adolescents and examined whether adolescents with behavior disorders, who are at risk for substance abuse, have deficits in decision making similar to those exhibited by adults with substance abuse. METHOD: Performance on the Gambling Task in two testing sessions separated by 1 week was assessed in 64 12-14-year-old adolescents (31 healthy, 33 with externalizing behavior disorders) and 52 adults (22 healthy, 30 with substance abuse). RESULTS: The healthy adolescents and the healthy adults had similar performance on the Gambling Task. Adolescents with behavior disorders performed more poorly than healthy adolescents, but only in the second testing session. In adults, overall Gambling Task performance did not differ between the healthy and substance abuse groups at either testing session, indicating no difference in learning of decision-making strategies between groups. However, adults with substance abuse performed more poorly than healthy adults during an early stage of the task, when participants presumably begin to understand the rewards and penalties involved in the task but are not yet sure of the actual risk of incurring penalities. CONCLUSIONS: The Gambling Task can be used with adolescents. Testing with the Gambling Task revealed a deficit in decision making in adolescents with behavior disorders, who are at risk for substance abuse. This deficit may represent a vulnerability factor for the development of substance abuse.

Adolescent↗
PubMed1995

YM796, a novel muscarinic agonist, improves the impairment of learning behavior in a rat model of chronic focal cerebral ischemia.

We studied effects of YM796, a novel muscarinic agonist, on behavioral, histological and regional cerebral blood flow changes in the chronic phase after focal cerebral ischemia in rats. YM796 (0.03, 0.1, 0.3 and 1 mg/kg) was administered orally once a day from the 7th to the 13th day after the permanent occlusion of left middle cerebral artery. On the 7th day, rats were trained in one-trial step-through passive avoidance task 45 min after drug administration. Test trials were carried out on the 8th and 14th days. Neurological deficits, including hemiplegia and abnormal posture, were observed on the 7th and 14th days. After the completion of behavioral studies, the rats were decapitated and cerebral infarction was measured. Regional cerebral blood flow was also measured by the hydrogen clearance technique 7 days after MCA occlusion. YM796 (0.1-1 mg/kg) significantly (P < 0.05) attenuated the impairment of learning behavior in a dose-dependent manner without affecting spontaneous locomotor activity. The ameliorating effect of YM796 (0.3 mg/kg) on the impaired learning behavior was significantly (P < 0.05) suppressed by intracerebroventricular injection of pirenzepine (10 micrograms/rat), an M1 antagonist. No significant difference in either neurological deficits or cerebral infarction was found between the vehicle- and YM796-treated groups. Further, YM796 (0.3 mg/kg) had little effect on the reduced blood flow in the ipsilateral frontal cortex 7 days after occlusion. These results suggest that YM796 improves the impaired learning behavior probably by activating central M1 receptors in a rat model of chronic focal cerebral ischemia.

Animals↗
PubMed1992

Conscious knowledge and changes in performance in sequence learning: evidence against dissociation.

Two experiments examined the relation between explicit knowledge and motor performance on the serial reaction time task developed by Nissen and Bullemer (1987). Tests of free recall and recognition of sequence components revealed that reliable explicit knowledge was acquired after an amount of practice that was hardly sufficient to improve mean motor performance. In addition, reaction time improvement was limited to the ending trials of the 3- and 4-trial sequence components that Ss recalled or recognized. These results were replicated in Experiment 3, in which Ss were trained under attentional distraction in the task developed by Cohen, Ivry, and Keele (1990). Overall, these findings undermine the most direct experimental support for the widespread view that conscious knowledge and performance in sequence-learning tasks tap 2 independent knowledge bases in normal Ss.

Adult↗
PubMed2003

Bootstrapped learning of novel objects.

Recognition of familiar objects in cluttered backgrounds is a challenging computational problem. Camouflage provides a particularly striking case, where an object is difficult to detect, recognize, and segment even when in "plain view." Current computational approaches combine low-level features with high-level models to recognize objects. But what if the object is unfamiliar? A novel camouflaged object poses a paradox: A visual system would seem to require a model of an object's shape in order to detect, recognize, and segment it when camouflaged. But, how is the visual system to build such a model of the object without easily segmentable samples? One possibility is that learning to identify and segment is opportunistic in the sense that learning of novel objects takes place only when distinctive clues permit object segmentation from background, such as when target color or motion enables segmentation on single presentations. We tested this idea and discovered that, on the contrary, human observers can learn to identify and segment a novel target shape, even when for any given training image the target object is camouflaged. Further, perfect recognition can be achieved without accurate segmentation. We call the ability to build a shape model from high-ambiguity presentations bootstrapped learning.

Animals↗
PubMed2001

Retarded learning: rigorous results from statistical mechanics.

We study learning of probability distributions characterized by an unknown symmetry direction. Based on an entropic performance measure and the variational method of statistical mechanics we develop exact upper and lower bounds on the scaled critical number of examples below which learning of the direction is impossible. The asymptotic tightness of the bounds suggests an asymptotically optimal method for learning nonsmooth distributions.

Learning↗
PubMed1994

Improving examples to improve transfer to novel problems.

People often memorize a set of steps for solving problems when they study worked-out examples in domains such as math and physics without learning what domain-relevant subgoals or subtasks these steps achieve. As a result, they have trouble solving novel problems that contain the same structural elements but require different, lower-level steps. In three experiments, subjects who studied example solutions that emphasized a needed subgoal were more likely to solve novel problems that required a new approach for achieving this subgoal than were subjects who did not learn this subgoal. This result suggests that research aimed at determining the factors that influence subgoal learning may be valuable in improving transfer from examples to novel problems.

Adult↗
PubMed2001

Probabilistic contingency learning with limbic or prefrontal damage.

A fundamental capacity of the human brain is to learn relations (contingencies) between environmental stimuli and the consequences of their occurrence. Some contingencies are probabilistic; that is, they predict an event in some situations but not in all. Animal studies suggest that damage to limbic structures or the prefrontal cortex may disturb probabilistic learning. The authors studied the learning of probabilistic contingencies in amnesic patients with limbic lesions, patients with prefrontal cortex damage, and healthy controls. Across 120 trials, participants learned contingent relations between spatial sequences and a button press. Amnesic patients had learning comparable to that of control subjects but failed to indicate what they had learned. Across the last 60 trials, amnesic patients and control subjects learned to avoid a noncontingent choice better than frontal patients. These results indicate that probabilistic learning does not depend on the brain structures supporting declarative memory.

Adult↗
PubMed2003

Spatial interference and response control in sequence learning: the role of explicit knowledge.

In several sequence learning studies it has been suggested that response control shifts from the stimuli to some internal representation (i.e., motor program) through the learning process. The main questions addressed in this paper are whether this control shift is related to explicit knowledge and whether the formation of these internal representations depends on the stimulus attributes. In one experiment we compared the learning of a response sequence triggered by either spatial location or location symbol (left-right) by using a serial response task (SRT). Symbols were presented at either a centered or random location. The results showed that in the symbolic conditions the shift of response control correlated with the emergence of explicit knowledge. Only participants with complete explicit knowledge seemed to learn the sequence structure beyond probabilistic information (response time "RT" did not depend on the frequency of the response). Moreover, these participants were able to overcome, when needed, spatial interference (RT was the same for both spatially corresponding and non-corresponding trials). However, when spatial location was relevant, RT was always faster, especially for more frequent responses. These results suggest that the relevant stimulus dimension (location or symbol) seems to engage different sequence learning mechanisms.

Adult↗
PubMed2003

Alcohol and error processing.

A recent study indicates that alcohol consumption reduces the amplitude of the error-related negativity (ERN), a negative deflection in the electroencephalogram associated with error commission. Here, we explore possible mechanisms underlying this result in the context of two recent theories about the neural system that produces the ERN - one based on principles of reinforcement learning and the other based on response conflict monitoring.

Alcohol Drinking↗
PubMed1996

Neural networks in petroleum engineering: a case study.

A multilayer neural network has been used for deciding which oil reservoir layer has to be perforated. Many network architectures were tested until we found those with the best generalization capability. The network performs better than human experts and its achievements are higher than the historical average in the test area. As in other applications of neural networks, the learning capability improves with more hidden neurons but the generalization does not.

Algorithms↗
PubMed1963

A fixed interval schedule in which the interval is initiated by a response.

The fixed interval schedule described requires the animal to initiate every time interval by making a response on a bar other than the one on which it is reinforced. This response, R(A), demarcates the postreinforcement pause (S(R)-R(A) interval) from the fixed interval pause (R(A)-R(B) interval) so that these pauses may be measured separately. Twelve rats and three monkeys, working in two-bar Skinner boxes, were trained and stabilized on this schedule. The resulting performances, presented for individual animals, are analyzed in terms of (1) the relative frequencies with which the animal waits various lengths of time between consecutive responses, (2) the relative frequencies with which various rates of responding appear, (3) the change in response rate throughout the fixed interval, (4) the average length of the postreinforcement pause, (5) the relative frequencies with which the animal waits different lengths of time between the R(A) and the first R(B), and (6) the average inter-response time as a function of the rank order in the fixed interval of the inter-response time. The joint interpretation of the several measures taken leads to the following conclusions: 1. The probability of an R(B) increases throughout the fixed interval. 2. The increase is discontinuous at the first R(B), at which point the probability increases sharply. 3. The frequency distributions of R(A)-R(B) pauses exhibit three discrete types of behavior with no intermediate cases. 4. The (main) mode of R(A)-R(B) interval length usually occurs just below the fixed interval requirement.

Animals↗
PubMed1996

Learning to commit or avoid the base-rate error.

When predicting an event, people neglect overall frequencies (base rates) of various possibilities. We have previously shown that this base-rate occurs not only with word problems, but also in a procedure with repeated trials: a sample cue followed by two choice options, one of which the subject must choose, with feedback regarding the correctness of the choice. Perhaps this base-rate error depends on people's histories of matching physically similar items. In support of this suggestions, we begin by showing that the base-rate error is eliminated with physically unrelated items. We then show that when the relation between items is again arbitrary, but is a relation that subjects already know, the error reappears. Finally we show that teaching subjects new arbitrary relations reintroduces the error in later testing. These experiments demonstrate a fundamental base-rate error dependent on learned relationships without interference from re-existing associations between cues and options, predictions may be made more optimally.

Concept Formation↗
PubMed2004

Intentional control and implicit sequence learning.

Sequence knowledge acquired by repeated exposure to targets in a speeded localization task was studied in 3 experiments that sought to test A. Destrebecqz and A. Cleeremans's (2001, 2003) claim that, under certain circumstances, the expression of such sequence knowledge cannot be brought under intentional control. In Experiment 1 participants were trained on either a deterministic or a probabilistic sequence and then performed a free-generation test under either inclusion or exclusion instructions. Participants were found to be capable of both expressing (inclusion) and avoiding expressing (exclusion) sequence knowledge. These results were confirmed in Experiment 2 with a more exact replication of Destrebecqz and Cleeremans's methodology. In Experiment 3 participants performed a trial-by-trial generation test under both inclusion and exclusion conditions after a much longer period of training. All the findings are consistent with the proposal that information acquired during sequence learning is explicit in nature.

Adult↗
PubMed2003

Alcohol-induced impairment of behavioral control: effects on the alteration and suppression of prepotent responses.

OBJECTIVE: Alcohol use in humans is associated with aggression and other socially inappropriate behaviors. These adverse effects have been attributed to an acute impairment of behavioral control, and research findings indicate that inhibitory aspects of behavioral control might be particularly vulnerable to the effects of alcohol. The present study tested the degree to which alcohol-induced impairment of behavioral control is due to a specific impairment of inhibitory mechanisms or due to a general information processing deficit. METHOD: Forty subjects (29 men) performed a cued reaction time task before and after receiving 0.65 g/kg alcohol or a placebo. Subjects performed the task under conditions that differed in the type of response needed to maintain behavioral control: response-suppression and response-alteration. RESULTS: Alcohol impairment was observed when behavioral controlwas dependent on response-suppression, but no impairment was observed when control relied on response-alteration. CONCLUSIONS: The findings point to the susceptibility of inhibitory processes by showing that alcohol can be particularly detrimental to behavioral control in situations where prepotent responses must be completely suppressed. Evidence for alcohol-induced impairment of inhibitory functions could provide important clues about basic behavioral mechanisms by which alcohol disrupts such higher order cognitive processes as working memory, learning and decision making.

Adult↗
PubMed1992

Recognition of multiunit neural signals.

An essential step in studying nerve cell interaction during information processing is the extracellular microelectrode recording of the electrical activity of groups of adjacent cells. The recording usually contains the superposition of the spike trains produced by a number of neurons in the vicinity of the electrode. It is therefore necessary to correctly classify the signals generated by these different neurons. This paper considers this problem, and a new classification scheme is developed, which does not require human supervision. A learning stage is first applied on the beginning portion of the recording to estimate the typical spike shapes of the different neurons. As for the classification stage, a method is developed, which specifically considers the case when spikes overlap temporally. The method minimizes the probability of error, taking into account the statistical properties of the discharges of the neurons. The method is tested on a real recording as well as on synthetic data.

Action Potentials↗