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PubMed2003

Phylogenetic signal in the song of crests and kinglets (Aves: Regulus).

Territorial song structures are often the most prominent characters for distinguishing closely related taxa among songbirds. Learning processes may cause convergent evolution of passerine songs, but phylogenetic information of acoustic traits can be investigated with the help of molecular phylogenies, which are not affected by cultural evolutionary processes. We used a phylogeny based on cytochrome b sequences to trace the evolution of territorial song within the genus Regulus. Five discrete song units are defined as basic components of regulid song via sonagraphic measurements. Traits of each unit are traced on a molecular tree and a mean acoustic character difference between taxon pairs is calculated. Acoustic divergence between regulid taxa correlates strongly with genetic distances. Syntax features of complete songs and of single units are most consistent with the molecular data, whereas the abundance of certain element types is not. Whether song characters are innate or learned was interpreted using hand-reared birds in aviary experiments. We found that convergent character evolution seems to be most probable for learned acoustic traits. We conclude that syntax traits of whole verses or subunits of territorial song, especially innate song structures, are the most reliable acoustic traits for phylogenetic reconstructions in Regulus.

Animals↗
PubMed2003

[Language acquisition and statistical learning].

Statistical learning is a basic mechanism of information processing in the human brain. The purpose lies in the extraction of probabilistic regularities from the multitude of sensory inputs. Principles of statistical learning contribute significantly to language acquisition and presumably also to language recovery following stroke. The empirical database presented in this manuscript demonstrates that the process of word segmentation, acquisition of a lexicon, and acquisition of simple grammatical rules can be entirely explained through statistical learning. Statistical learning is mediated by changes in synaptic weights in neuronal networks. The concept therefore stands at the transition to molecular biology and pharmacology of the neuronal synapse. It still remains to be shown if all aspects of language acquisition can be explained through statistical learning and which regions of the brain are involved in or capable of statistical learning. Principles of effective language training are obvious already. Most important is the massive, repeated interactive exposure. Conscious processing of the stimulus material may not be essential. The crucial principle is a high cooccurrence of language and corresponding sensory processes. This requires a more intense training frequency than traditional aphasia treatment programs provide.

Adult↗
PubMed2000

Competition among causes but not effects in predictive and diagnostic learning.

Causal asymmetry is one of the most fundamental features of the physical world: Causes produce effects, but not vice versa. This article is part of a debate between the view that, in principle, people are sensitive to causal directionality during learning (causal-model theory) and the view that learning primarily involves acquiring associations between cues and outcomes irrespective of their causal role (associative theories). Four experiments are presented that use asymmetries of cue competition to discriminate between these views. These experiments show that, contrary to associative accounts, cue competition interacts with causal status and that people are capable of differentiating between predictive and diagnostic inferences. Additional implications of causal-model theory are elaborated and empirically tested against alternative accounts. The results uniformly favor causal-model theory.

Adult↗
PubMed2002

The effect of category variability in perceptual categorization.

Exemplar and distributional accounts of categorization make differing predictions for the classification of a critical exemplar precisely halfway between the nearest exemplars of 2 categories differing in variability. Under standard conditions of sequential presentation, the critical exemplar was classified into the most similar, least variable category, consistent with an exemplar account. However, if the difference in variability is made more salient, then the same exemplar is classified into the more variable, most likely category, consistent with a distributional account. This suggests that participants may be strategic in their use of either strategy. However, when the relative variability of 2 categories was manipulated, participants showed changes in the classification of intermediate exemplars that neither approach could account for.

Attention↗
PubMed1997

Normal and abnormal reasoning in people with delusions.

People who experience delusions have been found to request less information prior to making a decision than control participants on tasks that are unrelated to the theme of the delusion (Huq, Garety & Hemsley, 1988). Two studies investigated whether people with delusions have an absolute deficit in reasoning or a more specific data-gathering bias. In Expt 1, 12 people with delusions, 12 people with depression and 12 normal controls were shown the results of spinning a supposedly biased coin. The evidence provided varied in the number of heads to tails. In normal controls a high ratio of head to tails produces a high estimate that the coin is biased. In this experiment, where the evidence gathered was predetermined by the experimenter, all groups of participants were shown to reason in a similar way. Experiment 2 tested whether a difference would exist between the groups in conditions where participants were free to determine the amount of evidence seen, in contrast to when all of them viewed the same evidence. Two jars of beads in opposite but equal ratios (e.g. 85:15, 15:85) were shown to 15 people with delusions, 15 with depression and 15 normal controls. On the basis of beads being drawn one at a time, it was the participants' task to determine which jar they came from. When free to decide when they wished, people with delusions decided on the basis of less evidence than the other groups. However, as in Expt 1, the group with delusions did not differ when made to view the same amount of beads as other participants. Therefore, people with delusions have a data-gathering bias rather than a difficulty in employing the data in reasoning. This "jump to conclusions' bias generalized to a less discriminable ratio of beads (60:40), and was not a consequence of impulsiveness or memory deficit.

Adolescent↗
PubMed2002

Contextual control of stimulus generalization and stimulus equivalence in hierarchical categorization.

The purpose of this study was to determine whether hierarchical categorization would result from a combination of contextually controlled conditional discrimination training, stimulus generalization, and stimulus equivalence. First, differential selection responses to a specific stimulus feature were brought under contextual control. This contextual control was hierarchical in that stimuli at the top of the hierarchy all evoked one response, whereas those at the bottom each evoked different responses. The evocative functions of these stimuli generalized in predictable ways along a dimension of physical similarity. Then, these functions were indirectly acquired by a set of nonsense syllables that were related via transitivity relations to the originally trained stimuli. These nonsense syllables effectively served as names for the different stimulus classes within each level of the hierarchy.

Adolescent↗
PubMed1992

Loss of the Kamin blocking effect in acute but not chronic schizophrenics.

Differences between research diagnostic criteria (RDC)-diagnosed acute and chronic schizophrenics and normal controls were studied using a Kamin blocking procedure. Blocking is an established animal learning procedure, thought by some researchers to reflect selective attention; decreased blocking indicates increased processing of irrelevant stimuli. It was predicted that this pattern would be obtained in acute schizophrenics, tested soon after admission, for two reasons: (1) evidence from previous clinical studies indicates that acute schizophrenics are more aware of nonsalient aspects of their environment than controls; and (2) blocking is disrupted in animals in a hyperdopaminergic state and restored by neuroleptic medication. This was the case: acute, but not chronic, schizophrenics showed disrupted blocking. This disruption was especially clear in those acute schizophrenics tested within 2 weeks of hospital admission. By the second test session (in a cross-over design), there was some evidence of normalization in performance in the acute schizophrenics. These findings are considered with regard to the dopamine hypothesis of schizophrenia.

Acute Disease↗
PubMed1998

Categorical perception effects induced by category learning.

The authors report a series of studies designed to determine whether effects similar to those observed in the innate categorical perception of color and phonemes are induced during the learning of simple unidimensional categories and more complex multidimensional ones. In Experiment 1 no evidence was found for such effects when stimuli varied on 1 dimension. Experiments 2 and 3 demonstrated a within-category compression effect but no between category expansion effect for stimuli varying in 2 dimensions. Compression only was also shown in Experiment 4, which used pictures of actual objects. Multidimensional scaling analyses illustrate how within-category compression without expansion was sufficient to produce categorical clustering of items in the similarity space. These analyses also show that learning changed the dimensional structure of similarity space. Results are compared with those from other studies exploring similar phenomena and with neural network simulations.

Adolescent↗
PubMed2000

Super-learning of causal judgements.

In three experiments, participants learned which of a variety of foods were capable of causing an allergic reaction in a hypothetical patient during training in which a compound of a treatment and a target food cue was paired with the reaction. In Experiment 1 the causal ratings of the target cue were increased if the treatment cue was pretrained as a preventative cause of the reaction. Experiments 2 and 3 demonstrated that the magnitude of this super-learning is unaffected by the order of compound and treatment cue training. The final study also showed that forward super-learning is not induced solely by simple exposure to the treatment cue prior to compound training but, rather, depends upon training the treatment cue as a preventative cause, whereas retrospective super-learning may be due merely to exposure of the treatment cue. These results are problematic for contingency-based accounts of causal induction but accord with modified and extended associative theories.

Adult↗
PubMed1992

Optimizing the use of information: strategic control of activation of responses.

Recent studies indicate that subjects may respond to visual information during either an early parallel phase or a later focused phase and that the selection of the relevant phase is data driven. Using the noise-compatibility paradigm, we tested the hypothesis that this selection may also be strategic and context driven. At least part of the interference effect observed in this paradigm is due to response activation during the parallel-processing phase. We manipulated subjects' expectancies for compatible and incompatible noise in 4 experiments and effectively modulated the interference effect. The results suggest that expectancies about the relative utility of the information extracted during the parallel and focused phases determine which phase is used to activate responses.

Adult↗
PubMed2000

A comparison of two response time models applied to perceptual matching.

Two models, a Poisson race model and a diffusion model, are fit to data from a perceptual matching task. In each model, information about the similarity or the difference between two stimuli accumulates toward thresholds for either response. Stimulus variables are assumed to influence the rate at which information accumulates, and response variables are assumed to influence the level of the response thresholds. Three experiments were conducted to assess the performance of each model. In Experiment 1, observers performed under different response deadlines; in Experiment 2, response bias was manipulated by changing the relative frequency of same and different stimuli. In Experiment 3, stimulus pairs were presented at three eccentricities: foveal, parafoveal, and peripheral. We examined whether the race and diffusion models could fit the response time and accuracy data through changes only in response parameters (for Experiments 1 and 2) or stimulus parameters (for Experiment 3). Comparisons between the two models suggest that the race model, which has not been studied extensively, can account for perceptual matching data at least as well as the diffusion model. Furthermore, without the constraints on the parameters provided by the experimental conditions, the diffusion and the race models are indistinguishable. This finding emphasizes the importance of fitting models across several conditions and imposing logical psychological constraints on the parameters of models.

Adult↗
PubMed2002

Memory seeding: representations underlying quantitative estimations.

N. R. Brown and R. S. Siegler (1996) found that training participants on a subset of country populations improved estimations for novel transfer country populations, an effect called seeding that remained intact over time. They attributed this effect to the abstraction by participants of a general metric framework for estimating populations not dependent on specific country anchors. In a series of 3 follow-up experiments, the authors found that training on seed populations produces both general metric information and durable specific country information. Moreover, minimal amounts of general (mean or range of populations) or specific (1 or 3 countries) information made available for inspection while estimating produced a significant seeding effect. Retention over long intervals was facilitated by both presenting 3 seed countries as opposed to 1 and providing names for the seed countries.

Adult↗
PubMed1999

A long-term stress exposure impairs maze learning performance in rats.

To elucidate hippocampal dysfunctions following chronic stress exposure, we evaluated the effect of chronic stress on maze learning performance, as assessed by a radial eight-arm maze task. In the 12-week stress sessions, male rats in the stress group were exposed to the stress of a 15-min immersion in cold water once a day and, rats in the control group were slightly handled. Rats in the stress group performed significantly poorly during the acquisition period (P < 0.01) and required more trials to attain at least seven correct choices in the first eight choices for five consecutive trials (P < 0.05). Together with our previous findings that chronic stress exposure damages the hippocampus histologically, we concluded that chronic stress exposure resulted in an impairment of maze learning performance, probably due to hippocampal damages.

Animals↗
PubMedDate not supplied

Vector representation of associative learning.

I. P. Pavlov [12] has shown that conditioned reflexes are selective both with respect to conditioned stimuli and to conditioned reflexes elicited by those conditioned stimuli. At the neuronal level selective aspects of conditioned stimuli are based on detectors selectively tuned to respective stimuli. The selective aspects of conditioned reflexes are due to command neurons representing specific unconditioned reflexes. It can be assumed that conditioned reflexes result from association between selective detectors and specific command neurons. The detectors activated by a conditioned stimulus constitute a combination of excitations--a detector excitation vector. The detector excitation vector acts on a command neuron via a set of plastic synapses--a synaptic weight vector. Plastic synapses are modified in the process of learning making command neuron selectively tuned to a specific conditioned stimulus. The selective tuning of a particular command neuron to a specific excitation vector referred to a conditioned stimulus is a basis of associative learning. The probabilities of conditioned reflexes elicited by conditioned and differential stimuli implicitly contain information concerning excitation vectors that encode respective stimuli. Contribution of the vector code to associative learning was explored combining differential color conditioning with intracellular recording from color-coding neurons. It was shown that colors in carps and monkeys are represented on a hypersphere in the four-dimensional space similar to human color space. The basis of the color space is constituted by red-green, blue-yellow, brightness and darkness neurons.

Animals↗