Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Generalization, Stimulus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,279 records · Page 71Linked to original sources
PubMed1980

A random process model of cognitive deficit in schizophrenia.

It is argued that in schizophrenic patients the process of selecting responses to incoming stimuli becomes increasingly random the more disturbed the patient is. This is seen as a disordered overextension of normal behavioral flexibility and variability. A model is proposed which considers the range of human behavior to be the result of perceptions of incoming stimuli compared to related analogs retrieved from memory. In the schizophrenic individual, the range of memory elements likely to be elicited by an input becomes abnormally large so that in the severely disturbed patient, behavior approaches randomness. The model is discussed in light of current thinking about schizophrenia, and data are presented in support of the new approach.

Anxiety↗
PubMed1993

Exaggerated anesthetic requirements in the preferentially anesthetized brain.

BACKGROUND: The brain is assumed to be the site of anesthetic action, but anesthetics have effects elsewhere, such as the spinal cord. A preferentially anesthetized goat brain model was used to determine the importance of anesthetic action in the brain. METHODS: Six goats were anesthetized with isoflurane; after tracheal intubation and insertion of a femoral arterial catheter, bilateral neck dissections were performed to isolate the external carotid arteries and external jugular veins. The occipital arteries were ligated to prevent vertebral blood from entering the carotid system. (Goats do not have direct, significant vertebral artery contributions to the brain, and they lack internal jugular veins.) Control isoflurane minimum alveolar concentration (MAC) was determined using a dew-claw clamp as the painful stimulus. Following this, cranial venous blood was drained into a bubble oxygenator in which an isoflurane vaporizer was placed in line with the gas flow. Oxygenator arterial isoflurane concentration was estimated from the isoflurane partial pressure in the oxygenator exhaust. Isoflurane administration via the lungs was discontinued and the isoflurane partial pressure in the blood delivered via the carotid artery was increased by an amount required to bracket the partial pressures permitting and preventing movement in response to dew-claw stimulation. The native circulation was reestablished and MAC determined again. RESULTS: Cerebral isoflurane requirements were 1.2 +/- 0.3% (mean +/- SD) before bypass, increased to 2.9 +/- 0.7% during bypass when the brain was preferentially anesthetized, and decreased to 1.3 +/- 0.1% after bypass. CONCLUSIONS: The results support the importance of subcortical structures, such as the spinal cord, in the generation of purposeful movement in response to a painful stimulus under general anesthesia.

Anesthesia↗
PubMed1999

Effects of drugs on responding under concurrent fixed-interval schedules and concurrent fixed-ratio schedules.

Pigeons were trained to respond under concurrent fixed-interval fixed-interval (concurrent FI FI) schedules with Fl values (in seconds) of 30/300, 60/240, 60/60, 240/60 and 300/30. A second group was trained to respond under concurrent fixed-ratio fixed-ratio (concurrent FR FR) with FR values of 10/40, 10/20, 20/20, 20/10 and 40/10. Under the concurrent Fl Fl schedules, pigeons responded much less often on the key with the higher reinforcement density than would be predicted basing on a perfect matching of the ratio of responses made to the ratio of reinforcers delivered, and the pigeons also showed a bias towards responding on the left key. Pentobarbital, methamphetamine, morphine and phencyclidine had little effect on bias, but high doses of methamphetamine, morphine and phencyclidine decreased undermatching. Under the concurrent FR FR schedules, pigeons responded almost entirely on the key with the higher reinforcement density. Only pentobarbital consistently disrupted this pattern of responding.

Animals↗
PubMed2000

Delta9-THC training dose as a determinant for (R)-methanandamide generalization in rats: a systematic replication.

Järbe et al. (1998a) trained rats to discriminate between (-)-delta9-tetrahydrocannabinol (delta9-THC) and vehicle, using different training doses in order to create assays with different efficacy demands, to examine whether (R)-methanandamide, an analog of the endogenous ligand anandamide, had lower efficacy than delta9-THC. Rats were initially trained with 3 mg/kg delta9-THC, then tested with (R)-methanandamide and delta9-THC. Thereafter, the rats were split into two groups and retrained with either 1.8 or 5.6 mg/kg delta9-THC, followed by additional tests with the two agonists. The current study systematically replicated this study in two groups of rats, trained from the outset to discriminate between vehicle and either 1.8 or 5.6 mg/kg delta9-THC, respectively. Two-lever operant drug discrimination procedures were used. The outcomes in the two studies were similar. In tests with (R)-methanandamide, full substitution occurred in the low-dose delta9-THC training group, whereas substitution was partial in the high-dose delta9-THC training group. (R)-Methanandamide in higher doses exerted marked suppression of lever pressing. In tests with delta9-THC, full substitution occurred in both delta9-THC-trained groups, and rates of responding were comparable to those observed during regular drug training sessions. In conclusion, both sets of data indicate that cannabinoid agonists either can have varying degrees of efficacy at a receptor site, or may produce their behavioral actions through multiple mechanisms, or both. Prevailing training-dose condition rather than prior training-dose history is the major determinant for the substitution pattern.

Animals↗
PubMed2003

Clonidine and yohimbine in opioid-dependent humans responding under a naloxone novel-response discrimination procedure.

Opioid-maintained volunteers were trained to distinguish between a low dose of the opioid antagonist naloxone (0.15 mg/70 kg, i.m.; i.e. Drug A) and placebo (i.e. Drug B), under an instructed novel-response drug discrimination procedure in which subjects identify the drug condition as 'A', 'B', or 'N' (neither A nor B - 'novel'). Once the discrimination was acquired, doses of naloxone, the alpha2-adrenergic antagonist yohimbine, the alpha2-adrenergic agonist clonidine, and the training dose of naloxone in combination with clonidine were tested. Naloxone and yohimbine each produced a dose-related increase and decrease in naloxone- and 'novel'-appropriate responding, respectively, with the naloxone stimulus partially generalizing to yohimbine. Clonidine produced primarily placebo-appropriate responding. Naloxone produced expected changes in self-reports, but effects of yohimbine and clonidine were unremarkable, and yohimbine was never identified as an opioid antagonist. Clonidine partially attenuated naloxone-occasioned responding in a non-dose-related manner, and attenuated some, but not all, naloxone-induced changes in self-report measures. Naloxone attenuated or enhanced several clonidine-induced changes in self-report and physiological measures. These findings indicate that adrenergic mechanisms are involved in the expression of opioid withdrawal, but the involvement is indirect.

Adrenergic alpha-Agonists↗
PubMedDate not supplied

Two-year-olds will name artifacts by their functions.

Do young children take functional information into account in naming artifacts? In three studies of lexical categorization, 112 children 2 years of age learned new names for novel artifacts with novel functions and then extended the names to new objects. The objects were designed to have functions that were causally related in simple and compelling ways to perceptible aspects of their physical structure. Despite only minimal opportunity to familiarize themselves with the objects, children generalized the names in accordance with the objects' functions. This result obtained even when children had to discover the functions of the named objects on their own (Experiment 2) and when all the test objects had some discernible function (Experiment 3). Two-year-olds name by function when they can make sense of the relation between the appearances and the functions of artifacts.

Analysis of Variance↗
PubMed2005

The training and transfer of real-world perceptual expertise.

A hallmark of perceptual expertise is that experts classify objects at a more specific, subordinate level of abstraction than novices. To what extent does subordinate-level learning contribute to the transfer of perceptual expertise to novel exemplars and novel categories? In this study, participants learned to classify 10 varieties of wading birds and 10 varieties of owls at either the subordinate, species (e.g., "great blue crown heron,""eastern screech owl") or the family ("wading bird,""owl") level of abstraction. During training, the amount of visual exposure was equated such that participants received an equal number of learning trials for wading birds and owls. Pre- and posttraining performance was measured in a same/different discrimination task in which participants judged whether pairs of bird stimuli belonged to the same or different species. Participants trained in species-level discrimination demonstrated greater transfer to novel exemplars and novel species categories than participants trained in family-level discrimination. These findings suggest that perceptual categorization, not perceptual exposure per se, is important for the development and generalization of visual expertise.

Adolescent↗
PubMed2005

Visual recognition: as soon as you know it is there, you know what it is.

What is the sequence of processing steps involved in visual object recognition? We varied the exposure duration of natural images and measured subjects' performance on three different tasks, each designed to tap a different candidate component process of object recognition. For each exposure duration, accuracy was lower and reaction time longer on a within-category identification task (e.g., distinguishing pigeons from other birds) than on a perceptual categorization task (e.g., birds vs. cars). However, strikingly, at each exposure duration, subjects performed just as quickly and accurately on the categorization task as they did on a task requiring only object detection: By the time subjects knew an image contained an object at all, they already knew its category. These findings place powerful constraints on theories of object recognition.

Adult↗
PubMedDate not supplied

When induction meets memory: evidence for gradual transition from similarity-based to category-based induction.

The ability to perform induction appears early; however, underlying mechanisms remain unclear. Some argue that early induction is category based, whereas others suggest that early induction is similarity based. Category- and similarity-based induction should result in different memory traces and thus in different memory accuracy. Performing induction resulted in low memory accuracy in adults and 11-year-olds, whereas 5-, and 7-year-olds were highly accurate (Experiment 1). After training to perform category-based induction, 5- and 7-year-olds exhibited patterns of accuracy similar to those of adults (Experiment 2). Furthermore, 7-year-olds, but not 5-year-olds, retained this training over time (Experiment 3). With novel categories, even adults performed similarity-based induction, exhibiting high memory accuracy (Experiment 4). These results suggest a gradual transition from similarity- to category-based induction with familiar categories.

Adolescent↗
PubMedDate not supplied

What does it look like and what can it do? Category structure influences how infants categorize.

Despite a large body of research demonstrating the kinds of categories to which infants respond, few studies have directly assessed how infants' categorization unfolds over time. Four experiments used a visual familiarization task to evaluate 10-month-old infants' (N = 98) learning of exemplars characterized by commonalities in appearance or function. When learning exemplars with a common function, infants initially responded to the common feature, apparently forming a category, and only learned the individual features with more extensive familiarization. When learning exemplars with a common appearance, infants initially learned the individual features and apparently only formed a category with more extensive familiarization. The results are discussed in terms of models of category learning.

Association Learning↗
PubMedDate not supplied

What leads children to adopt new strategies? A microgenetic/cross-sectional study of class inclusion.

Learning of class inclusion by 5-year-olds in response to empirical and logical explanations of an adult's answers was examined. Contrary to the view that young children possess an empirical bias, 5-year-olds learned more, and continued learning for longer, when given logical explanations of correct answers than when given empirical explanations. Once children discovered how to solve the problems, they showed few regressions. Many children in the microgenetic experiment followed the path of change anticipated from previous cross-sectional studies, but children in the cross-sectional part of the study seemed to follow a different path. Reasons for the superior effectiveness of the logical explanations were discussed.

Age Factors↗