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PubMed1998

Generalization and exclusive allocation of credit in unsupervised category learning.

A new way of measuring generalization in unsupervised learning is presented. The measure is based on an exclusive allocation, or credit assignment, criterion. In a classifier that satisfies the criterion, input patterns are parsed so that the credit for each input feature is assigned exclusively to one of multiple, possibly overlapping, output categories. Such a classifier achieves context-sensitive, global representations of pattern data. Two additional constraints, sequence masking and uncertainty multiplexing, are described; these can be used to refine the measure of generalization. The generalization performance of EXIN networks, winner-take-all competitive learning networks, linear decorrelator networks, and Nigrin's SONNET-2 network are compared.

Computer Simulation↗
PubMed1995

Generalization of the orienting response to significant stimuli: the roles of common and distinctive stimulus components.

This study focused on the effects of common and distinctive stimulus components on the generalization of the orienting response (OR) to significant stimuli. Compound pictorial stimuli were used as the relevant items memorized by the subjects. Skin conductance responses were measured during the subsequent presentation of a stimulus sequence that included a test stimulus that shared some common components with the relevant one. The two types of stimulus components (common and distinctive) were independently manipulated. As predicted by the feature-matching theory, both types of features affected OR generalization, but the distinctive components effect was due mainly to a large decline in OR with the introduction of the first distinctive component. As hypothesized, no interaction was observed between the effects of common and distinctive components. Contrary to expectations, similar OR generalization was obtained regardless of whether the test stimulus was constructed by deleting stimulus components from the relevant stimulus or by adding components to that stimulus.

Adult↗
PubMed1977

Suppression of the secondary immune response by specific antibody, when given together with the secondary antigenic stimulus.

It is generally believed that antibody-mediated immunosuppression can be only produced in non-primed individuals, and that this applies both to experimental animals and Rh-negative women at risk. However, in this paper it is reported that the additional injection of 0.2 ml of an antiserum to sheep erythrocytes (SE) together with a secondary antigenic stimulus of 10(8) SE into mice, primarily immunized by a tiny dose of 5 x 10(5) SE 28 days before, was capable of producing effective suppression of the secondary immune response.

Animals↗
PubMed2000

Mechanisms of generalization in perceptual learning.

Learning in many visual perceptual tasks has been shown to be specific to practiced stimuli, while new stimuli have to be learned from scratch. Here we demonstrate generalization using a novel paradigm in motion discrimination where learning has been previously shown to be specific. We trained subjects to discriminate directions of moving dots, and verified the previous results that learning does not transfer from a trained direction to a new one. However, by tracking the subjects' performance across time in the new direction, we found that their speed of learning doubled. Therefore, we found generalization in a task previously considered too difficult to generalize. We also replicated, in a second experiment, transfer following training with 'easy' stimuli, when the difference between motion directions is enlarged. In a third experiment we found a new mode of generalization: after mastering the task with an easy stimulus, subjects who have practiced briefly to discriminate the easy stimulus in a new direction generalize to a difficult stimulus in that direction. This generalization depends on both the mastering and the brief practice. The specificity of perceptual learning and the dichotomy between learning of 'easy' versus 'difficult' tasks have been assumed to involve different learning processes at different cortical areas. Here we show how to interpret these results in terms of signal detection theory. With the assumption of limited computational capacity, we obtain the observed phenomena--direct transfer and acceleration of learning--for increasing levels of task difficulty. Human perceptual learning and generalization, therefore, concur with a generic discrimination system.

Discrimination, Psychological↗
PubMed1995

Mianserin as a discriminative stimulus in rats: asymmetrical cross-generalization with scopolamine.

The present study was conducted to determine if the tetracyclic antidepressant mianserin could be established as a discriminative stimulus in rats. One group of rats was trained to discriminate mianserin (4.0 mg/kg, IP) from saline in a two-lever drug discrimination procedure, and a second group of rats was trained to discriminate the muscarinic cholinergic antagonist scopolamine (0.25 mg/kg, IP) from saline. Generalization testing with the training drugs yielded an ED50 of 0.502 mg/kg for the mianserin-trained rats and an ED50 of 0.048 mg/kg for the scopolamine-trained rats. Asymmetrical cross-generalization between mianserin and scopolamine was observed, because scopolamine produced mianserin-appropriate responding, but mianserin did not produce scopolamine-appropriate responding. This study is the first demonstration that rats can be trained to discriminate mianserin from saline and that antagonism of muscarinic cholinergic receptors is sufficient to produce mianserin-appropriate responding.

Animals↗
PubMed1975

Kinesthetic figural aftereffects in acute schizophrenia: a style of processing stimuli.

The Kinesthetic Figural Aftereffect test was administered to 106 psychiatric inpatients to assess styles of stimulus processing in schizophrenia. Three conditions were used: (1) standard stimulus conditions at the acute phase; (2) standard conditions, 7 wk. later, to evaluate stability over time; (3) reversed stimulus conditions to assess kinesthetic figural aftereffect generality under different stimulus conditions. Results indicated that: (1) schizophrenics reduced stimuli, but differences between patient groups were not significant. (2) Kinesthetic figural aftereffect stability over time was shown by nonschizophrenics (p less than .01) but not by schizophrenic and borderline patients. (3) All diagnostic groups reversed kinesthetic figural aftereffect responses under reversed stimulus conditions, e.g., former "augmenters" tended to reduce more under agumenting conditions, suggesting the importance of the specific stimulus conditions. (4) Acute schizophrenics showed a stimulus-governed style. (5) The results raise questions about kinesthetic figural aftereffects as a measure of response style.

Acute Disease↗
PubMed1979

Generalization of norcocaine to the discriminative stimulus properties of cocaine.

In rats trained to discriminate 10 mg/kg cocaine from 1 mg/kg saline, norcocaine, the N-demethylated metabolite, at doses of 2.5 mg/kg, 5 mg/kg and 10 mg/kg, produced a dose response curve similar to that of cocaine and generalized to cocaine at the two higher doses. As with cocaine, the discriminative stimulus produced by the norcocaine was partially attenuated by the dopaminergic antagonist pimozide and the amine depletor reserpine. Benzoylecgonine, benzoylnorecgonine and ecgonine methyl ester in doses of 10 mg/kg and 20 mg/kg did not generalize to cocaine.

Animals↗
PubMed1981

Effect of various stimulus parameters on electrically-induced catecholamine secretion by thin slices of bovine adrenal medulla.

We examined the role of various stimulus parameters in electrically-induced catecholamine secretion by thin slices of bovine adrenal medulla. The stimulus parameters examined were voltage, duration, pulse width, and frequency for square-wave monophasic pulses. As each was examined it was held constant at a selected value for the evaluation of subsequent stimulus characteristics. For 16 mm2 tissue slices, catecholamine secretion was approximately linearly related to stimulus voltage over the range 20--80 volts, with a threshold of 20 V. Increasing the voltage beyond 80 V did not enhance secretion. Similarly, catecholamine secretion was dependent upon the frequency of stimulation. For stimuli delivered at 50 V for a 10-sec interval there was a four-fold increase in secretion over the frequency range 10--100/sec. Increasing pulse width at a constant voltage (50 V) over the range 0.4--2.0 msec resulted in a four-fold increase in catecholamine secretion. For pulses of 50 V, 50/sec and 0.8 msec pulse width, secretion was dependent upon the duration of the stimulus. Enhanced secretion was evident for times as short as 2 sec; between 5 and 15 sec of stimulation catecholamine secretion was linearly related to stimulus duration. Over the range 2--15 sec there was a five-fold enhancement of secretion. Electrically-induced catecholamine secretion by slices was markedly dependent upon stimulus parameters. In general, it was enhanced by increasing voltage, stimulus duration, pulse width and frequency. For most experiments a good choice of stimulus parameters appears to be 50 V 10 sec duration, 0.8 msec pulse width delivered at a frequency of 50/sec. Maximizing all stimulus parameters resulted in a 17-fold enhancement of secretion.

Adrenal Medulla↗
PubMed1987

Variables influencing stimulus overselectivity and "tunnel vision" in developmentally delayed children.

Three variables (diagnosis, location of cues, and MA of learners) influencing stimulus control and stimulus overselectivity in autistic children were assessed. Eight autistic and 8 intellectually average children, matched on MA, were trained on two discrimination tasks; one task contained two "within-stimulus" (i.e., physically connected) cues; the other contained the same two cues presented "extra-stimulus" (i.e., physically separate). Generalization gradients were used following training to measure the degree of stimulus control acquired by each cue. Results showed: autistic subjects tended to respond overselectively only in the extra-stimulus condition; MA was positively correlated with breadth of learning; and when autistic children were overselective to one cue, some stimulus control was also acquired by the second cue. The notion of tunnel vision was discussed, as it may represent a "keystone" deficit interfering with stimulus control and learning by autistic children.

Adolescent↗
PubMed1977

Establishing a normal peer as a behavioral model for developmentally delayed toddlers.

The present investigation demonstrated a systematic teaching procedure for establishing a normal toddler as a peer-model for three children showing delayed development, each one under 27 mo. of age. For each delayed subject, training consisted of adult-directed prompting and social reinforcement contingent upon the delayed children's imitations of material use and motor responses emitted by a normal peer. Within-subjects multiple-baseline designs across responses were used to demonstrate intrasubject control over imitative responding. Indices of stimulus and response generalization were assessed through having the peer-model present the trained responses along with untrained responses in a situation free of adult prompting and social reinforcement for imitative responding. Results indicated that the training in peer-imitation was successful for establishing the peer-model's behavior in a stimulus control relationship with the imitative responding of the delayed children. Moreover, the findings generally demonstrated transfer of training across stimulus situations and responses. Implications for educational programming with developmentally delayed children are discussed.

Behavior Therapy↗
PubMed2003

Dopaminergic and cholinergic involvement in the discriminative stimulus effects of nicotine and cocaine in rats.

RATIONALE: Previous work has demonstrated asymmetrical cross-generalization between the discriminative stimulus effects of nicotine and cocaine: nicotine fully substitutes for cocaine, whereas cocaine only partially substitutes for nicotine. The factors responsible for the similarities and differences between the two drugs remain unclear. OBJECTIVE: The study tested the involvement of dopaminergic and/or cholinergic mechanisms in the discriminative stimulus effects of nicotine and cocaine. METHODS: One set of rats was trained to discriminate cocaine (8.9 mg/kg) from saline, and two other sets of rats were trained to discriminate nicotine (0.1 mg/kg) from saline. RESULTS: In cocaine-trained rats, among the cholinergic agonists studied only nicotine (0.01-0.56 mg/kg) produced full, dose-related substitution; nornicotine (1-5.6 mg/kg) substituted only partially, and lobeline (2.71-15.34 mg/kg) and pilocarpine (0.26-2.55 mg/kg) failed to engender any cocaine-appropriate responding. The nicotinic antagonist mecamylamine (1-5.6 mg/kg) failed to block cocaine's discriminative stimulus effects. The dopamine antagonist cis-flupentixol (0.48 mg/kg) blocked the substitution of nicotine for cocaine. In nicotine-trained rats, the dopamine uptake blockers cocaine, bupropion and nomifensine (0.2-26.1 mg/kg) each substituted only partially for nicotine, and cis-flupentixol (0.48-0.86 mg/kg) antagonized the discriminative stimulus effects of nicotine. CONCLUSIONS: Nicotine fully substitutes for cocaine because of its effects on dopamine transmission, and not because the discriminative stimulus effects of cocaine incorporate a cholinergic component. Substitution of nicotine for cocaine may depend more on nicotine-induced dopamine release than does the nicotine-trained discriminative stimulus; there may be differential dopaminergic involvement after acute and repeated treatment with nicotine or cocaine.

Acetylcholine↗
PubMed2005

The contribution of latent inhibition to reduced generalization after pre-exposure to the test stimulus.

Two experiments assessed the contribution of latent inhibition to the generalization-reducing effects of pre-exposure to the test stimulus using a taste aversion procedure in rats. In both experiments, lithium chloride induced illness was paired with a flavor compound (AX) of either salt or sugar (A or B) and hydrochloric acid (X). Generalization of the resulting aversion to a test compound (BX), was assessed after varying pre-exposure to BX, X, and B. Experiment 1 showed that generalization to BX was less when BX itself had been exposed than equivalent pre-exposure to either B and X separately or to B and a new compound (CX). Experiment 2 showed that levels of generalization varied directly as a function of the amount of pre-exposure to BX. The findings show that latent inhibition alone cannot account for the generalization-reducing effect of pre-exposure to BX.

Animals↗
PubMed1988

Discriminative stimulus control by the anxiogenic beta-carboline FG 7142: generalization to a physiological stressor.

Drug discrimination was employed to investigate the similarities between FG 7142-induced anxiogenesis and the stress produced by exposure to either a novel environment or to footshock. Eight rats were trained to discriminate between the stimulus properties of the beta-carboline FG 7142 (5.0 mg/kg) and its vehicle in a two-lever, food motivated operant task. Once trained, decreasing doses of FG 7142 produced fewer FG 7142-appropriate responses and the dose-response relationship yielded an ED50 of 1.45 mg/kg. Rats were subsequently subjected to two physiological/environmental stressors, footshock and novelty, and then tested in the discriminative paradigm. Exposure to novelty resulted in partial FG 7142-appropriate responding, whereas footshock sessions produced responding predominately on the FG 7142-appropriate lever. This is the first report of stimulus control by FG 7142 and it is likely that the interoceptive cue state produced by this compound is anxiogenic in nature, as reported to occur in man. The anxiogenic nature of the FG 7142 discriminative stimulus is supported by the generalization of FG 7142 to the state produced following stressful environmental manipulation.

Animals↗
PubMed1994

Sensitization and tolerance to the discriminative stimulus effects of mu-opioid agonists.

The discriminative stimulus effects of several mu-opioid agonists were examined under conditions of opioid sensitization or tolerance, i.e., before and after 1-week SC infusions of naloxone or mu-opioid agonists. Rats were trained to discriminate 3.0 mg/kg morphine from saline using a two-lever, discrete trial, shock-avoidance/escape procedure. The rats generalized completely to morphine, fentanyl, meperidine, buprenorphine, and etorphine, and partially to pentazocine. A 7-day infusion of naloxone (0.3 mg/kg per h) potentiated the discriminative stimulus effects of all of these drugs. The magnitude of the increased potency varied indirectly with the efficacy of the mu-opioid agonists; potency ratios (pre-infusion ED50/post-infusion ED50) ranged from 1.58 (etorphine) to 3.58 (pentazocine). Stimulus generalization to morphine, fentanyl, and meperidine also was examined following infusions of equieffective doses of each of these three drugs. Differences among drugs were generally small, and failed to reach statistical significance. Nonetheless, the induction of mu-opioid tolerance did seem to vary with the efficacy of the three mu-opioid agonists. Thus, meperidine (6.25 mg/kg per h), which has the lowest efficacy of the drugs infused, produced the greatest shift to the right of the stimulus-generalization curves of these three drugs; the post-meperidine PR ranged between 0.40 and 0.61. Fentanyl (0.1 mg/kg per h), a drug with a higher efficacy at mu-opioid receptors, did not produce tolerance to the discriminative stimulus effects of morphine, fentanyl, or meperidine; potency ratios ranged from 0.50 to 0.75. Potency ratios for buprenorphine, etorphine, fentanyl, meperidine, and morphine after 7-day morphine infusions (0.75 mg/kg per h) ranged from 0.38 (buprenorphine) to 0.80 (etorphine). Morphine induced significant tolerance only to the discriminative stimulus effects of fentanyl. Our results suggest that different cellular mechanisms underlie the development of tolerance and sensitization to the discriminative stimulus effects of mu-opioid agonists.

Animals↗
PubMed1982

Discriminative stimulus properties of the vasodilator, hydralazine: differential generalization with alpha 1 and alpha 2 adrenoreceptor drugs.

1. Male albino rats were trained to an operant procedure of lever pressing on an FR-10 schedule of food reinforcement to respond on one lever located on one side of the food cup after an injection of hydralazine (1,25 mg/kg), and to respond on an alternate lever located on the other side of the food cup after an injection of saline. 2. Seven out of ten rats learned the hydralazine-saline discrimination to the rigid criterion of selecting the correct lever for reinforcement on ten consecutive sessions. 3. The elicitation of the discriminative stimulus was dose-dependent (r = 0,98; p less than .001) with 100, 43, and 14% of the subjects selecting the hydralazine lever following hydralazine doses of 1,25; 0,32 and 0,08 mg/kg, respectively (ED50, 0,28 mg/kg). 4. A reduction in response rate and blood pressure was noted only at the 1.25 mg/kg dose. 5. No tolerance to the hypotensive effect of hydralazine was found. 6. In generalization tests, prazosin, an alpha 1 antagonist, was found to produce a dose-dependent generalization to hydralazine (ED50, 1, 25 mg/kg) while clonidine, an alpha 2 agonist, did not generalize. 7. These data indicate that hydralazine produces a discriminable interoceptive stimulus exact site of action of which is not known.

Animals↗
PubMed1987

Task difficulty, probability, and inter-stimulus interval as determinants of P300 from auditory stimuli.

The P300 event-related potential was elicited with auditory stimuli in 4 experiments which manipulated combinations of stimulus target probability (10% vs. 30%), task difficulty (easy vs. hard), and inter-stimulus interval (5 sec vs. 2 sec). P300 amplitude was smaller and peak latency longer for the more difficult relative to the easier tasks across experiments. Increases in stimulus target probability generally diminished P300 amplitude and shortened peak latency more for the easy relative to difficult task conditions. Increasing the number of non-target stimulus tones decreased P300 amplitude reliably, but increased latency only slightly. Task difficulty did not interact with variations in inter-stimulus interval which produced generally weak effects for both amplitude and latency. These findings suggest that P300 amplitude and latency obtained from auditory discrimination paradigms reflect processing difficulty independently of stimulus target probability unless differences in task requirements affect stimulus encoding.

Adult↗
PubMed1997

(R)-methanandamide, but not anandamide, substitutes for delta 9-THC in a drug-discrimination procedure.

Fourteen male rats were trained to discriminate between injections of 2 mg/kg delta-9-tetrahydrocannabinol (delta 9-THC) and vehicle in a 2-lever operant drug-discrimination paradigm. Following training, substitution tests using a cumulative dosing procedure revealed that anandamide (0.5-16 mg/kg ip), the putative endogenous camabinoid receptor ligand, failed to generalize to the discriminative stimulus properties of the training dose of delta 9-THC. However, dose-dependent generalization to the delta 9-THC cue was observed following administration of both CP-55,940 (0.05-0.8 mg/kg ip), a synthetic cannabinoid, and (R)-methanandamide (0.5-8 mg/kg ip), a metabolically stable analog of anandamide. Collectively, these results demonstrate a cannabinoid-specific in vivo effect of an anandamide compound and suggest that the naturally occurring form of anandamide may be metabolized too rapidly to produce a cannabimimetic intercceptive state when administered peripherally.

Animals↗
PubMedDate not supplied

An examination of the participation of neurons in readout from memory.

Adult cats were implanted with a movable microelectrode and were trained to perform for food reward in response to diffuse light flicker at two different frequencies. After substantial overtraining, the patterns of cell response (poststimulus histogram) were obtained during generalization trials, using an intermediate frequency stimulus. An average of 29% of the cells examined in lateral geniculate nucleus and visual cortex traverses showed statistically significant differences in the late component of the neuronal response when different responses to the same generalization stimulus were compared.

Animals↗