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PubMed1964

STIMULUS GENERALIZATION ALONG A LIGHT FLICKER RATE CONTINUUM AFTER DISCRIMINATION TRAINING WITH SEVERAL S-'S.

Four pigeons were trained with VI reinforcement to peck a key which was briefly illuminated by a flickering light. Generalization gradients were then obtained with nine different rates of flicker, four faster than S+ and four slower. Two birds were then trained to discriminate between S+ and the fastest stimulus (S-). These birds were then trained to discriminate between S+ and the two fastest stimuli, alternated as S-'s. This procedure was continued, adding one new S- at a time, until all four stimuli faster than S+ were S-'s. The remaining two birds were trained on this latter discrimination without intervening training. In a final stage, using the first two birds, the slowest stimulus was added as a fifth S-. Generalization gradients in extinction were obtained from each bird after each stage of training. As more stimuli from one end of the continuum served as S-'s, responding increased in the presence of stimuli from the other end of the continuum, and the gradient tended to become flattened at this end.

Animals↗

PubMedDate not supplied

Cocaine--stimulus generalization to MDA optical isomers: a reevaluation.

It has already been demonstrated that the psychoactive agent 1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDA) produces effects that are both hallucinogen-like and amphetamine or stimulant-like in animals. Hallucinogenic activity is associated primarily with the R(-)-isomer of MDA whereas stimulant activity is primarily associated with the S(+)-isomer. Because a previous report indicates that S(+)MDA fails to substitute for cocaine in rats trained to discriminate cocaine from vehicle, and because these findings are inconsistent with the purported stimulant nature of S(+)MDA, we reinvestigated the effect of both MDA isomers in rats. In this investigation, S(+)MDA doses of 1.25 and 1.5 mg/kg were found to produce > 80% cocaine-appropriate responding in rats trained to discriminate 8 mg/kg of cocaine from saline. However, consistent with a previous report, R(-)MDA resulted only in partial generalization. These new results support the hypothesis that the optical isomers of MDA produce distinguishable stimulus effects in rats and that S(+)MDA is the more stimulant isomer of MDA.

3,4-Methylenedioxyamphetamine↗

PubMed1984

Assessment of drug state dimensionality via drug-drug training and stimulus generalization testing.

A procedure for determining whether different drugs share a common stimulus dimension is described. This procedure uses the presence of post-discrimination generalization gradient asymmetry as an indication that the training stimuli lay along a common stimulus dimension. Separate groups of hungry pigeons were trained to discriminate a 15 mg/kg dose of phenobarbital which was associated with frequent food reinforcement (S+) from each of 9 different drug conditions which were associated with infrequent reinforcement (S-). S- stimuli were selected to represent a drug from a completely different class (amphetamine), a drug with biphasic effects which may partially correspond with the effects of phenobarbital (delta 9-THC), and a drug from the same class as the S+ (pentobarbital). Following discrimination training subjects were tested for generalization to five dosage levels (5, 10, 15, 20, 25 mg/kg) of phenobarbital. Steep symmetrical generalization gradients around the S+ indicated that delta 9-THC and d-1-amphetamine were both quite discriminable from phenobarbital, and that they were perceived by subjects as representing stimulus dimensions different from phenobarbital, and that it was perceived as lying on a stimulus dimension common to phenobarbital. This procedure may allow better understanding of how different drug states are perceived by animals as similar or dissimilar.

Amphetamines↗

PubMed1971

On the form of stimulus generalization curves for visual intensity.

Twelve pigeons were given successive discrimination training involving variable-interval reinforcement for key pecking in the presence of one intensity of monochromatic light randomly alternated with extinction for pecking during another intensity. All of the pigeons were then tested in extinction for generalization along the intensity dimension, and all showed a displacement of maximal responding from the positive stimulus in the direction opposite the negative stimulus. For six of the pigeons, for which the test included only three values beyond the positive stimulus, four showed peaked gradients but two did not, showing monotonic gradients with maximal responding to the most extreme test value. For another six pigeons tested over a wider range, all showed peaked gradients. Thus, when a sufficiently wide range of test values is employed, generalization gradients for visual intensity have the same peaked form as do gradients for qualitative visual dimensions such as wavelength or line angle.

Animals↗

PubMed1989

A role for stimulus generalization in conditional discrimination learning.

In each of three experiments on discrimination learning by rats, whether or not a 10-sec target stimulus was followed by food was determined by the nature of a 2-min background stimulus that accompanied it. A conditional discrimination was employed in Experiment 1 such that background A indicated food would follow one target but not the other, whereas this relationship between the targets and food was reversed in the presence of background B. Experiment 2 employed two feature-positive discriminations. Subsequent test trials revealed that the background for one discrimination was able to enhance responding during the target for the other discrimination. Experiment 3 employed a feature-positive and a feature-negative discrimination prior to test trials in which each target was presented separately during a compound of both background stimuli. The compound enhanced responding to the target from the feature-positive discrimination and reduced it to the target from the feature-negative discrimination. We suggest that to accommodate all these findings, the best explanation is provided by a configural model of Pavlovian conditioning.

Animals↗

PubMed1997

Stimulus generalization of fear responses: effects of auditory cortex lesions in a computational model and in rats.

The conditioning of fear responses to a simple acoustic stimulus (pure tone) paired with footshock can be mediated by the transmission of auditory information to the lateral nucleus of the amygdala from either the auditory thalamus or the auditory cortex. We examined the processing capacity of the thalamo-amygdala pathway by making lesions of the auditory cortex and testing the extent to which conditioned fear responses generalized to tones other than the one paired with footshock. Two studies were performed, one in an anatomically constrained computational model of the fear conditioning network and the other in rats. Stimulus generalization was unaffected in both. These findings support the validity of the model as an approach to studying the neural basis of conditioned fear learning, and in addition suggest that the thalamo-amygdala pathway, possibly by the use of population coding, is capable of performing at least crude stimulus discriminations.

Acoustic Stimulation↗

PubMedDate not supplied

PMMA-stimulus generalization to the optical isomers of MBDB and 3,4-DMA.

Psychoactive phenylisopropylamines can produce one or more of several different stimulus effects in animals. These effects are typified by the hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), the central stimulant amphetamine, and by N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA), an agent whose actions are not yet well understood. The optical isomers of two phenylisopropylamines known to lack DOM and amphetamine-stimulus character, that is N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminobutane (MBDB) and 1-(3,4-dimethoxyphenyl)-2-aminopropane (3,4-DMA), were examined in rats trained to discriminate 1.25 mg/kg of PMMA from vehicle. The PMMA stimulus (ED(50)=0.4 mg/kg) generalized to all four agents: S(+)-MBDB (ED(50)=0.8 mg/kg), R(-)-MBDB (ED(50)=2.0 mg/kg), S(+)-3,4-DMA (ED(50)=2.6 mg/kg) and R(-)-3,4-DMA (ED(50)=3.9 mg/kg). The results show that these agents produce stimulus effects similar to those produced by PMMA. Both isomers of MBDB have been previously demonstrated to substitute for N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA) in rats trained to discriminate MDMA from vehicle, but MBDB-trained animals failed to recognize DOM or amphetamine. Similar results were obtained with the 3,4-DMA optical isomers in the present investigation using rats trained to discriminate MDMA, DOM or (+)-amphetamine from vehicle; both isomers of 3,4-DMA substituted for an MDMA stimulus, but not for a DOM or amphetamine stimulus. Taken together, the evidence suggests that PMMA, S(+)-MBDB, R(-)-MBDB, S(+)-3,4-DMA, R(-)-3,4-DMA, and S(+)-MDMA can produce common stimulus effects in rats. The present findings also better define the PMMA stimulus and the structural requirements necessary to produce this type of stimulus effect.

DOM 2,5-Dimethoxy-4-Methylamphetamine↗

PubMed1969

Stimulus generalization of gravity.

In two experiments, squirrel monkeys were exposed to centrifugally generated, artificial gravity and trained to respond for food reinforcement at selected gravity (g) levels. Experiment I involved a single g value; in Exp. II, subjects were trained to discriminate among two or three g values. After training, generalization tests were administered over a 1.1-g to 2.1-g range. The major findings were as follows: (a) single-stimulus training yielded a linear relationship between percentage of responding and magnitude of gravity. (b) Two-valued discrimination training produced gradient peaks which were shifted from S(D) in a direction away from S(Delta). This effect was cancelled when S(D) was located equidistant between two S(Delta) stimuli. (c) Gradient form was independent of the S(D)-S(Delta) difference, but related to continuum location and/or intensity of discriminative stimuli.

Animals↗

PubMed1967

Stimulus generalization as signal detection in pigeons.

Pigeons that were reinforced for pecking at a single-wavelength responded to nearby wavelengths with lower rates. Response rates indicated the pigeons' certainty that the reinforced stimulus was present. The ratings yielded receiver operating characteristic functions that approximated straight lines on a double probability plot.

Animals↗

PubMed1964

STIMULUS GENERALIZATION OF THE EFFECTS OF PUNISHMENT.

Three pigeons were trained to respond to seven spectral stimulus values ranging from 490 to 610 mmu and displayed in random order on a response key. After response rates had equalized to these values, a brief electric shock was administered when the subject (S) responded to the central value (550 mmu) while positive reinforcement for all values was maintained. Initially, there was broad generalization of the resulting depression in response rate, but the gradients grew steeper in the course of testing. When punishment was discontinued, the rates to all values recovered, and equal responding to all stimuli was reattained by two of the Ss. Stimulus control over the effects of punishment was clearly demonstrated in the form of a generalization gradient; this probably resulted from the combined effects of generalization of the depression associated with punishment and discrimination between the punished value and neutral stimuli.

Animals↗

PubMed1978

The central tendency effect in stimulus generalization: the effect of sex of subject.

Eighty male and 80 female college students were shown a stimulus light of 525 nm, following instructions to remember it, and then were immediately tested for generalization (recognition) with a successively presented set of stimuli including 525 nm and six longer wavelength values. Subjects rated each test stimulus on a 6-point scale ranging from "surely same" as the original stimulus to "surely different." Both men and women showed a central tendency shift. Although the stimulus perceived as most likely to be the original (the mode) shifted to 545 nm in both groups, the men showed a greater mean shift than the women. Shifting was nearly complete in both groups within the first series of test stimuli with the men shifting faster. These findings replicate a 1972 report by Giurintano of greater central tendency shift in men than in women in a line angle generalization task, challenging an assumed analogy between our generalization task and the rod-and-frame test, in which women typically show the greater distortion. The analysis of central tendency shift within the first test series reveals that it occurs much earlier than previously believed.

Discrimination, Psychological↗

PubMed1982

Stimulus generalization of lifted weights in older and younger women.

Older (62 to 86 years) and younger (17 to 30 years) women were essentially similar in acquisition of weight discriminations and in generalized responding to a range of weights during postdiscrimination tests. In both age groups, acquisition was facilitated by increases in the difference between the positive and negative stimuli, and postdiscrimination gradients were displaced away from the value of the negative stimulus, particularly when it was the heavier of the training pair. The finding from personality test scores that the older women were more introverted than the younger ones, together with the absence of age differences in acquisition and generalization, does not support the Eysenck-Gray hypothesis that introversion influences conditioning processes. The results do suggest that basic conditioning processes are maintained with increasing age in healthy older adults.

Adolescent↗

PubMed1994

Electrical stimulation of the dorsal raphe nucleus as a discriminative stimulus: generalization to (+/-)-DOI.

Electrical stimulation of the dorsal raphe nucleus of Sprague-Dawley rats was used as the cue for discrimination using a taste aversion paradigm. Rats were trained to associate saccharin drinking during electrical stimulation of the dorsal raphe nucleus with LiCl injection after the session as the aversive unconditioned stimulus. In sessions without stimulation, rats were allowed to consume saccharin and received a saline injection after the session. Suppression of saccharin consumption during electrical stimulation was learned within 12 trials. Rats trained in the reverse discrimination, i.e., sessions with no electrical stimulation paired with LiCl injection, showed a similar learning curve. Animals injected prior to the session with the hallucinogenic 5-HT2 agonist (+/-)-DOI associated DOI with electrical stimulation of the dorsal raphe nucleus. Thus, animals may be trained to discriminate electrical stimulation of the dorsal raphe nucleus. Furthermore, animals generalize from activation of 5-HT2 receptors to electrical stimulation of the dorsal raphe nucleus.

Amphetamines↗

PubMed1988

Limited stimulus generalization between delta 9-THC and diazepam in pigeons and gerbils.

Pigeons trained to discriminate between the presence and absence of delta 9-THC (0.56 mg/kg, IM, intramuscularly) were tested with diazepam (5.6-30 mg/kg), administered IG (intragastrically), and were found to generalize the response associated with the THC training to the diazepam treatment only to a limited extent. Two groups of gerbils trained to discriminate between the presence and absence of IP (intraperitoneally) injected benzodiazepine agonists (5.6 mg/kg of diazepam and Ro 11-3128, respectively) generally did not generalize the drug response to IP administered THC (5.6 and 17.5 mg/kg). In addition, substitution testing with the dopamine autoreceptor blocker (+)-3PPP yielded non-drug responding in the pigeons. Hence neither proposed structural similarity between 3-PPP and THC, nor purported anxiolytic activity by 3-PPP (see Introduction) matched the THC-induced stimulus effects. The data are discussed with reference to the specificity of the THC cue or stimulus.

Animals↗

PubMed1966

Stimulus generalization: the ordering and spacing of test stimuli.

Twenty-four pigeons learned a successive discrimination between 500 mmu (S+) and 574 mmu (S-). When tested in extinction, some birds received stimuli around S+, with no S- presentations. These birds showed a positive peak shift, with maximum responding not at 550 mmu, but displaced to 538 mmu and 544 mmu. Other birds were tested with stimuli around S-, with no S+ presentations. These birds showed a negative shift, with least responding not at 574 mmu, but at 586 mmu. Though the first group was tested around S+ and the second around S-, total responding between groups did not differ. When retested on the other half of the continuum, however, birds that had gone from the S+ half to the S- half responded fewer times than those that had gone from the S- half to the S+ half. In a second experiment, reducing stimulus spacing from 6 mmu to 2 mmu produced flatter gradients and decreased the amount of positive shift. In a third experiment, birds were tested across the whole continuum with stimuli presented in serial order. A sequence from 538 mmu to 586 mmu produced no responding after the first part of the session; a sequence from 586 mmu to 538 mmu produced responding throughout the session.

Animals↗

PubMed2004

Stimulus generalization in two associative learning processes.

Recent studies involving nonlinear discrimination problems suggest that stimuli in human associative learning are represented configurally with narrow generalization, such that presentation of stimuli that are even slightly dissimilar to stored configurations weakly activate these configurations. The authors note that another well-known set of findings in human associative learning, cue-interaction phenomena, suggest relatively broad generalization. Three experiments show that current models of human associative learning, which try to model both nonlinear discrimination and cue interaction as the result of 1 process, fail because they cannot simultaneously account for narrow and broad generalization. Results suggest that human associative learning involves (a) an exemplar-based process with configural stimulus representation and narrow generalization and (b) an adaptive learning process characterized by broad generalization and cue interaction.

Cues↗

PubMed1975

Stimulus generalization of suppression in rats following aversively motivated instrumental or Pavlovian training.

Following 100 or 300 avoidance training trials, instrumental subjects and their yoked Pavlovian counterparts were tested for generalization of lick suppression along the frequency dimension of the avoidance conditioned stimulus. Gradients of stimulus control were evident after 300 instrumental avoidance training trials, and additional intradimensional Pavlovian discrimination training further sharpened the gradients. After 100 trials, the yoked Pavlovian subjects suppressed more than their instrumental counterparts. However, with increased Pavlovian training, flatter gradients with decreased suppression were obtained. Results from a second experiment revealed that, whereas Pavlovian experience decreased suppression to the tone, subjects suppressed drinking in the presence of static, environmental cues. Data from both experiments supported interpretations that stress the role of response control over environmental events.

Acoustic Stimulation↗

PubMed1977

Choice, time allocation, and response rate during stimulus generalization.

Six pigeons were trained to discriminate between two noise intensities using a procedure that assessed choice, time allocation, and response rate simultaneously and independently. Responses on the left or right key (R1 or R2) were respectively correct in the presence of two different intensities, S1 and S2. After a correct response, reinforcement became available for pecks on the center key. Reinforcement density for R1|S1 relative to R2|S2 was varied across experimental conditions. Generalization tests followed extensive training at each condition. As a function of stimulus intensity, proportions of initial choices of R2, of time spent in R2-initiated components, and of center-key responses emitted in R2-initiated components all yielded sigmoidal gradients of similar slope, which shifted slightly in location when relative reinforcement density changed. Changeovers were maximal where initial choice proportions approximated 0.5. Gradients relating the absolute number of center-key responses to stimulus intensity were also roughly sigmoidal, but were more sensitive to changes in reinforcement density. Gradients of momentary response rate also depended on reinforcement density. During training, large but transitory shifts in choice responding occurred when reinforcement density changed, while differences in momentary response rate developed slowly, suggesting separate control of choice and response rate by the contingencies of reinforcement.

Journal Article↗