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PubMed2002

Stimulus control topographies and tests of symmetry in pigeons.

Pigeons were tested for symmetry after A-B training under conditions designed to avoid problems that may prevent its emergence, namely the change of stimulus location in testing relative to training and the lack of requisite discrimination training. In Experiment 1, samples appeared in two locations during baseline training to minimize the impact of stimulus location. Experiments 2 and 3 included multiple-location training along with additional identity and symbolic matching training, respectively, to explicitly train all of the simultaneous and successive stimulus discriminations required for testing. Experiment 4 provided reinforcement for symmetrical matching relations with some stimulus sets (with multiple-location training) prior to symmetry testing with different sets. In all experiments, pigeons showed no evidence of symmetry despite the fact that baseline (A-B) matching transferred to novel locations. Additional tests for reflexivity (Experiment 2) yielded similar outcomes. These results indicate that the change in stimulus location is not the sole reason that pigeons do not show symmetry and increase the plausibility of arguments that symmetry and other indexes of stimulus equivalence may be beyond the capabilities of the pigeon.

Animals↗
PubMed1985

Critical fusion frequency in the central visual field.

The critical fusion frequency (CFF) was measured across the central visual field. Stimulus parameters were adjusted to ensure an increase in CFF at the fovea. Comparison was made between the foveal and extra-foveal CFF values. The study showed that, while the CFF may be highest at the fovea when the CFF values are generally low, stimulus parameter changes that increase the CFF result in a greater increase extra-foveally. Ultimately, then, the CFF maximum shifts from the fovea to an extra-foveal area. Under the experimental conditions used in the study, the maximum occurred approximately 10 degrees from fixation.

Flicker Fusion↗
PubMed1992

Further studies on N-methyl-1(3,4-methylenedioxyphenyl)-2-aminopropane as a discriminative stimulus: antagonism by 5-hydroxytryptamine3 antagonists.

Using a standard two-lever operant paradigm, male Sprague-Dawley rats were trained to discriminate 1.5 mg/kg N-methyl-1(3,4-methylenedioxyphenyl)-2- aminopropane (MDMA) from saline using a variable-interval 15-s schedule of reinforcement for food reward. Tests of stimulus antagonism were conducted to further define the mechanism of action of MDMA as a discriminative stimulus. Low doses of the 5-hydroxytryptamine1A (5-HT1A) antagonist NAN-190, the 5-HT2 antagonist pirenperone, and the dopamine antagonist haloperidol were able to somewhat attenuate the MDMA stimulus; however, none of these agents decreased MDMA-appropriate responding to less than 46%. The 5-HT3 antagonists zacopride and LY 278584 (ID50 = 0.02 micrograms/kg) antagonized the MDMA discriminative stimulus. Zacopride also attenuated the stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) in DOM-trained animals but not those of (+)amphetamine in (+)amphetamine-trained animals. Several possible mechanistic interpretations are provided but it is concluded that MDMA produces its stimulus effects via a complex mechanism involving both dopaminergic and serotonergic components.

3,4-Methylenedioxyamphetamine↗
PubMed2006

Cue-based preparation and stimulus-based priming of tasks in task switching.

In this study, we investigated the interaction of three different sources of task activation in precued task switching. We distinguished (1) intentional, cue-based task activation from two other, involuntary sources of activation: (2) persisting activation from the preceding task and (3) stimulus-based task activation elicited by the task stimulus itself. We assumed that cue-based task activation increases as a function of cue-stimulus interval (CSI) and that task activation from the preceding trial decays as a function of response-stimulus interval Stimulus-based task activation is thought to be due to involuntary retrieval of stimulus-associated tasks. We manipulated stimulus-based task activation by mapping each of the stimuli consistently to only one or the other of the two tasks. After practice, we reversed this mapping in order to test the effects of item-specific stimulus-task association. The mapping reversal resulted in increased reaction times and increased task shift costs. These stimulus-based priming effects were markedly reduced with a long CSI, relative to a short CSI, suggesting that stimulus-based priming shows up in performance principally when competition between tasks is high and that cue-based task activation reduces task competition. In contrast, lengthening the response-cue interval (decay time) reduced shift costs but did not reduce the stimulus-based priming effect The data are consistent with separable stimulus-related and response-related components of task activation. Further theoretical implications of these findings are discussed.

Adult↗
PubMed1988

Establishing auditory stimulus control over an eight-member equivalence class via conditional discrimination procedures.

Two eight-member equivalence classes of visual stimuli were established during three phases of a training program. In Phase 1, two training arrangements were compared. In one, 3 subjects were taught on different trials to select from a single pair of comparison stimuli (A1, A2) in response to eight sample stimuli that were trained in pairs (B1, B2; C1, C2; D1, D2; E1, E2). In the second arrangement, subjects were taught to select from four pairs of comparisons (B1, B2; C1, C2; D3, D2; E2, E2) in response to two samples (A1, A2). Training with the single pair of comparison stimuli resulted in the development of equivalence relations (B1C1, B2C2, D1B1, D2B2, B1E1, B2E2, C1D1, C2D2, C1E1, C2E2, D1E1, D2E2, and their reciprocals) between the sample stimuli without direct training of these relations. In the other training arrangement, these relations among the comparison stimuli developed in the performance of 1 subject only. In Phase 2, three new pairs of stimuli (F1, F2; G1, G2; H1, H2) were substituted for three of the original pairs (B1, B2; C1, C2; D1, D2) and the training arrangements for the groups were reversed. Following training, the performances that showed equivalence relations on the probes in the first phase also showed equivalence relations in the second phase. If such relations did not develop in the first phase, they did not do so in the second phase. In Phase 3, relations between stimuli across the two previous phases (e.g., B1F1, B2F2, B1G1, B2H2, C1F1, etc.) were investigated. The 4 subjects whose performances showed the development of these relations were taught to select one stimulus from each class (E1 and E2) in response to a verbal label (I1 and I2) and then were tested to see if the verbal label controlled responding to the remaining members of the class (e.g., I1A1, I2A2, I1B1, I2B2, etc.). For 3 subjects, this generalized control occurred; for the 4th, generalization occurred only after verbal training with a second pair of visual stimuli (F1 and F2). In retests several months later, these auditory-visual relations were found to be intact or, if not, were recovered without direct training.

Adolescent↗
PubMed1988

The chlordiazepoxide/pentylenetetrazol discrimination: characterization of drug interactions and homeostatic responses to drug challenges.

Rats were trained to discriminate chlordiazepoxide (CDP) from pentylenetetrazol (PTZ) in a two-lever food motivated discrimination task. Training drug doses were adjusted until subjects emitted approximately 50% of their responses on each of the two drug-appropriate levers during saline injection tests. Tests that followed injection of CDP/PTZ combinations illustrated a reciprocal antagonism between the two drugs. Saline-injection tests that followed large dose injections of CDP revealed a period of predominantly PTZ-appropriate responding that persisted after the initial period of predominantly CDP-appropriate responding. These data are interpreted to suggest that, unlike some other drugs that have been shown to antagonize the behavioral and CNS effects of benzodiazepines, the interoceptive stimulus generated by PTZ occupies a position opposite to that of CDP along some single affective continuum. In addition, these data suggest that drug/drug (DD) discriminations are capable of characterizing the interactions between training drugs. Finally, the data suggest that the CDP/PTZ discrimination is a sensitive detector of bidirectional shifts in interoceptive stimulus state along the CDP/PTZ continuum.

Animals↗
PubMed1990

Behavioral indices of neurotoxicity.

There are many classes of chemicals widely used in a number of commercial and industrial processes having a potential to affect adversely the nervous system. Because of their relative sensitivity to some agents and general noninvasive characteristics, functional measurements of neurotoxicity are being used with greater frequency, especially at the level of hazard identification. The neurobehavioral test battery used by the National Toxicology Program (NTP) includes motor activity, fore- and hindlimb grip strength, acoustic startle response, responsiveness to an adverse thermal stimulus and general health and clinical measures (body weight, autonomic signs, tremor, convulsions). These tests have been used in nearly 40 studies involving various dosing regimens with rats and mice. The NTP battery shows several salient features of an effective screen, including the ability to differentiate known neurotoxicants from nonneurotoxicants, identify certain types of neurological sequelae or profiles of neurotoxic effects and construct dose- and time-response data in a screening context. The extent to which the NTP battery has predictive validity is still being evaluated.

Animals↗
PubMed2005

The human pulvinar and stimulus-driven attentional control.

The present study compared the behavioral effects of sudden motion onsets or color changes (i.e., featural changes) with the effects of new objects (i.e., multiple changes). Experiments 1 and 2 showed that lesions of the pulvinar affect stimulus-driven attentional control only when it is triggered by featural changes, but not by new objects. Experiment 3 revealed that when appended on a new object, a featural change is processed as a part of a more massive new object: Its attentional effects are larger and remain undisturbed by lesions of the pulvinar. In Experiment 4 a temporal superiority effect was found for featural changes, but not for new objects in healthy subjects. These results suggest that featural changes and new objects may be processed through different pathways and that the pulvinar may be particularly involved in stimulus-driven attentional control by sudden events entailing featural changes.

Adult↗
PubMed1991

Emergent simple discrimination in children: transfer of stimulus control under non-reinforced conditions.

Previous research on humans suggests that simple discriminations may emerge if both stimuli, B1 and B2, are compounded with the stimuli of a previously trained discrimination, A1 (S+) and A2 (S-), and responding to the compounds, B1A1 and B2A2, is reinforced. Two questions were addressed. First, do simple discriminations also emerge if (a) only one stimulus, B1, is compounded with a training stimulus, A1 (S+) or A2 (S-); or with both training stimuli, A1 (S+) and A2 (S-); and (b) neither B1 nor B2 is compounded with the training stimuli? Second, do simple discriminations emerge if reinforcement in the presence of the AB compounds is withheld? Normal preschool children served as subjects. The study consisted of six experiments. Transfer occurred in all experiments regardless of whether both test stimuli, one test stimulus, or none of the test stimuli were compounded with the training stimuli under non-reinforced conditions. The results can be described by the following rules: Respond to any stimulus that includes a component of a "correct" stimulus of a previous discrimination. Otherwise, respond away from the stimulus that incorporates a component from an "incorrect" stimulus of a previous discrimination. The implications of data for sensory pre-conditioning and language-based accounts are discussed.

Attention↗
PubMed1989

Discriminative stimulus effects of nicotine in rats trained under different schedules of reinforcement.

There have been few comparisons between different schedules of reinforcement for establishing drugs as discriminative stimuli. Fixed-ratio (FR) 10 and tandem variable-interval 1-min FR-10 schedules have been compared directly in a conventional, nicotine-saline discrimination paradigm with food reinforcement in rats. The discrimination was acquired rapidly under both schedules, with stimulus control by nicotine (0.1 mg/kg SC) being very slightly superior under the FR schedule. In 5-min extinction tests with nicotine, rats maintained under the FR schedule yielded a clear dose-response curve with a bar-selection (quantal) index; in these rats, discrimination of nicotine appeared generally poor, and dose-response curves were shallow, when the percentage of drug-appropriate responding (quantitative index) was calculated. In contrast, rats under the tandem schedule yielded clear dose-response data with both indices. In tests with (+)-amphetamine full generalization was obtained with both schedules, and with both quantitative and quantal indices. Tests of generalization to morphine were negative regardless of the training schedule or index employed. In rats under the FR-10 schedule, overall response rates declined both within and across extinction tests; the relatively high rates of responding maintained by the tandem schedule were more sensitive to the response rate-decreasing effects of morphine and amphetamine. The results confirm that orderly data may be obtained with either a FR or a tandem schedule provided that an appropriate index of discriminative response is employed. The results generally support the validity of current practices, and there will probably be no marked differences between conclusions depending on which schedule is used.

Amphetamine↗
PubMed1999

Assessment of D3 versus D2 receptor modulation of the discriminative stimulus effects of (+)-7-OH-DPAT in rats.

Although there are presently no highly selective agonists for the D3 dopamine receptor, a number of compounds reported to bind with moderate selectivity to D3 receptors are currently employed to investigate the importance of D3 receptors in the behavioral effects of psychostimulant drugs. For example, 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT) has been used extensively to investigate the role of D3 receptors in the reinforcing and discriminative stimulus properties of cocaine and d-amphetamine. However, recent investigations with a relatively selective D3 antagonist, PNU-99194A, have led us to question the importance of D3 receptors in the discriminative stimulus effects of 7-OH-DPAT. In the present study, 16 male Sprague-Dawley rats were trained to discriminate (+)-7-OH-DPAT (0.03 mg/kg, subcutaneously (s.c.)) from saline in a two-choice operant procedure using a fixed-ratio 20 schedule of water reinforcement. Consistent with previous findings, PNU-99194A appeared to attenuate only partially (+)-7-OH-DPAT discrimination at a dose that disrupted responding in most subjects. Moreover, a highly selective D2 agonist, PNU-91356A, substituted completely and in a dose-dependent manner for (+)-7-OH-DPAT, while d-amphetamine produced only partial substitution for the training drug. These data indicate that D2 receptor actions appear to be more important than D3 receptor actions in exerting the discriminative stimulus effects of (+)-7-OH-DPAT. Continued efforts to determine the relative importance of D2 vs D3 receptor actions in the modulation of the discriminative stimulus effects of (+)-7-OH-DPAT are discussed.

Animals↗
PubMed2006

Formation of category representations.

Many formal models of categorization assume, implicitly or explicitly, that categorization results in the formation of direct associations from representations of the presented stimuli to representations of the experimentally provided category labels. In three categorization experiments employing a polymorphous classification structure (Dennis, Hampton, & Lea, 1973) and a partial reversal, optional shift procedure (Kendler, Kendler, & Wells, 1960), we provide evidence consistent with the hypothesis that learning a new classification problem results in the creation of category representations that mediate between representations of the stimulus and the label. This hypothesis can be instantiated through the AMBRY model (Kruschke, 1996).

Adult↗
PubMed1998

Operational terminology for stimulus exposure (SE) conditioning.

Nomenclature for simple types of learning is ambiguous and incomplete, as even commonly used terms such as 'habituation' and 'sensitization' are not applied consistently. One problem is a failure to distinguish between operational and theoretical constructs linguistically. Operational terminology for reporting behavioural results should be different from the language used in the discussion of learning theory. Thus, systematic operational terminology for simple types of conditioning is proposed. The most general category, stimulus exposure (SE) conditioning, is learning by exposure to a stimulus or to multiple stimuli where explicit inter-stimulus contingencies or instrumental reinforcers are not a part of training. Subtypes of SE conditioning are distinguished by the number of different stimuli used during training, by the method used to assess learning, and by the relationship between training stimuli and the assessment method. These categories include 'alteractive', 'iterative', 'heterostimic', and 'multistimic' conditioning. Learned responses are also categorized as reduction, enhancement, or transformation. SE conditioning categories combine with response terminology in phrases such as 'iterative reduction', which is a decrease in the response to a stimulus due to repeated presentation of that stimulus.

Animals↗
PubMed1981

The effects of electroconvulsive shock on the discriminative stimulus properties of d-amphetamine and apomorphine: evidence for dopamine receptor alteration subsequent ECS.

Sprague-Dawley male rats responding for sweetened milk on a variable interval 20 s schedule of reinforcement were trained to discriminate which of two levers to press on the basis of whether they had been injected with 1.0 mg/kg of d-amphetamine or saline prior to daily training sessions. Following acquisition of the discrimination a dose-response generalization function was determined by testing animals on 0.10, 0.15, 0.25, 0.35, 0.50 and 0.75 mg/kg of amphetamine. Subjects then received either three electroconvulsive shock (ECS) treatments of sham-ECS forty-eight hours after the final treatment all subjects were injected with 0.25 mg/kg of amphetamine and retested. ECS was found to enhance the ability of the animals to discriminate amphetamine. In a second experiment it was found that ECS also facilitated the ability of animals to discriminate the cue properties of apomorphine, a direct dopamine receptor agonist. These results suggest that dopamine receptor sensitivity is altered by electroconvulsive shock.

Animals↗
PubMed1985

Aversive stimulus properties of morphine: evaluation using the drug preexposure conditioned taste aversion paradigm.

Interpretation of the finding that positive-reinforcing drugs such as morphine also possess possible aversive properties, as revealed by their ability to induce a conditioned taste aversion (CTA), remains problematic. This issue was addressed in the present study using the drug preexposure CTA paradigm. Water-deprived rats were given noncontingent preexposure to one of three doses of morphine (2.5, 5.0, or 15.0 mg/kg) or drug vehicle. Subsequently, animals in each of these preexposure groups were presented with a novel 0.1% saccharin-flavored solution followed immediately by injection with one of the same three morphine doses or drug vehicle. This procedure was repeated at 5-day intervals until six saccharin presentations had been performed. Results indicated that while the three morphine doses were differentially potent as taste aversion-conditioning agents, they were equipotent as preexposure agents serving to disrupt CTA. These data suggest that preexposure to morphine's predominantly positive-reinforcing (and non-CTA-inducing) properties is sufficient for preexposure disruption of subsequent morphine CTA. A second experiment indicated that the minimal effective preexposure dose is between 0.3 and 1.25 mg/kg of morphine. It is suggested that an important commonality may exist between the discriminative stimulus properties of morphine as a CTA-inducing agent and as a positive reinforcer.

Animals↗
PubMed1981

Stimulus control of stereotypic responding: effects on target and collateral behavior.

Inhibitory stimulus control over stereotypic responding of two profoundly retarded adults was established. Discrimination training using the overcorrection technique was carried out under conditions where a light on one end of a series of five lights signalled the presence of the punishment contingency and the light on the other end signalled nonpunishment. Tests for generalization of inhibition were made to all five lights in the series, resulting in generalization gradients. A multiple-baseline procedure was employed in which both target (punished) and nontarget stereotypies were recorded. Steep generalization gradients were obtained, indicating that the subjects were able to make sharp discriminations between safe and unsafe conditions. Deceleration of the target stereotypy was accompanied by marked increases in rates of nonpunished stereotypies. Orderly generalization gradients were obtained for the collateral behavior as well.

Adult↗
PubMed1999

Discriminative-stimulus effects of triazolam and midazolam in rhesus monkeys.

The present study characterized the discriminative-stimulus effects of triazolam and midazolam in rhesus monkeys. Six monkeys discriminated 0.1 mg/kg of triazolam from vehicle under a fixed-ratio 5 (FR 5) schedule of stimulus-shock termination (SST). Four monkeys subsequently discriminated 0.56 mg/kg of midazolam from vehicle under the same schedule of reinforcement. Benzodiazepine (BDZ) agonists midazolam and diazepam, and the barbiturate pentobarbital, substituted for triazolam, and the non-competitive N-methyl-D-aspartate (NMDA) antagonist ketamine did not. Triazolam, diazepam, lorazepam, flunitrazepam, as well as the barbiturates amobarbital and pentobarbital, substituted for midazolam, and ketamine did not. The BDZ antagonist flumazenil antagonized both the triazolam and midazolam discriminative stimuli. Bretazenil, a low-efficacy BDZ agonist, did not substitute for the midazolam discriminative stimulus in three of the monkeys and shifted the midazolam dose-effect curve to the right; in a fourth monkey, bretazenil substituted for midazolam and shifted the midazolam dose-effect curve to the left. Schild analyses with flumazenil or bretazenil, in combination with midazolam, yielded slopes that deviated significantly from unity. While clearly supporting the notion that BDZ agonists produce stimulus effects by acting at the gamma-aminobutyric acidA (GABA(A)) receptor complex, these data also suggest that the discriminative-stimulus effects of midazolam might be mediated by more than one BDZ receptor subtype.

Animals↗