Nicotine-like discriminative stimulus effects of bupropion in rats.

Bupropion, a tobacco-cessation product, shares discriminative stimulus effects with cocaine and methamphetamine. The discriminative stimulus effects of these drugs, in turn, overlap with those of nicotine. This study investigated the overlap in discriminative stimulus effects of bupropion and nicotine. Rats were trained to discriminate 0.4 mg/kg (-)-nicotine from saline in 2-lever drug discrimination. Both nicotine and bupropion substituted for nicotine: however nicotine's effects were blocked by the nicotinic antagonist mecamylamine, whereas those of bupropion were not. These results suggest that bupropion may be producing its nicotine-like discriminative stimulus effect though a different mechanism that nicotine. Give bupropion's shared pharmacology with dopamine transport inhibitors, these effects may be produced in part through bupropion's actions on dopaminergic neurotransmission. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons learn stimulus identity and stimulus relations when both serve as redundant, relevant cues during same-different discrimination training.

The authors taught pigeons to discriminate displays of 16 identical items from displays of 16 nonidentical items. Unlike most same-different discrimination studies-where only stimulus relations could serve a discriminative function-both the identity of the items and the relations among the items were discriminative features of the displays. The pigeons learned about both stimulus identity and stimulus relations when these 2 sources of information served as redundant, relevant cues. In tests of associative competition, identity cues exerted greater stimulus control than relational cues. These results suggest that the pigeon can respond to both specific stimuli and general relations in the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distance and magnitude effects in sequential number discrimination by pigeons.

Number discrimination experiments with humans and monkeys have revealed distance and magnitude effects. When required to choose the more frequently occurring stimulus between two stimuli presented repeatedly in sequence, accuracy improves as the distance between number increases (distance effect) and decreases as distance is held constant and the size of the numbers increases (magnitude effect). These effects were shown in three experiments reported with pigeons as subjects. It was shown that a single model based on discrimination between noisy numerical representations could account for both the primate and bird findings. To model the pigeon data, an additional decay parameter was necessary to account for strong recency effects found for the influence on choice of terminal stimuli presented in a sequence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reinforcement magnitude modulation of rate dependent effects in pigeons and rats.

Response rate can influence the behavioral effects of many drugs. Reinforcement magnitude may also influence drug effects. Further, reinforcement magnitude can influence rate-dependent effects. For example, in an earlier report, we showed that rate-dependent effects of two antidepressants depended on reinforcement magnitude. The ability of reinforcement magnitude to interact with rate-dependency has not been well characterized. It is not known whether our previous results are specific to antidepressants or generalize to other drug classes. Here, we further examine rate-magnitude interactions by studying effects of two stimulants (d-amphetamine [0.32–5.6 mg/kg] and cocaine [0.32–10 mg/kg]) and two sedatives (chlordiazepoxide [1.78–32 mg/kg] and pentobarbital [1.0–17.8 mg/kg]) in pigeons responding under a 3-component multiple fixed-interval (FI) 300-s schedule maintained by 2-, 4-, or 8-s of food access. We also examine the effects of d-amphetamine [0.32–3.2 mg/kg] and pentobarbital [1.8–10 mg/kg] in rats responding under a similar multiple FI300-s schedule maintained by 2- or 10- food pellet (45 mg) delivery. In pigeons, cocaine and, to a lesser extent, chlordiazepoxide exerted rate-dependent effects that were diminished by increasing durations of food access. The relationship was less apparent for pentobarbital, and not present for d-amphetamine. In rats, rate-dependent effects of pentobarbital and d-amphetamine were not modulated by reinforcement magnitude. In conclusion, some drugs appear to exert rate-dependent effect which are diminished when reinforcement magnitude is relatively high. Subsequent analysis of the rate-dependency data suggest the effects of reinforcement magnitude may be due to a diminution of drug-induced increases in low-rate behavior that occurs early in the fixed-interval. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The dimensional nature of same–different discrimination behavior in pigeons.

We studied the dimensional nature of same–different discrimination behavior in pigeons. Birds first learned to discriminate between simultaneously presented displays of 16 identical items (Same arrays) and 16 nonidentical items (Different arrays), conditional on the color of the background. After discrimination mastery, we tested the birds with Mixture arrays comprising both identical and nonidentical items. Accuracy increased and reaction time decreased as the disparity in entropy (a measure of variability) between the arrays increased. As well, within each entropy disparity level, lower entropy values were more discriminable than higher entropy values. These results accord with a logarithmic relation between entropy and discriminative behavior and, thus, with the idea that the discrimination of Same from Different arrays follows Weber's Law. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Learning effects in the block design task: A stimulus parameter-based approach.

Learning effects were assessed for the block design (BD) task, on the basis of variation in 2 stimulus parameters: perceptual cohesiveness (PC) and set size uncertainty (U). Thirty-one nonclinical undergraduate students (19 female) each completed 3 designs for each of 4 varied sets of the stimulus parameters (high-PC/high-U, high-PC/low-U, low-PC/high-U, and low-PC/low-U), ordered randomly within a larger set of designs with mixed stimulus characteristics. Regression analyses revealed significant, although modest, learning effects in all conditions. Negative-logarithmic learning slopes (growth factors) were greatest for high-U/high-PC designs and smallest for low-U/low-PC designs. Comparison of these slopes with known Wechsler Adult Intelligence Scale (3rd ed.; D. Wechsler, 1997; and 4th ed.; D. Wechsler, 2008) BD subtest gain scores demonstrated that presenting novel test items matched on stimulus parameters in multiple administrations reduced learning effects compared with the repeated use of the same test items. The results suggest that repeated administration of novel test items of the BD subtest, matched for PC and U, would result in more accurate assessments of changes in examinees’ abilities over time than would the use of the same items. Difficulties inherent in implementing this method are also discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of the stimulus in Rorschach responses.

"It is apparent, from the studies reviewed, that the definition of Rorschach stimulus effects is more a task for the future than an accomplishment of the past. In fact, empirical concern with this question appears to have been something of an afterthought with users of the technique. Variation in the stimulus, in order to define an independent variable, has been such a standard procedure in psychological research that it is surprising to find it being applied only during very recent years to an analysis of the Rorschach. Other methods, as indicated, have contributed to the clarification of this problem, but they have not, as yet, gone very deeply." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The discrimination of sequences in stimulus events and the transmission of information.

Indicates the importance to psychologists of the communication model in analyzing behavior as a time series. Uses illustrations from the areas of clinical diagnosis, trouble shooting, and problem solving behavior to show how a time series analysis of behavior may be useful. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The moderating effects of stimulus valence and arousal on memory suppression.

This study examined the separate and combined effects of stimulus valence and arousal on retrieval inhibition. Participants performed Anderson and Green's (2001) memory suppression task with stimuli varying across dimensions of valence and arousal. Memory was tested through free and cued recall as well as speeded recognition. Results showed that both stimulus valence and arousal influenced the extent to which participants successfully inhibited retrieval, but not in the ways anticipated. Specifically, the strongest inhibition effects were for highly arousing, pleasant words. In addition, unpleasant stimuli that were suppressed were better recalled during both cued and free-recall tasks than pleasant stimuli that were suppressed. Across all tests of memory performance, there were no significant differences between the experimental conditions for highly arousing, unpleasant words. The implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditional same-different discrimination by pigeons: Acquisition and generalization to novel and few-item displays.

The authors explored whether pigeons can learn to discriminate simultaneously presented arrays of 16 identical (Same) visual items from arrays of 16 nonidentical (Different) visual items, when the correct choice was conditional on the presence of another cue: the color of the background. In one experiment, pigeons rapidly learned this task and, after training with arrays created from a 72-icon set, they exhibited nearly perfect transfer to novel testing arrays. In a second experiment, pigeons’ accuracy to 24-, 20-, 12-, and 8-icon arrays during later testing remained as high as accuracy to training arrays; although accuracy declined with 4- and 2-icon arrays, it was still significantly above chance. In both experiments, pigeons’ choice reaction time scores nicely complemented their choice accuracy scores. These results suggest that the conditional discrimination procedure is well suited to disclose same-different discrimination in pigeons and to elucidate the interaction between perception and abstraction in conceptual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Same–different texture discrimination in pigeons: Testing competing models of discrimination and stimulus integration.

The choice behavior of 6 pigeons performing a multidimensional same-different texture discrimination was examined. On each trial, they had to choose among 2 choice hoppers depending on whether a color, shape, or redundant (color and shape) target signal was present or not in a textured stimulus. Receiver operating characteristic (ROC) curves were produced by variations in the a priori signal presentation probabilities across conditions. Quantitative analyses of these ROC curves were used to evaluate different competing theories of discrimination (signal detection vs. high-threshold-default response models) and information integration (independent observations, additive integration, unidimensional models). The results suggested the structure of the pigeons' choice behavior in this same different discrimination was best described by an unequal variance signal detection model involving a unidimensional evidence variable (e.g., degree of difference). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus similarity in discrimination training upon wavelength generalization in pigeons.

Administered variable-interval training to 30 naive adult pigeons to peck a 550-nm light and then tested them for wavelength generalization. Ss were later assigned to 1 of 3 groups, matched for both relative generalization slope and response rate. One group then received successive discrimination training between the 555-nm stimulus (S+) and a vertical white line on a 555-nm background (S-); another group experienced the same S+ but a vertical white line on a black background as S-. A 3rd group received a comparable amount of single stimulus training with the 555-nm value. On a 2nd wavelength generalization test, the 1st group yielded greater sharpening of generalization than the 2nd group, whereas the 3rd group showed no change from Test 1. Results indicate that the sharpening of generalization gradients by discrimination training was directly related to the similarity of the discrimination training stimuli. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of concomitant colored and uncolored pictorial representations on the learning of stimulus words.

To study the effect of varying degrees of compounding signs of objects denoted by the words, twenty-five stimulus words were presented under three learning conditions: (a) Words alone, (b) words with their uncolored pictures, (c) words with their colored pictures. It was concluded that support was given the hypothesis that "with the number of presentations… held constant, the number of… words recalled by Ss should vary positively within limits with the number of simultaneously presented additional signs." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discriminative stimulus properties of (±)-fenfluramine: The role of 5-HT? receptor subtypes.

The role of serotonin 5-HT? receptors (5-HT?R) in the discriminative stimulus effects of fenfluramine was investigated. Male Sprague-Dawley rats were trained to discriminate (±)-fenfluramine (2 mg/kg ip) from saline using a 2-lever, water-reinforced paradigm. Drug-lever responding after fenfluramine was dose-dependent. The 5-HT2C/1BR agonist mCPP and the 5-HT2CR agonist MK 212 fully substituted, whereas the 5-HT2A/2CR agonist DOI partially substituted, for the training drug. The 5-HT2BR agonist BW 723C86 engendered saline-lever responding. The 5-HT2C/2BR antagonist SB 206553 completely antagonized the fenfluramine discrimination as well as the full substitutions of mCPP and MK 212 and the partial substitution of DOI. The selective 5-HT2AR antagonist M100907 partially suppressed the stimulus effects of fenfluramine, mCPP, and MK 212 and almost fully attenuated the partial substitution of DOI. RS 102221, a selective 5-HT2CR antagonist that does not cross the blood-brain barrier, did not alter the fenfluramine cue. Results demonstrate that the discriminative stimulus effects of fenfluramine are centrally mediated by 5-HT2CR and to some extent by 5-HT2AR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Superordinate categorization via learned stimulus equivalence: Quantity of reinforcement, hedonic value, and the nature of the mediator.

Three experiments examined superordinate categorization via stimulus equivalence training in pigeons. Experiment 1 established superordinate categories by association with a common number of food pellet reinforcers, plus it established generalization to novel photographic stimuli. Experiment 2 documented generalization of choice responding from stimuli signaling different numbers of food pellets to stimuli signaling different delays to food reinforcement. Experiment 3 indicated that different numbers of food pellets did not substitute as discriminative stimuli for the photographic stimuli with which the food pellets had been paired. The collective results suggest that the effective mediator of superordinate categories that are established via learned stimulus equivalence is not likely to be an accurate representation of the reinforcer, neither is it likely to be a distinctive response that is made to the discriminative stimulus. Motivational or emotional mediation is a more likely account. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Comparison of the Discriminative Stimulus Effects of Δ?-Tetrahydrocannabinol and O-1812, a Potent and Metabolically Stable Anandamide Analog, in Rats.

Efforts to determine whether Δ?-tetrahydrocannabinol (Δ?-THC) and anandamide elicit similar discriminative stimulus effects have yielded conflicting results. The difficulty in establishing a discriminative cue to anandamide may be due to its metabolic instability. Rats were trained to discriminate either Δ?-THC or O-1812, a metabolically stable anandamide analog, from vehicle to avoid this issue. O-1812 and Δ?-THC substituted for each other; however, both drugs were more potent in the O-1812-trained rats. Further, O-1812 only substituted for Δ?-THC at response rate decreasing doses. The CB? antagonist, SR141716A, blocked the discriminative stimulus effects of both drugs but augmented their rate effects. O-1839, a VR? agonist, failed to substitute for either cannabinoid. These results suggest that the discriminative stimulus effects of Δ?-THC and O-1812 are similar, but subtle differences also exist. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Second-order contrast based on the expectation of effort and reinforcement.

Pigeons prefer signals for reinforcement that require greater effort (or time) to obtain over those that require less effort to obtain (T. S. Clement, J. Feltus, D, H. Kaiser, & T. R. Zentall, 2000). Preference was attributed to contrast (or to the relatively greater improvement in conditions) produced by the appearance of the signal when it was preceded by greater effort. In Experiment 1, the authors of the present study demonstrated that the expectation of greater effort was sufficient to produce such a preference (a second-order contrast effect). In Experiments 2 and 3, low versus high probability of reinforcement was substituted for high versus low effort, respectively, with similar results. In Experiment 3, the authors found that the stimulus preference could be attributed to positive contrast (when the discriminative stimuli represented an improvement in the probability of reinforcement) and perhaps also negative contrast (when the discriminative stimuli represented reduction in the probability of reinforcement). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Additive and interactive effects of stimulus degradation: No challenge for CDP+.

[Correction Notice: An erratum for this article was reported in Vol 35(2) of Journal of Experimental Psychology: Learning, Memory, and Cognition (see record 2009-02753-020). The URL for the supplemental material was incomplete. The complete URL is http:dx.doi.org/10.1037/a0013738.supp.] S. O'Malley and D. Besner (2008) showed that additive effects of stimulus degradation and word frequency in reading aloud occur in the presence of nonwords but not in pure word lists. They argued that this dissociation presents a major challenge to interactive computational models of reading aloud and claimed that no currently implemented model is able to simulate additive effects in these conditions. In the current article, it is shown that the connectionist dual process model (CDP+) can simulate these effects because its nonlexical route is thresholded. The authors present a series of simulations showing that CDP+ can not only simulate the precise dissociation observed by O'Malley and Besner but more generally can produce additive effects for a wide range of parameter combinations and different sets of items. The nonlexical route of CDP+ was not modified post hoc to deal with the effects of stimulus quality, but it had been thresholded for principled reasons before it was known that these effects existed. Together, the effects of stimulus quality on word frequency do not challenge CDP+ but rather provide unexpected support for its architecture and processing dynamics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unconditioned stimulus devaluation effects in nutrient-conditioned flavor preferences.

Experiments with different temporal relations between the conditioned stimulus (CS) and the unconditioned stimulus (US) in conditioning assessed whether US devaluation effects can be obtained after nutrient-conditioned flavor preference learning. One flavor (CScarb) was paired with a carbohydrate, Polycose; a 2nd flavor (CSprot) was paired with a protein, casein; and a 3rd flavor (CS-) was presented by itself. Following conditioning, one of the nutrients was devalued through pairings with lithium chloride in the absence of the CS flavors. In a subsequent 2-bottle test, rats preferred CScarb over CSprot; however, this preference was smaller when the carbohydrate was devalued than when the protein was devalued. Results suggest that CS flavors are able to form associations with the sensory features of nutrient USs under a wide variety of circumstances. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociative effects of stimulus quality on semantic and morphological contexts in visual word recognition.

Semantic and morphological contexts were manipulated jointly with stimulus quality under conditions where there were few related prime-target pairs (i.e., low relatedness proportion) in a lexical decision experiment. Additive effects of semantic context and stimulus quality on RT were observed, replicating previous work. In contrast, morphological context interacted with stimulus quality. This dissociation is discussed in the context of Besner and colleagues' evolving multistage framework. The essence of the account is that 1) stimulus quality affects feature and letter levels, but not later levels, 2) feedback from semantics to the lexical level is inoperative under low relatedness proportion conditions (hence stimulus quality and semantic context yield additive effects), whereas 3) feedback from the lexical level to the letter level is intact, hence stimulus quality and morphological context produce an interaction by virtue of them affecting a common stage of processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)