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PubMed1995

Human symbolic matching-to-sample performance: Effects of reinforcer and sample-stimulus probabilities.

Four experiments, each with 6 human subjects, varied the distribution of reinforcers for correct responses and the probability of sample-stimulus presentation in symbolic matching-to-sample procedures. Experiment 1 held the sample-stimulus probability constant and varied the ratio of reinforcers obtained for correct responses on the two alternatives across conditions. There was a positive relation between measures of response bias and the ratio of reinforcers. Experiment 2 held the ratio of reinforcers constant and varied the sample-stimulus probability across conditions. Unlike previous studies that used pigeons as subjects, there was a negative relation between bias and the ratio of sample-stimulus presentations. In Experiment 3, the sample-stimulus probability and the reinforcer ratio covaried across conditions. Response bias did not vary systematically across conditions. In Experiments 1 to 3, correct responses were reinforced intermittently. Experiment 4 used the same procedure as Experiment 3, but all correct responses now produced some scheduled consequence. There was a positive relation between response bias and the ratio of reinforcers. The results suggest that human performance in these tasks was controlled by both the relative frequency of reinforced responses and the relative frequency of nonreinforced responses.

Journal Article↗
PubMedDate not supplied

Cuspal reinforcement in endodontically treated molars.

UNLABELLED: This in vitro study compared the ability of horizontal pins and a dental adhesive to reinforce the facial cusps of endodontically treated mandibular molars. Seventy-two mandibular molars were divided into six groups and mounted in acrylic blocks (n = 12). In Groups 1-5 standardized endodontic access and instrumentation in the coronal one-third of each root canal were completed. In Groups 1-4 the lingual cusps were reduced, leaving the buccal cusps intact. The facial cusps of the teeth in each group received one of the following modes of reinforcement: Group 1--no reinforcement; Group 2--dentin adhesive (Amalgambond Plus); Group 3--two horizontal TMS Minim pins; Group 4--two horizontal TMS Minim pins and Amalgambond Plus. Teeth in Group 5 were prepared for and restored with a complete cuspal coverage amalgam restoration using four vertical TMS Minim pins. Group 6 consisted of intact natural teeth. Using an Instron Universal Testing Machine, the lingual slope of the facial cusp of each specimen was loaded to failure using a compressive force applied at an angle 60 degrees to the long axis of the tooth. The mean fracture strengths for all groups were analyzed using a one-way ANOVA and Student-Newman-Keuls multiple range test (alpha = 0.05). Fracture patterns and modes of failure were also evaluated. RESULTS: The intact teeth (Group 6) were significantly more fracture resistant than all other groups, with the exception of Group 4 (combination of pins and adhesive). Group 1 (non-reinforced teeth) was significantly weaker than all other groups. Groups 2-4 (specimens with reinforced cusps) were not significantly different from each other. The use of horizontal pins or a combination of horizontal pins plus dentin adhesive for cuspal reinforcement resulted in significantly more teeth demonstrating favorable fracture patterns than did the use of adhesives alone. CONCLUSION: The buccal cusps of endodontically treated mandibular molars reinforced with a combination of horizontal pins and dentin adhesive were not significantly weaker than intact teeth. Of the restored teeth, those which had buccal cusps reinforced with horizontal pins and those treated with complete cuspal coverage amalgam restorations exhibited the most favorable restorative prognosis following cusp fracture.

Chi-Square Distribution↗
PubMed1993

In a low-versus high-dose drug discrimination task, random reinforcement in one drug state alters discriminative control only in that state.

This study investigated the effects of introducing random reinforcement training after a drug discrimination between 3.0 and 15.0mg/kg chlordiazepoxide had been acquired in rats; a two-lever food-rewarded operant procedure was used. Matched on the basis of dose-generalization test data, two dose-equisensitive groups were formed (A and B). Group A received 30 daily saline injections, which were followed by a random reinforcement session during which either left or right lever presses were reinforced on a probabilistic basis on each of the trials comprising a session. Group B received saline but no training or testing during this period. Subsequent testing revealed that responding conditioned to the low-dose training condition, but not to the high-dose training condition, was significantly changed in Group A. The randon reinforcement data further suggested that Group A did not discriminate saline from the low training dose. In Experiment 2, Group B of Experiment 1 was submitted to 30 random reinforcement training sessions, each preceded by a high training dose administration. Data showed that responding to the high dose, but not the low dose, was changed. For both experiments, chlordiazepoxide dose generalization following reacquisition was similar to that obtained before the random reinforcement phase. The findings indicate that the response pattern changed only for the stimulus condition present during random reinforcement. The random reinforcement manipulation did not disrupt the original discrimination between the high-and low-dose conditions.

Journal Article↗
PubMed1995

Effects of reinforcer sweetness and the D2/D3 antagonist raclopride on progressive ratio operant performance.

Previous studies have reported that DA receptor antagonists suppress most behaviours; however, a paradoxical increase in performance may be seen in tests of operant or consummatory behaviours maintained by very sweet rewards, which lie on the descending limb of the inverted U-shaped concentration-performance function (i.e., under conditions where performance decreases as sweetness increases). Despite the low performance levels associated with very sweet reinforcers, preference studies indicate that they are nonetheless more rewarding. In the present study, the hypothesis that reinforcer efficacy is monotonically related to reinforcer sweetness was tested using a geometric progressive ratio reinforcement schedule, in which increasing numbers of responses were required to earn successive reinforcers (1, 2, 4, 8,.); the amount of work the animal emits in order to obtain an increasingly infrequent reinforcer is assumed to provide a measure of the magnitude of its rewarding effect. Three groups of rats were trained on this schedule, using as reinforcers food pellets containing 1%, 10% and 95% sucrose, respectively. Under conditions of continuous sucrose-pellet reinforcement, the highest response rates were maintained by the 10% sucrose pellets. However, under the progressive ratio schedule, performance was monotonically related to sucrose concentration. The dopamine D2/D3 receptor antagonist raclopride dose-dependently suppressed progressive ratio performance in all three groups.

Journal Article↗
PubMedDate not supplied

The flexural properties of fiber-reinforced composite with light-polymerized polymer matrix.

PURPOSE: The aim of this study was to measure the flexural strength and the elastic modulus of composite resin with and without reinforcing fibers and to evaluate the reinforcing effect of various fibers. MATERIALS AND METHODS: A polyethylene fiber (Ribbond), a polyaramid fiber (Fibreflex), and three glass fibers (FibreKor, GlasSpan, Vectris) were used to reinforce composite resins. The flexural strength and elastic modulus of specimens in the three-point bending mode were measured using a universal testing machine at a cross-head speed of 1 mm/min after storage in water at 37 degrees C for 24 hours. All tests were carried out in a water bath at 37 degrees C. The data were analyzed using analysis of variance and the Sheffé test at P= 0.05. After testing, the fractured surface was evaluated using a scanning electron microscope at 50x, 500x, and 3,000x magnifications. RESULTS: Yield flexural strengths of nonreinforced resins were 48 to 56 MPa, and those of reinforced resins were 56 to 134 MPa. Ultimate flexural strengths of nonreinforced specimens were 96 to 119 MPa, and those of reinforced ones were 203 to 386 MPa. Elastic modulus of nonreinforced resin was 6 to 9 GPa, and fiber reinforcing increased the value to 9 to 15 GPa, while it had no effect in Ribbond. CONCLUSION: Most of the fibers used in this study increased both yield and ultimate flexural strengths of composite resins, with the exception of the yield strength of Vectris. GlasSpan, Fibreflex, and FibreKor were effective in reinforcing elastic modulus, while Ribbond had no effect on it. Unidirectional glass fibers and polyaramid fiber were effective in reinforcing both flexural strength and elastic modulus of composite resin.

Analysis of Variance↗
PubMed1983

Dissociable effects of d-amphetamine, chlordiazepoxide and alpha-flupenthixol on choice and rate measures of reinforcement in the rat.

The role of reinforcers in influencing choice was studied by use of a schedule that included a random intermixing of reinforced and explicitly non-reinforced components. The just-reinforced response had a high likelihood of being repeated (win-stay), although there was no differential reinforcement for doing so, whereas responses just followed by explicit non-reinforcement had a very low probability of repetition (lose-stay). Non-parametric indices based on the theory of signal detection were used to derive a choice measure of reinforcement which was independent of alterations in average response rate. Treatments with d-amphetamine (0.2-4.5 mg/kg), chlordiazepoxide (0.25-16 mg/kg) and alpha-flupenthixol (0.03-0.6 mg/kg) showed that changes in the choice measure could be dissociated from changes in the response rate. These findings were supported by extinction and satiation tests.

Animals↗
PubMed1992

Staff perceptions of reinforcer responsiveness and aberrant behaviors in people with mental retardation.

Perceptions by staff of the classes of reinforcers and aberrant behaviors of a sample of 470 people with predominantly severe or profound mental retardation were explored. Principal components analysis of a 45-item survey suggested eight classes of reinforcers: consumable, verbal-speaker, visual-motor, social, physical-contact, passive-observer, play, and academic reinforcers. Stepwise multiple regression was used to predict five classes of maladaptive behaviors as measured by the Aberrant Behavior Checklist (irritability, lethargy, stereotypy, hyperactivity, and inappropriate speech) from the eight classes of reinforcers. Each class of psychopathology was related to a unique set of predictors. All classes of psychopathology could be predicted by staff perceptions of underresponsiveness to social reinforcers and overresponsiveness to consumable reinforcers. The findings of organized structures of reinforcers and their covariation with pathological behaviors have implications for research and intervention as well as theoretical value in defining aberrant behaviors in people with mental retardation.

Adolescent↗
PubMed1991

Time-, schedule-, and reinforcer-dependent effects of pimozide and amphetamine.

Rats performed on two multiple random-interval schedules, in which sequences of ascending or descending reinforcement densities were balanced between the schedules and between the two halves of the session. Using a standard reinforcer (10% sucrose pellets), pimozide decreased response rates, while amphetamine increased responding. The effects of both drugs were schedule dependent: larger changes were evident in low response rate, reinforcement-lean components than in high response rate, reinforcement-rich components. Both effects were also time dependent, increasing over the course of the session; this casts serious doubt on the applicability of Herrnstein's matching law for studying agents acting on brain dopamine. Increasing the period of food deprivation increased response rates, while withdrawing food deprivation decreased responding. These effects were also schedule dependent, but were time dependent. Substituting 95% sucrose pellets for standard 10% sucrose pellets caused an immediate and sustained decrease in responding, and up to 10% of earned reinforcement was not consumed. Pimozide increased response rates within reinforcement-lean components and reinstated the complete consumption of earned reward typical of standard reinforcement. These apparently paradoxical effects may be consistent with a decrease in the rewarding properties of sucrose pellets. Despite low response rates, amphetamine did not affect responding maintained by 95% sucrose pellets but did further reduce the consumption of earned reward. These results call into question the generality of the rate-dependency principle in the action of psychomotor stimulants.

Amphetamine↗
PubMed1991

Evidence for an involvement of 5-hydroxytryptaminergic neurones in the maintenance of operant behaviour by positive reinforcement.

The possible involvement of the ascending 5-hydroxytryptaminergic (5HTergic) pathways in the maintenance of operant behaviour by positive reinforcement was examined using a quantitative paradigm based on Herrnstein's (1970) equation which defines a hyperbolic relationship between steady-state response rate and reinforcement frequency in variable-interval schedules. Nine rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei; 12 rats received sham injections. The rats were trained to steady-state in a series of variable-interval schedules of sucrose reinforcement affording a range of reinforcement frequencies. Herrnstein's equation was fitted to the data obtained from each rat and to the averaged data obtained from the two groups. The value of KH (the parameter expressing the reinforcement frequency needed to obtain the half-maximum response rate) was significantly lower in the lesioned group than in the control group; the values of Rmax (the parameter expressing the maximum response rate) did not differ significantly between the two groups. The levels of 5HT and 5-hydroxyindoleacetic acid in the parietal cortex, hippocampus, nucleus accumbens and hypothalamus were markedly reduced in all four regions in the lesioned group, but the levels of noradrenaline and dopamine were not significantly affected. The results indicate that damage to the central 5HTergic pathways resulted in an increase in the "value" of the sucrose reinforcer, without affecting the animals' response capacity. The results are consistent with the suggestion that the 5HTergic pathways may exert some limiting control on the "values" of certain reinforcers.

5,7-Dihydroxytryptamine↗
PubMed2006

Estimating the relative reinforcing strength of (+/-)-3,4-methylenedioxymethamphetamine (MDMA) and its isomers in rhesus monkeys: comparison to (+)-methamphetamine.

RATIONALE: (+/-)3,4-Methylenedioxymethamphetamine (MDMA) is an analog of methamphetamine (MA) and a drug of abuse. MA, MDMA, and its isomers release monoamine neurotransmitters with varying selectivities and would, therefore, be predicted to vary in their relative strength as reinforcers. OBJECTIVES: This study compared self-administration of MA, MDMA, and its isomers using a progressive-ratio schedule in rhesus monkeys. METHODS: Rhesus monkeys [n = 6, MA and MDMA; n = 5, (+)-MDMA and (-)-MDMA] were prepared with chronic i.v. catheters and allowed to self-administer cocaine or saline in daily baseline sessions. When responding was stable, MA (0.006-0.1 mg/kg per injection), MDMA (0.025-0.8 mg/kg injection), (+)-MDMA (0.025-0.8 mg/kg per injection), or (-)-MDMA (0.05-0.8 mg/kg per injection) was made available in test sessions. RESULTS: MA, MDMA, and (+)-MDMA functioned as positive reinforcers in all monkeys with a potency relationship of MA > (+)-MDMA > (+/-)-MDMA. Two of five monkeys took (-)-MDMA above saline levels. Dose-response relationships were biphasic for MA and (+/-)-MDMA, and asymptotic for (+)-MDMA. In terms of maximum number of injection per session, a measure of relative reinforcing strength, the order was MA > (+)-MDMA = (+/-)-MDMA > (-)-MDMA. CONCLUSIONS: MDMA and (+)-MDMA were consistent positive reinforcers, but weaker than MA, whereas (-)-MDMA was, at best, a weak reinforcer in some monkeys. The reinforcing strength of MDMA appears to derive primarily from (+)-MDMA. Because MDMA and its isomers have been shown to have relatively higher serotonin to dopamine releasing potency, these data support the hypothesis that increasing 5-HT releasing potency relative to DA is associated with weaker reinforcing effects.

Animals↗
PubMed2000

On the relationship between the dopamine transporter and the reinforcing effects of local anesthetics in rhesus monkeys: practical and theoretical concerns.

RATIONALE: Drugs that are self-administered appear to vary in their potency and effectiveness as positive reinforcers. Understanding mechanisms that determine relative effectiveness of drugs as reinforcers will enhance our understanding of drug abuse. OBJECTIVES: The hypothesis of the present study was that differences among dopamine transporter (DAT) ligands in potency and effectiveness as a positive reinforcers were related to potency and effectiveness as DA uptake inhibitors. Accordingly, self-administration of a group of local anesthetics that are DAT ligands was compared to their effects as DA uptake blockers in vitro in brain tissue. METHODS: Rhesus monkeys were allowed to self-administer cocaine and other local anesthetics i.v. under a progressive-ratio schedule. The same compounds were compared in standard in vitro DA uptake assays using monkey caudate tissue. RESULTS: The rank order of both potency and effectiveness as reinforcers was cocaine > dimethocaine > procaine > chloroprocaine. Tetracaine did not maintain self-administration. For inhibiting DA uptake, the potency order was cocaine > dimethocaine > tetracaine > procaine > chloro-procaine. At maximum, these compounds were equally effective in blocking DA uptake. Lidocaine did not inhibit DA uptake. CONCLUSIONS: The potency of local anesthetics as positive reinforcers is likely related to their potency as DA uptake inhibitors. Variation in their effectiveness as positive reinforcers was not a function of differences in effectiveness as DA uptake blockers, but may be related to relative potency over the concentrations that are achieved in vivo. Effects at sodium channels may limit the reinforcing effects of local anesthetics.

Anesthetics, Local↗
PubMed1985

Comparing autistic and normal children along the dimensions of reinforcement maximization, stimulus sampling, and responsiveness to extinction.

The purpose of this study was to assess autistic children's ability to maximize reinforcement, sample among available stimuli, and respond to extinction. Responding to five concurrent reinforcement schedules (CRF, FR 2, FR 4, FR 7, and FR 11) was monitored and compared to groups of mental age-matched and chronological age-matched normal children. When a given child consistently selected a given schedule of reinforcement, it was then put on extinction, and both perseveration and responding to the remaining (intact) schedules of reinforcement were monitored. The results showed, first, that while normal children selected the richest schedule of reinforcement, autistics did not maximize reinforcement, typically selecting one of the thinner schedules available. Second, the autistic children sampled less, and less efficiently, than the normal children. Third, the autistic children proved to be much less responsive to extinction, perseverating longer than the normal children before switching to a new reinforcement schedule. Fourth, whenever extinction proved to be a problem in the autistics, it was quickly achieved by a simple change in the stimulus conditions. These results are discussed as possible "keystone" deficits, which may be causally related to many of the behavioral deficits of autism and which might be important target behaviors for treatment.

Adolescent↗
PubMed1994

Tobacco abstinence, smoking cues, and the reinforcing value of smoking.

One definition of the reinforcing value of a drug is the degree to which an organism will work to obtain it. Male and female smokers (n = 8 each) engaged in a task involving concurrent schedules of reinforcement for responding to receive cigarette puffs versus money on four occasions, following overnight abstinence versus no abstinence and in the presence of a lit cigarette (smoking "cue") or with no cigarette (2 x 2 design). Reinforcement schedule for puffs ranged from variable ratio 4 (VR4) to VR32, with schedule order during the first five trials (VR4 first, VR32 first) counterbalanced and repeated in reverse sequence during the second five trials. Schedule for money remained at VR4 during all trials. Results indicated significantly greater responding for puffs after overnight abstinence and in the presence of the smoking cue, although effect of the cue was specific to the "leaner" VR schedules (VR16, VR32). Unexpectedly, not only was reinforcement schedule for puffs a significant determinant of responding, but the order of these schedules (i.e., VR4 first vs. VR32 first) produced a significant overall difference in responding for puffs, especially in the presence of the cue. There was no difference in responding between males and females. These findings indicate that the reinforcing value of smoking is increased by overnight abstinence, the presence of a lit cigarette under lean reinforcement conditions, and the order in which reinforcement schedules are presented.

Adult↗
PubMed1992

The spontaneously hypertensive rat (SHR) as an animal model of childhood hyperactivity (ADHD): changed reactivity to reinforcers and to psychomotor stimulants.

Childhood hyperactivity (attention-deficit hyperactivity disorder, ADHD) is a behavior disorder affecting 2-6% of grade-school children. The main symptoms are attention problems and hyperkinesis. The disorder is commonly treated with psychomotor stimulants, usually methylphenidate hydrochloride (ritalin) or d-amphetamine. Neither the cause of the disorder nor the basis of the effectiveness of the drug treatment is well understood. Differences in reinforcement processes have been implicated as part of the underlying problem. The main purpose of the present research was to investigate reinforcement processes and motor characteristics with and without stimulant medication in SHR, as an animal model of ADHD, and WKY controls, its normoactive progenitor strain. SHR behavior turned out to be more sensitive to immediate reinforcement and proportionately less sensitive to delayed reinforcement when compared to the behavior of WKY, as demonstrated by systematic changes in rates of responding throughout fixed-interval schedules of reinforcement of bar-presses by water. The psychomotor stimulants weakened the control by immediate reinforcers and strengthened the control by delayed reinforcers, with the effect of the drugs being more pronounced in WKY than in SHR. The results are consistent with clinical observations that ADHD children are less willing than others to accept "delayed gratification" and that methylphenidate increases the control of delayed reward over their behavior.

Analysis of Variance↗
PubMedDate not supplied

A variation of noncontingent reinforcement in the treatment of aberrant behavior.

We examined the effectiveness of a variation of noncontingent reinforcement (NCR) that incorporated a stimulus-delay procedure in the reduction of aberrant behavior maintained by positive reinforcement. Functional analyses for three individuals diagnosed with developmental disabilities indicated that their behaviors were maintained by positive reinforcement: one in the form of access to a tangible item, another by attention, and the third by physical contact. We implemented NCR with the delay procedure with two participants using reversal designs to evaluate effects. We also compared this NCR variation and DRO with the third participant to evaluate reinforcer-delivery rates. The variation of NCR was successful in reducing all aberrant behavior to near-zero levels. A comparison of reinforcer delivery between NCR with the stimulus-delay procedure and DRO demonstrated that the participant accessed more reinforcement with NCR. Results are discussed in the context of enhancing decelerative interventions with emphases on minimizing response effort for caregivers and maximizing access to reinforcement for the individuals.

Adult↗
PubMed2006

A reduced rate of in vivo dopamine transporter binding is associated with lower relative reinforcing efficacy of stimulants.

A slow onset of action has been hypothesized to weaken the reinforcing effects of drugs. The present study evaluated this hypothesis with slow-onset cocaine analogs, WIN 35428, RTI 31, and RTI 51. When cocaine or a cocaine analog was made available to rhesus monkeys (n = 4 or 5) for self-administration under a progressive-ratio (PR) schedule with a 1-h time-out between injections, all the drugs functioned as positive reinforcers. The maximum number of injections was in the order of cocaine > WIN 35428 > RTI 31 > RTI 51. In in vivo binding in rat striatum, equipotent doses of cocaine, WIN 35428, RTI 31, and RTI 51 were estimated to displace 25% of [(3)H]WIN 35428 binding at the dopamine transporters (DAT), respectively, 5.8, 22.4, 30.8, and 44.1 min after the intravenous injection. Further, relative reinforcing efficacy was correlated with rate of DAT binding such that slower displacement of [(3)H]WIN 35428 was associated with a weaker reinforcing effect. In in vitro binding in monkey brain tissue, the cocaine analogs had higher affinity for monoamine transporter sites, but similar affinity ratios of 5-HTT/DAT, compared to cocaine. Lastly, RTI 31 was shown to function as a positive reinforcer in drug-naïve rhesus monkeys under a fixed-ratio 1 schedule. Collectively, the data support the hypothesis that a slow onset at the DAT is associated with reduced reinforcing efficacy of DAT ligands. The data under both the PR and FR schedules, however, suggest that a slow onset at the DAT influence reinforcing effect only to a limited extent.

Animals↗
PubMed2005

Selective dopamine D3 receptor antagonism by SB-277011A attenuates cocaine reinforcement as assessed by progressive-ratio and variable-cost-variable-payoff fixed-ratio cocaine self-administration in rats.

In rats, acute administration of SB-277011A, a highly selective dopamine (DA) D(3) receptor antagonist, blocks cocaine-enhanced brain stimulation reward, cocaine-seeking behaviour and reinstatement of cocaine-seeking behaviour. Here, we investigated whether SB-277011A attenuates cocaine reinforcement as assessed by cocaine self-administration under variable-cost-variable-payoff fixed-ratio (FR) and progressive-ratio (PR) reinforcement schedules. Acute i.p. administration of SB-277011A (3-24 mg/kg) did not significantly alter cocaine (0.75 mg/kg/infusion) self-administration reinforced under FR1 (one lever press for one cocaine infusion) conditions. However, acute administration of SB-277011A (24 mg/kg, i.p.) progressively attenuated cocaine self-administration when: (a) the unit dose of self-administered cocaine was lowered from 0.75 to 0.125-0.5 mg/kg, and (b) the work demand for cocaine reinforcement was increased from FR1 to FR10. Under PR (increasing number of lever presses for each successive cocaine infusion) cocaine reinforcement, acute administration of SB-277011A (6-24 mg/kg i.p.) lowered the PR break point for cocaine self-administration in a dose-dependent manner. The reduction in the cocaine (0.25-1.0 mg/kg) dose-response break-point curve produced by 24 mg/kg SB-277011A is consistent with a reduction in cocaine's reinforcing efficacy. When substituted for cocaine, SB-277011A alone did not sustain self-administration behaviour. In contrast with the mixed DA D(2)/D(3) receptor antagonist haloperidol (1 mg/kg), SB-277011A (3, 12 or 24 mg/kg) failed to impede locomotor activity, failed to impair rearing behaviour, failed to produce catalepsy and failed to impair rotarod performance. These results show that SB-277011A significantly inhibits acute cocaine-induced reinforcement except at high cocaine doses and low work requirement for cocaine. If these results extrapolate to humans, SB-277011A or similar selective DA D(3) receptor antagonists may be useful in the treatment of cocaine addiction.

Animals↗
PubMed1984

Dextroamphetamine and individual susceptibility to reinforcement in verbal operant conditioning.

The present investigation was designed to study the relationships between extraversion, d-amphetamine and modes of reinforcement in verbal operant conditioning. A factorial design involving two levels of extraversion (extraverts and introverts), two reinforcement conditions ('good' and 'electric shock') and three treatments (placebo and two doses, 7.5 and 12.5 mg, of d-amphetamine) with repeated measures on the last factor was used. Sixty postgraduate female students were individually subjected to Taffel's verbal conditioning procedure. The study supported the following conclusions: (1) under the placebo condition, the extraverted subjects condition better with the rewarding reinforcer while the introverted subjects condition better with the punishing reinforcer; (2) under the influence of d-amphetamine, the extraverted subjects condition better with the punishing reinforcer while the conditioning scores of introverted subjects decrease with the punishing reinforcer but are not influenced with the rewarding reinforcer.

Adult↗