Interresponse Times Research Articles

THE ISOLATION OF MOTIVATIONAL, MOTORIC, AND SCHEDULE EFFECTS ON OPERANT PERFORMANCE: A MODELING APPROACH

Dissociating motoric and motivational effects of pharmacological manipulations on operant behavior is a substantial challenge. To address this problem, we applied a response-bout analysis to data from rats trained to lever press for sucrose on variable-interval (VI) schedules of reinforcement. Motoric, motivational, and schedule factors (effort requirement, deprivation level, and schedule requirements, respectively) were manipulated. Bout analysis found that interresponse times (IRTs) were described by a mixture of two exponential distributions, one characterizing IRTs within response bouts, another characterizing intervals between bouts. Increasing effort requirement lengthened the shortest IRT (the refractory period between responses). Adding a ratio requirement increased the length and density of response bouts. Both manipulations also decreased the bout-initiation rate. In contrast, food deprivation only increased the bout-initiation rate. Changes in the distribution of IRTs over time showed that responses during extinction were also emitted in bouts, and that the decrease in response rate was primarily due to progressively longer intervals between bouts. Taken together, these results suggest that changes in the refractory period indicate motoric effects, whereas selective alterations in bout initiation rate indicate incentive-motivational effects. These findings support the use of response-bout analyses to identify the influence of pharmacological manipulations on processes underlying operant performance.

Perfluorochemical (PFC) Exposure in Children: Associations with Impaired Response Inhibition

Perfluorinated chemicals (PFCs) have been used widely in consumer products since the 1950s and are currently found at detectable levels in the blood of humans and animals across the globe. In stark contrast to this widespread exposure to PFCs, there is relatively little research on potential adverse health effects of exposure to these chemicals. We performed this cross-sectional study to determine if specific blood PFC levels are associated with impaired response inhibition in children. Blood levels of 11 PFCs were measured in children (N = 83) and 6 PFCs: perfluorooctane sulfonate (PFOS), perfluorohexane sulfate (PFHxS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonamide (PFOSA), and perfluorodecanoic acid (PFDA) - were found at detectable levels in most children (87.5% or greater had detectable levels). These levels were analyzed in relation to the differential reinforcement of low rates of responding (DRL) task. This task rewards delays between responses (i.e., longer inter-response times; IRTs) and therefore constitutes a measure of response inhibition. Higher levels of blood PFOS, PFNA, PFDA, PFHxS, and PFOSA were associated with significantly shorter IRTs during the DRL task. The magnitude of these associations was such that IRTs during the task decreased by 29-34% for every 1 SD increase in the corresponding blood PFC. This study suggests an association between PFC exposure and children's impulsivity. Although intriguing, there is a need for further investigation and replication with a larger sample of children.

Assessing motivation in children using a progressive ratio task

The association of age and sex on the performance of a progressive ratio task was studied in 847 children, ages 4-14 years. Variations of this task have been used extensively with animals and to a lesser extent with humans to study factors that affect aspects of motivation. The participants in this study were required to press a response lever for nickel reinforcers during a 10 min period. One response was required to earn the first nickel and each subsequent nickel required an additional 10 more responses. Older children had a significantly higher breakpoint than younger children. This appeared to be mostly the result of older children having significantly shorter inter-response times than younger children. In addition, boys had significantly higher breakpoints than girls, especially at older ages. The results of this study illustrate that both age and sex influence the performance of this task and thus suggest that age and sex influence aspects of motivation in children. Further, characterization of performance of this task by humans facilitates comparisons with animal models and, thus, enhances its translational utility.

Vocal stereotypy in children with autism: Structural characteristics, variability, and effects of auditory stimulation

Two experiments were conducted to examine (a) the relationship between the structural characteristics (i.e., bout duration, inter-response time [IRT], pitch, and energy) and overall duration of vocal stereotypy, and (b) the effects of auditory stimulation on the duration and temporal structure of the behavior. In the first experiment, we measured the structural characteristics of vocal stereotypy in five children with autism during five 30-min free-operant sessions. The results suggested that the structure of vocal stereotypy varied considerably within and across participants. Furthermore, the overall duration of vocal stereotypy was positively correlated with bout duration and negatively correlated with IRT. In the second experiment, reversal designs were used to examine the effects of noncontingent access to auditory stimulation (i.e., music) on the vocal stereotypy of three participants. Music decreased engagement in vocal stereotypy for two of the participants. The reductions were mostly associated with a considerable increase in IRT. The implications of the results are discussed in terms of measuring the structural characteristics of vocal stereotypy to identify more effective matched stimuli and using music to facilitate the implementation of other interventions.

High schizotypal individuals manifest differential performance on time-based schedules of reinforcement

Experiments explored the performance of individuals with high schizotypal unusual experiences on time-based schedules of reinforcement: fixed interval (FI), and a differential reinforcement of low rate (DRL), schedule of reinforcements. Index of curvature analysis for the FI schedule, and inter-response time analysis for the DRL schedule, demonstrated that high scorers in unusual experiences responded after a longer period of time than low scorers. However, this was dependent on the presentation order of the schedules. Taken together, the results are consistent with disruptions in the timing performance of individuals with high psychometrically-defined unusual experiences.

Effect of methylphenidate on motivation in children with attention-deficit/hyperactivity disorder.

The effects of methylphenidate (MPH) on motivation were examined using a progressive ratio (PR) task in children who were prescribed MPH for the treatment of ADHD. Twenty-one children, 7 to 12 years of age, completed two test sessions, one under the effects of medication and one not. During each session, children pressed a lever to earn nickel reinforcers, where the first press resulted in a reinforcer and 10 additional presses were required for each subsequent reinforcer. Children on MPH had a significantly higher breakpoint than when off medication. This MPH-associated increase in the breakpoint manifested as a significant decrease in the interresponse times (IRT). Further, MPH administration resulted in a significant decrease in IRT variability. In contrast, MPH administration had no significant effects on the means and variability of postreinforcement pause duration. These results suggest that MPH increased motivation in children being treated for ADHD. Further, the inability of MPH to significantly reduce postreinforcement pause duration while simultaneously decreasing IRTs suggests that while MPH may increase motivation to perform an ongoing task, it may have little effect on the initiation of that task.

An experimental analysis of steady-state response rate components on variable ratio and variable interval schedules of reinforcement.

Three experiments explored a novel approach to analyzing the different components of response rate that are produced by exposure to free-operant schedules of reinforcement. It has been suggested that overall response rate comprises a tendency to initiate responding, and to continue to respond once the bout is initiated. Previous post hoc analyses of interresponse times (IRT) data have suggested several features of these different aspects of responding that the current experimental procedure broadly confirmed. Increasing the size of a variable interval (VI) schedule decreases the number of "burst-initiation" responses, but has less effect on responding once the burst has been initiated (Experiment 1); that the major difference between a variable ratio (VR) schedule and a VI schedule, is not in the number of "burst-initiation" responses, but in the number of "within-burst" responses, with shorter interresponse times that are emitted, with greater numbers of such "within-burst" responses being emitted on a VR schedule (Experiments 2 and 3).

Effects of positive and negative modulators of the γ-aminobutyric acid A receptor complex on responding under a differential-reinforcement-of-low-rate schedule of reinforcement in rats

Relatively little is known about the behavioral effects of the neurosteroids compared with other drugs that modulate the γ-aminobutyric acid A (GABAA) receptor complex. This study examined the acute effects of pregnanolone and dehydroepiandrosterone (DHEA) in male rats responding under a differential-reinforcement-of-low-rate schedule of reinforcement. For comparison, three positive modulators of the GABAA receptor (lorazepam, ethanol, and pentobarbital), one negative modulator (β-CCM), and one neutral modulator (flumazenil) were tested. Pregnanolone was also administered in combination with DHEA to test for antagonism between these substances. Pregnanolone, lorazepam, and pentobarbital produced increases in responding at intermediate doses, and ethanol and pentobarbital produced decreases in responding at the highest doses tested. However, all four drugs dose-dependently decreased reinforced responding by decreasing inter-response times. DHEA, β-CCM, and flumazenil did not increase responding at intermediate doses or decrease reinforced responding. DHEA did not competitively antagonize the disruptive effects of pregnanolone. In summary, pregnanolone and DHEA produced effects on differential-reinforcement-of-low-rate responding that are similar to other positive and negative GABAA modulators, respectively, and do not produce these effects through a single binding site.

RATE, PROBABILITY AND MATCHING: COMMENTS ON “THE IDENTITIES HIDDEN IN THE MATCHING LAWS, AND THEIR USES” BY DAVID THORNE

David Thorne's (2010) article, "The identities hidden in the matching laws, and their uses" performs a valuable service in pointing out alternative expressions of matching. However, some identities tend to obscure rather than illuminate empirical relationships. Three such problematic instances are discussed: interresponse time as a function of interval and ratio schedule parameters; probability equality as implying rate matching; the apparent simplicity of probabilistic functions, as opposed to response rate functions, of reinforcement rate.

Concurrent VR VI schedules: Primacy of molar control of preference and molecular control of response rates

In the first condition in Experiment 1, 6 rats were exposed to concurrent variable ratio (VR) 30, variable interval (VI) 30-sec schedules. In the next two conditions, the subjects were exposed to concurrent VI VI schedules and concurrent tandem VI-differential-reinforcement-of-high-rate VI schedules. For the latter conditions, the overall and relative reinforcer rates equaled those in the first condition. Only minor differences appeared in time allocation (a molar measure) across conditions. However, local response rate differences (a molecular measure) appeared between schedule types consistently with the interresponse times these schedules reinforced. In Experiment 2, these findings reappeared when the prior experiment was replicated with 5 subjects, except that the VR schedule was replaced by a VI plus linear feedback schedule. These results suggest that within the context tested, the molar factor of relative reinforcement rate controls preference, whereas the molecular factor of the relation between interresponse times and reinforcer probability controls the local response rate.

Effects of a Positive Allosteric Modulator of Group II Metabotropic Glutamate Receptors, LY487379, on Cognitive Flexibility and Impulsive-Like Responding in Rats

Orthosteric group II metabotropic glutamate receptor (mGluR) agonists are regarded as novel, effective medications for all major symptom domains of schizophrenia, including cognitive disturbances. mGluR2s also can be affected in a more subtle way by positive allosteric modulators (PAMs) characterized by a unique degree of subtype selectivity and neuronal frequency-dependent activity. Because currently available treatments for schizophrenia do not improve cognitive dysfunction, the main aim of the present study was to examine the effects of a mGluR2 PAM, N-(4-(2-methoxyphenoxy)-phenyl-N-(2,2,2-trifluoroethylsulfonyl)-pyrid-3-ylmethylamine (LY487379), on rat cognitive flexibility and impulsive-like responding, assessed in an attentional set-shifting task (ASST) and a differential reinforcement of low-rate 72 s (DRL72) schedule of food reinforcement. In addition, in vivo microdialysis was used to assess the drug's impact on cortical levels of dopamine, norepinephrine, serotonin, and glutamate. Rats treated with LY487379 (30 mg/kg) required significantly fewer trials to criteria during the extradimensional shift phase of the ASST. Under a DRL72 schedule, LY487379 (30 mg/kg) decreased the response rate and increased the number of reinforcers obtained. These effects were accompanied by the shift of the frequency distribution of responses toward longer inter-response time durations. LY487379 significantly enhanced extracellular norepinephrine and serotonin levels in the medial prefrontal cortex. In summary, the present study demonstrates that a mGluR2 PAM, LY487379, promotes cognitive flexibility and facilitates behavioral inhibition. These procognitive effects may contribute to the therapeutic efficacy of agents stimulating mGluR2 in schizophrenia.

EDITORIAL: TRANSLATIONAL RESEARCH IN JEAB

Psychology students are taught about the differences between basic and applied research. A popular research methods textbook, for instance, states that “the major goal of basic research is to acquire general information about a phenomenon, with little emphasis placed on applications to real-world examples of the phenomenon” (Bordens & Abbott, 2002, p. 19). Another text asserts that basic research “establishes a reservoir of data, theoretical explanations, and concepts that can be tapped by the applied researcher” (Kantowitz, Roediger, & Elmes, 1997, p. 17). Ideally, of course, students are taught that there is not always a clear boundary between basic and applied research, and that many psychological studies have characteristics of both. For instance, a study may examine the applicability of a behavioral principle or theory in a clinical population, and this research can be of real value to both basic and applied researchers. A good study of this type can assist applied researchers in developing more effective treatment procedures, while at the same time it can give basic researchers information about a behavioral principle's generality, its limitations, and possibly about ways to refine, extend, or improve it. JEAB is known mainly for publishing basic research on the behavior of individual organisms. Yet from its beginnings, this journal has published occasional articles that bridge the gap between basic and applied research. In its first few years, JEAB published reports on the operant control of stuttering (Flanagan, Goldiamond, & Azrin, 1958), on the behavior of psychiatric patients under basic reinforcement schedules (e.g., Ayllon & Azrin, 1964; Ayllon & Haughton, 1962; Hutchinson & Azrin, 1961), and on “The psychiatric nurse as a behavioral engineer” (Ayllon & Michael, 1959). In later years, there have been articles on teaching impulsive children to tolerate delays (Schweitzer & Sulzer-Azaroff, 1988), on the development of equivalence relations between visual stimuli and drugs (DeGrandpre, Bickel, & Higgins, 1992), on the transfer of arousal functions in spider-fearful individuals (Smyth, Barnes-Holmes, & Forsyth, 2006), and on how a summed-exponential model of interresponse time distributions can be used to analyze the durations of wars (Nevin, 2008). These are just a few examples of JEAB articles that have demonstrated the application of basic behavioral principles beyond the operant laboratory. This special issue on translational research, therefore, does not venture into completely new territory for JEAB, although it does reflect a recent trend in the behavioral sciences toward increased interest in research that extends basic principles of behavior beyond the laboratory. It seems very fitting that JEAB, as one of the primary journals that publishes original research on basic behavioral principles, should continue to feature research that demonstrates the extension of these principles to nonlaboratory situations. This special issue has two main purposes. The first is to showcase some of the excellent translational work that is currently being conducted in many different areas. The articles in this issue cover a wide assortment of topics and behavioral principles, ranging from an application of the matching law to the speech patterns of delinquent boys to an fMRI study on risk perception in pathological gamblers. There are indeed many different areas in which modern behavioral principles and concepts can be fruitfully applied. The second purpose of this special issue is to communicate our intention to publish more high-quality translational research as a regular part of future issues of JEAB. As an important step toward achieving this goal, I am pleased to announce that F. Charles (Bud) Mace has accepted the position of JEAB's first Editor for Translational Research. Researchers who conduct translational research are invited and encouraged to submit their manuscripts to this journal. Bud's extensive experience in the area of translational research will ensure that manuscripts on translational research receive competent and appropriate evaluation and feedback. This special issue, and our plans to include more translational research in the future issues, therefore represent the continuation of a long tradition for JEAB. In the five decades of JEAB's existence, basic research has produced a wealth of new knowledge about the behavior of individual organisms. The recent growth in the quantity and variety of translational research is a sign that the time is right for tapping into this reservoir of data, theoretical explanations, and concepts, and demonstrating their importance outside the laboratory.

Antidepressant-like or anxiolytic-like actions of topiramate alone or co-administered with intra-lateral septal infusions of neuropeptide Y in male Wistar rats

We tested the effects of intra-lateral septal infusions of neuropeptide Y (NPY) combined with systemic injections of topiramate in the DRL-72 s paradigm and the elevated plus-maze test in male Wistar rats. Intra-lateral septal infusions of desipramine (5.0 μg/μl; P < 0.05) or intra-lateral septal infusions of NPY (3.0 μg/μl, P < 0.05; 3.5 μg/μl, P < 0.05) or systemic injections of topiramate (20.0 mg/kg, P < 0.05; 30.0 mg/kg, P < 0.05) or subthreshold doses of topiramate (10.0 mg/kg) combined with intra-lateral septal infusions of subthreshold doses of NPY (2.5 μg/μl; P < 0.05) induced a dose-dependent increase in reinforced lever presses and a cohesive rightward shift of the inter-response time distribution in the DRL 72 s task. In the elevated plus-maze test, intra-lateral septal infusions of NPY (3.0 μg/μl, P < 0.05; 3.5 μg/μl, P < 0.05) or midazolam (10.0 μg/μl; P < 0.05) or systemic injections of topiramate (20.0 mg/kg, P < 0.05; 30.0 mg/kg, P < 0.05) or subthreshold doses of systemic injections of topiramate (10.0 mg/kg) combined with intra-lateral septal infusions of subthreshold doses of NPY (2.5 μg/μl; P < 0.05) increased the exploration of the open arms without affecting locomotion. In conclusion, intra-septal NPY has anxiolytic effects in the EPM, and antidepressant effects in the DRL 72 s test. Similarly, systemic topiramate has anxiolytic effects in the EPM, and antidepressant effects in the DRL 72 s test. Finally, a combination of subthreshold doses of NPY and topiramate together also have anxiolytic and antidepressant effects, suggesting a synergistic effect.

The triple reuptake inhibitor DOV216,303 exhibits limited antidepressant-like properties in the differential reinforcement of low-rate 72-second responding assay, likely due to dopamine reuptake inhibition

There is a need for antidepressants with novel mechanisms of action. One approach has been to develop compounds that inhibit reuptake of all three monoamines in the central nervous system, for example DOV216,303. Differential reinforcement of low-rate (72-s) responding is a behavioral test that is predictive of antidepressant-like properties. The effects of antidepressant compounds belonging to multiple classes, the anxiolytic diazepam and the antipsychotic haloperidol, were assessed in the DRL-72s task. Subsequently, the antidepressant-like properties of acute DOV216,303 were assessed. The selective serotonin reuptake inhibitor fluvoxamine, the preferential norepinephrine reuptake inhibitor desipramine and the tricyclic antidepressant imipramine exhibited antidepressant-like properties in the DRL-72s task. The atypical antidepressant bupropion, which inhibits dopamine and norepinephrine reuptake, and the selective dopamine transporter inhibitor GBR12909, changed reinforcement and response rates and inter-response time distribution in an opposite direction compared with the antidepressant compounds tested. The antipsychotic haloperidol exhibited antidepressant-like properties by increasing reinforcement rate, but failed to alter inter-response time distribution. Diazepam did not change reinforcement or response rates or inter-response time distribution. The triple reuptake inhibitor DOV216,303 significantly enhanced reinforcement rate at one intermediate dose, but exhibited similar effects as bupropion and GBR12909 on inter-response time distribution. The studies identified limited antidepressant-like properties of the triple reuptake inhibitor DOV216,303, likely due to dopamine transporter inhibition counteracting the effects of norepinephrine and serotonin transporter inhibition.

RESPONSE ACQUISITION AND FIXED‐RATIO ESCALATION BASED ON INTERRESPONSE TIMES IN RATS

The effectiveness of a fixed-ratio (FR) escalation procedure, developed by Pinkston and Branch (2004) and based on interresponse times (IRTs), was assessed during lever-press acquisition. Forty-nine experimentally naïve adult male Long Evans rats were deprived of food for 24 hr prior to an extended acquisition session. Before the start of the session, three food pellets were placed in the magazine. Otherwise, no magazine training, shaping, nor autoshaping procedure was employed. The first 20 presses each resulted in the delivery of a 45-mg food pellet. Then, the FR increased (2, 4, 8, 11, 16, 20, 25, 30) when each IRT in the ratio was less than 2 s during three consecutive ratios. Sessions lasted 13 hr or until 500 pellets were earned. On average, rats reached a terminal ratio of 11 (mean) or 16 (median) during the first session. Seven rats reached the maximum value of FR 30 and only one rat did not acquire the response. In most rats, a break-and-run pattern of responding characteristic of FR schedules began to develop in this acquisition session. Subsequently, the ratio-escalation procedure continued during daily 2-hr sessions. In these sessions, the starting ratio requirement was set at the terminal ratio reached in the previous session. Using this procedure, over half (26) of the rats reached the FR 30 requirement by the fourth session. These data demonstrate that a ratio-escalation procedure based on IRTs provides a time-efficient way of establishing ratio responding.

An Exploration of Remote History Effects in Humans: II. The Effects Under Fixed-Interval, Variable-Interval, and Fixed-Ratio Schedules

Five undergraduates responded under a fixed-ratio (FR) 145 schedule, and 5 others responded under a differential-reinforcement-of-low-rate (DRL) 20-s schedule. Both groups were then exposed to a differential-reinforcement-of- rates-with-pacing 1 s < interresponse time (IRT) ≤ 2 s schedule. Following this, probe sessions under fixed-interval (FI) 20-s, variable-interval (VI) 20-s, and Fr 145 schedules were interspersed among baseline sessions of the 1 s < IRT ≤ 2 s schedule. Response rates under the FI and VI schedules were higher for participants with a history of the FR schedule than for those with a DRL history. Under the FR schedule, such a systematic difference by remote histories was observed only during the first of the 3 probe sessions.

THE EFFECT OF CHANGES IN CRITERION VALUE ON DIFFERENTIAL REINFORCEMENT OF LOW RATE SCHEDULE PERFORMANCE

The differential reinforcement of low rate (DRL) schedule is commonly used to assess impulsivity, hyperactivity, and the cognitive effects of pharmacological treatments on performance. A DRL schedule requires subjects to wait a certain minimum amount of time between successive responses to receive reinforcement. The DRL criterion value, which specifies the minimum wait time between responses, is often shifted towards increasingly longer values over the course of training. However, the process invoked by shifting DRL values is poorly understood. Experiment 1 compared performance on a DRL 30-s schedule versus a DRL 15-s schedule that was later shifted to a DRL 30-s schedule. Dependent measures assessing interresponse time (IRT) production and reward-earning efficiency showed significant detrimental effects following a DRL schedule transition in comparison with the performance on a maintained DRL 30-s schedule. Experiments 2a and 2b assessed the effects of small incremental changes vs. a sudden large shift in the DRL criterion on performance. The incremental changes produced little to no disruption in performance compared to a sudden large shift. The results indicate that the common practice of incrementing the DRL criterion over sessions may be an inefficient means of training stable DRL performance.

Differential involvement of prefrontal cortex, striatum, and hippocampus in DRL performance in mice

Behavioral effects of neurotoxic lesions of the hippocampus, medial prefrontal (prelimbic, infralimbic and anterior cingulate) cortex or dorsal striatum were assessed using a DRL-10s schedule in mice. Post-operative acquisition data indicate that mice with hippocampal, but not prefrontal or striatal lesions received fewer reinforcements during daily 30-min sessions, and were less efficient in the timing of their responses. Additional analysis of inter-response-time (IRT) distributions revealed that the responses of hippocampal-lesioned mice exhibited undistinguishable responses for short IRTs (up to 9s). In addition, prefrontal-lesioned mice demonstrated a degradation of performance with further testing, and a flattened IRT distribution at late test phase, while striatal-lesioned mice behaved similarly to sham-lesioned mice. These results are interpreted in terms of known functions of the hippocampus in behavioral inhibition, and of the prefrontal cortex in executive control/decision making (and time production).

Effects of Amphetamine and Cocaine on Behavior Maintained by Differential Reinforcement of Low-Rate-Response (DRL) Schedule

Although a number of previous review articles cover the effects of psychostimulant drugs on the operant or schedule-controlled behavior, none of those had focused on the effects of amphetamine and cocaine on operant behavior exclusively maintained by differential reinforcement of low-rate response (DRL). This review (a) summarizes research on the psychopharmacology of amphetamines and cocaine that has been conducted using DRL behavior, (b) discusses the potential neural substrates underlying the aforementioned drug-induced behavioral alterations on the basis of the data from lesion studies, and (c) highlights two major behavioral components, behavioral inhibition and temporal control of DRL responding, that are altered by amphetamines and cocaine. Amphetamines and cocaine affect the development and/or performance of DRL behavior in dose related ways that can be differentiated on the basis of the specific types of behavioral alterations. In general, with the moderate but effective doses, these drugs significantly increase the total number of responses and decrease the number of reinforced responses. Although the burst responses with very short inter-response times (IRT's) are more likely increased by these drugs, this aspect of the drugs' effects were found to vary across studies that used different experimental procedures of shaping up or training the subject to perform DRL behavior. Both amphetamine and cocaine produce a leftward shift on the IRT frequency distribution curve compared to vehicle treatment. The effects of amphetamines and cocaine on DRL behavior as reviewed here further highlight the need for additional research to probe neurobehavioral mechanisms that may underlie DRL behavior as manifested by both burst responding and timing the emission of the operant response.

Explicit melioration by a neural diffusion model

When faced with choices between two sources of reward, animals can rapidly adjust their rates of responding to each so that overall reinforcement increases. Herrnstein's ‘matching law’ provides a simple description of the equilibrium state of this choice allocation process: animals reallocate behavior so that relative rates of responding equal, or match, the relative rates of reinforcement obtained for each response. Herrnstein and colleagues proposed ‘melioration’ as a dynamical process for achieving this equilibrium, but left details of its operation unspecified. Here we examine a way of filling in the details that links the decision making and operant conditioning literatures and extends choice proportion predictions into predictions about inter-response times. Our approach implements melioration in an adaptive version of the drift diffusion model (DDM), which is widely used in decision making research to account for response time distributions. When the drift parameter of the DDM is 0 and its threshold parameters are inversely proportional to reward rates, its choice proportions dynamically track a state of exact matching. A DDM with fixed thresholds and drift that is determined by differences in reward rates can produce similar, but not identical, results. We examine the choice probability and inter-response time predictions of these models, separately and in combination, and the possible implications for brain organization provided by neural network implementations of them. Results suggest that melioration and matching may derive from synapses that estimate reward rates by a process of leaky integration, and that link together the input and output stages of a two-stage stimulus–response mechanism.