Showing papers in "Journal of the Experimental Analysis of Behavior in 2015"

Opportunity costs of reward delays and the discounting of hypothetical money and cigarettes.

Abstract: Humans are reported to discount delayed rewards at lower rates than nonhumans. However, nonhumans are studied in tasks that restrict reinforcement during delays, whereas humans are typically studied in tasks that do not restrict reinforcement during delays. In nonhuman tasks, the opportunity cost of restricted reinforcement during delays may increase delay discounting rates. The present within-subjects study used online crowdsourcing (Amazon Mechanical Turk, or MTurk) to assess the discounting of hypothetical delayed money (and cigarettes in smokers) under four hypothetical framing conditions differing in the availability of reinforcement during delays. At one extreme, participants were free to leave their computer without returning, and engage in any behavior during reward delays (modeling typical human tasks). At the opposite extreme, participants were required to stay at their computer and engage in little other behavior during reward delays (modeling typical nonhuman tasks). Discounting rates increased as an orderly function of opportunity cost. Results also indicated predominantly hyperbolic discounting, the “magnitude effect,” steeper discounting of cigarettes than money, and positive correlations between discounting rates of these commodities. This is the first study to test the effects of opportunity costs on discounting, and suggests that procedural differences may partially account for observed species differences in discounting.

Change in delay discounting and substance reward value following a brief alcohol and drug use intervention

Abstract: The present study examined (1) the impact of a brief substance use intervention on delay discounting and indices of substance reward value (RV), and (2) whether baseline values and posttreatment change in these behavioral economic variables predict substance use outcomes Participants were 97 heavy drinking college students (588% female, 412% male) who completed a brief motivational intervention (BMI) and then were randomized to one of two conditions: a supplemental behavioral economic intervention that attempted to increase engagement in substance-free activities associated with delayed rewards (SFAS) or an Education control (EDU) Demand intensity, and Omax, decreased and elasticity significantly increased after treatment, but there was no effect for condition Both baseline values and change in RV, but not discounting, predicted substance use outcomes at 6-month follow-up Students with high RV who used marijuana were more likely to reduce their use after the SFAS intervention These results suggest that brief interventions may reduce substance reward value, and that changes in reward value are associated with subsequent drinking and drug use reductions High RV marijuana users may benefit from intervention elements that enhance future time orientation and substance-free activity participation

Accurate characterization of delay discounting: a multiple model approach using approximate Bayesian model selection and a unified discounting measure.

Abstract: The study of delay discounting, or valuation of future rewards as a function of delay, has contributed to understanding the behavioral economics of addiction. Accurate characterization of discounting can be furthered by statistical model selection given that many functions have been proposed to measure future valuation of rewards. The present study provides a convenient Bayesian model selection algorithm that selects the most probable discounting model among a set of candidate models chosen by the researcher. The approach assigns the most probable model for each individual subject. Importantly, effective delay 50 (ED50) functions as a suitable unifying measure that is computable for and comparable between a number of popular functions, including both one- and two-parameter models. The combined model selection/ED50 approach is illustrated using empirical discounting data collected from a sample of 111 undergraduate students with models proposed by Laibson (1997); Mazur (1987); Myerson & Green (1995); Rachlin (2006); and Samuelson (1937). Computer simulation suggests that the proposed Bayesian model selection approach outperforms the single model approach when data truly arise from multiple models. When a single model underlies all participant data, the simulation suggests that the proposed approach fares no worse than the single model approach.

The effects of the framing of time on delay discounting

Abstract: We examined the effects of the framing of time on delay discounting. Delay discounting is the process by which delayed outcomes are devalued as a function of time. Time in a titrating delay discounting task is often framed in calendar units (e.g., as 1 week, 1 month, etc.). When time is framed as a specific date, delayed outcomes are discounted less compared to the calendar format. Other forms of framing time; however, have not been explored. All participants completed a titrating calendar unit delay-discounting task for money. Participants were also assigned to one of two delay discounting tasks: time as dates (e.g., June 1st, 2015) or time in units of days (e.g., 5000 days), using the same delay distribution as the calendar delay-discounting task. Time framed as dates resulted in less discounting compared to the calendar method, whereas time framed as days resulted in greater discounting compared to the calendar method. The hyperboloid model fit best compared to the hyperbola and exponential models. How time is framed may alter how participants attend to the delays as well as how the delayed outcome is valued. Altering how time is framed may serve to improve adherence to goals with delayed outcomes.

Choice architecture: A review of why nudge: The politics of libertarian paternalism

Abstract: Sunstein argues for an exception to John Stuart Mill's principle that government should never interfere with a person's freedom of choice for the person's “own good” unless that choice will harm others. If a particular government-imposed contingency is soft rather than harsh, if it acts on means rather than ends, if all alternatives remain available, and if the person herself would ultimately have chosen the alternative now made less costly, more salient, or easier to obtain, then that governmental control is a nudge, and for Sunstein nudges are permissible. Sunstein couches his recommendations in a dichotomy between two internal processes (System 1 and System 2) corresponding to areas of the brain governing fast, intuitive thinking and slow, analytic thinking. Nudges nudge people in a direction governed by System 2. This internalization and dichotomization of what is essentially a continuum between long-term, more abstract contingencies and short-term, less abstract contingencies may divert the reader's attention away from the contingencies themselves. Such diversion, if it were taken seriously, would hinder the development of effective and at the same time gentle nudges. Fortunately, none of the nudges proposed by Sunstein depend on the “psychology” represented by System 1 and System 2. The book remains focused on choice architecture. The behavioristic reader can easily translate from neurocognitive to behavioral terms and so see nudges as means of bringing behavior under the control of wide and abstract reinforcer contingencies.

Behavioral economic analysis of stress effects on acute motivation for alcohol.

Abstract: Due to issues of definition and measurement, the heavy emphasis on subjective craving in the measurement of acute motivation for alcohol and other drugs remains controversial. Behavioral economic approaches have increasingly been applied to better understand acute drug motivation, particularly using demand curve modeling via purchase tasks to characterize the perceived reinforcing value of the drug. This approach has focused on using putatively more objective indices of motivation, such as units of consumption, monetary expenditure, and price sensitivity. To extend this line of research, the current study used an alcohol purchase task to determine if, compared to a neutral induction, a personalized stress induction would increase alcohol demand in a sample of heavy drinkers. The stress induction significantly increased multiple measures of the reinforcing value of alcohol to the individual, including consumption at zero price (intensity), the maximum total amount of money spent on alcohol (Omax), the first price where consumption was reduced to zero (breakpoint), and the general responsiveness of consumption to increases in price (elasticity). These measures correlated only modestly with craving and mood. Self-reported income was largely unrelated to demand but moderated the influence of stress on Omax. Moderation based on CRH-BP genotype (rs10055255) was present for Omax, with T allele homozygotes exhibiting more pronounced increases in response to stress. These results provide further support for a behavioral economic approach to measuring acute drug motivation. The findings also highlight the potential relevance of income and genetic factors in understanding state effects on the perceived reinforcing value of alcohol.

Impulsive choice, alcohol consumption, and pre‐exposure to delayed rewards: II. Potential mechanisms

Abstract: In a prior study (Stein et al., 2013), we reported that rats pre-exposed to delayed rewards made fewer impulsive choices, but consumed more alcohol (12% wt/vol), than rats pre-exposed to immediate rewards. To understand the mechanisms that produced these findings, we again pre-exposed rats to either delayed (17.5 s; n = 32) or immediate (n = 30) rewards. In post-tests, delay-exposed rats made significantly fewer impulsive choices at both 15- and 30-s delays to a larger, later food reward than the immediacy-exposed comparison group. Behavior in an open-field test provided little evidence of differential stress exposure between groups. Further, consumption of either 12% alcohol or isocaloric sucrose in subsequent tests did not differ between groups. Because Stein et al. introduced alcohol concentration gradually (3–12%), we speculate that their group differences in 12% alcohol consumption were not determined by alcohol’s pharmacological effects, but by another variable (e.g., taste) that was preserved as an artifact from lower concentrations. We conclude that pre-exposure to delayed rewards generalizes beyond the pre-exposure delay; however, this same experimental variable does not robustly influence alcohol consumption.

Delay discounting and the use of mindful attention versus distraction in the treatment of drug addiction: a conceptual review.

Abstract: In recent decades, researchers have integrated measurements of delay discounting, how the subjective valuation of a reward changes as a function of time, into their study of addiction. Research has begun to explore the idea that delay discounting may serve as both a marker for the effectiveness of existing treatments for addiction and a potential target for novel intervention strategies. As this work is in its infancy, many potentially significant connections between the construct of delay discounting and the treatment of addiction have yet to be explored. Here, we present a conceptual review highlighting novel points of intersection between delay discounting and two approaches to treating addiction that have become increasingly popular in recent years: those that focus on the development of mindfulness skills and those that emphasize the use of distraction techniques. Viewing these two techniques through the lens of delay discounting is particularly intriguing because of the very different way that they address the experience of drug cravings in the present moment (nonjudgmentally attending to vs. shifting attention away from subjective cravings, respectively). We propose that these opposing strategies for dealing with cravings may interact with delay discounting in ways that have important implications for treatment effectiveness.

Conditioned reinforcement and information theory reconsidered.

Abstract: The idea that stimuli might function as conditioned reinforcers because of the information they convey about primary reinforcers has a long history in the study of learning. However, formal application of information theory to conditioned reinforcement has been largely abandoned in modern theorizing because of its failures with respect to observing behavior. In this paper we show how recent advances in the application of information theory to Pavlovian conditioning offer a novel approach to conditioned reinforcement. The critical feature of this approach is that calculations of information are based on reductions of uncertainty about expected time to primary reinforcement signaled by a conditioned reinforcer. Using this approach, we show that previous failures of information theory with observing behavior can be remedied, and that the resulting framework produces predictions similar to Delay Reduction Theory in both observing-response and concurrent-chains procedures. We suggest that the similarity of these predictions might offer an analytically grounded reason for why Delay Reduction Theory has been a successful theory of conditioned reinforcement. Finally, we suggest that the approach provides a formal basis for the assertion that conditioned reinforcement results from Pavlovian conditioning and may provide an integrative approach encompassing both domains.

The effects of tact training on the development of analogical reasoning.

Abstract: This study assessed whether tact training would establish analogies as measured by equivalence-equivalence relations. In Experiment 1, six college students were trained to tact "same" or "different" in the presence of AB and BC compounds based on component class membership (e.g., A1B1 as "same", and A1B2 as "different"), and then tested on emergent tacts (BA, CB, AC, CA) and equivalence-equivalence relations. Only one of six participants passed all tests without remedial training. In Experiment 2, six college students were trained to tact only compounds belonging to the same class as "same". Three of six participants passed all tests without remedial training. In Experiment 3, six college students were trained to tact stimuli belonging to the same class with a common name prior to exposure to relational tact training. All participants passed tests without remedial training. In Experiment 4, eight college students were trained to tact stimuli belonging to the same class with a common name. Six participants passed without remedial training, while two, who did not tact the relation of the compounds, did not. Results from these studies suggest that simple discrimination of individual components and their relation in the form of tacts is related with equivalence performance.

Measurement of impulsive choice in rats: same- and alternate-form test-retest reliability and temporal tracking.

Abstract: Impulsive choice is typically measured by presenting smaller–sooner (SS) versus larger–later (LL) rewards, with biases towards the SS indicating impulsivity. The current study tested rats on different impulsive choice procedures with LL delay manipulations to assess same-form and alternate-form test– retest reliability. In the systematic-GE procedure (Green & Estle, 2003), the LL delay increased after several sessions of training; in the systematic-ER procedure (Evenden & Ryan, 1996), the delay increased within each session; and in the adjusting-M procedure (Mazur, 1987), the delay changed after each block of trialswithin asessionbased on each rat’s choices inthepreviousblock. Inaddition tomeasuringchoice behavior, we also assessed temporal tracking of the LL delays using the median times of responding during LL trials. The two systematic procedures yielded similar results in both choice and temporal tracking measures following extensive training, whereas the adjusting procedure resulted in relatively more impulsive choices and poorer temporal tracking. Overall, the three procedures produced

Is it patience or motivation? On motivational confounds in intertemporal choice tasks

Abstract: Intertemporal choices create a tension between amount maximization, which would favor the larger and later option (LL), and delay minimization, which would promote the smaller and sooner reward (SS). Two common interpretations of intertemporal choice behavior are discussed: looking at LL responses as indicative of self-control, and using intertemporal choices to assess delay aversion. We argue that both interpretations need to take into account motivational confounds, in order to be warranted by data. In intertemporal choices with prepotent, salient stimuli (e.g., food amounts, typically used with nonhuman primates), LL responses could also be indicative of failed inhibition of a "go for more" impulsive response-the opposite of self-control. Similarly, intertemporal choices can be used to measure delay aversion only with respect to the subject's baseline motivation to maximize the reinforcer in question, and this baseline is not always assessed in current experimental protocols. This concern is especially crucial in comparing intertemporal choices across different groups or manipulation. We focus in particular on the effects of reward types on intertemporal choices, presenting two experimental studies where the difference in behavior with monetary versus food rewards is the product of different baseline motivation, rather than variations in delay aversion. We conclude discussing the implications of these and other similar recent findings, which are far-reaching.

Emergence of visual–visual conditional discriminations

Abstract: We assessed the emergence of visual-visual conditional discriminations following training of vocal tact and intraverbal relations. Ten preschool-age children learned to vocally tact six visual stimuli, A1 through B3. Next, they learned to respond intraverbally to the dictated names of A1, A2, and A3 by vocalizing the names of B1, B2, and B3, respectively. Emergent A-B and B-A relations were tested in a visual-visual match-to-sample (MTS) task. Five of ten participants passed the test, with or without a prompt to tact the sample stimulus. Four of the five failed a reverse intraverbal test that involved responding to dictated names of B stimuli by vocalizing names of A stimuli. The remaining participants failed the MTS test, apparently due to failures to maintain the trained vocal responses throughout testing. Accurate MTS performance in the absence of bidirectional intraverbal relations appears to contradict Horne and Lowe's (1996) analysis of the possible role of intraverbal naming in emergent stimulus control.

Low-cost USB interface for operant research using Arduino and Visual Basic.

Abstract: This note describes the design of a low-cost interface using Arduino microcontroller boards and Visual Basic programming for operant conditioning research. The board executes one program in Arduino programming language that polls the state of the inputs and generates outputs in an operant chamber. This program communicates through a USB port with another program written in Visual Basic 2010 Express Edition running on a laptop, desktop, netbook computer, or even a tablet equipped with Windows operating system. The Visual Basic program controls schedules of reinforcement and records real-time data. A single Arduino board can be used to control a total of 52 inputs/output lines, and multiple Arduino boards can be used to control multiple operant chambers. An external power supply and a series of micro relays are required to control 28-V DC devices commonly used in operant chambers. Instructions for downloading and using the programs to generate simple and concurrent schedules of reinforcement are provided. Testing suggests that the interface is reliable, accurate, and could serve as an inexpensive alternative to commercial equipment.

Enhanced equivalence class formation by the delay and relational functions of meaningful stimuli

Abstract: Undergraduates in six groups of 10 attempted to form three 3-node 5-member equivalence classes (A → B → C → D → E) under the simultaneous protocol. In five of six groups, all stimuli were abstract shapes; in the PIC group, C stimuli were pictures with the remainder being abstract shapes. Before class formation, participants in the Identity-S and Identity-D groups were given preliminary training to form identity conditional discriminations with the C stimuli using simultaneous and 6 s delayed matching-to-sample procedures, respectively. In the Arbitrary-S and Arbitrary-D groups, before class formation, arbitrary conditional discriminations were formed between C and X stimuli using simultaneous and 6 s delayed matching-to-sample procedures, respectively. With no preliminary training, classes in the PIC and ABS groups were formed by 80% and 0% of participants, respectively. After preliminary training, class formation (yield) increased with delay, regardless of relational type. For each of the two delays, yield was slightly greater after forming arbitrary- instead of identity-relations. Yield was greatest, however, when a class contained a meaningful stimulus (PIC). During failed class formation, probes produced experimenter-defined relations, participant-defined relations, and unsystematic responding; delay, but not the relation type in preliminary training influenced relational and indeterminate responding. These results suggest how meaningful stimuli enhance equivalence class formation.

When good pigeons make bad decisions: Choice with probabilistic delays and outcomes.

Abstract: Pigeons chose between an (optimal) alternative that sometimes provided food after a 10-s delay and other times after a 40-s delay and another (suboptimal) alternative that sometimes provided food after 10 s but other times no food after 40 s. When outcomes were not signaled during the delays, pigeons strongly preferred the optimal alternative. When outcomes were signaled, choices of the suboptimal alternative increased and most pigeons preferred the alternative that provided no food after the long delay despite the cost in terms of obtained food. The pattern of results was similar whether the short delays occurred on 25% or 50% of the trials. Shortening the 40-s delay to food sharply reduced suboptimal choices, but shortening the delay to no food had little effect. The results suggest that a signaled delay to no food does not punish responding in probabilistic choice procedures. The findings are discussed in terms of conditioned reinforcement by signals for good news.

The transfer of Cfunc contextual control through equivalence relations.

Abstract: Derived relational responding is affected by contextual stimuli (Cfunc) that select specific stimulus functions. The present study investigated the transfer of Cfunc contextual control through equivalence relations by evaluating both (a) the maintenance of Cfunc contextual control after the expansion of a relational network, and (b) the establishment of novel contextual stimuli by the transfer of Cfunc contextual control through equivalence relations. Initially, equivalence relations were established and contingencies were arranged so that colors functioned as Cfunc stimuli controlling participants' key-pressing responses in the presence of any stimulus from a three-member equivalence network. To investigate the first research question, the three-member equivalence relations were expanded to five members and the novel members were presented with the Cfunc stimuli in the key-pressing task. To address the second goal of this study, the colors (Cfunc) were established as equivalent to certain line patterns. The transfer of contextual cue function (Cfunc) was tested replacing the colored backgrounds with line patterns in the key-pressing task. Results suggest that the Cfunc contextual control was transferred to novel stimuli that were added to the relational network. In addition, the line patterns indirectly acquired the contextual cue function (Cfunc) initially established for the colored backgrounds. The conceptual and applied implications of Cfunc contextual control are discussed.

Arbitrary conditional discriminative functions of meaningful stimuli and enhanced equivalence class formation

Abstract: Equivalence class formation by college students was influenced through the prior acquisition of conditional discriminative functions by one of the abstract stimuli (C) in the to-be-formed classes. Participants in the GR-0, GR-1, and GR-5 groups attempted to form classes under the simultaneous protocol, after mastering 0, 1, or 5 conditional relations between C and other abstract stimuli (V, W, X, Y, Z) that were not included in the to-be-formed classes (ABCDE). Participants in the GR-many group attempted to form classes that contained four abstract stimuli and one meaningful picture as the C stimulus. In the GR-0, GR-1, GR-5, and GR-many groups, classes were formed by 17, 25, 58, and 67% of participants, respectively. Thus, likelihood of class formation was enhanced by the prior formation of five C-based conditional relations (the GR-5 vs. GR-0 condition), or the inclusion of a meaningful stimulus as a class member (the GR-many vs. GR-0 condition). The GR-5 and GR-many conditions produced very similar yields, indicating that class formation was enhanced to a similar degree by including a meaningful stimulus or an abstract stimulus that had become a member of five conditional relations prior to equivalence class formation. Finally, the low and high yields produced by the GR-1 and GR-5 conditions showed that the class enhancement effect of the GR-5 condition was due to the number of conditional relations established during preliminary training and not to the sheer amount of reinforcement provided while learning these conditional relations. Class enhancement produced by meaningful stimuli, then, can be attributed to their acquired conditional discriminative functions as well as their discriminative, connotative, and denotative properties.

Effects of select and reject control on equivalence class formation and transfer of function

Abstract: The present study used a single-subject design to evaluate the effects of select or reject control on equivalence class formation and transfer of function. Adults were exposed to a matching-to-sample task with observing requirements (MTS-OR) in order to bias the establishment of sample/S+ (select) or sample/S- (reject) relations. In Experiment 1, four sets of baseline conditional relations were taught-two under reject control (A1B2C1, A2B1C2) and two under select control (D1E1F1, D2E2F2). Participants were tested for transitivity, symmetry, equivalence and reflexivity. They also learned a simple discrimination involving one of the stimuli from the equivalence classes and were tested for the transfer of the discriminative function. In general, participants performed with high accuracy on all equivalence-related probes as well as the transfer of function probes under select control. Under reject control, participants had high scores only on the symmetry test; transfer of function was attributed to stimuli programmed as S-. In Experiment 2, the equivalence class under reject control was expanded to four members (A1B2C1D2; A2B1C2D1). Participants had high scores only on symmetry and on transitivity and equivalence tests involving two nodes. Transfer of function was extended to the programmed S- added to each class. Results from both experiments suggest that select and reject controls might differently affect the formation of equivalence classes and the transfer of stimulus functions.

The effects of listener training on discriminative control by elements of compound stimuli in children with disabilities

Abstract: The purpose of the current study was to assess whether the establishment of listener relations with compound stimuli as samples and comparisons would lead to the emergence of: (1) speaker behavior in the form of tacts of the compound stimuli; (2) listener and tact responses for untaught compounds; and (3) listener and tact responses for the isolated properties of compounds. Participants were four boys diagnosed with autism and one diagnosed with intellectual disability. We taught participants to select among three compound comparisons consisting of combinations of shapes and patterns in the presence of the corresponding dictated word. Subsequently, we tested for the emergence of tacts for the trained compounds, as well as tact and listener relations for six untaught compounds and their properties. In general, results showed that the acquisition of listener relations led to the emergence of the corresponding tacts, as well as the emergence of listener and tact responses for untaught combinations for three out of five participants. By contrast, the other two participants showed responding characteristic of restricted stimulus control. These results suggest that the establishment of bidirectional relations between listener and speaker behaviors may facilitate the emergence of control by properties of compound stimuli.

Intraverbal naming and equivalence class formation in children.

Abstract: Six typically developing children between 5 and 7 years of age underwent match-to-sample training to establish three-member equivalence classes after first acquiring a unique name for each stimulus. Horne and Lowe's (1996) naming hypothesis predicts that under those circumstances, match-to-sample training contingencies may establish intraverbal relations between the unique names, which in turn guide correct responses on a subsequent test for stimulus equivalence. Following training of baseline relations (AB and AC), participants received an equivalence test followed by an intraverbal test. Performance on the two tests co-varied, such that three participants passed both tests, and three participants failed repeated administrations of both tests, including a modified version of the equivalence test designed to promote intraverbal responding. The participants who failed the equivalence test, however, did so primarily due to poor performance in transitivity trials, but performed accurately in symmetry trials. After training of a third relation (BC), all three participants performed accurately in a symmetry test for the remaining untrained relations (BA, CA, and CB); two of them in the absence of relevant intraverbal repertoires.

Delay-specific stimuli and genotype interact to determine temporal discounting in a rapid-acquisition procedure.

Abstract: The importance of delay discounting to many socially important behavior problems has stimulated investigations of biological and environmental mechanisms responsible for variations in the form of the discount function. The extant experimental research, however, has yielded disparate results, raising important questions regarding Gene X Environment interactions. The present study determined the influence of stimuli that uniquely signal delays to reinforcement on delay discounting in two inbred mouse strains using a rapid-acquisition procedure. BALB/c and C57BL/6 mice responded under a six-component, concurrent-chained schedule in which the terminal-link delays preceding the larger-reinforcer were presented randomly across components of an individual session. Across conditions, components were presented either with or without delay-specific auditory stimuli, i.e., as multiple or mixed schedules. A generalized matching-based model was used to incorporate the impact of current and previous component reinforcer-delay ratios on current component response allocation. Sensitivity to reinforcer magnitude and delay were higher for BALB/c mice, but within-component preference reached final levels faster for C57Bl/6 mice. For BALB/c mice, acquisition of preference across blocks of a component was faster under the multiple than the mixed schedule, but final levels of sensitivity to reinforcement were unaffected by schedule. The speed of acquisition of preference was not different across schedules for C57Bl/6 mice, but sensitivity to reinforcement was higher under the multiple than the mixed schedule. Overall, differences in the acquisition and final form of the discount function were determined by a Gene X Environment interaction, but the presence of delay-specific stimuli attenuated genotype-dependent differences in magnitude and delay sensitivity.

Emergent identity but not symmetry following successive olfactory discrimination training in rats

Abstract: The search for symmetry in nonhuman subjects has been successful in recent studies in pigeons (e.g., Urcuioli, 2008). The key to these successes has been the use of successive discrimination procedures and combined training on identity, as well as arbitrary, baseline relations. The present study was an effort to extend the findings and theoretical analysis developed by Urcuioli and his colleagues to rats using olfactory rather than visual stimuli. Experiment 1 was a systematic replication of Urcuioli's (2008) demonstration of symmetry in pigeons. Rats were exposed to unreinforced symmetry probes following training with two arbitrary and four identity conditional discriminations. Response rates on symmetry probe trials were low and provided little evidence for emergent symmetry in any of the seven rats tested. In Experiment 2, a separate group of six rats was trained on four identity relations and was then exposed to probe trials with four novel odor stimuli. Response rates were high on identity probe trials, and low on nonmatching probe trials. The similar patterns of responding on baseline and probe trials that were shown by most rats provided a demonstration of generalized identity matching. These findings suggest that the development of stimulus control topographies in rats with olfactory stimuli may differ from those that emerge in pigeons with visual stimuli. Urcuioli's (2008) theory has been highly successful in predicting conditions necessary for stimulus class formation in pigeons, but may not be sufficient to fully understand determinants of emergent behaviors in other nonhuman species.

The recurrence of negatively reinforced responding of humans

Abstract: The recurrence of negatively reinforced responding of humans was studied in three experiments. In each experiment during Baseline, key-pressing produced 3-s timeouts from a requirement to exert finger pressure on a force cell according to variable- or fixed-ratio schedules of reinforcement. In Experiment 1, resurgence was studied by arranging a differential-reinforcement-of-other-behavior schedule in the second phase, and extinction in the Test phase. In Experiment 2, ABA renewal was studied by extinguishing responding in the second phase in a different context and, in the Test phase, by presenting the Baseline-phase context when extinction still was in effect. In Experiment 3, reinstatement was studied by arranging extinction in the second phase, followed by the delivery of response-independent timeouts in the Test phase. Resurgence and renewal occurred consistently for each participant in Experiments 1 and 2, respectively. In Experiment 3, reinstatement was observed less consistently in four participants. The results of these experiments replicate and extend to negatively reinforced responding previous findings of the resurgence and renewal of positively reinforced responding obtained mainly with nonhuman animals.

The distribution of response bout lengths and its sensitivity to differential reinforcement.

Abstract: Response bouts are clusters of responses that occur in rapid succession and are punctuated by pauses during which the response does not occur. Under variable interval schedules of reinforcement, the number of responses in each bout (the bout length) varies among bouts. This experiment was aimed at determining whether the relative rate of reinforcement influenced the relative frequency of bouts of different lengths. Lever pressing in rats was reinforced under a tandem variable time (VT) 150-s fixed ratio (FR) X, where X could be 1 or 5 and varied randomly after each reinforcer. Two conditions were included: majority FR1 (mFR1) and majority FR5 (mFR5). In mFR1, 75% of reinforcers had a tandem FR requirement of 1 and 25% had a tandem FR requirement of 5; this distribution was reversed in mFR5. The dynamic bi-exponential refractory model of response bouts was fitted to the interresponse times (IRTs) in each condition. Model parameter estimates and IRTs were then used to simulate probable distributions of bout lengths. These distributions comprised a mixture of short geometrically-distributed bout lengths and long negative-binomially-distributed bout lengths. Long bouts were significantly longer in the mFR5 condition than in the mFR1 condition. In conjunction with previous data, the present study suggests that the prevalence of long bouts increases with the proportion of reinforcers with FR5 requirement. These results suggest that bouts of different lengths are sensitive to the rate at which they are reinforced.

Timing in response-initiated fixed intervals

Abstract: Different events can serve as time markers that initiate intervals in schedules of reinforcement. Pigeons were exposed to fixed-interval (FI) schedules in which the onset of the interval was signaled by the illumination of a key light or initiated by a peck to a lighted key. Food was delivered following the first response after the interval elapsed. In Experiment 1, three pigeons were exposed to a multiple schedule. One component was a standard FI schedule: Key light illumination signaled the onset of the interval. The other component was a response-initiated fixed-interval (RIFI) schedule: The first key-peck response determined the onset of the interval. In Experiment 2, three pigeons were exposed to a multiple FI-RIFI schedule of reinforcement and on occasional trials food was not delivered (i.e. "no-food" or "peak trials"). A yoking procedure equated reinforcement rates between the schedule types in both experiments. Absolute response rates early in the intervals were higher in the RIFI schedules of both experiments. Normalized response-rate gradients, ogive fits of normalized response gradients, and breakpoints were not systematically different for the schedule types in Experiment 1, indicating similar patterns of responding between interval onset and food delivery. However, during peak trials in Experiment 2 the duration of responding at a high rate was longer for RIFI schedules than FI schedules. This suggests that timing precision was reduced in the RIFI schedules and that relative "distinctiveness" of a time marker may determine its efficacy.

The logistics of choice

Abstract: The generalized matching law (GML) is reconstructed as a logistic regression equation that privileges no particular value of the sensitivity parameter, a. That value will often approach 1 due to the feedback that drives switching that is intrinsic to most concurrent schedules. A model of that feedback reproduced some features of concurrent data. The GML is a law only in the strained sense that any equation that maps data is a law. The machine under the hood of matching is in all likelihood the very law that was displaced by the Matching Law. It is now time to return the Law of Effect to centrality in our science.

Working‐memory training: Effects on delay discounting in male long evans rats

Abstract: Delay discounting describes the devaluation of a reward as the delay to the receipt of the reward increases. Because steep delay discounting is robustly correlated with a number of behavioral problems (e.g., substance dependence, gambling) and some evidence suggests steep discounting precedes and predicts drug-taking in humans and rats, this study sought to experimentally reduce rats' delay discounting. Human stimulant-dependent participants given working-memory training reportedly decreased their rates of discounting relative to a sham-training group (Bickel, Yi, Landes, Hill, & Baxter, 2011). To evaluate the cross-species generality of this effect, 38 male Long-Evans rats, matched on pretraining delay-discounting rates, were randomly assigned to receive 140 sessions of working-memory training or sham training (which required no memory of the sample stimulus). Large between-group differences in working memory were observed after training; however, posttraining delay-discounting rates were undifferentiated across groups. Potential explanations for these findings are discussed.

The arithmetic of discounting.

Abstract: Most current models of delay discounting multiply the nominal value of a good whose receipt is delayed, by a discount factor that is some function of that delay. This article reviews the logic of a theory that discounts the utility of delayed goods by adding the utility of the good to the disutility of the delay. In limiting cases it approaches other familiar models, such as hyperbolic discounting. In nonlimit cases it makes different predictions, generally requiring, inter alia, a magnitude effect when the value of goods is varied. A different theory is proposed for conditioning experiments. In it utility is computed as the average reinforcing strength of the stimuli that signal the delay. Both theories are extended to experiments in which degree of preference is measured, rather than adjustment to iso-utility values.