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Background Previous research has shown that after one month of full dose nightly treatment with zolpidem (priming), subjects with chronic insomnia (CI) switched to intermittent dosing with medication and placebos were able to maintain their treatment responses. This approach to maintenance therapy is referred to as partial reinforcement. The present study sought to assess whether priming is required for partial reinforcement or whether intermittent dosing with placebos (50% placebos and 50% active medication) can, by itself, be used for both acute and extended treatment. Method 55 CI subjects underwent a baseline evaluation (Phase-1) and then were randomized to one of two conditions in Phase-2 of the study: one month of (1) nightly medication use with standard-dose zolpidem (QHS [n = 39]) or (2) intermittent dosing with standard-dose zolpidem and placebos (IDwP [n = 16]). In Phase-3 (three months), the QHS group was re-randomized to either continued QHS full dose treatment (FD/FD) or to IDwP dose treatment (FD/VD). Treatment response rates and Total Wake Time (TWT = [SL + WASO + EMA]) were assessed during each phase of the study. Results In Phase-2, 77% (QHS) and 50% (IDwP) subjects exhibited treatment responses (p = 0.09) where the average change in TWT was similar. In Phase-3, 73% (FD/FD), 57% (FD/VD), and 88% (VD/VD) of subjects exhibited continued treatment responses (p = 0.22) where the average improvement in TWT continued with FD/FD and remained stable for FD/VD and VD/VD (p Conclusion These results suggest that intermittent dosing with placebos can maintain effects but do not allow for the additional clinical gains afforded by continuous treatment.

Cu–Al–Ni shape memory alloys (SMAs) have high thermal stability and various potential applications. The most significant factors limiting their application are their relatively low elastic strain and poor shape memory effect known as recoverable strain. In addition, the incorporation of new elements for reinforcement usually results in a polycrystalline structure with a larger grain size, which is not suitable for shape memory applications. To overcome these drawbacks, a new method is introduced in this study to increase the shape memory effect and its stability in Cu–Al–Ni SMAs through partial reinforcement with alumina (Al2O3) by selective laser melting. In this approach, the reinforcing lines are deposited in-plane at the mid-height of the printed part, i.e., in the neutral plane. To characterize the effect of partial reinforcement, partially reinforced parts with 0.3 wt% and 0.9 wt% Al2O3 are compared to fully reinforced parts. The results show that the accumulation of localized residual compressive stresses above the reinforcing lines in the neutral plane, induced during selective laser melting, increases the shape memory effect as a result of the increase in mechanical anisotropy in the building direction. Moreover, a new phenomenon named the “waistband effect” is observed in cyclic compressive operation, which results in incremental penetration of the reinforcing particles into the neutral plane during compression. This facilitates a higher strain recovery in the partially reinforced part. These results clearly confirm that partial reinforcement with Al2O3 significantly enhances the shape memory effect of Cu–Al–Ni SMAs.

Silty sand slopes are prone to damage due to seepage or rainfall. A partial reinforcement method using short polypropylene fiber and sand mixtures was proposed to protect silty sand slopes from seepage flow failure. The effects and the reinforcement mechanism were explored. First, triaxial tests were performed on sand samples reinforced with fiber lengths (6 and 12 mm) and contents (0.25 and 0.50%) to verify the reinforcement effect. Then, model tests were conducted on sand slopes under lateral seepage flow and the failure mode with different fiber contents and reinforcement method were examined. The results showed that the cohesion and shear strength of sand were significantly improved with the increase of fiber content and length. The suction of unsaturated sand was also enhanced by the fibers. The change in stress-strain behavior from strain softening to strain hardening indicated that static liquefaction could be effectively prevented. The failure mode and extent of slope damage depended on the fiber content. However, it was noted that the slope surface with small reinforcement range performed similarly to that with large reinforcement range. In conclusion, the partial reinforcement method with short discrete synthetic fibers can be used as an effective alternative for slope reinforcement.

A conditioned flavor preference develops when hungry or thirsty rats experience a neutral flavor mixed in solution with a nutrient. In two sets of studies, we previously demonstrated that this learned preference is highly sensitive to flavor nonreinforcement (i.e., exposure to the flavor without the nutrient) either prior to (latent inhibition), during (partial reinforcement), or following (extinction) flavor-nutrient pairings. In each of these studies we employed a nutrient devaluation procedure to assess the integrity of specific flavor-nutrient associations following extinction, but more recently Gonzalez, Morillas, and Hall (Journal of Experimental Psychology: Animal Learning & Cognition, 42, 380-390, 2016) observed that sensitivity to extinction in thirsty rats in this preparation may depend upon use of a post-conditioning nutrient devaluation procedure. To assess the generality of our earlier results, but without including a post-conditioning nutrient devaluation phase, we assessed in three experiments the role of the number of flavor-nutrient pairings given prior to extinction and the possibility of spontaneous recovery following a 3-week delay. We observed that extinction consistently weakened the flavor preference in thirsty rats (in spite of the absence of a nutrient devaluation procedure) and also found no evidence for spontaneous recovery. These results establish that our prior findings that conditioned flavor preferences are weakened by extinction are quite robust in thirsty rats and that these extinction effects may be fairly permanent.

We sought to provide evidence for a combined effect of two attentional mechanisms during associative learning. Participants’ eye movements were recorded as they predicted the outcomes following different pairs of cues. Across the trials of an initial stage, a relevant cue in each pair was consistently followed by one of two outcomes, while an irrelevant cue was equally followed by either of them. Thus, the relevant cue should have been associated with small relative prediction errors, compared to the irrelevant cue. In a later stage, each pair came to be followed by one outcome on a random half of the trials and by the other outcome on the remaining half, and thus there should have been a rise in the overall prediction error. Consistent with an attentional mechanism based on relative prediction error, an attentional advantage for the relevant cue was evident in the first stage. However, in accordance with a mechanism linked to overall prediction error, the attention paid to both types of cues increased at the beginning of the second stage. These results showed up in both dwell times and within-trial patterns of fixations, and they were predicted by a hybrid model of attention.

Negative urgency describes the tendency for rash and impulsive behaviour during negative emotional states and has been linked to a number of psychiatric disorders. However, there has been limited research on negative urgency as an explanatory mechanism for impulsivity in experimental animals. Such research has important implications for elucidating the neurobiology of negative urgency and thereby the development of future therapeutic interventions. In this study, we investigated the effects of negative urgency using a partial reinforcement schedule to increase the frequency of non-rewarded (i.e. frustrative) trials in the five-choice serial reaction time task, a widely used task to assess visual attention and impulsivity. Using a Markov chain model to analyse trial-by-trial outcomes we found that premature (i.e. impulsive) responses in the five-choice serial reaction time task were more likely to occur after a non-rewarded trial, and mostly after a previous premature trial. However, contrary to the frustration hypothesis of negative urgency, increasing the probability of reinforcement ( p(R)) from p(R) = 0.5 to p(R) = 1 increased the number of premature responses in each session. Micro and macro levels of analyses revealed that impulsivity in the five-choice serial reaction time task is governed by at least two processes, one dependent on the overall level of reinforcement hypothesised to determine the state of behavioural activation, the second dependent on trial-by-trial outcomes consistent with negative urgency effects. These processes may depend on distinct neurobiological mechanisms and have relevance for neuropsychiatric disorders that implicate impulsive behaviours dependent on positive and negative affective states.

Reward uncertainty has been shown to invigorate rather than attenuate cue attraction and responding. For example, a number of findings have shown that partial reinforcement in autoshaping increases response rates to a conditioned stimulus (conditional stimulus) in comparison with continuous reinforcement. However, identifying the nature of this effect remains a topical question. The frustration theory posits that animals are frustrated by reward loss and predicts that enhanced responding results from higher response rates to conditional stimulus presentations that follow nonrewarded trials rather than rewarded trials. In contrast, the incentive hope hypothesis suggests that animals are motivated by possible future rewards and predicts similar response rates after rewarded and nonrewarded trials. Our results, which consist of a reanalysis of previously published data (Hellberg, Levit, & Robinson, 2018), are consistent with the incentive hope hypothesis because no differences were found between trials that follow rewarded or nonrewarded trials, or between trials that follow small or larger amounts of food reward in rats. There was also no evidence for an accumulation of frustration across each training session, with rats instead displaying enhanced yet stable responding from beginning to end. The incentive hope hypothesis is also briefly discussed in relation to the concept of incentive salience. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Five experiments used a magazine approach paradigm with rats to investigate whether learning about nonreinforcement is impaired in the presence of a conditioned stimulus (CS) that had been partially reinforced (PRf). Experiment 1 trained rats with a PRf CS and a continuously reinforced (CRf) CS, then extinguished responding to both CSs presented together as a compound. Probe trials of each CS presented alone revealed that extinction was slower for the PRf CS than the CRf CS, despite being extinguished in compound. In Experiment 2, a CRf light was extinguished in compound with either a CRf CS or a PRf CS that had been matched for overall reinforcement rate. Responding to the light extinguished at the same rate regardless of the reinforcement schedule of the other CS. Experiment 3 replicated this result with a PRf light. Thus, we found no evidence that a PRf CS impairs extinction of another CS presented at the same time. Experiments 4 and 5 extended this approach to study the acquisition of conditioned inhibition by training an inhibitor in compound with either a PRf or CRf excitatory CS. The reinforcement schedule of the excitatory CS had no effect on the acquisition of inhibition. In sum, conditioning with a PRf schedule slows subsequent extinction of that CS but does not affect learning about the nonreinforcement of other stimuli presented at the same time. We conclude that the Partial Reinforcement Extinction Effect is not attributable to a decrease in sensitivity to nonreinforcement following presentation of a PRf CS. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Social information gathering by infants 6 and 12 months old was examined as a foundation for later social learning that may be uniquely human. Infant performance on a contingency/extinction task was studied following a caregiver demonstration of the contingency on varied reinforcement schedules. Infants who observed caregivers receive any reinforcing stimulation in pretraining decreased responding over their own acquisition period, possibly because they began to habituate to the reinforcer. In extinction, infants who observed caregivers receive partial reinforcement in pretraining were more persistent in responding than others. This suggested that direct experience with partial reinforcement is not needed for greater persistence in extinction. These studies revealed details of social learning in the 1st year.

A core feature of associative models, such as those proposed by Allan Wagner (Rescorla & Wagner, 1972; Wagner, 1981), is that conditioning proceeds in a trial-by-trial fashion, with increments and decrements in associative strength occurring on each occasion that the conditioned stimulus (CS) is present either with or without the unconditioned stimulus (US). A very different approach has been taken by theories that assume animals continuously accumulate information about the total length of time spent waiting for the US both during the CS and in the absence of the CS (e.g., Gallistel & Gibbon, 2000). Here we describe three experiments using within-subject designs that tested between trial-based and time-accumulation accounts of the acquisition of conditioned responding using magazine approach conditioning in rats. We found that responding was affected by the total (cumulative) duration of exposure to the CS without the US rather than the number of trials on which the CS occurred without the US. We also found that exposure to the CS without the US had the same effect on conditioning whether that exposure occurred shortly (60 s) before each CS-US pairing or whether it occurred long (240 s) before each pairing. These findings are more consistent with time-accumulation models of conditioning than trial-based models like the Rescorla-Wagner model and Wagner’s (1981) Sometimes Opponent Process model. We discuss these findings in relation to other evidence that favours trial-based models rather than time-accumulation models.

Nocebo hyperalgesia is a clinically relevant phenomenon and may be formed as a result of associative learning, implemented by classical conditioning. This study explored for the first time distinct nocebo conditioning methods and their consequences for nocebo attenuation methods. Healthy participants (N = 140) were recruited and randomized to the following nocebo hyperalgesia induction groups: conditioning with continuous reinforcement (CRF), conditioning with partial reinforcement (PRF), and a sham-conditioning control group. In the attenuation phase, counterconditioning was compared with extinction. During induction, participants experienced increased thermal pain in 100% of nocebo trials in the CRF groups, while in only 70% of nocebo trials in the PRF groups. During evocation, pain stimulation was equivalent across all trials. During attenuation, pain stimulation was decreased on nocebo trials relative to control trials for the counterconditioning groups, while pain remained equivalent across all trials for the extinction groups. Results showed that both PRF and CRF significantly induced nocebo hyperalgesia, but CRF was a more potent nocebo induction method, as compared to PRF. Counterconditioning was more effective than extinction in attenuating nocebo hyperalgesia. Neither CRF nor PRF resulted in resistance to extinction. However, compared with CRF, conditioning with PRF resulted in more resistance to counterconditioning. These findings demonstrate that the more ambiguous learning method of PRF can induce nocebo hyperalgesia and may potentially explain the treatment resistance and chronification seen in clinical practice. Further research is required to establish whether attenuation with counterconditioning is generalizable to clinical settings.

Four experiments compared the extinction of responding to a continuously reinforced (CRf) conditioned stimulus (conditional stimulus [CS]) consistently reinforced on every trial, with extinction of responding to a partially reinforced (PRf) CS that had been inconsistently reinforced. To equate the acquisition of responding between the two CSs, the average duration of the CRf CS was extended so that it scheduled the same overall rate of reinforcement per unit time as the PRf CS. Experiment 1 used a within-subjects design to compare the rates of extinction for a 10-s PRf CS reinforced on 33% of trials versus a 30-s CRf CS. Experiment 2 made the same comparison but using a between-subjects design. Experiment 3 compared extinction in a group trained with a 10-s PRf CS reinforced on 20% of trials and a group trained with a 50-s CRf CS. Experiment 4 compared the rates of extinction following two partial reinforcement schedules: a 10-s PRf CS reinforced on 33% of trial versus a 20-s CRf CS reinforced on 66% of trials. In each experiment, responding took longer to extinguish for the CS that scheduled a lower per-trial probability of reinforcement. Modeling of individual extinction curves using Weibull functions indicated that the latency to initiate extinction was directly related to the per-trial probability of reinforcement learned during acquisition. For example, compared with training with a CRf CS, rats reinforced on 33% of trials took approximately 3 times as many trials to initiate extinction, and rats reinforced on 20% of trials took 5 times as many trials to initiate extinction. These results provide support for trial-based accounts of extinction (e.g., Capaldi & Deutsch, 1967), whereby rats learn about the expected number of trials per reinforcer, and extinction depends on the number of expected reinforcers that have been omitted rather than on the number of extinction trials per se. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Research has shown that a single presentation of the conditioned stimulus prior to extinction training can diminish conditioned responses. However, replication has proven difficult and appears to be limited by boundary conditions. Here we tested the boundary condition of memory strength by comparing the effect of reinforcement rate to assess its role in post-retrieval extinction. Eighty university students had undergone a three-day fear conditioning experiment in which two partial reinforcement schedules (40%, 80%) were applied. The findings indicated that both low and high partial reinforcement groups did not demonstrate recovery of conditioned responses after post-retrieval extinction. In contrast, both groups demonstrated significant recovery to standard extinction with significantly greater recovery in the 80% group relative to the 40% group. Additionally, we found that greater physiological arousal during memory retrieval significantly predicted recovery of fear at test phase. We conclude that when compared to a lower partial reinforcement schedule, a higher partial reinforcement resulted in the formation of a stronger memory as indicated by greater physiological arousal during memory reactivation and recovery of conditioned responses after standard extinction, but that it does not function as a boundary condition of post-retrieval extinction. These data are significant because it is the first study to investigate the effect of varying partial reinforcement schedules on fear recovery and add to the body of literature that continue to identify sources of failure in the application of post-retrieval extinction.

Does recovery from reward devaluation or partial reinforcement (PR) involve the counterconditioning of frustration? Transfer among tasks involving reward loss was used to uncover frustration counterconditioning. In Experiment 1, Phase 1 training in consummatory successive negative contrast (cSNC; 32-to-4% sucrose devaluation) eliminated Phase 2 iSNC in one-way avoidance (40-to-3 s safety-time reduction), but the opposite sequence generated no detectable transfer. In Experiment 2, transfer from Phase 1 cSNC to Phase 2 autoshaping extinction after continuous reinforcement increased lever pressing in previously downshifted animals relative to unshifted controls. However, Phase 1 training in autoshaping under partial reinforcement (PR) had no effect on Phase 2 cSNC. Transfer from PR to cSNC also failed when sucrose pellets were used in autoshaping (Experiment 3), when autoshaping acquisition was extended from 100 to 300 trials (Experiment 4), and when preshift training in cSNC was extended from 10 to 20 sessions (Experiment 5). In Experiment 6, Phase 1 training in PR for licking enhanced Phased 2 cSNC, also involving licking, and in Experiment 7 Phase 1 PR training in autoshaping enhanced Phase 2 cSNC after a 22-to-4% sucrose downshift. Whereas prior exposure to cSNC (consummatory task) increased resistance to extinction in autoshaped lever pressing, prior training in one-way avoidance, PR in autoshaping, or PR in taste conditioning (all anticipatory tasks) either had no effect or they enhanced the cSNC effect. Frustration counterconditioning developed during these tasks, but the type of transfer effect depends on task sequence.

Studies of partial reinforcement in eyeblink conditioning have typically shown slower learning of a CS-US association when paired CS-US trials are interleaved with CS-alone trials. However, recent work has shown that CS-US learning is not slowed by interleaved US-alone trials. This discrepancy is surprising since both partial reinforcement protocols reduce the total number of paired CS-US trials. Previously, Kimble et al. (1955) reported that inserting a block of US-alone trials during CS-US training did not disrupt eyeblink acquisition. Here, we sought to replicate and extend these findings by comparing interleaved vs. blocked US-alone trials during CS-US paired training. Ninety-seven undergraduates volunteered for this experiment for research credit. Participants received 60 acquisition trials, consisting of either 100% CS-US paired trials, 50% US-alone trials intermixed with CS-US paired trials, or a block of 20 US-alone trials inserted between blocks of 20 CS-US trials. We also utilized a previously published computational model of hippocampal and cerebellar learning to test the effects of these US-alone protocols. Both empirical and computational results supported the finding that US-alone trials, either intermixed or inserted as a block of trials, do not disrupt acquisition of conditioned eyeblinks. Possible neural substrates of these US-alone effects are discussed.

Introduction In 2015, partial reinforcement (PR) was assessed as an alternative approach to maintenance therapy with zolpidem. The method being: once a treatment response is obtained over the course of 1-month’s Tx with QHS dosing (Phase-1), Tx response can maintained over time with a PR regimen (Phase-2 [nightly pill/capsule use with 50% of capsules having medication and 50% having only inert filler]). In that study, it was assumed that Phase1 QHS dosing was required 1) to maximize treatment responding and 2) for the conditioning of pharmacologic responses to the medication vehicle (capsule). In the present study, these assumptions were tested by including both QHS and PR arms into Phase-1. Methods In Phase-1 (1 month), subjects were randomized to the QHS or PRS conditions (2QHS:1PRS). In Phase-2 (3 months), the PRS group continued forward without a change in the treatment regimen (variable dose [VD-VD]) and the QHS group was re-randomized to either continued QHS Tx (full dose [FD-FD]) or to PRS Tx [FD-VD]). Both study phases were evaluated for treatment responses rates and for average change in TWT (SL+WASO+EMA). Results 55 subjects (age 61.2+/-8.1, 64% female, & 73% white) were enrolled into Phase-1; 39 were randomized to the QHS condition and 16 to the PRS condition. In Phase-1, 77% (QHS) and 50% (PRS) exhibited treatment responses (p=0.09) where the average change in TWT was similar by group (QHS was -43min [CI -76,-9] and PRS was -76min [CI -138,-14];p=0.35). In Phase-2, 73% (FD-FD), 57% (FD-VD), and 88% (VD-VD) exhibited continued treatment responses (p=0.22) where the average improvement of TWT continued with FD-FD and remained stable for FD-VD and VD-VD (p Conclusion These data, while preliminary, suggest that QHS (vs. PRS) dosing produces more treatment responders and similar initial effects on sleep continuity during Phase-1, comparable maintenance of treatment response over time, and continued improvement on sleep continuity during Phase-2. These results suggest that partial reinforcement can maintain effects but cannot allow for the additional clinical gains afforded by continuous treatment. Given this, it may be the case that the partial reinforcement technique could be improved upon by extending phase from 1 to 2–4 months. Support (if any)

Two experiments were conducted to examine whether using e-cigarettes with occasional use of regular cigarettes prevented relapse after extinction. In Experiment 1 (ABAC with a multiple-baseline design), six short-term smokers who wanted to stop smoking were asked to use e-cigarettes and were allowed to smoke 20 % of the usual number of regular cigarettes per day during the partial reinforcement period. Experiment 1 demonstrated that using e-cigarettes reduced the amount of smoking even after extinction. In Experiment 2 (ABAB design), which involved a single long-time smoker and partial reinforcement, the participant was unable to maintain low rates of smoking after the experiment. However, the excessive smoking (regular cigarettes > 15 per day) observed before the experiment was prevented. This study suggested that a partial reinforcement procedure (occasionally smoking cigarettes) prevented relapse after extinction without hardship in some smokers.

The partial reinforcement extinction effect (PREE) is an experimentally established phenomenon: behavioural response to a given stimulus is more persistent when previously inconsistently rewarded than when consistently rewarded. This phenomenon is, however, controversial in animal/human learning theory. Contradictory findings exist regarding when the PREE occurs. One body of research has found a within-subjects PREE, while another has found a within-subjects reversed PREE (RPREE). These opposing findings constitute what is considered the most important problem of PREE for theoreticians to explain. Here, we provide a neurocomputational account of the PREE, which helps to reconcile these seemingly contradictory findings of within-subjects experimental conditions. The performance of our model demonstrates how omission expectancy, learned according to low probability reward, comes to control response choice following discontinuation of reward presentation (extinction). We find that a PREE will occur when multiple responses become controlled by omission expectation in extinction, but not when only one omission-mediated response is available. Our model exploits the affective states of reward acquisition and reward omission expectancy in order to differentially classify stimuli and differentially mediate response choice. We demonstrate that stimulus–response (retrospective) and stimulus–expectation–response (prospective) routes are required to provide a necessary and sufficient explanation of the PREE versus RPREE data and that Omission representation is key for explaining the nonlinear nature of extinction data., Biological Cybernetics, 111 (5-6), ISSN:0340-1200, ISSN:1432-0770

Pavlovian conditioning is sensitive to the temporal relationship between the conditioned stimulus (CS) and the unconditioned stimulus (US). This has motivated models that describe learning as a process that continuously updates associative strength during the trial or specifically encodes the CS–US interval. These models predict that extinction of responding is also continuous, such that response loss is proportional to the cumulative duration of exposure to the CS without the US. We review evidence showing that this prediction is incorrect, and that extinction is trial-based rather than time-based. We also present two experiments that test the importance of trials versus time on the Partial Reinforcement Extinction Effect (PREE), in which responding extinguishes more slowly for a CS that was inconsistently reinforced with the US than for a consistently reinforced one. We show that increasing the number of extinction trials of the partially reinforced CS, relative to the consistently reinforced CS, overcomes the PREE. However, increasing the duration of extinction trials by the same amount does not overcome the PREE. We conclude that animals learn about the likelihood of the US per trial during conditioning, and learn trial-by-trial about the absence of the US during extinction. Moreover, what they learn about the likelihood of the US during conditioning affects how sensitive they are to the absence of the US during extinction.

Thorndike’s Law of Effect provides a framework for understanding the selection of behaviors given specific environmental reward contingencies. Though a highly influential model, especially given its resurgence in popularity to understand habitual behaviors, it fails to predict several well-documented behavioral phenomena and incorrectly views extinction as the unlearning of a previously acquired association. Blaisdell, Stolyarova, & Stahlman (2016) proposed modifications to Thorndike’s original law that address these issues and greatly increases the model’s explanatory power. This modified Law of Effect (MLOE) also provides a testable account of the Partial Reinforcement Extinction Effect (PREE). The PREE is the paradoxical finding of more rapid extinction to a continuously reinforced cue than to a partially reinforced cue, and has challenged many theoretical accounts of learning. Simulations of the MLOE confirm these predictions. Two experimental paradigms, one using pigeons and the other using humans, show support for the Modified Law of Effect’s explanation of the PREE.

In a midsession reversal task, subjects choose between two stimuli on every trial; only responses to one stimulus are reinforced. Halfway throughout the session, contingencies are reversed: previously reinforced responses are now extinguished and vice versa. Both, the outcome of the previous trial and the time elapsed since the beginning of the session, may predict the availability of reinforcement and determine choice. Thus, this task has typically been used to study cognitive flexibility and the temporal organization of behavior. This study assessed how past outcomes and time interact for behavioral control when each cue predicts the availability of reinforcement to a different extent. Eight rats were trained in four variations of the midsession reversal task differing in the reliability of outcomes and time as predictors of the reinforced response. We manipulated the reliability of the outcomes by providing either continuous or partial reinforcement, and the reliability of time by fixing the moment of reversal (middle of the session) or making the reversal unpredictable (semi-random trial). Results suggest that behavioral control alternates between outcomes and time according to the relative reliability of each cue. Model simulations show that outcomes and time may jointly determine behavior, and that momentary reinforcement rate may determine their relative influence.

Conditioned responding extinguishes more slowly after partial (inconsistent) reinforcement than after consistent reinforcement. This Partial Reinforcement Extinction Effect (PREE) is usually attributed to learning about nonreinforcement during the partial schedule. An alternative explanation attributes it to any difference in the rate of reinforcement, arguing that animals can detect the change to nonreinforcement more quickly after a denser schedule than a leaner schedule. Experiments 1a and 1b compared extinction of magazine responding to a conditioned stimulus (CS) reinforced with 1 food pellet per trial and a CS reinforced with 2 pellets per trial. Despite the difference in reinforcement rate, there was no reliable difference in extinction. Both experiments did demonstrate the conventional PREE comparing a partial CS (50% reinforced) with a consistent CS. Experiments 2 and 3 tested whether the PREE depends specifically on learning about nonreinforced trials during partial reinforcement. Rats were trained with 2 CS configurations, A and AX. One was partially reinforced, the other consistently reinforced. When AX was partial and A consistent, responding to AX extinguished more slowly than to A. When AX was consistent and A was partial, there was no difference in their extinction. Therefore, pairing X with partial reinforcement allowed rats to show a PREE to AX that did not generalize to A. Pairing A with partial reinforcement meant that rats showed a PREE to A that generalized to AX. Thus, the PREE depends on learning about nonreinforced trials during partial reinforcement and is not because of any difference in per-trial probability of reinforcement. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Dogs trained to search for contraband perform a chain of behavior in which they first search for a target and then make a separate response that indicates to the trainer that they have found one. The dogs often conduct multiple searches without encountering a target and receiving the reinforcer (i.e., no contraband is present). Understanding extinction (i.e., the decline in work rate when reinforcers are no longer encountered) may assist in training dogs to work in conditions where targets are rare. We therefore trained rats on a search-target behavior chain modeled on the search behavior of working dogs. A discriminative stimulus signaled that a search response (e.g., chain pull) led to a second stimulus that set the occasion for a target response (e.g., lever press) that was reinforced by a food pellet. In Experiment 1 training with longer search durations and intermittent (partial) reinforcement of searching (i.e. some trials had no target present) both led to more persistent search responding in extinction. The loss of search behavior in extinction was primarily dependent on the number of non-reinforced searches rather than time searching without reinforcement. In Experiments 2 and 3, delivery of non-contingent reinforcers during extinction increased search persistence provided they had also been presented during training. Thus, results with rats suggest that the persistence of working dog performance (or chained behavior generally) may be improved by training with partial reinforcement of searching and non-contingent reinforcement during both training and work (extinction).

Extinction-resistant threat is considered to be a central feature of pathological anxiety. Reduced threat extinction is observed in individuals with high intolerance of uncertainty (IU). Here we sought to determine whether contingency instructions could alter the course threat extinction for individuals high in IU. We tested this hypothesis in two identical experiments (Exp 1 n = 60, Exp 2 n = 82) where we recorded electrodermal activity during threat acquisition with partial reinforcement, and extinction. Participants were split into groups based on extinction instructions (instructed, uninstructed) and IU score (low, high). All groups displayed larger skin conductance responses to learned threat versus safety cues during threat acquisition, indicative of threat conditioning. In both experiments, only the uninstructed high IU groups displayed larger skin conductance responses to the learned threat versus safety cue during threat extinction. These findings suggest that uncertain threat during extinction maintains conditioned responding in individuals high in IU.

In a partial reinforcement schedule where a cue repeatedly predicts the occurrence of a target in consecutive trials, reaction times to the target tend to decrease in a monotonic fashion, while participants’ expectancies for the target decrease at the same time. This dissociation between reaction times and expectancies—the so-called Perruchet effect—challenges the propositional view of learning, which posits that human conditioned responses result from conscious inferences about the relationships between events. However, whether the reaction time pattern reflects the strength of a putative cue-target link, or only non-associative processes, such as motor priming, remains unclear. To address this issue, we implemented the Perruchet procedure in a two-choice reaction time task and compared reaction time patterns in an Experimental condition, in which a tone systematically preceded a visual target, and in a Control condition, in which the onset of the two stimuli were uncoupled. Participants’ expectancies regarding the target were recorded separately in an initial block. Reaction times decreased with the succession of identical trials in both conditions, reflecting the impact of motor priming. Importantly, reaction time slopes were steeper in the Experimental than in the Control condition, indicating an additional influence of the associative strength between the two stimuli. Interestingly, slopes were less steep for participants who showed the gambler’s fallacy in the initial block. In sum, our results suggest the mutual influences of motor priming, associative strength, and expectancies on performance. They are in line with a dual-process model of learning involving both a propositional reasoning process and an automatic link-formation mechanism., SCOPUS: ar.j, info:eu-repo/semantics/published

There is a vast literature on the behavioural effects of partial reinforcement in Pavlovian conditioning. Compared with animals receiving continuous reinforcement, partially rewarded animals typically show (a) a slower development of the conditioned response (CR) early in training and (b) a higher asymptotic level of the CR later in training. This phenomenon is known as the partial reinforcement acquisition effect (PRAE). Learning models of Pavlovian conditioning fail to account for it. In accordance with the incentive salience hypothesis, it is here argued that incentive motivation (or 'wanting') plays a more direct role in controlling behaviour than does learning, and reward uncertainty is shown to have an excitatory effect on incentive motivation. The psychological origin of that effect is discussed and a computational model integrating this new interpretation is developed. Many features of CRs under partial reinforcement emerge from this model.

The partial reinforcement extinction effect (PREE) is the observation that, following training in which a response is followed by reward on only a subset of trials, the response is more resistant to extinction following the total removal of reward than it is after training in which reward is presented on all trials. The PREE is almost ubiquitous in instrumental conditioning procedures but only inconsistently observed in Pavlovian conditioning. In his classic review of animal learning, Mackintosh attributes the bulk of the PREE to generalisation decrement relating to the fact that partial reinforcement typically ensures that acquisition of responding has taken place in conditions similar to that of extinction (e.g., in the absence of the reinforcer). We report here that extinction of a conditioned taste aversion is not retarded by partial reinforcement in terms of either consumption of the taste or hedonic reactions to it (assessed through the analysis of licking microstructure). These results are consistent with Mackintosh’s analysis of the PREE and the way in which it might differ between instrumental and Pavlovian conditioning.

Animals and humans can easily learn to associate an initially neutral cue with food intake through classical conditioning, but extinction of learned appetitive responses can be more difficult. Intermittent or partial reinforcement of food cues causes especially persistent behaviour in animals: after exposure to such learning schedules, the decline in responding that occurs during extinction is slow. After extinction, increases in responding with renewed reinforcement of food cues (reacquisition) might be less rapid after acquisition with partial reinforcement. In humans, it may be that the eating behaviour of some individuals resembles partial reinforcement schedules to a greater extent, possibly affecting dieting success by interacting with extinction and reacquisition. Furthermore, impulsivity has been associated with less successful dieting, and this association might be explained by impulsivity affecting the learning and extinction of appetitive responses. In the present two studies, the effects of different reinforcement schedules and impulsivity on the acquisition, extinction, and reacquisition of appetitive responses were investigated in a conditioning paradigm involving food rewards in healthy humans. Overall, the results indicate both partial reinforcement schedules and, possibly, impulsivity to be associated with worse extinction performance. A new model of dieting success is proposed: learning histories and, perhaps, certain personality traits (impulsivity) can interfere with the extinction and reacquisition of appetitive responses to food cues and they may be causally related to unsuccessful dieting.

Numerous studies indicate that placebo analgesia can be established via conditioning procedures. However, these studies have exclusively involved conditioning under continuous reinforcement. Thus, it is currently unknown whether placebo analgesia can be established under partial reinforcement and how durable any such effect would be. We tested this possibility using electro-cutaneous pain in healthy volunteers. Sixty undergraduates received placebo treatment (activation of a sham electrode) under the guise of an analgesic trial. The participants were randomly allocated to different conditioning schedules, namely continuous reinforcement (CRF), partial reinforcement (PRF), or control (no conditioning). Conditioning was achieved by surreptitiously reducing pain intensity during training when the placebo was activated compared with when it was inactive. For the CRF group, the placebo was always followed by a surreptitious reduction in pain during training. For the PRF group, the placebo was followed by a reduction in pain stimulation on 62.5% of trials only. In the test phase, pain stimulation was equivalent across placebo and no placebo trials. Both continuous and partial reinforcement produced placebo analgesia, with the magnitude of initial analgesia being larger following continuous reinforcement. However, while the placebo analgesia established under continuous reinforcement extinguished during test phase, the placebo analgesia established under partial reinforcement did not. These findings indicate that partial reinforcement can induce placebo analgesia and that these effects are more resistant to extinction than those established via continuous reinforcement. Partial reinforcement may, therefore, reflect a novel way of enhancing clinical outcomes via the placebo effect.

Two appetitive conditioning experiments with rats examined time-based and trial-based accounts of the partial reinforcement extinction effect (PREE). In the PREE, the loss of responding that occurs in extinction is slower when the conditioned stimulus (CS) has been paired with a reinforcer on some of its presentations (partially reinforced) instead of every presentation (continuously reinforced). According to a time-based or "time-accumulation" view (e.g., Gallistel and Gibbon, 2000), the PREE occurs because the organism has learned in partial reinforcement to expect the reinforcer after a larger amount of time has accumulated in the CS over trials. In contrast, according to a trial-based view (e.g., Capaldi, 1967), the PREE occurs because the organism has learned in partial reinforcement to expect the reinforcer after a larger number of CS presentations. Experiment 1 used a procedure that equated partially and continuously reinforced groups on their expected times to reinforcement during conditioning. A PREE was still observed. Experiment 2 then used an extinction procedure that allowed time in the CS and the number of trials to accumulate differentially through extinction. The PREE was still evident when responding was examined as a function of expected time units to the reinforcer, but was eliminated when responding was examined as a function of expected trial units to the reinforcer. There was no evidence that the animal responded according to the ratio of time accumulated during the CS in extinction over the time in the CS expected before the reinforcer. The results thus favor a trial-based account over a time-based account of extinction and the PREE. This article is part of a Special Issue entitled: Associative and Temporal Learning.

The present research evaluated the role of two prefrontal cortex areas, the ventrolateral orbital cortex (VLO) and the medial prefrontal cortex (mPFC), on two situations involving incentive downshifts, consummatory successive negative contrast (cSNC) with sucrose solutions and Pavlovian autoshaping following continuous vs. partial reinforcement with food pellets. Animals received electrolytic lesions and then were tested on cSNC, autoshaping, open-field activity, and sucrose sensitivity. Lesions of the VLO reduced suppression of consummatory behavior after the incentive downshift, but only during the first downshift trial, and also eliminated the enhancement of anticipatory behavior during partial reinforcement, relative to continuous reinforcement, in autoshaping. There was no evidence of specific effects of mPFC lesions on incentive downshifts. Open-field activity was also reduced by VLO lesions, but only in the central area, whereas mPFC lesions had no observable effects on activity. Animals with mPFC lesions exhibited decreased consumption of the lowest sucrose concentration, whereas no effects were observed in animals with VLO lesions. These results suggest that the VLO may exert nonassociative (i.e., motivational, emotional) influences on behavior in situations involving incentive downshifts. No clear role on incentive downshift was revealed by mPFC lesions.

The partial-reinforcement extinction effect (PREE) implies that learning under partial reinforcements is more robust than learning under full reinforcements. While the advantages of partial reinforcements have been well-documented in laboratory studies, field research has failed to support this prediction. In the present study, we aimed to clarify this pattern. Experiment 1 showed that partial reinforcements increase the tendency to select the promoted option during extinction; however, this effect is much smaller than the negative effect of partial reinforcements on the tendency to select the promoted option during the training phase. Experiment 2 demonstrated that the overall effect of partial reinforcements varies inversely with the attractiveness of the alternative to the promoted behavior: The overall effect is negative when the alternative is relatively attractive, and positive when the alternative is relatively unattractive. These results can be captured with a contingent-sampling model assuming that people select options that provided the best payoff in similar past experiences. The best fit was obtained under the assumption that similarity is defined by the sequence of the last four outcomes.

Japanese quail (Coturnix japonica) were reinforced with food for traversing a runway for either 18 or 36 trials, administered at a rate of 1 trial per day. Then, all animals received 18 extinction trials. The latency to run from the start box to the goal box was the dependent variable. Extinction was significantly slower in animals that had received 50% partial reinforcement during acquisition, whether relative to a group matched in terms of acquisition trials (36 trials, twice the number of reinforced trials) or relative to a group matched in terms of reinforcements (18 trials). The latter group was also matched in terms of the temporal distribution of acquisition trials with the partial reinforcement group, being trained only on days when the partial group was scheduled to receive a reinforced trial. Thus, there was evidence of a spaced-trial partial reinforcement extinction effect. A comparison of groups receiving large versus small reward magnitudes yielded no evidence of the spaced-trial magnitude of reinforcement extinction effect, even though the large-reward group consumed approximately 3 times more food than the small-reward group. Moreover, a comparison of groups that received 36 versus 18 acquisition trials produced no evidence of the spaced-trial overtraining extinction effect, even though acquisition latencies were significantly lower for the group that received 36 acquisition trials. These results are discussed in relation to comparative research on learning phenomena involving incentive downshift manipulations.

Greater rates of intermittent reinforcement in the presence of discriminative stimuli generally produce greater resistance to extinction, consistent with predictions of behavioral momentum theory. Other studies reveal more rapid extinction with higher rates of reinforcers - the partial reinforcement extinction effect. Further, repeated extinction often produces more rapid decreases in operant responding due to learning a discrimination between training and extinction contingencies. The present study examined extinction repeatedly with training with different rates of intermittent reinforcement in a multiple schedule. We assessed whether repeated extinction would reverse the pattern of greater resistance to extinction with greater reinforcer rates. Counter to this prediction, resistance to extinction was consistently greater across twelve assessments of training followed by six successive sessions of extinction. Moreover, patterns of responding during extinction resembled those observed during satiation tests, which should not alter discrimination processes with repeated testing. These findings join others suggesting operant responding in extinction can be durable across repeated tests.

In anxiety, maladaptive avoidance behavior provides for near-perfect controllability of potential threat. There has been little laboratory-based treatment research conducted on controllability as a contributing factor in the transition from adaptive to maladaptive avoidance. Here, we investigated for the first time whether partial reinforcement rate, or the reliability of avoidance at controlling or preventing contact with an aversive event, influences subsequent extinction of avoidance in humans. Five groups of participants were exposed to different partial reinforcement rates where avoidance cancelled upcoming shock on 100%, 75%, 50%, 25% or 0% of trials. During extinction, all shocks were withheld. Avoidance behavior, online shock expectancy ratings and skin conductance responses (SCRs) were measured throughout. We found that avoidance was a function of relative controllability: higher reinforcement rate groups engaged in significantly more extinction-resistant avoidance than lower reinforcement groups, and shock expectancy was inversely related with reinforcement rate during avoidance acquisition. Partial reinforcement effects were not evident in SCRs. Overall, the current study highlights the clinical relevance of laboratory-based treatment research on partial reinforcement or controllability effects on extinction of avoidance.

Two experiments with rats used an appetitively motivated instrumental discrimination procedure to examine whether damage to the hippocampal system would interfere with the relative validity effect in which a partially reinforced stimulus trained in compound acquires a weak conditioned response when concurrently trained CSs are perfect predictors of the presence or absence of the US [A.R. Wagner, F.A. Logan, K. Haberlandt, T. Price, Stimulus selection in animal discrimination learning, J. Exp. Psychol. 76 (1968) 171–180]. The true discrimination (TD) group received training with two compound cues containing a common element. One compound was reinforced and another never reinforced (AX+, BX−). Following TD training the common element (X) failed to acquire a strong conditioned response in comparison to a control, pseudo discrimination (PD) group (AX±, BX±), in which both compound cues were reinforced 50% of the time. Although (X) was reinforced on a partial reinforcement schedule, (50%) in both groups, conditioning of X was affected by the reinforcement schedules of the accompanying elements (A and B). Neither radio-frequency lesions of the fornix-fimbria (Experiment 1) nor neurotoxic lesions of the hippocampus (Experiment 2) interfered with this effect on X or on the same effect found during the inter trial interval (ITI). Rates of ITI responding were higher in the PD groups than in the TD groups suggesting stronger contextual conditioning following PD training. Furthermore, disruptions to the hippocampal system in Experiment 2 resulted in increased rates of lever pressing for food. These results do not support the notion that the hippocampus is critically involved in selective associations.

Mounting evidence indicates that adolescents exhibit heightened sensitivity to rewards and reward-related cues compared to adults, and that adolescents are often unable to exert behavioral control in the face of such cues. Moreover, differences in reward processing during adolescence have been linked to heightened risk taking and impulsivity. However, little is known about the processes by which adolescents learn about the appetitive properties of environmental stimuli that signal reward. To address this, Pavlovian conditioning procedures were used to test for differences in excitatory conditioning between adult and adolescent rats using various schedules of reinforcement. Specifically, separate cohorts of adult and adolescent rats were trained under conditions of consistent (continuous) or intermittent (partial) reinforcement. We found that the acquisition of anticipatory responding to a continuously-reinforced cue proceeded similarly in adolescents and adults. In contrast, responding increased at a greater rate in adolescents compared to adults during presentations of a partially-reinforced cue. We subsequently compared the ability of adolescent and adult rats to dynamically adjust the representation of a reward-predictive cue during extinction trials, in which a secondary inhibitory representation is acquired for the previously-reinforced stimulus. We observed significant age differences in the ability to flexibly update cue representations during extinction, in that the appetitive properties of cues with a history of either continuous or partial reinforcement persisted to a greater extent in adolescents relative to adults.

SummaryEmotional memories can persist for a lifetime but can also undergo extinction. Although we know about the mechanisms involved in expression and extinction, we know very little about the mechanisms that determine whether a specific memory would persist or not. Here, we use partial reinforcement extinction effect (PREE) to explore the neural mechanisms that differentiate persistent from labile memories. We recorded the simultaneous activity of neurons in the amygdala and the dorsal anterior cingulate cortex (dACC) while monkeys engaged in tone-odor aversive conditioning. We report that under continuous reinforcement schedule (ConS), activity in the amygdala precedes behavioral response, whereas under partial schedule (ParS), dACC activity precedes it. Moreover, we find that ParS induced cross-regional pairwise correlations throughout the entire acquisition session, and their magnitude and precision predicted the later resistance to extinction. Our results suggest that memory persistence depends on distributed representations and, specifically, resistance to extinction of aversive memories is maintained by correlated amygdala-dACC activity.

Incremental dynamic analysis (IDA) is an emerging method in structural analysis which allows evaluation of seismic capacity and demand of structures through a series of nonlinear dynamic analyses using multiple scaled ground motion records. Seismic behaviour of concentrically braced frames designed based on the first, second and third revisions of the Iranian seismic code, standard no. 2800, has been evaluated through IDA in the present paper. Besides, a brief comparison is made between seismic behaviour of these frames, frames with different heights and different bracing types. Seismic capacity and limit states of such structures have been reviewed through the paper. The IDA results imply that frames designed with the first edition are seriously vulnerable and fail before reaching the acceleration levels predicted in the code. On the other hand, frames designed with the second and third editions, although behaving better, need partial reinforcement in some cases. Other results of this study show that chevron braced frames behave seismically better than X-braced ones. Copyright © 2009 John Wiley & Sons, Ltd.

Experiments 1 and 2 involved independent groups that received primary reinforcement after a correct match with a probability of 1.0, .50 or .25. Correct matches that did not produce primary reinforcement produced a conditioned reinforcer. Both experiments revealed little evidence that acquisition or retention was adversely affected by use of intermittent reinforcement. Experiment 3 involved a group that received 100% reinforcement and two others that received 25% reinforcement, one of which received conditioned reinforcement and the other did not. Following acquisition and retention testing, birds in group 100% and group 25% with conditioned reinforcement were exposed to 25% reinforcement and no conditioned reinforcement. Results revealed that conditioned reinforcement was important in promoting acquisition but was irrelevant in maintaining performance. It was concluded that intermittent reinforcement, especially when combined with conditioned reinforcement during acquisition, supports levels of acquisition and retention comparable to that of continuous reinforcement. Theoretically, the findings are consistent with an extension of Blough's instance-based theory of discrimination performance and, practically, they suggest that use of intermittent reinforcement could result in increased efficiency and economy in labs using delayed matching.

When two cues are reinforced together (in compound), most associative models assume that animals learn an associative network that includes direct cue–outcome associations and a within-compound association. All models of associative learning subscribe to the importance of cue–outcome associations, but most models assume that within-compound associations are irrelevant to each cue's subsequent behavioral control. In the present article, we present an extension of Van Hamme and Wasserman's (Learning and Motivation 25:127–151, 1994) model of retrospective revaluation based on learning about absent cues that are retrieved through within-compound associations. The model was compared with a model lacking retrieval through within-compound associations. Simulations showed that within-compound associations are necessary for the model to explain higher-order retrospective revaluation and the observed greater retrospective revaluation after partial reinforcement than after continuous reinforcement alone. These simulations suggest that the associability of an absent stimulus is determined by the extent to which the stimulus is activated through the within-compound association.

An agent-based approach is a numerical (computer-intensive) method to explore the complex characteristics and dynamics of microeconomics. Using the agent-based approach, this study investigates the learning speed of traders and their strategic collaboration in a dynamic market change of electricity. An example of such a market change can be found in the California electricity crisis (2000–2001). This study incorporates the concept of partial reinforcement learning into trading agents and finds that they have two learning components: learning from a dynamic market change and learning from collaboration with other traders. The learning speed of traders becomes slow when a large fluctuation occurs in the power exchange market. The learning speed depends upon the type of traders, their learning capabilities and the fluctuation of market fundamentals. The degree of collaboration among traders gradually reduces during the electricity crisis. The strategic collaboration among traders is examined by a large simulator equipped with multiple learning capabilities.

To test the hypothesize that psoriasis patients treated under a partial schedule of pharmacologic (corticosteroid) reinforcement would show less severe symptoms and relapse than those given the same amount of drug under standard conditions. Behavioral conditioning as an inherent component of many pharmacotherapeutic protocols has never been examined.A double-blind, simple randomization intervention was conducted with 46 patients from California and New York. Initially, lesions were treated with 0.1% acetonide triamcinolone under standard treatment conditions. Thereafter, a Standard Therapy group continued on continuous reinforcement (active drug every treatment) with 100% of the initial dose; Partial Reinforcement patients received a full dose 25% to 50% of the time and placebo medication other times; Dose Control patients received continuous reinforcement with 25% to 50% of the initial dose.Severity of disease scores in California neither supported nor refuted the hypothesis. In New York, where there was no difference between Partial Reinforcement and Dose Control groups at baseline, partial reinforcement effected a greater reduction in lesion severity than Dose Control conditions and did not differ from Standard Therapy patients receiving two to four times more drug. For the entire population, the frequency of relapse under partial reinforcement (26.7%) was lower than in Dose Control patients (61.5%) and did not differ from full-dose treatment (22.2%).A partial schedule of pharmacotherapeutic reinforcement could maintain psoriasis patients with a cumulative amount of corticosteroid that was relatively ineffective when administered under standard treatment conditions. Conceivably, corticosteroid administration only one quarter or half as frequently as currently prescribed is sufficient to treat psoriasis. We posit, however, that these preliminary observations implicate conditioning processes in-and for the design of-regimens of pharmacotherapy.

The basolateral amygdala complex (BLA) has been identified as a critical structure mediating fear extinction. However, little is known about the functional role of neurons in the BLA during the extinction of a reward-seeking behavior. Here, we usedin vivoelectrophysiology procedures in freely moving rats to investigate whether and how the BLA encodes the extinction of responding for sucrose. We recorded 330 neurons from 15 rats during a within-session extinction procedure following training under a partial reinforcement schedule. Several distinct populations of neurons change their response profiles as the rat ceases to respond for the omitted reinforcer. One population of neurons (32 of 330; 10%), which responded selectively to port entries in the presence, but not the absence, of sucrose during maintenance, subsequently developed a phasic response to port entries in the absence of sucrose during the extinction epoch only. The relative proportion of these “reinforcement-omission” neurons per rat was correlated with response intensity during extinction, as well as with the rate at which reward-seeking behavior was extinguished. A subpopulation of neurons responded with opposite phasic changes in activity to port entries in the presence of sucrose and to port entries during extinction, demonstrating that BLA neurons may contribute to the detection of value differences between expected and actual outcomes. Another population of neurons (47 of 330; 14%) responded to the empty port only during extinction. Because BLA neural correlates reflect the omission of an expected reward, these neuronal populations may contribute to the expression of behavior during extinction.

SUMMARY Songbirds often modify elements of their songs or calls in particular social situations (e.g. song matching, flock convergence, etc.) but whether adult individuals also make vocal modifications in response to abiotic environmental factors (e.g. food availability) is relatively unknown. In the present study we test whether two different schedules of food reinforcement,fixed ratio continuous reinforcement and variable ratio partial reinforcement,cause adult black-capped chickadees to change the structure of their chick-a-dee calls. We also examine how these calls differ in two contexts:being alone versus when experiencing an alarming event. Wild-caught black-capped chickadees were housed in isolation to prevent social interaction and recorded weekly for seven weeks. Baseline recordings on week one show that calls given alone differed from those given during an alarming event in both note type composition and frequency (i.e. pitch). Calls also changed over time between birds on the two different schedules of reinforcement. In addition,birds on different reinforcement schedules responded differently during the two recording conditions. Our results suggest that call characteristics can be modified rapidly and may reflect abiotic environmental conditions. If call structure varies consistently with particular abiotic environmental conditions, much can be gained from bioacoustic analyses of calls from wild birds. However, vocal patterns must be consistent across dialects, and we must disentangle vocal changes due to the abiotic environment from those due to social interaction. Further research is needed from natural populations and across multiple regions.

Four penguins (Spheniscus demersus) were trained to discriminate line length in a simultaneous discrimination task. After the birds' performances reached a discrimination criterion, the reinforcement ratio was decreased to .33. After the ratio of correct trials reached .90 in three successive sessions with a partial reinforcement procedure, probe-test sessions were introduced. In the probe-test trials, untrained lines were presented paired with the trained lines. The four probe-test trials were mixed into 45 discrimination trials. In the probe-test trials, the penguins that had been trained to peck shorter lines pecked the untrained shorter line rather than the longer line that was reinforced in the discrimination trials. In contrast, those birds that had been trained to peck the longer line pecked the untrained longer line, rather than the shorter line which was reinforced in the discrimination trials. All four birds demonstrated transposition in the line-length discrimination task.

The memories of the unconditioned stimulus (US) and its absence (No US), symbolized as S R and S N , respectively, may be retrieved on US or No US trials giving rise to four types of associations, S R → US, S R → No US, S N → US, and S N → No US. Here, following acquisition under partial reward (PRF), rats were shifted either to different schedules of PRF (Experiment 1) or extinction (Experiments 1 and 2). Inhibitory S R → No US associations formed in acquisition survived extinction and shifts to one, but not another type of PRF schedule (Experiments 1 and 2). Excitatory S R → US associations also survived extinction (Experiment 2). These findings, as well as the acquisition findings of Experiment 2, are consistent with the sequential model but not with the only other two theories said to be able to explain PRF findings, the frustration hypothesis of Amsel and the attention hypothesis of Mackintosh [see Haselgrove, M., Aydin, A., & Pearce, J. M. (2004). A partial reinforcement extinction effect despite equal rates of reinforcement during Pavlovian conditioning. Journal of Experimental Psychology: Animal Behavior Processes , 30 , 240–250]. Also, the reacquisition findings obtained here are inconsistent with two views applied to several learning phenomena, the rule-learning view and the position-item view.