Bidirectional heart rate responses in rats associated with excitatory and inhibitory stimuli

Following classical conditioning to a shock-reinforced tone CS (T₁+), heart rate (HR) of three groups of rats was examined in response to a new reinforced tone (T₂+) and a nonreinforced light (L?) CS given during conditioned inhibition (T₂+ vs. T₁L?), discrimination conditioning (T₂+ vs. L?), or explicitly unpaired (T₂/L? vs. US alone) procedures. Decelerative HR reactions occurred to the reinforced T₂+ and T₂+ CSs. To the respective nonreinforced CSs, the conditioned inhibition group displayed diminished but sizable HR deceleration, the discrimination group showed near-zero responding, and the explicitly upaired group showed HR acceleration. Subsequent reversal conditioning to L was retarded in the conditioned inhibition and explicitly unpaired groups relative to the discrimination group. Group differences on combined-cue [T₂/L?) trials were not found. Both the HR responses during inhibitory training and the reversal-conditioning impairments suggest that inhibition may have been established to L? in the conditioned inhibition and explicitly unpaired groups.     

Pigeons’ memory for time: Assessment of the role of subjective shortening in the duration-comparison procedure

Pigeons were trained in a duration-comparison procedure to peck one key if the comparison duration (c) was 1 sec shorter than a standard duration (s), and another key if c was 1 sec longer than s. During training, the s-c delay was 1 sec, and the total duration of an s-c pair was not predictive of the correct choice. In Experiment 1, during equal-duration pair test trials, pigeons increasingly responded long (i.e., c τ s) as the s-c delay was lengthened. In Experiment 2, we demonstrated that s affected long responding on equal-duration test trials, even at the 8-sec s-c delay. In Experiment 3, long responding increased as the s-c delay was lengthened, even when stimulus conditions during the s-c delay differed from those during the intertrial interval (ITI). Additional analyses indicated that it was unlikely that the increase in long responding was due to the pigeons’ adding the s-c delay to c and comparing the total against the duration of s. The increase in long responding with an increase in s-c delay is more consistent with subjective shortening of s than with confusion between the s-c delay and the ITI.     

Decrement in distress to an aversive event during a conditioned positive opponent-process

During Phase 1, 24 rats received CS₁ (light)-shock trials while the remaining 24 rats received CS₁ and shock on a random control schedule. During Phase 2, all subjects were presented trials of CS₂ (tone)-shock. When CS₂ was subsequently presented immediately after CS, while subjects licked for water, it was found that subjects that had received CS₁-shock pairings during Phase 1 exhibited less suppression of licking to CS₂, indicating less distress, than control subjects. The results are compatible with the opponent-process theory and suggest the presence of a positive hedonic afterreaction to an aversive event which reduced distress to a following aversive event.     

Enhancement and reduction of associative retroactive cue interference by training in multiple contexts

Retroactive cue interference refers to situations in which a target cue X is paired with an outcome in phase 1 and a nontarget cue Z is paired with the same outcome in phase 2, with less subsequent responding to X being seen as a result of the phase 2 training. Two conditioned suppression experiments with rats were conducted to determine whether retroactive cue interference is similarly modulated by a manipulation that influences retroactive outcome interference (e.g., extinction). Both experiments used an ABC renewal-like design in which phase 1 training, phase 2 training, and testing each occurred in different contexts. Experiment 1 found that training the target association in multiple contexts without altering the number of training trials during phase 1 decreased retroactive cue interference (i.e., increased responding consistent with the target association). Experiment 2 found that training the interfering association in multiple contexts without altering the number of interference trials during phase 2 increased retroactive cue interference (i.e., decreased responding consistent with the target association). The possibility of similar mechanisms underlying cue interference and outcome interference is discussed.     

Associative structure of second-order conditioning in humans

Second-order conditioning (SOC; i.e., conditioned responding to S2 as a result of S1–US pairings followed by S2–S1 pairings) is generally explained by either a direct S2→US association or by an associative chain (i.e., S2→S1→US). Previous research found that differences in responses to S2 after S1 was extinguished often depended on the nature of the S2–S1 pairings (i.e., sequential or simultaneous). In two experiments with human participants, we examined the possibility that such differences result from S1 evoking S2 during extinction of S1 following simultaneous but not sequential S2–S1 pairings. This evocation of S2 by S1 following simultaneous pairings may have paired the evoked representation of S2 with absence of the outcome, thereby facilitating mediated extinction of S2. Using sequential S2-S1 pairings, both Experiments 1 and 2 failed to support this account of how extinction of S1 reduced responding to S2. Experiment 1 found that extinguishing S1 reduced responding to S2, while extinguishing S2 had little effect on responses to S1, although forward evocation of S1 during extinction of S2 paired the evoked representation of S1 with absence of the outcome. In Experiment 2, evocation of S2 during S1 nonreinforced trials was prevented because S2–S1 pairings followed (rather than proceeded) S1-alone exposures. Nevertheless, responding to S2 at test mimicked S1 responding. Responding to S2 was high in the context in which S1 had been reinforced and low in the context in which S1 had been nonreinforced. Collectively, these experiments provide additional support for the associative-chain account of SOC.     

Short-term retention of “surprising” events following different training conditions

Terry and Wagner (1975) have suggested that short-term retention of information about an event is enhanced if the occurrence of the event is surprising. To investigate this idea, we trained two groups of pigeons in a preparatory-releaser procedure in which half the trials started with the presentation of food (the preparatory event). The preparatory food presensation was signaled by an 8-sec white keylight in the signaled, but not in the unsignaled, group. After a retention interval, varying between 2 and 32 sec, the releaser stimulus (CS_R), a red keylight, was presented for 8 sec in the absence of any reinforcement. The remaining trials were initiated by the presentation of CS_R, and the first peck occurring 8 sec after the onset of CS_R was reinforced by food. The preparatory event controlled responding to CS_R at the short retention interval, with the level of control declining systematically with increasing retention intervals. On probe test trials, the presentation of the preparatory food event was preceded by a stimulus that had previously been paired (CS+) or unpaired with food (CS?). Discriminative responding to CSr was better following CS? than following CS+ in the unsignaled, but not the signaled, group. These results suggest that the enhanced retention following surprising preparatory events reflects a generalization decrement induced by changing the signaling conditions between training and testing.     

Renewal of extinguished instrumental responses: independence from Pavlovian processes and dependence on outcome value

The source of renewal of instrumental responding in rats was investigated. In Experiment 1, two responses (R1 and R2) were reinforced with one outcome (O1) in contexts A and B (i.e., R1→O1, R2→O1), and then R2 was extinguished in A and R1 was extinguished in B. At test, the rate of R1 was higher than that of R2 in context A, and the reverse was the case in context B: Renewed responding was independent of the Pavlovian context→O1 associations. In Experiment 2, all rats received R1→O1 and R2→O2 trials in A and then were placed in B, where they were sated on O2 and either did (Group Extinction) or did not (Group No Extinction) receive concurrent extinction of R1 and R2. At test, we found more responding in A than in B for Group Extinction, but not for Group No Extinction, and the renewed responding in A was as sensitive to the current value of the outcome as responding that had not been subject to extinction (i.e., the rate was higher for R1 than for R2). That is, the renewed responding was goal-directed. These results identify the removal of contextual inhibion of either the response or the response→outcome associaon as potenal bases for renewal, and the response→outcome associaon as the source of renewed responding.     

Effects of component training and subsequent sequencing of stimuli on shuttlebox avoidance responding of rats

The serial presentation of two different CSs, with each stimulus having an 8-sec duration (S1₈/S2₈), consistently has resulted in most of the shuttlebox avoidance responses being recorded to the S2 component. Experiment 1 attempted to attenuate this serial CS, delayed-response effect by conditioning the separate components of a serial CS prior to ordering them sequentially. Ten component-training trials were administered, with subjects receiving CS-US pairing to S1 only, S2 only, or to both S1 and S2 presented on separate trials. Two CS durations (8 or 16 sec) during this phase also were compared. Subjects were then given 100 avoidance test trials using the standard serial procedure. The 10 best avoidance responders in each group were selected for analysis. Shorter avoidance latencies were obtained only for subjects receiving component conditioning to S1. CS duration was not a factor in establishing the shorter latencies. Component conditioning to S2 resulted in increasing the total avoidances. Experiment 2 increased the number of component-training trials and the generality of the findings by using a different strain of rats and by extending the testing phase of the study so that all subjects could be included in the analysis. Comparable results were obtained. The theoretical implications of these data were discussed.     

Retrospective and prospective short-term memory in delayed response tasks in rats

Separate groups of rats were trained and tested on asymmetrically and symmetrically reinforced successive delayed matching-to-sample (DMTS) or delayed discrimination (DD) tasks in Experiment 1. Each rat received training and testing on symmetrically reinforced DMTS and DD tasks in Experiment 2. The only difference between each task was that the rats had to respond correctly to a light or tone test stimulus, S₂, if it matched a light or tone sample stimulus, S₁, in DMTS, but could respond to either S₂ if S₁ had been a particular stimulus in DD. Only correct leverpresses were reinforced in the asymmetrically reinforced version of each task. Both correct presses and correct omissions were reinforced in the symmetrically reinforced version of each task. Response biases to leverpress during tests for delayed responding to S₁ were reduced in both symmetrically reinforced tasks, but only in the DD task did such contingencies produce consistently poorer performance in responding to either S, in Experiment 1. Declines in accuracy of performance that occurred in both experiments were greater to the visual than to the auditory S₁ only in the DMTS tasks with increased intervals between S₁ and S₂. A third experiment, in which rats had to respond to S₂ if it matched S₁ (DMTS) or if S₂ mismatched S, (DMmTS), was carried out. Modality of S₁ similarly affected accuracy of delayed responding in each task, as in the first two experiments. Methodological and theoretical implications of these results are discussed in terms of Honig and Thompson’s (1982) dual-process theory of working memory.     

Target-absent controls in blocking experiments with rats

In three between-groups blocking experiments with rats, two concurrent and one forward, several common control procedures were employed: Reinforced trials with the putative blocking stimulus were either omitted entirely (Kamin control), replaced by unsignaled reinforcements (Wagner control), or replaced by reinforced trials with a different stimulus (C1 control). In each experiment, parallel treatments with the target stimulus absent during training served to examine the possibility that differential responding in tests with the target stimulus might be traced solely to differential exposure to the nontarget stimuli. In Experiment 1, responding by a concurrent blocking group during the test was no different than responding by a Kamin control group, and responding by a Wagner control group was greater than that of either of the other groups—a pattern of results, mirrored in the performance of the target-absent groups, that could be attributed to the elevation of contextual excitation by unsignaled reinforcement. In Experiment 2, responding in the test by a concurrent blocking group was no different than that by a C1 control group. In Experiment 3, a finding of less responding by a forward blocking group than by a C1 control group when the target stimulus was present during training, but not when it was absent, provided plausible evidence of blocking.     

The dual role of the context in postpeak performance decrements resulting from extended training

The context??s role in Pavlovian conditioning depends on the trial spacing during training, with massed trials revealing a function akin to that of discrete stimuli, and spaced trials revealing a modulatory function (Urcelay & Miller, Journal of Experimental Psychology. Animal Behavior Processes, 36, 268?C280, 2010). Here we examined the contextual determinants of a common but largely ignored effect: attenuated conditioned responding with extended reinforced training (i.e., a postpeak performance deficit [PPD]). Contextual sources of PPDs were investigated in four fear-conditioning experiments with rats. In Experiment 1, as the number of reinforced trials increased, conditioned responding decreased, even when testing occurred outside the training context. Experiment 2 revealed opposing influences of context on the PPD based on trial spacing, which interacted with whether testing occurred in the training context. This finding reconciles Experiment 1??s results with previous data (Bouton, Frohardt, Sunsay, Waddell, & Morris, Journal of Experimental Psychology. Animal Behavior Processes, 34, 223?C236, 2008). Experiment 3 suggested that extended training with these parameters did not lead to habituation to conditioned or unconditioned stimuli. In Experiment 4, few or many massed training trials were followed orthogonally by context extinction or no context extinction. After many pairings, context extinction reduced the PPD (i.e., enhanced responding), suggesting a competitive role of the context. These results, together with prior data suggesting that context modulates expressions of the PPD, are consistent with the view that contexts can play two distinctly different roles.     

Reacquisition following extinction in appetitive conditioning

In four experiments utilizing an appetitive conditioning preparation, reacquisition of conditioned responding was found to occur both rapidly and slowly following extinction. In Experiment 1, acquisition of responding to a tone that had been conditioned and extinguished occurred more rapidly than acquisition in either a group that received equivalent exposure to the food unconditioned stimulus or a “rest” control group that received only exposure to the apparatus in the first two phases. However, reacquisition was impaired relative to acquisition in a “learning-experienced” group that had previously received conditioning and extinction with a different stimulus. Experiments 2 and 3 produced similar results, but also found that high responding during reacquisition was confined to trials that followed reinforced, rather than nonreinforced, trials. Experiment 4, in which very few initial conditioning trials were used, produced reacquisition that was slow compared with both learning-experienced and rest controls. The results are consistent with a role for sequential learning: Reacquisition is rapid when animals have learned that reinforced trials signal other reinforced trials.     

Temporal determinants of occasion setting in feature-positive discriminations

Three experiments examined the acquisition and transfer of Pavlovian feature-positive discriminations (XA+, A?) in rat subjects. To identify the nature of the associations formed in those discriminations, the form of the conditioned responses (CRs) was examined. If the feature,X, and common element, A, cues started and ended together onXA compoud trials, associations betweenX and the food unconditioned stimulus (US) were acquired. If the onsets and/or terminations ofX preceded those of A,X acquired the ability to set the occasion for responding to A, that is, A evoked CRs only onXA compound trials. The acquisition of occasion setting was favored when (1) the onset of X preceded that of A, (2) the interval betweenX and A and/or the US was relatively long, and (3) the termination ofX occurred prior to the onset of A. The occasion-setting power ofX was fairly specific to A:X did not modulate responding evoked by another cue that had been first trained and then extinguished or by a cue that had been paired with the US only a few times. However,X did enhance responding to a cue that had been a common element in another, identical feature-positive discrimination. That transfer was somewhat greater if theX and A terminated together than ifX terminated prior to the onset of A. Implications for theories of stimulus control in Pavlovian conditioning are discussed.     

Savings in classical conditioning in the rabbit as a function of extended extinction

In the present experiments, savings phenomena following a limited amount of initial acquisition and extended extinction were examined. Experiments 1 and 2 compared rates of reacquisition following brief acquisition and various amounts of extinction in conditioning of the rabbit’s nictitating membrane and heart rate response, respectively. Experiment 3 compared rates of acquisition to a novel stimulus (e.g., light) following brief acquisition and various amounts of extinction to another stimulus (e.g., tone). In addition, in Experiment 3 recovery of responding to the extinguished stimulus during acquisition to the novel, cross-modal stimulus was examined. Experiments 1, 2, and 3 demonstrated that with a limited number of acquisition trials (1) there was a graded reduction in the rate of reacquisition as a function of the number of extinction trials in both conditioning preparations, (2) there was a graded reduction in the rate of cross-modal acquisition as a function of the number of extinction trials, but (3), in Experiment 3, recovery of responding to the extinguished stimulus during cross-modal training of the novel stimulus appeared uniformly robust even in the face of extended extinction.     

Herrnstein’s equation for the rates of responding during concurrent schedules

A modification of the nonlinear curve-fitting procedure proposed by Wetherington and Lucas (1980) was used to assess how well Herrnstein’s (1970) equation for the rates of responding during concurrent schedules described performance. The equation fitted some results very well, accounting for 80% or more of the variance in the data in studies that used moderate-duration changeover delays and provided the same positive reinforcers, operanda, and simple schedules in the two components. The equation fitted the data poorly in other studies. The k parameter changed with several variables; it was not as constant as Herrnstein (1974) suggested. R₀ did not fit Herrnstein’s interpretation as reinforcement from unprogrammed sources. Forty percent of all values of R₀ were negative, and another 23% were unreasonably large (greater than 50 reinforcers/h). The data suggest that Herrnstein’s equation is not a general theory of concurrent-schedule responding, and that Herrnstein’s interpretation of k and R₀ should be modified.     

Alternative accounts are preferable to value transfer theory: Commentary on Dorrance, Kaiser, and Zentall (1998)

Dorrance, Kaiser, and Zentall (1998) trained pigeons on two concurrent simultaneous discriminations (A₊B_?; C₊D_?), with interspersed single-stimulus trials in which responding to the two positive discriminanda was differentially reinforced (A₊; C_±). In each of four separate experiments, the birds showed a preference for stimulus B over stimulus D. Dorrance et al. concluded that the results of these experiments were best described in terms of value transfer theory (VTT; Fersen, Wynne, Delius, & Staddon, 1991). They reject the possibility that the results of these experiments might have been caused by differential nonreinforced experience with the test stimuli (B and D) on the basis of correlational analyses within each experiment. However, differences between experiments in choice of B over D are well predicted by differences in their history of reinforcement. Previous findings that were thought to favor VTT are also entirely consistent with a simpler associative analysis.     

Amount of training and reversal learning with singly presented stimuli in the rat

In a discrete trials multiple reversal experiment with singly presented stimuli, rats were given either 10 or 20 training trials per day for 2 days on each problem. All subjects improved progressively over reversals, but subjects with more training on each problem showed greater inhibition of responding to S? during reversal than those having less training. For both groups, the S? within sessions curve became steeper over reversals. Inhibition of responding to S? was greater on Day 2 of a reversal than on Day 1. The rat data are discussed in relation to those obtained from pigeons and goldfish.     

Instrumental performance and time between reinforcements: Intimate relation to learning or memory retrieval?

According to scalar expectancy theory (SET), instrumental performance is determined by the ratio of the time between reinforcements in the trial (T _T) to the overall time between reinforcements (T _O). Groups for which theT _O|T _T ratio is the same should perform similarly. According to the sequential-memory view, the memory of nonreward becomes a signal for reward, and thereby promotes strong responding, when that memory is retrieved on a reward trial. In each of three runway investigations employing rats in a runway, two groups were compared that had the sameT _O |T _T ratio but that differed in the tendency to retrieve the memory of nonreward on a rewarded trial. In each investigation faster running on critical nonrewarded trials was associated with the group having the stronger tendency to retrieve the memory of nonreward on a rewarded trial. These findings are consistent with the predictions of the sequential-memory view, as well as with certain earlier findings, but are inconsistent with SET. It was indicated that the groups compared here were matched along a considerable number of dimensions—an unprecedented number for a varied reward investigation.     

Narrowing down the conditions for extinction of Pavlovian feature-positive discriminations in humans

The aim of this study was to delineate the minimal conditions for extinction of Pavlovian modulation in humans. Previous experiments at our lab showed that, after X ? A+/A?C acquisition training, X?C trials did not extinguish differential X ? A+/A?C responding, while X ? A?C trials did. Additionally, X ? A?C extinction training seemed only to extinguish differential X ? A+/A?C responding, while leaving differential responding on a concurrently trained Y ? B+/B?C discrimination intact. It thus seemed that the X ? A+/A?C discrimination can only be extinguished by X ? A?C extinction trials. (Rescorla, Journal of Experimental Psychology: Animal Behavior Processes 12, 16?C24, 1986), on the other hand, found that the minimal conditions for extinction were broader in pigeons: Namely, he found that an acquired X ? A+/A?C discrimination could be extinguished by presenting the original feature X in combination with a different target (B) that was minimally trained as an exciter. We thus wanted to examine whether this was also the case in humans. We found that nonreinforced X ? B?C presentations did not abolish discriminative X ? A/A responding when target B was a nonreinforced stimulus. Nonreinforced X ? B?C trials did extinguish the X ? A+/A?C discrimination when target B had previously been trained as a target for modulation (X ? B+/B?C or Y ? B+/B?C training) or as a reinforced exciter (B+). Our results thusf parallel and extend those in nonhuman animals (Rescorla, Journal of Experimental Psychology: Animal Behavior Processes 12, 16?C24, 1986).     

Varied but not necessarily random: Human performance under variability contingencies is affected by instructions

The goal of the present study was to evaluate the role of verbal stimuli in the production of response variability in humans. College students were distributed into three groups and asked to type three-digit sequences. Participants in the systematic group were instructed to produce sequences according to a rule of their choice; those in the random group were instructed to produce sequences according to chance; and those in the control group were not instructed about how to produce sequences. The experiment employed an ABA design. During the A phases, low-frequent sequences were reinforced (variability contingency), whereas during the B phase, reinforcement was withdrawn (extinction). The results indicated the following: (1) The instructions were efficient at producing systematic and random-like patterns for the systematic and random groups, respectively; in the absence of instructions, a mix of both patterns was observed. (2) Behavior was sensitive to extinction independently of the instructions provided. (3) Systematic patterns favored a more equiprobable distribution of sequences across trials. (4) Reaction times were longer for responding in a systematic than in a random-like fashion. The present findings suggest that individual differences in meeting variability contingencies may be due, at least partially, to instructional control.