Differential second-order aversive conditioning using contextual stimuli

Two experiments were conducted to determine if contextual stimuli used as S₂ in a higher-order differential conditioning procedure would control the performance of rats. Discrete stimuli were first paired with footshock in a separate training context. During second-order training, a shock-associated discrete stimulus was presented in one of two discriminable observation chambers. Over 4 days of training, subjects engaged in more freezing in the context associated with an excitatory discrete S₁, relative to a context in which no discrete stimulus, or a stimulus that had been explicitly unpaired with shock delivery, was presented. After acquisition of the second-order discrimination, animals were returned to the original training context where they received a “signaled inflation” treatment designed to change the current value of S₁, and the US. This postconditioning manipulation did not selectively affect performance of defensive freezing or conditional analgesia in S₂.     

Memories of reward events and expectancies of reward events may work in tandem

A common assumption is that expectancies of reward events in instrumental tasks are established on the basis of Pavlovian conditioning. According to the tandem hypothesis, tested in the four runway investigations reported here employing rats, memories of reward events may serve as the conditioned stimuli eliciting expectancies. In Experiments 1–3, rats were trained under a schedule of partial reward (P), which did not produce increased resistance to extinction, and subsequently shifted to consistent reward (C). According to the tandem hypothesis, the shift to the C schedule should result in increased resistance to extinction if, as hypothesized, under the P schedule the memory of reward, S^R, came to elicit the expectancy of nonreward,_EN. This hypothesis was confirmed under a variety of conditions. It was shown that increased resistance to extinction could not be attributed to the P schedule alone, to the rats receiving two schedules, P and C, to stimuli other than S^R eliciting E_N, or to the rats forgetting reward-produced memories when expecting nonreward (Experiment 4). It was shown that the tandem hypothesis could explain the divergent findings obtained in prior studies employing a shift from P to C as well as in the present study.     

The role of within-trial location of the retention interval in rats’ delayed conditional discrimination performance

Rats were trained and tested on delayed conditional discriminations (DCDs) consisting of four possible light and tone stimulus sequences: light-light, tone-tone, light-tone, and tone-light. A lever was presented after the offset of the second or test stimulus, S₂. Two retention intervals (RIs) were present within the DCD task, one (RI-1) between the sample or first stimulus (S₁) and S₂, and the other (RI-2) between S₂ and presentation of the lever. Liquid reinforcement was contingent upon pressing only when S₂ matched S₁ in Experiment 1 or only when S₂ differed from S₁ in Experiment 2. RI-1 and RI-2 were separately increased to 5,10, and 20 sec from 1-sec training conditions. Increasing RI-1 produced greater declines in performance to light S₁ than to tone S₁ in both experiments. No such stimulus modality effect occurred for increases in RI-2 in these experiments. These results indicate that retrospection of S₁ occurred during RI-1 and prospection of a response decision and reward expectancy primarily occurred during RI-2.     

Impact of stimulus format and reward value on quantity discrimination in capuchin and squirrel monkeys

Quantity discrimination abilities are seen in a diverse range of species with similarities in performance patterns, suggesting common underlying cognitive mechanisms. However, methodological factors that impact performance make it difficult to draw broad phylogenetic comparisons of numerical cognition across studies. For example, some Old World monkeys selected a higher quantity stimulus more frequently when choosing between inedible (pebbles) than edible (food) stimuli. In Experiment 1 we presented brown capuchin (Cebus [Sapajus] paella) and squirrel monkeys (Saimiri sciureus) with the same two-choice quantity discrimination task in three different stimulus conditions: edible, inedible, and edible replaced (in which choice stimuli were food items that stood in for the same quantity of food items that were given as a reward). Unlike Old World monkeys, capuchins selected the higher quantity stimulus more in the edible condition and squirrel monkeys showed generally poor performance across all stimulus types. Performance patterns suggested that differences in subjective reward value might motivate differences in choice behavior between and within species. In Experiment 2 we manipulated the subjective reinforcement value of the reward by varying reward type and delay to reinforcement and found that delay to reinforcement had no impact on choice behavior, while increasing the value of the reward significantly improved performance by both species. The results of this study indicate that species presented with identical tasks may respond differently to methodological factors such as stimulus and reward types, resulting in significant differences in choice behavior that may lead to spurious suggestions of species differences in cognitive abilities.     

Second-order conditioning using a contextual stimulus as S1

Three experiments investigated the question of whether a spatial stimulus, a context, could function as S₁ in a second-order conditioning procedure. In each experiment, rat subjects were presented with S₁-US pairings by being given footshocks in one of two contexts. Forty-eight hours later, the experimental groups received S₂-S₁ pairings, during which a tone was presented in the training context. As measured by a lick-suppression test administered in a third context, rats were more fearful of the tone if it occurred in the context in which they had previously been shocked. The training context in each experiment apparently served to establish second-order fear conditioning to the tone.     

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.     

Reinstatement of postresponse stimuli prior to reward in delayed-reward discrimination learning by pigeons

Delayed-reward learning in pigeons was examined using a simultaneous red-green visual discrimination task in which the conditions during the delay interval were varied between groups. The nondifferential group received training in which the stimulus present during the 1-min delay was the same following a peck on the correct and incorrect colors. The other three groups received 1-min delay training in which different stimuli occurred in the delay interval following correct and incorrect choices. The differential group received continuous, differential stimuli during the delay. The reinstatement group received the differential stimuli in the 10 sec immediately following the choice and during the last 10 sec of the delay. The reversedcue group was treated in the same way, except that the 10-sec delay stimulus immediately following an incorrect response was also presented for 10 sec prior to reward on correct choices, and the stimulus following a correct response also occurred 10 sec before nonreward on incorrect choices. Nondifferential birds failed to learn the discrimination, while differential and reinstatement birds learned it readily. The reversed-cue birds learned to choose the incorrect stimulus. Differential and reinstatement birds showed no decrement in performance when the delay was increased to 2 min. These findings suggest that similarity of prereward and postresponse delay stimuli controls choice responding in long-delay learning, a finding compatible with both memorial and conditioned reinforcement interpretations.     

Primary frustration differences following brief partial-reinforcement acquisition under varying magnitudes of reward

In Experiment I, rats which had received six partially reinforced runway acquisition trials, with a reward magnitude of 60 sec access to wet mash on rewarded trials, showed less persistent responding over highly massed extinction trials than subjects which had received the same acquisition schedule but reward magnitudes of either 1 or 10 45-mg pellets. In Experiment II, rats which had received six partially reinforced placements into one compartment of a two-compartment box, with 60 sec access to mash on rewarded placements, jumped a hurdle faster to escape nonreward than subjects which had received the same reward schedule but 10 45-mg pellets on rewarded trials. The data supported a primary frustration analysis for reward-magnitude manipulations within brief partial-reinforcement schedules.     

Effects of sucrose concentrations on single-alternation performance in rats

In Experiment 1, rats received single-alternation training with 32% or 4% sucrose reward (Phase 1) followed by a shift in reward from 32% to 4%, and vice versa (Phase 2). In Phase 1, high reward facilitated alternation performance over low reward. In Phase 2, performance on rewarded trials increased as reward increased but was unchanged as reward decreased. Performance on nonrewarded trials showed negligible effects of shifts in reward. In Experiment 2, rats received goalbox placements with 32% or 4% sucrose alternated with nonreward in Phase 1; and in Phase 2, they received alternation runway training with the same or the opposite reward from that of placements. Performance on rewarded trials was faster, the higher the reward in runway training; performance on nonrewarded trials was slower, the higher the reward in placements. In Experiment 3, Phase 1 provided placements with 64%, 32%, 16%, or 4% sucrose or dry mash alternated with nonreward; Phase 2 provided alternation runway training with dry mash reward. Alternation prerformance developed more rapidly, the higher the sucrose concentration in placements. Only 64% sucrose produced performance superior to that for dry-mash placements.     

Pavlovian appetitive discriminative conditioning inAplysia californica

Three experiments demonstrated Pavlovian appetitive discrimination learning in the marine mollusc,Aplysia californica. In each experiment, subjects were exposed to two conditioned stimuli; one stimulus (CS+) was paired with food presentations and the other stimulus (CS?) was never followed by food. In Experiments 1 and 3 different chemosensory stimuli were used, and in Experiment 2 different tactile stimuli were used. For both types of conditioned stimuli, bite responses occurred significantly more often to the CS+ than to the CS?. Experiment 2 also showed thatAplysia could learn a reversal of this discrimination. Experiment 3 showed that nonreinforced presentations of CS+ resulted in a decline in the frequency of conditioned biting. The implications of these results for neurobiological analyses of learning are discussed.     

Fear-potentiated startle using three conditioned stimulus modalities

The capacities of three different conditioned stimulus modalities (light, noise, and airflow produced by a fan) to produce fear-potentiated startle were evaluated. Previous experiments have shown that following either light-shock or noise-shock pairings, both the light and noise conditioned stimuli acquire the ability to potentiate the acoustically elicited startle response in rats (the so-calledfear-potentiated startle effect). In Experiment 1, the ability of airflow produced by a fan to act as a conditioned stimulus was investigated. Rats were given either paired or impaired fan-shock training followed by a test for fear-potentiated startle. The fan conditioned stimulus potentiated startle only in the group given explicit fan-shock pairings. In Experiment 2, we evaluated the discriminability of the three conditioned stimulus modalities. Rats were given light, noise, or fan-shock pairings and were subsequently tested for fear-potentiated startle with the trained conditioned stimulus as well as the two remaining novel conditioned stimuli. Only the trained conditioned stimulus potentiated startle. These results show that fear-potentiated startle can be produced with three discriminable conditioned stimulus modalities, allowing the future use of fear-potentiated startle in the investigation of higher order conditioning phenomena.     

Hurdle-jump responding in the rat as a function of conspecific odor of reward and nonreward

A hurdle-jump escape response was employed to assess the laboratory rat’s aversion or attraction to different types of conspecific odor. Odorant donor subjects received 112 runway acquisition trials on a continuous reward schedule followed by 32 extinction trials, 112 acquisition trials on a 50% schedule of reward and nonreward followed by 32 extinction trials, or 144 “neutral” trials with no reward in the alley. Different groups of test subjects escaped from odor excreted by odorant subjects on (a) nonrewarded acquisition and extinction trials, (b) rewarded trials during continuous reinforcement, (c) rewarded trials during partial reinforcement, or (d) neutral trials; others escaped from a clean box. The principal findings were: (1) significant aversion to “odor of nonreward” appeared after the donor odorants had received 12 exposures to reward; (2) production of odor of nonreward by odorant subjects changed as a function of training experience with reward; (3) after repeated exposure to odor of nonreward, the escape response habituated; (4) greater or different odor excretion in extinction resulted from subjects trained on a continuous reward schedule than on a partial reward schedule. Relationships of the data to frustration theory were discussed, assuming that inferred differences in production of odor reflect differences in frustration reaction.     

Partial reinforcement delayed extinction effect after regularly alternating reward training

When extinction is delayed very long, the superior resistance to extinction of the random schedule group relative to the alternating schedule group disappears (partial reinforcement delayed extinction effect, PRDE). Two experiments assessed the effects of reinforcement/nonreinforcement on Trial 1 on the PRDE. Following extended partial reinforcement acquisition training in a runway, rats received extinction training after a short (1-day) or long (23-day) retention interval. The schedules used in Experiment 1 were: a single-alternation (SA) schedule beginning each day with a rewarded (r) trial, for Group r-SA; an SA schedule beginning with a nonrewarded (n) trial, for Group n-SA; and a random (Rd) schedule, for Group Rd. The schedules and group names used in Experiment 2 were r-SA, Rd, and r-Rd. The results were that (1) rats given r-SA schedules yielded considerable resistance under delayed extinction, (2) those given Rd and r-Rd schedules showed a decline in resistance to extinction over a long retention interval, (3) those given the n-SA schedule showed relatively low resistance at both retention intervals, although retention deficit was not greater than in the case of the Rd schedule, and thus, (4) the PRDE was found in both experiments, although only weakly in Experiment 1. The results indicated that a regularly alternating reward pattern was a more important determinant than was type of reward on Trial 1 for the PRDE. The PRDE due to differential retention deficits among schedules is discussed on the basis of dual-process associative sequential mechanisms and cognitive rule-encoding mechanisms.     

Effects of an aversive CS+ and CS− under deprivation upon successive classical appetitive and aversive conditioning

Rabbits under high or moderate water deprivation received in Stage 1 either paired (CS+), unpaired (CS?), or no-tone/shock presentations, with the pairings being appropriate for nictitating membrane conditioning. In Stage 2, all groups were given paired tone and water deliveries for jaw-movement conditioning, while, in Stage 3, all group received the tone and shock paired together for membrane conditioning. In Stage 2, the previously established aversive CS+ suppressed jaw-movement conditioning under high deprivation, and membrane CR decrements were directly related to deprivation. Also in Stage 2, the aversive CS? raised jaw-movement conditioning under moderate deprivation. In Stage 3, membrane CR performance immediately returned in the aversive CS+ group. For the other groups, conditioning was faster under high, relative to moderate, deprivation; however, the initial membrane CR occurrence required more trials if unpaired presentations were used in Stage 1. These results suggest that CSs can acquire both opponent-process and associative effects expressed according to the prevailing training conditions.     

Proactive interference, recency, and associative strength: Comparisons of black-capped chickadees and dark-eyed juncos

Black-capped chickadees (Parus atricapillus) and dark-eyed juncos (Junco hyemalis) were required to match to the last item from a series of up to three stimuli differing in both location and color. When rewarded for pecking the target stimulus during the study phase of each series, black-capped chickadees demonstrated proactive interference (PI) from stimuli presented prior to the target, whereas juncos did not. When they made an error, chickadees were more likely than were juncos to choose a distractor from the study series rather than a novel stimulus. When reward was no longer associated with presentation of the final target sample in a series, juncos also suffered PI. These results indicate that chickadees and juncos differ in the degree to which the recency of stimuli and the associative strength of stimuli control correct matching.     

Effects of sequences of sucrose reward magnitudes with short ITIs in rats

Two experiments assessed the role of aftereffect learning in rats rewarded with sucrose solutions. In Experiment 1, rats were trained in a single straight runway for two trials on each of 18 days, each trial terminating with either large (20% scurose) or small (3% sucrose) reward. The ITI was 3–5 min. The sequence of daily rewards for each of four groups was small-small (SS), small-large, (SL), large-small (LS), or large-large (LL). Response patterning and a simultaneous negative contrast effect were observed in LS and SL relative to the consistently rewarded controls. During 10 massed extinction trials, resistance to extinction was greatest for Group SL, followed in order by Groups SS, LL, and LS. Experiment 2 examined single alternation of large and small rewards administered for 10 trials on each of 31 days with an ITI of 60 sec. Reward for one group was 20% or 3% sucrose while another received 1 or 10 45-mg Noyes pellets. Appropriate patterning developed only in the food-pellet rewarded animals. The overall results suggest that sucrose rewards may produce high-amplitude and long-duration aftereffects which interfere with learning in designs employing several massed daily trials, but which may facilitate learning—relative to food-pellet rewards—with longer intertrial intervals and fewer daily trials.     

Second-order conditioning of the conditioned emotional response: Some methodological considerations

Employing rats in a CER procedure, the present study sought to determine the extent to which the second-order conditioning effects reported by Rizley and Rescorla (1972) represented first-rather than second-order conditioning. Subjects receiving first-order pairings of flashing light (CS₁) and shock followed by second-order pairings of noise (CS₂) and CS₁ displayed greater suppression to CS₂ than did control subjects receiving second-order pairings in the absence of first-order conditioning. This was true whether or not control subjects had experienced unsignaled shock or habituation to CS₁ prior to CS₂CS₁ pairings. Simple stimulus pairings did produce some suppression to CS₂, however. The procedure developed by Rizley and Rescorla (1972) appears to be a reliable means for producing and studying second-order aversive conditioning.     

Effects of interrun interval on serial learning

Two groups of five rats each received a decreasing quantity of food reward, 14-7-3-1-0 .045-g food pellets, over successive runs in a runway. The interrun interval (IRI) separating runs within each of two daily pattern repetitions (trials) was 10 sec (short, S) or 4–5 min (long, L) and varied over four successive phases of training in the order indicated by the group names, that is, Groups SLSS and LLLS. Anticipation of the 0-pellet element developed more rapidly in Group SLSS than in Group LLLS, but did eventually occur at the long IRI. Anticipation was eliminated by the increase in IRI experienced by Group SLSS in Phase 2 and by the decrease in IRI experienced by Group LLLS in Phase 4. The results are discussed with reference to the effects of changes in stimulus context accompanying IRI shifts on retrieval of task-specific knowledge and with reference to the possible signal value established to IRI-specific stimuli.     

Appetitive-aversion interactions: Facilitation of aversive conditioning by prior appetitive training in the rat

In Experiment 1, four groups of rats received conditioned suppression training in which a tone was reinforced with shock. If the tone had been previously paired with response-independent food, aversive conditioning was slightly facilitated by comparison to control groups preexposed either to the tone randomly associated with food or to the tone and food unpaired. However, by comparison to a control which was not preexposed to the tone, animals receiving prior pairings of the tone and food showed retarded aversive conditioning. Experiment 2 replicated the facilitation in aversive conditioning after the tone had been paired with food relative to the random control condition and demonstrated that this difference occurred even if the tone and background stimuli continued to be associated with response-independent food during aversive conditioning. This result suggests that pairing a stimulus with an appetitive reinforcer reduces the retardation of aversive conditioning produced by stimulus preexposure.     

Effects of reinforcement-paired stimuli on general activity

Two experiments were performed to explore the mechanisms responsible for the increase in activity that occurs in response to stimuli which have been paired with reinforcement (S^R. The first experiment showed a sharp increase in activity to S^R-paired stimuli under conditions in which subjects were not required to perform any instrumental response to obtain the S^R. This result seemed to rule out reinforcement of instrumental “food getting” behavior as the mechanism responsible for the learned activity increases. A second experiment used an “omission training” procedure to further explore the mechanisms underlying the activity increase. In this experiment, S^R was omitted on those trials on which activity increases were present during the stimulus. In this condition, no increases in activity were observed during the stimulus. There was, however, the characteristic increase in activity in a yoked-control group which received the same number and distribution of stimulus-paired S^Rs. The results of the second experiment open the possibility that increases in activity to S^R -paired stimuli could be due to the adventitious reinforcement of motor behavior rather than the Pavlovian conditioning of a motivational state.