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.     

Effects of partial vs consistent reward in noncontingent pairings of stimuli with reward: A noncontingently produced positive contrast effect

Rats received pairings of two stimuli with reward noncontingently in the Skinner box. During noncontingent pairings, the bar was immobilized. For Group CC 100% of the presentations of both stimuli were rewarded (S₁ ±, S₂ ±), for Group PP 50% of the presentations of each stimulus were rewarded (S₁, ±, S₂±), and for Group PC one stimulus was followed by reward on 50% of its presentations, while the second stimulus was followed by reward on 100% of its presentations (S₁ ±, S₂ ±). A fourth group received the stimuli and reward nonpaired. In a subsequent rewarded test phase, the response facilitating effects of the stimuli were evaluated. In the test phase all groups that received reward paired with S₁, and S₂ performed better in the presence of S₁ and S₂ than the group for which the stimuli were not paired with reward. For groups that received the stimuli paired with reward, a difference due to schedule of reward occurred when schedule of reward was varied within Ss (Group PC), but not when varied between Ss (Group PP vs Group CC). The specific form of this finding was that Group PC’s performance in the presence of S₂ ± was more vigorous than its performance in the presence of S₁ ± and was more vigorous than the performance of Groups PP and CC to S₂. Group PC’s performance to S₁ ± did not differ from that of Groups PP and CC to S₁.     

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.     

The learned function of food-deprivation cues: A role for conditioned modulation

Rats trained in one context to use stimuli arising from food deprivation as discriminative signals for shock were tested in other contexts to assess the basis of conditioned responding (i.e., freezing or behavioral immobility). In Experiment 1, discriminative control by 24-h food-deprivation cues failed to promote transfer responding in a test context that had no association with shock. This indicated that food deprivation cues had little direct excitatory power. However, transfer of behavioral control by 24-h food-deprivation cues was obtained in a context paired with shock only when the rats were 19 h water deprived. This finding agrees with the idea that food-deprivation cues become conditioned modulators of the capacity of external stimuli to activate their association with an unconditioned stimulus. In Experiment 2, rats trained to use 24-h food-deprivation cues as signals for shock exhibited significantly greater transfer performance when the transfer context had undergone partial extinction relative to when the transfer context had undergone only simple excitatory training. This finding with deprivation cues and transfer contexts (1) paralleled earlier results obtained with discrete (auditory and visual) conditioned modulators and transfer targets, and (2) posed difficulties for associative summation and generalization interpretations of transfer performance.     

Transfer between Pavlovian facilitators and instrumental discriminative stimuli

Two experiments assessed the degree to which Pavlovian facilitators were interchangeable with instrumental discriminative stimuli (S^ds). In Experiment 1, rats were trained in a Pavlovian paradigm in which one stimulus (i.e., a facilitator) signaled the reinforcement of another stimulus (i.e., a target). Next, the rats were given instrumental discrimination training in which an S^d signaled the reinforcement of barpressing. A transfer test then assessed the capacity of the Pavlovian facilitator to promote barpressing. The results showed that the facilitator promoted significant barpressing, both when it was presented alone and when it was presented in compound with the S^d. Reliable transfer was not obtained with a “pseudofacilitator” control stimulus that, during training, was uninformative about the reinforcement of its target. Experiment 2 showed that a stimulus trained as an instrumental S^d reliably augmented responding to a stimulus previously trained as a target in a Pavlovian facilitation paradigm. A “pseudo-S^d” that, during training, was uninformative about the reinforcement of barpressing failed to promote such transfer. These results show that Pavlovian facilitators and instrumental S^ds are interchangeable to a significant degree, and suggest that facilitators and S^ds may act via similar mechanisms.     

Contextual cues and the retrieval of competing memories of goal events

In Experiment 1, four groups of rats were initially trained on a discrimination which established a stimulus as a signal for reinforcement. That signal was then presented during subsequent partial reinforcement training in a way that could potentially interfere with retrieval of the memory of nonreinforcement (S^N) on the preceding trial either because (1) thestorage and retrieval contexts for S^N were different (retrieval failure hypothesis), or (2) the memory of reinforcement produced by the signal acted as a competing memory (competing memory hypothesis). Experiment 1 supported the competing memory hypothesis. In Experiment 2, we investigated the effect of stimulus change on the capacity of the context to retrieve a competing memory of a temporally remote reinforcement event with which the context was strongly associated. Retrieval of a competing memory was impaired by differences between the storage and retrieval contexts in a manner analogous to the effect of context on retrieval of a reinforcement event memory from an immediately preceding trial.     

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.     

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.     

Deprivation level and choice in pigeons: a test of within-trial contrast

Within-trial contrast has been proposed as a mechanism underlying preferences for stimuli that follow relatively more aversive events over stimuli that follow less aversive events. In this study, we manipulated deprivation level to test within-trial contrast predictions. In Experiment 1, pigeons encountered two discriminative stimuli, one presented when they were deprived and the other when they were prefed. When later given a choice between the two stimuli, pigeons strongly preferred the stimulus encountered when deprived, independently of their deprivation level at test. In Experiment 2, pigeons learned two simultaneous discriminations, one when deprived and the other when prefed. Here, subsequent tests between the two S⁺ or the two S⁻ stimuli revealed no consistent preferences. These contrasting findings suggest that differential aversiveness is necessary but not sufficient to induce preferences via within-trial contrast.     

Chemosensory-based contextual conditioning inHermissenda crassicornis

In two experiments, the marine molluskHermissenda crassicornis was exposed to context discrimination training. In one context, defined by the presence of a diffuse chemosensory stimulus (shellfish extract A), brief, unsignaled, unconditioned stimuli (USs; high-speed rotation) were presented; in a second context, defined by the presence of shellfish extract B, no USs were presented. Animals were then tested (at both 1.5 and 24 h) by exposing them to small pieces of the shellfish meat used to define the two contexts. The latency to strike at the meat served as an index of the context-US association. In Experiment 1, the latency to strike at the cue associated with rotation was reduced relative to both preconditioning strike latencies and the associatively neutral cue. However, in a two-choice test where the animals could approach the conditioned or neutral stimulus, the animals regularly avoided the stimulus paired with rotation. Moreover, if, following conditioning, the animals were presented with an unsignaled rotation in the conditioned context or the neutral context, the animals exhibited more effective defensive clinging (an unconditioned reflex normally elicited by rotation) in the conditioned context, suggesting that it “prepared” the animal for the aversive US. In total, these results demonstrate thatHermissenda is capable of making associations to diffuse background (contextual) stimuli. Moreover, the results suggest that pairing the chemosensory cue with an aversive US elicits a strike response inHermissenda when the animal is placed in forced contact with the cue and an active avoidance response when the animal can choose between that cue and a neutral cue.     

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 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.     

Range effects using instrumental choice procedures

Pigeons were trained to discriminate visual flicker-rate stimuli using two types of instrumental choice procedures. One experiment used a free-operant concurrent schedule with multiple schedule components. Two additional experiments used a two-alternative, discrete-trial procedure. In all experiments, the range of training stimuli was manipulated across conditions. Results from all three experiments showed typical range effects on discrimination performance. That is, performance declined with increases in the overall range of variation of training stimuli. These range effects occurred with either continuous response rate measures or discrete choice measures. Moreover, range effects appeared with relatively high or low levels of overall discrimination accuracy and with either symmetrical or asymmetrical extensions of stimulus range. The results of these experiments suggest that increasing stimulus range influences both perceptual sensitivity and bias to response alternatives.     

Determinants of value transfer and contrast in simultaneous discriminations by pigeons

In a simultaneous discrimination involving a positive (S+) and a negative (S₋) stimulus, positive value appears to transfer from the S+ to the S₋. However, negative value does not appear to transfer from the S₋ to the S+. Instead, when sufficient experience with the contingencies associated with responding to the S₋ is provided, it appears that the presence of the S₋ enhances the value of the S+ (i.e., a contrast effect is found). The purpose of the present experiments was to further examine the influence of the S+ on the S₋ in a simultaneous discrimination (between subjects in Experiment 1 and within subjects in Experiment 2). In both experiments, we found that under typical training conditions, given little direct experience with the value of the S₋, value transfers from the S+ to the S₋. If sufficient experience with the value of the S₋ is provided, however, contrast between the S+ and the S₋ can be demonstrated. Thus, in a simultaneous discrimination, value transfer from the S+ to the S₋ depends on the animal’s having responded relatively little to the S₋.     

Stimulus preexposure speeds or slows subsequent acquisition of associative learning depending on learning test procedures and response measure

Prior exposure to a conditioned stimulus (CS) typically results in latent inhibition—slower acquisition of associative learning about that stimulus in subsequent training. Here, we found that CS preexposure had different effects on the appetitive conditioning of rats with a sucrose unconditioned stimulus (US) depending on training test procedures, the similarity of preexposure and training procedures, and the choice of response measure. Preexposure to a visual or an auditory stimulus produced facilitation of acquisition of food-cup-directed responding when both of those cues were (separately) paired with sucrose delivery in the training test (Experiments 1 and 3). By contrast, the same preexposure procedure resulted in latent inhibition of food-cup learning if the second stimulus in the test phase was of the same modality as the preexposed stimulus (Experiment 2). In Experiment 3, latent inhibition was enhanced if both phases included a single CS or both phases included both auditory and visual CSs, compared to treatments in which only one CS was presented in one phase but two CSs were presented in the other phase. In Experiment 4, preexposure of an auditory cue slowed subsequent learning about it if the context was salient but enhanced learning if the context was of weaker salience. Finally, a measure of general activity revealed latent inhibition after preexposure in all conditions in all 4 experiments. We discuss the results within several classes of latent inhibition theories, none of which provides a comprehensive account.     

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.     

Retrieval of memory in the pigeon by context manipulations

In Experiment 1, 12 pigeons were given eight sessions of VI single stimulus training with a color in a particular context followed by eight sessions of similar training with a line angle in another context. On the next day, half of the subjects were tested for wavelength and angularity generalization in each of the two contexts, a procedure that was thus consistent with training for one dimension and inconsistent for the other. The subjects made significantly more responses to each training stimulus under the consistent context condition, but there was no difference in absolute or relative generalization slopes. In Experiment 2, 12 pigeons were trained as in Experiment 1, but during generalization testing they were exposed to both contexts sequentially. Under the consistent context condition, the subjects responded more to the two training stimuli and yielded sharper absolute and relative wavelength generalization gradients: Under the inconsistent context condition, responding to the training wavelength was substantially disrupted. Thus, under appropriate testing conditions, contextual control over both the amount and the selectivity of responding can be demonstrated.     

Sample duration and type of stimuli in delayed matching-to-sample in rhesus monkeys

Two experiments were performed to determine the effect of sample duration (0.1, 2, and 4 sec), delay interval (.03, 4, 8, 16, and 32 sec), and type of stimulus (color and shape) on the matching performance of rhesus monkeys. In Experiment 1, the 15 possible delay-duration combinations were randomly presented in blocks of 15 trials. In Experiment 2, each duration was held constant and the five delays randomly presented. Then each delay interval was held constant with the three durations randomly varied. Matching performance increased as sample duration increased (ps < .01 and .005), while length of delay did not significantly affect performance. The type of stimuli paired in the matching test significantly affected performance (ps < .05 and .10) with the shape/shape choices leading to the poorest performance. Stimulus discriminability and amount of training with brief sample durations were implicated as significant determinants of matching performance.     

First- and second-order configural sensitivity for greeble stimuli in baboons

Previous studies on nonhuman primates have shown inconsistencies in their processing of first- and secondorder relational properties of facial stimuli. Using greeble stimuli sharing configural properties with faces, this study assessed configural processing in baboons. Five baboons were trained to recognize a positive stimulus among pairs of greebles in a two-alternative forced choice task. They were then tested with new stimulus pairs involving either a first-order version, with modifications in global qualitative spatial relations, or a second-order version, with modifications of finer spatial relations. Performance remained above chance in all test conditions, including when only second-order cues were available, but it was higher for first-order trials. It is proposed that an extensive training with greebles led to the processing of second-order relational properties. These results demonstrate that configural sensitivity is not restricted to faces in baboons and suggest that a common mechanism may support configural processing for face and nonface stimuli.     

Higher order occasion setting

Higher order occasion setting with serially presented stimuli was investigated in an appetitively motivated, discrete-trial operant study with rats. Reinforcement of barpressing during an occasion-setting light (a discriminative stimulus) was contingent on immediately preceding second-order occasion setters (i.e., a click train or a buzzer served as a conditional discriminative stimulus). Moreover, the meanings of the clicks and buzzer were themselves indicated by a third-order occasion setter that preceded them (i.e., a white noise acted as a second-order conditional discriminative stimulus). Subjects responded more frequently and had shorter latencies to the first response in the presence of the light on trials during which barpressing was reinforced than on trials during which barpressing was not reinforced. The likelihood that the subjects solved the problem by responding to unique compound stimuli was minimized by the insertion of a 5-sec gap between the different controlling stimuli presented on each trial. Thus, these subjects appear to have mastered a second-order conditional discrimination, which is equivalent to third-order occasion setting if the discriminative stimulus (light) is viewed as a first-order occasion setter. Although the subjects learned to respond appropriately to each of the compound stimuli, differences in responding to specific stimuli were consistent with a higher order feature-positive effect. Some implications of higher order occasion setting are discussed, including the issue of independence between the different levels of occasion setting signaled by a single stimulus.