Grasping in the pigeon (Columba livid): Stimulus control during conditioned and consummatory responses

Control of beak opening (gape) and peck location was examined in pigeons. Feeding pecks showed accurate guidance that positioned the seed between the beaks. At the moment of contact with the seed, gape was proportional to seed diameter, although pecks with gape less than seed diameter were more frequent following an increase in seed size during a meal. There were no substantial differences between pigeons trained to keypeck with autoshaping and those trained with operant conditioning procedures. With either procedure, water reinforcement produced keypecks with the beak closed; seed reinforcers of different sizes produced means for gape proportional to the seed diameters. Black or white circular stimuli of different sizes projected as conditioning signals had little influence upon gape, but a greater percentage of responses was directed to white stimuli. These results indicate that visual stimuli elicit and orient the peck, whereas the adjustment of gape also involves the somatosensory stimuli provided during previous experience with a particular reinforcer or food type.     

Classical conditioning of jaw movements in the pigeon: Acquisition and response topography

Previous studies have shown (1) that the form of the pigeon’s conditioned keypecking response resembles that of its ingestive pecking response, (2) that both ingestive and conditioned pecking in the pigeon are compound responses, including both transport (neck-movement) and gape (jaw-movement) components, and (3) that during operant conditioning or autoshaping of pecking behavior, the gape component comes under the associative control of the CS. In the present study, the gape component was experimentally isolated and a classical conditioning paradigm (water US) was used to bring jaw movements under the control of a CS (light). The results indicate that the topography of the jaw-movement CR is very similar to, though more variable than, that of the UR. They are consistent with the hypothesis that reported similarities in the form of ingestive and conditioned pecking responses reflect, in part, classical conditioning of the gape component.     

Dissociation of the effect of reinforcer type and response strength on the force of a conditioned response

A dissociation between the effect of reinforcer type and response strength on the force of the pigeon’s keypeck response was shown in three experiments. In Experiment 1, pigeons were trained to peck two conditioned stimuli, one paired with water and another paired with grain. The pigeons made more forceful pecks for grain than for water and also showed a tendency, albeit an unreliable one, to respond on a higher percentage of food trials than water trials. In Experiment 2, the pigeons from Experiment 1 were satiated with either food or water and were then presented with the two conditioned stimuli in an extinction test. It was found that, regardless of the drive state, the pigeons made more forceful pecks to the stimulus that predicted food than to the stimulus that predicted water. In the thirsty group, however, this difference in force was not accompanied by a difference in the percentage of trials with a response. In Experiment 3, pigeons trained with a single reinforcer pecked more often on instrumentally reinforced trials than on Pavlovian conditioning trials, but there was no difference in the force of the pecks. Taken together, these results imply that differences in response strength cannot account for the difference between the force of food- and water-reinforced pecks. Instead, stimulus-substitution theory may provide the best account of the topography of the two types of pecks.     

The role of response-reinforcer associations increases throughout extended instrumental training

Two experiments examined the effects of extended training on the development of response-reinforcer associations. Rats were trained by using various food reinforcers to make multiple instrumental responses. Subsequently, those reinforcers were devalued by being paired with a toxin. The presence of response-reinforcer associations was inferred from the decrease in the likelihood of a response following devaluation of its reinforcer. Such response-reinforcer associations are known to contribute to performance after moderate amounts of training. These experiments addressed the question of whether the contribution of those associations remains constant, increases, or decreases with more extended training. Experiment 1 found that even after a response had been extensively trained with one reinforcer, the substitution of a new reinforcer produced new associations between the response and that new reinforcer. After extended training, a response continued to acquire new associations with a reinforcer, as indexed by the impact of a devaluation procedure. Experiment 2 directly compared the contribution of reinforcers used extensively and moderately with the same response. It found that devaluation of the extensively used reinforcer more effectively reduced performance of the response, suggesting that the associations formed with additional training contribute to performance of the response. These experiments indicate that the contribution of response-reinforcer associations does not decrease but, instead, continues to grow throughout the course of extended instrumental training.     

Instrumental response topographies of rats

Experiments 1, 2, and 3 showed that food-deprived rats responding for food pellets made significantly more long-duration leverpresses than water-deprived rats responding for water drops. These experiments further showed that this difference in instrumental response topography is long-lived, and depends neither upon idiosyncrasies of the experimental chamber nor upon severity of deprivation conditions. In Experiment 4, food-deprived rats responding for food pellets made significantly more long-duration leverpresses than did either food- or water-deprived rats responding for sucrose solution. Human judges in Experiment 5 were able to correctly identify instrumental leverpress responses by rats as being for food or water based solely on previous viewings of other rats drinking water or eating food pellets. It appears that instrumental response topographies in rats vary depending principally upon the reinforcer received, and that these instrumental response topographies resemble consummatory response topographies.     

A behavior systems view of responding to probe stimuli during an interfood clock

Two experiments used a behavior systems approach to relate the form of responses during an interfood clock to the temporal distance of the individual clock stimuli to food. Stimuli proximate to food should better control a focal search mode and related responses, whereas stimuli temporally distant from food should better control a general search mode and related responses. Experiment 1 conditioned two groups of rats with a sequence of four equal-length 12-sec clock stimuli that terminated with food and then tested for the conditioning of a general search mode by presenting an unconditioned moving probe stimulus (either a rolling ball bearing or a rotating mechanical door) during each of the clock stimuli. Consistent with a behavior systems view, contact with the ball bearing was markedly greater during a clock stimulus distant from food. The absence of similar differential contact of the door across the clock stimuli showed that the effect was specific to the ball bearing rather than a general response to stimulus dimensions of movement and sound. Experiment 2 showed that the general search mode was controlled by the clock stimulus rather than the passage of time.     

Selective reinstatement of stimulus-outcome associations

In two experiments, the possibility of outcome-selective reinstatement of conditioned responding was examined. Evidence for outcome-selective reinstatement of previously extinguished appetitively conditioned magazine responses by rats was observed in both Pavlovian (Experiment 1) and discriminated instrumental conditioning (Experiment 2) procedures. In both experiments, stimulus-elicited magazine responses occurred more in the presence of a stimulus whose reinforcer was reinstated than they did in the presence of another stimulus whose reinforcer was not reinstated. This effect was observed after both brief and extensive amounts of extinction. Outcome-selective reinstatement of instrumental leverpressing, however, was not observed, although nonselective reinstatement of magazine responding and leverpressing was obtained in Experiment 2. Overall, the data from these studies challenge existing theories of reinstatement, and they provide additional evidence of the importance of outcome-specific processes in the control of learned performance.     

Temporal integration and instrumental conditioned reinforcement

Stimuli associated with primary reinforcement for instrumental behavior are widely believed to acquire the capacity to function as conditioned reinforcers via Pavlovian conditioning. Some Pavlovian conditioning studies suggest that animals learn the important temporal relations between stimuli and integrate such temporal information over separate experiences to form a temporal map. The present experiment examined whether Pavlovian conditioning can establish a positive instrumental conditioned reinforcer through such temporal integration. Two groups of rats received either delay or trace appetitive conditioning in which a neutral stimulus predicted response-independent food deliveries (CS1→US). Both groups then experienced one session of backward second-order conditioning of the training CS1 and a novel CS2 (CS1–CS2 pairing). Finally, the ability of CS2 to function as a conditioned reinforcer for a new instrumental response (leverpressing) was assessed. Consistent with the previous demonstrations of temporal integration in fear conditioning, a CS2 previously trained in a trace-conditioning protocol served as a better instrumental conditioned reinforcer after backward second-order conditioning than did a CS2 previously trained in a delay protocol. These results suggest that an instrumental conditioned reinforcer can be established via temporal integration and raise challenges for existing quantitative accounts of instrumental conditioned reinforcement.     

Conjunctive differentiation of gape during food-reinforced keypecking in the pigeon

The pigeon’s keypecking response includes both a head-transport (peck) and a jaw-movement (gape) component. Because the two components are mediated by different effector systems, they may potentially be viewed as orthogonal responses. A response differentiation procedure was used to bring gape amplitude under operant control. The procedure employed a conjunctive response requirement in which reinforcement was contingent upon both gaping and key contact. The key-contact requirement was held constant, while the gape contingency was systematically varied to reinforce either decreases or increases in gape amplitude with respect to baseline. The procedure was effective in shifting the gape distributions in both the upward and downward directions and in inducing new gape values that deviated from the baseline in the reinforced direction. These observations indicate that gape may be brought under operant control. However, subjects showed a bias in the differentiation of the gape response, such that larger gapes were more readily differentiated than smaller gapes. The results are discussed in relation to the methodological utility of the paradigm, the problem of biological constraints on learning, and the heuristic utility of a response components analysis.     

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.     

Sign-tracking (autoshaping) in rats: A comparison of cocaine and food as unconditioned stimuli

A series of experiments was performed to determine whether sign-tracking would occur in rats with intravenous (i.v.) cocaine as the unconditioned stimulus. In Experiment 1, a retractable lever paired with food produced strong sign-tracking, but a lever paired with one of three doses of i.v. cocaine did not elicit any approach or contact behavior. Experiment 2 demonstrated that doses of cocaine that did not elicit sign-tracking would function as a positive reinforcer for a lever contact operant. In Experiment 3, an artificialconsummatory response was added to make the cocaine reinforcement episode more behaviorally comparable to that occasioned by food. Although the rats readily performed this response when it was required to receive cocaine infusions, they still did not contact a lever that signaled the availability of these infusions. It appears that cocaine is different from other positive reinforcers (e.g., food, water, warmth, or intracranial stimulation) in that it will not produce sign-tracking in rats.     

Directed approach responses and positive conditioned suppression in the rat

Three experiments evaluated an alternative to accounts of positive conditioned suppression that stress central (i.e., motivational or emotional) states. This “competing-response” interpretation was tested by analyzing directed movements that develop in rats during a visual or an auditory stimulus (CS) that signals an appetitive reinforcer (US) in a situation where the subject is also emitting an instrumental response for food. In each experiment, positive conditioned suppression (i.e., a reduction in the rate of such instrumental responding during CS presentations) was accompanied by responses directed toward the CS source and/or the US-delivery site. In Experiment 1, a diffuse (auditory) CS signaled a US delivered at some specific place in the chamber and rats approached the US-delivery site during CS. In Experiments 2 and 3, the spatial proximity of a localized visual CS and US-delivery site determined whether CS-directed or US-directed behavior predominated during the CS. The results suggest that the topographies of conditioned responses on any positive conditioned suppression procedure depend upon the spatial arrangements of features that elicit and support these behaviors. They further suggest that the identification of these features and their spatial arrangements is necessary for the analysis of appetitive classical-instrumental interactions.     

The effects of qualitative and quantitative variation in the US on individual components of Pavlovian appetitive conditioned behavior in rats

The form of rats’ Pavlovian conditioned responses to visual and auditory conditioned stimuli (CSs) paired with a variety of unconditioned stimuli (USs) was examined in three experiments using direct behavioral observation techniques. In Experiment 1, the form of conditioned behavior occurring most frequently during later portions of the CS-US interval depended only on which of several appetitive USs was used, but the form of behavior occurring most frequently during early portions of the CS-US interval depended only on the nature of the CS. US-dependent behaviors resembled the response to the US, and CS-dependent behaviors resembled the original orienting response (OR) to the CS. In Experiment 2, the use of larger magnitude appetitive USs resulted in higher frequencies of US-dependent behaviors, but lower frequencies of CS-dependent behaviors in the presence of auditory and visual CSs. In Experiment 3, US-dependent conditioned behavior to auditory and visual CSs paired with shock was more frequent when high-intensity shocks were used, but CS-dependent behavior was more frequent when low-intensity shocks were used. These results suggested that Pavlovian conditioned responding may involve two independent types of behavior—one appropriate to the US and another based on the original OR to the CS.     

Rats’ responses to a moving object related to food or water: A behavior-systems analysis

The present experiments compared rats’ responses to a moving object (a rolling ball bearing) related to either food or water under both Pavlovian and operant contingencies. In Experiment 1, food-restricted rats contacted food-related bearings more frequently and with more complex response patterns than water-restricted rats contacted water-related bearings. Food-related contacts occurred with shorter latency, longer average duration, and increased likelihood of dig, carry, and chew. Experiment 2 revealed that once contact with the bearing had been established, its form persisted despite changes in the type of reward and restriction. In Experiment 3, rats that were simultaneously food and water restricted learned to discriminate between painted and unpainted bearings related to food versus no food, water versus no water, and food versus water. Again, food-related bearings produced more complex, although not more frequent, interactions than did water-related bearings. In none of the experiments did rats lick the ball bearing related to water. The results supported a behavior-system approach, but not the stimulus-substitution or arbitrary-operant accounts of conditioned-response topography.     

Stimuli associated with the cancellation of food and its cues enhance eating but display negative incentive value

Initially neutral conditioned stimuli paired with food often acquire motivating properties, including serving as secondary reinforcers, enhancing instrumental responding in Pavlovian-instrumental transfer procedures, and potentiating food consumption under conditions of food satiation. Interestingly, cues associated with the cancellation of food and food cues may also potentiate food consumption (e.g., Galarce and Holland, 2009), despite their apparent negative correlations with food delivery. In three experiments with rats, we investigated conditions under which potentiation of feeding by such “interruption stimuIi” (ISs) develops, and some aspects of the content of that learning. Although in all three experiments ISs enhanced food consumption beyond control levels, they were found to act as conditioned inhibitors for anticipatory food cup entry (Experiment 1), to serve as conditioned punishers of instrumental responding (Experiment 2), and to suppress instrumental lever press responding in a Pavlovian instrumental transfer procedure (Experiment 3). Furthermore, when given concurrent choice between different foods, an IS enhanced consumption of the food whose interruption it had previously signaled, but when given a choice between performing two instrumental responses, the IS shifted rats’ choice away from the response that had previously yielded the food whose interruption had been signaled by IS (Experiment 3). Thus, the effects of an IS on appetitive responses were opposite to its effects on consummatory responding. Implications for our understanding of learned incentive motivation and the control of overeating are discussed.     

A test of two methods for extinguishing Pavlovian conditioned inhibition

Two experiments were performed using rats in a conditioned suppression procedure to test two different methods for extinguishing Pavlovian conditioned inhibition. In both experiments, a target stimulus, X, was made inhibitory by giving discrimination training of the form A+ AX?. Then, in Experiment 1, an attempt was made to extinguish the inhibition conditioned to X by presenting nonreinforced occurrences of X, of AX, and of A. Testing for conditioned inhibition took the form B+ BX?. It was found that the extinction procedure did not weaken the inhibitory properties of X. Experiment 2 attempted to extinguish the inhibition conditioned to X by presenting X randomly and independently of the reinforcer, electric grid shock. This procedure appeared to weaken inhibition quickly and permanently.     

The residual deprivation effect in instrumental conditioning as a function of deprivation level at the time of exposure to the reinforcer

The effect of food deprivation level at the time of initial exposure to a subsequent food reinforcer was investigated in two experiments. In Experiment 1, deprivation at the time of initial exposure influenced the subsequent acquisition and extinction of an instrumental response. In Experiment 2, the residual deprivation effect associated with a reduction in deprivation level occurred only when rats initially experienced the reinforcer at a high, as compared with a low, deprivation level. Results were discussed in terms of the assumption that the limits of incentive generated by a reinforcer are influenced by the deprivation state at the time of first exposure to that reinforcer.     

The role of habituation of the response to LiCl in the US-preexposure effect

In two experiments, rats received preexposure consisting of six intraperitoneal injections of lithium chloride (LiCl). This treatment reduced the magnitude of the unconditioned response (UR; suppressed consumption of a novel flavor) evoked by an additional injection (Experiment 1) or by oral consumption (Experiment 2) of LiCl. In both experiments, preexposure also attenuated the acquisition of a conditioned aversion with an LiCl injection as the unconditioned stimulus (US) but had no effect on the aversion produced when the US was oral consumption of LiCl (Experiment 2). These results are consistent with the view that the reduced ability of the preexposed US to serve as a reinforcer depends on blocking by injection-related cues and is independent of habituation of the UR recorded in the present study. Possible interpretations of this dissociation are discussed.     

The effects of changeover delays of fixed or variable duration on concurrent variable-interval performance in pigeons

The effects of changeover delays of fixed or variable duration on concurrent variable-interval performance in pigeons were investigated in a series of three experiments. Experiment 1 compared the effects of a fixed, variable, or variable signaled changeover delay on interchangeover times and responding during and after the changeover delay. The duration of the changeover delays was systematically varied in Experiment 2, and the relative reinforcement frequencies were manipulated in Experiment 3. Interchangeover times were found to be shorter when changeover delays of variable duration were compared with those of fixed duration. Changeover delays of fixed duration produced higher response rates during the changeover delay than after the changeover delay had elapsed; changeover delays of variable duration produced such differences to a lesser extent. It was concluded that the changeover delay in concurrent variable-interval schedules of reinforcement functionally acts as a delay period to the next opportunity for reinforcement, possibly serving as a conditioned reinforcer for the behavior preceding it (the interchangeover time) and as a discriminative stimulus for the behavior in its presence (response rates during the delay).