Microstructural analysis of conditioned and unconditioned responses to maltodextrin

The microstructure of licking responses was analyzed to investigate the interaction between unconditioned responses to maltodextrin and the responses to flavor cues previously associated with maltodextrin. Experiment 1 demonstrated that although the consumption of maltodextrin peaked at intermediate concentrations, the mean lick cluster size showed a positive, monotonic increase with concentration. In Experiment 2, a (conditioned stimulus) CS+ flavor was paired with 16% maltodextrin, whereas a CS- flavor was paired with 2% maltodextrin. During test, consumption of the CS+ was higher than that of the CS- when the flavors were combined with 2% maltodextrin, but not when combined with 16% maltodextrin. In contrast, cluster size was larger with the CS+ than with the CS-, regardless of the concentration of maltodextrin present on test. Previous analyses of licking microstructure indicate that cluster size reflects the palatability of the ingested solution. Thus, the present results indicate that flavor conditioning can change the palatability of the cue flavors. Adding the CS+ flavor to maltodextrin produced results analogous to increasing the concentration of maltodextrin (in terms of both consumption and licking microstructure measures), which is consistent with the idea that after conditioning, responses to the CS+ flavor and to the unconditioned stimulus are mediated via the same representation.     

Encoding of the unconditioned stimulus in Pavlovian conditioning

Three experiments, using rats, demonstrated the encoding of a food unconditioned stimulus (US) in a simple Pavlovian conditioning paradigm. In all three studies, one stimulus was used to signal the delivery of pellets and a different stimulus was used to signal the delivery of sucrose. In Experiment 1, postconditioning devaluation of one of the food USs selectively reduced the frequency of conditioned magazine-directed behavior during the stimulus trained with that US. In Experiment 2, transfer of the stimuli to instrumental responses resulted in selective depression of the response trained with a different outcome. In Experiment 3, acquisition of stimulus-outcome learning was impaired by unsignaled intertrial presentations of the same outcome but not of a different outcome. These results indicate that a detailed representation of the outcome is encoded in the normal course of Pavlovian conditioning.     

Intertrial interval and unconditioned stimulus durations in autoshaping

Four groups of pigeons were exposed to an autoshaping procedure in which a 20-sec key illumination preceded the presentation of response-independent grain, The groups differed according to the duration of feeder access and the intertriai intervals, If feeder durations are not included in the time between trials, two of the groups had identical intertriai intervals. If feeder durations are included, each of the other two groups was identical to one of the first two in terms of the intertriai interval, The speed of acquisition and maintained measures of responding were directly related to the duration of the interval from food offset to signal onset, Groups exposed to equivalent intertriai intervals and different feeder durations did not differ from one another on these measures, The results were interpreted as evidence that feeder durations were not included in the functional intertrial interval and that feeder duration, per se, did not affect autoshaped responding.     

Context sensitivity of conditioned suppression following preexposure to the conditioned stimulus

Conditioned suppression in rats is often unaffected when the context (or set of background stimuli) is changed following conditioning. This suggests that responding to the conditioned stimulus (CS) can be relatively insensitive to the context in which the CS is presented. In two experiments, we examined whether sensitivity to contextual stimuli is affected by preexposure to the CS. In Experiment 1, when the CS was novel at the outset of conditioning, conditioned suppression was not affected when the context was changed following conditioning. However, when the CS had been preexposed, responding was weaker when extinction occurred outside of the conditioning context. In Experiment 2, responding was again sensitive to the test context, regardless of whether preexposure occurred in the conditioning context or in an alternate context. These results suggest that the extent to which responding is sensitive to context can depend on the conditioning history of the CS.     

Conditioned and unconditioned stress-induced analgesia: Stimulus preexposure and stimulus change

Aversive events such as electric shock lead to analgesia. There have been differing views with regard to whether the aversive event itself can lead to analgesia as a direct unconditioned reaction, or whether the analgesia is instead a reaction to fear conditioned to cues present during shock or to other associative processes initiated by the aversive event. Maier (1989, 1990) has argued that aversive events such as shock lead to both types of analgesia, with the type observed depending on test conditions. Unconditioned analgesia was argued to be present soon after shock, with conditioned analgesia replacing the unconditioned form if the subject is allowed to remain in the shock environment. Consistent with this argument, the experiments reported here show that (1) preexposure to the environment in which shock later occurs has no effect on the analgesia soon after shock, but eliminates the later analgesia; (2) the initial postshock analgesia is unaffected by removing the subject from the shock environment to a different environment, but the later reaction is prevented by such a change; (3) returning the subject to the shock environment after confinement in a nonshock environment rearouses an analgesic reaction; and (4) this rearousal does not occur if the subject has first been confined to the shock environment without shock.     

Behavior patterns in pigeons during autoshaping with an incremental conditioned stimulus

Pigeons were trained on a variant of the autoshaping procedure in which a keylight stimulus of increasing brightness was used to signal the passing of a 30-sec interfood interval (IFI). Key-pecking developed in all subjects within the first session (65 trials). Within trials, pecking began midway through the IFI, increased throughout the remainder, and decreased just before food delivery. Other behavioral stereotypies were also recorded: Low light levels were associated with a retreat to the rear of the test chamber, and medium light levels (during the midportion of the IFI) were associated with high rates of pacing toward and away from the food source. Probe trials revealed that pecking, pacing, and retreat were all under strong stimulus control; that is, when the light was held constant at its lowest or highest brightness, or when the brightness ramp was presented in reverse order, the behavior pattern almost invariably remained tied to stimulus brightness. Results are discussed in terms of associative and nonassociative sources of the form and sequential characteristics of the behavior.     

Effects of proximal unconditioned stimulus preexposure on ingestional aversions learned as a result of taste presentation following drug treatment

Taste aversions were conditioned by exposing subjects to a 1.0% saccharin solution 30 min after an injection of lithium chloride. The aversion learning was disrupted if subjects had also received an additional lithium injection some time earlier (Experiments 1–3). This interference effect of US preexposure was a decreasing function of the preexposure interval, beyond the optimal interval (105 min) for observing the phenomenon (Experiment 1), and was directly related to the dose of the preexposure injection (Experiment 2). No interference with conditioning occurred at short (e.g., 30-min) preexposure intervals (Experiment 1), probably because under these circumstances the preexposure injection itself conditioned a strong aversion (Experiment 4). At moderate (105-min) but not at short (30-min) preexposure intervals, the interference with aversions learned as a result of taste exposure following drug injection was comparable to the interference with learning in a more conventional forward conditioning procedure (Experiments 3 and 4). These findings are similar to previously documented effects of proximal CS- and US-preexposure and are consistent with recent stimulus rehearsal and opponent-process theories.     

Blocking of the sexual conditioning of differentially effective conditioned stimulus objects

The blocking phenomenon was investigated in the sexual response system of male Japanese quail. Access to a live female quail served as the unconditioned stimulus (US). The same audiovisual cue served as the pretrained stimulus in all of the experiments. Following asymptotic conditioning of the audiovisual cue, a second conditioned stimulus (CS2) was added. In Experiment 1, CS2 was a rectangular wood block that had little or no resemblance to a female quail and could not support copulatory behavior. In Experiment 2, CS2 was a terrycloth object that had no quail parts but could support copulatory behavior, and, in Experiment 3, CS2 was a terrycloth object that had a taxidermically prepared head of a female quail added. The terrycloth-only object supported more rapid conditioning than did the wood block, but the blocking effect was obtained with both kinds of stimuli. Approach responding to the terrycloth + head object required pairing it with copulatory opportunity, and the terrycloth + head object supported at least as rapid conditioning as did the terrycloth-only object. However, responding to the terrycloth + head object was not blocked by the pretrained audiovisual cue. These results indicate that the blocking effect occurs in sexual conditioning even with stimulus objects that can support copulation. However, the addition of species-typical head cues to an object makes that object such a powerful stimulus that conditioned approach responding to it cannot be blocked by a previously conditioned arbitrary audiovisual cue.     

Amplitude of the rabbit’s unconditioned nictitating membrane response in the presence of a conditioned inhibitor

Using a light or backshock as the reinforced CS (A) and a tone or backshock as the conditioned inhibitor (X), rabbits experienced conditioned inhibition training in an A+/AX? paradigm. Following training, the amplitude of the unconditioned nictitating membrane response elicited by a mild (.5-mA) paraorbital shock was measured in the presence of X and AX and expressed as a percentage of the amplitude of the UR to the shock presented alone. In Experiment 1, the effect of X and AX on UR amplitude for conditioned inhibition animals was compared with that of control animals treated to a variety of pretest procedures. In general, UR amplitude in the presence of X exceeded that observed to the US presented alone. There was no consistent difference between the experimental and control groups. In Experiments 2–5, A test trials were added as an alternative reference point. Again, UR amplitude increased rather than decreased UR amplitude. In addition, X as a conditioned inhibitor enhanced the facilitating effect of A on UR amplitude in four out of five experiments. These findings have implications for theories of the “locus of action” of conditioned inhibitors.     

Circadian-temporal context and latent inhibition of conditioned taste aversion: Effect of restriction in the intake of the conditioned taste stimulus

Latent inhibition of conditioned taste aversion (CTA) is sensitive to changes in the temporal context. A change in the time of day of conditioning with respect to the time of day of the preexposure can disrupt the latent inhibition. This contextual change in the time of day may reveal a temporal specificity of latent inhibition. The optimum procedure to induce this temporal specificity is not well established. For example, it has been shown that a long period of habituation to temporal contexts is one factor that can determine the effect. However, the experimental conditions on the conditioning day that facilitate this phenomenon are unknown. The aim of this study is to elucidate whether a restriction in the intake of the conditioned taste stimulus affects the temporal specificity of latent inhibition. Two main groups of Wistar rats were tested in a latent inhibition of CTA paradigm, in which the temporal specificity of this phenomenon was analyzed by a change in the time of day of conditioning. The intake of the taste stimulus was restricted in the conditioning day in one of the groups, but this restriction was not applied in the other group. The results indicated temporal specificity of latent inhibition only in the group without restriction, but not in the group with limitation in the intake of the taste stimulus during conditioning. These findings can help to elucidate the characteristics of the procedure to induce temporal specificity of latent inhibition.     

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.     

Maintenance of observing responses with the less highly valued stimulus in pigeons

Previous research has shown that the more valued stimulus will maintain observing responses but the less valued stimulus will not. In the first part of this experiment, it was shown that the removal of the stimulus associated with the fixed-ratio component of a multiple schedule (mult FI 2 min, FR 35) abolished observing responses. In the next part, the ratio stimulus was phased out by making it available during some ratios but not during others. Observing responses were maintained following the phasing procedure even when all ratio stimuli were unavailable. In the third part, all stimuli, both ratio and interval, were unavailable. Observing responses declined under this condition and increased again when the stimulus associated with the interval was again made available. It is hypothesized that observing responses will be maintained as long as they permit the maintenance of a discrimination.     

Facilitation and impairment of conditioning in the preweanling rat after prior exposure to the conditioned stimulus

Olfactory aversion conditioning of preweanling rats, 10 or 18 days postnatal, was tested after some had been given nonreinforced experience with the to-be-conditioned odor stimulus. In three experiments, it was established that the amount of prior exposure to the CS determined the effectiveness of conditioning. For both ages, odor-shock conditioning was more likely impaired with longer durations of preexposure. This effect was more apparent in the older animals. Low to moderate degrees of prior exposure to the CS under some conditions facilitated, rather than impaired, olfactory conditioning in the 10-day-old rat. This result is in agreement with one previous study in which facilitation in learning was reported for this age after short-term preexposure to the CS. The present study adds to previous data on differential effects of CS preexposure on conditioning. Although the conditions under which facilitation rather than impairment occurs are not yet clear, age-related differences in the effects of CS preexposure were apparent in the present experiments.     

Conditioning with taste as the CS in conditioned flavor preference learning

There appear to be unconditioned affective reactions to the four basic tastes: liking for sweet and salt and disliking for sour and bitter. We attempted to modify these reactions by pairing the tastes with calories and with sweeter tastes. Differing sucrose concentrations were ineffective in reversing the preference for salt over citric acid or for saccharin over quinine. We could, however, reverse the preference for salt over citric acid, producing an actual preference for sour over salt, by using sucrose and saccharin as the reinforcers. The initial reactions to tastes could also be modified by reducing the initial difference in affect produced by the tastes through mixing both tastes with sucrose.     

The effects of compound stimulus preexposure of two elements differing in salience on the acquisition of conditioned suppression

Conditioned attention theory (CAT) of latent inhibition (LI) states that parallel learning processes occur during reinforced and nonreinforced stimulus presentation. The present experiments investigated the effects of nonreinforced preexposure of either a compound CS or elements of that compound which differed in salience. Three predictions were advanced: (1) Both the compound and its elements will show an increase in LI as a function of the number of preexposures; (2) the two elements will show different levels of LI, with more LI accruing to the more salient element; (3) overshadowing will occur during compound preexposure. Two experiments, using rats as subjects and a conditioned suppression test, are reported. In Experiment 1, groups received 0, 20, 40, or 80 nonreinforced preexposures to a compound whose elements differed in salience. The results of the subsequent test confirmed predictions 1 and 2. Experiment 2, in which groups were preexposed to either the elements or the compound, provided evidence for an overshadowing effect, confirming prediction 3 from CAT.     

Injected flavor as a CS in the conditioned aversion preparation

Three experiments were conducted to determine the effectiveness of intravenous (IV) flavor injections in the formation of conditioned taste aversions and in the attenuation of neophobia. In Experiment 1, two groups of rats were permitted to drink either a .1% saccharin solution or tap water followed immediately by IV injections of lithium chloride (LiCl), and two more groups were given IV injections of a 2% saccharin solution followed immediately by IV injections of either LiCl or distilled water. Injected flavor did not serve as an effective CS for the conditioning of an aversion to .1% saccharin. The second experiment employed a two-bottle procedure to detect attenuation of neophobia using the injected-flavor technique. It was found that, whether saccharin had been injected intravenously (2%), injected intraperitoneally (2% IP), or orally consumed (.1%), neophobia for .5% saccharin was attenuated equally relative to controls. CS-US intervals were manipulated in the final experiment such that IP injections of 2% saccharin solution were followed 0–480 min later by IP injections of LiCl. In this case, it was shown that injected flavor (2% saccharin) could act as an effective CS if the US was delayed (optimally about 120 min) and when the test solution was .1% saccharin. The delay gradient found in Experiment 3 was interpreted as a generalization gradient where optimum conditioning was displayed at the point where the concentration of saccharin circulating in the animal at the time of illness onset most closely matched the concentration of the test solution.     

Retention of conditioned autonomic and behavioral responses in preweanling rats: Forgetting and reinstatement

Preweanling rats, 16 days of age, responded to an olfactory conditioned stimulus (CS) paired with a shock unconditioned stimulus (US) with increases in heart rate and behavioral activation. In two experiments this finding was replicated and, in addition, it was found that the form of these conditioned responses (CRs) changed after a retention interval. When tested 24 h after CS-US pairings, the subjects displayed a decrease in heart rate accompanied by CS-elicited freezing. Giving two unsignaled shocks prior to the delayed test effectively reinstated the tachycardia and behavioral arousal CRs. The results are discussed in terms of contextual influences on the form of the CR and how changes in the magnitude of context fear may alter responding to an olfactory CS.     

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.