Conditioning of simultaneous and serial feature-positive discriminations

Three experiments with rat subjects examined the development of simultaneous and serial feature-positive discriminations in appetitive conditioning. In Experiment 1, reinforced presentations of a simultaneous light-tone compound were intermixed with nonreinforced presentations of either the light or the tone. The compound stimulus acquired conditioned behaviors of a form characteristic of the predictive feature alone; the element common to reinforced and nonreinforced trials did not evoke conditioned behavior. In Experiment 2, reinforced presentations of a serial light-trace-tone compound were intermixed with nonreinforced tone-alone presentations. The light feature stimulus acquired conditioned behaviors characteristic of visual CSs. The tone stimulus, common to reinforced and nonreinforced trials, evoked conditioned behaviors characteristic of auditory CSs, but only when preceded by the light. In Experiment 3, variations in the interval between the light and tone on reinforced trials had little effect on responding to the light CS but substantially altered the pattern of responding to the tone CS. These results suggested that simultaneous and serial feature-positive discriminations may be solved differently. Performance in simultaneous feature-positive discriminations may be determined solely by associations between the feature stimulus and the reinforcer, but performance in serial discriminations may also involve the acquisition of a conditional cue function to the feature.     

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.     

Positive and negative patterning in human classical skin conductance response conditioning

Three experiments on classical differential conditioning of the human skin conductance response to elemental and compound stimuli are reported. Subjects in Experiment 1 received both positive and negative patterning training, followed by either positive or negative patterning transfer tests on new stimuli. In positive patterning, a compound of two stimuli is reinforced and its elements are nonreinforced. In negative patterning, the elements are reinforced and the compound is nonreinforced. Subjects in Experiments 2 and 3 received either positive or negative patterning during training, followed by transfer tests on new stimuli. In Experiment 2, the transfer series began with new elements, after which their compound was presented; in Experiment 3, the new compound was presented first in the transfer series, and then the separate elements were administered. All three experiments provided evidence of the acquisition of positive patterning, while negative patterning was found only in Experiments 2 and 3. Positive patterning transferred to new stimuli, indicating that it was not attributable solely to summation of sub-threshold excitation conditioned to the elements on reinforced compound trials. This finding, coupled with the negative patterning found in Experiments 2 and 3, provided support for the unique cue hypothesis. It was concluded that the assumed unique cue constituted a learned “rule,” and that the actual elemental stimuli were neither perceptually nor otherwise modified during the conditioning process.     

Savings test for associations between neutral stimuli

Three experiments showed a savings procedure to be an effective and sensitive alternative to sensory preconditioning procedures as a measure of associations among neutral stimuli. Experiment 1 showed that within-compound associations developed more rapidly in reinforced appetitive serial compound conditioning when nonreinforced preexposure to the serial compound was given than when separate element or no preexposure was given. Experiment 2 showed the savings effect to be highly stimulus specific. Experiment 3 examined the facilitation of serial compound conditioning after either simultaneous or serial nonreinforced preexposure to the elements of the compound. The results of that experiment were consistent with those of analogous sensory preconditioning experiments. When preexposure involved only the two elements of the subsequently reinforced compound, serial preexposure produced more savings than simultaneous preexposure. But when preexposure involved a three-stimulus procedure like that used by Rescorla (1980b), simultaneous preexposure resulted in more savings. Advantages of the savings procedure over sensory preconditioning as a measure of association among neutral stimuli are discussed.     

Summation and configuration in patterning schedules with the rat and rabbit

Discrimination between a tone + light compound and its components in positive and negative patterning schedules was examined. In the positive schedule, reinforced compound presentations (C+) were intermixed with unreinforced component presentations (T?, L?). In the negative schedule, the compound was unreinforced (C?) and the components were reinforced (T+, L+). In Experiment 1, appetitive conditioning of rats’ anticipatory magazine responses was used, and in Experiment 2, aversive conditioning of the rabbit’s nictitating membrane response was used. Both experiments revealed that the positive patterning schedule consistently produced rapid acquisition of appropriate discriminative responding. The results of the negative patterning schedule were more complex. Specifically, the results of Experiment 1 demonstrated that naive rats initially showed rapid acquisition of the negative patterning discrimination. However, schedule reversals revealed that experience with the positive patterning schedule virtually abolished subsequent acquisition of discriminative responding under the negative patterning schedule. The results of Experiment 2 revealed that naive rabbits showed very slow acquisition of discriminative responding under the negative patterning schedule. The results are discussed in relation to the unique-stimulus hypothesis, a contextual encoding hypothesis, and a configural hypothesis.     

Effects of CS preexposure on inhibition of delay

Two experiments examined the effects of preexposure to a stimulus on the subsequent acquisition of conditioned suppression by rats. Variations in the level of suppression within conditioning trials were noted so thatinhibition of delay (taken here to mean less suppression at the beginning of a trial than at the end) could be detected. Inhibition of delay was observed both during the acquisition of suppression and (in Experiment 1) when suppression began to wane with continued postasymptotic training. Preexposure to the to-be-conditioned stimulus retarded acquisition of suppression and slowed the appearance of inhibition of delay both in acquisition and (in Experiment 1) in postasymptotic performance. Experiment 2 demonstrated that inhibition of delay was attenuated during conditioning that followed preexposure in which the stimulus was paired with a weak reinforcer. These results provide no support for the suggestion that preexposure to a stimulus retards later conditioning because it allows the subject to acquire information about stimulus duration that in turn fosters the development of inhibition of delay. Rather, they are compatible with the suggestion that preexposure causes the stimulus to lose associability.     

Effects of compound or element preexposure on compound flavor aversion conditioning

Two experiments with rat subjects examined conditioning of an aversion to a compound flavor stimulus after preexposing the compound, its constituent elements, or no explicit flavor stimulus. Experiment 1 used a short-term procedure in which preexposure and conditioning treatments occurred on the same day; Experiment 2 used a long-term procedure in which more extensive preexposure was administered several days before conditioning. In both experiments, preexposure of the elements slowed conditioning to the compound more than did preexposure of the compound itself. These effects were apparently not mediated by changes in pseudoconditioned or neophobic responses. The results were related to Lubow’s conditioned attention theory of stimulus preexposure effects.     

Enhancement of conditioned inhibition via an extinction treatment

Rats were used in a conditioned-suppression paradigm to determine whether an extinction treatment would enhance a moderately developed conditioned inhibitor (CS?). To dissipate unconditioned suppression to the training stimuli, the subjects were first habituated to the stimuli and then given Pavlovian conditioned-inhibition (CI) training involving reinforced presentations of a clicker and nonreinforced compound presentations of that stimulus and the intended CS?, either a light or a tone. Thereafter, experimental subjects received presentations of their CS? by itself, whereas controls received no further training. Following the occurrence and loss of conditioned suppression to the CS? in the extinction phase, summation and retardation tests showed enhanced CI for the experimental subjects relative to both the controls and their own earlier levels of inhibitory performance. In fact, the enhanced inhibition for the experimental subjects approximated that shown by a comparison group for which the CS? had been strongly developed as an inhibitor. These findings suggest that an excitatory representation is associated with the CS? early in CI training, and that subsequent presentations of the CS? by itself strengthen its inhibitory effect by allowing it to be nonreinforced in the presence of that representation.     

Some determinants of second-order conditioning

In a Pavlovian conditioning situation, an initially neutral stimulus may be made excitatory by nonreinforced presentations in compound with an established conditioned excitor [i.e., second-order conditioning (SOC)]. The established excitor may be either a punctate cue or the training context. In four conditioned suppression experiments using rats, we investigated whether SOC phenomena parallel other cue interaction effects. In Experiment 1, we found that the response potential of a target stimulus was directly related to the intertrial interval when SOC was mediated by a punctate cue, and inversely related to the intertrial interval when SOC was mediated by the training context. Experiment 2 demonstrated that punctate- and context-mediated SOC are oppositely affected by posttraining context extinction, and Experiments 3 and 4 demonstrated that context- and punctate-mediated SOC are differentially affected by conditioned stimulus (Experiment 3) and unconditioned stimulus (Experiment 4) preexposure treatments. These findings parallel phenomena in conditioned inhibition and cue competition situations.     

Representations of single and compound stimuli in negative and positive patterning

In four experiments, rats were trained on different patterning discriminations before being tested with compounds composed of novel combinations of the trained stimuli. In Experiment 1, rats were trained on a negative-patterning schedule (A+ B+ AB-) intermixed with reinforced presentations of a second compound (CD+). On a subsequent test, the rats responded more to two novel compounds, AC and BD, than to A and B, but less than to CD. In Experiment 2, rats were trained on two concurrent negative-patterning discriminations (A+ B+ AB-, C+ D+ CD-). On test, they responded more to AC and BD than to AB and CD, but less than to the single stimuli. In Experiment 3, rats were trained on two concurrent positive-patterning discriminations (A-B- AB+, C- D- CD+). On test, their response rates to AC and BD were not different from the response rates to the trained compounds (AB and CD). Finally, in Experiment 4, rats were trained on a positive- and negative-patterning discrimination concurrently. Once again, on test, response rates to AC and BD were not different from responding on reinforced trials of the trained discriminations (A+, B+, and CD+). We discuss the implications of these findings for elemental and configural models of stimulus representation.     

Extinction of enhanced latent inhibition

Hungry rats were used in a classical conditioning procedure in which visual stimuli were paired with food. Conditions in which nonreinforced exposure to a nontarget stimulus was followed by exposure to a simultaneous compound nontarget/target stimulus (a blocking procedure) resulted in enhanced latent inhibition to the target relative to exposure to the nontarget, followed by exposure to the target stimulus alone. A third phase of nonreinforced exposure training, in which the target was exposed alone following the compound, reduced levels of latent inhibition relative to results obtained with the blocking procedure. Experiments also suggested that this was not the result of restoration of associability by the omission of an expected presentation of the nontarget stimulus in the final preexposure phase. These results suggest that enhanced latent inhibition is due to summation of a direct-target-no-event association and a second-order association of these elements via target-nontarget and nontarget-no-event association. Exposure to the target after compound exposure extinguished the target-nontarget association and reduced the sources of no-event learning for the target.     

Overshadowing by food of stimulus control by a keylight in a two-element serial compound

Pigeons were given successive discrimination training in which pecking during a choice period when the key was white was either reinforced or not, depending upon the prior presence or absence of a discriminative stimulus, which was a two-element serial compound. The compound consisted of a keylight and food, with food presented second or first in a forward or backward pairing for different groups of pigeons. In Experiment 1, the sequence was an S+ indicating reinforced trials, while in Experiment 2, the sequence was an S? indicating nonreinforced trials. Following acquisition of discriminated operant behavior, a sequence generalization test was administered during which all possible orders of the two stimuli were presented on test trials prior to the onset of the choice period. The results showed that food overshadowed stimulus control by the color of the light on the key on the sequence-generalization test, independently of whether food was presented first or second during training and independently of whether food was associated with reinforcement or nonreinforcement. The similarity of results for the two experiments suggests that overshadowing occurs independently of whether the compound is a discriminative stimulus for reinforcement or nonreinforcement. Simultaneous presentation of elements of a compound stimulus is not necessary for overshadowing because the phenomenon was captured with sequentially presented stimuli.     

Effects of pretraining on acquisition of novel configural discriminations in human predictive learning

In two experiments, participants acquired one of two target configural discriminations (a biconditional or negative patterning discrimination) in a predictive learning task. In Experiment 1, participants were pretrained with either a configural or an elemental discrimination; in Experiment 2, they were pretrained with a configural discrimination, an elemental discrimination, or a control discrimination that was not expected to bias them toward elemental or configural processing. In both experiments, acquisition of the target configural discriminations was faster after configural pretraining than after elemental pretraining. In addition, the negative patterning discrimination was acquired faster than the biconditional discrimination. Finally, the results of Experiment 2 were more consistent with the notion that elemental pretraining hindered acquisition of the target discriminations than with the notion that configural pretraining enhanced their acquisition. Implications of these findings are discussed.     

Effect of extended training on generalization of latent inhibition: an instance of perceptual learning

Four experiments examined generalization of latent inhibition (LI) as a function of the length of preexposure in a conditioned taste aversion procedure with rats. Experiment 1 showed that one or four nonreinforced presentations of a flavor compound (BX) retarded subsequent conditioning to another compound (AX). However, after eight presentations of BX, conditioning to AX occurred at the same rate as with no preexposure. These results indicate that generalization of LI decreased as the length of preexposure to BX increased. Experiment 2 replicated this effect of reducing generalization, as well as demonstrating that LI actually increased as the length of preexposure to AX increased. Experiment 3 extended the generality of the effect to a procedure in which both BX and AX were preexposed. Experiment 4 demonstrated a similar reducing-generalization effect when generalization of LI from BX to X was assessed. All of these data are consistent with the notion that prolonged preexposure to BX enhances its discriminability. Different learning mechanisms that might be responsible for this perceptual learning effect are discussed.     

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.     

Differential trace conditioning to temporal compounds

Rats were reinforced for responding following the presentation of a light-tone temporal compound, each component having a .5-sec duration separated by a .5-sec empty interval. For different groups, nonreinforced presentations of the compound in the reverse order and either or both of the components separately were included in each session. Results indicated a progressive increase in difficulty as the number of nonreinforced events increased, with behavior being strongly affected by the first component of the compound. Nevertheless, differential performance under the most demanding conditions demonstrate the rat’s ability to acquire a temporal compound discrimination, which suggests an interpretation based on interacting stimulus traces.     

Appetitive latent inhibition in rats: Now you see it (sign tracking), now you don’t (goal tracking)

Latent inhibition (LI), the retardation of Pavlovian acquisition after nonreinforced preexposure to the conditioned stimulus, is a popular paradigm for studying basic attentional and memory processes from both behavioral and neurobiological perspectives. It is argued that whether LI emerges depends on the behavioral measure used to index conditioning. An experiment with rats demonstrates that stimulus preexposure retards the development of sign-tracking responses directed at the stimulus, but not the development of goal-tracking responses directed at the site of food delivery. These results are consistent with models that explain LI in terms of a deficit in retrieval.     

Addition versus deletion as a signal

Subjects typically show superior discriminative performance when a distinguishing feature appears on reinforced rather than nonreinforced trials. The phenomenon is usually attributed to the relative predictiveness of the reinforcer by different stimulus elements. However, stimulus addition may be more effective than stimulus deletion as a signal. By removing the standard intertriai intervals, we made addition and deletion equally predictive of the reinforcer in four operant experiments involving between- and within-subject comparisons. Pigeons consistently performed better on operant discriminations when the addition rather than deletion of an auditory or visual stimulus served as the cue for food. This general finding persisted despite manipulation of the relative duration and localizability of the signal. Thus mere presence as opposed to absence plays a role in the feature-positive superiority, an outcome that may reflect a fundamental, biologically based difference between addition and deletion as effective signals of reinforcement.     

A feature positive effect in conditioned suppression

A conditioned suppression experiment with rats studied the development of two discriminations involving two conditioned stimuli, A and X. In one discrimination (AX+/A?), compound presentations of A and X signaled shock and presentations of A alone signaled no-shock. In the other discrimination (A+/AX?), A alone signaled shock and AX signaled no-shock. AX+/A? discriminations were learned more rapidly than their A+/AX? counterparts. These results, which resemble the feature-positive effect of Jenkins and Sainsbury (1969, 1970), are discussed in terms of Rescorla and Wagner’s (1972) theory of conditioning and also in terms of stimulus intensity mechanisms.     

Reacquisition following extinction in appetitive conditioning

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