Loss of associability by a conditioned inhibitor

In each of three experiments two groups of rats received inhibitory conditioning to one stimulus. Prior to a test phase of excitatory conditioning to this stimulus, one group was repeatedly exposed to the inhibitory stimulus by itself while the other group received no such exposure. Excitatory conditioning occurred most slowly in the group which received the exposure training. The first experiment indicated that this difference was not due to the exposure treatment enhancing the inhibitory properties of the stimulus. The results of Experiment III confirmed this conclusion and also indicated that the differences between the two groups during testing were due to differences in the associability of the inhibitory stimulus.     

Redistributing control between the elements of a compound stimulus

Twenty-eight pigeons were given discrimination training. Four groups were run in which for 0, 2, 4 and 9 sessions of training colour was an irrelevant cue and tone was relevant. Generalization tests were given in extinction; the training colour (C₁) and another colour (C₂) were presented with tone (T) and noise (N). Responding to these four stimulus combinations, TC₁, TC₂, NC₁ and NC₂, allowed the assessment of control by colour and tone. A reduction of control by colour and an increase in control by tone were found to be positively related to the amount of training with colour irrelevant. Tests showed a strong inverse relationship between control by colour and tone.     

Control of responding by the elements of a compound discriminative stimulus and by the elements as individual discriminative stimuli

In the first of two studies, the responding of four albino rats was differentially reinforced in the presence of noise and light together and then tested in the presence of the noise and the light separately during extinction. The light exercised substantially more control of responding than did the noise. In the second study the responding of a similar group of four rats was differentially reinforced in the presence of the noise and the light separately. Control of responding by the light developed more rapidly than control by the noise. Results suggest that levels of control by stimuli after differential reinforcement with respect to the stimuli together can be predicted by the rates of development of control during differential reinforcement with respect to the stimuli separately.     

Attention in the pigeon: testing for excitatory and inhibitory control by the weak elements.

In two experiments, pigeons were trained on a successive discrimination between a color and either a compound S+ or a compound S- consisting of a form superimposed on a second color. Two stimulus control tests followed discrimination training: an attention test in which the form and colors used in training were presented singly and in combination, and then a resistance-to-reinforcement test using the form element of S+ or S- and a novel form. In the attention test, the birds trained with a compound S+ responded most to the S+ compound, less to the S+ color alone, and still less to the S+ form on a dark key. Few responses were made to the negative stimulus, either alone or with the S+ form added. The birds trained with a compound S- pecked most at the S+ color and to a compound of the S+ color with the S- form added. The resistance-to-reinforcement test showed that the birds trained with a compound S+ responded more to the S+ form than to a novel form. However, the birds trained with a compound S- did not reliably respond more to a novel form than to the S- form. These findings suggested that the form element of a compound S+ gains some excitatory control, but the form element of a compound S- does not acquire inhibitory control. The possibility existed that low levels of responding to the S+ form on a dark background in the first experiment were due to use of a darkened key to separate S+ and S- periods during discrimination training. However, the essential findings were the same in a second experiment in which darkening of the chamber separated S+ and S- periods.     

Evidence for inhibitory associations between the unique elements of two compound flavours

In each of two experiments, rats were pre-exposed to two flavoured solutions, saline-lemon and sucrose-lemon. For group ALT, trials with one solution alternated with trials with the other. Group BLK received all trials with one solution in a block, before any trials with the other. An associative theory suggests that the alternating, but not the blocked, schedule would establish an inhibitory association between sucrose and saline. To provide a retardation test of this inhibition, some animals in each group were then given a single pairing of saline and sucrose, experienced sodium depletion, and were finally tested for their consumption of sucrose. Sodium depletion increased consumption of sucrose more in group BLK than in group ALT. In groups given no saline-sucrose pairing, sodium depletion had only a small effect on sucrose consumption, which was the same in both groups. After multiple pairings of saline and sucrose, sodium depletion had an equally large effect on sucrose consumption in both ALT and BLK groups. These results imply that alternating pre-exposure to two compound solutions does establish an inhibitory association between their unique elements, and thus provide support for an associative theory of perceptual learning.     

Restoring the associability of a pre-exposed CS by a surprising event

Three experiments are reported which use rats and the conditioned suppression technique. The first two confirmed a previous finding that prior exposure to a stimulus predicting a weak shock retards further learning when this same stimulus is subsequently used to signal a stronger shock. They further showed that this loss of stimulus associability could be attenuated by inserting trials on which the stimulus was presented alone in the absence of shock before the phase of training with the stronger shock. Experiment III demonstrated that, for animals given prior exposure to two stimuli, the insertion of nonreinforced trials with one of the stimuli will restore the associability only of that stimulus. These results are taken to show that a surprising event (the omission of an expected shock) can restore the associability of a pre-exposed conditioned stimulus.     

Summation of excitatory and inhibitory control produced by traditional tone-shock contingencies and autocontingencies

Previous research has demonstrated that rats can use unsignaled shock to predict subsequent periods free from shock. This shock-no shock stimulus arrangement, termed an autocontingency, has appeared less likely to exert behavioral control when a traditional tone-shock contingency was simultaneously available. The present research examined the generality of CS-US contingency dominance in a conditioned suppression paradigm by using a summation test in which “probe” stimuli derived from tone-shock contingencies were superimposed upon responding maintained by an autocontingency. In experiment 1, an inhibitory CS accelerated responding only when responding was normally suppressed by the autocontingency. In experiment 2, an excitatory CS failed to yield conditioned suppression during an inhibitory (accelerative) period produced by the autocontingency. Unlike our previous findings (e.g., Davis, Memmott & Hurwitz, 1975), these results do not support a general notion of tone-shock contingency dominance over autocontingencies. Behavioral control by autocontingencies appears robust and “holds its own” in summation with both excitatory and inhibitory CSs derived from traditional contingencies.     

Blocking of inhibitory conditioning within a serial conditioned stimulus-conditioned inhibitor compound: Maintenance of acquired behavior without an unconditioned stimulus

Well-trained classically conditioned stimuli, presented unreinforced, were protected from extinction when they were followed by a signal of the omission of the reinforcer (conditioned inhibitor Konorskian type) in eight cats. An aversive classical conditioning paradigm with shock as the reinforcer was used. Of several behavioral (leg flexion, vocalization) and organismic arousal (heart rate, respiration rate, respiration amplitude) measures of conditioned responses, the respiration amplitude changes were found to be most informative for the continuous assessment of elicited arousal of low and medium intensity. In all subjects conditioned stimuli presented during extinction in serial compound with the conditioned inhibitor elicited larger responses than did conditioned stimuli presented alone during extinction. The mechanism of protection from extinction in a paradigm in which the elicitor of learned behavior occurs prior to the conditioned inhibitor provides the organism with the mechanism for the maintenance of learned behavior in the absence of a reinforcer.     

Verbal self-reports about matching to sample: effects of the number of elements in a compound sample stimulus.

Adults' self-reports about their choices in a delayed matching-to-sample task were studied as a function of the number of elements (one, two, or three) in a compound sample stimulus. Signal-detection analyses were used to examine control of self-reports by the number of sample elements, by the speed and accuracy of choices reported about, and by several events contingent on self-reports. On each matching-to-sample trial, a sample element appeared as one of two comparison stimuli. Choice of the matching element, if made within 500 ms of the onset of the comparison stimuli, produced points worth money or chances in a drawing for money, depending on the subject. After each choice, subjects pressed either a "yes" or "no" button to answer a computer-generated query about whether the choice met the point contingency. The number of sample elements in the matching-to-sample task varied across trials, and events contingent on self-reports varied across experimental conditions. In Experiment 1, the conditions were defined by different combinations of feedback messages and point consequences contingent on self-reports, but self-reports were systematically influenced only by the sample-stimulus manipulation. Self-report errors increased with the number of sample elements. False alarms (inaccurate reports of success) were far more common than misses (inaccurate reports of failure), and false alarms were especially likely after choices that were correct but too slow to meet the point contingency. Sensitivity (A') of self-reports decreases as the number of sample elements increased. In addition, self-reports were more sensitive to choice accuracy than to choice speed. All subjects showed a pronounced bias (B'H) for reporting successful responses, although the bias was reduced as the number of sample elements increased and successful choices became less frequent. Experiment 2 demonstrated that the failure of point contingencies to influence self-reports in the first experiment was not due to a general ineffectiveness of the point consequences. Rates of inaccurate self-reports decreased when they resulted in point losses and increased when they resulted in point gains.     

Some determinants of inhibitory stimulus control

Interspersed reinforcement and extinction during discrimination learning generate a U-shaped gradient of inhibition about the stimulus correlated with extinction. The present work showed that extinction is not a necessary determinant of inhibitory stimulus control. In Exp. I, a reduction in the rate of reinforcement, through a shift from a multiple variable-interval 1-min variable-interval 1-min schedule to a multiple variable-interval 1-min variable-interval 5-min schedule, resulted in a post-discrimination line orientation gradient of inhibition about the stimulus correlated with the variable-interval 5-min schedule. In Exp. II, the rates of reinforcement, correlated with a pair of stimuli, were held constant during a shift from a multiple variable-interval 1-min variable-interval 1-min schedule to a multiple variable-interval 1-min differential-reinforcement-of-low-rate schedule. Inhibitory stimulus control about the stimulus correlated with the differential reinforcement of low rate was obtained. In both experiments, a reduction in the rate of responding during one stimulus and behavioral contrast during the other stimulus preceded the observation of inhibitory stimulus control.     

Changes in pain reactivity induced by unconditioned and conditioned excitatory and inhibitory stimuli

In three experiments we investigated the effects of aversive-conditioning components on the reactivity of rats to pain. After training in Experiment 1 with a discrete conditioned stimulus (CS) for a shock unconditioned stimulus (US), different groups were exposed to the CS, US, CS/Us compound, just the training context, or none of those immediately prior to a hot-plate test assessing the latency of a paw-lick response. Relative to no exposure and context alone, the CS produced a shorter latency--that is, an apparent sensitization effect--whereas the US produced a longer latency--that is, a hypoalgesic effect--that was actually augmented by the CS/US compound. Furthermore, whereas the US-induced hypoalgesia was unaffected by the opiate antagonist, naloxone, hypoalgesia produced by the CS/US compound was appreciably decremented by the drug. Experiment 2 showed the same effects with parameters more typical of conditioning research. Experiment 3 compared signals for the presence (CS+) and absence (CS-) of the US. The CS- did not itself affect pain reactivity, but in inhibited the effects of the CS+, US, and CS+/US compound. Collectively, the results suggest that a CS+sensitizes the animal to imminent events and also potentiates an opioid reaction that supplants the less effective nonopioid hypoalgesia induced by the US. In contrast, a CS- functions as a general moderator of excitation, inhibiting both sensitization and hypoalgesic effects, whether opioid or nonopioid.     

Formation of excitatory and inhibitory associations between absent events

Considerable evidence indicates that associations may be formed between two events even when one or both of them is absent at the time of learning. Previously, some researchers asserted that excitatory associations are formed when associatively activated representations for two events are paired, whereas others claimed that inhibitory associations are formed. In three experiments, the authors investigated the nature of tone-sucrose learning when associatively activated representations of those events were paired in the absence of either of the events themselves. Experiment 1 found substantial excitatory learning when the tone surrogate preceded the sucrose surrogate in training. Experiment 2 evaluated other accounts for the results of Experiment 1, and Experiment 3 found evidence for inhibitory tone-sucrose learning when the tone and sucrose surrogates were presented in simultaneous or backward order. The results indicated that the nature of representation-mediated learning is influenced by some of the same variables as more standard associative learning.     

Response summation to a compound stimulus in a context of choice

Key pecks by two groups of pigeons were reinforced on concurrent schedules. For group Ē, pecks were reinforced during either a visual or an auditory stimulus; for group E, an additional, extinction component was available, during which both visual and auditory stimuli were absent. After training, both groups were given a compound test to measure preference among four stimuli, the three used in training plus a compound of the visual and auditory stimulus. Group E showed preference for the compound, emitting more pecks and spending more time in this stimulus than in other stimuli. Group Ē showed no preference between the compound and visual stimulus, nor between the auditory stimulus and the absence of both stimuli, but preferred the former pair over the latter pair of stimuli.     

Discrimination by pigeons of mixture and uniformity in arrays of stimulus elements

In 5 experiments, pigeons learned to discriminate uniform arrays of colored elements from mixed arrays containing 2 colors in various proportions. When only the uniform arrays were positive, mixture-negative gradients were obtained. When only the arrays containing equal numbers of red and blue elements were positive, mixture-positive gradients were obtained. When elements of different colors from 2 independent mixture-negative discriminations were recombined, mixture-negative gradients were obtained with the transfer patterns. When elements from a mixture-negative discrimination were combined with a new set of positive elements, responding was not suppressed. Appropriate combinations of the elements in mixture discriminations reduce responding, but the elements themselves do not acquire inhibitory properties.     

Assessments of changes in the effective salience of stimulus elements as a result of stimulus preexposure

Rats received exposure to 3 flavor compounds, AX and BX, presented in alternation, and CX, presented on a separate block of trials. The hypothesis that this treatment would leave B effectively more salient than C was tested in 3 ways. Experiment 1 showed that the unconditioned response evoked by B was stronger than that evoked by C. Experiment 2 showed that B was more effective than C when used as a reinforcer in a sensory preconditioning procedure. Experiment 3 showed that B was learned about more readily than C as a conditioned stimulus in flavor aversion conditioning. Alternating preexposure to 2 similar stimuli may protect their distinctive features from the loss of salience normally produced by nonreinforced exposure to a stimulus.     

Loss of control by a less valid or by a less salient stimulus compounded with a better predictor of reinforcement

An unsalient stimulus, or one imperfectly correlated with reinforcement, may acquire significant control over responding, provided that it is the only available signal for reinforcement, but may fail to acquire control if it is reinforced only in conjunction with a second, more salient or more valid stimulus. A stimulus imperfectly correlated with reinforcement may also lose control over responding if having initially been reinforced in isolation, it is subsequently reinforced only in conjunction with another, more valid stimulus. If the effects of relative salience are to be explained in exactly the same way as those of relative validity, we should expect a similar loss of control by an unsalient stimulus, A, if, after initial consistently reinforced trials to A alone, subjects subsequently receive reinforcement only in the presence of a compound stimulus, A + B. Two experiments on discrete-trial discrimination learning in pigeons and one on conditioned suppression in rats confirm this expectation. The results have implications for theories of selective association in conditioning and discrimination learning.     

Contralateral transfer of inhibitory and excitatory eyelid conditioning in the rabbit

In Experiment I, rabbits received training to establish a clicker as a conditioned inhibitor. In a subsequent test phase this stimulus was used as a signal for shock either to the eye reinforced during initial training or to the opposite eye. Learning to the clicker was slower in both conditions than in the appropriate control groups. The second experiment replicated the results of those subjects trained and tested with opposite eyes and ruled out the possibility that the slower learning was due to the effects of latent inhibition. Experiment III demonstrated that excitatory conditioning to a clicker to one eye facilitated future excitatory conditioning to that stimulus to the opposite eye. These results are consistent with the view that inhibitory and excitatory conditioning both involve the acquisition of a general, motivational conditioned response which is capable of mediating the transfer of conditioning across different response systems.     

Developing and demonstrating inhibitory stimulus control over repetitive behavior

Developing inhibitory stimulus control over repetitive behavior minimizes the social and learning disruptions caused by this behavior while allowing individuals to continue to access this source of reinforcement at nonproblematic times. These procedures involve allowing repetitive behaviors to occur in some stimulus conditions (S+) and blocking the repetitive behavior in order to disrupt the response–reinforcer relation in other stimulus conditions (S‐) such that the onset of the S‐ period results in rapid and sustained reductions in repetitive behavior. However, the demonstration of stimulus control exerted by the S‐ has often been confounded with participants' exposure to programmed reductive contingencies (i.e., behavior is reduced due to direct contact with contingencies rather than the programmed antecedent stimuli). The current study both developed and demonstrated the suppressive effects of S‐ presentation upon repetitive behavior with two children diagnosed with autism spectrum disorders. These demonstration techniques involved (a) introducing the S‐ into novel environments without the programmed contingencies that we used to establish discriminative control, (b) evaluating the reductive effects of programmed contingencies with and without the associated discriminative stimuli, and (c) evaluating latencies to the onset of repetitive behavior given S+ and S‐ presentations.