Contextual conditional discriminations

Three experiments used a discriminated operant procedure to study conditional discrimination learning in rats. The first experiment showed that rats were capable of learning a biconditional discrimination in which two contexts served as conditional cues signalling the reinforcement contingencies associated with two discriminative stimuli. The discrimination was learned equally well when one discriminative stimulus signalled food, the other its absence, and when one stimulus signalled food, the other extinction plus mild footshock.

In Experiment 2 it was shown that prior training on such a conditional discrimination enhanced the subsequent context specificity of simple conditioning relative to control groups of animals for whom the prior training had not been conditional. Experiment 3 showed that a reversal of the significance of one pair of discriminative stimuli produced no spontaneous reversal in performance to a second, target, pair.

The pattern of results is best accounted for by an analysis of contextual conditional discrimination learning in terms of stimulus configurations and offers no support for the notion that rats may learn a general conditional rule or set.     

Pigeons learn stimulus identity and stimulus relations when both serve as redundant,relevant cues during same-different discrimination training

The authors taught pigeons to discriminate displays of 16 identical items from displays of 16 nonidentical items. Unlike most same-different discrimination studies--where only stimulus relations could serve a discriminative function--both the identity of the items and the relations among the items were discriminative features of the displays. The pigeons learned about both stimulus identity and stimulus relations when these 2 sources of information served as redundant, relevant cues. In tests of associative competition, identity cues exerted greater stimulus control than relational cues. These results suggest that the pigeon can respond to both specific stimuli and general relations in the environment.     

Delayed and current stimulus control in successive discriminations

In a successive discrimination in which successively alternating red and green hues signaled component variable-interval schedules, sensitivity of the ratio of responses in the two components to variation in the component reinforcer ratio decreased systematically during the course of the component. This decrease in stimulus control or discrimination over the course of the component was shown to be the result of delayed control of responding during the component by the stimulus transition between components. When the red–green stimulus transition was altered by interpolating a white stimulus at the end of each 60-s component, discrimination at the beginning of the component (measured by the power-function exponent for sensitivity to reinforcement) was reduced. Conditions with the white stimulus inserted in other quarters of the component indicated that the current discriminative stimulus exerts control over responding throughout the component, whereas during about the first half of the component, response differentials are influenced by the transition between discriminative stimuli.     

Some determiners of attention

Three experiments, using a total of 13 pigeons, examined the stimulus control acquired by the separate components of a compound visual stimulus transilluminating the pecking key. Experiment I measured the control acquired by components of compound discriminative stimuli used in discrimination training. Experiment II sought to demonstrate the effect of pretraining a single stimulus discrimination on control acquired by each component in a compound stimulus discrimination. It also investigated the effect of training the compound stimulus discrimination before the single stimulus discrimination. Experiment III sought a continuous stimulus control function when pretraining stimulus intensities were varied. The results suggest that the extent to which a bird "pays attention" to a stimulus, defined in terms of the degree of stimulus control acquired by that stimulus, is determined by how well it previously learned to discriminate that stimulus from other stimuli.     

An inexpensive and automated method for presenting olfactory or tactile stimuli to rats in a two-choice discrimination task

An inexpensive and automated method for presentation of olfactory or tactile stimuli in a two-choice task for rats was implemented with the use of a computer-controlled bidirectional motor. The motor rotated a disk that presented two stimuli of different texture for tactile discrimination, or different odor for olfactory discrimination. Because the solid olfactory stimuli were placed outside the chamber in metal pods with a mesh at front for odor sampling, "washout" of odors between trials was not necessary. To avoid differential auditory cues from motor rotation, the stimuli were arranged such that on each trial the motor always rotated exactly one quarter revolution (in 1 s), left or right, to present the next stimulus at trial start. To illustrate the use of the equipment, 2 rats were trained on tactile discrimination and 2 rats on olfactory discrimination. The rats sampled the stimulus on the disk through a port on the back wall by sniffing at it (olfactory) or touching it (tactile). The task was a go-left/go-right discrimination with the stimulus on the disk being discriminative for which lever provided reinforcement. The rats reached a stable level above 90% correct after 21 and 32 training sessions for tactile and olfactory discrimination, respectively. The article outlines how the equipment was constructed from low-cost components. Inputs from and outputs to the equipment were implemented through the parallel port of a personal computer without the use of a commercial interface board. The method of automated and low-cost presentation of olfactory or tactile stimuli should be of use for a variety of experimental situations such as matching-to-sample and cross-modal discrimination.     

Olfactory discrimination, reversal learning, and stimulus control in rats.

Rats were trained to discriminate lights, tones, or odors and then given a series of discrimination reversals. Only rats trained with odors showed positive transfer on the first reversal and acquisition of a reversal set. Other experiments demonstrated that rats preferentially attend to odors when presented in compound with lights or tones; that odors exert more discriminative control than tones in tests using compound stimuli of competing sign; and that after pretraining on the positive stimulus, acquisition of an odor but not a light discrimination occurs with virtually no errors. These results demonstrate the importance of stimulus modality in the establishment of stimulus control and the need for more careful analysis of stimulus factors in cross-species comparisons of learning ability.     

The interaction between discriminative stimuli and outcomes during instrumental learning

Rats were trained on a biconditional discrimination in which the delivery of a food pellet stimulus signalled that pressing on one of two levers would be reinforced, whereas the delivery of a sucrose solution stimulus signalled that the reward was contingent on pressing the other lever. The outcome was the same food type as the discriminative stimulus in the congruent group but the other food type in the incongruent group. Both responses were rewarded with the same outcome in the same group. All the three groups learned the discrimination at statistically indistinguishable rates. Prefeeding one of the outcomes selectively reduced the associated response thereby demonstrating that responding was mediated by a representation of the outcome. Moreover, the outcome of one trial controlled responding on the next trial in accord with the stimulus function of the food type. These results are discussed in relation to the associative structures mediating the discriminative control of instrumental performance.     

A DISCRIMINATION TRAINING PROCEDURE TO ESTABLISH CONDITIONED REINFORCERS FOR CHILDREN WITH AUTISM

Although conditioned reinforcers are used in many behavioral intervention programs for individuals with developmental disabilities, little research has been conducted to determine optimal methods for establishing conditioned reinforcers. An early method that has received relatively little research attention is to condition a neutral stimulus as a discriminative stimulus and then use the stimulus as a programed consequence during skill acquisition. The current study evaluated the effects of a discrimination training procedure on establishing conditioned reinforcers for three children with autism. For all participants, previously neutral stimuli reinforced behaviors after acquiring discriminative properties during discrimination training. Copyright © 2014 John Wiley & Sons, Ltd.     

Instrumental learning as a result of omission training on wheel running

The present experiment sought to provide unequivocal evidence of instrumental learning under omission training. Hungry rats received free food reinforcement while spontaneously running in a wheel. For an omission group, running postponed or cancelled reinforcers in the presence of a discriminative stimulus (SD) requiring subjects to reduce responding to earn food. Background food presentations were then yoked to reinforcement delivered in the presence of the discriminative stimulus. For a control group, which received the same stimulus presentations, reinforcement delivery was yoked to the experimental group at all times. The procedure allowed both within- and between-subject comparisons between omission and response-independent schedules. The response-reinforcer delay under the omission contingency was adjusted so as to equate reinforcement frequency in the presence and absence of the SD. As the SD was not correlated differentially with reinforcement and the running response did not involve approach or withdrawal to the site of food delivery, the successful discrimination performance observed in this experiment cannot be accounted for by appeal to implicit classical conditioning. Instead, it is suggested that decreased running in the presence of the discriminative stimulus was based on the animals' veridical representation of the negative contingency between the response and reinforcement.     

Stimulus control in a simple instrumental task: The role of internal and external stimuli

Two experiments using rats in a straight alley runway task tested the hypothesis that standard stimuli such as tones and lights (“external” stimuli) and schedule-generated aftereffect stimuli (“internal” stimuli) operate similarly and are similarly subject to the compounding rules specified by R. A. Rescorla and A. R. Wagner (In A. Black & W. Prokasy (Eds.), Classical conditioning II: Current theory and research. New York: Appleton-Century-Crofts, 1972). The experimental task was an instrumental analog of the classic blocking experiment (L. J. Kamin, In M. R. Jones (Ed.). In Experiment 1, blocking of an external discriminative stimulus by a different asymptotic discrimination was accomplished. In Experiment 2, blocking of an internal stimulus discrimination by an asymptotic external stimulus discrimination was obtained. The present results support the view that internal and external stimuli are indeed similar and function in the same manner with regard to blocking of stimulus control.     

Effects of discrete-trial and free-operant procedures on the acquisition and maintenance of successive discrimination in rats.

Rats were trained on a successive discrete-trial discrimination between two tonal stimuli to examine the effects of availability of a lever during intertrial intervals. In the discrete-trial condition, in which a lever was removed from the chamber during intertrial intervals, 10-s trials were initiated by the presentation of both discriminative stimulus and lever. In the free-operant condition, in which a lever was present during both trials and intertrial intervals, 10-s trials were initiated only by the presentation of a discriminative stimulus. Experiment 1 employed 50-s intertrial intervals and demonstrated that discriminative performances were acquired faster and maintained better in the free-operant conditions than in the discrete-trial conditions. Experiment 2 employed 5-s intertrial intervals and showed that poor discriminative performances in the discrete-trial conditions were improved. These results indicate that the presentation of a lever to start a trial can overshadow or mask the control by a discriminative stimulus and thereby obstruct the acquisition and maintenance of discriminative performances. Furthermore, the overshadowing or masking effects are strengthened as a function of the duration of intertrial intervals.     

Effective use of the blank comparison procedure in simple discrimination by infant capuchin monkeys: A methodological note

In studies of simple and conditional discrimination, procedures are needed to measure those aspects of stimuli that control behavior. The blank comparison procedure is one such procedure. It was designed explicitly for assessing S+ and S- functions when discriminative stimuli are presented simultaneously. In this procedure, a neutral stimulus serves sometimes as S+ and sometimes as S-. Its discriminative function is defined in relation to other stimuli in the display. The present study aimed to prepare 2 infant female capuchin monkeys for the effective use of the blank comparison procedure in a simple discrimination task. First, simple discrimination training was applied up to a stable accuracy criterion of ≥90%. This training was followed by the replacement of S+ and then of S- stimuli with new stimuli. Ultimately, trials with the blank comparison were introduced. Following this sequence, both monkeys immediately displayed highly accurate blank-comparison performances without the need for stimulus control shaping or other preparatory discrimination training. Thus, this procedure sequence may be an efficient, effective method for establishing blank-comparison baselines for experimental analyses of S+/S- discriminative functions and perhaps for other applications in teaching simple and conditional discrimination performances to this species and others.     

Discriminative stimulus properties of drugs: a brief history and a selective review

A brief history of the background of drug discrimination research is given, focusing on the concepts of "drug dissociation" or state-dependent learning; an alternative explanation to the state dependency concept is to view the drug as a discriminative stimulus. In drug discrimination learning both a qualitative and a quantitative dimension is identified as governing the discrimination, examples of which are provided in the text. Examples of how drug discrimination techniques may assist in future research are outlined.     

Rate of response as a visual social stimulus

In Exp. 1, a high rate of responding (chain pulling) of a stimulus monkey was established as a visual positive discriminative stimulus for the operant behavior (bar pressing) of an observer monkey. The terminal performance of the observer under conditions in which a high rate of response of the stimulus monkey alternated in a variable temporal arrangement with a zero rate of response of the stimulus monkey (negative discriminative stimulus) was essentially the same as when nonbehavioral stimuli are correlated with the availability of reinforcement. By manipulating the schedule of reinforcement to change the rate of responding of the stimulus subject without changing its rate of reinforcement, Exp. 2 showed that the effective behavioral stimulus for the observer was the rate of chain pulling by the stimulus subject. A novel intermediate rate of responding by the stimulus monkey resulted in an intermediate rate (generalization) on the part of the observer during an extinction test. These experiments demonstrated that the rate of responding of one organism can function as a discriminative stimulus to control the rate of responding of another organism; and that the rate of responding is similar to other physical stimuli in terms of discrimination and generalization.     

Stimulus control of Pavlovian facilitation

Two experiments were conducted using an autoshaping procedure with pigeons to examine whether dimensional stimulus control by a Pavlovian facilitator parallels the control established following operant discrimination training. Facilitation training consisted of the presentation of a black vertical line on a white background as the B stimulus in a feature-positive discrimination in which the A stimulus (white keylight) was followed by grain presentation only if preceded by B. In this way, B facilitates or sets the occasion for pecking at A. Subsequent testing for generalization along the line-orientation dimension produced decremental gradients when the facilitation paradigm incorporated an explicit feature-negative stimulus (B−). These results parallel the decremental control obtained following operant discrimination training and suggest that Pavlovian facilitators and instrumental discriminative stimuli are functionally equivalent.     

Relationships between the determinants of performance in serial feature-positive discriminations

Three experiments using an appetitive behavioral observation procedure with rats investigated the effects of various pre- and postdiscrimination treatments on learning and performance in serial feature-positive discriminations. Previous work suggests that performance in this discrimination is based on feature-unconditioned stimulus (US) associations, feature-common element associations, and a conditional occasion-setting relation. Experiment 1 examined the effects of prediscrimination reinforcement of the various components of the discrimination. Experiments 2 and 3 investigated the effects of various postdiscrimination nonreinforcement and reinforcement procedures, respectively, on performance of previously established discriminative responding. The results of the present studies and those of previous work are interpreted to show that the conditional occasion-setting relation may be independent of feature-US associations and may not be dependent on feature-common element associations. The implications of assumming that rats used conditional information independently of simple associations are discussed.     

Dissociating prelexical and postlexical processing of affective information in the two hemispheres: effects of the stimulus presentation format

Using a lexical decision task, the authors investigated whether brain asymmetries in the detection of emotionally negative semantic associations arise only at a perceptually discriminative stage at which lexical analysis is accurate or can already be found at crude and incomplete levels of perceptual representation at which word-nonword discrimination is based solely on guessing. Emotionally negative and neutral items were presented near perceptual threshold in the left and right visual hemifields. Word-nonword discrimination performance as well as the bias to classify a stimulus as a "word" (whether or not it actually is a word) were assessed for a normal, horizontal stimulus presentation format (Experiment 1) and for an unusual, vertical presentation format (Experiment 2). Results show that while the two hemispheres are equally able to detect affective semantic associations at a prelexical processing stage (both experiments), the right hemisphere is superior at a postlexical, perceptually discriminative stage (Experiment 2). Moreover, the findings suggest that only an unusual, nonoverlearned stimulus presentation format allows adequate assessment of the right hemisphere's lexical-semantic skills.     

Discrimination learning as a function of stimulus location along an auditory intensity continuum

Eight groups of rats were trained on an auditory intensity discrimination in which the discriminative stimuli were separated by 10 decibels (db). Four pairs of stimuli were selected from different regions along a 60–100 db (SPL) intensity continuum. Counterpart groups were trained on each stimulus pair, with the relative intensity positions of the reinforced stimulus (S^D) and the non-reinforced stimulus (S^Δ) reversed for the two groups. Discrimination acquisition curves were compared to determine whether stimuli separated by equal logarithmic units were of comparable “difficulty”, and to determine the relative effectiveness of an S^D serving as the more versus less intense member of a stimulus pair. It was concluded that: (1) When S^D is the more intense, auditory intensities of constant logarithmic separation are graded in “difficulty” along the intensity continuum; high intensity discriminative stimuli are most readily discriminated. When S^Δ is the more intense, this graded effect is not evident. (2) For a given continuum location, discrimination is inferior when S^Δ is the more intense. This effect is most pronounced at the high intensity end of the continuum and is chiefly attributable to differences in the rate of S^Δ responding.     

Observational learning of two visual discriminations by pigeons: a within-subjects design.

Pigeon's observational learning of successive visual discrimination was studied using within-subject comparisons of data from three experimental conditions. Two pairs of discriminative stimuli were used; each bird was exposed to two of the three experimental conditions, with different pairs of stimuli used in a given bird's two conditions. In one condition, observers were exposed to visual discriminative stimuli only. In a second condition, subjects were exposed to a randomly alternating sequence of two stimuli where the one that would subsequently be used as S+ was paired with the operation of the grain magazine. In a third experimental condition, subjects were exposed to the performance of a conspecific in the operant discrimination procedure. After exposures to conspecific performances, there was facilitation of discriminative learning, relative to that which followed exposures to stimulus and reinforcement sequences or exposures to stimulus sequences alone. Exposure to stimulus and food-delivery sequences enhanced performance relative to exposure to stimulus sequences alone. The differential effects of these three types of exposure were not attributable to order effects or to task difficulty; rather, they clearly were due to the type of exposure.     

Nicotine vs. Ethanol Discrimination: Extinction and Spontaneous Recovery of Responding

Studies regarding extinction and spontaneous recovery of the discriminative stimulus effects of drugs are limited. Eight rats were initially trained to discriminate nicotine (0.4 mg/kg) vs. ethanol (800 mg/kg). For four rats, itraperitaneal (IP) administrations of nicotine fifteen minutes prior to fifteen-minute training sessions served as a discriminative stimulus (SD) for predicting food-reinforced lever pressing (VI-1 min). On other sessions ethanol functioned in predicting nonreinforcement (SA). The stimulus roles of the drugs were counterbalanced for the remaining four rats. SA and SD sessions alternated quasi-randomly with two daily sessions at 1000 and 1400 hours. Discriminative control was not disrupted following ten extinction sessions under a non-drug/saline condition, but was disrupted following extinction sessions under the original training drugs. Instances of spontaneous recovery (SR) occurred throughout extinction under the drug condtions. There was no evidence for SR two weeks following extinction, but partial recovery four weeks following the final extinction phase. Contextual status (context renewal) had neither a restorative or disruptive impact on extinguished or discriminated responding, respectively. These results support and extend the limited number of other studies by demonstrating extinction and spontaneous recovery of responding discriminated by two distinct drugs. Some theoretical interpretations regarding history effects and training in the context of drug discrimination are entertained.