Stimulus specificity in avoidance learning

The present experiments address the issue of stimulus specificity in fear and avoidance learning. First, it was established that light stimuli are effective warning signals (WS) in shuttle avoidance. Then light stimuli were shown to produce conditioned suppression in the conditioned emotional response situation comparable to that produced by noise conditioned stimuli. Finally, the effectiveness of noise onset and noise offset as feedback signals was tested. This was assessed under conditions of immediate and delayed termination of a light WS. Delayed termination of a light WS interfered with avoidance learning and the introduction of noise offset as a feedback signal enhanced it. The only demonstration of stimulus specificity was the failure of noise onset to function as a feedback signal.     

Time limits for completing fixed ratios. II. Stimulus specificity

Pigeons were exposed to two stimuli that were each correlated with the same fixed-ratio schedule. During one stimulus, the ratio had to be completed in more than a specified time for food to be presented. During the other, the ratio had to be completed in less than a specified time. Failures to meet the time criterion produced a timeout and reset the ratio. Treating the entire behavioral sequence generated by a fixed-ratio schedule as a unitary response and scheduling differential reinforcement with respect to the duration of the sequence produced effects comparable to those observed previously with individual responses. The times taken to complete the ratios conformed to the time criteria under both stimulus conditions. Similar effects have been observed with differential reinforcement of the duration of individual responses and in experiments specifying running speed criteria under discrete trial conditions.     

Sodium amylobarbitone and responses to nonreward

Three experiments are reported testing two alternative hypotheses concerning the behavioural effects of sodium amylobarbitone (SA): (1) that it blocks the after-effect of nonreward; (2) that it blocks conditioned frustration, elicited by stimuli associated with nonreward. In support of (2) Experiment I showed that SA given in acquisition abolished the partial reinforcement extinction effect (PREE) when rats were run at one trial a day in an alley for food reward on a continuous (CRF) or partial (PRF) reinforcement schedule. Experiment II showed that, in the goal section, the effect of the drug on the PREE was due to its presence during acquisition and was not due to state dependency; but the effect of the drug in the start section was consistent with state dependency of the PREE. In Experiment III, in opposition to (1) and again in support of (2), SA given to rats trained to show patterned running for water reward on a single alternation schedule blocked patterning by increasing running speeds on nonreward trials, not by decreasing running speeds on rewarded trials.     

Stimulus control of habits: Evidence for both stimulus specificity and devaluation insensitivity in a dual-response task

Goal-directed and habitual actions are clearly defined by their associative relations. Whereas goal-directed control can be confirmed via tests of outcome devaluation and contingency-degradation sensitivity, a comparable criterion for positively detecting habits has not been established. To confirm habitual responding, a test of control by the stimulus–response association is required while also ruling out goal-directed control. Here we describe an approach to developing such a test in rats using two discriminative stimuli that set the occasion for two different responses that then earn the same outcome. Performance was insensitive to outcome devaluation and showed stimulus–response specificity, indicative of stimulus-controlled behavior. The reliance of stimulus–response associations was further supported by a lack of sensitivity during the single extinction test session used here. These results demonstrate that two concurrently trained responses can come under habitual control when they share a common outcome. By reducing the ability of one stimulus to signal its corresponding response–outcome association, we found evidence for goal-directed control that can be dissociated from habits. Overall, these experiments provide evidence that tests assessing specific stimulus–response associations can be used to investigate habits.     

Transfer of approach responding between punishment, frustrative nonreward, and the combination of punishment and nonreward

Rats trained to make an approach response with either partial reward, intermittent punishment, or a combination of partial reward and intermittent punishment, were tested for persistence to extinction, punishment with reward, or punishment during extinction. Partial reward, alone or with punishment, produced greates resistance to extinction, while intermittent punishment, alone or with partial reward, produced greatest persistence to punishment with reward. Transfer of persistence from partial reward to punishment with reward and intermittent punishment to extinction was also demonstrated. However, partial reward alone did not increase persistence to punishment during extinction, whereas intermittent punishment and partial reward combined with intermittent punishment did increase such persistence. These results were interpreted in Amsel's (1958, 1962) conditioning-model theory by extending the hypothesized similarity of frustrative nonreward and punishment.     

The other side of the coin: Cognitive properties of nonreward

In this comment, I examine Amsel’s theory in the light of rats’ reaction not to frustrative non-reward per se, but to the more complicated case in which frustrative nonreward is part of a rule-based sequence of reward quantities. The discussion goes beyond Amsel’s emphasis on dispositional memory to consider cognitive and representational memory—the signaling properties of reinforcement and nonreinforcement. The strengths and weaknesses of Amsel’s theory are discussed with the fresh perspective that this viewpoint provides, and some issues emerge that may be fruitful for further study.     

On Stimulus Generalization and Stimulus Classes

Stimulus generalization has been defined as the spread of effect of reinforcement for responses emitted in the presence of one stimulus to different stimuli presented under extinction conditions. As a result of stimulus generalization, novel stimuli come to exert stimulus control over members of the response class. Studies in the applied behavior analysis literature, however, have reported experimental preparations that included prompting and reinforcement procedures during what were claimed to be stimulus generalization conditions. These studies violated the procedural requirement that stimulus generalization be tested under extinction conditions. Responses that come under the control of a class of stimuli may do so by direct training or by stimulus generalization. It is desirable for organisms to respond in the presence of members of an appropriately constructed stimulus class, but we should understand the mechanism of entry into the class by its members. If inaccurate claims of stimulus generalization are made when training procedures are used in the ostensible generalization conditions, the robustness of the original training procedures will be over estimated. By adhering to the operational requirements of behavioral definitions, we could better understand the power and limits of our educational and training procedures.     

Stimulus control: part I

In his effort to distinguish operant from respondent conditioning, Skinner stressed the lack of an eliciting stimulus and rejected the prevailing stereotype of Pavlovian "stimulus-response" psychology. But control by antecedent stimuli, whether classified as conditional or discriminative, is ubiquitous in the natural setting. With both respondent and operant behavior, symmetrical gradients of generalization along unrelated dimensions may be obtained following differential reinforcement in the presence and the absence of the stimulus. The slopes of these gradients serve as measures of stimulus control, and they can be steepened without applying differential reinforcement to any two points along the test dimension. Increases and decreases in stimulus control occur under the same conditions as those leading to increases and decreases in observing responses, indicating that it is the increasing frequency and duration of observation (and perhaps also of attention) that produces the separation in performances during discrimination learning.     

Stimulus control: part II

The second part of my tutorial stresses the systematic importance of two parameters of discrimination training: (a) the magnitude of the physical difference between the positive and the negative stimulus (disparity) and (b) the magnitude of the difference between the positive stimulus, in particular, and the background stimulation (salience). It then examines the role these variables play in such complex phenomena as blocking and overshadowing, progressive discrimination training, and the transfer of control by fading. It concludes by considering concept formation and imitation, which are important forms of application, and recent work on equivalence relations.     

Reduced approach motivation following nonreward: Extension of the BIS/BAS scales

The current study describes the development and validation of a new subscale to be used with the BIS/BAS scales (Carver & White, 1994). This subscale measures lowered approach motivation following nonreward. Factor analysis of the new subscale was carried out within a sample of 308 University students, test–retest reliability was established within a sample of 62 individuals, and construct validity was explored in a sample of 86 individuals by comparing scores on the new subscale with those on an existing self-report measure of apathy and on a behavioural measure of persistence. Reliability and validity of the new frustrative nonreward responsiveness subscale was found to be adequate within the populations studied. The findings are discussed in relation to theoretical accounts of BAS and BIS sensitivity.     

Stimulus Equivalence: Effects Of A Default-response Option On Emergence Of Untrained Stimulus Relations

Human subjects were exposed to a concurrent-chains schedule in which reinforcer amounts, delays, or both were varied in the terminal links, and consummatory responses were required to receive points that were later exchangeable for money. Two independent variable-interval 30-s schedules were in effect during the initial links, and delay periods were defined by fixed-time schedules. In Experiment 1, subjects were exposed to three different pairs of reinforcer amounts and delays, and sensitivity to reinforcer amount and delay was determined based on the generalized matching law. The relative responding (choice) of most subjects was more sensitive to reinforcer amount than to reinforcer delay. In Experiment 2, subjects chose between immediate smaller reinforcers and delayed larger reinforcers in five conditions with and without timeout periods that followed a shorter delay, in which reinforcer amounts and delays were combined to make different predictions based on local reinforcement density (i.e., points per delay) or overall reinforcement density (i.e., points per total time). In most conditions, subjects' choices were qualitatively in accord with the predictions from the overall reinforcement density calculated by the ratio of reinforcer amount and total time. Therefore, the overall reinforcement density appears to influence the preference of humans in the present self-control choice situation.