Food-paired stimuli as conditioned reinforcers: effects of d-amphetamine.

Seven pigeons were studied in two experiments in which key pecks were reinforced under a second-order schedule wherein satisfaction of variable-interval schedule requirements produced food or a brief stimulus. In the second part of each session, responses produced only the brief stimulus according to a variable-interval schedule (food extinction). For the 4 pigeons in Experiment 1, the response key was red throughout the session. In separate phases, the brief stimulus was either paired with food, not paired with food, or not presented during extinction. d-Amphetamine (0.3 to 10.0 mg/kg) dose-dependently reduced food-maintained responding during the first part of the session and, at intermediate dosages, increased responding during the extinction portion of the session. The magnitude of these increases, however, did not consistently depend on whether the brief stimulus was paired, not paired, or not presented. It was also true that under nondrug conditions, response rates during extinction did not differ reliably depending on pairing operations for the brief stimulus. In Experiment 2, 3 different pigeons responded under a procedure wherein the key was red in the component with food presentations and blue in the extinction component (i.e., multiple schedule). Again, d-amphetamine produced dose-related decreases in responding during the first part of a session and increases in responding in the second part of the session. These increases, however, were related to the pairing operations; larger increases were observed when the brief stimulus was paired with food than when it was not or when it was not presented at all. Under nondrug conditions, the paired brief stimulus controlled higher response rates during extinction than did a nonpaired stimulus or no stimulus. These findings suggest that d-amphetamine can enhance the efficacy of conditioned reinforcers, and that this effect may be more robust if conditioned reinforcers occur in the context of a signaled period of extinction.     

Stimulus Presentation Ratios And The Outcomes For Correct Responses In Signal-detection Procedures

Three pigeons were trained to discriminate between two line orientations (S₁ and S₂). A left-key peck was correct when S₁ was presented, and a right key-peck was correct when S₂ was presented. In all procedures, correct responses were occasionally reinforced with food paired with the presentation of the magazine light. Incorrect responses produced a blackout. Six detection procedures were used. In the first, the signal presentation ratio was varied across conditions and the reinforcer ratio was allowed to covary. In the second, the signal presentation ratio was held constant at 1:1 and the reinforcer ratio varied across conditions. In the third, the signal presentation ratio was varied across conditions and the reinforcer ratio was held constant at 1:1. In these three procedures, correct responses that were not scheduled for reinforcement were followed by blackout. The remaining three procedures repeated those described above with one procedural change: Nonreinforced but correct trials were followed by the presentation of the magazine light. Birds showed systematic preferences for the key associated with the stimulus presented or reinforced most often. There was no change in the birds' performance over changes in the feedback for nonreinforced but correct responses.     

Examination of ambiguous stimulus preferences with duration-based measures

Items that produced ambiguous results in an approach-based preference assessment were reassessed using a duration-based assessment. The reinforcing effects of three items on free-operant responding were subsequently tested. The results suggested that the duration-based assessment produced slightly more differentiated results and that predictions about reinforcer value, based on this assessment, were accurate.     

Transfer tests of stimulus value in concurrent chains

We report two experiments that use transfer tests to investigate whether in concurrent chains the value of a terminal-link stimulus is affected by the alternate terminal link. In Experiment 1, two groups of pigeons were trained on multiple concurrent-chains schedules in which switching between the schedules was via pecking a changeover key. For one group, the terminal links were fixed-interval 8 s versus fixed-interval 16 s in one component and fixed-interval 16 s versus fixed-interval 32 s in the other component. For a second group, the terminal links were variable-interval 10 s versus variable-interval 20 s in one component and variable-interval 20 s versus variable-interval 40 s in the other. After sufficient baseline training had been given so that performances had stabilized, transfer tests were conducted in which the two chains with equal terminal-link schedules were presented together as a new concurrent pair. For 6 of the 7 subjects, initial-link responding changed fairly rapidly during the test in the manner predicted if the values of the terminal links were equal. In Experiment 2, pigeons were trained on multiple concurrent chains using a two-key procedure, and the terminal links were the same variable-interval schedules as in Experiment 1. After baseline training, transfer tests were conducted that assessed (a) the relative reinforcing strength of the terminal-link stimuli in a novel initial-link situation and (b) the relative ability of those stimuli to evoke responding. The data from the reinforcing strength test were consistent with those from Experiment 1, but those from the evocation strength test were not. Although this discrepancy shows that responding in transfer tests is not solely a function of stimulus value, the results from both experiments suggest, overall, that value is determined by the stimulus—reinforcer relation independently of the alternative terminal link.     

Behavior of rats under fixed consecutive number schedules: effects of drugs of abuse.

Four rats responded under a simple fixed consecutive number schedule in which eight or more consecutive responses on the run lever, followed by a single response on the reinforcement lever, produced the food reinforcer. Under this simple schedule, dose-response curves were determined for diazepam, morphine, pentobarbital, and phencyclidine. The rats were then trained to respond under a multiple fixed consecutive number schedule in which a discriminative stimulus signaled when the response requirement on the run lever had been completed in one of the two fixed consecutive number component schedules. Under control conditions, the percentage of reinforced runs under the multiple-schedule component with the discriminative stimulus added was much higher than the percentage of reinforced runs under the multiple-schedule component without the discriminative stimulus. All of the drugs decreased the percentage of reinforced runs under each of the fixed consecutive number schedules by increasing the conditional probability of short run lengths. This effect was most consistently produced by morphine. The drugs produced few differences in responding between the multiple fixed consecutive number components. Responding under the simple fixed consecutive number schedule, however, was affected at lower doses of the drugs than was responding under the same fixed consecutive number schedule when it was a component of the multiple schedule. This result may be due to the difference in schedule context or, perhaps, to the order of the experiments.     

Reinforcer frequency and restricted stimulus control.

Stimulus control was evaluated in 3 individuals with moderate to severe mental retardation by delayed identity matching-to-sample procedures that presented either one or two discrete forms as sample stimuli on each trial. On pretests, accuracy scores on one-sample trials were uniformly high. On two-sample trials, the correct stimulus (i.e., the one that subsequently appeared in the comparison array) varied unpredictably, and accuracy scores were substantially lower, suggesting that both sample stimuli did not exert stimulus control on every trial. Subjects were then given training sessions with the one-sample task and with a new set of four stimuli. For two of the stimuli, correct matching responses were followed by reinforcers on a variable-ratio schedule that led to a high reinforcer rate. For the other two stimuli, correct responses were followed by reinforcers on a variable-ratio schedule that led to a substantially lower reinforcer rate. Results on two-sample tests that followed showed that (a) on trials in which comparison arrays consisted of one high reinforcer-rate and one low reinforcer-rate stimulus, subjects most often selected the high-rate stimulus; and (b) on trials in which the comparison arrays were either two high reinforcer-rate stimuli or two low reinforcer-rate stimuli and the samples were one high reinforcer- and one low reinforcer-rate stimulus, accuracy was higher on trials with the high-rate comparisons. These results indicate that the frequency of stimulus control by high reinforcer-rate samples was greater than that by low reinforcer-rate samples. Following more training with the one-sample task and reversed reinforcement schedules for all stimuli, the differences in stimulus control frequencies on two-sample tests also reversed. These results demonstrate experimental control by reinforcement contingencies of which of two sample stimuli controlled selections in the two-sample task. The procedures and results may prove to be relevant for understanding restricted stimulus control and stimulus overselectivity.     

Comparison of Different Feedback Procedures in Second Language Vocabulary Learning

Research into the learning of Second Language (SL) vocabulary by beginning learners has indicated that the simultaneous presentation of the First and Second Language words results in blocking of the learning process by the familiar First Language (FL) word. Previous research also suggests that blocking by the First Language can be eliminated by bringing it in as informative feedback (either as a written or spoken word). Our experiments were designed to further extend this research. The use of a picture, either as feedback or simultaneously presented with its equivalent, along with the aural feedback and the conventional procedures were investigated in Experiment 1. Results revealed that pictures blocked the learning process less than the written FL word when both were presented with their SL referent. When used as feedback, however, pictures were not as good as the spoken FL word. Experiment 2 demonstrated that aural feedback was the best type of feedback when compared with the picture and written FL presentations, and that the picture feedback was better than the written feedback. Taken together, the results of these two studies showed that all forms of feedback overcame the problem of blocking created by simultaneous presentation of the FL and SL words, and that aural feedback was the most effective feedback procedure. It was suggested that the superiority of aural feedback was likely to be a consequence of the use of a different input channel to that of the visually presented written SL word.     

Effects of idiosyncratic stimulus variables on functional analysis outcomes.

As the methods for the functional analysis of problem behavior have continued to develop, there has been a greater focus on the specificity of controlling variables, both antecedents and consequences. Accelerating research interest in the role of antecedents reveals that a large array of stimulus variables can influence the rate of problem behavior. Indeed, the variety of these stimuli is so great that it is sometimes possible to overlook specific stimulus variables during initial assessment. The present study shows that a failure to identify these very specific (idiosyncratic) stimulus variables is serious because their presence can systematically alter the outcomes of functional analyses that are designed to assess the motivation of problem behavior. Guidelines are therefore discussed concerning when to suspect that idiosyncratic stimuli might be acting to influence assessment data, thereby promoting a search for additional stimulus variables whose identification can aid in improving the design of functional analysis conditions.     

TEACHING CHILDREN TO SPELL: DECREASING CONSONANT CLUSTER ERRORS BY ELIMINATING SELECTIVE STIMULUS CONTROL

Six elementary-aged children were taught to spell words containing initial consonant clusters (CCs). They were trained to select printed words in response to the corresponding spoken words using computerized matching-to-sample procedures. After each training session, they were tested for spelling with a constructed-response transfer test. Based on previous selective stimulus control research, we hypothesized that only the first letter of an initial CC might control spelling when CC spelling errors are made. Thus, a critical-difference matching-to-sample training condition that required the children to respond to both letters of the CC to be correct was compared to a multiple-difference training condition that required the children to respond to only one letter of the pair. Results showed that children made fewer errors during the multiple-difference training condition than during the critical-difference training condition. On the constructed-response transfer tests, however, more overall errors and CC errors were made in the multiple-difference condition than in the critical-difference condition, and the words trained in the multiple-difference condition required more training sessions to reach criterion. All children improved their spelling of novel CC words by the completion of training. If normal classroom or home reading was to be supplemented by computer tasks of the kind used here, some spelling problems could be circumvented without costly intervention by a teacher or a special trainer.     

Acquisition of stimulus control while introducing new stimuli in fading.

After establishing discrimination between a red positive stimulus and a green negative stimulus, the lowest intensity colors that restricted all responding to the positive stimulus were determined. Then, two new white lines differing in terms of line orientation were each superimposed on one of the colors and were increased in intensity. Thereafter, the intensity of the colors was decreased and eventually eliminated. Probe stimuli consisting of the lines presented against dark backgrounds were presented before each change of stimulus intensity, and probe responding was used to assess the control acquired by various dimension of the new stimuli during the course of fading. The lines acquired control of responding while they were being introduced, and control was strengthened as the colors were attenuated. Such a locus of acquisition was attributed to the starting intensity of the original controlling stimuli and was explained in terms of stimulus blocking. Finally, using probes while introducing the new stimuli enhanced the acquisition of control by the new stimuli.