How to teach a pigeon to maximize overall reinforcement rate

In two experiments deviations from matching earned higher overall reinforcement rates than did matching. In Experiment 1 response proportions were calculated over a 360-response moving average, updated with each response. Response proportions that differed from the nominal reinforcement proportions, by a criterion that was gradually increased, were eligible for reinforcement. Response proportions that did not differ from matching were not eligible for reinforcement. When the deviation requirement was relatively small, the contingency proved to be effective. However, there was a limit as to how far response proportions could be pushed from matching. Consequently, when the deviation requirement was large, overall reinforcement rate decreased and pecking was eventually extinguished. In Experiment 2 a discriminative stimulus was added to the procedure. The houselight was correlated with the relationship between response proportions and the nominal (programmed) reinforcement proportions. When the difference between response and reinforcement proportions met the deviation requirement, the light was white and responses were eligible for reinforcement. When the difference between response and reinforcement proportions failed to exceed the deviation requirement, the light was blue and responses were not eligible for reinforcement. With the addition of the light, it proved to be possible to shape deviations from matching without any apparent limit. Thus, in Experiment 2 overall reinforcement rate predicted choice proportions and relative reinforcement rate did not. In contrast, in previous experiments on the relationship between matching and overall reinforcement maximization, relative reinforcement rate was usually the better predictor of responding. The results show that whether overall or relative reinforcement rate better predicts choice proportions may in part be determined by stimulus conditions.     

Parametric effects of reinforcement frequency, amount of reinforcement, and required response force on sheltered workshop behavior

Three experiments involving parametric manipulation of reinforcement contingencies were performed with retardates in an automated Sheltered Workshop token economy. Experiment I showed that with amount of reinforcement held constant, work rates were positively related to reinforcement rates on fixed-interval schedules and inversely related to reinforcement rates on fixed-ratio schedules. Experiment II demonstrated an interaction between frequency of ratio reinforcement and torque required to complete a work unit: work rates were positively related to reinforcement rates when required response force was high and negatively related to reinforcement rates when required response force was low. Experiment III revealed that, with reinforcement frequency held constant, there was in inverse relationship between amount of reinforcement and work rate.     

Alternative response training, differential reinforcement of other behavior, and extinction in squirrel monkeys (Saimiri sciureus)

In Experiment I, (a) extinction, (b) extinction plus reinforcement of a discrete alternative response, and (c) differential reinforcement of other behavior were each correlated with a different stimulus in a three-component multiple schedule. The alternative-response procedure more rapidly and completely suppressed behavior than did differential reinforcement of other behavior. Differential reinforcement of other behavior was slightly more effective than extinction alone. In Experiment II, reinforcement of specific alternative behavior during extinction and differential reinforcement of other behavior were used in two components, while one component continued to provide reinforcement for the original response. Once again, the alternative-response procedure was most effective in reducing responding as long as it remained in effect. However, the responding partially recovered when reinforcement for competing behavior was discontinued. In general, responding was less readily reduced by differential reinforcement of other behavior than by the specific alternative-response procedure.     

Elicited responding to signals for reinforcement: the effects of overall versus local changes in reinforcement probability

Pigeons were studied on a three-component multiple schedule where all reinforcement was independent of responding. Two components were cued by different keylights and were associated with different rates of reinforcement. The third was always a no-key period associated with extinction. After a few sessions, pecking was elicited by the keylights signalling the reinforcement and continued to be maintained indefinitely. The duration and sequence of the three components were varied to determine if the primary controlling variable was differences in the overall probability of reinforcement, or if it was the immediate change in reinforcement signalled by the onset and/or offset of the stimulus. Both variables were found to control behavior. When 30-sec components were used, the primary controlling variable was the overall probability of reinforcement, but when 3-min components were used, overall probability had little effect. Control by local changes in reinforcement also occurred, although the type of local control varied both across subjects and experimental conditions. Some behaviors were controlled more by the change in reinforcement signalled by the onset of the stimulus, while others were controlled more by the change signalled by the offset of the stimulus.     

Behavioral aftereffects of reinforcement and its omission as a function of reinforcement magnitude

Rats responded on a multiple fixed-interval fixed-interval schedule of reinforcement. Each complete cycle of the multiple schedule was separated from the next by a relatively long period of timeout from all schedule contingencies. A response at the end of the second component of each cycle was always reinforced with an invariant reinforcement magnitude, while reinforcement magnitude and reinforcement omission were systematically varied in the first component. Response rate in the first component was a monotonic function of reinforcement magnitude in that component. These changes in response rate in the first component did not affect response rate in the second component. When reinforcement was omitted on 50% of occasions in the first component, following reinforcement there was a reduction in response rate in the second component that was monotonically related to reinforcement magnitude. Following reinforcement omission there was an increase in response rate in the second component that was unrelated to reinforcement magnitude. When reinforcement was omitted on 100% of occasions in the first component, behavioral contrast was observed.     

Behavioral contrast and relative reinforcement frequency in two multiple schedules

After preliminary variable-interval training, one group of pigeons was trained on a series of multiple variable-interval low-rate reinforcement schedules, while another group was trained on a series of multiple variable-interval fixed-ratio reinforcement schedules. Contrast effects were observed as variable-interval baseline rate changed in a direction away from the change in reinforcement frequency in the other component. The effects of the variable-interval component on performance in the low-rate and fixed-ratio reinforcement components in the multiple schedules were assessed by comparing the birds' performances on each of these schedules alone. Fixed-ratio reinforcement schedules showed a susceptibility to contrast effects, low-rate reinforcement schedules did not. The rate of reinforcement in fixed-ratio schedules at which no interaction occurred in the multiple schedules was higher than that in variable-interval 1-min schedules, suggesting that pigeons may prefer time-based, rather than response-based, reinforcement.     

Independence of stimulus discriminability from absolute rate of reinforcement in a signal-detection procedure.

Three experiments are reported in which two pigeons were trained to detect differences in stimulus duration under varying levels of absolute rate of reinforcement. Two red stimuli, differing in duration, were arranged probabilistically on the center key of a three-key chamber. On completion of the center-key duration, the center keylight was extinguished and the two side keys were illuminated white. Correct responses were left-key pecks following the shorter duration and right-key pecks following the longer duration. In Experiment 1, relative rate of reinforcement for correct responses was held constant and absolute rate of reinforcement was varied in seven conditions from continuous reinforcement to a variable-interval 90-second schedule. In Experiment 2, relative rate of reinforcement was manipulated across three different absolute rates of reinforcement (continuous reinforcement, variable-interval 15-second, and variable-interval 45-second). Stimulus discriminability was unaffected by changes in absolute or relative rates of reinforcement. Experiment 3 showed that discriminability was also unaffected by arranging the same consequences (three-second blackout) for unreinforced correct responses and errors.     

Establishing preference for unreliable reinforcement in adults with dual diagnoses

We evaluated the choice responding of three adults dually diagnosed with developmental and psychiatric disabilities using concurrent schedules of reinforcement. Specifically, participants were given a choice between a response option resulting in reliable reinforcement and a response option resulting in unreliable reinforcement. Our primary purpose was to shift preference from reliable to unreliable reinforcement via the systematic presentation of stimuli during delay intervals. A second purpose was to evaluate the effectiveness of intervening stimuli in shifting preference at differing delay-to-reinforcement intervals. Preference for unreliable reinforcement was first examined in the absence of stimulus presentations during delays, at three different delay values. Next, we aimed to establish preference for unreliable reinforcement by presenting pictures of reinforcers during delays preceding unreliable reinforcement. Preference was again examined at three different delay values. In the absence of stimulus presentations during delays, participants were shown to prefer reliable reinforcement, particularly at the longer delay value. When stimuli were presented during the delays, two of the three participants preferred unreliable reinforcement, particularly the longer the delay value. These results suggest that the presentation of intervening stimuli during delays may help facilitate tolerance for unreliable reinforcement.     

Reinforcement uncertainty enhances preference for choice in humans

Under concurrent‐chains schedules of reinforcement, participants often prefer situations that allow selection among alternatives (free choice) to situations that do not (forced choice). The present experiment examined the effects of reinforcement probability on choice preferences. Preferences for free versus forced choice were measured under a condition in which participants' choices were always reinforced (reinforcement probability of 1.0) and a condition in which outcomes were uncertain (reinforcement probability of 0.5). Forty‐four college students participated and preferences were examined under a concurrent‐chains schedule of reinforcement. Participants preferred free choice under uncertain reinforcement, but a bias toward free choice was not observed when reinforcement was certain. These results align with previous findings of preference for free choice under conditions of uncertainty, but suggest that preference may be dependent upon probabilistic reinforcement contingencies in the terminal links of the concurrent‐chains arrangement. Thus, reinforcement probability is an important variable to consider when conducting similar studies on the value of choice.     

Effect of intermittent reinforcement on acquisition and retention in delayed matching-to-sample in pigeons

Experiments 1 and 2 involved independent groups that received primary reinforcement after a correct match with a probability of 1.0, .50 or .25. Correct matches that did not produce primary reinforcement produced a conditioned reinforcer. Both experiments revealed little evidence that acquisition or retention was adversely affected by use of intermittent reinforcement. Experiment 3 involved a group that received 100% reinforcement and two others that received 25% reinforcement, one of which received conditioned reinforcement and the other did not. Following acquisition and retention testing, birds in group 100% and group 25% with conditioned reinforcement were exposed to 25% reinforcement and no conditioned reinforcement. Results revealed that conditioned reinforcement was important in promoting acquisition but was irrelevant in maintaining performance. It was concluded that intermittent reinforcement, especially when combined with conditioned reinforcement during acquisition, supports levels of acquisition and retention comparable to that of continuous reinforcement. Theoretically, the findings are consistent with an extension of Blough's instance-based theory of discrimination performance and, practically, they suggest that use of intermittent reinforcement could result in increased efficiency and economy in labs using delayed matching.     

Molar versus local reinforcement probability as determinants of stimulus value.

During one component of a multiple schedule, pigeons were trained on a discrete-trial concurrent variable-interval variable-interval schedule in which one alternative had a high scheduled rate of reinforcement and the other a low scheduled rate of reinforcement. When the choice proportion between the alternatives matched their respective relative reinforcement frequencies, the obtained probabilities of reinforcement (reinforcer per peck) were approximately equal. In alternate components of the multiple schedule, a single response alternative was presented with an intermediate scheduled rate of reinforcement. During probe trials, each alternative of the concurrent schedule was paired with the constant alternative. The stimulus correlated with the high reinforcement rate was preferred over that with the intermediate rate, whereas the stimulus correlated with the intermediate rate of reinforcement was preferred over that correlated with the low rate of reinforcement. Preference on probe tests was thus determined by the scheduled rate of reinforcement. Other subjects were presented all three alternatives individually, but with a distribution of trial frequency and reinforcement probability similar to that produced by the choice patterns of the original subjects. Here, preferences on probe tests were determined by the obtained probabilities of reinforcement. Comparison of the two sets of results indicates that the availability of a choice alternative, even when not responded to, affects the preference for that alternative. The results imply that models of choice that invoke only obtained probability of reinforcement as the controlling variable (e.g., melioration) are inadequate.     

Choice between reliable and unreliable outcomes: mixed percentage-reinforcement in concurrent chains.

Pigeons' choices between alternatives that provided different percentages of reinforcement in mixed schedules were studied using the concurrent-chains procedure. In Experiment 1, the alternatives were terminal-link schedules that were equal in delay and magnitude of reinforcement, but that provided different percentages of reinforcement, with one schedule providing, reinforcement twice as reliably as the other. All pigeons preferred the more reliable schedule, and their level of preference was not systematically affected by variation in the absolute percentage values, or in the magnitude of reinforcement. In Experiment 2, preference for a schedule providing 100% reinforcement over one providing 33% reinforcement increased systematically with increases in the duration of the terminal links. In contrast, preference decreased systematically with increases in the duration of the initial links. Experiment 3 examined choice with equal percentages of reinforcement but unequal delays to reinforcement. Preference for the shorter delay to reinforcement was not systematically affected by variation in the absolute percentage of reinforcement. The overall pattern of results supported predictions based on an extension of the delay-reduction hypothesis to choice procedures involving mixed schedules of percentage reinforcement.     

Reinforcement schedule thinning following treatment with functional communication training

We evaluated four methods for increasing the practicality of functional communication training (FCT) by decreasing the frequency of reinforcement for alternative behavior. Three participants whose problem behaviors were maintained by positive reinforcement were treated successfully with FCT in which reinforcement for alternative behavior was initially delivered on fixed-ratio (FR) 1 schedules. One participant was then exposed to increasing delays to reinforcement under FR 1, a graduated fixed-interval (FI) schedule, and a graduated multiple-schedule arrangement in which signaled periods of reinforcement and extinction were alternated. Results showed that (a) increasing delays resulted in extinction of the alternative behavior, (b) the FI schedule produced undesirably high rates of the alternative behavior, and (c) the multiple schedule resulted in moderate and stable levels of the alternative behavior as the duration of the extinction component was increased. The other 2 participants were exposed to graduated mixed-schedule (unsignaled alternation between reinforcement and extinction components) and multiple-schedule (signaled alternation between reinforcement and extinction components) arrangements in which the durations of the reinforcement and extinction components were modified. Results obtained for these 2 participants indicated that the use of discriminative stimuli in the multiple schedule facilitated reinforcement schedule thinning. Upon completion of treatment, problem behavior remained low (or at zero), whereas alternative behavior was maintained as well as differentiated during a multiple-schedule arrangement consisting of a 4-min extinction period followed by a 1-min reinforcement period.     

The effects of reinforcer pairing and fading on preschoolers' snack selections

The effects of reinforcement pairing and fading on preschoolers' snack selections were evaluated in a multiple baseline design. Baseline preferences for snack options were assessed via repeated paired-item preference assessments. Edible, social, and activity-based reinforcers were then exclusively paired with a less preferred snack option. Once the snack paired with reinforcement was selected most frequently, the three types of reinforcement were systematically faded. Frequent selections of the previously less preferred snack option were produced with paired reinforcement, but were disrupted for all children as the paired reinforcement was reduced to low levels. These data showed that paired reinforcement was initially effective in increasing preference for the originally less preferred snack options, but more permanent changes in the value of the snack options were not achieved. Conditions for producing persistent changes in children's snack choices are discussed.     

Effects of variations in local reinforcement rate on local response rate in variable interval schedules

Rats trained to lever press for sucrose were exposed to variable-interval schedules in which (i) the probability of reinforcement in each unit of time was a constant, (ii) the probability was high in the first ten seconds after reinforcement and low thereafter, (iii) the probability was low for ten seconds and high thereafter, (iv) the probability increased with time since reinforcement, or (v) the probability was initially zero and then increased with time since reinforcement. All schedules generated similar overall reinforcement rates. A peak in local response rate occurred several seconds after reinforcement under those schedules where reinforcement rate at this time was moderate or high ([i], [ii], and [iv]). Later in the inter-reinforcement interval, local response rate was roughly constant under those schedules with a constant local reinforcement rate ([i], [ii], and [iii]), but increased steadily when local reinforcement rate increased with time since reinforcement ([iv] and [v]). Postreinforcement pauses occurred on all schedules, but were much longer when local reinforcement rate was very low in the ten seconds after reinforcement ([iii]). The interresponse time distribution was highly correlated with the distribution of reinforced interresponse times, and the distribution of postreinforcement pauses was highly correlated with the distribution of reinforced postreinforcement pauses on some schedules. However, there was no direct evidence that these correlations resulted from selective reinforcement of classes of interresponse times and pauses.     

Partial reinforcement effects in instrumental escape conditioning

In Experiment I acquisition and extinction of instrumental escape conditioning with rats (N = 64) were studied as a function of reinforcement magnitude under conditions of partial and continuous reinforcement. In Experiment II the effects of partial and continuous reinforcement were studied in rats (N = 96) during acquisition followed by small, medium, and large reductions in reinforcement magnitude. A water-tank escape apparatus was used with temperature as the relevant variable. It was found that (1) with large reinforcement magnitude a continuously reinforced group was superior in acquisition to one that was partially reinforced; there were no differences with small reinforcement; (2) disruptive effects of a nonreinforced trial (a) appear early in learning, (b) are quite strong after each nonreinforced trial, and (c) persist through several succeeding reinforced trials; (3) major competing behaviors persist throughout acquisition for small reinforcement magnitude regardless of schedule, decline with large reinforcement (more so with continuous than with partial), and return to a high level in extinction for all conditions; (4) the partial reinforcement extinction effect occurs after large reinforcement but not after small, and it appears only with large reductions in reinforcement magnitude which approach extinction conditions. Only the first part of the last finding appears to be consistent with the appetitive conditioning literature.     

Resistance to the response-decrementing effects of response-independent reinforcement produced by delay and non-delay schedules of reinforcement

In two experiments, animals were initially exposed to response-dependent schedules of food before exposure to response-independent reinforcement matched for overall rate and temporal distribution of reinforcers to the preceding condition. In Experiment I, response decrements during the response-independent phase were smaller after delayed reinforcement training than after a comparable immediate reinforcement schedule, for both doves and rats. In Experiment II variable-interval and variable-ratio schedules, both with either immediate or delayed reinforcement, were used with rats. Both the delayed reinforcement schedules produced resistance to subsequent response-independent reinforcement, but response decrements were larger after either of the immediate reinforcement conditions. It was concluded that the critical factor in response maintenance under response-independent reinforcement was the type of response-reinforcer contiguities permitted under the response-dependent schedule rather than perception of response-reinforcer “contingencies”. If the response-dependent schedule was arranged so that behaviours other than a designated operant (key pecking or lever pressing) could be contiguous with food, responding was maintained well under response-independent schedules.     

Choice: Effects of changeover schedules on concurrent performance

The components of concurrent schedules were separated temporally by placing interval schedules on the changeover key. The rates of responding on both the main and changeover keys were examined as a function of the reinforcement rates. In the first experiment, the sensitivity of main-key performance to changing reinforcement rates was inversely related to the temporal separation of components, and changeover performance was monotonically related to the ratio of the reinforcement rates. In the second experiment, when the ratio of the reinforcement rates was scheduled to remain constant while the frequency of reinforcement was varied, changeover performance did not remain constant. A “sampling” interpretation of changeover responding was proposed and subsequently tested in a third experiment where extinction was always scheduled in one component and the frequency of reinforcement was varied in the second component. It was concluded that changeover performance can be interpreted using molar measures of reinforcement and that animals sample activities available to them at rates which are controlled by relative reinforcement rates.     

Signalled reinforcement in multiple and concurrent schedules

Five pigeons were exposed to multiple and concurrent variable-interval, variable-interval reinforcement schedules in which reinforcement availability in one component was never signalled. During certain phases of the experiment, reinforcement availability in the other component was signalled. Behavioral contrast was observed in seven of eight instances when reinforcement availability in the multiple schedules was signalled. Under the concurrent schedules in which reinforcement availability was signalled, the subjects did not always allocate more time to (prefer) the component containing non-signalled reinforcement, as would be predicted by an account of behavioral contrast holding that contrast results from the introduction of a less-preferred condition in one component of a multiple schedule.     

Assessment and choice: an operant simulation of foraging in patches

Pigeons were presented with an operant simulation of two prey patches using concurrent random-ratio schedules of reinforcement. An unstable patch offered a higher initial reinforcement probability, which then declined unpredictably to a zero reinforcement probability in each session. A stable patch offered a low but unvarying reinforcement probability. When the reinforcement probability declined to zero in a single step, the birds displayed shorter giving-up times in the unstable patch when the ratio between the initial reinforcement probabilities in the unstable and stable patches was greater and when the combined magnitude of the reinforcement probabilities in the two patches was greater. When the unstable patch declined in two steps, the birds behaved as if their giving-up times were influenced heavily by events encountered during the most recent step of the double-step change. This effect was observed, however, only when the reinforcement probability in that step was .04, not when it was .06. All of these data agree with the predictions of a capture-probability model based on a comparison of the estimated probability of receiving a reinforcer in the current patch with that in alternative patches.