Unsignaled Component Research Articles

Rate matching, probability matching, and optimization in concurrent ratio schedules.

Much research has documented rate matching in concurrent variable-interval schedules, but comparatively little research has examined performance in concurrent variable-ratio schedules, except in discrete-trials procedures that sometimes produce probability matching. One should expect that the two types of schedule would result in different performances, because ratio schedules cannot improve with time the way interval schedules do; ratio schedules lack the temporal dynamics of interval schedules. The present experiment exposed rats to concurrent variable-ratio schedules. Seven unsignaled components were presented in random order within each daily session, with probability ratios ranging from 1:8 to 8:1. Three conditions were studied that varied the overall probability of food while leaving probability ratios the same. Choice appeared to conform to probability matching, because sensitivities in the rate-matching relation were close to 0.5, whereas sensitivities to probability ratio were close to 1.0. The sensitivities alone, however, could not confirm probability matching, because undermatching to rate occurs often. Analyses at smaller time scales supported the interpretation of probability matching. In particular, control by food deliveries was highly local in concurrent variable-ratio schedules, in contrast with concurrent variable-interval schedules, in which control is extended. Activity continued to switch between alternatives throughout components, contradicting optimal sampling theory.

Baseline-dependency: How genotype and signaled delays influence amphetamine's effects on delay discounting

RationaleDelay discounting, in which an animal chooses between a small, immediate or large, delayed reinforcer, is an experimental model of impulsivity. In previous studies, d-amphetamine has both increased and decreased preference for larger-delayed reinforcers depending on experimental conditions. ObjectiveIdentify genotype X environment interactions responsible for these disparate findings in a single study and assess the hypothesis that baseline-dependence unifies d-amphetamine's effects. MethodsDelay discounting by BALB/c and C57Bl/6 mice was evaluated using a choice procedure in which six delays to a larger reinforcer were presented in a single session. Components were presented both with and without stimuli that uniquely signaled reinforcer delays. d-Amphetamine's (0.1–1.7 mg/kg) effects on delay and magnitude sensitivity were assessed when specific stimuli did or did not uniquely signal the delay to a larger reinforcer. d-Amphetamine's effects were determined using a model-comparison approach. ResultsDuring baseline, magnitude and delay sensitivity were identical across signal conditions for BALB/c mice and generally greater than the C57Bl/6 mice. For C57Bl/6 mice, magnitude and delay sensitivity were higher during the signaled than the unsignaled component. Amphetamine decreased delay sensitivity during both components for BALB/c mice, but this effect was attenuated by delay-specific stimuli. For C57Bl/6 mice, amphetamine decreased their high magnitude and delay sensitivity when delays were signaled and, conversely, increased the low magnitude and delay sensitivity when delays were unsignaled. ConclusionsBALB/c mice showed high delay and magnitude sensitivity regardless of signal conditions. C57Bl/6's magnitude and delay sensitivity depended on signaling. d-Amphetamine usually decreased high baseline delay- and magnitude sensitivity and increased low sensitivities, a baseline-dependence that occurred regardless of whether delay sensitivity was driven by biological (genotype) or environmental (signaling) variables. The C57Bl/6 mouse may be a good model of environmentally-induced impulsivity while BALB/c mice could model impulsivity with a strong genetic contribution.

Choice with frequently changing food rates and food ratios

In studies of operant choice, when one schedule of a concurrent pair is varied while the other is held constant, the constancy of the constant schedule may exert discriminative control over performance. In our earlier experiments, schedules varied reciprocally across components within sessions, so that while food ratio varied food rate remained constant. In the present experiment, we held one variable-interval (VI) schedule constant while varying the concurrent VI schedule within sessions. We studied five conditions, each with a different constant left VI schedule. On the right key, seven different VI schedules were presented in seven different unsignaled components. We analyzed performances at several different time scales. At the longest time scale, across conditions, behavior ratios varied with food ratios as would be expected from the generalized matching law. At shorter time scales, effects due to holding the left VI constant became more and more apparent, the shorter the time scale. In choice relations across components, preference for the left key leveled off as the right key became leaner. Interfood choice approximated strict matching for the varied right key, whereas interfood choice hardly varied at all for the constant left key. At the shortest time scale, visit patterns differed for the left and right keys. Much evidence indicated the development of a fix-and-sample pattern. In sum, the procedural difference made a large difference to performance, except for choice at the longest time scale and the fix-and-sample pattern at the shortest time scale.

STIMULUS EFFECTS ON LOCAL PREFERENCE: STIMULUS—RESPONSE CONTINGENCIES, STIMULUS—FOOD PAIRING, AND STIMULUS—FOOD CORRELATION

Four pigeons were trained in a procedure in which concurrent-schedule food ratios changed unpredictably across seven unsignaled components after 10 food deliveries. Additional green-key stimulus presentations also occurred on the two alternatives, sometimes in the same ratio as the component food ratio, and sometimes in the inverse ratio. In eight experimental conditions, we varied the contingencies surrounding these additional stimuli: In two conditions, stimulus onset and offset were noncontingent; in another two, stimulus onset was noncontingent, and offset was response contingent. In four conditions, both stimulus onset and offset were contingent, and in two of these conditions the stimulus was simultaneously paired with food delivery. Sensitivity to component food ratios was significantly higher when stimulus onset was response contingent compared to when it was noncontingent. Choice changes following food delivery were similar in all eight conditions. Choice changes following stimuli were smaller than those following food, and directionally were completely determined by the food-ratio:stimulus-ratio correlation, not by the stimulus contingency nor by whether the stimulus was paired with food or not. These results support the idea that conditional reinforcers may best be viewed as signals for next-food location rather than as stimuli that have acquired hedonic value, at least when the signals are differential with respect to future conditions.

Choice in a variable environment: effects of unequal reinforcer distributions.

Six pigeons were trained in a procedure in which sessions included seven unsignaled components, each offering two pecking keys, and each providing a potentially different reinforcer ratio between the two keys. Across conditions, various combinations of reinforcer ratios and reinforcer-magnitude ratios were used to create unequal reinforcer distributions between the two alternatives when averaged across a session. The results extended previous research using the same basic procedure that had included only reinforcer distributions symmetrical around 1:1. Data analyses suggested that the variables controlling choice operated at a number of levels: First, individual reinforcers had local effects on choice; second, sequences of successive reinforcers obtained at the same alternative (continuations) had cumulative effects; and, third, when these sequences themselves occurred with greater frequency, their effects further cumulated. A reinforcer obtained at the other alternative following a sequence of continuations (a discontinuation) had a large effect and apparently reset choice to levels approximating the sessional reinforcer ratio.

Separation of drug effects on timing and behavioral inhibition by increased stimulus control.

Impulsive behavior may represent, in part, a failure of behavioral inhibition (the ability to delay or inhibit a response). In this study, use of a multiple signaled-unsignaled differential-reinforcement-of-low-rates (DRL) 15-s schedule allowed examination of drug effects in conditions in which level of stimulus control differed. Results showed that whereas diazepam increased premature responding during signaled and unsignaled DRL components, amphetamine and delta9-tetrahydrocannabinol increased premature responding primarily during unsignaled components when timing was necessary for efficient performance on the task. In contrast, pimozide and desipramine increased long-delay responses across both components, resulting in longer mean interresponse times. Collectively, these results suggest that the use of different levels of stimulus control may aid in separation of drug effects on timing and other behavioral processes, including behavioral inhibition.

SCHEDULE INTERACTIONS INVOLVING PUNISHMENT WITH PIGEONS AND HUMANS

The principal aim of the present experiments was to assess whether punishment increased or decreased the rate of unpunished behavior (contrast and induction, respectively) for which reinforcement rate was held constant, with physical and nonphysical punishers (electric shock and response cost), pigeon and human subjects, signaled and unsignaled components (multiple and mixed schedules), and the presence or absence of a blackout period between components. Across the three experiments there were 20 punishment conditions. Induction was found in nine of those, less consistent response‐rate reduction was found in three, contrast was found in four, and in four there was no change in responding from conditions without punishment. Contrast occurred consistently only with multiple schedules during the first exposure to electric‐shock punishment. Induction and no change, however, were found with every combination of the independent variables studied. Four conclusions regarding the interactions between punished and unpunished responding emerged from the present results: (a) Both contrast and induction occurred with the reinforcement rate held constant and a blackout between components, (b) induction was more common than contrast, (c) contrast occurred only in the presence of a stimulus different from that correlated with the punisher, and (d) contrast diminished with prolonged exposure to punishment. None of the current theoretical accounts of punishment contrast can explain the present results.

Behavioral effects of toluene are modulated by stimulus control

Behavior that is strongly controlled by environmental stimuli is less susceptible to disruption by certain chemicals than is such behavior not under strong external control. To determine whether toluene's effects can also be minimized by environmental stimuli, two varieties of a fixed consecutive number schedule were studied. With one, a lever press response was reinforced with milk only if preceded by a minimum of eight consecutive responses on a second lever, no cues indicating that the minimum number had been reached. With the other, a combination of lights and a tone served as a discriminative stimulus signaling the completion of the minimum response number. In an experiment studying these schedules separately, rats were exposed to toluene concentrations up to 3000 ppm for 4-hr periods immediately before their performance was tested. Toluene reduced the accuracy of both types of behavior in a concentration-related fashion. Clear differential effects occurred, with the signaled behavior, i.e., that under stronger stimulus control, showing less disruption by toluene. Similar results were produced after 2-hr exposures with a multiple schedule in which the signaled and unsignaled performances alternated within a single session. Response rate changes were observed at 560 ppm, but changes in rate were independent of effects on the accuracy of performance. The EC50 for significant behavior disruption was 1081 ppm for the unsignaled component of the multiple schedule; the EC10 was 480 ppm. No performance disruption was observed in the signaled component below 1780 ppm. The finding of differential sensitivity could be useful in guiding the development of more sensitive tests of performance impairment.

Multiple Schedules of Escape-Avoidance with Sequential Warning Stimuli

Three rats were trained to escape electric shock by satisfying a continuous (CRF) or differential reinforcement of low rate (DRL) escape schedule. These escape schedules, accompanied by visual cues, were randomly alternated at 5-min intervals in a multiple schedule format. Each escape schedule was linked with a 20-sec avoidance component (R-S = 20 sec), in which responses prevented the occurrence of escape periods. Three 5-sec duration, auditory and visual warning stimuli (WS) were provided during the R-S intervals. Later, signaled avoidance components alternated with unsignaled components. In general, all subjects produced the high (CRF) and low (DRL) escape rates expected. The data produced during the shock off intervals revealed that avoidance was higher in the DRL escape components relative to the CRF escape components. Signaled avoidance produced superior avoidance relative to unsignaled avoidance. All 3 rats responded to the first two WS instead of waiting until the last WS appeared. The differential escape rates, in conjunction with the differential avoidance performances, indicated evidence of reliable stimulus control by the various cues associated with the various escape-avoidance schedules employed.

Interaction effects in a multiple schedule of signaled and unsignaled reinforcement

Pigeons received baseline training on an equal-valued multiple unsignaled variable-interval/signaled variable-interval schedule. This procedure resulted in high and low response rates during the unsignaled and signaled components, respectively. Behavior during each component was then separately extinguished. Extinction of the unsignaled component resulted in positive contrast in the signaled variable-interval component. When reinforcement was withheld during the signaled component, marked increases in responding during this component occurred, and responding in the presence of the signal was very resistant to extinction. Accompanying the breakdown of the discrimination during the signaled component was an increase in the rate of responding in the unsignaled variable-interval component (i.e., positive induction). The implications of these results for several theories of behavioral contrast are considered.

Further evidence of interaction between deprivation effects and stimulus control of responding: III

Four pigeons were given baseline training under a multiple VI 60-sec/VI 60-sec schedule of food reinforcement. One component was correlated with a red key light to which a white light was added in order to signal the availability of a reinforcer. Under the other component, the key light was green at all times. This procedure resulted in few responses under the signaled component, except when the reinforcer was available, and consistent responding at high rates under the unsignaled component. Variations in hours of deprivation produced small increases in responding under the unsignaled component and no change under the signaled component. Systematic changes in body weight produced greater differential effects under the two components. Increases in deprivation resulted in increased responding during the unsignaled component, with little or no change in the rate of responding under the signaled component. The results suggest that when stimulus control results in low rates of response the influence of deprivation is diminished in relation to its effects upon behavior which is controlled at a high rate by a specific stimulus.