Home cage feeding time controls responding under multiple schedules

Eleven rats were exposed to a multiple variable-interval 1-min variable-interval 1-min schedule of reinforcement. All rats were initially fed a daily ration of food in the home cages immediately after the end of each session. In a later phase of the experiment, the same amount of food was fed 1 h after the end of each session. Later, five rats were again fed immediately after each session. Amount of food received and deprivation level in terms of percent of free feeding weight were constant across conditions. Response rates decreased within each session under immediate feeding. When feeding was delayed, rates in each component of the multiple schedule increased throughout the session and the decreasing trends were generally eliminated. The results suggest that home cage feeding time, apart from changes in deprivational level, is an important variable in the control of behavior in experimental sessions.     

Differences between rates of responding emitted during simple and multiple schedules

Pigeons pecked keys for food reinforcers delivered by several variable-interval and multiple variable-interval schedules. The rates of responding emitted during the simple schedules were not systematically different from the rates emitted during the multiple schedules when the components of the multiple schedule were identical. The rates of responding emitted during the components were usually greater than the rates emitted during comparable simple schedules when the components were more favorable than the added components of the multiple schedules. Response rates during the components were not significantly lower than those during comparable simple schedules when the components were less favorable. The observation of higher rates of responding during the more favorable components conforms to a prediction of several additive theories (e.g., Rachlin, 1973) but violates a prediction of Herrnstein’s (1970) theory. However, the additive theories are brought into question by the fact that changing the location of the discriminative stimuli did not change the pattern of results.     

Behavioral contrast and responding during multiple food-food,food-water,and water-water schedules

Five pigeons pecked lighted keys for food reinforcers delivered by several multiple variable interval 2-min variable interval 2-min schedules. At different times, the components of the multiple schedule both supplied food reinforcers, both supplied water, or one supplied food and the other supplied water. Rates of responding during the water component of the food-water schedule were lower than the rates during comparable components of the water-water schedules (negative contrast). But, the rates of responding during the food component of the food-water schedule were not greater than the rates of responding during comparable components of the food-food schedules (absence of positive contrast) at two different levels of water deprivation. These results raise questions about several theories of behavioral contrast, and they may restrict the scope of any theory that attributes positive and negative contrast to symmetrical factors.     

Component duration effects in multiple schedules

Previous research has produced conflicting results regarding the effects of component duration on interactions in multiple schedules. In Experiment 1, potential sources of this conflict were evaluated. Both the effects of absolute reinforcement rate and carry-over effects (hysteresis) from a preceding condition were isolated. When 10-sec components were used, the sensitivity of relative response rate to relative reinforcement rate was affected very little by hysteresis effects and absolute reinforcement rate, but it was systematically reduced as a function of the number of prior conditions. Sensitivity to relative reinforcement rate was also substantially higher with the 10-sec components than with 2-min components. In Experiment 2, this effect of component duration was decomposed into two separate effects. Contrast effects during presentation of a target component with a constant reinforcement rate were greater the shorter the target component was itself; but they were smaller the shorter the alternative component in which reinforcement rate was varied. The latter effect was smaller and more unreliable across subjects. The existence of these two separate effects demonstrates that the usual method of studying component duration—that is, holding all components equal in duration—systematically causes underestimation of the effects of the component duration, and obscures the different processes controlling the two effects.     

Adjunctive behavior in multiple schedules of reinforcement

A recent theory of timing (Killeen & Fetterman, 1988) suggests that adjunctive behaviors may act as discriminative cues for the passage of time and that the rate of transition between those behaviors is affected by the rate of reinforcement within the experimental context. Is the rate of transition between behaviors correlated with the rate of reinforcement? What is the context in which rate of reinforcement is calibrated? If rate of transition is correlated with reinforcement frequency, does this correlation change with extended training? Four pigeons were trained on multiple fixed-time schedules of reinforcement, with one component always FT 15 sec, the other either FT 15 sec, FT 45 sec, or FT 5 sec. Behavior was coded into one of 12 categories. Response distributions in the constant component shifted when rate of reinforcement was varied in the other component and eventually shifted back toward their original location.     

Within-session changes in responding during concurrent schedules that employ two different operanda

Five rats responded on several concurrent schedules in which pressing a key produced reinforcers in one component and pressing a lever produced reinforcers in the other component (Experiment 1). Four pigeons responded on several concurrent keypeck treadlepress schedules (Experiment 2). The programmed rates of reinforcement varied from 15 to 240 reinforcers per hour in different conditions. Rates of responding usually changed systematically within experimental sessions, and the changes were similar for the two components of a concurrent schedule. These results imply that within-session changes in responding may not confound the predictions of theories that describe the ratio of the rates of responding during the two components of concurrent schedules. Instead, within-session changes may be controlled by a mechanism that integrates the reinforcers obtained from the two components.     

Habituation may contribute to within-session decreases in responding under high-rate schedules of reinforcement

Two experiments tested the hypothesis that habituation contributes to within-session decreases in responding. In Experiment 1, rats’ leverpressing was reinforced under a fixed ratio (FR) 4 schedule throughout the baseline sessions. During the dishabituation sessions, the first 21 min and the last 21 min were FR 4; dishabituating events occurred during the middle 3 min. The dishabituating events altered the manner of reinforcer delivery in four different ways. Response rates increased after all dishabituating events. In Experiment 2, rats responded on several FR and variable ratio (VR) schedules. The ratio requirement varied from 3 to 15. Within-session decreases in responding were steeper during FR schedules than during VR schedules. In addition, response rates were well described as linear functions of cumulative number of food pellets eaten within sessions. These results support the habituation hypothesis but do not rule out the possibility that other satiety variables might contribute simultaneously.     

Influence of schizotypy on responding and contingency awareness on free-operant schedules of reinforcement

Schedules of reinforcement typically produce reliable patterns of behaviour, and one factor that can cause deviations from these normally reliable patterns is schizotypy. Low scorers on the unusual experiences subscale of the Oxford-Liverpool Inventory of Feelings and Experiences performed as expected on a yoked random-ratio (RR), random-interval (RI) schedule of reinforcement, with significantly higher rates of responding on the RR schedule than in the RI schedule. However, high scorers in UE showed no such differences between response rates between the RR and RI schedules. In addition, contingency awareness scores were high, and did not differ in low UE scorers for both types of schedule, whilst awareness scores differed significantly between the schedules in high UE scorers, with more awareness of the RR schedule than the RI one. These results suggest that, as well as being unable to differentiate between the RR and RI schedules in terms of response rates, high UE scorers are also unable to verbally describe the RI schedule parameters.     

Stimulus control in multiple variable-ratio schedules of reinforcement

One component of a multiple variable-ratio 150 variable-ratio 150 schedule remained unchanged while the reinforcement schedule of the other component was periodically changed to extinction and then returned to variable ratio 150. When the reinforcement schedule of the changed component was an unmodified variable ratio 150 schedule, the magnitude of negative contrast during baseline recovery was equal to the magnitude of positive contrast observed during the previous change from multiple variable-ratio 150 variable-ratio 150 to multiple variable-ratio 150 extinction. When the schedule of the changed component was modified during baseline recovery so that responses terminating interresponse times greater than the average baseline interresponse time in the unchanged component were not reinforced, the magnitude of the unchanged-component response rate decrease was reduced. The magnitude of negative contrast was attenuated even though response and reinforcement rates in the variable component increased to levels at or above their prior multiple variable-ratio 150 variable-ratio 150 baseline levels. The results support a general theory that negative contrast results from both (1) the removal of certain positive-contrast-producing operations and (2) changes in the interresponse time-reinforcer relations that occur as a byproduct of schedule manipulations.     

Choice responding following multiple schedule training

Pigeons’ choice responding on 10-sec interpolated probes was studied after baseline training on multiple variable-interval variable-interval schedules of food reinforcement. Unreinforced choice following training with three different relative reinforcement rates (Experiment 1), with a 3-ply multiple schedule (Experiment 2), and with three different relative reinforcement durations (Experiment 3) was examined. Least squares lines were fit to choice relative response rate and schedule relative response rate as functions of training relative reinforcement rate; choice slope was significantly greater than schedule slope in all three experiments. This result is counter to the prediction of Herrnstein’s (1970) theory that these slopes should not differ. Luce’s (1959) theory also failed to account for the data. It was concluded that choice responding was controlled by both approach to the stimulus associated with the smaller mean interreinforcer interval or the longer duration, and avoidance of the other stimulus.     

Herrnstein’s equation for the rates of responding during concurrent schedules

A modification of the nonlinear curve-fitting procedure proposed by Wetherington and Lucas (1980) was used to assess how well Herrnstein’s (1970) equation for the rates of responding during concurrent schedules described performance. The equation fitted some results very well, accounting for 80% or more of the variance in the data in studies that used moderate-duration changeover delays and provided the same positive reinforcers, operanda, and simple schedules in the two components. The equation fitted the data poorly in other studies. The k parameter changed with several variables; it was not as constant as Herrnstein (1974) suggested. R₀ did not fit Herrnstein’s interpretation as reinforcement from unprogrammed sources. Forty percent of all values of R₀ were negative, and another 23% were unreasonably large (greater than 50 reinforcers/h). The data suggest that Herrnstein’s equation is not a general theory of concurrent-schedule responding, and that Herrnstein’s interpretation of k and R₀ should be modified.     

Pavlovian conditioning in multiple contexts: Competition between contexts for comparator status

Water-deprived rats were used to investigate the effects of training a CS in more than one context on conditioned lick suppression. In each experiment, partial reinforcement of the CS was intermingled with unsignaled presentations of the US. In Experiment 1, subjects were either trained in one context alone, trained consecutively in two contexts (such that all training in one context occurred prior to any training in the second context), or trained alternately in two contexts. Following training, the first context, the second context, or neither context was extinguished. Testing of the CS occurred in a third (neutral) context. To the extent that either training context became established as a comparator stimulus for the CS, the comparator hypothesis (Miller & Matzel, 1988) predicts an increase in excitatory responding to the CS following extinction of that context. Subjects trained in a single context exhibited appreciable fear of the CS only when the CS’s training context had been extinguished. Additionally, subjects trained consecutively in the two contexts showed increased fear of the CS following extinction of the second, but not the first training context (i.e., a recency effect). Subjects trained alternately in the two contexts showed no increased fear of the CS as a result of either context alone being extinguished. In Experiment 2, subjects trained alternately in two contexts showed increased fear of the CS only when both training contexts were extinguished, suggesting that both training contexts had become comparator stimuli. These data indicate that multiple training contexts can either compete or act synergistic-ally in modulating responding to a Pavlovian trained CS as a function of the order of training in the different contexts.     

Duration of components and response rates on multiple fixed-ratio schedules

Pigeons were exposed to a two-component multiple fixed-ratio X fixed-ratio Y schedule of reinforcement in which X was always less than Y. Components were equal in duration and alternated at rates that varied between 2 sec and 23.5 h. Relative response rate in the FR X component: (1) increased as the duration of components increased between 2 sec and 15 min, (2) was at a maximum between 15 min and 6 h, and (3) decreased as the duration of components increased from 6 h to 23.5 h. The changes in relative response rate were attributable primarily to changes in absolute response rates during the FR Y schedule as absolute response rates during the FR X schedule were relatively invariant. These results pose complexities for several theoretical formulations.     

Sum of responding as a function of sum of reinforcement on two-key concurrent schedules

Four pigeons pecked for food reinforcers delivered by several two-key concurrent schedules. The sum of the rates of reinforcement provided by the component schedules varied from 25 to 300 reinforcers/h. The ratio of the rates of reinforcement remained constant at 1:4. The sum of the rates of responding generated by the component schedules increased with increases in the sum of the rates of reinforcement which the components provided. The increase in response rate was predicted by equations proposed by Catania (1963) and by Herrnstein (1970). But the data conformed more closely to Herrnstein’s equation.     

Contrast during multiple schedules with different component response requirements

Positive and negative behavioral contrast were examined when pigeons were required to keypeck in one component and treadle press in the other component of a series of multiple schedules. The experimental conditions were constructed so that the positive and negative contrast groups were exposed to complementary conditions. Positive keypeck and negative treadle-press contrast occurred in all subjects. Positive treadle-press contrast seemed to depend on the order of schedule presentation. Only one subject exhibited strong negative keypeck contrast. The results indicate that symmetrical conditions are not sufficient to produce positive and negative contrast for a given response when topographically different responses are used in the components of a multiple schedule. The results are globally consistent with the competition theory of behavioral contrast.     

The isolation of stimulus-reinforcer associations established with multiple schedules

Multiple schedules established stimulus-reinforcer (S-S^R) associations on baselines in which equal response rates and patterning were maintained in all components. Subsequently, stimuli associated with an increase in reinforcement but no change in ongoing response rate were compounded. For one experimental group, free-operant avoidance (FOA) was programmed in tone and in light while variable-interval (VI) food reinforcement was effective in their simultaneous absence (T + L). The opposite stimulus-schedule combinations were programmed for the other. Both groups remained in their VI components 85% of the session on schedule preference tests, and on a stimulus compounding test emitted approximately 1.5 times as many responses to tone-plus-light (T + L) as to tone or light alone. This is the first report of additive summation to combined discriminative stimuli associated with only an increase in reinforcement. Nondifferentially trained controls who had the same contingency effective in tone, light, and T + L-VI or FOA—showed neither preference among schedule components or summation during stimulus compounding, indicating that nonassociative stimulus factors made no contribution to either resultant in the experimental animals. Evidence supporting an algebraic combination of response and reinforcement associations is presented, and functional similarities between transfer-of-control studies and the stimulus compounding tests of the experimental groups in the present experiment are discussed.     

Rates of responding in the pigeon generated by simple and complex schedules which provide the same rates of reinforcement

Four pigeons pecked for food reinforcement on variable interval 1-min schedules and on the variable-interval 1-min components of multiple, concurrent, and pseudoconcurrent schedules. The pseudoconcurrent schedule provided only one schedule of reinforcement; but, any reinforcer could be collected by responding on either of two keys. The rate of responding generated by the variable interval schedule was not greater than the rates of responding generated by the components of the complex schedules. But, the rate of reinforcement obtained from the variable interval schedule was greater than the rates of reinforcement obtained from the components of the multiple schedule. These results may contradict the equation proposed by Herrnstein (1970). The equation predicts that the rate of responding generated by a schedule of reinforcement will be greater when the schedule appears alone, than when it appears as one component of a complex schedule.     

Conjunctive schedules of reinforcement IV: Effects on the pattern of responding of changes in requirement at reinforcement

The effects of different schedule requirements at reinforcement on patterns of responding by pigeons were assessed under conjunctive schedules with comparable response-number requirements, Under one conjunctive schedule (conjunctive fixed-interval fixed-ratio schedule), a response was reinforced after a 6-min interval had elapsedand a specific minimum number of responses had been emitted, Under a second conjunctive schedule, a response was reinforced after the 6-min fixed interval and upon completion of a tandem schedule requirement (conjunctive fixed-interval tandem schedule), This schedule retained the same required minimum number of responses as the first conjunctive schedule, but responses were never reinforced according to a fixed-ratio schedule; the tandem schedule was comprised of a fixed-ratio and a small (.1 to 10.0 sec) fixed-interval schedule, Under the conjunctive fixed-interval fixed-ratio schedule, responding was characterized by an initial pause, an abrupt transition to a high response rate, and a second transition to a lower rate that prevailed or slightly increased up to reinforcement, Under the conjunctive fixed-interval tandem schedule, pauses were extended, response rates were lower, and the initial high rate of responding was generally absent, The above effects depended upon the size of the fixed interval of the tandem schedule, The distinct pattern of responding generated by conjunctive fixed-interval fixed-ratio schedules depends upon occasional reinforcement of fixed-ratio responding and not merely on the addition of a minimum number of required responses.     

Specification of the stimulus-reinforcer relation in multiple schedules: Delay and probability of reinforcement

Control of pigeons’ keypecking by a stimulus-reinforcer contingency was investigated in the context of a four-component multiple schedule. In each of three experiments, pigeons were exposed to a schedule consisting of two two-component sequences. Discriminative stimuli identifying each sequence were present only in Component 1, which was 4, 6, or 8 sec in duration, while reinforcers could be earned only in Component 2 (30 sec in duration). Control by a stimulus-reinforcer contingency was sought during Component 1 by arranging a differential relation between Component 1 cues and schedule of reinforcement in Component 2. In Experiment 1, rate of keypecking during Component 1 varied with the presence and absence of a stimulus-reinforcer contingency. When a contingency was introduced, rate of keypecking increased during the Component 1 cue associated with the availability of reinforcement in Component 2. In Experiment 2, the stimulus-reinforcer contingency was manipulated parametrically by varying the correlation between Component 1 cues and Component 2 schedules of reinforcement. Responding in Component 1 varied as a function of strength of the stimulus-reinforcer contingency. The relatively high rates of Component 1 responding observed in Experiments 1 and 2 pose difficulties for conceptions of stimulus-reinforcer control based on probability of reinforcement. In these two experiments, the stimulus-associated probabilities of reinforcement in Component 1 were invariant at zero. An alternate dimension of stimulus-reinforcer control was explored in Experiment 3, in which Component 1 cues were differentially associated with delay to reinforcement in Component 2, while probability of reinforcement was held constant across components. When the stimulus-reinforcer contingency was in force, rate of responding in Component 1 varied inversely with delay to reinforcement in Component 2. In a quantitative analysis of data from Experiments 2 and 3, relative rate of responding during Component 1 was strongly correlated with two measures of relative delay to reinforcement.