Antecedent reinforcement contingencies in the stimulus control of an auditory discrimination

In order to assess possible confounding of discriminative stimulus effects with those produced by the reinforcing stimulus, three groups of four rats each were trained for 45 hr on a variable-interval 1-min reinforcement program. Two groups were run on a multiple variable-interval extinction schedule in which the reinforcement stimulus (S^D) and the nonreinforcement stimulus (S^Δ) were two intensities of a 4-kHz (cps) tone separated by 40 or 10 db. The third group was run on a mixed schedule with a single intensity constantly present. The mixed-schedule animals showed no discrimination of the reinforcement program. Under the multiple schedule, the highest S^Δ rates were obtained after S^D intervals, regardless of the reinforcement availability in the S^D interval. These local rate variations in S^Δ were small in proportion to those produced by the S^D versus S^Δ intensities.     

Punishment by SD associated with fixed-ratio reinforcement

Two pigeons were trained with positive reinforcement on a multiple FR VI 2 schedule. The VI 2 component was held constant while the FR component was changed from ratios of 1 to 300. After responding had stabilized at each FR value, VI responses produced briefly either the fixed-ratio S^D or a stimulus uncorrelated with either schedule component. Compared to the effects of the uncorrelated stimulus change, the fixed-ratio S^D produced a decrease in VI responding proportional to the size of the FR requirement. It is concluded that stimuli associated with high FR schedules served as punishment for the ongoing behavior.     

Behavioral effects of pairing an SD with a decreasing limited-hold reinforcement schedule

Four pigeons were trained on a multiple reinforcement schedule consisting of two limited-hold schedules, one in which a discriminative stimulus (S^D) accompanied the periodic reinforcement contingency, and one in which the discriminative stimulus was omitted. The duration of the limited-hold in each component of the multiple schedule was reduced in parallel steps. It was shown that behavioral differences between the two schedules were attenuated by this manipulation of temporal parameters. When S^D was reduced in duration, three out of four pigeons responded with extremely high S^Δ rates, despite the regular pairing of S^Δ with the reinforcement contingency. These high rates qualitatively resembled the rapid rates emitted on the analogous no-S^D component.     

Escape from SD associated with fixed-ratio reinforcement

Throughout ascending and descending fixed-ratio (FR) sequences, rats were allowed to terminate the FR stimulus control by pressing a time-out (TO) lever. To minimize chance or accidental responses on this second lever, three presses were required to produce the 30-sec S^Δ period. As FR performance became more “strained,” there was an increased predisposition to escape from the time-in stimulus complex. The generality of this finding was extended by obtaining recoverability (independent of the direction of stimulus change) of the FR-TO function in the descending series. Typically, escapes were produced only during the post-reinforcement pause; however, under a mixed FR FR schedule, their occurrence shifted to a point within the inter-reinforcement interval corresponding to the unreinforced completion of the lower ratio component. It appears that the point where the rat can discriminate the size of the ratio requirement will be the place where TOs are imposed. This inference was supported by a substantial increase in TO frequency accompanying a shift from CRF to extinction on the FR lever. Finally, the escape lever was placed on a progressively increasing FR schedule and later extinguished to demonstrate that the TO condition was in fact reinforcing.     

The effects of unavoidable shocks on a multiple schedule having an avoidance component

Two dogs were maintained on a multiple schedule having both a food reinforced and an avoidance component (Mult VI 1′ S^Δ Avoid_{SS20 RS20} S^Δ). The effects of superimposing an Estes-Skinner procedure for delivering unavoidable shocks on all components of the multiple schedule were observed. The buzzer-shock pairing of the Estes-Skinner procedure produced an increased rate of responding on the avoidance component of the schedule and also on the S^Δ components. No persistent change in rate was observed on the food component during the pre-shock stimulus. Control performances on all components could be regained by either extinguishing or eliminating the buzzer-shock pairing. Extinction of the avoidance responding had little effect on the increased rates of responding produced by the Estes-Skinner procedure on the S^Δ and avoidance extinction components and did not lead to a conditioned suppression of the food reinforced responding. Rate of responding during the pre-shock stimulus was observed to be relatively independent of changes in the maintaining schedules. Responding during the pre-shock stimulus could be conditioned and maintained after an extensive history of avoidance extinction.     

Stress-induced breakdown of an appetitive discrimination

Rats trained to discriminate between S^D and S^Δ for food reinforcement showed marked impairments in this discrimination when strong, unavoidable shocks occurred at the termination of a third stimulus. The predominant feature of this impairment was a supernormal rate of unreinforced (S^Δ) behavior. Shocks delivered without exteroceptive warning also led to a discriminative breakdown. The effect was a direct function of shock intensity. When behavior was strongly suppressed in the third stimulus by response-correlated shock (“punishment”), instead of unavoidable shock, breakdowns were only temporary; as soon as responding recovered from its overall suppression, discriminative performance returned to normal. The discriminative deterioration may be interpreted as an emotional by-product of frequent aversive stimulation, but accidental contingencies could also have played a role.     

Operant control of vocal behavior in the cat

Evidence of operant control of vocal behavior in the cat is presented: (1) On mult FR 12 S^Δ schedule, cats miaowed rapidly during periods of S^D and much less or not at all during S^Δ. (2) This control was re-established following reversal of stimuli. (3) The frequency distribution of response durations was shifted to both shorter and longer values by the differential reinforcement of shorter or longer response durations respectively. Since both the frequency and duration of vocal responses were shown to be under the control of the schedule of reinforcement, it is concluded that at least some of the vocal behavior of the cat is susceptible to operant control.     

The effect of drugs on a fixed-ratio performance suppressed by a pre–time-out stimulus,

Pecking was reinforced by a fixed-ratio schedule with food, and responses during a red light produced a time out. If the bird did not respond during the red light, the light terminated and the bird could complete the FR schedule of positive reinforcement uninterrupted. The bird stopped responding during the red light sufficiently to avoid most of the possible time outs. In general, the pre–time-out stimulus suppressed responding more when the FR schedule was large than when it was small. The occurrence of the pre–time-out stimulus in the fixed ratio produced FR strain and extreme curvature atypical of normal fixed ratios of this size. Amobarbital, pentobarbital, chlorpromazine, and d-amphetamine injected when the FR performance was strained by the pre–time-out procedure produced marked increases in responding. The drug administration lowered the rate of responding only at larger doses; and then this occurred predominantly just after the injection.     

Some notes on time out from reinforcement

Pigeons produced food on a fixed-ratio schedule by pecking at one key, and an S^Δ period by pecking at a second (switching) key. Switching behavior was examined as a function of (a) size of the fixed ratio, (b) whether the S^Δ was of fixed duration or could be determined by the bird, (c) the introduction of a novel food S^D, (d) extinction of food responding, and (e) the stimuli associated with the S^D and S^Δ conditions. No monotonic relationship was obtained between ratio size and switching behavior. Switching behavior was, however, influenced by many variables. The results suggest that an interpretation of switching behavior in terms of its being reinforced by the removal of aversive conditions, is open to considerable question.     

Generalization and discrimination as a function of the SD — SΔ intensity difference

Three groups of four rats were trained on an auditory-intensity discrimination for 21 days. The S^D-S^Δ intensity difference for Group I was 10 db; for Group II, 20 db; and for Group III, 30 db. Following the initial discrimination training, the animals were tested for generalization of the bar-press response to seven novel S^Δ's which were presented intermingled with the original S^D and S^Δ values. Conclusions: (1.) The amount of simple discrimination training required to obtain fairly stable differences in S^D and S^Δ responding is an inverse function of the magnitude of the stimulus difference between S^D and S^Δ. (2.) Generalization gradients obtained immediately following simple discrimination training exhibit a maximum displaced from S^D in a direction also away from S^Δ. (3.) Gradients obtained following continued exposure to the multivalued S^Δ situation show a fairly stable maximum at the S^D value. (4.) Although the gradients tend to fall off systematically on either side of the continuum as distance from S^D is increased, they decrease most rapidly on the S^Δ limb of the gradient.     

Discrimination learning as a function of stimulus location along an auditory intensity continuum

Eight groups of rats were trained on an auditory intensity discrimination in which the discriminative stimuli were separated by 10 decibels (db). Four pairs of stimuli were selected from different regions along a 60–100 db (SPL) intensity continuum. Counterpart groups were trained on each stimulus pair, with the relative intensity positions of the reinforced stimulus (S^D) and the non-reinforced stimulus (S^Δ) reversed for the two groups. Discrimination acquisition curves were compared to determine whether stimuli separated by equal logarithmic units were of comparable “difficulty”, and to determine the relative effectiveness of an S^D serving as the more versus less intense member of a stimulus pair. It was concluded that: (1) When S^D is the more intense, auditory intensities of constant logarithmic separation are graded in “difficulty” along the intensity continuum; high intensity discriminative stimuli are most readily discriminated. When S^Δ is the more intense, this graded effect is not evident. (2) For a given continuum location, discrimination is inferior when S^Δ is the more intense. This effect is most pronounced at the high intensity end of the continuum and is chiefly attributable to differences in the rate of S^Δ responding.     

Discrimination of a response-independent component in a multiple schedule

Pigeons were trained to respond in non-differential reinforcement pre-discrimination training, with a multiple variable-interval 1-min variable-interval 1-min schedule. Each bird then received discrimination training with a multiple variable-interval 1-min variable-time 1-min schedule. Thus, discrimination training was between response-dependent (variable-interval) and response-independent (variable-time) schedules with the rate of reinforcement equated. In Experiment I, only three sessions of non-differential reinforcement preceded discrimination training and for half the birds, a 0° line was correlated with the response-dependent schedule; for the remaining birds the 0° line was correlated with the response-independent schedule. Post-discrimination gradients of excitatory stimulus control were obtained from the former group, while the latter group showed little evidence of post-discrimination stimulus control by the 0° line. Differential responding to the variable-time schedule was not accompanied by behavioral contrast to the variable-interval schedule. In Experiment II, 20 sessions of non-differential reinforcement preceded discrimination training and the 0° line was correlated with variable-time reinforcement for each bird. Differential responding to the 0° line was accompanied by negative induction to the variable-interval schedule and by inhibitory stimulus control about the 0° line during a post-discrimination generalization test.     

The effect of multiple S periods on responding on a fixed-interval schedule: IV. Effect of continuous S with only short S probes

Pigeons were studied under FI 500 sec in which an S^Δ was present throughout the interval except during the terminal 50-sec segment and one earlier 50-sec segment. Very little responding occurred during the presence of S^Δ. The rate of responding in the earlier 50-sec S^D segments was lower than in the terminal S^D segment. There was a clear trend for the rate of responding in the earlier S^D segment to be progressively higher the later it occurred in the course of the FI 500 sec. This trend was shown roughly to parallel the increasing rate of responding in a conventional FI 500 sec with no interruption by S^Δ. Since the changing tendency to respond through the FI survives massive disruption by S^Δ, it is concluded that the control of responding through the FI does not require continuous mediating behavior. It is suggested that it is the decaying retroactive influence of the reinforcer on responses that occurred longer and longer before the reinforcer occurred which produces the familiar scalloped pattern of responding under FI schedules.     

The effect of multiple SΔ periods on responding on a fixed-interval schedule: III. Effect of changes in pattern of interruptions, parameters and stimuli

Pigeons responding under fixed-interval schedules of reinforcement were interrupted by S^Δ periods during the course of the intervals. Whether intervals were interrupted by 1, 2, or 5 S^Δ periods, the general scalloped pattern of FI responding persisted. Parameter values up to 27¾ hr for the FI and 2¾ hr for the individual S^Δ interruptions were studied. The results further weaken the hypothesis that the FI pattern of responding depends crucially on control of responding by continuously chained mediating behavior.     

Solution of the intermediate size problem by pigeons

Pigeons learned to respond to the middle-sized member (S^D) of a set of three simultaneously presented stimuli with responses to the S^D reinforced on a VI 1 schedule. They were then tested for several days with other sets of three stimuli. One procedure presented reinforcements on a VI 1 schedule during the test independent of the stimulus chosen when a reinforcement was programmed. The tests were also given under extinction conditions. With the testing carried out with extinction, preference consistently was for the test stimulus most similar in physical size to the S^D. However, when the tests were with reinforcement, random responding resulted. Another effect of testing with reinforcement was an increase in incorrect responding with the training set. Such a test procedure was unsatisfactory for determining the effective aspect of the S^D. The conclusion, based on the data of the extinction series, was that pigeons learned the intermediate size problem on the basis of the discrimination of absolute stimulus properties.     

Interactions between the discriminative and aversive properties of punishment

Punishment acquires a discriminative property when it is selectively paired with either reinforcement or extinction. At the milder punishment intensities, the discriminative control exerted by punishment is similar to the discriminative control exerted by a response-produced neutral (nonaversive) stimulus. However, the effect of the aversive property is apparent as the intensity of the punishment is increased. The aversive property of the punishment acts to enhance the discriminative control when the punishment is selectively applied during extinction periods, and to attenuate the discriminative control when the punishment is selectively applied during reinforcement periods. One major difference was found between the control exerted by the punishment and the response-produced neutral simulus: Responding greatly increased after the S^Δ punishment but not after the S^Δ neutral stimulus; this increase in responding was independent of the punishment intensities studied.     

Effects of varying cycle length in a tau reinforcement schedule

A temporally defined reinforcement schedule within the tau system of classification was studied, with pigeons as subjects and with cycle length as the independent variable. As cycle length decreased, response rates increased, responses-per-reinforcement went through a maximum, while the number of reinforcements-per-session increased. The first two functions are attributed to changes in the discriminability of the τ^D and τ^Δ components of the cycle, while the latter seems to result from changes in the relative durations of reinforcement time and τ^Δ time.     

The effect of multiple SΔ periods on responding on fixed-interval schedule: II. in a primate

A squirrel monkey was subjected to a fixed-interval pattern of reinforcement. During the course of each interval a bright white light was repeatedly presented. In the presence of the white light, a response was never immediately followed by food; the white light thus functioned as S^Δ. Responding was interrupted during the S^Δ periods, but in the squirrel monkey as in the pigeon, these interruptions did not destroy the characteristic scalloped pattern of the cumulatively recorded responding through each interval.     

Automaintenance,contrast, and contingencies: Effects of local vs. overall and prior vs. impending reinforcement context

The pigeon's keypeck was investigated in a variety of multiple schedules of response-independent or -dependent reinforcement. Experiments 1 and 2 found that keypecking developed to a reinforcement-associated cue that signaled an increase in local rate of reinforcement, but signaled either no change or a decrease in the overall rate of reinforcement, defined as that prevailing in the cue's absence. In Experiment 3 a greater rate of responding to a target stimulus was observed when it was preceded by a second signal—associated with the same, or a lower, rate of reinforcement—and followed by extinction than when this temporal sequence was reversed. In Experiment 4 responding to a target cue increased when either a temporally prior or a subsequent reinforcement-associated cue was changed to signal extinction. Experiment 5 examined the conditioned reinforcing effectiveness of target cues in two types of situations varying the local context of reinforcement. Stimuli associated with selected target components of a response-dependent multiple schedule of reinforcement could appear as the terminal-link consequences in a two-link chain schedule. Enhanced responding during a target cue which accompanied the introduction of an extinction period following this cue was paralleled by an increase in the conditioned reinforcement effects of this cue. No such increase was found for target cues in which an enhancement of responding had been produced by the interposition of an extinction period prior to the cue.     

Memories of reward and nonreward regulate the extinction and reacquisition of both excitatory and inhibitory associations

The memories of the unconditioned stimulus (US) and its absence (No US), symbolized as S^R and S^N, respectively, may be retrieved on US or No US trials giving rise to four types of associations, S^R → US, S^R → No US, S^N → US, and S^N → No US. Here, following acquisition under partial reward (PRF), rats were shifted either to different schedules of PRF (Experiment 1) or extinction (Experiments 1 and 2). Inhibitory S^R → No US associations formed in acquisition survived extinction and shifts to one, but not another type of PRF schedule (Experiments 1 and 2). Excitatory S^R → US associations also survived extinction (Experiment 2). These findings, as well as the acquisition findings of Experiment 2, are consistent with the sequential model but not with the only other two theories said to be able to explain PRF findings, the frustration hypothesis of Amsel and the attention hypothesis of Mackintosh [see Haselgrove, M., Aydin, A., & Pearce, J. M. (2004). A partial reinforcement extinction effect despite equal rates of reinforcement during Pavlovian conditioning. Journal of Experimental Psychology: Animal Behavior Processes, 30, 240–250]. Also, the reacquisition findings obtained here are inconsistent with two views applied to several learning phenomena, the rule-learning view and the position-item view.