Within-session changes in operant responding when gerbils ( Meriones unguiculatus ) serve as subjects

Recent research has demonstrated that rate of responding frequently changes in a robust and systematic manner during experimental sessions in which organisms engage in operant responding. One potential cause for these changes in response rate is that levels of exploration change during experimental sessions and that high levels of exploration interfere with operant responding. Several studies have shown that gerbils (Meriones unguiculatus) explore at a constant rate during experimental sessions. The present study examined the response pattern produced by gerbils responding for food delivered by several simple schedules of reinforcement. Results indicated that robust changes (between 200 and 400%) in response rate occurred during the experimental sessions. These data argue against a role for exploration in the production of within-session changes in operant response rate. This material is based on work supported by the National Science Foundation under grant number IBN-9207346 awarded to FKM. The authors would like to thank Kelly S. Johnson, Samantha Swindell, and Dawn Miller for their help and useful suggestions concerning this project.     

Operant reinforcement of an autonomic response: two studies

Two successive studies were conducted to determine the possibility of operant reinforcement of nonspecific galvanic skin resistance responses. In the first study, with five experimental and three control subjects who served for 20 to 30 min a day for 10 days, all experimental subjects learned to emit more nonspecific galvanic skin resistance responses than their ad hoc matched controls. In a second study, nine experimental and nine control subjects were matched for first-day levels of reactivity and yoked for operant reinforcement schedules. Significant differences between the two groups were found on the last day of conditioning and during extinction. Six of the nine experimental subjects showed higher cumulative rate curves than their matched and yoked controls. The concomitant measures (basal resistance, heart rate, etc.) all supported this finding. It was suggested that operant reinforcement of autonomic response tends to maintain a certain level of responding in contrast to persistent adaptation in the control group.     

Effects of post-session wheel running on within-session changes in operant responding

This study tested the effects of post-session wheel running on within-session changes in operant responding. Lever-pressing by six rats was reinforced by a food pellet under a continuous reinforcement (CRF) schedule in 30-min sessions. Two different flavored food pellets were used as reinforcers. In the wheel conditions, 30-min operant-sessions with one of the flavored pellets were followed by 30-min free-wheel running sessions. Meanwhile, in the home conditions, rats’ operant responding was reinforced by the other flavored pellets during 30-min operant-sessions, and the rats were then returned to their homecages. All rats were exposed to 4 wheel and 4 homecage sessions. Operant responding was lowered during the wheel conditions. However, post-session running did not alter the within-session pattern of operant responding. These effects were practically identical to the effects of drug-induced taste-aversion learning on within-session changes in operant responding, suggesting similar mechanisms in both taste-aversion preparations.     

Effects of operant conditioning on the GSR

Each of nine Ss was run for 11 daily sessions. Except for the first (operant level) and last two (extinction) sessions, 500-ohm drops in skin resistance were followed by reinforcement (light). These reinforcement periods lasted 20 min and were preceded by 10-min control periods during which no reinforcement was administered. Although the results showed no evidence for operant conditioning of the GSR, they did indicate that increased emission of GSR's occurred during the reinforcement period. This effect was shown to hold for Ss with low operant levels of GSR's but not for Ss with high operant levels.     

A PARADIGM FOR OPERANT CONDITIONING IN BLOW FLIES (PHORMIA TERRAE NOVAE ROBINEAU‐DESVOIDY, 1830)

An operant conditioning situation for the blow fly (Protophormia terrae novae) is described. Individual flies are trained to enter and reenter a hole as the operant response. Only a few sessions of contingent reinforcement are required to increase response rates. When the response is no longer followed by food, the rate of entering the hole decreases. Control procedures revealed that rate of responding is not a simple overall result of feeding or of aging. The flies entered into the hole only if the response was required to obtain the food.     

Operant and nonoperant vocal responding in the mynah: Complex schedule control and deprivation-induced responding

Several recent studies have been concerned with operant responses that are also affected by nonoperant factors, (e.g., biological constraints, innate behavior patterns, respondent processes). The major reason for studying mynah vocal responding concerned the special relation of avian vocalizations to nonoperant emotional and reflexive systems. The research strategy was to evaluate operant and nonoperant control by comparing the schedule control obtained with the vocal response to that characteristic of the motor responses of other animals. We selected single, multiple, and chain schedules that ordinarily produce disparate response rates at predictable times. In multiple schedules with one component where vocal responding (“Awk”) was reinforced with food (fixed-ratio or fixed-interval schedule) and one where the absence of vocal responding was reinforced (differential reinforcement of other behavior), response rates never exceeded 15 responses per minute, but clear schedule differences developed in response rate and pause time. Nonoperant vocal responding was evident when responding endured across 50 extinction sessions at 25% to 40% of the rate during reinforcement. The “enduring extinction responding” was largely deprivation induced, because the operant-level of naive mynahs under food deprivation was comparable in magnitude, but without deprivation the operant level was much lower. Food deprivation can induce vocal responding, but the relatively precise schedule control indicated that operant contingencies predominate when they are introduced.     

Effect of signaled reinforcement on response variability

Three experiments examined the effect of signaling reinforcement on rats' lever pressing on contingencies that reinforced variable responding to extend the exploration of signaled reinforcement to a schedule that has previously not been examined in this respect. In Experiment 1, rats responding on a lag-8 variability schedule with signaled reinforcement displayed greater levels of variability (U values) than rats on the same schedule lacking a reinforcement signal. In Experiment 2, rats responding on a differential reinforcement of least frequent responses schedule also displayed greater operant variability with a signal for reinforcement compared with rats without a reinforcement signal. In Experiment 3, a reinforcement signal decreased the variability of a response sequence when there was no variability requirement. These results offer empirical corroboration that operant variability responds to manipulations in the same manner as do other forms of operant response and that a reinforcement signal facilitates the emission of the required operant.     

Punishment shock intensity and basal skin resistance

The relationship between punishment shock intensity and basal skin resistance (BSR) was investigated in two sessions with human females selected for their ability to maintain a fairly substantial operant rate under a wide range of shock intensities. In both sessions each button-pressing response was reinforced with a counter tally. Subjects were paid one cent for each 20 counts. In session 1, punishment followed each response during alternate 4-min periods; in session 2 punishment was programmed in all 4-min periods. Shock intensities were presented randomly among the 4-min shock periods, with the restriction that the first three presentations occurred in ascending order. Operant responding showed some suppression at higher shock intensities in session 1, with substantial recovery in most subjects during session 2. Respondent behavior was characterized by greater activity at successively higher intensities, with recovery at all shock levels, especially the lowest levels, apparent during the second session.     

Sensitization and habituation regulate reinforcer effectiveness

We argue that sensitization and habituation occur to the sensory properties of reinforcers when those reinforcers are presented repeatedly or for a prolonged time. Sensitization increases, and habituation decreases, the ability of a reinforcer to control behavior. Supporting this argument, the rate of operant responding changes systematically within experimental sessions even when the programmed rate of reinforcement is held constant across the session. These within-session changes in operant responding are produced by repeated delivery of the reinforcer, and their empirical characteristics correspond to the characteristics of behavior undergoing sensitization and habituation. Two characteristics of habituation (dishabituation, stimulus specificity) are particularly useful in separating habituation from alternative explanations. Arguing that habituation occurs to reinforcers expands the domain of habituation. The argument implies that habituation occurs to biologically important, not just to neutral, stimuli. The argument also implies that habituation may be observed in “voluntary” (operant), not just in reflexive, behavior. Expanding the domain of habituation has important implications for understanding operant and classical conditioning. Habituation may also contribute to the regulation of motivated behaviors. Habituation provides a more accurate and a less cumbersome explanation for motivated behaviors than homeostasis. Habituation also has some surprising, and easily testable, implications for the control of motivated behaviors.     

Reinforcer value may change within experimental sessions

Large and systematic changes in response rates often occur within sessions during operant conditioning procedures. In the present experiment, we asked whether the value of the reinforcer that supports responding also changes within sessions. Pigeons pecked a key for mixed grain available throughout the session. Occasionally, wheat was also provided for pecking a second key. The ratio of the rates of responding for mixed grain and wheat, a frequently used measure of relative reinforcer value, changed significantly within sessions when mixed grain was provided at high, but not at low, rates. Habituation to the reinforcer provides the most likely explanation for these changes in reinforcer value. Eventually, habituation may provide a unified explanation for the within-session changes in behavior that occur when many species of subjects respond on a wide variety of tasks.     

Within-session Response Patterns On Conjoint Variable-interval Variable-time Schedules

Operant responding often changes within sessions, even when factors such as rate of reinforcement remain constant. The present study was designed to determine whether within-session response patterns are determined by the total number of reinforcers delivered during the session or only by the reinforcers earned by the operant response. Four rats pressed a lever and 3 pigeons pecked a key for food reinforcers delivered by a conjoint variable-interval variable-time schedule. The overall rate of reinforcement of the conjoint schedule varied across conditions from 15 to 480 reinforcers per hour. When fewer than 120 reinforcers were delivered per hour, the within-session patterns of responding on conjoint schedules were similar to those previously observed when subjects received the same total number of reinforcers by responding on simple variable-interval schedules. Response patterns were less similar to those observed on simple variable-interval schedules when the overall rate of reinforcement exceeded 120 reinforcers per hour. These results suggest that response-independent reinforcers can affect the within-session pattern of responding on a response-dependent schedule. The results are incompatible with a response-based explanation of within-session changes in responding (e.g., fatigue), but are consistent with both reinforcer-based (e.g., satiation) and stimulus-based (e.g., habituation) explanations.     

Suppression of random-ratio and acceleration of temporally spaced responding by the same prereward stimulus in monkeys

A 1-min tone and light signal that preceded two free pellets of food suppressed the random-ratio responding of four rhesus monkeys, but accelerated the same subjects' responding on a differential-reinforcement-of-low-rate schedule in separate sessions. Both schedule-specific interactions occurred during the first presentations of the signal that previously had been paired with food outside the operant sessions. Thus, neither effect was adventitiously produced. In two subjects, both the direction and magnitude of the prereward change in differential-reinforcement-of-low-rate responding appeared related to baseline response rates: the more rapid the baseline responding, the less was the acceleration during the signal. Suppression and acceleration did not appear as dichotomous effects with separate parameters, but as related effects at least partly determined by the characteristics of the baseline operant performance.     

Determinants of human operant heart rate conditioning: a systematic investigation of several methodological issues.

Three methodological issues of concern within the literature on human operant heart rate conditioning were assessed utilizing a number of techniques for data reduction. The type of statistical approach largely determined the conclusions to be drawn about 2 issues: (a) differences and similarities between heart rate acceleration and deceleration learning and (b) changes in conditioning over a number of sessions. Three techniques yielded data that confounded between- and within-session shifts in tonic heart rate. A fourth method of data reduction (contrasts between pretrial and trial responding) involved no such difficulty. This method of analysis most accurately represented changes in operant heart rate that occurred within and between conditioning sessions.     

A method for analyzing changes in response efficiency.

Although experimental effects typically are evaluated by summarizing levels of responding across time (e.g., calculating the mean levels of problem behavior during 10‐min sessions), these data summaries may obscure important mechanisms that may be responsible for changes in responding. A case study is reported to illustrate alternative methods of data analysis when decreasing trends in responding may be due to increases in response efficiency.     

Conditioned suppression as a sensitive baseline for social facilitation

The key pecking of pigeons maintained on a variable-interval schedule of food reinforcement was suppressed during occasional presentations of a warning stimulus paired with electric shock. On alternate sessions, a co-actor pigeon was visible in an adjoining chamber where it emitted the same food-reinforced key peck during the warning stimulus that signalled shock for the subject. With no shock and at low shock intensities, where the subject's responding was not suppressed or suppressed only slightly, the co-actor had little effect. At the higher shock intensities, where the subject's responding was reduced by at least 40%, the response rate during the warning stimulus was consistently higher when the co-actor was present. One explanation of these results assumes a special relationship between social stimuli and aversive stimuli in which the presence of another animal reduces emotional reactions and thereby allows operant responses to increase. This was not the case here because the mere presence of the co-actor did not maintain social facilitation. Rather, the present results, taken in conjunction with previous findings, suggest that changes in social and non-social variables which affect the rate of food-reinforced responding may produce proportionately larger changes in responding when that responding is suppressed by aversive stimulation than when it is not.     

Signaled Delay of Reinforcement: Effects of Postconditioning Manipulation of Context Associative Strength on Instrumental Performance

Two experiments examined the influence of postconditioning treatments of contextual cues on instrumental responding acquired with a signaled delay of reinforcement schedule. In Experiment 1, mere exposure to the conditioning context after instrumental training resulted in an attenuated response rate during an extinction test. In the second experiment, responding was decreased by exposure to the contextual cues or sessions in which signaled noncontingent reinforcements occurred. The greatest response decrement, however, occurred following unsignaled noncontingent food presentations. The results are discussed with respect to the different roles of contextual cues on operant responding.     

Positive and negative conditioned suppression in the pigeon: Effects of the locus and modality of the CS

In Experiment I, four pigeons were exposed to trials in which a 12-sec key light illumination was followed by free food. These trials were superimposed upon a baseline of key pecking for food reinforcement on a variable-interval schedule. When the signal for food was on the operant key, response rate was substantially higher during the signal than during the baseline procedure. When the signal was on a second, signal key, operant responding was suppressed during the signal and substantial pecking of the signal key occurred. The sum of signal key and operant key pecks far exceeded the operant baseline rate of responding. An explanation of opposite results obtained with rats and pigeons as subjects in experiments of this type was suggested in terms of the spatial relation between the signal for free food and the operant target which usually characterizes these experiments. Experiment II assessed the importance of signal location when shock rather than food was the US. Suppression of operant key pecking was unaffected by signal location. Experiment III assessed the relative effectiveness of visual and auditory stimuli (clicks) as signals for food and shock, and found that all combinations of signal and US were equally effective in suppressing operant key responding. The three experiments together suggested that the identification of important effects of species—typical behavior in one experimental situation does not imply that there will be like effects in similar situations.     

Compounding discriminative stimuli controlling free-operant avoidance

The performances of three rats were stabilized on a multiple schedule that maintained responding by a free-operant avoidance schedule during independent presentations of tone and light. The simultaneous absence of these stimuli signalled shock-free periods and controlled response cessation. Subsequently, test sessions were administered consisting of independent presentations of each stimulus and these stimuli compounded (tone-plus-light). During an extinction test, additive summation was observed to the compounded stimuli, i.e., more responses were emitted to the compound than to either tone or light. During a series of 28 maintenance-test sessions in which the shock schedule remained operative, the compounded stimuli produced a generally enhanced response rate and fewer pauses terminating with shock than either single stimulus condition. These results extend the generality of free-operant additive summation to responding maintained by aversive control. In addition, a comparison of the present study with previous experiments reporting additive summation of positively reinforced responding indicates that similar variables—rate and aversive differences between training stimulus conditions—should be considered in accounting for response distributions during stimulus compounding when responding is controlled by either positive or negative contingencies.     

Procedure for operant conditioning of the dog

Most reports arising from operant conditioning procedures have little or no emphasis on the actual behavior shaping or acquisition phase of the responses which are the cumulative frequency of the well-practiced act. There is a need for more detail for beginners or those desiring a clearer understanding of procedures leading to the finally reported data. The procedure reported here is typically used to compare animal subjects or conditions, such as drugs, both in the acquisition and final phases of behavior. Beginning with an unconditional response (e.g. feeding) a bridging stimulus is paired in classical conditioning fashion. From that point on the bridging stimulus and UCS (feeding—or shock) are used immediately as reward or reinforcement only for responses “in the direction of the final desired behavior. The number of timed standardized behavior shaping sessions to criterion is the best index of acquisition phase performance and the total number bar presses or the rate of bar pressing (slope) is the usual index of operant responding. With timid animals it is often necessary to administer tranquilizers.