Stimulus control of differential-reinforcement-of-low-rate responding

Five pigeons were given single-stimulus training on an 8-sec differential-reinforcement-of-low-rate schedule followed by steady-state generalization training using 12 wavelength stimuli. Three birds had a high percentage of reinforced responses on the training schedule and flat generalization gradients of total responses. The birds with fewer reinforced responses had much steeper generalization gradients. Generalization gradients plotted as a function of both stimulus wavelength and interresponse time showed that for most birds, stimulus control was restricted to responses with long interresponse times. Responses with very short interresponse times were not under stimulus control and there was some evidence of inhibitory control of short interresponse times. Interresponse-times-per-opportunity functions, plotted as a function of stimulus wavelength, showed that stimulus wavelength controlled the temporal distribution of responses, rather than the overall rate of response. The data indicate that the differential-reinforcement-of-low-rate schedule generates several response categories that are controlled in different ways by wavelength and time-correlated stimuli, and that averaging responses regardless of interresponse-time length obscures this control.     

The long-term effect of high- and low-rate responding histories on fixed-interval responding in rats

Tell rats were given extended lever-press training on a fixed-interval (FI) 30-s food reinforcement schedule from the outset or following exposure to one or two previous reinforcement schedules. For 4 rats the previots schedule was either fixed-ratio 20, which generated high response rates, or differential-reinforcement-of-low-rate 20 s, which produced low response rates. For 4 additional rats the extended training on FI 30 s was preceded by experience with two schedules: fixed-ratio 20 followed by differential-reinforcement-of-low-rate 20 s; or the same two schedules in the reverse order. Fixed-interval response rates were initially affected by the immediately preceding schedule, but after 80 to 100 sessions, all traces of prior schedule history had disappeared. The results also showed no long-term effect of schedule history on the interfood-interval patterns of responding on the FI 30-s schedule. These results support one of the most central tenets of the experimental analysis of behavior: control by the immediate consequences of behavior.     

Drug discrimination in rats under concurrent variable-interval variable-interval schedules

Eight rats were trained to discriminate pentobarbital from saline under a concurrent variable-interval (VI) VI schedule, on which responses on the pentobarbital-biased lever after pentobarbital were reinforced under VI 20 s and responses on the saline-biased lever were reinforced under VI 80 s. After saline, the reinforcement contingencies programmed on the two levers were reversed. The rats made 62.3% of their responses on the pentobarbital-biased lever after pentobarbital and 72.2% on the saline-biased lever after saline, both of which are lower than predicted by the matching law. When the schedule was changed to concurrent VI 50 s VI 50 s for test sessions with saline and the training dose of pentobarbital, responding on the pentobarbital-biased lever after the training dose of pentobarbital and on the saline-biased lever after saline became nearly equal, even during the first 2 min of the session, suggesting that the presence or absence of the training drug was exerting minimal control over responding and making the determination of dose-effect relations of drugs difficult to interpret. When the pentobarbital dose-response curve was determined under the concurrent VI 50-s VI 50-s schedule, responding was fairly evenly distributed on both levers for most rats. Therefore, 6 additional rats were trained to respond under a concurrent VI 60-s VI 240-s schedule. Under this schedule, the rats made 62.6% of their responses on the pentobarbital-biased lever after pentobarbital and 73.5% of their responses on the saline-biased lever after saline, which also is lower than the percentages predicted by perfect matching. When the schedule was changed to a concurrent VI 150-s VI 150-s schedule for 5-min test sessions with additional drugs, the presence or absence of pentobarbital continued to control responding in most rats, and it was possible to generate graded dose-response curves for pentobarbital and other drugs using the data from these 5-min sessions. The dose-response curves generated under these conditions were similar to the dose-response curves generated using other reinforcement schedules and other species.     

Conditioned reinforcement and discrimination performance

Pigeons were trained in a three-key chamber to peck one side key in the presence of a vertical line on the center key and to peck the other side key in the presence of a horizontal line. Correct choice responses were reinforced with food according to fixed- and variable-ratio, fixed-interval, and differential-reinforcement-of-long-latency schedules of reinforcement. For each schedule, the birds performed under each of two conditions: (1) each correct choice response produced a brief presentation of stimuli intermittently paired with food, then the next trial; (2) each correct choice response produced an intertrial interval only. For all schedules except one long latency schedule, response rates were higher under the condition of brief stimulus presentation than under the comparable control condition. Presentation of brief magazine stimuli increased choice accuracy. The amount of change in accuracy was correlated with the rate of food presentation. Performance under the schedules with highest food reinforcement rates showed no enhancement; performance under the schedules with the lowest reinforcement rates showed the greatest enhancement.     

Motivational control of impulsive behavior interacts with choice opportunities

Impulsive behavior has been investigated through choice between a smaller/immediate reinforcer and a larger/delayed reinforcer, or through performance on a differential reinforcement of low rate (DRL) schedule. In the present study, we investigated a methodological divergence between these two procedures: in the former procedure, delay is a consequence of the subject's own choice, whereas in the later procedure, subjects are explicitly reinforced for delaying a response. In Experiment 1, 7 rats maintained at 80% of their free-feeding weights showed poorer efficiency of lever-pressing responses on a DRL 30-s schedule than when they were maintained at 90% of free-feeding weight. In Experiment 2, 16 rats were subjected to a concurrent chain schedule: the initial link was concurrent fixed ratio 1 fixed ratio 1, and each of these alternatives was followed by a short-DRL requirement with a one pellet reinforcer or a long-DRL requirement with a three pellet reinforcer. In one block of trials, rats were not allowed to choose between the two terminal links (forced-choice), whereas in the other block of trials rats were allowed to choose freely between the two terminal links (free-choice). Compared with rats maintained at 95% of their free-feeding weights, rats maintained at 80% of their free-feeding weights showed poorer efficiency in the terminal links’ DRL schedule performance (just as in Experiment 1), but this difference was shown only in the forced-choice blocks. These results indicate that motivational control of DRL schedule performance interacts with type of choice-making opportunity and highlight the direct comparison of motivational control of impulsive choice and DRL schedule performance.     

Effects of a brief novel stimulus during temporally spaced responding: Evidence for external inhibition?

Following training on schedules which differentially reinforce low rates of responding (DRL), three rats were exposed to a procedure to test for external inhibition. During test trials, a tone was presented midway in the DRL interval and the latency to the next response recorded. The incidence of external inhibition (defined in terms of the latency and its relative probability) appeared to be positively related to the size of the DRL schedule and not to measures of the subject’s “efficiency” on the schedule. An alternative view to the “pure” disinhibition hypothesis is presented which stresses the disruption of collateral behavior sequences which maintain responding under the DRL schedule.     

The role of response force on the persistence and structure of behavior during extinction

Behavior Momentum Theory has emerged as a prominent account of resistance to change in both basic and applied research. Although laboratory studies often define precise, repeatable responses, application research often deals with response classes that may vary widely along a number of dimensions. In general, Behavior Momentum Theory has not addressed how response dimensions impact resistance to change, providing an opportunity to expand the model in new directions. Four rats pressed a force transducer under a multiple variable interval (VI) 60‐s VI 60‐s schedule of reinforcement. In one component, responses satisfied the schedule only if the response force fell within a “low” force band requirement; responses in the other schedule were required to satisfy a “high” force band. Once responding stabilized, extinction was programmed for three sessions. Then, the procedures were replicated. The results showed that response force came under discriminative control, but force requirements had no impact on resistance to extinction. In a follow‐up condition, the schedule was changed to a multiple VI 30‐s VI 120‐s schedule and the low‐force band operated in both components. The results showed that behavior maintained by the VI 30‐s schedule was generally more resistant to extinction. A secondary analysis showed that force distributions created under baseline maintained during extinction. Overall, the results suggest that differential response force requirements prevailing in steady state do not affect the course of extinction.     

DISCRIMINATION OF VARIABLE SCHEDULES IS CONTROLLED BY INTERRESPONSE TIMES PROXIMAL TO REINFORCEMENT

In Experiment 1, food‐deprived rats responded to one of two schedules that were, with equal probability, associated with a sample lever. One schedule was always variable ratio, while the other schedule, depending on the trial within a session, was: (a) a variable‐interval schedule; (b) a tandem variable‐interval, differential‐reinforcement‐of‐low‐rate schedule; or (c) a tandem variable‐interval, differential‐reinforcement‐of‐high‐rate schedule. Completion of a sample‐lever schedule, which took approximately the same time regardless of schedule, presented two comparison levers, one associated with each sample‐lever schedule. Pressing the comparison lever associated with the schedule just presented produced food, while pressing the other produced a blackout. Conditional‐discrimination accuracy was related to the size of the difference in reinforced interresponse times and those that preceded it (predecessor interresponse times) between the variable‐ratio and other comparison schedules. In Experiment 2, control by predecessor interresponse times was accentuated by requiring rats to discriminate between a variable‐ratio schedule and a tandem schedule that required emission of a sequence of a long, then a short interresponse time in the tandem's terminal schedule. These discrimination data are compatible with the copyist model from Tanno and Silberberg (2012) in which response rates are determined by the succession of interresponse times between reinforcers weighted so that each interresponse time's role in rate determination diminishes exponentially as a function of its distance from reinforcement.     

Differential reinstatement predicted by preextinction response rate

Reinstatement refers to the recovery of previously extinguished responding by the responseindependent delivery of a stimulus that was a reinforcer in training. Two experiments were conducted to examine relative reinstatement following the training of differential preextinction response rates, either with equal (Experiment 1) or unequal (Experiment 2) preextinction reinforcement rates. In Experiment 1, each of 3 pigeons first pecked at relatively high rates in the tandem variable-time 117-sec fixed-interval 3-sec component of a multiple schedule and at lower rates in a separate tandem variableinterval 117-sec fixed-time 3-sec component. Reinforcement rates were equal between components. Pecking then was extinguished in each component, before being reinstated under a multiple variabletime 120-sec variable-time 120-sec schedule. Greater reinstatement occurred in the component previously correlated with higher rates of pecking. In Experiment 2, in an initial condition, the mean rate of lever pressing for one group of 8 rats was significantly higher under a fixed-ratio 3 schedule than for another group of 8 rats under a fixed-ratio 1 schedule. Mean reinforcement rate was significantly higher for the group exposed to the fixed-ratio 1 schedule. For each group, lever pressing then was extinguished, before being reinstated under a variable-time 30-sec schedule. Significantly greater mean reinstatement occurred for the group previously exposed to the fixed-ratio 3 schedule. These results suggest that differential reinstatement may be predicted by preextinction response rate, perhaps independently of preextinction reinforcement rate.     

Response discriminative and reinforcement factors in stimulus control of performance on multiple and chained schedules of reinforcement

Discriminative control of the response rates of two groups of rats was equated by training them to cease bar pressing in light-out no-tone ( + ) and to respond during tone and light. Multiple-schedule subjects received food at the same rate for responding during tone or light as for nonresponding in + . For the chained-schedule subjects responding in tone or light only produced + where food was received for nonresponding. In extinction tests multiple-schedule subjects emitted approximately twice the responses to tone-plus-light as to tone or light presented individually (additive summation). The rats trained on the chained schedule, in which the tone and light each controlled substantial response rates but were never paired with food, showed no summation when the tone and light were presented together. The results indicate that discriminative control of response rates and reinforcement differences between schedule components determine stimulus control.     

Group behavior of rats under schedules of reinforcement

Groups of three rats were placed in a chamber containing one response lever and one water dispenser. A variety of schedule conditions were explored including fixed ratio, extinction, satiation, fixed interval, fixed time, differential reinforcement of low rates, and discrimination learning. Each group was treated as a single unit, with the collective lever responses emitted by the three rats being the main dependent variable. Group responding was found to be controlled by the reinforcement schedules in an orderly and consistent manner. However, the groups often paused less and responded faster than individual rats working under identical conditions.     

Discrimination between outcomes in instrumental learning: Effects of preexposure to the reinforcers

In two experiments rats received instrumental training with two response levers, one response being reinforced by sucrose solution and the other by sucrose pellets. Prior to a test session, on which both levers were made available in the absence of reinforcement, the rats were given free access to one of the reinforcers, a procedure known to reduce its value. It was found that the rats responded at a lower rate on the lever that had produced the now-devalued reinforcer, but that this effect was substantial only in rats that had received preexposure to the two reinforcers before instrumental training was begun (Experiment 1). Experiment 2 demonstrated that this effect was obtained only when presentations of the two reinforcers were presented according to an inter-mixed schedule during preexposure. It is suggested that this result constitutes an instance of the perceptual learning effect in which intermixed preexposure to similar events enhances their discriminability.     

Compound stimulus control by discriminative stimuli associated with high and moderate response rates

Four rats received water on a fixed-ratio schedule for lever pressing in the presence of a tone (or light) stimulus and on a variable-interval schedule in the presence of a light (or tone) stimulus. Following stabilization of a high response rate during the fixed-ratio component and a moderate response rate during the variable-interval component, brief periods with the light and tone presented simultaneously but with no responses reinforced were inserted into the regular training schedule. Response rates during the compound stimuli were intermediate between the response rates controlled by the individual fixed-ratio and variable-interval associated stimuli.     

Escape behavior under continuous reinforcement as a function of aversive light intensity

In 11 male albino rats, lever-pressing responses, maintained under a CRF escape schedule with light as the aversive stimulus, were examined at each of five intensities, viz., 2.5, 18, 105, 190, and 386 ft-C. The function relating reciprocal of latency of the escape response to aversive light intensity passed through a maximum.     

Differential reinforcement of low rates performance by impulsive and reflective children

Third-grade boys classified as either cognitively impulsive or reflective were reinforced for key pressing according to a DRL (differential reinforcement of low rates) 6-sec schedule of reinforcement. Half of each group received instructions about the behavioral requirements for obtaining reinforcements. Prior to DRL training, impulsive Ss showed a low probability of key press responding at long interresponse time (IRT) intervals while reflective Ss exhibited an equal probability of terminating either short or long IRTs. During training and in the absence of instructions, impulsives exhibited a less precise temporal discrimination, characterized by a greater predominance of response bursts (0–2 sec IRTs) following reinforcements, than reflective Ss. While impulsive and reflective Ss displayed similar frequencies of collateral behavior between successively reinforced responses, impulsives engaged in the reinforced response more frequently and tended (p < .08) to obtain fewer reinforcements. Instructions served to enhance the DRL performance.     

The effects of beta-noradrenergic receptor blockade on acquisition of eyeblink conditioning in 3-month-old F344 rats

There is evidence that blocking beta-noradrenergic receptors will cause deficits in some forms of learning. We investigated the effects of systemic injections of 1, 5, and 10 mg/kg doses of propranolol on acquisition of delay eyeblink conditioning in 3-month-old Fischer 344 rats. We presented a 3-kHz, 90-dB tone as a conditioning stimulus and a 6 psi airpuff as our unconditioned stimulus to freely moving rats. We monitored eyelid activity using EMG signals. The treatment subjects were injected with either propranolol or saline 0.5 h prior to daily training sessions. Two groups of control subjects, one receiving injections of saline and one receiving injections of 5 mg/kg propranolol, received daily training sessions with unpaired and randomized presentation of the tone and airpuff. Each daily training session for the treatment groups consisted of 27 paired training trials and 3 conditioned stimulus-alone training trials. Rats injected with saline vehicle or with 1 mg/kg propranolol achieved a 60% or better learned response rate within two training sessions. Rats injected with 5 or 10 mg/kg propranolol never achieved a response rate significantly different from animals that received unpaired, random presentations of the tone and airpuff stimuli. These results agree with prior studies from our lab that have shown a dose-dependent effect of beta-noradrenergic receptor blockade on learning in rabbit eyeblink conditioning as well as in a runway, motor learning paradigm. We believe that the beta-noradrenergic system plays an important role in learning and memory in more than one cerebellar-dependent learning paradigm.     

Response elimination in rats with schedules of omission training, including yoked and response-independent reinforcement comparisons

After rats were trained to lever press, response elimination began with factorial combinations of fixed vs variable and adjusting vs constant omission training schedules. A time interval scheduling reinforcement remained the same in a constant schedule, and its length was increased as response rate declined in the adjusting schedule. A variable time (VT) response-independent reinforcement schedule followed response elimination to test the durability of response cessation. Experiment I included groups whose reinforcement was yoked to that received by the omission schedule groups. Rate of response elimination was faster with an adjusting than a constant schedule, and slightly faster with a variable than a fixed schedule. There were no significant differences in rate of response elimination between omission schedule and yoked groups. Shorter delay of reinforcement tended to increase rate of response elimination. In the subsequent VT durability test all groups displayed near-zero response rates. In Experiment II adjusting fixed and variable omission schedules, including yoked groups, were compared with fixed time (FT) and VT reinforcement schedules. Response elimination was slower in the FT and VT groups, and they responded more in a subsequent VT durability test. It was concluded that differential reinforcement of other behavior fails to account for these omission training effects, and suggestions were made for an analysis based on the correlation between response and reinforcement rate.     

Acquisition and maintenance of postshock response pattern in nondiscriminated avoidance with rats

Five experimentally naive albino rats were placed under a nondiscriminated lever-press avoidance schedule in which the delay to the next shock for responses after a shock was longer than the delay for responses after a response. Four rats acquired the postshock response pattern and maintained it for a prolonged period. The results revealed that postshock responding was under operant control and was not purely shock-elicited. It was suggested that the two kinds of response-shock interval, i.e. the shock-response-shock interval and the response-response-shock interval, could and should be independently controlled in nondiscriminated avoidance schedules.     

Low-response-rate conditioning history and fixed-interval responding in rats.

Bar presses by one group of rats were conditioned under a differential-reinforcement-of-low-rate reinforcement schedule immediately prior to conditioning under a fixed-interval schedule. In a second group of rats, bar presses were conditioned first under a differential-reinforcement-of-low-rate schedule and then under a fixed-ratio schedule prior to conditioning under a fixed-interval schedule. Low response rates occurred under the fixed-interval schedule only when it was immediately preceded by low-rate conditioning. Otherwise, fixed-interval responding was similar to responding under the fixed-ratio schedule. This finding suggests that responses of laboratory animals are sensitive to immediate history, and, unlike human responses, are relatively insensitive to a history of low-rate conditioning when it is followed by high-rate conditioning.     

Neuromuscular Control of Posture in the Infant and Child

This study explored the effects of vision and maturation on the characteristics of neuromuscular responses underlying balance control in both seated and standing children of five age groups (3½–5 months, 8–14 months, 2–3 years, 4–6 years, and 7–10 years). A platform was used to unexpectedly disturb the child’s balance in the anterior or posterior direction. Responses of the leg, trunk, and neck muscles were recorded using surface electromyograms.

Vision was not required for the activation of these responses in any of the age groups tested. However, comparison of muscle response latencies of standing children to posterior platform translation in the two visual conditions showed a significant reduction in latency for neck flexors in the 2- to 3-year-olds with vision removed and an increase in the total number of monosynaptic reflexes. No reduction in latency was found in the older age groups. The hypothesis of a shift from an early long latency visual dominance to a shorter latency proprioceptive one during childhood is discussed.

Postural control showed a cephalo-caudal developmental gradient with postural responses appearing first in the neck, then trunk, and finally, legs, as children developed from 3 to 14 months of age. A wide variety of response patterns was seen in the 3- to 5-month-olds, indicating that postural responses are not functional prior to experience with stabilizing the center of mass.