Effects of reinforcement rate and delay on the acquisition of lever pressing by rats.

The acquisition of lever pressing by naive rats, in the absence of shaping, was studied as a function of different rates and unsignaled delays of reinforcement. Groups of 3 rats were each exposed to tandem schedules that differed in either the first or the second component. First-component schedules were either continuous reinforcement or random-interval 15, 30, 60 or 120 s; second-component schedules were fixed-time 0, 1, 3, 6, 12, or 24 s. Rate of responding was low under continuous immediate reinforcement and higher under random-interval 15 s. Random interval 30-s and 60-s schedules produced lower rates that were similar to each other. Random-interval 120 s controlled the lowest rate in the immediate-reinforcement condition. Adding a constant 12-s delay to each of the first-component schedule parameters controlled lower response rates that did not vary systematically with reinforcement rate. The continuous and random-interval 60-s schedules of immediate reinforcement controlled higher global and first-component response rates than did the same schedules combined with longer delays, and first-component rates showed some graded effects of delay duration. In addition, the same schedules controlled higher second-component response rates in combination with a 1-s delay than in combination with longer delays. These results were related to those from previous studies on acquisition with delayed reinforcement as well as to those from similar reinforcement procedures used during steady-state responding.     

Differential effects of cocaine and pentobarbital on fixed-interval and random-interval performance

Reports have indicated that the behavioral effects of a drug can be related to the nondrug control rate of behavior in the absence of the drug. To investigate the purported relationship between control rate and drug rate, squirrel monkeys were trained under a fixed-interval 300-s schedule of stimulus-shock termination, a procedure that engendered a wide range of response rates. A light illuminated the experimental chamber during the fixed interval, and the first lever press after 300 s had elapsed terminated the light for 30 s and precluded an electrical stimulus to the tail. Following acute intramuscular administration of cocaine (0.03-0.56 mg/kg), overall rate increased and different control rates of responding, during different parts of the fixed interval, converged toward a common rate. Subsequently, the schedule was changed to a multiple fixed-interval 300-s random-interval 300-s schedule; performance during the random-interval component was characterized by steady responding at a uniformly high rate. Analysis of fixed-interval and random-interval performances following acute cocaine administration revealed convergence of response rates toward a common, uniform rate. Pentobarbital (0.3-10.0 mg/kg) only decreased overall rate, and different control rates of responding during the fixed interval did not converge toward a common rate. The results indicate that this type of analysis can be useful in comparing pharmacological agents from different classes and that the rate at which responding becomes uniform can provide a quantitative behavioral end point for characterizing drug effects on behavior.     

Self-control in male and female rats

Eight male and 8 female Wistar rats were exposed to a discrete-trial procedure in which they chose between the presentation of a small (one pellet) or a large (three pellets) reinforcer. The delay to the small and large reinforcer was 6.0 s in the first condition of Experiment 1. Subjects consistently chose the large reinforcer. When the delay to the small reinforcer was decreased to 0.1 s in the next experimental condition, all subjects continued to choose the large 6.0-s delayed reinforcer. When the contingencies correlated with the two levers were reversed in the next experimental condition, the majority of subjects (5 males and 6 females) still chose the large delayed reinforcer over the small immediately presented reinforcer. The delay to the small reinforcer was maintained at 6.0 s, but the delay to the large reinforcer was varied among 9.0, 15.0, 24.0, and 36.0 s in Experiment 2, in which 4 males and 4 females participated. Most subjects consistently chose the large increasingly delayed reinforcer, although choice for the small 6.0-s delayed reinforcer developed in some females when the large reinforcer was delayed for 24.0 or 36.0 s. These choice patterns were not predicted from a literal application of a model that says choice should favor the alternative correlated with the higher (amount/delay) ratio.     

Temporal distributions of responding during discrete-trial omission training in rats

Within-session temporal distributions of responding were investigated in three experiments using rats pressing a lever in a discrete-trial omission procedure. This schedule entailed 60, one-minute trials, and a sucrose solution was made available at the end of each trial in which no lever press occurred. In Experiment I, nonnaive rats acquired and maintained responding during this training. Moreover, the probability of a response during any session showed a strong and reliable tendency to increase from the beginning to the end of the session. These results were replicated in Experiment II, using naive animals. In Experiment III, alterations were made in the training procedure, including elimination of response-contingent and noncontingent stimulus changes. Results indicate that stimulus change may be sufficient to maintain low levels of responding whether or not this change is contingent on responding.     

The effects of reinforcement frequency and response requirements on the maintenance of behavior.

Six rats responded under fixed-interval and tandem fixed-interval fixed-ratio schedules of food reinforcement. Basic fixed-interval schedules alternated over experimental conditions with tandem fixed-interval fixed-ratio schedules with the same fixed-interval value. Fixed-interval length was varied within subjects over pairs of experimental conditions; the ratio requirement of the tandem schedules was varied across subjects. For both subjects with a ratio requirement of 10, overall response rates and running response rates typically were higher under the tandem schedules than under the corresponding basic fixed-interval schedules. For all subjects with ratio requirements of 30 or 60, overall response rates and running response rates were higher under the tandem schedules than under the corresponding basic fixed-interval schedules only with relatively short fixed intervals. At longer fixed intervals, higher overall response rates and running rates were maintained by the basic fixed-interval schedules than by the tandem schedules. These findings support Zeiler and Buchman's (1979) reinforcement-theory account of response strength as an increasing monotonic function of both the response requirement and reinforcement frequency. Small response requirements added in tandem to fixed-interval schedules have little effect on reinforcement frequency and so their net effect is to enhance responding. Larger response requirements reduce reinforcement frequency more substantially; therefore their net effect depends on the length of the fixed interval, which limits overall reinforcement frequency. At the longest fixed intervals studied in the present experiment, reinforcement frequency under the tandem schedules was sufficiently low that responding weakened or ceased altogether.     

Control rate of response or reinforcement and amphetamine's effect on behavior.

The roles of control response rate and reinforcement frequency in producing amphetamine's effect on operant behavior were evaluated independently in rats. Two multiple schedules were arranged in which one variable, either response rate or reinforcement frequency, was held constant and the other variable manipulated. A multiple differential-reinforcement-of-low-rate seven-second yoked variable-interval schedule was used to equate reinforcement frequencies at different control response rates between multiple-schedule components. Amphetamine increased responding under the variable-interval component. In contrast, amphetamine decreased responding equivalently between components of a multiple random-ratio schedule that produced similar control response rates at different reinforcement frequencies. The results provide experimental support to the rate-dependency principle that control rate of responding is an important determinant of amphetamine's effect on operant behavior.     

Choice and the rate of punishment in concurrent schedules

Rats' responses on two levers were reinforced according to independent random-interval 1.5-min food schedules. In addition, both lever presses were intermittently punished according to several concurrent random-interval random-interval shock schedules. For the left, the scheduled rate of punishment was kept constant according to a random-interval 6-min schedule. For the right, the rate of punishment varied. As the frequency of punishment for the right lever press increased, its rate decreased. The rate of the left punished lever press increased, however, even though its scheduled reinforcement rate and punishment rate remained unchanged.     

Chlordiazepoxide effects on ethanol self-administration: dependence on concurrent conditions.

Experiments examined the effects of acute doses of chlordiazepoxide upon ethanol self-administration in the rat. A concurrent-schedule procedure was used that employed choice between ethanol (5%) and a second fluid (either water or a 1% sucrose solution). When ethanol and water were the available fluids, chlordiazepoxide at doses of 15 and 20 mg/kg reduced ethanol-reinforced responding and intake, with a greater reduction occurring at the 20 mg/kg dose. However, when ethanol and sucrose were concurrently available, in many rats only the 20 mg/kg dose of chlordiazepoxide reduced ethanol-reinforced responding. The differences in dose response function occurred in most animals without large changes in the baseline ethanol-reinforced responding across the two concurrent conditions. Thus the dose-effect curve relating chlordiazepoxide and ethanol self-administration can be altered, dependent upon the nature of the concurrently available reinforcers.     

Sequential Analyses of Adolescent,Mother, and Father Behaviors in Distressed and Nondistressed Families

The Response Class Matrix was used to compare sequential relations among behaviors in clinic families with a problem adolescent and those in non-clinic families with an adolescent under two experimental conditions, discussing a problem and planning something together. Clinic dyads manifested significantly more negative an les problem-solving behavior overall. When the family was planning something together, clinic mothers responded to their adolescents' negative behavior significantly more often with negative behavior and less often with problem-solving than did their nonclinic counterparts. Clinic adolescents responded to their mothers' negative behavior significantly more often with negative behavior and with less problem-solving than non-clinic adolescents, both when planning something together and when discussing a problem. These patterns were not observed with fathers. When the family was planning something together, clinic adolescents responded to both their mothers' and fathers' problem-solving with significantly more negative and less problem-solving behavior than did non-clinic adolescents. Results are discussed in terms of the aversive nature of the family environment for clinic adolescents, and the differences between mothers' and fathers' interactions with adolescents.