Effects of chlordiazepoxide and cocaine on concurrent food and avoidance-of-timeout schedules

The aversiveness of timeout from response-dependent and response-independent food deliveries as a function of delivery rate

Seven experiments with rats assessed the aversiveness of timeout using punishment and avoidance procedures. Experiments 1 and 2 considered the contributions of stimulus change, suspending the response-reinforcer contingency, response prevention, the general disruption in the reinforcement schedule during time-in, and overall decreases in reinforcement. Results support the conclusion that response-contingent timeouts punish behavior because they are signaled periods during which an ongoing schedule of positive reinforcement is suspended. Experiments 3, 4, and 5 assessed effects of the reinforcement rate during time-in on the punitive efficacy of timeout and, for comparison, electric shock. Evidence for a direct relation between reinforcement rate and punitive efficacy was equivocal. In Experiments 6 and 7, responding avoided timeout from response-independent food deliveries. Responding was acquired rapidly when it avoided timeouts from free deliveries of pellets or a sucrose solution, but not when it avoided free deliveries of water. At steady-state, avoidance rates and proficiency were directly related to the rate of pellet or sucrose deliveries. The relation between the nature of the time-in environment and the aversiveness of timeout was clear in our avoidance experiments, but not in our punishment experiments. We discuss interpretive problems in evaluating the aversiveness of timeout in the punishment paradigm.

Timeout postponement without increased reinforcement frequency

Three experiments were conducted to examine pigeons' postponement of signaled extinction periods (timeouts) from a schedule of food reinforcement when such responding neither decreased overall timeout frequency nor increased the overall frequency of food reinforcement. A discrete-trial procedure was used in which a response during the first 5 s of a trial postponed an otherwise immediate 60-s timeout to a later part of that same trial but had no effect on whether the timeout occurred. During time-in periods, responses on a second key produced food according to a random-interval 20-s schedule. In Experiment 1, the response-timeout interval was 45 s under postponement conditions and 0 s under extinction conditions (responses were ineffective in postponing timeouts). The percentage of trials with a response was consistently high when the timeout-postponement contingency was in effect and decreased to low levels when it was discontinued under extinction conditions. In Experiment 2, the response-timeout interval was also 45 s but postponement responses increased the duration of the timeout, which varied from 60 s to 105 s across conditions. Postponement responding was maintained, generally at high levels, at all timeout durations, despite sometimes large decreases in the overall frequency of food reinforcement. In Experiment 3, timeout duration was held constant at 60 s while the response-timeout interval was varied systematically across conditions from 0 s to 45 s. Postponement responding was maintained under all conditions in which the response-timeout interval exceeded 0 s (the timeout interval in the absence of a response). In some conditions of Experiment 3, which were designed to control for the immediacy of food reinforcement and food-correlated (time-in) stimuli, responding postponed timeout but the timeout was delayed whether a response occurred or not. Responding was maintained for 2 of 3 subjects, suggesting that behavior was negatively reinforced by timeout postponement rather than positively reinforced by the more immediate presentation of food or food-correlated (time-in) stimuli.

Avoidance of time-out from response-independent food presentation: effects of chlordiazepoxide and buspirone

Five male Wistar rats were exposed to a two- component multiple schedule. In one component, signaled by a tone, food pellets were presented on a random-time 120-s schedule. In the other component, food pellets were presented on a random-time 30-s schedule. Pellets were only presented during a 10-s time-in period that alternated with a 50-s time-out period, unless the subject pressed a lever to postpone time-out presentation by 20 s. Response-independent food pellets were never presented within 2 s of this avoidance response. For most subjects avoidance rates were consistently higher when response-independent food pellets were delivered infrequently than when they were delivered more often. The amount of time spent in time-in varied considerably between subjects but was not consistently related to the frequency of response-independent pellet presentation. Once stable response rates were established subjects were intraperitoneally injected with different doses of chlordiazepoxide (1, 3, 10, 17, or 30 mg/kg) or buspirone (0.1, 0.3, 1.0, 1.7, 3.0, or 4.2 mg/kg). Low doses of chlordiazepoxide either did not affect or slightly increased avoidance response rates, whereas higher doses (10 mg/kg and up) produced a dose-dependent decrease in avoidance responding. The time subjects spent in the presence of stimuli associated with the availability of response-independent food either did not change or increased slightly after the lower doses of chlordiazepoxide, while it decreased dose dependently following the higher doses. Low doses of buspirone increased avoidance rates in subjects first exposed to chlordiazepoxide, but did not alter rates in the remaining subjects. Intermediate doses of buspirone decreased avoidance rates more in the component with the lower frequency of pellet presentation, higher doses further decreased response rates. The amount of time spent in the presence of stimuli associated with pellet presentation was minimally affected by the lower doses of buspirone, but decreased dose dependently following the higher doses. The results of this experiment add further credence to the notion that the behavioral effects of drug administration may depend on nonpharmacological variables including, but not limited to, the nature of the consequent event.