Effects of chlorpromazine and d-amphetamine on escape and avoidance behavior under a temporally defined schedule of negative reinforcement

Chlorpromazine hydrochloride and d-amphetamine sulphate were administered to two rats responding on a baseline temporally defined schedule of negative reinforcement which produced both “escape-like” and “avoidance-like” behavior. The effects of these drugs appeared similar to those expected on the more customary sort of non-cued avoidance schedule.     

Facilitation and suppression of responding under temporally defined schedules of negative reinforcement

Two parameters for scheduling aversive stimulus presentations were studied systematically by specifying concurrent and independent probabilities of electric shock delivery for the occurrence and for the non-occurrence of a lever-press response. After preliminary training on a free-operant shock-avoidance schedule, 16 rhesus monkeys were divided into four groups, each group being assigned one shock distribution on a continuum from fixed interval to a widely ranging variable interval. Within groups, each subject was successively exposed to three values of response-dependence of shock delivery on a continuum from response-independent shock to complete dependence of shock on response occurrence (“punishment”). Introduction of shock following avoidance training produced initial response facilitation followed by suppression. Responding during both the facilitation and suppression periods was maximal when the shock schedule was periodic and response independent. Responding decreased as the inter-shock intervals were made more variable across groups, and as shock delivery was made increasingly response dependent within individual subjects.     

Effects of cycle length on performance on a temporally defined avoidance schedule

Three rats were trained on a temporally defined avoidance schedule logically similar to a fixed-interval, limited-hold positive reinforcement schedule. This avoidance schedule was composed of time periods during which responses had no scheduled consequences alternating with time periods during which a response precluded shock. As with fixed-interval length and response rate on positive reinforcement schedules, an inverse relationship was obtained between the length of the no-consequence interval and response rate during the no-consequence interval. An inverse relationship was also obtained between the length of the no-consequence interval and the per cent of shocks avoided. A rate increase within the no-consequence interval, similar to that typically produced by fixed-interval positive reinforcement procedures, was displayed by one of the rats where the no-consequence interval was at intermediate values and frequency of shock was relatively high. The introduction of a discriminative stimulus correlated with the avoidance interval produced typical discriminated avoidance behavior as well as alterations in temporal patterning of responses during the no-consequence interval in the two rats exposed to this procedure. These alterations in temporal patterning disappeared when the discriminative stimulus was removed. The results were consonant with those reported in the literature involving food reinforcement and fixed-interval, limited-hold schedules.     

Delayed reinforcement in a multiple schedule

Three rats and a pigeon were first trained on a two-component multiple schedule in which reinforcement in the two components occurred immediately after a response. Later, reinforcement in one component was delayed by a few seconds. During both stages of the experiment, reinforcement was scheduled by equal variable- (pigeon) or random-interval (rats) schedules in the two components. The main effect of the delayed reinforcement was to increase the rate of responding in the unchanged (non-delay) component. This behavioral contrast effect did not appear in all cases to be dependent upon a reduction in the rate of responding or the frequency of reinforcement in the delay component. This finding suggests that a reduction in response rate and/or reinforcement frequency in one component of a multiple schedule may not be a necessary prerequisite for the occurrence of behavioral contrast. This finding is, however, consistent with an explanation that suggests that behavioral contrast results from the introduction of a less-preferred condition in one component of a multiple schedule, since it is known that animals “prefer” immediate to delayed reinforcement.     

Aversive aspects of a schedule of positive reinforcement

Six male White Carneaux pigeons were trained to peck at one of two keys to obtain food on several fixed-ratio schedules of reinforcement. Concurrently, the first response on a second key could, I—change the conditions of visual stimulation and remove the food reinforcement contingency, II—change the conditions of stimulation and have no effect upon the reinforcement contingency, or III—do nothing. The second response on the stimulus change key always restored baseline conditions. When second-key responses produced a stimulus change, the number of such responses was a function of the ratio value on the first key. Typically, second-key responses occurred before the start of fixed-ratio runs. The duration of stimulus change periods was an exponential function of the number of responses required for reinforcement when the possibility for reinforcement was not disturbed by periods of stimulus change (Condition II).     

Response latency as a function of reinforcement schedule

Four Ss were trained to press and hold down a telegraph key in the presence of a light. Subsequent release of the key during a tone was followed by water reinforcement. The schedule of reinforcement for key release was varied, and its effects on the latency (RT) of key release to the tone were studied. Both median RT and variability of RT were found to be inversely related to frequency of reinforcement as determined by the schedule.     

Aversive aspects of a fixed-interval schedule of food reinforcement

The key pecking of pigeons was reinforced according to a fixed-interval schedule of reinforcement. The pigeons were also given the opportunity to attack a restrained target pigeon. The attack rates during the sessions of fixed-interval reinforcement were higher than during the operant level sessions in four of the five pigeons. Most attack occurred during the post-reinforcement pause in key pecking. It was suggested that a fixed-interval schedule of positive reinforcement possesses aversive properties, the most aversive of which are located during the post-reinforcement pause.     

Polydipsia induced by a schedule of brain stimulation reinforcement

Rats pressed a lever for a signaled brain stimulation reinforcement on either fixed-interval or fixed-ratio schedules. Both schedules induced polydipsia, with a median water intake of 22.5 ml (about four times the control level) in 3-hr sessions. The stimulation did not directly elicit drinking or other behaviors. In a second experiment, two out of four rats became polydipsic during extinction following a continuous schedule of brain stimulation reinforcement. The results were compared with previous attempts to induce polydipsia with a schedule of brain stimulation reinforcement and were discussed in terms of polydipsia as a model of human “compulsive” behaviors.     

Stimulus control of responding during a fixed-interval reinforcement schedule

During training sessions, pecks by pigeons on a response key illuminated by a vertical line of white light resulted in reinforcement and an ensuing blackout according to a fixed-interval schedule. Training sessions were followed by dimensional stimulus control test sessions during which the orientation of the line present throughout the fixed interval was varied. Inverted U-shaped (excitatory) gradients of responding, with maximum responding occurring in the presence of the vertical line, were observed during the terminal part of the fixed interval. U-shaped (inhibitory) gradients of responding, with minimum responding occurring in the presence of the vertical line, were observed during the early part of the fixed interval when the preceding interval had terminated with reinforcement and blackout but not when the preceding interval had terminated with blackout only. These results suggest that the dimensional control by the stimulus present throughout the fixed interval is of a conditional variety. Whether the fixed-interval stimulus exerts inhibitory or excitatory dimensional control depends upon the presence and absence, respectively, of stimuli associated with reinforcement.     

A response-initiated fixed-interval schedule of reinforcement

On a tandem fixed-ratio one fixed-interval schedule, the first response after reinforcement initiates a fixed interval of time and the first response after the interval has elapsed is reinforced. Pigeons trained with that schedule of food reinforcement paused after reinforcement for a period of time that approximated the fixed-interval duration for values of that duration ranging from 3.75 to 60 sec. Cumulative records revealed response patterns best described as break-and-run.     

Bias and sensitivity to reinforcement in a concurrent-chain schedule

Six pigeons were trained on concurrent-chain schedules in which the initial links were either dependent (Experiment 1) or independent (Experiment 2) concurrent variable-interval schedules and the terminal links were fixed-duration delays to reinforcement in blackout. A changeover delay of three seconds operated in the initial links. Both the initial- and terminal-link schedule values were varied over 61 experimental conditions. An analysis of the data using the generalized matching law showed that the sensitivity of initial-link response allocation to the frequency of terminal-link production was independent of both the duration of the terminal-link delays and, though less clearly, of the duration of the initial-link schedules. Sensitivity of initial-link response allocation to terminal-link reinforcer-rate ratios was a joint function of the terminal-link durations and the smaller average initial-link duration. The results showed that the generalized matching law is useful in analyzing concurrent-chain schedule performance and that a changeover delay in the initial links eliminates some terminal- to initial-link interactions that have made quantitative predictions for concurrent-chain performances difficult.     

Effects of a DRL contingency added to a fixed-interval reinforcement schedule

Following 30 days of reinforcement for the bar press response of two white rats on 30-sec fixed-interval (FI), a DRL component was added so that a minimal interresponse time (IRT) for the reinforced response, in addition to the FI variable, was necessary for reinforcement. Marked control over response rate by the superimposed DRL requirement was demonstrated by an inverse hyperbolic function as the DRL component was increased from 1 to 24 sec within the constant 30-sec FI interval. Interresponse time and post-reinforcement (post-S^R) “break” distributions taken at one experimental point (DRL = 24 sec) suggested that a more precise temporal discrimination was initiated by an S^R than by a response, since the relative frequency of a sequence of two reinforced responses appeared greater than that of a sequence of a non-reinforced response followed by a reinforced one. This latter finding was confirmed with new animals in a follow-up experiment employing a conventional 24-sec DRL schedule.     

Time-dependent contrast effects in a multiple schedule of food reinforcement

Four rats were rewarded for running in a wheel under two alternating conditions of food reinforcement. These periods of frequent and infrequent reinforcement, each accompanied by a particular stimulus, were presented a number of times in each daily session. Following shifts from high to low frequency of reinforcement, responding decreased suddenly and markedly, and then recovered within the next few minutes. The magnitude of this temporary depression was an increasing function of the duration of the immediately preceding component of high-frequency reinforcement. A transient elevation in performance, which did not vary with the duration of the prior component, was noted in two subjects following shifts from low to high frequency of reinforcement. The elevation and depression effects did not appear simultaneously during the 48 experimental sessions. A possible relation between the difficulty of the discrimination and the extent of contrast effects is discussed.     

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.