Conditioned suppression in goldfish as a function of shock-reinforcement schedule

The conditioned suppression technique (Estes and Skinner, 1941) was employed to study the effects of partial-shock reinforcement in the goldfish. Lever-pressing behavior of hungry goldfish was suppressed in the presence of a flashing light that had been previously paired with electric shocks. Fish that acquired the suppression under 50% and 100% shock-reinforcement, respectively, were subjected to repeated presentations of the flashing light alone. This procedure revealed a more rapid extinction of the suppressed behavior in the 50% than in the 100% shocked group. The finding was compared with those from other experiments and possible reasons for the differences were examined.     

Conditioned suppression or facilitation as a function of the behavioral baseline

Rats were exposed to a multiple schedule of reinforcement. During one component, a bar-press was followed by reinforcement only if it occurred between 15 and 20 sec after the previous response. This differential-reinforcement-of-low-rate (DRL) schedule produced a typical slow rate of responding. During the other component, reinforcement followed the first response to be emitted during limited periods of time which occurred at fixed intervals. These fixed-interval schedules with a limited hold produced higher response rates, described as `interval' or `ratio-like' behavior. Responding during the DRL component increased in frequency during a tone which ended with an unavoidable shock of low intensity, but decreased during the tone when the shock intensity was raised. The `interval' and `ratio-like' responding decreased in frequency during the tone at all shock intensities. Initial acceleration of the DRL responding appeared to be due to adventitious punishment of collateral behavior which was observed between the bar-presses. The more severe conditioned suppression during the fixed-interval components might be the result of the lower probability of reinforcement after any single response.     

Conditioned suppression of counting behavior in rats

Three rats were trained on a schedule in which a response on lever B was reinforced only if it was preceded by a minimum number of consecutive responses on lever A. The minimum requirement was 27 A responses for Rat 1, and 20 A responses for Rats 2 and 3. The schedule maintained high rates of responding on lever A, and a slow, spaced pattern of responding on lever B. The mean number of consecutive responses on lever A was slightly greater than the minimum required. The effect of superimposing on this behavior a stimulus that ended with an unavoidable shock was the suppression of responding on both levers during the pre-shock stimulus. Responses on lever A were more suppressed, and the proportion of relatively short response runs on lever A during the pre-shock stimulus increased. With all three rats, the mean number of consecutive responses on lever A during the pre-shock stimulus decreased to a value below the minimum requirement for reinforcement of the subsequent B response.     

Conditioned suppression of bar-pressing behavior by stimuli associated with drugs

Ten naive male albino rats were trained to press a bar under a variable-interval 30-sec schedule with water as the reinforcer in two experiments. This behavior was disrupted by chlorpromazine in Experiment I (two rats) and by lysergic acid diethylamide (LSD) in both Experiment I (two rats) and Experiment II (six rats). The administration of the drug was paired with an originally neutral white light. After several pairings with either drug, the light also depressed behavior. When the light was no longer paired with drug, the depression effect extinguished much faster than is usually observed in conditioned suppression studies.     

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.     

Conditioned suppression as a psychophysical technique for the cat

A modified conditioned suppression paradigm coupled with a new training apparatus has been applied to gathering sensory data in the cat. The method excels in that training, data collection, and reliability are quickly achieved and it can be used with subtle stimulus changes.     

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.     

Conditioned suppression with extinction as the signalled stimulus

The key pecking of pigeons that was maintained by a 60-sec random-interval schedule of food reinforcement was suppressed during a variable-duration warning stimulus that signalled a 5-min extinction period. The onset of the extinction period immediately followed the termination of the warning signal and was independent of the subject's responses. All subjects eventually showed nearly complete suppression of responding during the warning stimulus.     

Conditioned reinforcement as a function of duration of stimulus

Pigeons were provided with three keys. Pecking the center key produced grain on a schedule that alternated at unpredictable times between a variable-interval component and extinction. On concurrent variable-interval schedules, pecking either side key produced a stimulus associated with the variable-interval component on the center key provided that said schedule was currently in effect. The independent variable was the length of time this stimulus remained on the keys. Pecking one side key produced the stimulus for 27 seconds, whereas the duration produced by pecking the other key varied for successive blocks of sessions. For the first four birds, the values tested were 3, 9, 27, and 81 seconds. For the second group, numbering three birds, the values tested were 1, 3, 9, and 27 seconds. The dependent variable was the proportion of total side key pecks that occurred on the variable key. For all birds, the function was positive in slope and negative in acceleration. This finding supports a formulation that ascribes the maintenance of observing responses in a normal setting to the fact that the subject exposes itself to the positive discriminative stimulus for a longer mean duration than it does to the negative stimulus.     

Analysis of fixed-ratio behavior maintained by drug reinforcers.

Behavior maintained by intravenously delivered alfentanil, cocaine, or ketamine was assessed using a fixed-ratio schedule of reinforcement. As the dose of each drug was increased, rate of responding also increased up to a maximum. Further increases in dose resulted in decreased response rates (inverted U-shaped curve). An analysis of postreinforcement-pause-time and run-time measures for the ascending limb of the inverted U-shaped functions revealed that behavior was characterized by systematic decreases in both pause time and run time as dose and rate increased. An examination of the descending limb of the dose-response functions revealed that lowered response rates for cocaine and ketamine were correlated with increases in run time and small and inconsistent effects on postreinforcement pause time. Behavior maintained by rate-reducing doses of alfentanil was characterized by lengthened postreinforcement pauses with small increases in run time. These data suggest that at larger doses, drug reinforcers may have unconditioned or direct effects on the behavior that the drug is maintaining, and more important, that the nature of these unconditioned effects depends on the drug that is maintaining behavior.     

Conditioned suppression by a stimulus associated with nalorphine in morphine-dependent monkeys

Three rhesus monkeys, physically dependent on morphine, were trained to press a lever for food on a fixed ratio of 10 responses. A tone, initially a neutral stimulus, was aperiodically presented every third or fourth session, 5 min before and after the intravenous injection of nalorphine, a morphine antagonist which produces an immediate withdrawal syndrome in morphine-dependent monkeys. After several sessions, conditioned suppression of food-lever response rate was observed. Conditioned bradycardia, emesis, and excessive salivation also occurred. In 40 to 45 sessions the conditioned suppression of food-lever response rate and the conditioned autonomic changes were extinguished by presenting pairings of a tone and saline injection. The monkeys were then reconditioned by presenting the tone aperiodically, every third or fourth session, 5 min before and after the intravenous injection of nalorphine. Results were similar to the initial conditioning sessions. Two rhesus monkeys not dependent on morphine were stabilized on a food schedule similar to that used for the first three monkeys. These monkeys showed no change in food-lever response rate during or after nalorphine injections.     

Fixed-interval behavior maintained by conditioned reinforcement

The key-pecking of a pigeon was reinforced with grain on an 18-min second-order schedule. During the 18 min, a key peck which completed a 3-min fixed interval produced a stimulus of 0.5-sec duration. The first 3-min fixed interval completed after 18 min resulted in primary reinforcement. Behavior characteristic of fixed-interval schedules was produced on both the 3-min components and the 18-min schedule. This performance was shown to be enhanced whenever the 0.5-sec stimulus was also presented before the presentation of grain.     

Persistent behavior maintained by unavoidable shocks

Squirrel monkeys were trained on a multiple schedule in which 10-min periods on a continuous shock avoidance schedule, indicated by a yellow light, alternated with 10-min periods on a 1.5-min variable interval schedule of food reinforcement (VI 1.5). A white light indicated that VI 1.5 was in effect, except for the middle 2 min of the period on VI 1.5, in which a blue light appeared and terminated with the delivery of a 0.5-sec unavoidable shock. Stable response rates developed in the avoidance and VI 1.5 components. However, the highest response rates occurred in the blue, preshock stimulus. A series of experiments showed that responding in the blue stimulus persisted even when responding had been extinguished on both the VI schedule of food reinforcement and the shock avoidance schedule. Responding in the blue stimulus ceased when the blue stimulus terminated without shock or when it terminated with a response-contingent shock. Each time responding ceased, it was restored by terminating the blue stimulus with an unavoidable shock. When the blue stimulus was on throughout each session and unavoidable shocks were delivered at regular 10-min intervals, responding was well maintained. These results show that in monkeys that have been trained on a continuous avoidance schedule, unavoidable shocks can maintain responding even under conditions where responses have no programmed consequences.