Conditioned suppression of an avoidance response

A signal followed by shock was presented at irregular intervals during a free-operant avoidance schedule. The effects of this procedure were studied in terms of the rate of unavoided shock in the presence and absence of the signal and the rate of response before and during the signal. Three shock intensities were employed. Response enhancement as well as response suppression were observed; irrespective of changes in responding, shock rates substantially increased during signalled periods compared to non-signalled periods. Shock rates in non-signalled periods were generally higher than during training.     

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.     

Conditioned suppression of free-operant avoidance

The responses of white rats were maintained on an unsignalled free-operant avoidance schedule. Superimposed on the avoidance schedule was a blinking white light followed immediately by response-independent electric shock. Duration of the light stimulus was either 1 or 3 min. Avoidable shock was 1.5 mA; response-independent shock was 7.5 mA. Suppression of responding during the light stimulus (both durations) developed over sessions. Responding immediately following the response-independent light-shock sequence was neither suppressed nor accelerated. The similarity is noted between the present result and findings of “positive conditioned suppression”.     

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.     

Potentiation of the acoustic startle response by a conditioned stimulus paired with acoustic startle stimulus in rats

The hypothesis that the standard acoustic startle habituation paradigm contains the elements of Pavlovian fear conditioning was tested. In a potentiated startle response paradigm, a startle stimulus and a light conditioned stimulus (CS) were paired. A startle stimulus then was tested alone or following the CS. Freezing behavior was measured to index conditioned fear. The startle response was potentiated on CS trials, and rats froze more in CS than in non-CS periods. In Experiment 1, response to a previously habituated, weak startle stimulus was potentiated. In Experiment 2, response to the same stimulus used as the unconditioned stimulus (US) in training was potentiated. This CS-potentiated response retarded the course of response decrements over training sessions as compared with an explictly unpaired control group. Conditioned fear is a standard feature of this habituation paradigm, serves to potentiate the startle response, and provides an associative dimension lacking in the habituation process per se.     

Control of avoidance by a response-produced stimulus

Three pigeons were trained to press a foot pedal to postpone electric shock. The safety signal was a tone of 1000 Hz, which sounded for 5 sec following each press; silence therefore served as a warning signal. After the performance approached asymptote, test sessions were interspersed among the training sessions. Following a warm up, the shock was omitted (extinction), and no tone or a tone of 250, 500, 1000, 2000, or 4000 Hz was presented following each press for the remainder of the session. Gradients of generalization plotted in terms of the number of times the tone was produced on each test peaked at 1000 Hz, indicating that the performance was controlled by the frequency. Since this dimension is orthogonal to absence of tone, the gradient cannot be attributed to differences in the magnitude of change in the warning signal. It was concluded that response-produced stimuli reinforce avoidance behavior.     

Double discrimination avoidance with a single stimulus

Four white rats were trained to avoid electric shocks by depressing a bar after the onset of a stimulus and releasing it after termination of the stimulus. All subjects acquired the behavior of holding the bar in the presence of the stimulus and releasing it in the absence of the stimulus, but one animal almost always required a "priming" shock. The others exhibited a high level of shock avoidance.     

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.     

Social facilitation of responses during a stimulus paired with electric shock

Key-pecking responses of a pigeon were maintained by a variable-interval schedule of food reinforcement. The responses were suppressed during the occasional presentation of a warning stimulus paired with electric shock. The presence of a second pigeon emitting the same response for food reinforcement reduced the suppression that otherwise occurred during the warning stimulus when the second pigeon was absent. These results reveal that the social facilitation phenomenon can be used to restore behavior that is suppressed by a conditioned aversive 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.     

Conditioned adaptation to prismatic displacement with a tone as the conditional stimulus

Adaptation to prismatic displacement was conditioned to a tone in 72 min of training by employing Taylor’s alternation training technique. The alternation consisted of two training conditions. In one, S was exposed to the prism and tone; in the other, S was exposed to neither. After training, the pointing to a visual target test measured more aftereffects of adaptation when the tone was present than when it was absent. Conditioning was obtained in two testing situations: (1) with the training goggles still worn by S, and (2) with the goggles removed.