Acquisition and maintenance of Sidman avoidance with paired rat subjects

Rat Ss were used to study the acquisition and maintenance of Sidman avoidance as a function of either single or paired training. Ss receiving paired training failed to acquire the leverpress response even after a block of individual training sessions. Within the paired training condition, Ss that were housed separately evidenced better acquisition than Ss housed as pairs. When Ss that were efficiently avoiding under individual training conditions were paired, avoidance was severely disrupted.     

Autoshaping in the rat: Interposing delays between responses and food

Rats were exposed to an autoshaping procedure in which each lever-contact or leverpress delayed trial offset and, hence, food delivery. Yoked subjects received identical trial-food pairings as did delay subjects. This procedure was studied at two delay values (2.5 and 10.0 sec) in experimentally naive rats and those which had previously received 25 sessions of autoshaping. The delay procedure retarded the acquisition of autoshaped responding in naive subjects and reduced responding for experienced subjects. Yoked subjects responded at higher levels than did delay subjects throughout training.     

A comparison of signaled vs. unsignaled free-operant avoidance in wild and domesticated rats

Three experiments compared the performance of domesticated hooded rats and nondomesticated black rats under signaled and unsignaled free-operant leverpress avoidance. There was no difference between groups in asymptotic shock rates under unsignaled avoidance; however, the black rats avoided much more successfully when the signal was present, while the hooded rats showed little or no improvement. When a longer signal was employed (10 vs. 5 sec), the effects were essentially the same. The black rats generally had higher response rates, and this difference was most pronounced in extinction, where the hooded rats made very few responses. The domesticated rats received a disproportionately large number of shocks early in the session (warm-up) under unsignaled avoidance, but this tendency was much less pronounced for the black rats. However, both groups showed appreciable amounts of warm-up during signalled avoidance. The findings are discussed in terms of differences in levels of activation/arousal between domesticated and nondomesticated animals.     

Two independent effects of variation in intertrial interval upon leverpress avoidance learning by rats

Variation in the intertrial interval (ITI) preceding a given trial is shown to have an independent and opposite effect upon leverpress avoidance performance to that caused by variation in ITI after a trial. This finding accounts for the opposite effect of overall ITI upon leverpress avoidance to its effect upon one-way avoidance without recourse to an associative explanation. The implications of this finding for recent discussions of response constraints upon avoidance learning is discussed.     

Defensive responding and leverpress topography compatibility: Effects of shock intensity,S-S interval,and lever position

The degree of compatibility between defensive responding and leverpress topography was investigated. Rats were trained to leverpress on a Sidman avoidance schedule for one 60-min session. Measures of defensive responding (jumping and rearing) were recorded during initial training. Shock intensity (.5, 1.0, and 2.0 mA) and S-S interval (1, 3, and 5 sec) were varied in Experiment 1. S-S interval had no effect on defensive responding or on performance. Rate of jumping was an increasing function of intensity only at lower intensities. Both jumping and rearing were significantly correlated with leverpressing. Shock intensity (1.0 and 2.0 mA) and lever position (3.02 and 16.83 cm) were varied in Experiment 2. Response rate was an increasing function of intensity at the high lever position but not at the low position. Correlations between rearing and leverpressing, and between jumping and leverpressing, were not significant for either lever position. Bolles’ (1970) theory of species-specific defense reactions was invoked to account for initial facilitated performance.     

Operant response topographies of rats receiving food or water reinforcers on FR or FI reinforcement schedules

Separate groups of food- and water-deprived rats pressed a lever for food or water, respectively, on continuous reinforcement and various fixed-ratio and fixed-interval reinforcement schedules. Food-reinforced rats on continuous, FR 2-, or FI 10-sec schedules showed consistently longer mean lever contact durations per leverpress than did water-reinforced rats on the same schedules. Mean lever-contact-duration differences between food- and water-reinforced rats were greatly attenuated or disappeared under FR 4-, FR 8-, FI 20-sec, and FI 30-sec schedules of reinforcement. These results are interpreted as supporting earlier hypotheses that there are respondent components of operantly conditioned and autoshaped leverpresses, but that these respondent components weaken with partial reinforcement and the leverpress topography comes under the control of operant contingencies.     

Inhibition of delay of the two-way avoidance response and warning-signal salience

Effects of extended training (nine sessions, 50 trials each) on two-way avoidance response latencies were studied. For each rat, auditory and visual warning signals (CS) were presented on separate trials, either according to a Gellermann series or in 25-trial blocks. Intermittent presentation of the two kinds of trials yielded shorter latencies and higher levels of avoidance performance in response to the noise CS than in response to the darkness CS. Presentation of trials in blocks revealed stronger response-eliciting properties of stimuli presented during the second half of the session than of those presented during the first half. A significant decrease of avoidance performance in the early portions of the delay period, an index of inhibition of delay, was obtained on auditory trials presented in the second half of the sessions. Results indicate that strong fear of the warning signal is required for inhibition of delay of avoidance responses.     

Flavor avoidance learning based on missing calories but not on palatability reduction

Avoidance of a target flavor can be produced by providing rats with a highly nutritious solution of 20?% maltodextrin (20?%Malto) in some sessions and a 3?% maltodextrin (3?%Malto) solution containing the target flavor in intermixed sessions. Since 20?%Malto is both more nutritious and more palatable than 3?%Malto, flavor avoidance could arise because the flavor signals either a reduction in calories or reduced palatability, or both. Pilot testing established that rats strongly preferred 3?%Malto plus 0.1?% saccharin to both unflavored 3?%Malto and unflavored 20?%Malto. The two main experiments tested whether the palatability difference, which the pilot data had suggested was larger than the difference between 20?%Malto and 3?%Malto, could produce flavor avoidance. In both experiments, one group of rats were given 3?%Malto plus 0.1?% saccharin on some days, intermixed with other days on which this group was given 3?%Malto plus the target flavor, almond. Neither when trained and tested under conditions of food deprivation (Experiment 1) nor when trained and tested sated (Experiment 2) did palatability reduction produce almond avoidance. In contrast, calorie reduction produced almond avoidance under both conditions. These results suggest that flavor avoidance can be produced by intermixed training involving solutions that differ in nutritious value and palatability, but not when they differ only in palatability.     

Instrumental electrodermal conditioning in the monkey (Cebus albifrons): Acquisition and long-term retention

EightCebus albifrons monkeys received 25 sessions of discriminative operant conditioning of the skin conductance response (SCR), with colored lights as discriminative stimuli and with Sidman avoidance (SS-40 sec, RS-40 sec) scheduled during one light and response-contingent shock during the other, Discriminative stimulus segments were separated by 30-sec periods of time-out from shocks and lights, Two extinction sessions were run 3 months after training, Almost from the beginning of conditioning, the monkeys made significantly more unelicited skin conductance responses in the avoidance periods than in punishment, The monkeys’ heart rates also increased significantly, but there was no difference between avoidance and punishment, SCR frequency during extinction continued to differentiate significantly between avoidance and punishment, and there was a significant increase in this differentiation from the last conditioning session to the first extinction session, but the difference then reduced in the second session, The results indicated that monkey’s SCRs are influenced by instrumental reinforcement contingencies somewhat in the same fashion as those of humans.     

Blocking as a function of added cue intensity

Twelve rats were initially trained to leverpress for water in the presence of a tone. Responses in the absence of the tone were never reinforced. Following this pretraining, a novel light cue was simultaneously compounded with all presentations of the tone as a relevant but redundant predictor of reinforcement. For three different groups of subjects, the light cue was of either bright, moderate, or dim intensity. After compound training, all subjects experienced nonreinforced presentations of each of the two components of the compound. Results indicated that the relative degree of control exerted by the light over behavior increased with increases in light (added cue) intensity.     

Changes in inhibition during differential eyeblink conditioning with increased training

Three experiments examined inhibitory learning in rats, using Pavlovian and differential inhibitory eyeblink conditioning procedures. Experiment 1 was designed to compare summation and retardation effects following Pavlovian conditioned inhibition (A1/XA) or differential inhibition (A1/X) training using auditory and visual conditioned stimuli (CSs). After ten 100-trial sessions of training, both Pavlovian conditioned inhibition and differential inhibition produced a retardation effect. However, a summation effect was obtained only for rats given Pavlovian conditioned inhibition training. Experiment 2 showed that increasing differential inhibition training to twenty 100-trial sessions produced summation and retardation effects. In Experiment 3, rats were trained with either ten or twenty 100-trial sessions of intramodal inhibitory training with two tone CSs (2 kHz vs. 8 kHz). Summation and retardation effects were obtained after only 20 sessions of differential conditioning. The findings indicate that extensive training is needed to establish conditioned inhibition with intermodal or intramodal differential conditioning.     

The preference of rats for free or response-produced food

Three experiments were performed to investigate the preference of rats for either free or response-produced food. Rats were trained to free feed in an operant chamber and then to leverpress for food. Subsequently, they were given a choice between continuing to leverpress for food on CRF, FR 2, and FR 10 schedules or free feeding. In three experiments the independent variable was the method of free-food presentation: A fixed free-food dish was used in the first experiment, a movable dish in the second, and a large flat dish in the third experiment. The results of the three experiments were very similar, with most of the rats showing a preference for the free food. This preference increased further when more than one response was required to produce a food pellet. These results contradict any conclusion that rats have a generalized tendency to prefer response-produced to free food but provide no answer to the question of why rats do on occasion respond for food in the presence of free food.     

Eliminating behavior with omission and extinction after varying amounts of training

After rats were trained to leverpress for 1, 3, 9, or 27 days on a variable interval reinforcement schedule, omission training was compared with extinction in effectiveness of response elimination. Extinction produced faster response elimination than omission, although both procedures eventually led to equal response elimination. Resistance to response elimination increased with length of baseline training, although this effect did not interact with omission vs extinction. A test of the durability of elimination effects followed, using a response-independent variable time reinforcement schedule. After extinction, resumption of responding in the durability test increased with length of baseline training, but there was little response resumption following omission regardless of the length of the baseline training. These results amplify and extend previous findings which show omission to be an effective and durable response elimination method.     

Shuttlebox avoidance to intense white noise: Acquisition and the Kamin effect in rats

Experiment I demonstrated shuttlebox avoidance conditioning using intense white noise as a UCS. Ten rats were given 25 trials a day for 6 days. Escape latencies declined and avoidance responses increased over trial blocks. Experiment II provided support for a functional similarity between shock as a UCS and intense noise as a UCS by demonstrating the Kamin effect following incomplete shuttlebox training to noise. Separate groups of rats were given 25 trials followed by an additional 25 trials either 0, 1, 4, or 24 h later. The U-shaped Kamin effect was evident in the avoidance measure. A similar but inverted U-shaped function was obtained for the escape latency measure. Escape latencies were longer on retraining than on original training at 1 h but not at 0, 4, or 24 h after original training.     

Effects of cross-modal transfer on direct and reversal learning in the rat

In the first experiment, using within- and between-sensory modality CSs, direct and reversal transfer of active avoidance learning was studied in 48 male and 48 female albino rats. Training in each of two sessions employed either a high- or low-intensity light or noise CS. The analyses of both raw score data and proportional or savings score data indicated significant cross-modal transfer in direct as well as reversal learning conditions. Although females learned faster than males, there were no sex differences in amount of transfer. A second experiment, which examined the potential of compound conditioning within the cross-modal learning procedures, replicated the cross-modal results of the first experiment without finding evidence for compound conditioning. These results are interpreted in terms of specific and nonspecific transfer effects during avoidance learning.     

Conservation,matching, and the variable-interval schedule

The conservation model was generalized to the variable-interval schedule by incorporating the concept of unscheduled instrumental responses, those which occur in the time before the next setup is due. Thirsty rats responded in constant-duration sessions on two 7-sec schedules that required one leverpress for 25 and 50 licks at a water tube and on a 14-sec 25-lick schedule. In accordance with the model, total licks decreased linearly as total presses increased, and the schedules facilitated leverpressing and suppressed licking relative to paired baseline levels of responding. While the matching model also gave a satisfactory fit to instrumental responding under the schedules, its two constants, representing asymptotic rate of responding and extraneous reinforcement, had anomalous values which led the model to predict that response rate would decrease as the rate of reinforcement increased, directly opposing its prediction for the constant-consumption experiments of its previous tests.     

Are “no-drug” cues discriminated during drug-discrimination training?

Rats were trained in a two-lever operant chamber to discriminate the presence versus the absence of a drug. During drug sessions, the training procedure involved reinforcing presses on lever 1 with saccharin-sweetened water but not reinforcing presses on lever 2. During no-drug sessions, only presses on lever 2 were reinforced. After this discrimination was learned, each rat was trained to discriminate presence versus absence of a second drug. All rats learned this second discrimination. Finally, the rats were tested to determine whether they could still discriminate the first drug, as well as other pharmacologically related compounds; most rats could. Training drugs were phenobarbital 30–35, nicotine 0.4, amphetamine 0.4, cyproheptadine 7, phencyclidine 4, cyclazocine 1.5, fentanyl 0.04, and scopolamine 0.2 mg/kg. The results indicate that drug versus no-drug discrimination training does not disrupt discriminative control previously established with a different drug. When considered in combination with the results obtained during substitution tests conducted after drug-versus-no-drug training, the data suggest that, instead of discriminating drug cues versus no-drug cues, rats discriminate presence versus absence of particular drug cues.     

Acquisition and retention of dark avoidance by the toad,Xenopus laevis (Daudin)

Young toads,Xenopus laevis, were trained for dark avoidance in a passive avoidance paradigm using electric shock in a fully automatic training and recording procedure. Dark avoidance was acquired within approximately 30 min and was retained on retesting 24 h later. Comparison of the performance of the toads during training and during retesting was used as an indicator for saving or reinforced retention. Control experiments demonstrated that changes in behavior were due to learning and not to nonassociative effects such as pseudoconditioning, increased sensitization to shock, or acquaintance with the testing apparatus.     

Instrumental response topographies of rats

Experiments 1, 2, and 3 showed that food-deprived rats responding for food pellets made significantly more long-duration leverpresses than water-deprived rats responding for water drops. These experiments further showed that this difference in instrumental response topography is long-lived, and depends neither upon idiosyncrasies of the experimental chamber nor upon severity of deprivation conditions. In Experiment 4, food-deprived rats responding for food pellets made significantly more long-duration leverpresses than did either food- or water-deprived rats responding for sucrose solution. Human judges in Experiment 5 were able to correctly identify instrumental leverpress responses by rats as being for food or water based solely on previous viewings of other rats drinking water or eating food pellets. It appears that instrumental response topographies in rats vary depending principally upon the reinforcer received, and that these instrumental response topographies resemble consummatory response topographies.     

Functional differentiation of adjunctive drinking and wheel running in rats

Food-deprived rats were exposed to a schedule in which a brief stimulus was presented approximately once every 60 sec. The first leverpress to occur in the presence of the stimulus always turned it off, and produced a food pellet 50% of the time. When the rats were given concurrent access to water, a running wheel, or both, drinking predominated during intervals initiated by pellet delivery, while running predominated during intervals initiated without food. When allowed to obtain all of their food pellets at the beginning of a session, rats drank less and ran more than when the intermittent schedule was in effect, and most drinking occurred within the first half of the session, while running was distributed throughout the session. Adjunctive drinking and wheel running appear to be functionally different, drinking being schedule-induced and food-bound, running being neither.