Free operant avoidance behavior in hooded rats: IRTs and response chains

Twenty-five hooded rats were given 50 avoidance training sessions with leverpress IRTs obtained during as well as between sessions. Five qualitatively different shapes to the IRT profiles were found: single- or double-peaked shapes, positively or negatively accelerated shapes, and U-shaped distributions. Both the specific shape of the profile and the stability of that shape during a session were related to the avoidance proficiency of an individual rat. Six rats received two additional training sessions, with the final 30 min of each videotaped to obtain frequency counts of nine behavior categories. The observational data showed that avoidance-proficient rats typically incorporated the leverpress requirement into repetitive response chains.     

Renewal after the extinction of free operant behavior

Four experiments were performed to explore the role of context in operant extinction. In all experiments, leverpressing in rats was first reinforced with food pellets on a variable interval 30-s schedule, then extinguished, and finally tested in the same and a different physical context. The experiments demonstrated a clear ABA renewal effect, a recovery of extinguished responding when conditioning, extinction, and testing occurred in contexts A, B, and A, respectively. They also demonstrated ABC renewal (where conditioning extinction and testing occurred in contexts A, B, and C) and, for the first time in operant conditioning, AAB renewal (where conditioning, extinction, and testing occurred in contexts A, A, and B). The latter two phenomena indicate that tests outside the extinction context are sufficient to cause a recovery of extinguished operant behavior and, thus, that operant extinction, like Pavlovian extinction, is relatively specific to the context in which it is learned. AAB renewal was not weakened by tripling the amount of extinction training. ABA renewal was stronger than AAB, but not merely because of context A’s direct association with the reinforcer.     

Multiple determinants of “blocking” effects on operant behavior

Blocking was investigated in a free-operant procedure by presenting a response-contingent signal prior to reinforcer delivery. At issue was the way in which blocking effects previously reported with this procedure are related to conditioned reinforcement effects, also previously found with similar procedures. Signal presentation decreased response rate when delay of reinforcement was 0 or .5 sec, but the signal increased response rate when the delay of reinforcement was increased to 3 sec. Thus, which effect (blocking or conditioned reinforcement) occurred depended critically on the response-reinforcer interval.     

The functional equivalence of operant behavior and foraging

Many researchers have used the controlled procedures of operant methodology to test the predictions of foraging theory on the assumption that foraging is operant behavior and operant behavior is foraging. This experiment tested the assumption that leverpressing is functionally equivalent to search effort. Four rats were exposed to two situations: a naturalistic foraging situation (a “patch”) and a standard operant chamber. Each condition represented a different prey density on the patch and a corresponding change in the probability of reinforcement in the chamber. The average number of presses per pellet was linearly related to the density of pellets on the patch. This result indicates that leverpresses were functionally equivalent to search effort.     

Extinction of operant behavior: An analysis based on foraging considerations

In two experiments, the frequency of food reinforcement provided by variable interval (VI) schedules prior to extinction was varied. In the first experiment, two-component multiple schedules resulted in a greater number of responses in extinction in the presence of the stimulus previously associated with the richer of the two component schedules than that previously associated with the leaner schedule. In the second experiment, different groups of animals were trained on different VI schedules. Responding in extinction was analyzed into bouts of responding showing that the number of response bouts increased and the number of responses per bout decreased with decreasing frequency of reinforcement during training. These data are compatible with an analysis of operant behavior based on an analogy to processes that presumably-occur-in naturalistic foraging situations. According to this analogy, behavior associated with search for a food source (i.e., number of response bouts) and that of procurement of food from a source (i.e., responses per bout) represent aspects of behavior that are differentially strengthened by different VI schedules. Extinction serves to reveal this differential strengthening.     

Training effects on contrafreeloading in rats housed in operant chambers

Four rats were trained to press a bar for food pellets and then were housed in operant chambers for 6 continuous days of choice-testing between obtaining pellets freely or by barpressing. There were two additional 3-day choice periods following more barpress training. It was found that (1) animals preferred to secure food by barpressing when initially placed in the choice situation and immediately following additional barpress training; (2) there was a subsequent decrease to very low levels of response-dependent food taken during choice testing; and (3) opening the chambers for daily maintenance during choice-testing caused a temporary increase in barpressing for food. Thus the previously reported stability of high rates of barpressing in the presence of free food is, at least in part, dependent upon short testing sessions.     

Effects of preweaning environmental enrichment on later problem-solving behavior in rats

Two experiments investigated the importance of visual sensory modality in mediating enriched environmental effects during the preweaning period, and the importance of onset and duration of the enriched experience during the same period. Rat mothers and pups were exposed together in an enriched environment for either 7 or 11 days at different periods from Day 1 to Day 21. Also included was a group of rats which received only handling from Day 11 to Day 21 postpartum and another group in which the mothers were exposed to the enriched environment during the last trimester of pregnancy. Some rats were tested at 27 days of age, and others were tested at 64 days of age in the Hebb-Williams maze test. It was found that exposure in the enriched environment for a period of 7 days before the eyes opened improved rats’ problem-solving behavior above that of control rats and to the level of rats which received such experience after the eyes had opened. Handling of rats did not improve problem-solving behavior, nor did exposure during the gestation period. It was concluded that vision is not the most important factor in mediating effects during the preweaning period, since improvement in problem-solving behavior can occur before the visual system is fully developed. It was suggested that the beneficial enrichment effects might be mediated by the mother, who, in some way, transmits additional stimulation to the infant rat during this early stage of development.     

Effects of CSs for food and water upon rats barpressing for different magnitudes of food reinforcement

Forty-eight albino rats were first exposed to randomly intermixed, noncontingent presentations of one pellet, six pellets, and water. For each of three groups, a CS+ was paired with one of the reinforcers, while the other two reinforcers and a CS? were presented alone. Then half the subjects experienced a six-pellet reward and half experienced a one-pellet reward for leverpresses during a light S^D. Finally, on test trials, the CS+ or CS? was compounded with the light. Latencies on test trials indicated that responding for the one-pellet reward was significantly more disrupted by a CS+ for six pellets than by the CS+ for one pellet or the CS+ for water. Responding for the six-pellet reward was disrupted by the CS+ for one pellet somewhat more than by the CS+ for six pellets or water, but not significantly so. This pattern of results is partially consistent with an associative model of transfer and appears to contradict a motivational account of such effects.     

Effects of exteroceptive feedback and safe-box confinement durations on escape behavior in rats

In Experiment 1, rats received escape training in which an exteroceptive feedback cue occurred in the safe box, and safe-box confinement durations of 5 or 20 sec were combined orthogonally with shock-box confinement durations of 5 or 20 sec. Exteroceptive feedback reliably facilitated escape performance relative to no-feedback controls when safe-box confinement was relatively longer than shock-box confinement. Confinement duration also facilitated performance in the absence of exteroceptive feedback. In Experiment 2, escape training with or without feedback was followed by extinction either with the feedback condition of prior training or with the opposite feedback condition. Feedback presentations in extinction reliably increased responding. Feedback removal reliably decreased responding relative to feedback controls. Introduction of feedback in extinction reliably enhanced performance relative to no-feedback controls.     

关于素数个数的又一个不等式

对于正实数x,设π（x）表示适合p≤x的素数p的个数.对于正整数k、n,设fk（n）=π（x）＋π（2kx）＋…＋π（nkx）及Sk（n）=1k＋2k＋…＋nk.证明了：当x≥4且n≥[（k＋1）e1.2]时,fk（n）≥π（Sk（n）x）.     

Effects of conspecific odor on rats’ position and behavior in an open field

When rats were tested in a novel open field, half of which had previously been occupied by a conspecific, they tended to enter the predecessor half first and subsequently spent more time in this half. There was proportionally more sniffing of the floor, sniffing of the air, and grooming in the predecessor half compared with the clean one, and proportionally less ambulating, rearing, and sniffing of the wall. Time spent in the predecessor half was unaffected by whether or not the predecessor had been tested under a relatively stressful condition (strong illumination), but rats tested after a “stressed” conspecific ambulated and reared less and showed more inactivity and thigmotaxis. Predecessor influence may be mediated by qualitative and/or quantitative differences in odor associated with urine traces, an influence that could affect results during routine successive open-field testing.     

Contextual control of operant behavior: evidence for hierarchical associations in instrumental learning

Recent research has suggested that operant responses can be weakened when they are tested in new contexts. The present experiment was therefore designed to test whether animals can learn a context–(R–O) relation. Rats were given training sessions in context A, in which one response (R1; lever pressing or chain pulling) produced one outcome (O1) and another response (R2; chain pulling or lever pressing) produced another outcome (O2) on variable interval reinforcement schedules. These sessions were intermixed with training in context B, where R1 now produced O2 and R2 produced O1. Given the arrangement, it was possible for the animal to learn two distinct R–O associations in each specific context. To test for them, rats were then given aversion conditioning with O2 by pairing its presentation with lithium-chloride-induced illness. Following the aversion conditioning, the rats were given an extinction test with both R1 and R2 available in each context. During testing, rats showed a selective suppression in each context of the response that had been paired with the reinforcer subsequently associated with illness. Rats could not have performed this way without knowledge of the R–O associations in effect in each specific context, lending support to the hypothesis that rats learn context–(R–O) associations. However, despite a complete aversion to O2, responding was not completely suppressed, leaving the possibility open that rats form context–R associations in addition to context–(R–O) associations.     

The “disinhibition” of extinguished operant behavior in pigeons: Trial-tempo shifts and novel stimulus effects

After conditioning and extinction of keypecking with 25-see intertrial intervals between key illuminations, an immediate change to 5-sec intertrial intervals reinstated pecking during trials. Brief illuminations of the chamber during intertrial intervals also temporarily restored extinguished keypecking. The same manipulations of trial tempo and chamber illumination usually weakened well established, still reinforced keypecking. No recovery of extinguished behavior occurred when the intertrial interval was shifted upward from 5 sec to 25 sec. These and other behavioral findings were examined in relation to (a) Pavlov’s and Skinner’s research and views on “disinhibition” and “external inhibition” and to (b) analogous phenomena in physiological studies of habituation and dishabituation. The reliable evidence of disinhibition obtained in the present experiments suggests the involvement of an inhibitory process in extinction.     

Factors affecting schedule-induced wood-chewing in rats: Percentage and rate of reinforcement,and operant requirement

In Experiment 1, rats were allowed to acquire either schedule-induced drinking or schedule-induced wood-chewing behavior under a fixed-interval (FI) 60-sec schedule of food reinforcement, following which food was omitted from 20% and then 50% of interreinforcement intervals. Omission of food severely disrupted induced drinking but had relatively little effect on induced wood-chewing. Experiment 2 investigated wood-chewing as a function of reinforcement rate, using a range of FI schedules from 5 to 180 sec in duration. Both the amount of chewing per session and the relative time spent chewing were bitonically related to reinforcement rate. In Experiment 3, schedule-induced chewing that had been acquired under a response-dependent schedule was found to persist under a response-independent schedule. Induced wood-chewing resembles other induced behaviors in important respects, but quantitative differences are also apparent.     

Extinction of rats’ barpressing in the presence of free food

In two experiments, hungry rats received four extinction sessions in the presence of free food. When the free food was removed for eight subsequent extinction sessions, the animals made significantly fewer responses than did control groups which received no intervening sessions. The results are contrary to those of Enkema et al (1972). From the results of additional groups of rats which received four intervening sessions of free food only, empty chamber, or time in home cage, it was concluded that the presence of free food caused the diminution in extinction responding.     

Effects of prior response-contingent reinforcement on superstitious behavior

Three pigeons were exposed to fixed-time (FT) 15 sec, fixed-interval (FI) 15 sec for performing an arbitrary response, a reversal back to FT 15 sec, and then extinction (no reinforcement). During each phase, a computer-controlled tracking system continuously recorded the position of the bird’s head as it moved freely in the experimental chamber. During the first exposure to FT 15 sec, all 3 birds developed a pattern of feeder-wall-directed behavior with occasional circular excursions from the feeder immediately following reinforcement. During FI 15 sec, all birds performed the arbitrary operant, which consisted of contacting a virtual target sphere near the rear of the chamber, and did not engage in feeder-wall-directed behavior. During the reversal back to FT 15 sec, the birds developed a behavior sequence consisting of moving in the direction of the target sphere after reinforcement, followed by feeder-wall-directed behavior prior to the next reinforcement. During extinction, either moves toward the target sphere or wall-directed behavior occurred separately, interspersed with reappearance of the two as a sequence, followed by cessation of both members of the behavior sequence. These findings indicate that prior reinforcement of an arbitrary response can affect the location and form of superstitious behavior that develops near the beginning of the interreinforcement interval, but that other factors (e.g., immediacy of reinforcement) affect the location and form of the behavior near the end of the interval. The findings can be interpreted in the context of superstitious chaining.