Random Time Schedule Research Articles

Spatial distribution of behavior under concurrent random-time schedules of water

A study was designed to explore the effects of concurrent random-time delivery of water on the spatial dimensions of behavior with five different continuous measures in time and space. Four water-deprived male-Wistar rats were exposed to two concurrent random time schedules of water delivered in two dispensers located at opposite walls of an enlarged experimental chamber. In five different phases, the scheduled frequency of water deliveries remained constant while their distribution in each of two dispensers varied systematically. The continuous record of rat location through the experimental chamber was analyzed in terms of the directionality, vigor, variation, preference, and persistence of behavior. Directionality and preference showed systematic variations as the number of dispensers providing water and their timing changed, vigor and variation remained relatively constant through the experimental phases, and persistence showed a slight decrease across phases. Results support the argument that molar continuous measures depict extended moment-to-moment changes in behavioral dimensions usually not considered in the typical procedures recording discrete repetitive responses.

CaMKII antagonism in the ventral tegmental area impairs acquisition of conditioned approach learning in rats

This study investigated the role of calcium2+/calmodulin-dependent protein kinase II (CaMKII), a protein in the second messenger pathway of NMDA receptors, in the ventral tegmental area (VTA) in the acquisition and performance of conditioned approach learning. Male Long-Evans rats (N = 79) were exposed to 3 (to test acquisition) or 7 (to test performance) conditioning sessions in which they received 30 paired presentations of a light stimulus (CS) and a food pellet (US) on a random time schedule. These conditioning sessions were then followed by one 30-min session without the CS or US and lastly by a CS-only test session, where only the light stimulus was presented (without food) according to the same schedule as the conditioning sessions. Bilateral intra-VTA injections of KN93 (vehicle, 3.0, 4.5 or 6.0 μg/0.5 μL), a CaMKII inhibitor, were administered prior to each conditioning session to test effects on the acquisition of conditioned approach or prior to the CS-only test session to test effects on the performance of conditioned approach. KN93, when given prior to conditioning sessions, significantly reduced the number of conditioned approach responses emitted during CS presentations in the CS-only test. When KN93 was given prior to the CS-only test it had no effect. These results suggest that CaMKII activation in the VTA is necessary for the acquisition, but not the performance, of reward-related learning.

Relapse of operant behavior after response elimination with an extinction or an omission contingency.

The present study compared relapse after responding was eliminated by extinction or omission training in rats. In Experiment 1, lever pressing was reinforced with food pellets in Context A and then eliminated with either extinction or omission training in Context B. The response was then tested in Contexts A and B in either the presence or absence of free food pellets delivered on a random time schedule. All rats showed higher responding when tested in Context A than Context B, and there was little evidence that omission training attenuated this ABA renewal effect. Noncontingent pellets increased responding after extinction but not after omission. However, when responding on the last day of response elimination was compared to responding during the test in the response-elimination context, there was some evidence that omission-trained rats showed a small increase in responding even when tested with free pellets. Results of Experiment 2 suggest this increase was not due to differences in the temporal distribution of pellets during elimination and the test, and that the result might be due to mere removal of the omission contingency, but any such effect is small and difficult to detect statistically. The results provide new information about factors generating relapse after omission training.

RESPONSE ACQUISITION WITH INTERMITTENT IMMEDIATE AND DELAYED CONDITIONED REINFORCEMENT

The acquisition of lever pressing by rats was studied under intermittent immediate and delayed conditioned reinforcement. Rats were exposed to two schedules operating concomitantly. One was a random-time schedule that delivered reinforcers on average of once per min. Each such reinforcer was paired with a 1-s illumination of a cue light located above the lever. The other was a tandem random-interval (RI) t₁ - s fixed-time (FT) t₂ - s schedule that controlled the rate and the delay of the illumination of the cue-light after a given lever press. For the RI, t₁ was 7.5, 15 or 30 s. For the FT, t₂ was 0, 1, 2, 4, 8, 16 or 32 s. Three rats each were exposed to each combination of RI and FT values for 40 sessions. Response rates decreased with longer response-conditioned reinforcer (S(r)) delays under the three different overall rates of S(r). At most response-S(r) delays, absolute response rates were higher with RI 15 s than with RI 30 s but both were similar to those obtained with RI 7.5 s. The results were similar to those from previous research on response acquisition with delayed primary reinforcement. These findings suggest that a previously neutral stimulus that has been correlated with primary reinforcement can reinforce new responses even when the conditioned reinforcer is intermittent and delayed from the responses that produce it.

Omission Learning after Instrumental Pretraining

Hungry rats were pretrained to press two levers on a concurrent schedule for food pellets. Following either limited or extended pretraining, presentations of a sucrose solution were programmed on a random time schedule while the animals continued pressing on a concurrent schedule for food pellets. Presses on one of the levers—the omission lever—postponed deliveries of the sucrose solution scheduled to occur within a fixed period of time following the press, whereas presses on the other, control lever had no effect on the random time contingency. The animals pressed less frequently on the omission lever than on the control lever following limited pretraining but failed to discriminate between the two levers following extended pretraining. The insensitivity to the omission contingency produced by extended pretraining was due to either the number of presses performed during the initial training or the number of reinforced presses, rather than the number of reinforcers received. Finally, the insensitivity of ...

Effects of a short behavioural intervention for dental flossing: randomized‐controlled trial on planning when, where and how

Regular dental flossing has been widely recommended to prevent periodontal diseases. Nevertheless, compliance is below a desirable level. This study evaluates the effects of a brief behavioural intervention on dental flossing and determines whether the effects of such an intervention are stronger in a specific subgroup of individuals (those intending to floss regularly=implemental mindset). Behavioural intervention (planning when, where and how to floss) trial was conducting with 194 participants assigned to an intervention or a control group by a random time schedule; the primary outcome was validated self-report of flossing behaviour. Follow-up data were collected 2 and 8 weeks post-intervention. Individuals receiving the planning intervention significantly outperformed those in the control condition at both the 2- and the 8-week follow-up (4.24 times flossing/week versus 3.9 at 2 weeks; 4.02 versus 2.98 at 8 weeks). Intervention effects were stronger in individuals in the implemental mindset. Dropout rates were higher for participants who received the planning intervention but were not in the implemental mindset. Planning interventions are an economic and effective way to change oral self-care behaviour, and are more effective in individuals in an implemental mindset.

Choice Behavior in Pigeons Maintained With Probabilistic Schedules of Reinforcement

Pigeons were trained in three experiments with a two-key, concurrent-chains choice procedure. The initial links were equal variable-interval schedules, and the terminal links were randomtime schedules with equal average interreinforcement intervals. Across the three experiments, the pigeons either stayed in a terminal link until a reinforcer was delivered or were returned to the initial links if a reinforcer was not delivered after the first unit time interval. The results showed that choice responding in concurrent chains is a complex function of (a) local factors, such as the immediacy of reinforcement in a terminal link, and (b) overall factors, such as the overall interreinforcement interval as calculated over both initial and terminal links of the chain. However, the local factors are generally stronger when the two factors are directly opposed.

Effects of concurrent random-time schedules on the spatial distribution of behavior in rats

We evaluated the effects of concurrent random temporal contingencies of water delivery on the location of rats' behavior. In this experiment, two concurrent random-time schedules delivered water in two dispensers that were located at opposite ends of the chamber, and provided complementary frequencies of water deliveries while the overall number of deliveries stayed constant. Time allocation in the areas adjacent to each water dispenser covaried with water deliveries, although no proportional relation was found. Rats showed a preference for the area where water was initially presented. The results point to the importance of examining spatial properties and patterning of behavior.

Observing behavior: effects of rate and magnitude of primary reinforcement.

Four experiments examined the free-operant observing behavior of rats. In Experiment 1, observing was a bitonic function of random-ratio schedule requirements for the primary reinforcer. In Experiment 2, decreases in the magnitude of the primary reinforcer decreased observing. Experiment 3 examined observing when a random-ratio schedule or a yoked random-time schedule of primary reinforcement was in effect across conditions. Removing the response requirement for the primary reinforcer increased observing, suggesting that the effects of the random-ratio schedule in Experiment 1 likely were due to an interaction between observing and responding for the primary reinforcer. In Experiment 4, decreasing the rate of primary reinforcement by increasing the duration of a random-time schedule decreased observing monotonically. Overall, these results suggest that observing decreases with decreases in the rate or magnitude of the primary reinforcer, but that behavior related to the primary reinforcer can affect observing and potentially affect measurement of conditioned reinforcing value.

Contingencies of Superstition: Self-Generated Rules and Responding During Second-Order Response-Independent Schedules

Nacogdoches Independent School District Experimental conditions explored the development of fallacious rules and assessed the rates and durations of superstitious responding by children under the influence of standard and second-order response-independent reinforcement. During the presentation of computer-generated math problems, subjects in Experiment 1 had access to a computer and keyboard. Group 1 received second-order, random-time (RT) reinforcement by way of a coin toss graphic procedure (mean reinforcement rate of 1/min). This procedure rendered an effect analogous to a "slot-machine" and matching icons produced monetary re inforcement displayed on the computer screen. A second group obtained response-independent reinforcement according to a standard random-time (RT) 30-s schedule (mean reinforcement rate of 2/min). A control group received no scheduled consequences but was exposed to the same demand conditions. After 10 min , students in all groups answered questions regarding "why" they had performed problems. Subsequently, experimental subjects were exposed to the same conditions for 10 min after which reinforcement was terminated; however, a series of problems remained available for solving. Over the course of the experiment, and particularly during extinction, Group 1 subjects performed at higher rates and longer durations. Experiment 2 replicated Experiment 1, but it examined the effects of second-order response-independent reinforcement on fixed-time (FT) schedules. Students who had been exposed to second-order response-independent reinforcement demonstrated higher rates and longer durations of problem solving. Outcomes suggest that, -independent of FT or RT schedules, second-order response-independent contingencies appear to generate elaborate fallacious rules and particularly long durations of superstitious responding.

Within-person relationships among pain intensity, mood and physical activity in chronic pain: a naturalistic approach

Fifty-seven chronic pain patients rated their pain intensity, mood and activity level, at a random time schedule, eight times a day during 6 consecutive days, according to the Experience Sampling Method (ESM). Within-person correlations among pain intensity, mood and activity level were calculated. We found pain intensity to be significantly associated with mood. However, the associations between pain intensity and activity level, and activity level and mood could not be supported. Further, we examined whether the relationship between pain intensity and mood was the result of a pattern across the day. Results showed that pain intensity and mood were worst in the morning and improved during the afternoon among participants whose pain intensity and mood were correlated significantly. We suggest that attentional as well as behavioural processes might explain the established day pattern of pain intensity and mood.

Acquisition of i.v. amphetamine and cocaine self-administration in rats as a function of dose.

The effect of dose on the acquisition of i.v. amphetamine and cocaine self-administration was examined. Three unit doses of amphetamine (0.03, 0.06 and 0.12 mg/kg) and three unit doses of cocaine (0.05, 0.2 and 0.8 mg/kg) were tested in separate groups of ten (amphetamine) or 13 (cocaine) rats. Autoshaping methods were used to train rats to press a lever that resulted in drug infusion under a fixed-ratio (FR) 1 schedule. A daily 6-h autoshaping component non-contingently delivered 60 infusions according to a 60-s random time schedule with ten infusions delivered during the first half of each h. Each day autoshaping sessions were followed by a 6-h self-administration session. The criterion for acquisition was a 5-day period during which a daily mean of 100, 50 or 25 infusions for the three amphetamine doses and 400, 100 or 25 infusions were earned during the 6-h self-administration period for the three cocaine doses, respectively. As dose increased, more rats per group acquired drug self-administration and the mean number of days to meet the acquisition criterion decreased. The percentage of rats acquiring amphetamine self-administration increased with dose and ranged from 80 to 100%. Only one rat at the lowest cocaine dose met the acquisition criterion, but 100 percent of the rats at the two higher doses acquired. During the last 2 days of acquisition, mean infusions decreased and mean drug intake (mg/kg) increased as dose increased. On the last day of acquisition, the time course of infusions during the 6-h self-administration component was characterized by a steady rate of infusions per hour, and number of infusions was inversely related to dose. These findings indicate that the initial available dose of a drug is an important determinant of the rate and probability that successful acquisition will occur.

Provocation frequency and its role in determining the effects of smoked marijuana on human aggressive responding

Five male subjects participated in an experiment to determine how variations in provocation frequency, manipulated before and after smoking marijuana, would affect free-operant aggressive responding. Two response buttons, A and B, were available. Pressing button A was maintained by a fixed-ratio 100 schedule of point presentation. Subjects were instructed that the completion of each fixed-ratio 10 on button B resulted in a point subtraction from a second subject (who was in fact fictitious). Button B responses were defined as aggressive, since they ostensibly resulted in the presentation of an aversive stimulus (i.e., point subtraction) to another person. Aggressive responding was engendered by a random-time schedule of point subtraction and maintained by the initiation of intervals free from point subtraction. Points subtracted from the subjects were attributed to the fictitious other subject. The effects of smoking placebo and 3.58% w/w Delta-9-tetrahydro-canabinol marijuana cigarettes, on aggressive responding under four different provocation conditions, were studied: (1) low provocation before and low provocation after smoking; (2) low provocation before and high provocation after smoking; (3) high provocation before and low provocation after smoking; and (4) high provocation before and after smoking. Manipulating the level of provocation frequency immediately before smoking marijuana had no effect on the number of aggressive responses emitted after smoking marijuana. Rather, the provocation frequency immediately after smoking marijuana was important. After smoking active marijuana cigarettes, aggressive responding was significantly suppressed, relative to placebo, under the high provocation condition but not under the low provocation condition. As a result, the effects of marijuana on aggression appear to be largely determined by the environmental conditions (i.e., level of provocation frequency and/or rate of aggressive responding) present immediately after smoking marijuana. This finding may help to account for some of the inconsistencies observed in previous studies, where marijuana has been found to both increase and decrease aggressive responding.

HUMAN AGGRESSIVE RESPONSES MAINTAINED BY AVOIDANCE OR ESCAPE FROM POINT LOSS

During 50-min sessions, 6 male human subjects could press either Button A or Button B available as nonreversible options. Button A presses were nonaggressive responses and earned points according to a fixed-ratio 100 schedule. Prior to the experiment subjects were instructed that every 10 (fixed-ratio 10) Button B presses (aggressive responses) subtracted a point from a fictitious 2nd subject. A random-time schedule of point loss was used to engender aggressive responding. The instructions attributed these point losses to the Button B presses of the subject's fictitious partner. Aggressive responding either escaped or avoided point loss by initiating an interval free of point loss. The duration of the interval was varied systematically across sessions. Avoidance contingencies maintained a high rate of aggressive responding over 30 sessions in the absence of point loss. Escape contingencies also maintained aggressive responding across sessions, with rates of aggressive responding corresponding to rates of point loss.

Delaying reinforcement in an autoshaping task generates adjunctive and superstitious behaviors

Rats were autoshaped to touch a lever upon its insertion into an operant chamber on a 45 s random time schedule. Occurrence of a reinforced touch on each of 12 lever insertions per session and nose-pokes at the retracted lever were monitored, as was exploratory rearing activity. Delays of 2, 4 or 8 s interposed between the retraction of the lever, which occurred either after 15 s or after a touch response, and delivery of the food pellet reward, resulted in progressively slower acquisition of the extended lever touch response. However, if rats had already acquired the response under immediate reinforcement conditions, the delays subsequently introduced did not cause a decline in autoshaped touch responding. Nose-pokes at the retracted lever occurred during both intertrial and reinforcement delay intervals over the course of autoshaping. The appearance and frequency of these (adjunctive or superstitious) behaviors depended upon the reinforcement delay and behavioral history. These interval behaviors offer measurements of learning not based on arbitrary criteria; they thus provide information about effects on endpoints, or a more global approach to learning.

Do random time schedules induce polydipsia in the rat?

The present experiments investigated the role of signals for pellet delivery in the development of polydipsia on random time schedules. In Experiment 1, when an explicit signal or auditory stimulation from pellet dispenser operation was available to the rats, polydipsia developed in all ofthe animals. In Experiment 2, animals receiving signaled pellet deliveries developed poly­ dipsia more quickly than those receiving unsignaled pellet deliveries. Furthermore, behavioral observations suggested that animals showing polydipsia in the unsignaled group may have been able to detect the operation of the pellet dispenser despite our attempt to mask such cues. In Experiment 3, the information value of pellet-dispenser cues was degraded by the operation of an empty pellet dispenser during the interpellet interval. Under these conditions, almost all animals did not develop polydipsia and the data suggest that for the few that did, pellet-dispenser cues were probably not responsible. Thus, the present findings suggest two conclusions: (1) In studies reporting polydipsia on random schedules, the animals may have been inadvertently provid­ ed with cues for pellet availability, and (2) although Pavlovian conditioning may be an impor­ tant modulator of adjunctive behavior, other factors must also be considered.

A reevaluation of the CS− hypothesis for schedule-induced polydipsia under intermittent schedules of pellet delivery

Lashley and Rosellini (1980) have recently suggested that schedule-induced polydipsia (SIP) is determined by the occurrence of absolute periods within schedules of periodic food delivery which are associated with a low probability of food delivery, that is, CS− periods. To assess this hypothesis, SIP was examined in the present experiments under three schedules—fixed time, variable time, and random time (RT)—which differed in probability of occurrence and/or duration (Experiment 1), and under a range of RT schedules in which the CS− period was systematically varied by changing the interpellet interval (Experiment 2). In both experiments, the level and temporal distribution of SIP did not seem to be related to the absolute period associated with the absence of food. Instead, SIP was more systematically related to the average length of the interpellet interval and, therefore, to the average period associated with no food. It was suggested that drinking under intermittent schedules of pellet delivery, that is, SIP, is determined by an average CS− period and not by an absolute period associated with the unavailability of food.

THE ROLE OF CONTINGENCIES AND “PRINCIPLES OF BEHAVIORAL VARIATION” IN PIGEONS' PECKING

Staddon and Simmelhag's proposal that behavior is produced by "principles of behavioral variation" instead of contingencies of reinforcement was tested in two experiments. In the first experiment pigeons were exposed to either a fixed-interval schedule of response-contingent reinforcement, an autoshaping schedule of stimulus-contingent reinforcement, or a fixed-time schedule of noncontingent reinforcement. Pigeons exposed to contingent reinforcement came to peck more rapidly than those exposed to noncontingent reinforcement. Staddon and Simmelhag's "principles of behavioral variation" included the proposal that patterns (interim and terminal) were a function of momentary probability of reinforcement. In the second experiment pigeons were exposed to either a fixed-time or a random-time schedule of noncontingent reinforcement. Pecking showed a constant frequency of occurrence over postfood time on the random-time schedule. Most behavior showed patterns on the fixed-time schedule that differed in overall shape (i.e., interim versus terminal) from those shown on the random-time schedule. It was concluded that both the momentary probability of reinforcement and postfood time can affect patterning.

Modulation of schedule-induced polydipsia by Pavlovian conditioned states

It has previously been porposed that Random-Interval schedules fail to induce polydipsic drinking in rats because such schedules fail to provide gradients of reinforcement probability. In the present study, food-deprived rats received single pellet meals delivered on either a Fixed-Time or a Random-Time 120-sec schedule, with half of each group receiving signalled, and half unsignalled, pellet deliveries. Acquisition of polydipsia was retarded in animals exposed to the Random-Time Unsignalled condition. However, the imposition of a CS+ for pellet delivery on the identical Random-Time schedule resulted in levels of polydipsia comparable to those obtained in both Fixed-Time conditions. These results suggest that the establishment of a Pavlovian conditioned inhibitory signal, as well as local periods of low reinforcement probability, may be sufficient for the development of schedule-induced behaviors such as polydipsia.

Effects of electric stress on glucose metabolism, glucose-stimulated cyclic adenosine 3',5'-monophosphate accumulation and 45Ca++ efflux in isolated pancreatic islets from rats fed with a high fat diet.

The effects of the electric stress on glucose oxidation, cyclic adenosine 3', 5'-monophosphate (AMP) accumulation and 45Ca++ efflux in response to glucose were studied in pancreatic islets isolated from rats fed on a control (C) or a high fat diet (F) for 12 weeks. The half of rats on each diet were subjected to electrical shocks in the random time schedule for 1 hr per day for the last 3 weeks of the feeding period (group C-S and F-S). The remaining rats were not given any shocks (group C-NS and F-NS). The rats in F-S group had the high levels of plasma epinephrine, dopamine and blood glucose. The basal content of cyclic AMP after 20 min of incubation with 2.8 mM glucose was decreased in islets from F-S group without affecting insulin release. After 20 min of incubation with 25 mM glucose, the cyclic AMP content in islets from F-S group, which was identical with that in F-NS group, was only 50% of that in C-S group. Insulin release in response to high glucose was significantly inhibited in islets from F-S group. In spite of a remarkable increase of cyclic AMP content in islets from C-S group, insulin release did not differ from that in C-NS group. Glucose (16.7 mM)-stimulated 45Ca++ efflux from the perfused islets was greatly inhibited by the high fat diet rather than by stress. The rate of glucose oxidation with 16.7 mM glucose was decreased in islets from F-S group. It is suggested that the decreased insulin release in response to glucose provoked by the combined effects of the feeding of a high fat diet and electric stress may be mediated by changes of the adenylate cyclase-cyclic AMP system on the plasma membrane of the B-cell or be related to changes in glucose metabolism in islets.