Session duration and the VI response function: Within-session prospective and retrospective effects

Two experiments examined the effects of session duration on responding during simple variable-interval schedules. In Experiment 1, rats were exposed to a series of simple variable-interval schedules differing in both session duration (10 min or 30 min) and scheduled reinforcement rate (7.5 s, 15 s, 30 s, and 480 s). The functions relating response rate to reinforcement rate were predominantly monotonic for the short (10-min) sessions but were predominantly bitonic for the long (30-min) sessions, when data from the entire session were considered. Examination of responding within sessions suggested that differences in the whole-session data were produced by a combination of prospective processes (i.e., processes based on events scheduled to occur later in the session) and retrospective processes (i.e., processes based on events that had already occurred in the session). In Experiment 2, rats were exposed to a modified discrimination procedure in which pellet flavor (standard or banana) predicted session duration (10 min or 30 min). All rats came to respond faster during the short (10-min) sessions than during the first 10 min of the long sessions. As in Experiment 1, the results seemed to reflect the simultaneous operation of both prospective and retrospective processes. The results shed light on the recent controversy over the form of the variable-interval response function by identifying one variable (session duration) and two types of processes (prospective and retrospective) that influence responding on these schedules.     

The behavioral economics of production.

In two experiments, thirsty rats licked an empty spout instrumentally for water delivered at a neighboring spout. Each such pair of spouts constituted a work station, and one, two, or three stations were available in the test enclosure. In 1-hr sessions, the rats worked alone or in the company of 1 or 2 other rats, and performed either five, 10, or 40 licks at the empty spout for each water delivery. The total number of empty-spout licks, summed across rats and stations, increased with the empty-lick requirement and, with some exceptions, the number of rats in the enclosure and the number of work stations available. A Cobb-Douglas production function, with instrumental responding as an output and the three independent variables as inputs, accounted for a significant percentage of the variance. Contrary to that function, output failed to increase with additional rats (or work stations) when the number of work stations (or rats) was relatively small.     

DRL interresponse-time distributions: quantification by peak deviation analysis.

Peak deviation analysis is a quantitative technique for characterizing interresponse-time distributions that result from training on differential-reinforcement-of-low-rate schedules of reinforcement. It compares each rat's obtained interresponse-time distribution to the corresponding negative exponential distribution that would have occurred if the rat had emitted the same number of responses randomly in time, at the same rate. The comparison of the obtained distributions with corresponding negative exponential distributions provides the basis for computing three standardized metrics (burst ratio, peak location, and peak area) that quantitatively characterize the profile of the obtained interresponse-time distributions. In Experiment 1 peak deviation analysis quantitatively described the difference between the interresponse-time distributions of rats trained on variable-interval 300-s and differential-reinforcement-of-low-rate 72-s schedules of reinforcement. In Experiment 2 peak deviation analysis differentiated between the effects of the psychomotor stimulant d-amphetamine, the anxiolytic compound chlordiazepoxide, and the antidepressant desipramine. The results suggest that peak deviation analysis of interresponse-time distributions may provide a useful behavioral assay system for characterizing the effects of drugs.     

SELECTIVE ASSOCIATIONS PRODUCED SOLELY WITH APPETITIVE CONTINGENCIES: THE STIMULUS-REINFORCER INTERACTION REVISITED

In studies reporting stimulus-reinforcer interactions in traditional conditioning paradigms, when a tone-light compound was associated with food the light gained stimulus control, but when the compound was paired with shock avoidance the tone gained control. However, the physical nature of the reinforcerrelated events (food vs. shock) presented in the presence of the tone-light compound was always confounded with the conditioned hedonic value of the compound's presence relative to its absence. When the compound was paired with shock, its presence was negative relative to its absence (which was shock-free). In contrast, when the compound was paired with food, its presence was positive relative to its absence (which was food-free). The present experiment dealt with this confounding effect by conditioning a tone-light compound to be positive or negative, relative to its absence, solely with food reinforcement. One group of rats received food for responding in the presence of the tone-light compound and no food in its absence. The other group also responded in the presence of the compound, but received food only in its absence. These rats were trained on a chained schedule in which responding in the presence of the tone-light compound produced a terminal link signaled by the absence of the compound; responding ceased in the terminal link because it delayed food delivery. In a test session to assess stimulus control by the elements of the compound, tone and light were presented separately under extinction conditions. Rats that had been exposed to a positive correlation between food and the compound emitted almost double the responses in the presence of the light as in the presence of the tone. In comparison, rats that had been exposed to a negative correlation emitted only two thirds as many responses in the presence of the light as in the presence of the tone. Because this selective association was produced using only food, it appears that the contingencies under which a reinforcer is presented, rather than (or as well as) its physical properties, can generate the selective associations previously attributed to “stimulus-reinforcer interactions.” This could mean that regardless of the class of reinforcer that ultimately maintains responding (appetitive or aversive), the contingency-generated hedonic value of the compound stimulus may influence the dominant modality of stimulus control.     

The relationship between feeding rate and patch choice.

Rats in a laboratory foraging simulation searched for sequential opportunities to feed in two patches that differed in the rate at which food pellets were delivered (controlled by fixed-interval schedules) and in the size of the pellets. The profitability of feeding in each patch was calculated in terms of time (grams per minute) and in terms of effort (grams per bar press). These values were the result of the imposed fixed interval, the size of the pellets, and the rate at which the rats pressed the bar in each condition. The rats ate more food and larger meals, but not more frequent meals, at the patch offering the higher rate of food consumption, calculated as grams per minute. The relative intake at any patch was a function of the relative rate of intake during meals at that patch compared to the other patch. Rats respond to explicit manipulations of feeding time in the same manner as they respond to manipulations of feeding effort.     

The effects of schedule history and the opportunity for adjunctive responding on behavior during a fixed-interval schedule of reinforcement.

The effects of schedule history and the availability of an adjunctive response (polydipsia) on fixed-interval schedule performance were investigated. Two rats first pressed levers under a schedule of food reinforcement with an interresponse time greater than 11 s, and 2 others responded under a fixed-ratio 40 schedule. All 4 were then exposed to a fixed-interval 15-s schedule. Water was continuously available under these conditions, but after responding became stable on the fixed-interval schedule, access was experimentally manipulated. With water freely available, subjects did not display characteristic fixed-interval response rates and patterns (i.e., scalloping or break-and-run). Instead, they exhibited predictable, stable patterns of behavior as a function of their schedule histories: Subjects with the interresponse-time history exhibited low response rates, and those with the fixed-ratio history exhibited high rates. Manipulating the amount of water available resulted in marked changes in response rates for rats with the interresponse-time history but not for those with the fixed-ratio history. The results illustrate the multiple causation of behavior by its previous and current schedules of reinforcement and other concurrent factors.     

Response specificity in animal timing.

The stimuli that control responding in the peak procedure were investigated by training rats, in separate sessions, to make two different responses for food reinforcement. During one type of session, lever pressing was normally reinforced 32 s after the onset of a light. During the other type of session, chain pulling was normally reinforced either 8 s after the onset of one auditory cue or 128 s after the onset of a different auditory cue. For both types of sessions, only the appropriate manipulandum was available, and 20% of the trials lasted 240 s and involved no response-contingent consequences. Rats were then tested with the auditory cues in the presence of the lever and the light in the presence of the chain. If the time of reinforcement associated with each stimulus was learned, response rates should peak at these times during transfer testing. However, if a specific response pattern was learned for each stimulus, little transfer should occur. The results did not clearly support either prediction, leading to the conclusion that both a representation of the time of reinforcement and the rat's own behavior may control responding in this situation.     

Body Weight Reduction by Water Deprivation and Schedule-Induced Phenomena

On of the most important factors in the generation of schedule induced polydipsia, and schedule induced self-injection of drugs is the prior reduction of the animals' body weight to 80% of their free-feeding weight by food deprivation. It is suggested that reductio of body weight to 80% by water deprivation should produce similar results. The series of experiments reported here showed that rats reduced to 80% body weight by water deprivation did not develop either schedule-induced polydipsia or schedule induced wheelrunning. The results thus suggest that body weight reduction may not be a critical condition in the development of schedule-induced phenonmena.     

The double-alternative, double-start experimental apparatus: A new procedure for measuring preference

A new experimental chamber is described that permits rats to demonstrate behavioral preference for one of two conditions by running towards a goal chamber by one of two routes that are correlated with the different conditions. In a preliminary study, rats chose a route correlated with relatively lower shock, demonstrating the sensitivity of the apparatus. We also report evidence using this device that, of 10 rats tested, all preferred unsignaled rather than signaled, inescapable, unavoidable shock.     

小剂量吗啡对大鼠活动性的影响

腹腔注射不同剂量吗啡,观察各组大鼠在给药后不同时间的活动性（ｌｏｃｏｍｏｔｏｒａｃｔｉｖｉｔｙ,ＬＡ）,连续给药８天,每天给药后９５ｍｉｎ内,每间隔１５ｍｉｎ,记录大鼠５ｍｉｎ内在限定空间中所走格数。结果表明：随吗啡给药剂量或次数增加,ＬＡ呈升高趋势;使大鼠ＬＡ明显兴夯的适宜低剂量为４ｍｇ／ｋｇ／ｄａｙ,该剂量下每天药后１５－２０ｍｉｎＬＡ为峰值,而且此时段ＬＡ逐日升高,至第８日出现下降趋势,此毕