Presession Feeding Research Articles

Reward shifts in forced-choice and free-choice autoshaping with rats.

Successive negative contrast (SNC) involves a disruption of behavior when the paired reward is unexpectedly reduced from a large to a small amount, relative to a control always receiving the small amount. Five experiments with rats explored SNC in the Pavlovian autoshaping procedure in which a retractable lever is paired with the delivery of food pellets. In Experiment 1, a 12-to-2 pellet downshift either early in training (after 3 sessions) or late in training (after 20 sessions) yielded no significant evidence of SNC either in terms of lever pressing or goal entries. Experiment 2 showed that presession feeding (another form of reward devaluation) suppressed lever pressing in nonreinforced tests early in training. However, no statistical evidence of lever pressing suppression was found late in training. Presession feeding also suppressed lever pressing late in training if the test session included reinforcements. Experiment 3, using reward downshift, showed that adding a nontarget lever produced no statistical evidence of response suppression to the target lever during the downshift. Lever pressing to the target lever increased and goal entries tended to decrease after a 12-to-2 pellet downshift. Using a within-subject design and two target levers with distinct reward values (Experiment 4), reward downshift produced evidence of lever pressing enhancement in single-lever trials, but lever pressing suppression and a switch in preference to the unshifted lever in nonreinforced free-choice trials. Experiment 5 replicated these within-subject SNC effects, but found only modest evidence for a successive positive contrast effect in free-choice behavior. These results suggest that autoshaping in rats may induce response invigoration in forced-choice situations, but response suppression in free-choice situations. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Choice between delayed food and immediate oxycodone in rats

The choice to seek immediate drug effects instead of more meaningful but delayed rewards is a defining feature of addiction. To develop a rodent model of this behavior, we allowed rats to choose between immediate intravenous delivery of the prescription opioid oxycodone (50μg/kg) and delayed delivery of palatable food pellets. Rats preferred food at delays up to 30s, but they chose oxycodone and food equally at 60-s delay and preferred oxycodone over food at 120-s delay. Comparison of food-drug choice, food-only, and drug-only conditions indicated that food availability decreased drug intake, but drug availability increased food intake. In the food-only condition, food was effective as a reinforcer even when delayed by 120s. Pre-session feeding with chow slowed acquisition of food and drug self-administration, but did not affect choice. To establish procedures for testing potential anti-addiction medications, noncontingent pre-treatment with oxycodone or naltrexone (analogous to substitution and antagonist therapies, respectively) were tested on a baseline in which oxycodone was preferred over delayed food. Naltrexone pre-treatment decreased drug intake and increased food intake. Oxycodone pre-treatment decreased drug intake, but also produced extended periods with no food or drug responding. These findings show that the contingencies that induce preference for drugs over more meaningful but less immediate rewards in humans can be modeled in rodents, and they suggest that the model could be useful for assessing the therapeutic potential of treatments and exploring the underlying behavioral and neural mechanisms involved in addiction.

Contrafreeloading, reinforcement rate, and behavioral momentum

Contrafreeloading involves organisms working for food when an identical source of food is freely available. The present study assessed whether training reinforcement rates influenced contrafreeloading by arranging a within-subject and within-session design using pigeons. Across different alternating discriminative stimuli, variable-interval schedules arranged leaner (30 per hour) and richer (120 per hour) rates of food reinforcement. Responding decreased but persisted in the presence of free food during the session (i.e., contrafreeloading). Further, responding tended to be similar between components initially but greater persistence emerged in the richer component with additional exposure. With pre-session feeding, responding did not change systematically across test sessions and tended to be more persistent in the richer component. Greater persistence with greater training reinforcement rates is generally consistent with an influential theory of response persistence, behavioral momentum theory. However, the different patterns of responding across test sessions between pre- and within-session feeding reveals multiple behavioral processes involved in contrafreeloading that have yet to be fully understood. Behavioral momentum theory could provide a useful theoretical framework for understanding and quantifying the behavioral processes underlying contrafreeloading.

Experience with dynamic reinforcement rates decreases resistance to extinction.

The ability of organisms to detect reinforcer-rate changes in choice preparations is positively related to two factors: the magnitude of the change in rate and the frequency with which rates change. Gallistel (2012) suggested similar rate-detection processes are responsible for decreases in responding during operant extinction. Although effects of magnitude of change in reinforcer rate on resistance to extinction are well known (e.g., the partial-reinforcement-extinction effect), effects of frequency of changes in rate prior to extinction are unknown. Thus, the present experiments examined whether frequency of changes in baseline reinforcer rates impacts resistance to extinction. Pigeons pecked keys for variable-interval food under conditions where reinforcer rates were stable and where they changed within and between sessions. Overall reinforcer rates between conditions were controlled. In Experiment 1, resistance to extinction was lower following exposure to dynamic reinforcement schedules than to static schedules. Experiment 2 showed that resistance to presession feeding, a disruptor that should not involve change-detection processes, was unaffected by baseline-schedule dynamics. These findings are consistent with the suggestion that change detection contributes to extinction. We discuss implications of change-detection processes for extinction of simple and discriminated operant behavior and relate these processes to the behavioral-momentum based approach to understanding extinction.

Pavlovian conditioning enhances resistance to disruption of dogs performing an odor discrimination.

Domestic dogs are used to aid in the detection of a variety of substances such as narcotics and explosives. Under real-world detection situations there are many variables that may disrupt the dog's performance. Prior research on behavioral momentum theory suggests that higher rates of reinforcement produce greater resistance to disruption, and that this is heavily influenced by the stimulus-reinforcer relationship. The present study tests the Pavlovian interpretation of resistance to change using dogs engaged in an odor discrimination task. Dogs were trained on two odor discriminations that alternated every six trials akin to a multiple schedule in which the reinforcement probability for a correct response was always 1. Dogs then received several sessions of either odor Pavlovian conditioning to the S+ of one odor discrimination (Pavlovian group) or explicitly unpaired exposure to the S+ of one odor discrimination (Unpaired group). The remaining odor discrimination pair for each dog always remained an unexposed control. Resistance to disruption was assessed under presession feeding, a food-odor disruptor condition, and extinction, with baseline sessions intervening between disruption conditions. Equivalent baseline detection rates were observed across experimental groups and odorant pairs. Under disruption conditions, Pavlovian conditioning led to enhanced resistance to disruption of detection performance compared to the unexposed control odor discrimination. Unpaired odor conditioning did not influence resistance to disruption. These results suggest that changes in Pavlovian contingencies are sufficient to influence resistance to change.

Effects of inter-food interval on the variety effect in an instrumental food-seeking task. Clarifying the role of habituation

Food variety increases consumption and the rate of instrumental behavior that is reinforced by food in humans and animals. The present experiment investigated the relationship between the variety effect and habituation to food by testing the role of the interval between successive food presentations on responding in an operant food-seeking task. Habituation to food was expected at short, but not long, interfood intervals. The effects of variety on food's long-term reinforcing value were also tested. Four groups of rats were trained to lever-press on different random-interval (RI) schedules of reinforcement to earn 45-mg food pellets. Half the rats in each group received an unpredictable mix of grain and sucrose pellets, while the other half consistently received sucrose pellets. Response rate began at a high rate and then decreased within each 30-min session for groups that received short inter-pellet intervals (i.e., RI-3 s and RI-6 s reinforcement schedules) but not in groups that received longer inter-pellet intervals (i.e., RI-12 s and RI-24 s). A variety effect in the form of higher responding in the mix group than the sucrose-only group was also only evident at the shorter intervals. Habituation and variety effects were also most evident with the short intervals when we controlled for the number of reinforcers earned, suggesting that they were not merely due to rapid satiation. The variety effect also appeared quickly when groups trained with longer inter-pellet intervals (RI-12 s and RI-24 s) were transitioned to shorter intervals (RI-3 s and RI-6 s). There was no effect of variety on resistance to extinction or on resistance to the response-suppressing effects of pre-session feeding. The results more clearly link this version of the variety effect to the short-term effect of variety on food habituation.

Are preference and resistance to change convergent expressions of stimulus value?

Behavioral momentum theory asserts that preference and relative resistance to disruption depend on reinforcement rates and provide converging expressions of the conditioned value of discriminative stimuli. However, preference and resistance to disruption diverge when assessing preference during brief extinction probes. We expanded upon this opposing relation by arranging target stimuli signaling equal variable-interval schedules across components of a multiple schedule. We paired one target stimulus with a richer reinforced alternative and the other with a leaner alternative. Furthermore, we varied reinforcement rates for the paired alternatives to assess the effects of manipulating relative conditioned value on preference and resistance to disruption by presession feeding, intercomponent food, and extinction. We replicated the opposing relation between preference and resistance to disruption but varying reinforcement rates for the paired alternatives did not systematically affect preference or resistance to disruption beyond levels observed in our initial condition. Importantly, we found that only preference between the target stimuli was related to relative baseline response rates in the presence of those stimuli. These findings suggest that preference during extinction probes might reveal more about baseline response rates between concurrently available alternatives than relative conditioned value. Resistance to disruption, conversely, appears to better reflect conditioned value because it is less confounded with baseline response rates and is a function of all sources of reinforcement obtained in the presence of a stimulus context.

Differential reinforcement and resistance to change of divided-attention performance

Behavioral momentum theory provides a framework for understanding how conditions of reinforcement influence instrumental response strength under conditions of disruption (i.e., resistance to change). The present experiment examined resistance to change of divided-attention performance when different overall probabilities of reinforcement were arranged across two components of a multiple schedule. Pigeons responded in a delayed-matching-to-sample procedure with compound samples (color + line orientation) and element comparisons (two colors or two line orientations). Reinforcement ratios of 1:9, 1:1, and 9:1 for accurate matches on the two types of comparison trials were examined across conditions using reinforcement probabilities (color/lines) of .9/.1, .5/.5, and .1/.9 in the rich component and .18/.02, .1/.1, and .02/.18 in the lean component. Relative accuracy with color and line comparisons was an orderly function of relative reinforcement, but this relation did not depend on the overall rate of reinforcement between components. The resistance to change of divided-attention performance was greater for both trial types in the rich component with presession feeding and extinction, but not with decreases in sample duration. These findings suggest promise for the applicability of quantitative models of operant behavior to divided-attention performance, but they highlight the need to further explore conditions impacting the resistance to change of attending.

TEMPORAL CONTEXT, PREFERENCE, AND RESISTANCE TO CHANGE

According to behavioral momentum theory, preference and relative resistance to change in concurrent-chains schedules are correlated and reflect the relative conditioned value of discriminative stimuli. In the present study, we explore the generality of this relation by manipulating the temporal context within a concurrent-chains procedure through changes in the duration of the initial links. Consistent with previous findings, preference for a richer terminal link was less extreme with longer initial links across three experiments with pigeons. In Experiment 1, relative resistance to change and preference were related inversely when responding was disrupted with response-independent food presentations during initial links, replicating a previous finding with rats. However, more food was presented with longer initial links, confounding the disrupter and initial-link duration. In Experiment 2, presession feeding was used instead and eliminated the negative relation between relative resistance to change and preference, but relative resistance to change was not sensitive to relative terminal-link reinforcement rates. In Experiment 3, with more extreme relative terminal-link reinforcement rates, increasing initial-link duration similarly decreased preference and relative resistance to change for the richer terminal link. Thus, when conditions of disruption are equal and assessed under the appropriate reinforcement conditions, changes in temporal context impact relative resistance to change and preference similarly.

Sessiones de pre-alimentación aumentan los efectos de la cocaina sobre la conducta de presionar una palanca en ratas reforzada con comida

Lever pressing of rats deprived to 80% of their free-feeding weights was maintained on a fiexed-ratio 30 schedule of food reinforcement. The experimental session was composed of five, 3- min periods in which the houselight was on and the fixed-ratio 30 shcedule was in effect alternating with fice, 6-min black-out periods during which responding was not reinforced. When rares of pressing during lights-on periods were stable, cocaine was admnistered at the start of each blackout period. Cumulative doses reveived were 3.0, 5.6 10.0, 17.0 and 30.0 mg/kg. In the other test sessions, saline was administered ah the start of each backout. The effects of saline and cocaine administration were determined under two deprivation conditions. In one, rats were fed either 10.0 g or 5.0 g of rat chow 2 hrs prior to the session. In the other, rats were hadled identically but received no food, When no pre-session feeding ocurred, saline administration slightly increased response rates of some rats. Cocaine generaly produced dose-dependent decreases in rates abd did so at lower doses when rats had been pre-fed compared to when they had not. Thus, pre-session feeding made response rates more sensitive to the rate-reducing effects of cocaine.

RESISTANCE TO CHANGE AND FREQUENCY OF RESPONSE‐DEPENDENT STIMULI UNCORRELATED WITH REINFORCEMENT

Stimuli uncorrelated with reinforcement have been shown to enhance response rates and resistance to disruption; however, the effects of different rates of stimulus presentations have not been assessed. In two experiments, we assessed the effects of adding different rates of response-dependent brief stimuli uncorrelated with primary reinforcement on relative response rates and resistance to change. In both experiments, pigeons responded on variable-interval 60-s schedules of food reinforcement in two components of a multiple schedule, and brief response-dependent keylight-color changes were added to one or both components. Although relative response rates were not systematically affected in either experiment, relative resistance to presession feeding and extinction were. In Experiment 1, adding stimuli on a variable-interval schedule to one component of a multiple schedule either at a low rate (1 per min) for one group or at a high rate (4 per min) for another group similarly increased resistance to disruption in the components with added stimuli. When high and low rates of stimuli were presented across components (i.e., within subjects) in Experiment 2, however, relative resistance to disruption was greater in the component presenting stimuli at a lower rate. These results suggest that stimuli uncorrelated with food reinforcement do not strengthen responding in the same way as primary reinforcers.

Disruption of temporal discrimination and the choose-short effect

The present experiment examined the effects of several disruptors on temporal discrimination. Pigeons responded under a 0-delay symbolic matching-to-sample procedure in which responses to one key color were reinforced following the presentation of four shorter sample durations, and responses to another key color were reinforced following the presentation of four longer sample durations. Steady-state performance was disrupted by presession feeding, intertrial-interval food, visual distraction, and extinction. All disruptors decreased temporal-discrimination accuracy. Analyses of the fitted cumulative normal functions indicated that decreases in accuracy were produced mainly by decreases in overall stimulus control rather than specific effects on timing. In addition, all disruptors selectively decreased accuracy on long-sample trials--a choose-short effect. This effect is interpreted in terms of decreased attention to the samples under disruption. Current theories of the choose-short effect do not appear to easily account for these results.

RESISTANCE TO CHANGE OF RESPONDING MAINTAINED BY UNSIGNALED DELAYS TO REINFORCEMENT: A RESPONSE‐BOUT ANALYSIS

Previous experiments have shown that unsignaled delayed reinforcement decreases response rates and resistance to change. However, the effects of different delays to reinforcement on underlying response structure have not been investigated in conjunction with tests of resistance to change. In the present experiment, pigeons responded on a three-component multiple variable-interval schedule for food presented immediately, following brief (0.5 s), or following long (3 s) unsignaled delays of reinforcement. Baseline response rates were lowest in the component with the longest delay; they were about equal with immediate and briefly delayed reinforcers. Resistance to disruption by presession feeding, response-independent food during the intercomponent interval, and extinction was slightly but consistently lower as delays increased. Because log survivor functions of interresponse times (IRTs) deviated from simple modes of bout initiations and within-bout responding, an IRT-cutoff method was used to examine underlying response structure. These analyses suggested that baseline rates of initiating bouts of responding decreased as scheduled delays increased, and within-bout response rates tended to be lower in the component with immediate reinforcers. The number of responses per bout was not reliably affected by reinforcer delay, but tended to be highest with brief delays when total response rates were higher in that component. Consistent with previous findings, resistance to change of overall response rate was highly correlated with resistance to change of bout-initiation rates but not with within-bout responding. These results suggest that unsignaled delays to reinforcement affect resistance to change through changes in the probability of initiating a response bout rather than through changes in the underlying response structure.

RATE OF CONDITIONED REINFORCEMENT AFFECTS OBSERVING RATE BUT NOT RESISTANCE TO CHANGE

The effects of rate of conditioned reinforcement on the resistance to change of operant behavior have not been examined. In addition, the effects of rate of conditioned reinforcement on the rate of observing have not been adequately examined. In two experiments, a multiple schedule of observing-response procedures was used to examine the effects of rate of conditioned reinforcement on observing rates and resistance to change. In a rich component, observing responses produced a higher frequency of stimuli correlated with alternating periods of random-interval schedule primary reinforcement or extinction. In a lean component, observing responses produced similar schedule-correlated stimuli but at a lower frequency. The rate of primary reinforcement in both components was the same. In Experiment 1, a 4:1 ratio of stimulus production was arranged by the rich and lean components. In Experiment 2, the ratio of stimulus production rates was increased to 6:1. In both experiments, observing rates were higher in the rich component than in the lean component. Disruptions in observing produced by presession feeding, extinction of observing responses, and response-independent food deliveries during intercomponent intervals usually were similar in the rich and lean components. When differences in resistance to change did occur, observing tended to be more resistant to change in the lean component. If resistance to change is accepted as a more appropriate measure of response strength than absolute response rates, then the present results provide no evidence that higher rates of stimuli generally considered to function as conditioned reinforcers engender greater response strength.

The resistance to change of observing.

Observing responses produce contact with discriminative stimuli and have been considered analogous to attending. Many studies have examined the effects of reinforcement rate on the resistance to change of simple operant behavior, but nothing is known about the resistance to change of observing. Two experiments examined the effects of primary reinforcement rate on the resistance to change of observing behavior of pigeons. In Experiment 1, a multiple schedule of observing-response procedures was arranged. In a rich component, observing responses produced stimuli correlated with a high rate of random-interval (RI) reinforcement or extinction. In a lean component, observing responses produced stimuli correlated with a lower rate of RI reinforcement or extinction. In both components, observing responses produced the multiple-schedule stimuli on a fixed-interval 0.75-s schedule. In Experiment 2, a similar procedure was used, but observing in the rich and lean components produced schedule-correlated stimuli on an RI 15-s schedule. Observing in the rich component occurred at a higher rate and was more resistant to disruptions produced by presession feeding and response-independent food deliveries during intercomponent intervals. Despite more frequent observing during unsignaled periods of extinction than unsignaled periods of RI reinforcement, observing during extinction periods was less resistant to change. In addition, replicating the usual result, responding on the food key was generally more resistant to change in the presence of stimuli associated with higher reinforcement rates. These results suggest that quantitative descriptions of resistance to change derived with simple food-maintained responding may be applicable to observing, and perhaps by extension, to attending.

Within-Session Decreases in Operant Responding as A Function of Pre-Session Feedings

The effect of supplemental feedings on pigeons’ within-session changes in operant key-pecking was investigated. In different conditions, the feeding was either Purina Pigeon Checkers or mixed grain. The feedings were delivered 1, 4, and 12 hr prior to an experimental session. Responding changed significantly and systematically within sessions for all conditions. During the 1- and 4-hr pre-session feeding phases, absolute rates of responding were more suppressed and within-session decreases in responding were steeper when the reinforcer and supplemental feed were both mixed grain than when they differed. During the 12-hr pre-feeding phase, responding was unaffected by whether the supplemental food was similar to or differed from the food within the session. The results of the present experiment are generally consistent with the idea that habituation to the reinforcer contributes to within-session decreases in operant responding (e.g., McSweeney & Roll, 1998).

WITHIN‐SESSION CHANGES IN THE VI RESPONSE FUNCTION: SEPARATING FOOD DENSITY FROM ELAPSED SESSION TIME

Previous studies examining the relationship between response rate and reinforcement rate on variable-interval schedules (the variable-interval response function) have confounded elapsed session time with within-session changes in food density. The present experiments attempted to manipulate these factors independently and thus isolate their effects on responding. In Experiment 1, 7 rats pressed a bar for food on a series of four variable-interval schedules (7.5 s, 15 s, 30 s, and 480 s). Elapsed session time was held constant while food density was manipulated via a presession feeding. Changes in food density altered the form of the variable-interval response function, independently of elapsed session time. In Experiment 2, 8 rats responded on the same series of variable-interval schedules as in Experiment 1, but food density was held constant and elapsed session time was manipulated via the use of timeout periods. The results revealed no evidence for an effect of elapsed session time independent of food density. The present results extend a recent analysis of the variable-interval response function by Dougan, Kuh, and Vink (1993) by identifying food density as an important factor determining the form of the function. The present results also help clarify the controversy over the correct empirical form of the variable-interval response function by further defining the variables responsible for differences in the form of that function.