Effects of a response-reinforcer relation on elicited pecking.

Three pigeons were exposed for 22 sessions to a variant of a multiple variable-time 1-min extinction reinforcement schedule in the presence of a white key. A 1.5-s stimulus change (red) preceded each 1-min component during which food was delivered and a 1.5-s stimulus change (green) preceded each extinction component. The variable-time 1-min schedule was then changed to a variable-interval 1-min schedule for several sessions and then returned to variable time 1-min. During the first exposure to noncontingent reinforcer delivery, two of the three birds pecked frequently during the 1.5-s red stimulus but not during the other components. The third bird did not keypeck. The addition of a response-reinforcer relation resulted in all three birds pecking during the red stimulus as well as during the white stimuli. Pecking rates were usually highest during red. Response rates during green remained low. The subsequent removal of the response contingency resulted in a decrease in responding during white, and for two of the three birds, a decrease in responding during the red stimulus. The results support an interpretation of signal key pecking in stimulus separation procedures as elicited key pecking controlled by the stimulus-reinforcer relation.

Control of responding during stimuli that precede transitions in reinforcement frequency.

Pigeons' responses were reinforced on a variant of a mixed variable-interval extinction schedule of reinforcement in which the transition to the higher reinforcement rate was signaled by a trace stimulus projected on the response key prior to the onset of the component correlated with food delivery. In the first of two experiments, the duration of the trace stimulus preceding the component correlated with food delivery was varied from 1.5 to 50.0 s and in the second experiment, the reinforcement frequency in the same component was varied from 10 to 60 reinforcers per hour. Pigeons pecked at the trace stimulus preceding the onset of the component correlated with food delivery even though responding was not reinforced in its presence and only one of the changes in reinforcement rate (i.e., from extinction to reinforcement) was signaled. The rate of pecking during the trace stimulus was a function of its duration but not of the reinforcement frequency in the following component. Higher rates generally occurred at the shorter trace-stimulus durations. Component responding following the offset of the trace stimulus was under discriminative control of the trace stimulus whether or not responding occurred in the presence of the trace stimulus.

Ethanol consumption of free feeding animals during restricted ethanol access.

The present experiments demonstrated that the within session patterns of ethanol consumption of animals given unrestricted access to both food and water can be controlled by altering the schedule of access to ethanol. The first experiment demonstrated that the number of ethanol responses emitted per bout was inversely related to the number of one hour access periods presented per session. In a second experiment, ethanol access was limited to only the dark period of a 12 hour light-dark cycle. Total daily ethanol responding was similar to that of animals that had access to ethanol 23 hours a day. Further restrictions on ethanol availability by restricting access to the last 20 minutes of each hour of the dark period, resulted in an increase in the number of responses emitted per bout.

Patterns of ethanol and water consumption as a function of restricted ethanol access and feeding condition.

Sixteen male albino rats were divided into two groups of eight animals and maintained at either their free-feeding or at 80% of their free-feeding weight. For four animals, access to 8% ethanol was unrestricted, for the remaining four, access was restricted to eight 20-min access periods per day. Mean amounts of ethanol consumed per bout were greater during restricted access than during unrestricted access for food-deprived animals but not for free-feeding animals. Total daily ethanol consumption was greatest when animals were food deprived and access to ethanol unrestricted. Total fluid consumption and the within session distribution of water and ethanol responding were affected by feeding condition. For food-deprived animals, the amount of water consumed per session remained relatively constant. The increase in ethanol consumption over sessions resulted in an increase in total fluid consumption. For the free-feeding animals, increases in ethanol consumption resulted in decreases in water consumption so that total fluid consumption remained constant. In addition, food-deprived animals consumed all their daily water intake at the beginning of each session when food was present. Free-feeding animals consumed water throughout the session.

Patterns of ethanol consumption as a function of the schedule of ethanol access.

The present experiment demonstrated that patterns of ethanol consumption can be controlled by altering the schedule of ethanol availability. Thirty-two male albino rats, maintained at 80% of their ad libitum weight, were first exposed to 10 base-line sessions in which access to either 8 or 32% ethanol was unrestricted. Each subject was then exposed to one of four restricted access schedules for 30 sessions. During each 23-hr session, the ethanol access period was held constant at 20 min while the time between ethanol access periods was either 70, 160, 340 or 700 min. After restricted access, all subjects were returned to unrestricted access for 10 sessions. Water was continually available throughout the experiment. When ethanol access periods occurred every 70 or 160 min, animals at both concentrations consumed more ethanol (grams per kilogram) than during the initial period of unrestricted access. When the time between ethanol access periods was 340 or 700 min, animals consumed an equal amount or half as much, respectively, as during unrestricted access. Analysis of responding revealed that the mean amount of ethanol consumed per bout was greater during restricted than during unrestricted access. The longer the time between access periods the greater the amount consumed per bout. Upon return to unrestricted access, total daily consumption increased, but the amount consumed per bout decreased to base-line levels.

Stimulus control of respondent and operant key pecking: A single key procedure.

Pigeons' responses to a uniformly illuminated response key were either reinforced on a variable-interval one-minute schedule of reinforcement or extinguished for one-minute periods. When 1.5 second signals were presented at the beginning of each component, so as to differentially predict reinforcement, the pigeons pecked at the signals, at rates higher than rates during the remainder of the component. When the brief signals were not differentially predictive of reinforcement, pecking in their presence decreased to near zero levels. Similar results were obtained with signals based upon colors and upon line orientations. Changes in rates of (unreinforced) pecking occurred during the signal whether pigeons responded differentially during the remainder of the component or not. Experiment II demonstrated that the presence of the signal correlated with extinction was not necessary for pecking to develop at the signal which preceded the component in which responding was intermittently reinforced. The experiments demonstrated a clear dissociation of respondent control from operant control of a response. In addition, operant behavior was shown to be relatively insensitive to differing rates of reinforcement, as compared to the sensitivity of respondent behavior to differing rates of reinforcement produced by the very same operant behavior.

Increasing the rate of ethanol consumption in food- and water-satiated rats.

The effects of food satiation, ethanol concentration, and the schedule of ethanol availability on the rate of ethanol consumption were investigated in rats. In Experiment 1 separate groups were exposed to 6.2 or 12.5% w/v ethanol and unlimited access to food. The food and ethanol were available concurrently for one to three hours daily. After approximately 15 sessions unlimited food was available whenever ethanol was not available. The rate of ethanol consumption was positively related to ethanol concentration and negatively related to duration of ethanol availability. In Experiment 2 similar procedures were followed, except rats had unlimited access to food throughout the experiment. The results were similar to Experiment 1. In Experiment 3 separate groups were exposed to 6.2 and 12.5% w/v ethanol for one hour every other day; unlimited food was available throughout the experiment. The results were similar to the one-hour availability groups in Experiments 1 and 2. In all experiments ethanol consumption rates increased to levels above baseline and above the usual ethanol metabolic rate found in rats. The results demonstrated new combinations of ethanol availability and non-availability durations that were sufficient to significantly increase the rate of ethanol consumption.

Time allocation in concurrent schedules: the effect of signalled reinforcement.

The responses of five pigeons were reinforced on concurrent variable-interval variable-interval reinforcement schedules in which changeover key responses changed the stimulus and reinforcement schedules associated with the food key. While the reinforcement availability in one component remained unchanged throughout the experiment, the reinforcement availability in the other component was, during several conditions, signalled by the onset of an additional discriminative stimulus. During unsignalled conditions, both the relative frequency of responding and the relative time spent in each component approximated the obtained relative reinforcement frequency in each component. The effect of signalling reinforcer availability in one component was to (1) reduce responding in the signalled component to near-zero levels, and (2) increase the relative time in the unsignalled component, without a corresponding increase in the obtained relative reinforcement frequency. The magnitude of the increase in relative time in the unsignalled component decreased as the overall frequency of reinforcement increased. This deviation in the matching relation between relative time and the obtained relative reinforcement frequency was eliminated if the overall reinforcement frequency was increased before the signal was introduced and then, without removing the signal, gradually reduced.

A molecular analysis of multiple schedule interactions: negative contrast.

The present experiments investigated the relationship between changes in the relative reinforced interresponse-time distributions and the occurrence of positive and negative contrast in multiple variable-interval-variable-interval and multiple variable-interval-extinction schedules of reinforcement. Experiment I demonstrated that changes in the interresponse-time distributions were consistently correlated with response-rate changes referred to as positive and negative contrast. Corresponding changes in the reinforced interresponse-time distributions suggested that negative contrast resulted as an inductive effect of selectively reinforcing long interresponse times in the altered component at the moment the baseline schedule was reintroduced. Experiment II demonstrated that the magnitude of the negative-contrast effect could be significantly decreased if the altered component schedule was modified in order to prevent the reinforcement of these interresponse times during the first few sessions of baseline recovery. The results supported a proposal that interresponse time-reinforcer relations may act as amplifiers or attenuators of negative contrast.

Signalled reinforcement and multiple schedules.

The responses of four pigeons were first reinforced in the presence of two different wave-lengths (green and red) on a two-ply multiple schedule with identical variable-interval 3-min schedules of reinforcement associated with each component. While the constant-component reinforcement schedule remained unchanged during the experiment, the schedule associated with the variable component was changed to (1) signalled variable time, (2) unsignalled variable time, or (3) signalled variable interval. The probability with which the availability of the reinforcer was signalled in the variable-interval schedules was either 0.5 or 1.0. Positive contrast occurred in both signalled variable-interval and variable-time schedules, but only when the availability of all the variable-component reinforcers was signalled. Signalling the availability of only 50% of the reinforcers in signalled variable-interval schedules resulted in negative induction. The present data suggest that positive behavioral contrast resulting from signalled reinforcer availability is due to the presence of an extinction-correlated stimulus.

Signalled reinforcement in differential-reinforcement-of-low rate schedules.

At several fixed and variable minimum reinforced interresponse times, a stimulus was added to differential-reinforcement-of-low-rate schedules to signal the availability or nonavailability of reinforcement. As the minimum reinforced interresponse time increased, the rate of unreinforced responding decreased. Changing from fixed to variable minimum interresponse time in the basic differential-reinforcement-of-low-rate schedule further decreased the rate of unreinforced responding. Both effects were to some degree reversible. For fixed minimum reinforced interresponse times of 30 sec or shorter, most unreinforced responses terminated interresponse times just short of that required for reinforcement. The minimum reinforced interresponse time and the number of short response latencies (