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Schedule-induced drinking in humans: A potential factor in excessive alcohol use
Drug and Alcohol Dependence, 16 (1985) Elsevier Scientific Publishers Ireland Ltd.
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117-132
SCHEDULE-INDUCED DRINKING IN HUMANS: A POTENTIAL FACTOR IN EXCESSIVE ALCOHOL USE*
TERESA
F. DOYLE and HERMAN H. SAMSON**
Department Washington,
of Psychology and Alcoholism Seattle, WA 98195 (U.S.A.)
and Drug Abuse
Institute,
University
of
(Received April 24th, 1985)
SUMMARY
The timed delivery of monetary reinforcement by a computer-controlled slot machine altered the amount of fluid drunk adjunctively by human subjects. In separate experiments, subjects were allowed access to one of three fluids, water, non-alcoholic beer, or alcoholic beer, while receiving monetary reinforcement from the slot machine on one of two Fixed-Interval schedules (F130 s or FI90 s). The largest difference in intake between the two schedule conditions occurred when water was the fluid available, but a similar trend in consumption was observed in the other studies. Greater consumption occurred when reinforcement was presented on the FISO-s schedule, which was predicted from previous studies using animals. The possible interaction of schedule-induced drinking with other variables known to influence human alcohol consumption is discussed. Key words: Alcohol - Schedule-induced drinking - Humans
INTRODUCTION
Whether one views alcoholism as a biomedical disease, a behavior disorder or a breach of morality, it is a problem of excessive drinking. Many factors regulate all types of drinking, and while the hydration state of an individual can play a role, in most cases fluid ingestion by humans is due *These studies were supported in part by grants from the Alcoholism and Drug Abuse Institute of the University of Washington and the National Institute on Alcohol Abuse and Alcoholism (K02 AA00066). **Supported by a Research Scientist Development Award from the National Institute on Alcohol Abuse and Alcoholism (K02 AAOOO66). 0376-8716/85/$03.30 0 1985 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
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to non-homeostatic factors. When alcoholic beverages are consumed, drinking has little to do with body water regulation. Instead, psychological and pharmacological factors interact to control intake [ 11. Some of the factors which affect alcohol drinking include environmental setting [2], alcohol expectancy effects [3], prior drinking history [4] and alcohol dependence [4]. Of primary importance to an understanding of the problems related to alcohol consumption is the identification of factors resulting in excessive drinking. Based on studies using animals, adjunctive behaviors have been suggested as playing a role in excessive alcohol use [ 5,6]. ‘Adjunctive behaviors’ are behaviors that arise as a consequence of an intermittent schedule of reinforcement [ 7] . If a given schedule of reinforcement results in an increase of a non-contingently-reinforced behavior, then that schedule is labelled a ‘generator’ schedule and the increased, non-contingentlyreinforced behavior is termed adjunctive. The schedule of contingent reinforcement is critical to the generation of adjunctive behavior. In the initial demonstration of adjunctive behavior, rats were fed their daily food rations over 5 h as small pellets (45 mg) available every minute (FIGO-s schedule) and the animals consumed large amounts of water which was available non-contingently {8]. This excessive drinking only occurred when the daily food ration was delivered over a range of specified time intervals [ 91; very short or very long FI schedules failed to induce excessive water intake. For rats and monkeys, FI schedules of 90-120 s have been found to generate the maximum adjunctive drinking [lo]. This particular type of adjunctive behavior was called ‘schedule-induced polydipsia’, and has been intensively studied since its discovery [6]. The nature of an adjunctive behavior is not directly related to the nature of the reinforcement, nor is the occurrence of the adjunct contingent for delivery of the reinforcer [ 71. Yet adjunctive behaviors are reliably emitted by a variety of species [8,11-141. Schedule-induced polydipsia has been used to produce high daily ethanol intakes in rats [ 151. This drinking eventually leads to the development of physical dependence on ethanol as evidenced by severe abstinence symptomatology when the ethanol is withdrawn [ 51. Rats on this type of schedule typically consume between 10 and 13 g/kg of ethanol per day, maintaining high blood ethanol levels [ 5,151. Several studies of adjunctive behaviors have been done in humans ]16231. At least three investigations have demonstrated that normal humans will drink non-alcoholic beverages adjunctively, the subjects consuming more while under an intermittent schedule of reinforcement than they had when no schedule was in effect [l&20,23]. In those studies, drinking was not the only behavior monitored, as subjects were given the opportunity to display a wide variety of adjunctive behaviors; the occurrence of drinking, then, was simply noted as one of a variety of behaviors that occurred when an interval schedule of reinforcement was in effect. In the following experi-
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merits, the examination of adjunctive behavior will focus exclusively on adjunctive drinking, to determine whether the delivery of reinforcement at specified intervals can reliably result in increased fluid consumption by humans. EXP’ERIMENT
1
This study was performed with water as the available fluid to determine whether schedule-induction will occur with a fluid having little reinforcing properties of its own in fluid-sated individuals. Method Subjects. Forty-six subjects (26 males and 20 females) from introductory psychology courses at the University of Washington participated in the study. Subjects received course credit for participating and were recruited through the Department of Psychology Human Subject Pool. Apparatus and materials. An Apple II+ equipped with a programmable real-time clock was used. Computer output was displayed on a Zenith 13 inch color monitor. During the playing session, a graphic representation of a slot machine was shown with a message below reading ‘Earnings = $X.Xx.’ Activation of hand-held controls (which required both hands for operation) resulted in the three slots on the slot machine picture rotating for approximately 3 s, stopping one at a time to display an apparently random result. The computer was programmed to display a winning result only after a certain amount of time had elapsed (Fixed Interval reinforcement schedules). If the time interval for reinforcement had elapsed prior to operation, a winning combination would appear and the subject’s eamings would be increased. Winning results were controlled by a repeating serial sequence of nine different winning combinations. The amount of the increase in earnings was variable, depending upon the winning combination presented and the schedule condition to which the subjects had been assigned, but average earnings per minute were equated for both schedule conditions. Losing combinations were a serial progression through 15 sequences, and for each losing play, $0.05 was deducted from the subject’s earnings. Responses in time and reinforcement delivery were recorded and saved on disk at the end of the session for later analysis. Three types of commercially available low-sodium crackers were used in the experiment: ‘Wheat Thins’ and ‘Triscuit’ (low salt varieties) (Nabisco Brands, East Hanover, NJ) and ‘Krispy’ crackers with unsalted tops (Sunshine Biscuits, Inc., New York, NY). All were purchased locally. Procedure During the game-playing portion of the experiment, subjects were in front of the color video screen and given a hand-held control unit. jects were given explicit instructions about the time element involved ‘pay-off’ from the slot machine, but were not told how long the time
seated Subwith interval
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was between reinforcements. They were not allowed to use watches or any other timing device to estimate the time interval; however, any other strategy (such as counting to themselves) was allowed. The computer was out of sight, but the subjects were told that the game was computer-controlled. A play of the slot machine occurred when the subject responded using the hand-held control unit. Reinforcements were delivered on one of two FI schedules. Half the subjects were reinforced on a FI30-s schedule and the other half were reinforced on a FISO-s schedule. To equate reinforcements earned during the 30-min playing period, the FI90 reinforcements were three times the size of those delivered in the F130 condition. Each subject began play with $2.50. Every response cost the subject $0.05, which was deducted from the total shown on the video screen. In the event that a subject, due to bad plays of the machine, lost all the money with which he or she had started, the subject was not allowed to ‘go into the hole’, but was allowed to continue playing. It was found in pilot work that allowing subjects to accrue debt further encouraged random responding. Reinforcements were added to the dollar amount shown on the screen. At the end of the experiment, the subjects were paid the amount shown on the screen. In pilot work it was demonstrated that the schedule of reinforcement affected the fluid intake of those subjects who spontaneously initiated drinking while playing the game. However, a majority of the pilot subjects failed to drink at all. Therefore, to initiate drinking, a cracker-tasting task was instituted as a primer for drinking. Subjects were told that the purpose of the experiment was to examine the effect of elapsed time on perceived taste. They were given three cracker types and asked to rate them on spiciness, saltiness and overall taste. During the cracker rating, subjects were required to consume 30 ml of water, sipping between each cracker type. Subjects were told that the drinking was required to wash the taste from their mouths in order to obtain a more objective rating. Following the rating task, the subjects had a 30-min period playing the slot machine game. They were told that the game would act as a distractor between two taste tests. The subjects were instructed in the operation of the game and informed that they could win up to $6.00 if they concentrated on playing. During game playing, a paper cup and a decanter of water were placed beside the subject. Before leaving the room for the duration of the game, the investigator filled the cup and told the subject that if he or she wanted to drink while playing, that was all right. At the start of the experiment, a measured 1000 ml of water was placed in the decanter and the fluid remaining at the end of the experiment (including that remaining in the drinking cup) was used as the measure of ingestion. Results Of the 46 subjects run in the experiment, 22 were excluded from the analysis: six because they did not drink any water during game-playing
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and 16 because they apparently failed to understand the instructions and responded in a non-schedule control pattern. Most of the latter group were not native English speakers. As can be seen in Fig. 1, subjects who understood the instructions successfully approximated the interval between reinforcements and made responses suggestive of FI responding. Subjects who did not understand the instructions responded almost continually (Fig. l), and though they received the same number of reinforcements as subjects whose responding was schedule-controlled, earned little or no money because of the deductions of the $0.05 for each response. While the excluded subjects are of interest to the study of human operant behavior, their failure to exhibit schedule-controlled responding was considered sufficient reason for their exclusion from data analysis. Of the 24 subjects who both drank and demonstrated schedule-related responding, 12 were tested on a F130-s reinforcement schedule and the remaining 12 were tested on a FISO-s reinforcement schedule. A significant difference in amount drunk during the 30-min game-playing was found between the two schedules (t(1,23) = 2.56; P < 0.05). Individual consumption data are presented in Fig. 2. In the FI90 condition, an average of 285 ml was consumed, while in the F130 condition, an average of 175 ml was consumed. The subjects in the F130 schedule condition earned an average of $4.22, while subjects in the FI90 condition earned $5.05 on the average. This difference was not statistically significant.
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Fig. 1. Representative cumulative response records for schedule-controlled and scheduleindependent responding. Axis scale indicates 10 min/unit X-axis, 65 responses/unit Y-axis.
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Fig. 2. Individual consumption data for each schedule condition of water experiment. Subjects’ numbers alongside individual data points (circles). Mean consumption for each schedule condition (stars t /- S.E.M.).
Discussion
The results of the above experiment indicate that, as in animal experiments, a FISO-s schedule of reinforcement induces greater fluid intake than the F130-s schedule. While the results do not demonstrate that fluid consumption was excessive, schedule-induced polydipsia in animals is observed usually after sessions lasting 3-5 h [lo] ; perhaps, if the subjects had had 3-5 h of scheduled reinforcement, they too would have exhibited polydipsia. Regardless, obtaining increased drinking within the single 30-min session suggests that the interval of the delivery of reinforcement can alter human fluid ingestion. To determine whether the schedule-induction effect is observed when subjects believe they are consuming an alcoholic beverage, Expt. 2 was performed. The same game and reinforcement schedules were employed, but a different rating task was used to initiate drinking.
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Method Subjects. Thirty-two subjects (19 males and 13 females) participated in the study. They were recruited through advertising in the campus newspaper. Subjects were paid $5.00 (in addition to their winnings on the slot machine) for participating. All subjects were at least 21 years of age. Apparatus and materials. The game-playing apparatus of Expt. 1 was used in this study. A commercial non-alcoholic beer (‘Near Beer’, Goetz original pale, Pearl Brewing Co., San Antonio, TX) was the fluid available for consumption. Alcohol content of less than 0.5% by volume was specified by the manufacturer. Pilot testing determined that consumption of 1065 ml of Near Beer (the entire amount available to subjects) in 30 min resulted in no measurable breath alcohol. Procedure Identical game playing instructions and schedules as in Expt. 1 were employed. The subjects were told they would be asked to rate several brands of beer and that the purpose of the experiment was to determine how their perceptions of the beers changed over a period of time. Only a single type of non-alcoholic beer was actually used in the study. This deception was employed to avoid both direct ethanol effects on gameplaying and any effect poor taste of the non-alcoholic beer may have had on drinking following tasting. Upon entering the experiment, the subjects were given the beer-tasting task. Three-shot glasses (approx. 30 ml each), supposedly containing different beers, were ingested and rated in a manner similar to that used in the cracker-tasting task. Subjects were asked to compare two of the beers to another designated the ‘standard’. As in Expt. 1, the subjects were then left alone for 30 min to play the slot machine game, and told that it was all right to drink the standard beer while playing. Results Of the 32 subjects run in the study, four were excluded from the data analysis for the following reasons: two failed to consume any fluid at all during game-playing and two did not understand the instructions. The data from 15 subjects in the FI90 condition and 13 in the F130 condition were used in the analysis. During debriefing, all subjects stated that they thought they had been drinking alcoholic beer. The subjects in the FI90 condition drank more during the 30-min session than those in the F130 condition, but this difference was not statistically significant. Subjects in the FI90 condition drank on the average 364 ml while subjects in the F130 condition had an average intake of 306 ml. Individual subject consumption data is presented in Fig. 3. Subjects in the F130 condition won an average of $4.20, while subjects in the FI90 condition averaged $5.09. This difference in earnings was also not statistically significant.
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Discussion As in Expt. 1, an increase in the amount ingested was found for the schedule condition (FI90 s) which has been shown in animals to result in polydipsia, though the difference in consumption between the two groups was smaller and not statistically significant. When absolute consumption levels of the subjects from both Expt. 1 and 2 are compared, the subjects in both schedule conditions of Expt. 2 have a greater intake than their counterparts in Expt. 1, However, a post hoc analysis found no statistically significant difference in the intakes between the two groups. Though the difference in intakes between the two experiments was not significant, the data do suggest that, in addition to the schedule of reinforcement, the subjects’ consumption in the ‘told alcohol’ condition may have been influenced by alcohol expectancy effects [ 31. This was further implicated by the two subjects who drank more than 800 ml of ‘Near Beer’, suggesting that their consumption was governed by factors in addition to those experimentally manipulated. By comparison, the subject who consumed most water in Expt. 1 drank 430 ml. Since the subjects in Expt. 2
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did not actually receive alcohol, the experience of the pharmacological effects of alcohol could not have influenced their consumption. Virtually all of the subjects in Expt. 2 made comments regarding the unpleasant taste of the beers during the tasting task. Their poor ratings of the beers did not, however, keep most subjects from drinking during the game-playing session. To examine the influence of expectancies of alcohol effects on consumption, Expt. 3 was performed with the subjects’ knowledge that they were consuming non-alcoholic beer. EXPERIMENT3
Method Subjects. Twenty subjects (13 males and 7 females) from introductory psychology courses at the University of Washington participated in the study. The subjects were recruited from the Department of Psychology Human Subject Pool and received class credit for participating. Apparatus and materials. The same slot machine apparatus as in Expts. 1 and 2 was used in this study. The fluids consumed in Expt. 3 were three types of commercially available non-alcoholic beer. In addition to Goetz ‘Near Beer’ (detailed in Expt. 2), the study used ‘Kingsbury Brew’, (G. Heileman Brewing Co., Seattle, WA) and ‘Birell Brewers Gold’, (Swiss Gold A.G., Tumwater, WA). All three contain less than 0.5% alcohol by volume according to the manufacturers, and pilot testing determined that consumption of the entire amount available to subjects in 30 min resulted in no measurable breath alcohol. Procedure The procedure followed in Expt. 3 was exactly that of Expt. 2 with two exceptions: the subjects were told that the beers were non-alcoholic and the subjects actually consumed three different types of non-alcoholic beer during the taste-rating task. The standard used in this study was Goetz ‘Near Beer’, which was available during game-playing as in Expt. 2. Results Only 5 of the original 20 subjects were considered suitable for inclusion in the analysis of the data. Of those who were excluded, 11 did not drink any ‘Near Beer’ during the game-playing session, three operated the machine continuously and never came under schedule control, and one did not speak English well enough to understand the instructions. Two subjects in the FI90 condition and three in the F130 condition remained. Mean fluid intakes for the F130 and FI90 conditions were 238 ml and 302 ml, respectively. There was no statistically significant difference between the groups. Though the results of the present study are not statistically significant, the trend of higher consumption by the FI90 group is still evident.
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Discussion Most subjects in this experiment volunteered that the taste of the nonalcoholic beers was unpleasant and gave that as the reason they chose not to drink any more than what was required for the taste-rating task. More than half the subjects in this study did not drink during the game-playing session. The subjects in Expt. 2 were asked to consume exactly the same beverage, and yet only 2 of 32 subjects in that study refused to drink more than what was required for the taste rating. This difference in the initiation of drinking could be attributed to the expectancies associated with drinking alcohol independent of taste, as both groups of subjects rated the taste of the beers as poor. To determine whether increased drinking due to schedule-induction effects would occur when subjects were actually drinking alcoholic beer, Expt. 4 was performed. EXPERIMENT
4
Method Subjects. Twenty-three subjects (20 males and 3 females) participated. They were recruited through advertising in the campus newspaper. All were at least 21 years of age. Subjects were paid $5.00 (in addition to their winnings on the slot machine) for participating. Apparatus and materials. The game playing apparatus used in the previous studies was also employed in Expt. 4. A commercially available generic beer (General Brewing Company, Vancouver, WA, 98660) was the fluid used for tasting and game-playing. Alcohol content of 3.6% by volume is specified by the manufacturer. Procedure Prior to their participation in the experiment, all subjects were administered a medical screening and drinking habits questionnaire to ensure that alcohol ingestion was not contraindicated. Individuals who reported ever having been concerned about the amount of their alcohol drinking, or who had ever been told by a professional that they are or might be alcoholic were excluded from participation. The procedures employed in this study were exactly those of Expt. 2, with the addition of breath alcohol determinations immediately prior to, and following the termination of, the experiment. Results The data of 17 subjects are included in the analysis. Three subjects were excluded because they operated the slot machine continuously and failed to come under schedule control, two subjects worked on homework while they played (and therefore engaged in behaviors which competed with drinking), and one subject did not drink during the playing session. Eight
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of the 17 subjects were in the FI90 condition and there were 9 in the F130 condition. The average intake for the FI90 and F130 conditions was 538 ml and 385 ml, respectively; this difference was not statistically significant. The fluid consumed by each subject is presented in Fig. 4. The average breath alcohol measured at the termination of the experiment was 2 mg%, and the two groups were not statistically different. There was no significant difference in earnings from the slot machine between the two schedule conditions. Discussion As in Expts. 2 and 3, the trend of greater consumption by the FI90 subjects was observed in Expt. 4, though the difference between schedule conditions was not statistically significant. An examination of the selfreported ‘typical’ drinking habits of the subjects, collected as part of the initial subject screening, provided evidence of a possible confound with schedule condition as an influence on consumption in the study. Three of the four greatest consumers in the study (subjects B8, B12 and B15; see Fig. 4) were also among the highest weekly drinkers included in the
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study. Since schedule-induced polydipsia could be considered to be an augmentation of typical drinking (as opposed to a drinking initiation procedure), it is possible that the drinking of these two subjects was not influenced by the schedule of reinforcement because they hadn’t yet drunk what they typically drink in the given time that the schedule was in effect. If the data of subjects B8, B12 and Bl5 are excluded, the difference between the FI90 and F130 schedule conditions is statistically significant (t(1,14) = 2.08, P = 0.05). There was a marked difference in the average amounts consumed in both schedule conditions of the beer study as compared to both the ‘Near Beer’ studies. A post hoc analysis of the taste ratings (Mann-Whitney U test) revealed a highly significant difference between the experiments: subjects drinking ‘Near Beer’ rated the taste of the non-alcoholic beers consistently lower than the beer groups rated the alcoholic beer (z = 3.90, P < 0.0001). Obviously, taste can be most influential in determining intake, and in the present studies, may have interacted with the influence of the reinforcement schedules. GENERAL
DISCUSSION
Taken together, the four experiments indicate that in humans, the scheduled delivery of a reinforcer can affect the amount of fluid ingested (Fig. 5). Although statistically significant results were obtained only in the water
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experiment, a similar trend in consumption, i.e. greater consumption by the FI90 groups as compared to the F130 conditions, was observed in all four experiments. The differences between schedule conditions in the studies utilizing non-alcoholic beer are slight, however. It is clear that the intermittent delivery of reinforcement is not the only factor influencing total consumption in the above experiments nor, most likely, in natural drinking settings. At least two other factors can be identified as operational in the above studies: taste of the beverage and the expectancies of alcohol effects resulting from past history with alcohol. The taste of the available fluid may have been influential in increasing mean consumption from the ‘Near Beer’ to the alcoholic beer experiments. As can be seen in Fig. 5, average intake was increased when subjects actually received real beer, even though subjects in the ‘told alcohol’ condition thought they were drinking real beer. The significantly lower ratings of the non-alcoholic beers as compared to the ratings of the alcoholic beer also provide evidence that taste factors served to suppress drinking in the told-alcohol/receive ‘Near Beer’ group. The influence of drinking history is also illustrated in Fig. 5. Omitting the told ‘Near Beer’ group (from which few inferences can be drawn due to the small number of subjects who drank) it can be seen that the difference in consumption between schedule conditions was greatest for the water group, followed by the group that received alcoholic beer, with the smallest difference observed in the told-alcohol/receive ‘Near Beer’ group. The schedule differences observed for the beer and told-alcohol conditions would be expected if recognition of some pharmacological cue of alcohol consumption contributes to ingestion. Since all of the subjects in the beer and told-alcohol conditions had, in their drinking histories, experienced alcohol’s pharmacological effects, it could be presumed that they knew roughly how much they needed to consume in order to experience the onset of some pharmacological cues. Though the subjects in the told-alcohol/receive ‘Near Beer’ condition all believed they were drinking alcohol, none of them could have experienced any of these pharmacological cues, despite an average consumption of approximately 10 oz of ‘beer’ in the 30 min of play. Research on the subjective detection of alcohol cues has shown that drinkers can recognize the onset of ethanol effects at blood alcohol levels as low as 1 or 2 mg%, comparable to those achieved in the beer experiment [24,25] and that detection can occur within 20 min [26]. Therefore, one hypothesis for the diminished influence of the reinforcement schedule on the drinking of the told-alcohol/receive ‘Near Beer’ group woud be that the lack of pharmacological cues maintained more drinking in the F130 condition, thus reducing any differences that schedule induction might have generated. In addition, the poor taste of the non-alcoholic beer probably suppressed total ingestion as compared to the beer group, thus further minimizing schedule effects. The alcoholic beer group had recorded breath ethanol levels which suggested that they probably experi-
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enced some pharmacological cues from drinking. So, in the beer group, alcohol cues may have helped to regulate drinking and allowed the schedule contingencies to influence intake as well. In an empirical assessment of unrestricted beer drinking by college students in groups, it was found that individuals typically drink at high rate when drinking begins, but after lo-15 min, drinking changes to a slower, moderate rate [ 271. Although these findings are the result of observations of individuals drinking in groups, they suggest that individuals may attempt to maintain certain intoxication levels following an initial high drinking rate. It is possible that the initial high drinking rate is maintained until a match between expectancy from past drinking history and physiological feedback cues occurs. At that point, drinking patterns are altered to a slower rate. It is hypothesized that it is during the latter phase of drinking regulation that factors such as schedule induction may exert a major control. The absolute total consumption at which the transition to the slowed rate occurs is highly variable across individuals [ 271. In the present study, it is possible that some of the beer drinking subjects (for example, the three highest drinking subjects) did not drink to the transition point in the time allotted for game-playing. It may be that until subjects reach a certain level of physiological feedback, their drinking is less controlled by the influence of other factors, such as schedule manipulations. Thus, subjects are probably more influenced by drinking history at the onset of drinking, but once they have achieved their typical level of initial intoxication cues, schedule induction may be influential in determining rate of further intake. When drinking regulation is not directly influenced by physiological feedback, schedule control should be more closely evidenced, as was the case in the water study. This remains, however, a testable hypothesis and a topic for future study. There appears to be no need to require the schedule delivery of a food source to induce adjunctive drinking in humans provided drinking has been initiated. As was observed in the above studies, the scheduled delivery of monetary reinforcement, usually considered to be unrelated to drinking, produced an increase in ingestion on the FI90 schedule. In other investigations of adjunctive behaviors in humans, the scheduling of such diverse reinforcers as maze-solving, visual access to an opponent’s play, money and candy have resulted in increases in equally diverse behaviors such as smoking, grooming, drinking and vocalization [ 18-20,221. This is not a result unique to the human. While early examinations of adjunctive behavior utilized intermittent food reinforcement to generate polydipsia in the rat, scheduled food reinforcement has subsequently been used to generate excessive aggressive behavior in monkeys and pigeons [ 28,291, pica in monkeys [ 301, air-licking in rats [ 311, and excessive wheel-running in rats [ 321. Thus, it is not the nature of the reinforcer that determines the nature of the excessive behavior. More likely, the excessive behavior demonstrated in a particular situation is dependent upon the options for behavior available in that environment and the relative reinforcing capacities of other available stimuli.
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The increased drinking in the present studies occurred at the same fixed interval schedule of reinforcement known to produce ethanol and water polydipsia in rats using food reinforcement [5,6]. Adjunctive behavior in animals is related to the reinforcement schedule in what Falk has described as a bitonic function; the amount of adjunctive behavior increases with the length of the interval between reinforcements up to a point, but diminishes when the interval is lengthened further [ 61. While the present studies demonstrated the expected difference in ingestion generated by the FI30- and FISO-s schedules, further experimentation is needed to determine whether adjunctive drinking is abolished at longer time intervals. This would be an important observation since, if some component of excessive drug use is a result of adjunctive behavior, then extending or shortening the interval between reinforcers generating that behavior could aid in alleviating the problem. It is evident that schedule-induction is not the only factor influencing consumption in alcohol-drinking situations; the above results indicate that there are a number of factors which interact to control the rate of ingestion and the amount consumed. It appears that schedule-induction is a weak determinant of alcohol consumption when experienced drinkers begin to drink. However, once drinking has progressed beyond its rapid initial rate, schedule-induction may become a factor in controlling the ensuing rate of consumption and may be a determinant of excessive consumption. It is conceivable that in many human situations, the frequency (or schedule) of social reinforcement could result in the induction of adjunctive behaviors, one of which could be increased alcohol consumption. Schedule-induction did affect the ingestion of fluid in the above studies. What remains to be demonstrated is that excessive alcohol consumption can be influenced by the schedule of reinforcement and that the scheduling of social interaction, for example, can act as a generator schedule. ACKNOWLEDGMENTS
The authors wish to thank J. Seather, M. Malakooti, and J. Samett for assistance in performing the studies. Special thanks to Drs. N.J. Kenney and M.R. Banaji for their critical reading of the manuscript. REFERENCES 1 B. Tabakoff, P.B. Sutker and C.L. Randall (Eds.), Medical and Social Aspects of Alcohol Abuse, Plenum Press, New York, 1983. 2 T.C. Harford and L.S. Gaines (Eds.), Social Drinking Contexts, U.S. Government Printing Office, NIAAA Research Monograph, No. 7, 1981. 3 G.A. Marlatt and D.J. Rohsenow, Cognitive processes in alcohol use: expectancy and the balanced placebo design, in: N.K. Mello (Ed.), Advances in Substance Abuse: Behavioral and Biological Research, Vol. 1, JAI Press, Greenwich, 1980, pp. 159201. 4 J.H. Mendelson and N.K. Mello. New Engl. J. Med., 301 (1979) 912. 5 J.L. Falk and H.H. Samson, Pharmacol. Rev., 27(4) (1976) 449.
132 6 J.L. Falk, The experimental generation of excessive behavior, in: S.J. Mule (Ed.), Behavior in Excess, The Free Press, New York, 1981, pp. 313-337. 7 J.L. Falk, Physiol. Behav., 6 (1971) 557. 8 J.L. Falk, Science, 133 (1961) 195. 9 J.L. Falk, J. Exp. Anal. Behav., 10 (1967) 199. 10 J.L. Falk, Ann. N.Y. Acad. Sci., 157 (1969) 569. 11 C.R. Schuster and J.H. Woods, Psychol. Rep., 19 (1966) 823. 12 M.E. Shanab and J.L. Peterson, Psychon. Sci., 15 (1969) 51. 13 T. Palfai, C.L. Kutscher and J.P. Symons, Physiol. Behav., 6 (1971) 461. 14 J.H. Porter, N.N. Sozer and T.P. Moeschl, Physiol. Behav., 21 (1978) 151. 15 J.L. Falk, H.H. Samson and G. Winger, Sci. 177 (1972) 811. 16 R. Karchanoff, R. Leveille, J.P. McLelland and M.J. Wayner, Physiol. Behav., 11 (1973) 395. 17 M. Wallace and G. Singer, Physiol. Behav., 17 (1976) 849. 18 J. Clarke et al., Physiol. Behav., 18 (1977) 159. 19 M. Wallace, A. Sanson and G. Singer, Physiol. Behav., 20 (1978) 203. 20 J.H. Fallon, J.D. Allen and J.A. Butler, Physiol. Behav., 22 (1979) 1089. 21 T.A. Looney and P.S. Cohen, Biobehav. Rev., 6 (1982) 15. 22 J.H. Porter, R.T. Brown and P.A. Goldsmith, Physiol. Behav., 28 (1982) 609. 23 R.G. Granger, J.H. Porter and N.L. Christoph, Physiol. Behav., 33 (1984) 153. 24 C. Bois and M. Vogel-Sprott, Q. J. Stud. Alcohol, 35 (1974) 86. 25 R.P. Benton, W.P. Banks and R.E. Vogler, J. Stud. Alcohol, 43(11) (1982) 1137. 26 L.O. Persson, L. Sjoberg and E. Svesson, Psychopharmacology, 68 (1980) 295. 27 H.H. Samson and K. Fromme, Drug Alcohol Depend. 14 (1984) 141. 28 R.K. Flory, J. Exp. Anal. Behav., 12 (1969) 825. 29 J. DeWeese, Exp. Anal. Behav., 27 (1977) 419. 30 J. Villareal, Schedule-induced pica. Paper presented to the Eastern Psychological Association, Boston, 1967. 31 J. Mendelson and J. Chillag, Physiol. Behav. 5 (1971) 535. 32 D. Levitsky and G. Collier, Physiol. Behav. 3 (1968) 571.
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SCHEDULE-INDUCED DRINKING IN HUMANS: A POTENTIAL FACTOR IN EXCESSIVE ALCOHOL USE*
TERESA
F. DOYLE and HERMAN H. SAMSON**
Department Washington,
of Psychology and Alcoholism Seattle, WA 98195 (U.S.A.)
and Drug Abuse
Institute,
University
of
(Received April 24th, 1985)
SUMMARY
The timed delivery of monetary reinforcement by a computer-controlled slot machine altered the amount of fluid drunk adjunctively by human subjects. In separate experiments, subjects were allowed access to one of three fluids, water, non-alcoholic beer, or alcoholic beer, while receiving monetary reinforcement from the slot machine on one of two Fixed-Interval schedules (F130 s or FI90 s). The largest difference in intake between the two schedule conditions occurred when water was the fluid available, but a similar trend in consumption was observed in the other studies. Greater consumption occurred when reinforcement was presented on the FISO-s schedule, which was predicted from previous studies using animals. The possible interaction of schedule-induced drinking with other variables known to influence human alcohol consumption is discussed. Key words: Alcohol - Schedule-induced drinking - Humans
INTRODUCTION
Whether one views alcoholism as a biomedical disease, a behavior disorder or a breach of morality, it is a problem of excessive drinking. Many factors regulate all types of drinking, and while the hydration state of an individual can play a role, in most cases fluid ingestion by humans is due *These studies were supported in part by grants from the Alcoholism and Drug Abuse Institute of the University of Washington and the National Institute on Alcohol Abuse and Alcoholism (K02 AA00066). **Supported by a Research Scientist Development Award from the National Institute on Alcohol Abuse and Alcoholism (K02 AAOOO66). 0376-8716/85/$03.30 0 1985 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
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to non-homeostatic factors. When alcoholic beverages are consumed, drinking has little to do with body water regulation. Instead, psychological and pharmacological factors interact to control intake [ 11. Some of the factors which affect alcohol drinking include environmental setting [2], alcohol expectancy effects [3], prior drinking history [4] and alcohol dependence [4]. Of primary importance to an understanding of the problems related to alcohol consumption is the identification of factors resulting in excessive drinking. Based on studies using animals, adjunctive behaviors have been suggested as playing a role in excessive alcohol use [ 5,6]. ‘Adjunctive behaviors’ are behaviors that arise as a consequence of an intermittent schedule of reinforcement [ 7] . If a given schedule of reinforcement results in an increase of a non-contingently-reinforced behavior, then that schedule is labelled a ‘generator’ schedule and the increased, non-contingentlyreinforced behavior is termed adjunctive. The schedule of contingent reinforcement is critical to the generation of adjunctive behavior. In the initial demonstration of adjunctive behavior, rats were fed their daily food rations over 5 h as small pellets (45 mg) available every minute (FIGO-s schedule) and the animals consumed large amounts of water which was available non-contingently {8]. This excessive drinking only occurred when the daily food ration was delivered over a range of specified time intervals [ 91; very short or very long FI schedules failed to induce excessive water intake. For rats and monkeys, FI schedules of 90-120 s have been found to generate the maximum adjunctive drinking [lo]. This particular type of adjunctive behavior was called ‘schedule-induced polydipsia’, and has been intensively studied since its discovery [6]. The nature of an adjunctive behavior is not directly related to the nature of the reinforcement, nor is the occurrence of the adjunct contingent for delivery of the reinforcer [ 71. Yet adjunctive behaviors are reliably emitted by a variety of species [8,11-141. Schedule-induced polydipsia has been used to produce high daily ethanol intakes in rats [ 151. This drinking eventually leads to the development of physical dependence on ethanol as evidenced by severe abstinence symptomatology when the ethanol is withdrawn [ 51. Rats on this type of schedule typically consume between 10 and 13 g/kg of ethanol per day, maintaining high blood ethanol levels [ 5,151. Several studies of adjunctive behaviors have been done in humans ]16231. At least three investigations have demonstrated that normal humans will drink non-alcoholic beverages adjunctively, the subjects consuming more while under an intermittent schedule of reinforcement than they had when no schedule was in effect [l&20,23]. In those studies, drinking was not the only behavior monitored, as subjects were given the opportunity to display a wide variety of adjunctive behaviors; the occurrence of drinking, then, was simply noted as one of a variety of behaviors that occurred when an interval schedule of reinforcement was in effect. In the following experi-
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merits, the examination of adjunctive behavior will focus exclusively on adjunctive drinking, to determine whether the delivery of reinforcement at specified intervals can reliably result in increased fluid consumption by humans. EXP’ERIMENT
1
This study was performed with water as the available fluid to determine whether schedule-induction will occur with a fluid having little reinforcing properties of its own in fluid-sated individuals. Method Subjects. Forty-six subjects (26 males and 20 females) from introductory psychology courses at the University of Washington participated in the study. Subjects received course credit for participating and were recruited through the Department of Psychology Human Subject Pool. Apparatus and materials. An Apple II+ equipped with a programmable real-time clock was used. Computer output was displayed on a Zenith 13 inch color monitor. During the playing session, a graphic representation of a slot machine was shown with a message below reading ‘Earnings = $X.Xx.’ Activation of hand-held controls (which required both hands for operation) resulted in the three slots on the slot machine picture rotating for approximately 3 s, stopping one at a time to display an apparently random result. The computer was programmed to display a winning result only after a certain amount of time had elapsed (Fixed Interval reinforcement schedules). If the time interval for reinforcement had elapsed prior to operation, a winning combination would appear and the subject’s eamings would be increased. Winning results were controlled by a repeating serial sequence of nine different winning combinations. The amount of the increase in earnings was variable, depending upon the winning combination presented and the schedule condition to which the subjects had been assigned, but average earnings per minute were equated for both schedule conditions. Losing combinations were a serial progression through 15 sequences, and for each losing play, $0.05 was deducted from the subject’s earnings. Responses in time and reinforcement delivery were recorded and saved on disk at the end of the session for later analysis. Three types of commercially available low-sodium crackers were used in the experiment: ‘Wheat Thins’ and ‘Triscuit’ (low salt varieties) (Nabisco Brands, East Hanover, NJ) and ‘Krispy’ crackers with unsalted tops (Sunshine Biscuits, Inc., New York, NY). All were purchased locally. Procedure During the game-playing portion of the experiment, subjects were in front of the color video screen and given a hand-held control unit. jects were given explicit instructions about the time element involved ‘pay-off’ from the slot machine, but were not told how long the time
seated Subwith interval
120
was between reinforcements. They were not allowed to use watches or any other timing device to estimate the time interval; however, any other strategy (such as counting to themselves) was allowed. The computer was out of sight, but the subjects were told that the game was computer-controlled. A play of the slot machine occurred when the subject responded using the hand-held control unit. Reinforcements were delivered on one of two FI schedules. Half the subjects were reinforced on a FI30-s schedule and the other half were reinforced on a FISO-s schedule. To equate reinforcements earned during the 30-min playing period, the FI90 reinforcements were three times the size of those delivered in the F130 condition. Each subject began play with $2.50. Every response cost the subject $0.05, which was deducted from the total shown on the video screen. In the event that a subject, due to bad plays of the machine, lost all the money with which he or she had started, the subject was not allowed to ‘go into the hole’, but was allowed to continue playing. It was found in pilot work that allowing subjects to accrue debt further encouraged random responding. Reinforcements were added to the dollar amount shown on the screen. At the end of the experiment, the subjects were paid the amount shown on the screen. In pilot work it was demonstrated that the schedule of reinforcement affected the fluid intake of those subjects who spontaneously initiated drinking while playing the game. However, a majority of the pilot subjects failed to drink at all. Therefore, to initiate drinking, a cracker-tasting task was instituted as a primer for drinking. Subjects were told that the purpose of the experiment was to examine the effect of elapsed time on perceived taste. They were given three cracker types and asked to rate them on spiciness, saltiness and overall taste. During the cracker rating, subjects were required to consume 30 ml of water, sipping between each cracker type. Subjects were told that the drinking was required to wash the taste from their mouths in order to obtain a more objective rating. Following the rating task, the subjects had a 30-min period playing the slot machine game. They were told that the game would act as a distractor between two taste tests. The subjects were instructed in the operation of the game and informed that they could win up to $6.00 if they concentrated on playing. During game playing, a paper cup and a decanter of water were placed beside the subject. Before leaving the room for the duration of the game, the investigator filled the cup and told the subject that if he or she wanted to drink while playing, that was all right. At the start of the experiment, a measured 1000 ml of water was placed in the decanter and the fluid remaining at the end of the experiment (including that remaining in the drinking cup) was used as the measure of ingestion. Results Of the 46 subjects run in the experiment, 22 were excluded from the analysis: six because they did not drink any water during game-playing
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and 16 because they apparently failed to understand the instructions and responded in a non-schedule control pattern. Most of the latter group were not native English speakers. As can be seen in Fig. 1, subjects who understood the instructions successfully approximated the interval between reinforcements and made responses suggestive of FI responding. Subjects who did not understand the instructions responded almost continually (Fig. l), and though they received the same number of reinforcements as subjects whose responding was schedule-controlled, earned little or no money because of the deductions of the $0.05 for each response. While the excluded subjects are of interest to the study of human operant behavior, their failure to exhibit schedule-controlled responding was considered sufficient reason for their exclusion from data analysis. Of the 24 subjects who both drank and demonstrated schedule-related responding, 12 were tested on a F130-s reinforcement schedule and the remaining 12 were tested on a FISO-s reinforcement schedule. A significant difference in amount drunk during the 30-min game-playing was found between the two schedules (t(1,23) = 2.56; P < 0.05). Individual consumption data are presented in Fig. 2. In the FI90 condition, an average of 285 ml was consumed, while in the F130 condition, an average of 175 ml was consumed. The subjects in the F130 schedule condition earned an average of $4.22, while subjects in the FI90 condition earned $5.05 on the average. This difference was not statistically significant.
/=I30
SCHEDULE-INDEPENDENT F130
F/90
RESPONDING F/90
Fig. 1. Representative cumulative response records for schedule-controlled and scheduleindependent responding. Axis scale indicates 10 min/unit X-axis, 65 responses/unit Y-axis.
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Discussion
The results of the above experiment indicate that, as in animal experiments, a FISO-s schedule of reinforcement induces greater fluid intake than the F130-s schedule. While the results do not demonstrate that fluid consumption was excessive, schedule-induced polydipsia in animals is observed usually after sessions lasting 3-5 h [lo] ; perhaps, if the subjects had had 3-5 h of scheduled reinforcement, they too would have exhibited polydipsia. Regardless, obtaining increased drinking within the single 30-min session suggests that the interval of the delivery of reinforcement can alter human fluid ingestion. To determine whether the schedule-induction effect is observed when subjects believe they are consuming an alcoholic beverage, Expt. 2 was performed. The same game and reinforcement schedules were employed, but a different rating task was used to initiate drinking.
123 EXPERIMENT 2
Method Subjects. Thirty-two subjects (19 males and 13 females) participated in the study. They were recruited through advertising in the campus newspaper. Subjects were paid $5.00 (in addition to their winnings on the slot machine) for participating. All subjects were at least 21 years of age. Apparatus and materials. The game-playing apparatus of Expt. 1 was used in this study. A commercial non-alcoholic beer (‘Near Beer’, Goetz original pale, Pearl Brewing Co., San Antonio, TX) was the fluid available for consumption. Alcohol content of less than 0.5% by volume was specified by the manufacturer. Pilot testing determined that consumption of 1065 ml of Near Beer (the entire amount available to subjects) in 30 min resulted in no measurable breath alcohol. Procedure Identical game playing instructions and schedules as in Expt. 1 were employed. The subjects were told they would be asked to rate several brands of beer and that the purpose of the experiment was to determine how their perceptions of the beers changed over a period of time. Only a single type of non-alcoholic beer was actually used in the study. This deception was employed to avoid both direct ethanol effects on gameplaying and any effect poor taste of the non-alcoholic beer may have had on drinking following tasting. Upon entering the experiment, the subjects were given the beer-tasting task. Three-shot glasses (approx. 30 ml each), supposedly containing different beers, were ingested and rated in a manner similar to that used in the cracker-tasting task. Subjects were asked to compare two of the beers to another designated the ‘standard’. As in Expt. 1, the subjects were then left alone for 30 min to play the slot machine game, and told that it was all right to drink the standard beer while playing. Results Of the 32 subjects run in the study, four were excluded from the data analysis for the following reasons: two failed to consume any fluid at all during game-playing and two did not understand the instructions. The data from 15 subjects in the FI90 condition and 13 in the F130 condition were used in the analysis. During debriefing, all subjects stated that they thought they had been drinking alcoholic beer. The subjects in the FI90 condition drank more during the 30-min session than those in the F130 condition, but this difference was not statistically significant. Subjects in the FI90 condition drank on the average 364 ml while subjects in the F130 condition had an average intake of 306 ml. Individual subject consumption data is presented in Fig. 3. Subjects in the F130 condition won an average of $4.20, while subjects in the FI90 condition averaged $5.09. This difference in earnings was also not statistically significant.
124
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Discussion As in Expt. 1, an increase in the amount ingested was found for the schedule condition (FI90 s) which has been shown in animals to result in polydipsia, though the difference in consumption between the two groups was smaller and not statistically significant. When absolute consumption levels of the subjects from both Expt. 1 and 2 are compared, the subjects in both schedule conditions of Expt. 2 have a greater intake than their counterparts in Expt. 1, However, a post hoc analysis found no statistically significant difference in the intakes between the two groups. Though the difference in intakes between the two experiments was not significant, the data do suggest that, in addition to the schedule of reinforcement, the subjects’ consumption in the ‘told alcohol’ condition may have been influenced by alcohol expectancy effects [ 31. This was further implicated by the two subjects who drank more than 800 ml of ‘Near Beer’, suggesting that their consumption was governed by factors in addition to those experimentally manipulated. By comparison, the subject who consumed most water in Expt. 1 drank 430 ml. Since the subjects in Expt. 2
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did not actually receive alcohol, the experience of the pharmacological effects of alcohol could not have influenced their consumption. Virtually all of the subjects in Expt. 2 made comments regarding the unpleasant taste of the beers during the tasting task. Their poor ratings of the beers did not, however, keep most subjects from drinking during the game-playing session. To examine the influence of expectancies of alcohol effects on consumption, Expt. 3 was performed with the subjects’ knowledge that they were consuming non-alcoholic beer. EXPERIMENT3
Method Subjects. Twenty subjects (13 males and 7 females) from introductory psychology courses at the University of Washington participated in the study. The subjects were recruited from the Department of Psychology Human Subject Pool and received class credit for participating. Apparatus and materials. The same slot machine apparatus as in Expts. 1 and 2 was used in this study. The fluids consumed in Expt. 3 were three types of commercially available non-alcoholic beer. In addition to Goetz ‘Near Beer’ (detailed in Expt. 2), the study used ‘Kingsbury Brew’, (G. Heileman Brewing Co., Seattle, WA) and ‘Birell Brewers Gold’, (Swiss Gold A.G., Tumwater, WA). All three contain less than 0.5% alcohol by volume according to the manufacturers, and pilot testing determined that consumption of the entire amount available to subjects in 30 min resulted in no measurable breath alcohol. Procedure The procedure followed in Expt. 3 was exactly that of Expt. 2 with two exceptions: the subjects were told that the beers were non-alcoholic and the subjects actually consumed three different types of non-alcoholic beer during the taste-rating task. The standard used in this study was Goetz ‘Near Beer’, which was available during game-playing as in Expt. 2. Results Only 5 of the original 20 subjects were considered suitable for inclusion in the analysis of the data. Of those who were excluded, 11 did not drink any ‘Near Beer’ during the game-playing session, three operated the machine continuously and never came under schedule control, and one did not speak English well enough to understand the instructions. Two subjects in the FI90 condition and three in the F130 condition remained. Mean fluid intakes for the F130 and FI90 conditions were 238 ml and 302 ml, respectively. There was no statistically significant difference between the groups. Though the results of the present study are not statistically significant, the trend of higher consumption by the FI90 group is still evident.
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Discussion Most subjects in this experiment volunteered that the taste of the nonalcoholic beers was unpleasant and gave that as the reason they chose not to drink any more than what was required for the taste-rating task. More than half the subjects in this study did not drink during the game-playing session. The subjects in Expt. 2 were asked to consume exactly the same beverage, and yet only 2 of 32 subjects in that study refused to drink more than what was required for the taste rating. This difference in the initiation of drinking could be attributed to the expectancies associated with drinking alcohol independent of taste, as both groups of subjects rated the taste of the beers as poor. To determine whether increased drinking due to schedule-induction effects would occur when subjects were actually drinking alcoholic beer, Expt. 4 was performed. EXPERIMENT
4
Method Subjects. Twenty-three subjects (20 males and 3 females) participated. They were recruited through advertising in the campus newspaper. All were at least 21 years of age. Subjects were paid $5.00 (in addition to their winnings on the slot machine) for participating. Apparatus and materials. The game playing apparatus used in the previous studies was also employed in Expt. 4. A commercially available generic beer (General Brewing Company, Vancouver, WA, 98660) was the fluid used for tasting and game-playing. Alcohol content of 3.6% by volume is specified by the manufacturer. Procedure Prior to their participation in the experiment, all subjects were administered a medical screening and drinking habits questionnaire to ensure that alcohol ingestion was not contraindicated. Individuals who reported ever having been concerned about the amount of their alcohol drinking, or who had ever been told by a professional that they are or might be alcoholic were excluded from participation. The procedures employed in this study were exactly those of Expt. 2, with the addition of breath alcohol determinations immediately prior to, and following the termination of, the experiment. Results The data of 17 subjects are included in the analysis. Three subjects were excluded because they operated the slot machine continuously and failed to come under schedule control, two subjects worked on homework while they played (and therefore engaged in behaviors which competed with drinking), and one subject did not drink during the playing session. Eight
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of the 17 subjects were in the FI90 condition and there were 9 in the F130 condition. The average intake for the FI90 and F130 conditions was 538 ml and 385 ml, respectively; this difference was not statistically significant. The fluid consumed by each subject is presented in Fig. 4. The average breath alcohol measured at the termination of the experiment was 2 mg%, and the two groups were not statistically different. There was no significant difference in earnings from the slot machine between the two schedule conditions. Discussion As in Expts. 2 and 3, the trend of greater consumption by the FI90 subjects was observed in Expt. 4, though the difference between schedule conditions was not statistically significant. An examination of the selfreported ‘typical’ drinking habits of the subjects, collected as part of the initial subject screening, provided evidence of a possible confound with schedule condition as an influence on consumption in the study. Three of the four greatest consumers in the study (subjects B8, B12 and B15; see Fig. 4) were also among the highest weekly drinkers included in the
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study. Since schedule-induced polydipsia could be considered to be an augmentation of typical drinking (as opposed to a drinking initiation procedure), it is possible that the drinking of these two subjects was not influenced by the schedule of reinforcement because they hadn’t yet drunk what they typically drink in the given time that the schedule was in effect. If the data of subjects B8, B12 and Bl5 are excluded, the difference between the FI90 and F130 schedule conditions is statistically significant (t(1,14) = 2.08, P = 0.05). There was a marked difference in the average amounts consumed in both schedule conditions of the beer study as compared to both the ‘Near Beer’ studies. A post hoc analysis of the taste ratings (Mann-Whitney U test) revealed a highly significant difference between the experiments: subjects drinking ‘Near Beer’ rated the taste of the non-alcoholic beers consistently lower than the beer groups rated the alcoholic beer (z = 3.90, P < 0.0001). Obviously, taste can be most influential in determining intake, and in the present studies, may have interacted with the influence of the reinforcement schedules. GENERAL
DISCUSSION
Taken together, the four experiments indicate that in humans, the scheduled delivery of a reinforcer can affect the amount of fluid ingested (Fig. 5). Although statistically significant results were obtained only in the water
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experiment, a similar trend in consumption, i.e. greater consumption by the FI90 groups as compared to the F130 conditions, was observed in all four experiments. The differences between schedule conditions in the studies utilizing non-alcoholic beer are slight, however. It is clear that the intermittent delivery of reinforcement is not the only factor influencing total consumption in the above experiments nor, most likely, in natural drinking settings. At least two other factors can be identified as operational in the above studies: taste of the beverage and the expectancies of alcohol effects resulting from past history with alcohol. The taste of the available fluid may have been influential in increasing mean consumption from the ‘Near Beer’ to the alcoholic beer experiments. As can be seen in Fig. 5, average intake was increased when subjects actually received real beer, even though subjects in the ‘told alcohol’ condition thought they were drinking real beer. The significantly lower ratings of the non-alcoholic beers as compared to the ratings of the alcoholic beer also provide evidence that taste factors served to suppress drinking in the told-alcohol/receive ‘Near Beer’ group. The influence of drinking history is also illustrated in Fig. 5. Omitting the told ‘Near Beer’ group (from which few inferences can be drawn due to the small number of subjects who drank) it can be seen that the difference in consumption between schedule conditions was greatest for the water group, followed by the group that received alcoholic beer, with the smallest difference observed in the told-alcohol/receive ‘Near Beer’ group. The schedule differences observed for the beer and told-alcohol conditions would be expected if recognition of some pharmacological cue of alcohol consumption contributes to ingestion. Since all of the subjects in the beer and told-alcohol conditions had, in their drinking histories, experienced alcohol’s pharmacological effects, it could be presumed that they knew roughly how much they needed to consume in order to experience the onset of some pharmacological cues. Though the subjects in the told-alcohol/receive ‘Near Beer’ condition all believed they were drinking alcohol, none of them could have experienced any of these pharmacological cues, despite an average consumption of approximately 10 oz of ‘beer’ in the 30 min of play. Research on the subjective detection of alcohol cues has shown that drinkers can recognize the onset of ethanol effects at blood alcohol levels as low as 1 or 2 mg%, comparable to those achieved in the beer experiment [24,25] and that detection can occur within 20 min [26]. Therefore, one hypothesis for the diminished influence of the reinforcement schedule on the drinking of the told-alcohol/receive ‘Near Beer’ group woud be that the lack of pharmacological cues maintained more drinking in the F130 condition, thus reducing any differences that schedule induction might have generated. In addition, the poor taste of the non-alcoholic beer probably suppressed total ingestion as compared to the beer group, thus further minimizing schedule effects. The alcoholic beer group had recorded breath ethanol levels which suggested that they probably experi-
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enced some pharmacological cues from drinking. So, in the beer group, alcohol cues may have helped to regulate drinking and allowed the schedule contingencies to influence intake as well. In an empirical assessment of unrestricted beer drinking by college students in groups, it was found that individuals typically drink at high rate when drinking begins, but after lo-15 min, drinking changes to a slower, moderate rate [ 271. Although these findings are the result of observations of individuals drinking in groups, they suggest that individuals may attempt to maintain certain intoxication levels following an initial high drinking rate. It is possible that the initial high drinking rate is maintained until a match between expectancy from past drinking history and physiological feedback cues occurs. At that point, drinking patterns are altered to a slower rate. It is hypothesized that it is during the latter phase of drinking regulation that factors such as schedule induction may exert a major control. The absolute total consumption at which the transition to the slowed rate occurs is highly variable across individuals [ 271. In the present study, it is possible that some of the beer drinking subjects (for example, the three highest drinking subjects) did not drink to the transition point in the time allotted for game-playing. It may be that until subjects reach a certain level of physiological feedback, their drinking is less controlled by the influence of other factors, such as schedule manipulations. Thus, subjects are probably more influenced by drinking history at the onset of drinking, but once they have achieved their typical level of initial intoxication cues, schedule induction may be influential in determining rate of further intake. When drinking regulation is not directly influenced by physiological feedback, schedule control should be more closely evidenced, as was the case in the water study. This remains, however, a testable hypothesis and a topic for future study. There appears to be no need to require the schedule delivery of a food source to induce adjunctive drinking in humans provided drinking has been initiated. As was observed in the above studies, the scheduled delivery of monetary reinforcement, usually considered to be unrelated to drinking, produced an increase in ingestion on the FI90 schedule. In other investigations of adjunctive behaviors in humans, the scheduling of such diverse reinforcers as maze-solving, visual access to an opponent’s play, money and candy have resulted in increases in equally diverse behaviors such as smoking, grooming, drinking and vocalization [ 18-20,221. This is not a result unique to the human. While early examinations of adjunctive behavior utilized intermittent food reinforcement to generate polydipsia in the rat, scheduled food reinforcement has subsequently been used to generate excessive aggressive behavior in monkeys and pigeons [ 28,291, pica in monkeys [ 301, air-licking in rats [ 311, and excessive wheel-running in rats [ 321. Thus, it is not the nature of the reinforcer that determines the nature of the excessive behavior. More likely, the excessive behavior demonstrated in a particular situation is dependent upon the options for behavior available in that environment and the relative reinforcing capacities of other available stimuli.
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The increased drinking in the present studies occurred at the same fixed interval schedule of reinforcement known to produce ethanol and water polydipsia in rats using food reinforcement [5,6]. Adjunctive behavior in animals is related to the reinforcement schedule in what Falk has described as a bitonic function; the amount of adjunctive behavior increases with the length of the interval between reinforcements up to a point, but diminishes when the interval is lengthened further [ 61. While the present studies demonstrated the expected difference in ingestion generated by the FI30- and FISO-s schedules, further experimentation is needed to determine whether adjunctive drinking is abolished at longer time intervals. This would be an important observation since, if some component of excessive drug use is a result of adjunctive behavior, then extending or shortening the interval between reinforcers generating that behavior could aid in alleviating the problem. It is evident that schedule-induction is not the only factor influencing consumption in alcohol-drinking situations; the above results indicate that there are a number of factors which interact to control the rate of ingestion and the amount consumed. It appears that schedule-induction is a weak determinant of alcohol consumption when experienced drinkers begin to drink. However, once drinking has progressed beyond its rapid initial rate, schedule-induction may become a factor in controlling the ensuing rate of consumption and may be a determinant of excessive consumption. It is conceivable that in many human situations, the frequency (or schedule) of social reinforcement could result in the induction of adjunctive behaviors, one of which could be increased alcohol consumption. Schedule-induction did affect the ingestion of fluid in the above studies. What remains to be demonstrated is that excessive alcohol consumption can be influenced by the schedule of reinforcement and that the scheduling of social interaction, for example, can act as a generator schedule. ACKNOWLEDGMENTS
The authors wish to thank J. Seather, M. Malakooti, and J. Samett for assistance in performing the studies. Special thanks to Drs. N.J. Kenney and M.R. Banaji for their critical reading of the manuscript. REFERENCES 1 B. Tabakoff, P.B. Sutker and C.L. Randall (Eds.), Medical and Social Aspects of Alcohol Abuse, Plenum Press, New York, 1983. 2 T.C. Harford and L.S. Gaines (Eds.), Social Drinking Contexts, U.S. Government Printing Office, NIAAA Research Monograph, No. 7, 1981. 3 G.A. Marlatt and D.J. Rohsenow, Cognitive processes in alcohol use: expectancy and the balanced placebo design, in: N.K. Mello (Ed.), Advances in Substance Abuse: Behavioral and Biological Research, Vol. 1, JAI Press, Greenwich, 1980, pp. 159201. 4 J.H. Mendelson and N.K. Mello. New Engl. J. Med., 301 (1979) 912. 5 J.L. Falk and H.H. Samson, Pharmacol. Rev., 27(4) (1976) 449.
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