JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR

CONTEXT DEPENDENT CHANGES IN THEREINFORCING STRENGTH OFSCHEDULE-INDUCED DRINKING

GENE M. HEYMAN AND ARTURO BOUZAS

HARVARD UNIVERSITY ANDUNIVERSIDAD NACIONAL AUTONOMA DE MEXICO

Previous experiments show that the opportunity to engage in schedule-induced respondingis reinforcing. In this experiment, the reinforcing strength of schedule-induced drinkingwas measured. Four rats were trained on a concurrent-chain schedule. The two terminallinks provided food pellets on identical fixed-time schedules. In addition, one terminal linkalso provided the opportunity to press a button that operated a water dipper. In this link,the rats showed polydipsic drinking. Button-pressing rate for polydipsic drinking was abitonic function of pellet rate, and it was possible to describe the relationship with aslightly modified version of the matching equation for primary reinforcement. This equa-tion also closely fit the data from other studies. Initial-link response rates, however, did notappear to be influenced by the availability of water in the terminal links. Control condi-tions suggested that the reinforcing strength of polydipsia was strongly bound to the con-text provided by periodic food reinforcement.Key words: schedule-induced drinking, concurrent-chain schedule, reinforcement strength,

matching law, drive, button press, lever press, rats

It is possible to arrange a contingency inwhich schedule-induced responding reinforcesan instrumental response (Falk, 1966). For ex-ample, in one study pigeons were trained towork on a ratio schedule for the opportunityto engage in schedule-induced aggressionagainst other pigeons (Cherek, Thompson, &Heisted, 1973); similarly rats can be trained topress a lever in order to engage in polydipsia(Killeen, 1975). These findings introduce thepossibility that the quantitative theory thatapplies to primary reinforcers, the matchinglaw (Herrnstein, 1970), may also apply to thereinforcing properties of schedule-inducedresponding. Cohen (1975) has tested thishypothesis. He trained rats on concurrent vari-able-interval, variable-interval (conc VI VI)

Portions of this paper were presented at the Ameri-can Psychological Association Meetings, San Francisco,1977. We thank Jim Mazur, Joseph Mendelson, A. W.Logue, and Sara Shettleworth for their helpful com-ments on an earlier version of the paper. The researchwas supported by NIMH grant MH 15494 to HarvardUniversity. During the preparation of this paper, Ar-turo Bouzas was a postdoctoral fellow at the Universityof Toronto and obtained support from the MexicanCouncil of Science and Technology and a National Re-search Council of Canada grant A 0140 to Jerry Hogan.Reprints may be obtained from Gene M. Heyman,Department of Psychology and Social Relations, Har-vard University, Cambridge, Massachusetts 02138.

schedules that provided approximately equalrates of food reinforcement at each schedule.In addition, one schedule also supported poly-dipsic drinking. The rats spent more time atthis alternative, and Cohen argued that themagnitude of the difference in time propor-tions was predicted by the matching law. (Upto then, the matching law had generally beenrestricted to describing the effects of food andshock on response rate.)The study described below tests the gener-

ality of Cohen's findings. A concurrent-chainschedule was used to measure the reinforcingstrength of polydipsia. This procedure pro-vides a means for assessing the following issues.First, the difference in time proportions thatCohen observed may have occurred because therats simply had one less activity at the food-only alternative. The structure of the chainprocedure (see below) automatically removesthis possible confound. Second, there is somereason to believe that the reinforcing strengthof polydipsia will depend on whether the sub-jects are in the initial , choice, link or theterminal , consequence, link. For example,the temporal pattern of schedule-induced re-sponding suggests that it depends on havingrecently eaten (e.g., Killeen, 1975; Staddon,1977). If this is the case, the opportunity toengage in polydipsia may be reinforcing when

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1980, 33, 327-335 NUMBER 3 (MAY)

G. M. HEYMAN and A. BOUZAS

the subject is in the terminal link but not rein-forcing when the subject is in the initial link.Alternatively, the reinforcing power of poly-dipsia may extend to both links as is com-monly the case for primary reinforcers (e.g.,Fantino, 1977). Third, the chain procedureprovides a convenient way to measure the rein-forcing strength of polydipsia in two differentstimulus conditions, the initial and terminallinks.

METHOD

SubjectsFour male Lashley-Black rats without previ-

ous experimental histories served. They weremaintained at approximately 85% of theirfree-feeding body weights. Except for one con-trol condition, described below, water wasavailable in the home cages.

ApparatusA modified two-lever experimental chamber

(20.5 cm by 23.5 cm by 19.5 cm) was enclosed

Fig. 1. The front panel of the experimental chamber.Pellets were delivered into the top opening; the waterdipper was accessible through the bottom opening. Be-low the right lever was a Plexiglas button that operatedthe dipper.

in a sound attenuating box. Figure 1 presentsa drawing of the front panel. Two sets -ofstimulus lights, left and right, could be il-luminated from behind with white light. Theresponse levers, one below each set of lights,were operated by a force of more than .20 N.A recessed receptacle for the delivery of foodpellets (Noyes 45-mg chow bits) was locatedbetween the levers, 8 cm from the floor. Di-rectly below the pellet window was a secondopening which gave access to the water dip-per. The dipper was operated by a Plexiglasbutton situated directly below the right lever.A houselight and buzzer (Sonalert) were at-tached to the roof of the chamber. White noisemasked extraneous sounds, and a PDP-8E com-puter (Digital Equipment Corporation) con-trolled the sequence of experimental eventsand recorded data.

ProcedurePreexperimental training. The rats were

water deprived for 24 hours and shaped tobutton press on a continuous reinforcementschedule for water. For each rat, only one ses-sion of training proved necessary.Experimental sessions. The basic experi-

mental procedure was a concurrent-chainschedule in which one terminal link providedaccess to water. In the initial link, left andright lever presses produced correspondingterminal-link states according to a conc VI 40-sec VI 40-sec schedule. The VI timer intervalswere approximately exponentially distributed(Fleshler & Hoffman, 1962), and the schedulewas arranged so that there was an approxi-mately equal number of left and right ter-minal-link entries independent of the distri-bution of left and right initial-link responses(Stubbs 8c Pliskoff, 1969).There were two types of terminal-link

states: one for left-lever entries, the other forright-lever entries. In each, food pellets weredelivered on identical, response-independentfixed-time (FT) schedules. In addition, oneterminal link also provided access to water.In this link, a button press operated the dipperfor 1.2 sec. The availability of water was sig-naled by an intermittent tone from the buzzer,and left and right terminal-link entries werefurther distinguished by the front panel lights.The initial link was signaled by the onset ofthe houselights and offset of the front panellights.

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REINFORCING STRENGTH OF POLYDIPSIA

Table 1

Summary of the initial-link relative response rates: aindicates baseline sessions; water was not available andleft side response proportions are given; b indicatessessions that rats were water deprived; c indicates ses-sions in which a conc VR 40 VR 40 replaced conc VI40-sec VI 40-sec schedule in the initial link.

Percentage of initial-

Water- link responses to sideassociated with water-Fixed- avminable available terminal link

interval link Subjects: Control(sec) (left or right) 1 2 3 4 condition

15 - .52 .48 .45 .52 a15 R .46 .52 .57 .4815 L .51 .49 .57 .6030 L .53 .51 .51 .5030 R .50 .52 .58 .5360 L .53 .43 .51 .4760 R .42 .54 .65 .5930 L .67 .52 .57 .62 b30 R .61 .65 .63 .54 b10 L .55 .43 .47 .5210 R .55 .57 .59 .528 L .49 .42 .45 .48 c8 R .47 .62 .59 .53 c3.6 R .48 .55 .57 .61

Table 1 lists the sequence of conditions. Theterminal-link FT values were varied from 3.6sec to 60 sec, and the availability of water was

alternated between the left and right sides to

control for possible position preferences. EachFT value was generally run for 30 sessions: 15sessions with water available in the left ter-minal link and 15 sessions with water availablein the right terminal link. Additional controlmeasures are coded by the lowercase letters inthe rightmost column. They were as follows:In the initial experimental condition, a, waterwas not available in either terminal link. Inthe eighth and ninth conditions, b, the ratswere water deprived. The water bottles were

removed from the home cage, and the ratsreceived their total water ration in the experi-mental sessions. In the twelfth and thirteenthconditions, c, a concurrent variable-ratio,variable-ratio (conc VR 40 VR 40) schedulereplaced the conc VI 40-sec VI 40-sec schedulein the initial links.One additional condition is not listed in

Table 1. The rats were given a type of free-feeding condition in order to evaluate non-

polydipsic drinking rates. In these sessions,no stimuli were presented, the water dipperwas always available, and 150 pellets were

delivered during the first 5 min of the sessionon an FT 2-sec schedule. This was the fastestrate of delivery at which the pellet dispenserreliably operated (and it took the rats longerthan 5 min to eat the 150 pellets so that thefree-feeding criterion was met).The duration of the terminal link and the

number of terminal-link entries each sessionwere varied from condition to condition sothat the rats would earn approximately 100pellets a session. For example, in the first 11conditions, the duration of the terminal linkwas 104 sec. Thus, when the FT value was 30sec, the rats received 3 pellets during theterminal-link state, and the session terminatedafter 33 terminal-link entries or 60 min, whichever came first. For the FT 8 sec condition,the terminal-link duration was 111 sec, andfor the FT 3.6 condition, the terminal-linkduration was 39 sec.

RESULTS

Terminal-Link Responding: Polydipsia.Event recorder tracings showed that in most

conditions, pellet delivery was followed by atleast one button press for water, and we oWserved that each button press was followed bydrinking from the dipper. The temporal pat-tern of button pressing for water and its raterelative to the free-feeding condition con-forms to previous accounts of polydipsia (cf.Falk, 1971; Staddon, 1977). Rats 1, 2, and 3developed polydipsic drinking within the firstfew sessions of the initial water-available con-dition, FT 15 sec, whereas Rat 4 did not de-velop polydipsia until the first FT 30-seccondition.

Figure 2 shows the temporal pattern ofwater-dipper operations and pellet deliveriesfor Rat 1 in the initial FT 30-sec condition.The perpendicular slashes on the upper lineof the recorder tracing were triggered by thepellet dispenser; the rectangular excursions onthe lower line were triggered by the 1.2-sec

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Fig. 2. The temporal pattern of pellet delivery anddrinking for Rat 1 in the FT 30-sec condition. Thepattern is the same as in studies in which water isdirectly available from a spout (cf. Staddon, 1977). Allthe rats showed a similar pattern.

329

G. M. HEYMAN and A. BOUZAS

10) 300 500 700 900 1100 100 300 500 700 900

PELLETS PER HOUR110o

Fig. 3. The rate of button pressing for water as a function of pellet rate. Pellets were obtained on an FTschedule; each button press operated the dipper for 1.2 sec. The equation is a simple modification of the equa-

tion that describes the rate of instrumental responding as a function of rate of primary reinforcement (see text).

operation of the water dipper. As in previousstudies of polydipsia, eating was closely fol-lowed by a burst of drinking, with the drink-ing usually occurring within the first half ofthe interpellet interval. All the rats showed a

similar pattern.Figure 3 shows the rate of button pressing

for water as a function of pellet rate. Thefilled circles are the average of two determina-tions, the open circles are a single determina-tion, and the triangle is from the condition inwhich a meal of 150 pellets was delivered on

an FT 2-sec schedule at the beginning of thesession and water was available continuously.The data were averaged from the last 5 ses-

sions of the included conditions.The solid line is a modified version of the

equation which describes the effect of primaryreinforcement on instrumental behavior. Theoriginal equation (Herrnstein, 1970), is

B=kRR+Re' (1)

where B is operant response rate, R is rein-forcement rate, k is a fitted constant whichestimates the asymptotic rate of B, and Re isa second fitted constant which estimates therate of unscheduled competing reinforcers,for example, those produced by grooming,

gnawing, etc. (for a fuller account, see Herrn-stein, 1970). In words, Equation 1 says the rateof reinforced behavior is proportional to itsrelative reinforcement rate.

Equation 1 has been confirmed repeatedlyfor instrumental responding for primary rein-forcement (de Villiers & Herrnstein, 1976).With a simple modification to account for thetime spent eating, we found that it also de-scribed the relationship between the rate ofbutton pressing in order to engage in poly-dipsia and the rate of primary reinforcementon the FT schedule. In addition (see below),this modified version of Equation 1 providedan equally good account of polydipsic lickingfor rats (Flory, 1971) and rhesus monkeys (Al-len & Kenshalo, 1976).

First, assume that the reinforcing strengthof polydipsia varies proportionally with theprimary reinforcement rate on the supportingintermittent schedule. Second, take into ac-

count that polydipsia depends on prior eatingand is thus constrained by the time spenteating. The simplest result is

B=W+kW *[(T-E)/T] (2)

for T -E. For this study, the left side givesthe rate of button pressing for the opportunity

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330

REINFORCING STRENGTH OF POLYDIPSIA

to engage in polydipsic drinking. On the rightside, k is the asymptotic button pressing rate,

W is the reinforcing strength of polydipsia,which is assumed to vary proportionally withpellet rate, and in the denominator, Rw is therate of competing, unscheduled reinforcers,measured in units of W. The second term on

the right expresses the fact that polydipsia de-pends on prior eating and that the rats couldnot eat and button press simultaneously: Tis the scheduled interpellet time, the FT value,and E is eating time, which was estimatedfrom the data. In words, Equation 2 says thatin between bouts of eating on a periodic foodschedule, the reinforcing strength of poly-dipsia is proportional to the relative rate offood reinforcement. Therefore, the overallrate of polydipsic drinking will not necessarilybe a monotonic function of food reinforce-ment rate: when the interreinforcement in-tervals are relatively long compared to theeating time, an increase in reinforcement ratewill produce an increase in schedule-induceddrinking rate; but when the interreinforce-ment intervals approach the eating time, therewill be little time available for drinking.

Figure 3 shows that Equation 2 describedbutton pressing for polydipsia about as well,or better, than Equation 1 does for instru-mental behavior (cf. de Villiers & Herrnstein,1976). The parameters k, Rw, and E were fit

by the method of least squares, and the me-

dian amount of variance accounted for was

.98. The new parameter, E, for eating timewas about the same for each rat, which agrees

with the observation that for rats such behav-iors as licking and wheel running occur at

constant rates (see, e.g., Premack, 1965), andthe absolute values, 2.70 to 3.25 sec, agree withour observations of the interruption of buttonpressing due to eating. (Note, it can be shownthat the additional parameter, E, does not ac-

count for the quality of the fit for the left legof the functions.)The open triangles indicate the rate of but-

ton pressing in the condition that 150 pelletswere delivered on an FT 2-sec schedule duringthe first 5 min of the session. As noted above,this rate of delivery produced a free-feedingsituation, with pellets quickly piling up in thetray. Correspondingly, drinking did not showthe polydipsic pattern produced by periodicreinforcement. In fact, event recorder tracinqsand observation indicated that drinking did

not occur until all 150 pellets had been con-sumed, and even though the rats obtained atleast 50% more pellets in the free-feedingcondition than in any other, the drinking ratewas the minimum observed.

Initial-Link ResultsFigure 4 shows the individual and average

initial-link relative response frequencies forentering the terminal link with water avail-able as a function of pellet rate. Except forthe baseline condition, each point is the aver-age of two determinations: one when waterwas associated with the left terminal link; theother when the water was associated with theright terminal link. (Recall that, in baseline,water was not available in either terminallink.) The vertical bars show a standard devia-tion unit. The data were averaged from thelast 5 sessions of each condition.In experimental conditions, the first four

points, relative response frequencies were ap-proximately .50. Rats 1 and 2 pressed thelevers independently of the location of water,even though they engaged in polydipsia. Rats3 and 4 showed a slight preference to enter thewater-available terminal link. However, forRat 4 the difference between responding onthe two levers was never greater than onestandard deviation unit. Consequently, therewas no trend as a function of pellet rate, andcollapsing across conditions and subjects, therewas an average bias of 2% to respond at thelever associated with the water-available ter-minal link.The fifth point in Figure 4 (control 1) shows

the effect of replacing the initial-link conc VIVI schedule with a conc VR VR schedule.This change was made because it has beenreported that concurrent ratio schedules am-plify relative response rate differences (e.g.,Rachlin & Green, 1972). However, for the op-portunity to engage in polydipsia, the concur-rent ratio schedule did not increase preference.In fact, the average difference in first-linkresponse frequencies decreased to about 1%.The sixth point in Figure 4 (control 2)

shows the effect of water deprivation on first-link relative response rates. We removed thewater bottles from the home cages so that ex-perimental sessions provided the rats their onlyaccess to water. When water deprived, all therats showed a clear preference to enter thewater-available terminal link. This establishes

331

332 G. M. HEYMAN and A. BOUZAS

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PELLETS PER HOURFig. 4. Relative response rates for entering the terminal link that provided access to the water dipper. The

data were averaged from the last 5 sessions of a condition. The bars indicate a standard deviation unit. In con-trol 1, a conc VR VR schedule was substituted for a conc VI VI schedule in the initial link. In control 2, therats were water deprived in the home cage.

REINFORCING STRENGTH OF POLYDIPSIA

that it was possible for the rats' behavior inthe initial, choice, link to come under controlof consequences in the terminal links. It alsoshould be noted that other aspects of the re-sults indicated that the rats discriminated be-tween the two terminal links. In the terminallink which did not provide water, which wassignaled by the absence of the intermittenttone, the rats rarely pressed the button forwater.

Figure 5 shows the temporal pattern of but-ton pressing for water for Rat 1 when it waswater deprived in the home cage. The uppertracing is from the first two water side ter-minal-link entries of the session. Rat 1 begandrinking as soon as it entered the terminallink and continued to do so independently ofpellet deliveries. That is, unlike polydipsicdrinking, see Figure 2, water-deprived drink-ing did not show a temporal dependency oneating. The lower tracing shows the temporalpattern of button pressing in the last two waterside terminal-link entries from this same ses-sion. Near the end of the session, Rat 1 re-sumed the polydipsic pattern it had shownwhen not water deprived. Presumably, drink-ing early in the session was motivated by thirst,whereas drinking late in the session was poly-dipsic. This apparent change in drive statessuggests that in condition c even greater initiallink preferences would have occurred had itbeen possible to maintain water deprivationthroughout each session. To our knowledge,these are the first data that give evidence oftwo modes of drinking within a single, rela-tively brief period (not greater than 60 min).

DISCUSSIONContext dependent changes in polydipsia's

reinforcing strength. The view that there wasa link-correlated change in drive state is con-sistent with the major findings. Assume thatthe drive to engage in polydipsia depends onthe following factors: (a) food deprivation,(b) having recently eaten, and (c) cues thatsignal the unavailability of food (cf. Staddon,1977). Consequently, the terminal link wouldactivate the drive and empower polydipsiawith reinforcing strength (Brown & Herrn-stein, 1975), but the initial link would notsince food pellets were not obtained there.

However, there is the possible objection thatthe rats actually preferred to enter the ter-

PELLET I

R-1

WATEROPE

Fig. 5. The temporal pattern of drinking for Rat 1when it was water deprived. The upper tracing is fromthe beginning of the session. Drinking was independentof eating. The bottom tracing is from the end of thesame session. The difference is apparently due to thesatiation of thirst.

minal link with water available, but that theprocedure did not provide a sensitive enoughmeasure. This criticism is answered in part,at least, by the results from the condition inwhich the rats were water deprived in thehome cages. First-link response proportionsshifted in favor of the water-available link(see Figure 4). In addition, it is well estab-lished that concurrent-chain procedures pro-duce systematic initial-link preferences (Fan-tino, 1977; Herrnstein, 1964). Other accounts(e.g., Falk, 1977) may also be relevant, butwhatever the etiology of the reinforcing powerof polydipsia, once released it controls re-sponding in the way described by the relativelaw of effect (Herrnstein, 1970).The quantitative relationship between rate

of schedule-induced drinking and rate of pri-mary reinforcement. The rate of schedule-induced drinking is approximately constant(e.g., Allen & Kenshalo, 1976; Flory, 1971).This suggests that Equation 2 would have pre-dicted the rate of polydipsic licking with aboutthe same precision as it did polydipsic buttonpressing. Data reviewed from other studiesshow this to be the case. Figure 6 displays therate of schedule-induced licking as a functionof food pellet rate for two rhesus monkeys,Tonto and Jason (Allen & Kenshalo, 1976) andthree rats, 2, 3, and 4 (Flory, 1971). Tonto andJason obtained banana pellets on a series offixed-interval (FI) schedules. The best fittingeating times, E, for both monkeys were ap-proximately the same, 9.5 sec. The values forT were calculated from the obtained reinforce-nment rates rather than the scheduled ones, asshown in Figure 3, since in an FI schedule thereinforcer depends on a response. Given thelong eating times and short FI intervals, Equa-

333

G. M. HEYMAN and A. BOUZAS

w

z 604 120tzo 25 2 60 120 160 240 60 120 I60 240

c_ 26 Allen and Kensholo (1976) TONTO JASON2-

k = 15.5 k = 98.5Rw = 50.5 Rw=224

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64-

16 64 9612 160 192 224 256 2 32036 4 912160192 224256266 320 32 4

PELLETS PER HOUR

Fig. 6. Rate of polydipsic licking as a function of food pellet rate. Tonto and Jason are rhesus monkeys (Al-len & Kenshalo, 1976). Subjects 2, 3, and 4 are rats (Flory, 1971). The equation is a simple modification of theequation that describes the rate of instrumental responding as a function of rate of primary reinforcement (seetext and Figure 2).

tion 2 predicted bitonic functions. Theamount of variance accounted for was .92for Tonto and .95 for Jason. Data for Rats 2,3, and 4 were derived from Figure 4 ofFlory's paper (1971). The curves are not bi-tonic because Flory did not use Fl intervalsshorter than 20 sec. An increasing functiondoes not delimit a value for eating time,E, so that we selected 3 sec on the basis of ourresults (Figure 3). The amount of varianceaccounted for ranged from .92 to .98.Although Equation 2 generally accounted

for over 95% of the variance in the bitonicdata (Figures 3 and 6), there was a systematicdeviation between the obtained and predictedvalues. For both rats and monkeys, the maxi-mum obtained drinking rate was invariably(in 6 of 6 cases) greater than the maximum pre-dicted drinking rate. This is because Equation2 does not take into account the temporal pat-tern of induced drinking. The term (T -E) / T, see Equation 2, implies that eating willinterfere with induced drinking independentlyof the length of the interfood interval, T.However, the data show that the probabilityof induced drinking declines as a function oftime since eating (e.g., Staddon, 1977). There-fore, eating is more likely to constrain the rateof schedule-induced drinking in a short inter-

val than in a long interval, and consequentlyEquation 2 will underestimate the maximum.For example, the event recorder tracingsshowed that the rats rarely pressed the buttonfor water in the last 15 sec of the 30-sec inter-pellet intervals (see Figure 3), whereas in the8-sec and 3.6-sec intervals, the majority of but-ton presses for water were in the second halfof the intervals. Equation 2, therefore, doesnot provide a complete theory of the reinforc-ing strength of polydipsia.The shape of the curves in Figure 3 and

Figure 6 is also pertinent to Killeen's theoryof behavioral arousal (1975). Killeen deriveda mathematical model of behavior on inter-mittent schedules that quite successfully de-scribes the temporal pattern of polydipsia.However, the model (Killeen, Hanson, & Os-borne, 1978) implies a linear relationship be-tween food reinforcement rate and schedule-induced drinking rate, whereas Figures 3 and6 and other data (e.g., Cohen, 1975) consis-tently show a curvilinear relationship. There-fore, some modification of Killeen's otherwisepowerful model would seem to be in order.Although Equation 2 successfully described

the rate of schedule-induced drinking in threedifferent studies, it may not apply to the de-scription of other types of induced behaviors.

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REINFORCING STRENGTH OF POLYDIPSIA 335

For example, data from three experiments onschedule-induced attack were analyzed (re-viewed by Staddon, 1977), and the obtainedrates differed widely from those predicted byEquation 2. This discrepancy, however, maybe due to a procedural constraint. In eachstudy (Cherek et al., 1973; Cohen & Looney,1973; Flory, 1969), an attack that occurredwithin 15 sec of the next scheduled food de-livery delayed that delivery for another 15 sec.The subjects, pigeons, appeared to learn thiscontingency so that it is likely that the rate ofattack was inhibited in a way that did not takeplace in the studies of schedule-induced drink-ing.Summary. The data displayed in. Figures 3,

4, and 6 are easily summarized if it is as-sumed that the reinforcing strength of poly-dipsia depends on the stimulus conditions pro-vided by periodic food schedules. In theterminal link, periodic eating induced a drivethat empowered polydipsia with reinforcingstrength, whereas in the initial link the condi-tions for polydipsia were not met, and, there-fore, responding at the two levers was con-trolled by food pellet rate alone. Importantly,once the reinforcing power of polydipsia wasengendered, it maintained response rates ac-cording to a well-established quantitative ver-sion of the law of effect (de Villiers & Herrn-stein, 1976).

REFERENCESAllen, J. D., & Kenshalo, D. R. Jr. Schedule-induced

drinking as a function of interreinforcement intervalin the rhesus monkey. Journal of the ExperimentalAnalysis of Behavior, 1976, 26, 257-267.

Brown, R., & Herrnstein, R. J. Psychology. Boston:Little, Brown, 1975.

Cherek, D. R., Thompson, T., & Heistad, G. T. Re-sponding maintained by the opportunity to attackduring an interval food reinforcement schedule.Journal of the Experimental Analysis of Behavior,1973, 19, 113-123.

Cohen, I. L. The reinforcement value of schedule-induced drinking. Journal of the ExperimentalAnalysis of Behavior, 1975, 23, 37-44.

Cohen, P. S., & Looney, T. Schedule-induced mirrorresponding in the pigeon. Journal of the Experimen-tal Analysis of Behavior, 1973, 19, 395-408.

de Villiers, P. A., & Herrnstein, R. J. Toward a lawof response strength. Psychological Bulletin, 1976,83, 1131-1153.

Falk, J. L. The motivational properties of schedule-induced polydipsia. Journal of the ExperimentalAnalysis of Behavior, 1966, 9, 19-25.

Falk, J. L. The nature and determinants of adjunctivebehavior. Physiology and Behavior, 1971, 6, 577-588.

Falk, J. L. The origin and functions of adjunctive be-havior. Animal Learning and Behavior, 1977, 5,325-335.

Fantino, E. Conditioned reinforcement: Choice andinformation. In W. K. Honig & J. E. R. Staddon(Eds.), Handbook of operant behavior. EnglewoodCliffs, N.J.: Prentice-Hall, 1977.

Fleshler, M., & Hoffman, H. S. A progression for gen-erating variable interval schedules. Journal of theExperimental Analysis of Behavior, 1962, 5, 529-530.

Flory, R. K. Attack behavior as a function of mini-mum inter-food interval. Journal of the Experimen-tal Analysis of Behavior, 1969, 12, 825-828.

Flory, R. K. The control of schedule-induced polydip-sia: Frequency and magnitude of reinforcement.Learning and Motivation, 1971, 2, 215-227.

Herrnstein, R. J. Secondary reinforcement and rateof primary reinforcement. Journal of the Experi-mental Analysis of Behavior, 1964, 7, 27-36.

Herrnstein, R. J. On the law of effect. Journal of theExperimental Analysis of Behavior, 1970, 13, 243-266.

Killeen, P. On the temporal control of behavior. Psy-chological Review, 1975, 82, 89-115.

Killeen, P. R., Hanson, S. J., & Osborne, S. R. Arousal:Its genesis and manifestation as response rate. Psy-chological Review, 1978, 85, 571-581.

Premack, D. Reinforcement theory. In D. Levine (Ed.),Nebraska symposium on motivation. Lincoln: Uni-versity of Nebraska Press, 1965.

Rachlin, H., & Green, L. Commitment, choice, andself-control. Journal of the Experimental Analysisof Behavior, 1972, 17, 15-22.

Staddon, J. E. R. Schedule-induced behavior. In W. K.Honig & J. E. R. Staddon (Eds.), Handbook of op-erant behavior. Englewood Cliffs, N.J.: Prentice-Hall, 1977.

Stubbs, D. A., & Pliskoff, S. S. Concurrent respondingwith fixed relative rate of reinforcement. Journal ofthe Experimental Analysis of Behavior, 1969, 12,887-895.

Received September 7, 1979Final acceptance November 13, 1979