ehaviorology oday Volume 13, Number 2, Fall 2010 (issn … · 2008-11-23 · Page 4 (issn...

�ehaviorology �oday � Volume 13, Number 2, Fall 2010 (issn 1536–6669) Page 3

Multiple Selectorsin the Control of

Simultaneously EmittableResponses

Stephen F. LedouxState University of New York at Canton

Editor’s Note: Occasionally, Behaviorology Today (BT)includes a piece that has gone through a full peer–reviewprocess. According to BT policy, when this is the case, avery clear notice to that effect is to be included with thepiece. In compliance with this policy: .

This paper extensively revises the author’s report ofan earlier research study (Ledoux, a) to highlightthe impact further research based on this study mighthave on the natural science understanding of complexhuman behavior. Initially, the earlier report was drasti-cally shortened for submission to Behaviorology, thefully peer reviewed journal of (The InternationalBehaviorology Association) for peer review. As a result ofthat review, in January the editor of Behaviorology,Carl Cheney, accepted the piece for publication pendingrevisions that essentially involved putting back in mostof the material that had been removed. This was donebut the result ended up being, predictably, too long forpublication there. So the work appears here instead(although it had appeared in in virtually its presentform in Origins and Components of Behaviorology[Ledoux, /]).—Ed.�

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…There is no denying the importance of themethods and equipment which have been devisedfor long–sustained research, but there is also muchto be said for an experiment that lasts half anhour—and for a quick and comprehensive look at thefine grain of the behavior in the cumulative record.(B.F. Skinner, 1976. “Farewell my LOVELY!”)

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�his paper improves and broadens the author’s reportof a past behaviorological research study (Ledoux, a).In its present form this paper discusses (a) the question ofcomplex behaviors, especially multiple operants, and(b) an experiment on such operants using a method in-volving multiple reinforcer sources which the author de-veloped in to help study these operants. In additionthe paper discusses (c) how this method makes possible aresearch project that replicates basic research on funda-mental operant processes while extending that replicationto more complex, multiple operants, and (d) how such aresearch project can be a systematic and purely inductiveinvestigation and cataloging of what happens when vari-ous basic contingencies include complex behaviors of themultiple operant type.

This paper refers to many research studies related tosimultaneously selectable or simultaneously emittableoperants. These studies appeared in the literature of“behavior analysis” when that was the preferred name forbehaviorological science. That was near the end of thetime period during which this natural science tempo-rarily shared a history with the non–natural discipline ofpsychology (see Ledoux, a). The perspective of thispaper respects that history as well as the evolutionaryperspective shared by the different levels of life–sciencedisciplines (see Glenn & Madden, ; also see Fraley &Ledoux, , Ch. ). As a practical result, this paper usessome terms that, while of more recent origin than thereported study, are still consistent with that history andperspective (e.g., “postcedents” and “selectors”; seeLedoux, b; Vargas, ).

The simultaneous occurrence of operant responses isan aspect of the behavior of animals, especially humans.Operants regularly, although not always, operate on theenvironment in ways that provide the selectors that actupon these operants as their own selecting consequences.Since selectors affect any operant whose occurrence pre-cedes them, an operant that occurs simultaneously, oreven nearly so, with one or more other operants may beaffected by the occurrence of any selectors following anyof these operants. In addition, the operant that is produc-ing a particular selecting consequence is sometimes dis-criminable, and at other times it may not be; this mayalso affect the selection processes. The effective under-standing of why people do what they do, and what can bedone about it, requires investigation of these phenomena.

In the dozen years since the research reported here onsimultaneously selectable and simultaneously emittablemultiple operants was done, the study of complex humanbehavior has little pursued work on such operants. In-stead researchers have focused on other valuable researchlines (e.g., on stimulus equivalence; see Sidman, ).Some possibly important discoveries must await research

(issn 1536–6669) �ehaviorology �oday � Volume 13, Number 2, Fall 2010

into the effects of simultaneous selectors on simulta-neously emittable multiple operants.

Introduction

Sometimes complex behavior appears not to be “sensitive”to observed contingencies (i.e., it does not change in waysthat observers of those contingencies would predict). Manyreasons for this are possible. For instance, some possiblycompeting contingencies may not be visible to observers.The reasons in particular cases are often unknown. Re-search should focus on discovering and controlling forthese reasons. But research should also do more.

Behaviorological research should develop and pro-mote the use of procedures that improve the sensitivity ofbehavior to the contingencies in effect because the verac-ity of data–based conclusions relies on behavior beingsensitive to those contingencies. This especially holds instudies of concurrent operants where interactions oftenoccur that might confound the data. Thus, the search forprocedures producing greater independent sensitivity ofeach operant in a multiple operant study is a continuingone. Research on parameters such as the length ofchange–over delays (s) exemplify this search (Allison& Lloyd, ; Fantino, Squires, Delbruck, & Peterson,; Pliskoff, ; Stubbs & Pliskoff, ).

Efforts to enlarge the range of behaviors affected bysensitivity enhancing procedures should also increase.Unfortunately, this does not appear to have been the casewith previous concurrent operant research where the ap-plication of sensitivity enhancing procedures has beenlimited to behaviors for which these procedures can es-tablish response independence (from confounding sched-ule effects) through response succession.

The discussion in the next three sections reviews thatsituation, offers a possible explanation of why it occurred,and suggests a line of research using a new procedure toimprove “sensitivity” (i.e., functional response indepen-dence) and reduce concurrent superstition, all withoutrequiring response succession. This research line alsoseeks to expand the range of behaviors that show enoughsensitivity to make studying them productive. One typeof behavior that can be included in the expanded range issimultaneously reinforceable concurrent human oper-ants. (“Simultaneously reinforceable” means that a re-sponse on one manipulandum can be selected at the sametime that a response on another manipulandum is se-lected; this implies that the manipulanda are simulta-neously available, and that the responses aresimultaneously emittable.)

The pivot point for discussing the historical context,present status, and future behaviorological research pos-sibilities with respect to simultaneously reinforceable

concurrent operants is Charles Catania’s book chapter“Concurrent Operants” (Catania, ). At the time theresearch reported in this paper occurred, this chapter wasthe seminal treatment of issues affecting research in con-current operants, including formal aspects of programming,classification of concurrent operants, schedule effects, lo-cal interactions, quantitative relations, and various prefer-ences. This book chapter set the pace for nearly allsubsequent concurrent operant research. But that turnedout to be, in some ways, a hindrance as well as a help.

Historical BackgroundOne difficulty is that Catania’s book chapter did not

attempt to deal with simultaneously reinforceable concur-rent operants. In addition, his discussions of procedures,subjects, and future lines of research were such as to re-duce researchers’ further interest in this type of concur-rent operants. This section, after dealing with the issue ofdefinitions, will review studies that are relevant to simul-taneously reinforceable concurrent operants, and therebyexpand on Catania’s coverage.

Definitions. In Schedules of Reinforcement, Fersterand Skinner () defined concurrent operants as:

Two or more responses, of different to-pography at least with respect to locus,capable of being executed with little mu-tual interference at the same time or inrapid alteration, under the control ofseparate programming devices (e.g., re-sponses to two keys present at the sametime under separate schedules). (p. ,emphasis added)

Catania quotes this definition on his first page, but heproceeds to say “In the case of concurrent operants, theorganism’s alternatives are…to emit one or another of theavailable operants” (p. ). But for his definition to agreewith the Ferster/Skinner definition, it would have to read“…to emit one or another or both of the available oper-ants.” This difference is significant; Catania’s definitionled, as will be seen, to constraints on the directions sub-sequent researchers were inclined to take.

The basis of this definitional omission, which pertainsto the question of whether response succession is requiredor not for response independence, and why, will be de-tailed later. For now, successive responses, in Catania’sview, are required as they make the occurrence of concur-rent superstitions avoidable (Catania and Cutts, ,defined concurrent superstition as the accidental correla-tion of one operant with the reinforcement produced bya different operant; compare this with simple superstitionwhich is a correlation of a response with accidental, non–contingent reinforcement). Catania () further sug-gests that the use of a is the most reasonable way toobtain successive responses. But s may not be neces-


sary because obtaining successive responses is only oneway to generate independence of schedule effects.

Related research. Ferster (, ) follows thedefinition of concurrent operants that he published withSkinner. In his study, the responses were simulta-neously emittable and simultaneously reinforceable.Chimpanzees pressed two keys, one with each hand. Theschedule for the two keys was concurrent () variableinterval () fixed ratio () (i.e., ).These schedules were selected because, when presentedsingly, they generate quite different yet stable responsepatterns; so when presented concurrently, the researchermight more quickly notice changes in the responsepattern under either schedule. Results showed onlyminor changes in schedule patterns from those typical ofsingle schedules, and it would be difficult to attributethese changes solely, even mainly, to superstitious effectsfrom simultaneous reinforcement of both responses byone or the other schedule. One interesting observationwas that the subjects continued to operate the key, atthe same rate as before, while eating food from the maga-zine with the hand.

Ferster () preferred to use simultaneously rein-forceable operants because “the time spent changing backand forth between the keys would interfere with the char-acteristic performance under the single schedule of rein-forcement” (p. ). Ferster also points out the relevanceof studying simultaneously reinforceable operants to suchhuman behaviors as piano playing where sometimes eachhand must deal with a different rhythm, as well asdifferent notes. And he mentions an additional benefitfrom studying these operants. The rate from one key canbe used to measure any emotional side effects fromchanges in the schedule on the other key.

Ferster’s study was expanded in his study.This time the chimps were exposed to a variety of con-current schedules, including fixed interval () componentsin complex schedules that involved both concurrent andmultiple () schedules like – . While the data showed fairly consistent indepen-dence of schedule effects for each key, some observationswere especially interesting. Virtually no scallops appearedduring s; less responding occurred, from more pausing,on the key during runs; extinction on the keycorrelated with a small decrement in responding; andchimps do not usually sustain high s (e.g., ), butthese chimps did, perhaps due to minimal superstitiouseffects of occasional reinforcers, especially those occur-ring during an run. (Such an effect is worthy of re-search in its own right as a possible additional behaviormaintenance procedure, or resistance to extinction proce-dure, in the technology of behavior control.)

Between the appearance of Ferster’s two studies,Sidman () published a study using simultaneously re-

inforceable concurrent operants and more than one sourceof reinforcement. (This was one of two such studies; theother was Hearst, .) Actually, in Sidman’s study, theuse of dual reinforcer sources was forced by the nature ofthe schedules. Sidman investigated the effects of a super-imposed pre–shock stimulus on concurrent schedules ofavoidance and food reinforcement. He initially trainedmonkeys on , avoidance schedules, and in-cluded, in some phases, a “free” shock with a pre–shockstimulus. He then tested for any effects, on relative ratesof lever pressing, from the superimposition of the freeshock/pre–shock stimulus on the , avoidanceschedule. Even after making various parameter changeson the , avoidance schedule, his results consistentlyshowed responding being highly controlled by theavoidance contingency. This superstition occurred re-gardless of whether the response topographies were thesame ( levers) or different (a lever and a chain). SoSidman then changed the components to compo-nents. From repeating the basic procedure with conc ,avoidance schedules, his results indicated separation ofeach response class. Thus, Sidman’s study exemplifieswhat will be seen to be a common problem. When resultsof using s as concurrent schedule components are com-pared with results from using components involvingother schedules, the results are associated with a greaterdegree of concurrent superstition.

Five other studies (in the order discussed here: Segal,; Lane, ; Hearst, ; Bruner & Revusky, ;Catania & Cutts, ) are relevant to the question of deal-ing with concurrent superstition, particularly in simulta-neously reinforceable concurrent operants. Each will bedescribed in turn, while the various reasons for their rel-evance will be summarized at the end of this section.

Segal () was interested in demonstrating experi-mental control over (differential reinforcement oflow rate) timing behavior by setting up another responseas the timing behavior itself, but on an independentschedule. She did this by training rats to press two leverson . (The responses were not simulta-neously reinforceable unless the rats could span the fiveinches that separated the levers.) Then, extinction ()replaced one schedule component or the other (some-times ; other times ). Addi-tional component combinations were also tested. Thedata showed that each concurrent component affectedthe other, at least initially when it was introduced. Forinstance, after being replaced by extinction, when the component was re–introduced, the response pat-tern was temporarily disrupted, recovering within a fewsessions. Thus, in this study, the occurrence of concurrentsuperstition, even with time–based schedules, was not alasting effect.


Lane () investigated the effects of various schedules on the chirping and pecking of chicks(responses which, in his view, were not incompatible intopography). While the responses were thus simulta-neously reinforceable, he found that they were seldomemitted simultaneously. More importantly, he observedsome superstitious relations between the two operants andtheir respective schedules. The rate of chirping changedin the same direction as the rate of pecking, when thepecking schedule was altered. Thus, in this study, whilethe responses seldom occurred simultaneously, concur-rent superstition was still observed with ratio–basedschedules; Lane suggested four possible reasons, but theseare relevant to the present paper only as reminders thatthe sources of superstitious effects are many.

Hearst () was interested in whether d–amphet-amine would suppress operant response rates as it doesconsummatory responses. He found that it did so, in adose–related manner, by exposing rats to different drugdoses after they had been trained to press two levers con-currently ( ). The relevance of this studyto the present topic is mainly procedural, for while thelevers were too far apart for responses to be simulta-neously emittable, this study is the only other study be-sides Sidman () to use two different reinforcersources. As with Sidman’s study, the use of two sourceswas forced by an aspect of the study; in this case it wasforced because one reinforcer was food and the other re-inforcer was water.

Bruner and Revusky () wanted to make overt,and record, the “collateral” behavior occurring in the in-terval prior to the availability of a response–produced re-inforcer on a schedule. They did this by havinghumans press four telegraph keys on a schedule. (The was >. but <..) The keyswere simultaneously available but the responses were notofficially simultaneously emittable (and therefore not si-multaneously reinforceable) as instructions were used togenerate response succession; the subjects had been in-structed to press only one key at a time. The data clearlyshowed each subject emitting a respectively different butstereotyped pattern of superstitious behavior. Thus, thisstudy also shows superstition with human subjects ontime–based schedules, with responses that were successiverather than simultaneously reinforceable.

Catania and Cutts (), from an interest in control-ling concurrent superstition, attempted to gain experi-mental control over button–press responses of humansubjects on a schedule. In their proce-dure, some subjects experienced no ; others had a fullsession with a ; for still others, a began some-time in the session. Data showed that a decreasedthe amount of superstitious responding.

The work of Catania and Cutts () represents awatershed for research bearing on the present topic priorto the appearance of Catania’s book chapter. Thisstudy lays the foundation for saying that concurrent su-perstition must be avoided—and response independencegenerated—through a procedure that separates responses intime (i.e., generates response succession) such as a .Still, the authors go on to point out a number of charac-teristics about humans that may make even s inad-equate for this purpose. Furthermore, the subjects hadbeen instructed to press only one button at a time, soeven the responses of those subjects experiencing no swere not officially simultaneously emittable. Other obser-vations of Catania and Cutts () are also worth not-ing. There was much variability in superstition acrosssubjects who experienced no . On the other handeven subjects with s for their full session showed vari-ous superstitions. These facts provide some good reasonsto seek alternative procedures to s for avoiding con-current superstitions, especially with human subjects(and these reasons are in addition to the incompatibilityof s with simultaneously emittable, simultaneouslyreinforceable operants).

Historically, Catania’s book chapter appearedbefore the last two studies to be discussed. But since itsimpact is felt mainly in the next section of this paper, itwill be sufficient here to note that in the end, Cataniaadvised researchers studying concurrent operants to avoidconcurrent superstitions by generating response indepen-dence through the use of s, making responses succes-sive. With few exceptions, researchers have abided byCatania’s advice. Two exceptions will be discussed(Striefel, ; then Harrison, ).

In Striefel’s () study, human subjects operatedseparate levers under different concurrent pairs. Tendifferent pairs were tested per subject. For all subjectsthe initial preference was always for the shorter of the pairof components. Then, a time–out period was intro-duced at the completion of each preferred component.This period was increased in one–second increments un-til the subject switched from the preferred but punishedcomponent of the pair to the previously non–preferredand unpunished component. After the number of com-pleted “non–preferred” ratios had reached a criterion, anew concurrent pair was introduced. Data showedthat as the difference between the components of the pairs increased, the time–out duration which generatedswitching also increased. Procedurally, while the leverswere simultaneously available, the responses were notofficially simultaneously emittable as the subjects were in-structed to operate only one lever at a time. The study ispertinent to the present topic for this reason, as well asfor not using any .


In Harrison’s () study, the responses were onlypotentially simultaneously reinforceable due to the trial–by–trial nature of the procedure (where the first responsemade ended the trial). Harrison trained rats to press onelever in the presence of sound from one speaker, and an-other lever in the presence of sound from anotherspeaker. The discriminative stimulus () was the positionof the sounding speaker. For some subjects, respondingon the lever adjacent to the speaker that sounded was re-inforced; for other subjects, non–adjacent respondingwas reinforced. Data showed that rats that were rein-forced for adjacent responding learned the discriminationquickly and with very little non–adjacent responding.However, rats that were reinforced for non–adjacent re-sponding learned much more slowly. Also, the latter ratsstarted out responding on the non–reinforced lever (thelever adjacent to the sounding speaker) at a high ratewhich increased before extinguishing (though never com-pletely) as responding on the reinforced lever (the non–adjacent lever) gained strength. Further experimentscontrolled for novelty and respondent conditioning ex-planations of this effect, which seems less reminiscent ofconcurrent superstition than of the type of behaviors ob-served in autoshaping studies (discussed by Staddon &Simmelhag, ).

Historical background summary. A review of somecharacteristics of the studies that have been considered herewill help summarize their contents and highlight their rel-evant aspects. These characteristics fall into three catego-ries: the species of the subject, the status of the particularoperants involved regarding simultaneous reinforcement,and the presence and nature of any superstition.

The subjects in these studies fit four classifications:birds (Lane, , with chicks); rodents (Harrison, ;Hearst, ; and Segal, ; all with rats); non–humanprimates (Ferster, , , with chimps; Sidman, ,with monkeys); and humans (Bruner & Revusky, ;Catania & Cutts, ; and Striefel, ).

Regarding the second category of characteristics, eachstudy can be classified (a) as using actually simultaneouslyreinforceable concurrent operants, (b) as using concur-rent operants whose status as being actually simulta-neously reinforceable is ambiguous and in need ofqualification, or (c) as using only potentially simulta-neously reinforceable concurrent operants. While none ofthese studies used non–simultaneously reinforceable op-erants, qualifications to the status of the operants in mostof these studies should be noted. (Non–simultaneouslyreinforceable operants are “biologically successive” oper-ants such as pigeons make when faced with two keys topeck which they are genetically incapable of pecking si-multaneously for they have but one head. Catania []refers to these as incompatible operants.)

Three studies used actually simultaneously reinforce-able operants. These are the studies by Ferster (, )and by Sidman ().

For three other studies (Harrison, ; Lane, ;and Segal, ) the possible use of actually simulta-neously reinforceable operants requires qualification.Segal’s rats had to be able to span the five inches separat-ing the two levers if their responses were to be simulta-neously reinforceable, and Segal did not comment onwhether or not the rats could or did accomplish this un-likely reach. Lane’s chicks seldom emitted their responsessimultaneously, and Lane offered no special commentsabout this phenomenon. And Harrison’s trial–by–trialprocedure made it difficult to say more about the re-sponses he studied other than that they were procedurallysimultaneously emittable.

The other four studies used potentially simulta-neously reinforceable operants. They can be classified ac-cording to the manner in which their simultaneousreinforcement status came to be only potential ratherthan actual. One method to do this is to completely sepa-rate the responses through the structure of the apparatus;these responses might then be called “structurally succes-sive” (as when Hearst, , spaced the levers so far apartthat they could not be pressed simultaneously). Anothermethod that detracts from the simultaneity of the re-sponses is the practice of instructing human subjects notto emit more than one response at a time; this makes theresponses “instructionally successive” (as with Bruner &Revusky, ; Catania & Cutts, ; and Striefel, ).A third method involves the use of a contingency;this makes the responses “contingently successive” (aswith Catania & Cutts, ).

The third category of characteristics shared by thesestudies concerns the presence and nature of superstitiouseffects, or their absence (i.e., response independence).Each study deserves separate comment on this matteras the particular schedules involved differ from one studyto the next.

� Ferster () found little or no su-perstition with .

� Sidman () found consistent con-current superstition with ,avoidance schedules, but obtainedseparation of response classes with , avoidance schedules.

� Ferster () found fairly consis-tent independence of scheduleeffects with complex schedules like – ,though his chimps’ sustaining ofhigh s may be due to an adventi-tious schedule interaction.


� Segal () observed initial but tem-porary superstitious effects when ex-tinction replaced either componentof a schedule.

� Lane (), using various schedules, found that chirping alwayschanged in the same manner thatpecking changed when only theschedule component for peckingwas altered.

� Hearst () saw little or no supersti-tion with a scheduleand structurally successive responses.(For these components, usingwidely separated manipulanda—rather than s—generated re-sponse independence.)

� Bruner and Revusky () obtained“elegant” (in the engineering sense)superstitious effects with a schedule and responsesmade successive, but not independent,by instructions (and again, no s).

� Catania and Cutts (), using , and responses madesuccessive by instructions, found su-perstition even with the use of a ,though more was observed in the ab-sence of a .

� Striefel () did not report any su-perstition from using pairswith an incrementing time–out pe-riod (to generate preference match-ing), and with responses madesuccessive by instructions.

� Harrison () observed supersti-tious effects with his trial–by–trialprocedure, but these were not seenas appropriately tacted as “concur-rent superstition.”

Of all of these studies, only the last two were under-taken after the publication of Catania’s influential book chapter. This phenomenon is significant for thenext two sections which discuss why it happened andwhat might be done next.

Tentative ExplanationBetween the appearance of Catania’s book chap-

ter and (when the present study was conducted) theliterature offered no other studies that came any closerthan Striefel () and Harrison () to dealing withthe topic of simultaneously reinforceable concurrent op-erants. There are reasons for this paucity of research.

What can be done about that will be addressed in thenext section.

Catania () himself provided some of the reasonsfor the paucity in research on simultaneously rein-forceable concurrent operants. Catania was concernedwith the possibility of concurrent superstition, whichhe defined in his book chapter as “the accidentalstrengthening or maintenance of one operant by rein-forcement programmed for another” (p. ). Re-searchers need to eliminate the possibility of suchevents occurring. But methods to do this that retainedfull response simultaneity were little examined. Instead,the most common methods used to try to avoid concur-rent superstition involved trying to make responses inde-pendent by not allowing them to occur simultaneously,which makes the responses successive. However, makingresponses successive is not a guarantee that the responseswill be independent.

Various procedures are successful at making concur-rent responses successive (not simultaneously emittable/reinforceable), as has been seen with the studies alreadydiscussed. The two types of responses that these proce-dures encompass are those that are successive becausethey are incompatible (e.g., a pigeon’s pecking responsesto two separate, even if close together, keys), and re-sponses that are compatible but also successive by virtueof some research technique. These techniques include(a) separating the response manipulanda physically sothat the subject cannot operate them at the same time,(b) using instructions that allow the operation of but onemanipulandum at a time, (c) using s, (d) using vari-ous combinations of these techniques, and (e) additionaltechniques not directly relevant to the present study suchas the “Findley” procedure (Findley, ). Catania ()dealt briefly with most of these methods, but concen-trated his efforts on the .

With good reason Catania prefers s as the tech-nique of choice. Both before and after his bookchapter, so much of the research on concurrent operantswas using pigeons as subjects. Since their key peck re-sponses, being biologically successive, cannot be simulta-neous, there is no reason for researchers using pigeons totry to control concurrent superstition with a techniquethat allows response simultaneity. Yet these biologicallysuccessive responses necessarily involve switching fromone key to the other, and the switching response itself canbecome a separate, superstitiously controlled operant. Inthis situation s are valuable because they lessen thechance of switching being adventitiously reinforced.

Also, s dovetail with the solution to another pro-cedural problem that can arise with subjects whose re-sponses are biologically successive. When the procedureinvolves concurrent ratio schedules, responding can belimited to the more favorable schedule; the subject does


not contact the other schedule. The solution is to use in-terval schedules; each schedule requires but one responsefor reinforcement after the interval ends. Responses canbe (and are) made on the less favorable key during the fa-vorable interval, and some of these responses get rein-forced. Thus, the nature of interval schedules (withresearchers seeming to prefer schedules) brings thesubject into contact with all the contingencies. However,responding on both alternatives with biologically succes-sive responses under s necessarily involves switching,with its own problem (i.e., concurrent superstition, as al-ready described, which is more likely with s as the dis-cussion of Sidman’s study noted) and its ownsolution (s).

Overall, then, when studying contingencies usingbiologically successive responses (like pigeons and keypecks), s and s work especially well together, asCatania suggests. The s generate responding on bothalternative manipulanda while the s lessen the chanceof adventitious reinforcement of switching. Thus, satis-factory independence of schedule effects (i.e., responseindependence) can be achieved.

However, those solutions are not helpful when study-ing contingencies involving simultaneously emittable/re-inforceable responses. For instance, when Sidman ()could not get schedule effect independence using s, heachieved independence of schedule effects using s(rather than s, which would have eliminated the si-multaneous reinforcement status of the responses). Un-fortunately, the possibilities suggested by Sidman’sfindings received minimal treatment in Catania’s bookchapter. The findings of other relevant studies (alreadydiscussed) shared the same fate. Catania’s treatment ofthe literature showed and encouraged a preference amongresearchers to avoid concurrent superstition by using in-compatible operants (if possible) and then forcing furtherresponse succession—and hopefully independence—byusing s.

Catania never said that incompatible responses ands were the only options for avoiding concurrent su-perstition. However, since the most common responses,in studies involving concurrent schedules, were pigeons’biologically successive key pecks, to which these optionsapply, it is not that surprising that so little work has beendone with simultaneously reinforceable responses, towhich these options do not apply.

Tentative explanation summary. There are severalreasons to seek alternative procedures to s to avoidconcurrent superstition, especially with human subjects.The research studies that have been reviewed here werediscussed because few dealt with s or incompatibleresponses. Yet none of them could be properly describedas being overwhelmed by superstition. Some of themeven showed how s sometimes are not effective.

Ferster () stated a clear preference for simultaneouslyreinforceable responses, and he pointed out the relevanceof these to human behavior. Catania and Cutts ()drew attention to some characteristics of humans that ar-gue against the use of s with human subjects. Ands simply do not allow study of more complex behav-ior in the form of simultaneously emittable and rein-forceable responses because they force responsesuccession. Other techniques that generate response suc-cession, along with s, simply cannot be used with re-sponses that reflect the complexity of behavior, especiallyhuman behavior; they are not adequate analogs of “reallife” behavior patterns.

So, especially if human behavior is the behavior ofconcern, and/or if s and other response–successiontechniques are inappropriate because simultaneouslyreinforceable responses are the object of study, thenhow can concurrent superstition be avoided? Fortu-nately, other techniques besides those leading to re-sponse succession seem to be available to generatesensitivity to contingencies.

Possible ResolutionOne important characteristic of the studies already

discussed has not yet received much attention. That char-acteristic is the number of reinforcer sources used in theresearch. All but two studies (Sidman, ; Hearst, )used one reinforcer source, such as a single food magazineor hopper, located between the two manipulanda. Sidman,as well as Hearst used two sources because their respectiveprocedures forced them to do so; the use of two sourceswas not the point of the research. Yet the orderliness oftheir data suggests that the use of multiple reinforcersources is worthy of being studied for its own sake.

“Multiple sources” refers to the reinforcer or otherselector sources in a situation in which each manipulan-dum has its own physically associated selector source(e.g., a separate food magazine or point counter or handslapper located near each lever or chain or key). Multiplesources should be studied because the problem of concur-rent superstition may actually be a problem of some am-biguity in the contingencies that results from having onlyone shared selector source (i.e., some concurrent supersti-tion may be an artifact of the experimental apparatus).Multiple sources may prove to be more discriminablethan one source with respect to which response producesany particular selector. If the contingencies used to com-pare single and multiple sources involve reinforcementfor every response (continuous reinforcement frequency,or ) and extinction (), then the potential fordefinitive results is increased; since these contingenciesare maximally different, a single source of reinforcementhas the most opportunity to control responding withoutsuperstitious effects. If greater superstitious effects are ob-


served with single sources than with multiple sources,under these contingencies, then the multi–selector sourceprocedure gains support. A whole area of behavior, com-plex behavior, particularly human behavior, may be ex-posed to more thorough investigation: the area ofsimultaneously selectable operants.

Possible resolution summary. What is desired issensitivity to the contingencies. Successive responses maynot be required to achieve this, and in any case are incon-gruent with simultaneously selectable operants. Theseoperants comprise an inadequately studied, and poten-tially significant area in behaviorological science. Onlymore research will resolve the question of whether ornot the use of multiple selector sources will be able toachieve the independence of schedule effects thatwould indicate experimental control over sensitivity tothe contingencies.

The present study addressed that question by com-paring the effectiveness of a single reinforcer source (asource that was shared by responses on two manipu-landa) with the effectiveness of dual reinforcer sources(sources that were each physically associated with adifferent response manipulandum). This study assessedthe relative effects of the single reinforcer source versusdual reinforcer sources for simultaneously emittableand simultaneously reinforceable responses using con-current schedules involving and contingencieswith human subjects.

Method

SubjectsFrom the many college students (in an introductory

social science course) who volunteered to serve as sub-jects, the seven who participated were selected on the ba-sis that their schedule matched the experimenter’slaboratory schedule. Two subjects were right–handedmales, aged and , and five subjects were females,with ages between and (mean of .). Of these five,one was left–handed.

All subjects were taking, as non–majors, their firstcollege behavior–related course. They were all naiveabout the natural science of behaviorology in general andabout this experiment in particular. The subjects knewthat they would receive a small number of bonus pointsfrom their class professor for participating. They werealso told, prior to volunteering, that it was possible forparticipants to earn a maximum of one dollar ($.)from each of their four to eight experimental sessions,and that each session would be about to minuteslong. Furthermore, they were asked not to discuss the ex-periment with other subjects or anyone else. (All subjects

reported at the end of the study that they had compliedwith this request.)

All subjects experienced all levels of the independentvariable, with a within–subjects design involving bothwithin–session and between–session comparisons. How-ever, two subjects did not complete all parts of the experi-ment. One of these (subject ; subjects are referred to bycode letters) became ill and was unable to return, afterthe within–session comparison, to participate in the be-tween–session comparison. The other (subject ) was avictim of a scheduling error, and so participated only inthe between–session comparison. All five remaining sub-jects participated in both the within–session and be-tween–session comparisons. All subjects were free towithdraw from the study at any time without penalty,and were so informed.

At the end of the study, all subjects were given the fullamount of one dollar for each session that they com-pleted, regardless of how many points–for–money theyearned during each session (they had not been informedthat this would occur). They were also fully briefed at thistime about the purposes, procedures, results, and possibleconclusions of the study.)

ApparatusA room approximately . m long by . m wide by

. m high served as the human operant chamber. Thewall was painted navy gray, while the ceiling was black.The brick floor was unpainted and uncovered. A lightfixture, with eight –inch–long florescent tubes, hungfrom the ceiling. A single door provided access. A two–way mirror, cm wide by cm high, was blockedoff from the outside except for a cm square sectionin a lower corner which could be used for observationduring a session. A non–oscillating air–circulation fanwas used to mask possible noises from adjacent rooms.A comfortable chair for the subject and a small table forthe subject’s stimulus/response/consequence panel werethe only furnishings in the room. Figure shows the typi-cal arrangement of subject, chair, table, and panel duringa session.

The subject’s panel was made by putting a wooden,black face plate at a ° angle (leaning away from thesubject) onto a wooden, yellow box shell measuring cm deep at the base, cm high at the rear, and cmacross the front. The face plate measured cm deepand cm across. Two standard Acme telegraph keysextended out from the box, beneath the face plate. Thecenter of each key was placed cm from the side edge ofthe box. A force of .±. (± g) would displaceeither key through the ±. mm distance required toclose its circuit.

The face plate contained various stimuli. Directlyabove each key, cm from the bottom edge of the face


plate, was a pair of lights. In the center of the face platewas another pair of lights on the same level as the twoside pairs of lights. Each pair of lights was associated witha counter. The left light of each pair was one of threewhite lights used together as pacing lights. The right lightof each pair was yellow and flashed when its associatedcounter was incremented as part of the occurrence ofreinforcement. Above each pair of lights was its associatedVeeder–Root, six–digit counter, model –. Whenincremented, these counters would sound an audibleclick. No counter could be returned to zero except by theexperimenter, for the reset knobs were removed duringexperimental sessions. A red light was placed cm aboveeach side counter. If this light was off, no consequence ofany sort was programmed for the key on the correspond-ing side, as if the key was disconnected from the pro-gramming equipment. These are called “key–connected”lights. In the center, on the same level as the key–con-nected lights, was a green light used as a house light. Asession was in progress so long as this light remainedon. Below the house light was a circular switch. This wasto be used as a panic switch with which a subject couldend the session prematurely. (Its use, however, was notwithout consequences.)

The subject’s panel was connected by cable to a com-puter, an interface, and two cumulative recorders (one for

the responses made by each hand) located in anotherroom across the hall. A Digital Equipment Corporation / computer controlled the programming of thesequence of events in each session automatically. Pro-gramming was supplied through Super software(Snapper & Inglis, ) operated through a inter-face (provided by State Systems, Inc. of Kalamazoo, ).By this arrangement data collection, including the opera-tion of the cumulative recorders, was also automatic. Two Gerbrands cumulative recorders (Model ) wereused. Paper drive gears with a : ratio (commonly called“pigeon gears”) were used to obtain a paper movementrate of cm per hour.

Figure shows (a) the arrangement of responsemanipulanda and stimuli on the subject’s panel, and(b) the two cumulative recorders used for primarydata collection.

ProceduresThe basic experimental question was whether one

source of reinforcement, or two sources of reinforcement,would be more effective—with less superstitious respond-ing—in controlling simultaneously reinforceable concur-rent human operants. In addressing this question, certainprocedures were used.

Figure 1. Typical arrangement of subject, chair, table, and panel.

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General procedures. Instructions to the subjectsconcerned the operation of the panel, and their task.Regarding the operation of the panel, instructionsincluded these:

� The session begins when the greenlight goes on, and ends when thegreen light goes off.

Figure 2. Arrangement of (a) response manipulanda and stimulion the subject’s panel, and (b) the two cumulative recorders.

A. Arrangement of the subject’s panel.

B. Arrangement of the cumulative recorders.

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� In the first session only one red lightwill come on at a time; work only onthe key beneath the red light that ison. If the white lights [the pacinglights] flash, press the operating keyat a speed such that the yellow lightwill flash whenever the white lightflashes. After the first session, nowhite lights are ever used.

� In all subsequent sessions both redlights will either be on or be off to-gether. When they are on, both keysare operating. This does not meanthat both keys will necessarily beequally effective in producing points.With both red lights on, you maywork on one or the other or bothkeys. When the red lights are off, it isa rest period and neither key will beoperating. [No subject was observedto use a key whose associated redlight was out.]

� Use the left hand with the left keyand the right hand with the rightkey. [No subject was observed todo otherwise.]

� Sometimes key pressing producespoints that are added up on acounter. Each point is accompaniedby a flash of the yellow light belowthe counter. [Points and flashes werethe anticipated and observed condi-tioned added reinforcers for keypressing responses.]

� Sometimes both the points producedby the left key and the points pro-duced by the right key appear on thecenter counter only. At other timesthe points produced by left key press-ing appear only on the left counter,and the points produced by right keypressing appear only on the rightcounter. Points never appear on allthree counters at the same time.

� If, for any reason, you want to endthe session before the green light goesoff, you can do so by turning theknob located below the green light.However, if you do this, you forfeit% of your earned points for thatsession. [No subject ever used thispanic switch.]

Regarding the subject’s task, instructions included these:� Points equal money! The more points

you generate, the more money youearn. Since a fixed amount of moneyis available for each session ($.),while the number of points availablefor each session varies, the amount ofmoney you receive will be that per-cent of the money available thatequals the percent you earned of thepossible points.

� Your task is to generate as manypoints as possible, working on one orthe other or both keys. While work-ing on both keys, press both keys atthe same time. [Responses were si-multaneously emittable and, withoutbringing any other special contingen-cies to bear, it was preferred that theybe emitted simultaneously.]

The daily routine for each subject began with her orhis arrival at the laboratory. Each was asked for his or herwatch as watches were not allowed in the experimentalroom. The instructions were then reviewed and the ses-sion began. When the session was over, the subject wasgiven a receipt which stated that she or he had earned upto one dollar for that session, and that all earnings wouldbe paid at the end of the study.

The four sessions planned for each subject included(a) a training session, (b) a session of one versus two re-inforcer sources as a within–session comparison, (c) a ses-sion with only one reinforcer source throughout as thefirst part of a between–session comparison, and (d) a ses-sion with two reinforcer sources throughout as the sec-ond and last part of the between–session comparison.Table depicts the sequence of sessions received by eachsubject. Several abbreviations, which are used in the tableas well as in later text, are introduced here: Subjects aredesignated by letters ( through ). The two differenttypes of training sessions are represented by and . Thewithin–session comparison session is represented by . Thetwo sessions of the between–session comparison are rep-resented by (using one reinforcer source) and (usingtwo reinforcer sources). Subjects and also experi-enced two other sessions, represented by and , thatwere part of another study that assessed one versus tworeinforcer sources on variable ratio () schedules (re-ported in Ledoux, b). These sessions occurred afterthe and sessions, but before the and sessions.

Each session lasted about minutes. Each subjectwas to participate in each of the four planned sessions onthe basis of one session per day. However, due to sched-uling concerns, two of the seven subjects had two of theirsessions on the same day. Subject had the last two ses-


sions ( and ) on the same day, some hours apart,while subject had the first two sessions ( and ) onthe same day, back to back.

In addition to the separate cumulative records foreach hand, data collection included recording the num-ber of responses and reinforcements for each hand duringeach component pair, as well as the duration of eachcomponent pair. From these, response and reinforcementrates could be calculated for each hand under each com-ponent pair. (A component pair is a pair of schedules,one for each hand, in effect concurrently, that comprisesone of six components in each session.)

Training sessions. The training session had beenoriginally designed for both an earlier study (Ledoux,b) as well as for the present study, even though two schedules were among its component pairs. However,the initial response rates of early subjects showed toomuch variability, perhaps partly due to early fatigue forsome subjects who were observed to press the keys at ahigh rate initially. The use of some of the panel lights as“pacing lights,” along with the instructions regardingtheir use, in the training session was predicted to help de-crease the variability of subjects’ initial response rates. Sothe training session was designed and successfully usedwith the pacing lights, and also, for the rest of the presentstudy, without the schedules.

In the single, central counter served as the rein-forcer source throughout the session. The subject oper-ated each hand alone, alternating with the other hand,with a second time–out between schedules. At firsteach hand was under for reinforcements, theneach hand was under for reinforcements, andfinally each hand was under for reinforcements.

In the subject also operated each hand alone, alter-nating with the other hand after a second time–outevery reinforcements. The illumination of one or theother key–connected light indicated which key—andthus which hand—to use. At first each hand workedwhile the pacing lights flashed every . of a second, withreinforcements accruing on the center counter. Theneach hand worked without the pacing lights operating,and with the reinforcements still accruing on the centercounter. Next each hand worked with the pacing lightsagain operating, but reinforcements accrued on the sidecounter associated with the key in use. Finally each handagain worked without the pacing lights operating, andwith reinforcements still accruing on the side counter as-sociated with the key in use.

Experimental sessions. Each of the three experimen-tal sessions involved both hands being able to operatetheir respective keys at the same time throughout a se-quence of six component pairs where one hand was on

Session SequenceSubject

1 2 3 4 5 6

AS T1* W** A1*** A2 B1 B2

BS T1 W A1 A2 B1 B2

CS T1 W B1 B2

DS T2 W B1 B2

ES T2 W

FS T2 B1 B2

GS T2 B1 W B2

* Different types of training sessions are represented by T1 and T2.** The within–session comparison session is represented by W.*** The between–session comparison sessions are represented by A1 and A2, and by B1

and B2. (A1 and A2 are parts of another study; see text.)

Table 1. Sequence of sessions received by each subject.


while the other hand was on either or .The component pairs were separated by a rest period(time–out) of seconds duration. For all experimentalsessions the rest period, and thus the change from onepair of schedules to the next, occurred as soon as oneor the other hand had produced reinforcements.Table depicts the number of reinforcement sources,and the sequence of component pairs, used in the threeexperimental sessions.

During the session (the within–session comparisonsession) the first three component pairs used the singlereinforcer source (i.e., the center counter). The re-maining three component pairs were sequenced exactlyas the first three but used the dual reinforcer sources(i.e., the side counters).

The and sessions (the between–session com-parison sessions) followed a course similar to the courseof the session. During the session (the first of the

two sessions comprising the between–session compari-son) the single reinforcer source of the center counter wasused throughout the series of six concurrent componentpairs. During the session (the second of the two ses-sions comprising the between–session comparison) thedual reinforcer sources of the side counters were usedthroughout a repetition of the series of six concurrentcomponent pairs used in the session.

Results

The basic dependent variable in this study was the rate ofresponse for each hand during each component pair. Ingeneral, while the response rate was high for the hand on irrespective of the number of reinforcer sources, therate was low for the hand on under two separatesources but high for the hand on under one source.

Component Pair Sequence* # of ReinforcerSources per

Session TypeLeft Hand Right Hand

component pair

WSession

(within–sessioncomparison)

CRFCRFEXTCRFCRFEXT

CRFEXTCRFCRFEXTCRF

1**11

2***22

B1Session

(first part of thebetween–session

comparison)

CRFCRFEXTCRFEXTCRF

CRFEXTCRFCRFCRFEXT

1(one source used

throughout)**

B2Session

(last part of thebetween–session

comparison)

All component pairs repeat B1 sequence.2

(two sources usedthroughout)***

* Read down for sequence of pairs.** “One source” always refers to the center counter/light.*** “Two sources” always refers to the side counters/lights.

Table 2. Number of conditioned reinforcer sources, and sequences ofcomponent pairs, for within–session and between–session comparisons.


Figures , , , , and show the left and right handcumulative records for some subjects from each of thethree experimental sessions. These examples are typical ofthe data of all the subjects. In these records, the cumula-tive recorder pens are not used the same way under both

Figure shows the left hand and right hand cumula-tive records for subjects and during the session.The response rates are high and steady for each hand ofboth of these subjects under the single–source conditionregardless of whether the contingency involves a

Figure 3. Cumulative records of left and right hand responding forsubjects BS and GS during the within–session comparison session (W).

LeftHand

CRF CRF EXT CRF CRF EXTSubject BS

RightHand

CRF EXT CRF CRF EXT CRF10 Minutes

400

Res

pons

es

CRF CRF EXT CRF CRF EXT

LeftHand

Subject GS

RightHand

CRF EXT CRF CRF EXT CRF

One SourceW Session

Two Sources

single–source and dual–source condi-tions. The pens are used in the usualmanner under the two–source condi-tion; the hatch marks of the responsepen indicate reinforcements (making athick black line, due to the sched-ule) along the slope of the responseline, while changes from one compo-nent pair to the next are noted by theoffset or reset of the event pen acrossthe bottom of each record. However,under the single–source condition, penuse is reversed with respect to reinforcerhatch marks and component–changemarks; reinforcements are shown ashatch marks (again making a thickblack line, due to the schedule) butalong the flat of the event pen line,while changes from one componentpair to the next are noted by the offsetor reset of the response pen on theslope of the response line.

A further reason for using the re-corder pens in those ways is that, bydoing so, the records could graphicallydepict whether or not reinforcementsappeared on a source associated withthe hand/key that produced those rein-forcements. Under two sources therecord shows each reinforcer hatchmark right on the pen step for the re-sponse that produced that reinforcer.However, under one source, while thereinforcer hatch marks still appear onthe record of the hand that producedthem (along the event pen line of thatrecord) they do not appear with the ac-tual responses that produced them.This is a way of showing that underone source the reinforcements appearedon a counter not physically associatedwith either key (the center counter),while under two sources each reinforce-ment does appear on a counter physi-cally associated with one or the otherkey (the counter on the same side as thekey that produced the reinforcement).


schedule or . Under the dual–source condition,their response rates remain high and steady under ,and decrease to zero under . The extinction curveof the right hand of under the dual–source condi-tion, as aesthetic as it might be, is not typical of most

made a single testing–like response on the key aftereach points earned on the key. No other subjectdisplayed this type of pattern (a professor, examining thispattern, expressed the hope that this reality–testing stu-dent would apply for graduate school).

Figure 4. Cumulative records of left and right hand responding forsubjects ES and DS during the within–session comparison session (W).

LeftHand

10 Minutes

LeftHand

Subject DS

RightHand

W SessionOne Source Two Sources

RightHand

CRF CRF EXT CRF CRF EXTSubject ES



CRF CRF EXT CRF CRF EXT

400

Res

pons

es

other subjects. The right hand, dual–source extinction “curve” of ismore typical of other subjects’“curves” under the first occurrence ofa dual–source contingency.

Figure shows the left hand andright hand cumulative records forsubjects and during the session.For , rates under all contingen-cies are high and steady. However, theinitial single–source contingencywas effective in eliminating right handresponding. Yet in the next component,the contingency on the left handwas ineffective, as shown by the per-sistence of a high and steady rate.Subject reported that respondingdid not begin in this component un-til after an extra minute or so of“rest” had been taken. Subject wasthe only subject who, after beingaffected by an contingency underthe single–source condition, wasunaffected by that same contingency inthe subsequent single–source /component in the same session. Forsubject the record shows a high andsteady response rate under all con-tingencies, as well as under the initial,single–source contingency (on theright hand). However, under the re-maining contingencies, includingthe second single–source contin-gency, responding is eliminated.

Figure and Figure show the lefthand and right hand cumulativerecords for subjects and , respec-tively, during the and sessions.The response rates are high and steadyfor each hand of both of these subjectsduring the single–source session irre-spective of whether the contingency in-volves or . During thedual–source session, their responserates remain high and steady under, and decrease to zero under .Although Figure is too reduced toshow it well, throughout all dual–source contingencies, subject


RightHand

LeftHand

10 Minutes

B2 SessionB1 Session(Two Source)(One Source)

CRF CRF EXT CRF EXT CRF

CRF EXT CRF CRF CRF EXT



Subject GS

Figure 5. Cumulative records of left and right hand responding for subject GSduring the between–session comparison sessions (B1 and B2).

400

Res

pons

es

B2 SessionB1 Session(One Source) (Two Source)

RightHand

LeftHand





10 Minutes

Subject BS

Figure 6. Cumulative records of left and right hand responding for subject BSduring the between–session comparison sessions (B1 and B2).

400

Res

pons

es


Figure shows the left hand and right hand cumula-tive records for subject during the and sessions.Regardless of whether the condition in effect is single–source or dual–sources, the response rates for both handsare high and steady under . However, with the excep-tion of one single–source contingency, whenever ahand is under , the response rate drops to zero. Theone exception is the first single–source contingency,on the right hand, where the response rate remains highand steady throughout. Also, more responding can beseen as having occurred at the beginning of the other contingencies under the single–source condition beforeabruptly ceasing, than under the dual–source condition.

The data for subject is particularly relevant as itshows that some subjects do come under some control of contingencies even in the single–reinforcer sourcecondition. Yet for all subjects responding is eventually ifnot immediately eliminated by any contingency un-der the dual–reinforcer source condition. This compara-tive result between the single–source condition and thedual–source condition is the most reliable, salient andsignificant result of the study.

An elaboration of the number of responses madein extinction, both during the session and during

the and sessions, allows further comparison be-tween the single–source condition and the dual–source condition. Tables and list the actualnumber, for all subjects, of responses on keys that wereprogrammed with an contingency.

Table depicts the number of responses in extinctionfor each subject during the session. In this table, thereference to the conditions (single–source or dual–source) is a column heading.

Table depicts the number of responses in extinctionfor each subject during the and sessions. However,in this table, the reference to the conditions (single–source or dual–source) is a row heading.

Comparisons between the single–source conditionand the dual–source condition yield two basic observa-tions. In most cases, the number of responses made on the key under the single–source condition is of the samemagnitude as the number of responses made on the key,which had to be pressed times before the compo-nents would change. Where this is not the case, a glanceat the single–source components of the cumulativerecord (or Tables or ) would reveal an example inwhich responding on the key had ceased sometimeduring the single–source component. The session data

RightHand

LeftHand

B2 Session

(Two Source)

B1 Session

(One Source)10 Minutes


CRF EXT CRF CRF CRF EXT CRF EXT CRF CRF CRF EXT


Subject DS

Figure 7. Cumulative records of left and right hand responding for subject DSduring the between–session comparison sessions (B1 and B2).

400

Res

pons

es


show only two cases out of possible cases where re-sponding under a single source was sensitive to . The session data show only seven cases out of possiblecases that fit this description. All of these cases aremarked with an asterisk in Tables and . Contrast thisinformation with the fact that the number of responsesmade on the key under the dual–source condition is al-ways less than one–third of the 1000 responses required of thehand operating the key to change components. The cu-mulative records show responding on the key underthe dual–source condition to have always ceased duringthe component. In summary, under the single–sourcecondition, subjects were sensitive to in of cases;under the dual–source condition, they were sensitive in of cases (i.e., under the single source of caseswere insensitive to , while under dual sources none of cases were insensitive to ).

Rate of response data corroborates number of re-sponse data. Table presents rate of response data foreach hand of each subject in each component of the session. Table presents rate of response data for eachhand of each subject in each component of the and sessions. (For both tables, minutes were rounded towhole numbers.)

considerable superstitious responding. This was the caseeven though the single–source condition in this studyhad the greatest possible chance to control respondingwithout superstitious effects due to the concurrent use oftwo schedules, and , that are maximally differentin terms of the availability of reinforcement under each.

The data indicate that when human subjects’ simul-taneously emittable responses (here, key pressing) are si-multaneously reinforceable under and contingencies, the operant under is seldom sensitiveto that contingency when the setting involves a singlesource of reinforcement not physically associated withany of the manipulanda. On the other hand, these sub-jects were always sensitive to the contingency whenthe setting involved two sources of reinforcement, eachphysically associated with a different manipulandum.These results suggest, in comparison with the usual singlesource of reinforcement, that, for multiple operants, mul-tiple sources of reinforcement are (a) more discriminablewith respect to which response produced any particularreinforcer, and (b) more effective in generating sensitivityto the contingencies.

Facing Extinction–Contingency SensitivityHowever, the responding of three of the subjects in

this study was sensitive to an contingency under thesingle–source condition in one or more of the /

Sequence of extinction contingenciesin the W session*

Subject Single reinforcer source Dual reinforcer sources1st EXT 2nd EXT 3rd EXT 4th EXT

AS

BS

CS

DS

ES

GS

973

843

918

778

18**

842

1061

1155

978

107**

1266

1094

332

111

10

14

232

28

21

19

6

3

10

6

* Each row presents the data for one session.** See text.

Table 3. Number of responses in extinction for all subjects during the within–session comparison session.

Discussion

This research addressed thequestion of how to obtain sen-sitivity to contingencies withmultiple operant behaviorsthat are simultaneously emit-table and simultaneously rein-forceable. In this study theeffectiveness of a single rein-forcer source (a source that isshared by responses on twomanipulanda) was comparedwith the effectiveness of dualreinforcer sources (sources thatare each physically associatedwith a different response ma-nipulandum). Multiple oper-ants that simultaneouslyproduced reinforcers frommultiple sources, each physi-cally associated with a differentresponse manipulandum, showedno responding that could rea-sonably be labeled supersti-tious, while multiple operantsthat produced reinforcers fromsingle, shared sources showed


components in one or both of the sessions that involvedsingle–sources. One subject (—see Figure ) was sensi-tive to the contingency in the first of the two /components in the first half of the session. Anothersubject (—see Figures and ) was both (a) sensitive tothe contingency in the second of the two /components in the first half of the session, and (b) sen-sitive to the contingency in the second, third, andfourth (of four) / components in the session.The third subject (—see Table ) was sensitive to the contingency in all four of the / componentsin the session. In suggesting explanations for these oc-currences, a number of factors can be considered; any ofthese may have operated singly or in combinations in anyparticular instance of sensitivity.

One possible explanation of some of the instances ofsingle–source effectiveness of an contingency is thechange in reinforcement density from one componentpair to the next. When a / component is followedby a / component, a % reduction in rein-forcement density for simultaneous responding occurs (as

The second single–source / component of the session for subject , however, also needs explain-ing. In this component, the only remaining single–source / component in the session, the alreadyreduced reinforcement density remained the same, and did not eliminate responding on the key. (Eventhough such insensitivity is basically unsurprising, its oc-currence after an –sensitive / component is acuriosity demanding attention.) This component andthe preceding component were identical except for thereversal of the hand producing reinforcement. Perhaps inthis case the lack of sensitivity to extinction occurreddue to a sequence effect. The reinforcement density oneach key would have reversed, with one hand changingfrom every response being reinforced to none being rein-forced, while the other hand changed from no responsesbeing reinforced to every response being reinforced.However, all reinforcers continued to accrue only on thecenter, single source. The key on which responding in ex-tinction occurred in this second / component wasactually the key for the hand on which the opposite con-

Subject # of Session*Sources

Sequence of extinctioncontingencies in theB1 and B2 sessions

1st EXT 2nd EXT 3rd EXT 4th EXT

AS 1 B1AS 2 B2

BS 1 B1BS 2 B2

CS 1 B1CS 2 B2

DS 1 B1DS 2 B2

FS 1 B1FS 2 B2

GS 1 B1GS 2 B2

83971

76831

8417

7868

61**144

85516

118780

123914

9859

139**6

17**59

144813

121567

120417

8618

77**7

22**29

140812

81461

84812

9332

151**2

8**51

83410

* Each row presents the data for one session (B1 or B2).** See text.

Table 4. Number of responses in extinction for all subjects duringthe between–session comparison sessions.

will be seen, this reduction maybe irrelevant if responding is al-ternating rather than simulta-neous). Although, under thesingle–source condition, all re-inforcements accrue on theshared, center counter, this re-duction may still have madethe density in the /component discriminable (inthe usual functional sense, notin any “agency” sense; seeBaum, [Also, see Fraley, inpress.—Ed.]) from the greaterdensity of the preceding / component, ultimately re-sulting in the contingencyeffectively controlling keyresponding (eliminating thatresponding) for some subjects.The responding of subject (Figure ) in the first single–source component of the ses-sion, and subject (Figure )in the third single–sourcecomponent of the session,and subject (Table ) in thefirst and third single–sourcecomponent of the session,provides examples of the pos-sible effects of the reinforce-ment–density change.


tingency had produced all of the reinforcers—but on thecenter, single source—in the preceding component. Therelevance of this possibility needs further research, andthe matter is not considered to have been given an ad-equate account here.

Subject (Figures and ) and subject (Table )often differed from subject . The responding of bothsubject (in the second single–source / compo-nent of the session and the second and fourth single–source / components of the session), andsubject (in the second and fourth single–source / components of the session), provides examples inwhich a single–source contingency was effective in a/ component that was preceded by a /component, regardless of whether or not the contin-gency had been effective in that preceding component.The explanation of these subjects’ responding being sen-sitive to the contingency under most single–source/ components is incomplete. It may involve yetanother possible explanation of single–sourceeffectiveness of an contingency. This explanationconcerns some subjective observations. Those subjectswho were sensitive to single–source contingencies(e.g., subject ) were often observed to emit pressing re-sponses on the two keys in a noticeably alternating pat-tern—first one hand, then the other hand, then the onehand, and so on—that made their responses sequentialand successive rather than simultaneous (potential rea-sons offered by subjects for this pattern included keepingtime with hummed music and avoiding fatigue). How-ever, those subjects who were not sensitive to single–source contingencies (e.g., subjects and ) wereobserved to emit pressing responses in a simultaneouspattern, each hand pressing its key essentially at the sametime as the other hand, rather than sequentially. Is this anobservation of a functional relationship? This questionneeds to be researched, although generating response suc-cession (e.g., through s) is a standard practice for re-ducing concurrent superstition even though it eliminatesresponse simultaneity.

In studying that question the effect of equipmentfunctioning on response patterns needs to be considered.Due to the constraints of computer functioning andlogic, no two responses could be measured as simulta-neous. They could, however, still be considered func-tionally simultaneous; for instance, they could occurduring the same clock tick (on the order of one to fivenanoseconds). Yet even if they actually occurred simul-taneously, the computer necessarily dealt with them ina sequential manner, according to state table priorityrules. In essence, any pair of actually or functionallysimultaneous responses had an artifactual, enforceddelay (a sort of minimal ).

That delay did not seem to play any noticeable partin the contingencies. Subjects who were observed to re-spond “simultaneously” (i.e., whose responding approxi-mated the artifactual delay) were not sensitive tosingle–source contingencies. On the other hand sub-jects who were observed to respond “sequentially” (i.e.,

Com

pone

nt p

airs

in t

he W

ses

sion

Subj

ect

Sing

le–s

ourc

e co

ndit

ion

Dual

–sou

rce

cond

itio

nCR

F-LH

CRF-

RHCR

F-LH

EXT-

RHEX

T-LH

CRF-

RHCR

F-LH

CRF-

RHCR

F-LH

EXT-

RHEX

T-LH

CRF-

RH

AS

BS CS DS ES GS

219

269

267

295

216

267

181

217

266

217

194

229

207

274

275

299

238

278

201

231

252

232

4 234

225

250

283

32 226

272

212

217

289

296

178

248

239

236

285

276

217

259

238

218

233

192

162

223

226

379

287

305

235

279

75 36 3 4 55 8

6 6 2 1 2 2

266

316

314

322

235

315

Tabl

e 5.

Eac

h ha

nd’s

num

ber o

f res

pons

es p

er m

inut

e in

eac

h co

mpo

nent

of t

he W

ses

sion

for e

ach

subj

ect.


whose responding contained delays, between the alter-nating responses in any pair of responses, that were con-siderably longer than the artifactual delay, possibly on theorder of . to . seconds) were sensitive to single–source contingencies. A parametric study to assess the effectsof very short s (. to . seconds) may determine

a minimal duration at which one reinforcer sourcecan be effective in generating sensitivity to contingencieswith simultaneously reinforceable responses. The impor-tant point for the present study, however, is that the two–source procedure was always effective in controllingresponding, regardless of whether the subjects emitted se-

Subj

ect

/ # of

/ Se

ssio

n/ S

ourc

es /

Com

pone

nt p

airs

in t

he B

1 and

B2

sess

ions

CRF-

LHCR

F-RH

CRF-

LHEX

T-RH

EXT-

LHCR

F-RH

CRF-

LHCR

F-RH

EXT-

LHCR

F-RH

CRF-

LHEX

T-RH

AS

1B1

AS

2B2

BS1

B1BS

2B2

CS1

B1CS

2B2

DS1

B1DS

2B2

FS1

B1FS

2B2

GS

1B1

GS

2B2

220

282

269

316

310

273

287

244

273

257

268

282

167

234

211

272

239

241

267

178

245

221

201

235

235

274

285

323

311

274

301

316

231

317

245

294

197 19 219 10 262 2 237

3 20 46 209 5

251

23 297

4 269 3 44 2 6 20 282

4

212

288

239

318

273

296

314

327

344

341

195

306

143

264

305

287

304

282

317

293

312

314

251

286

247

225

261

232

245

181

246

224

267

288

204

234

222

20 293

5 254 2 25 2 8 10 274 4

183

302

243

298

295

300

321

319

373

329

194

310

241

280

301

320

284

294

310

343

331

324

268

307

196 17 255 4 265 1 47 1 3 17 224 3

Tabl

e 6

. Eac

h ha

nd’s

num

ber o

f res

pons

es p

er m

inut

e in

eac

h co

mpo

nent

of t

he B

1 and

B2

sess

ions

for e

ach

subj

ect.

quential or simultaneous responses.While previously no procedure seemedadequate to the task, the two–sourceprocedure enables the further study ofsimultaneous operants.

One additional curiosity should bementioned. While the key re-sponding of subject was supersti-tious in the first single–source /component in the session, it did ex-tinguish under the contingency inthe second and only remaining single–source / component in this ses-sion. At the later session, respondingon the key again occurred in thefirst single–source / component(although in all other / compo-nents in this session, key respond-ing extinguished). This reappearance ofresponding under in the firstsingle–source / component inthe later session is an example remi-niscent of spontaneous recovery. Thispossibility also needs further research.

Under the single–source condi-tion, no surprise occurs when keyresponding is insensitive to the contingency, though some related cir-cumstances can arouse further curios-ity. The potential explanations for key responding being sensitive to an contingency under the single–source condition can be summarized.(a) When a / component wasfollowed by a / component inwhich –key responding was sensi-tive to , one possibly responsiblefactor may have been the reduction inreinforcement density. (b) When a / component, in which –keyresponding was sensitive to , wasfollowed by another / compo-nent in which –key responding wasnot sensitive to , one possibly re-sponsible factor (though such insensi-tivity is basically unsurprising) mayhave been a sequence effect. And(c) when a / component, regard-


less of whether –key responding was sensitive to or not, was followed by another / component inwhich –key responding was sensitive to , one pos-sibly responsible factor may have involved responses be-ing emitted in a distinctly alternating, sequential mannerrather than simultaneously. These and other factors, suchas the possible occurrence of some sort of spontaneous re-covery, deserve further investigation.

Other Considerations and ImprovementsDuring the study a number of other factors had the

potential to affect the results. These factors included(a) the subjects’ age, sex, and handedness, (b) the twodifferent types of training sessions, (c) the occurrence ofthe extra sessions involving schedules for anotherstudy, (d) the occurrence, for some subjects, of two ses-sions on the same day, and (e) the occurrence, for onesubject, of the session between the and sessions.While these factors were not explicitly assessed for theireffects, no aspect of the data seemed to be systematicallyrelated to any of them.

Overall, the dual reinforcer source procedure usedhere makes the study of simultaneously reinforceable op-erants viable by generating adequate schedule–effect inde-pendence—and thereby limiting the concurrentsuperstition commonly present when only one reinforcersource is used—without, by definition, requiring re-sponse succession. Consequently, a whole category ofcomplex behavior, the category of simultaneously emit-table, simultaneously selectable operants, is opened tomore effective study.

Some improvements that would facilitate further re-search must be mentioned. Two of these concern the ma-nipulanda and the point counters used in the presentstudy. Manipulanda that are more controllable than tele-graph keys would be preferred. The resulting capability ofprecisely adjusting the response requirement, in terms ofboth force and duration, would enhance the resolution ofboth the experimenter’s control of the variables and theanalysis of the results. Similar advantages would accruefrom the use of digital, or computer generated and dis-played, counters whose speed and accuracy are greaterthan the electro–mechanical counters used in this study.

The problem with the use of electro–mechanicalcounters was that they required an electrical impulse afull tenth of a second in duration to guarantee their con-sistent operation. This was quite slow and raised the pos-sibility of some reinforcers being skipped during highrate response bursts. The state table avoided this bycounting reinforceable responses in a variable anddecrementing that variable for each delivered reinforcer.This was cumbersome for two reasons. First, delays be-came possible between a response and the occurrence ofthe reinforcer it produced; while these were extremely

short, they were nonetheless longer than the virtually in-stantaneous changes normally expected from computer–controlled equipment. Secondly, the necessity of thisstate–table technique (caused by using the available butold electro–mechanical counters) put constraints on thetypes of parametric manipulations that could be made,especially with regard to reinforcement parameters (e.g.,reinforcer magnitude). Fortunately, the primary concernsof this study were molar in nature and so showed noproblematic effects from these equipment limitations.More molecular and necessary experimental analyses willnot likely be as fortunate, and so should be undertakenonly with more appropriate equipment.

Another class of independent variables, relevant toboth the present study and future studies, concerns sub-jects. Humans typically bring to experiments verbal rep-ertoires and differential histories with respect to bothinstructions and “self–instructions” (rules and rule–gov-erned, or verbally–mediated, behavior). The latter may beespecially relevant to the present study to the extent thatit bears on functional relations. A subject might behavedifferently depending on his or her history regarding ver-bal rules and self–instructions particularly with respect toexperience with the workings of equipment such asmight comprise experimental apparatus. For instance, ahistory that results in a subject stating to herself or him-self that “equipment either works or doesn’t work” couldpredispose that subject to continue pressing both keysunder one reinforcer source in spite of a change from on both keys to on one key. The present study heldinstructions consistent across conditions; it did not applyany other control procedure with respect to any aspect ofsubject history.

Instructions and history variables would also be likelyto generate behavior that differs from the behavior otheranimals might emit under the same contingencies. Oneaspect of the data, while not relevant to the overall con-clusions of the present study, implies that those variablesmay indeed have been operating. Different subjectsshowed different response patterns in extinction. Onlyone subject showed an extinction curve similar to thosetypically generated by other animal subjects; this wassubject (see the right hand record in Figure ). Anothersubject made simple testing–like responses on the key after each points, or so, was earned on the key; this was subject (see the session records in Fig-ure ). After a burst of responses under the contin-gency, the other subjects were more likely simply to stop key responding completely, with virtually no “curve”at all (although each pattern is slightly different). On aspeculative level, it may be possible that these differenttypes of extinction curves are due to the different andunanalyzed verbal repertoires and histories that the sub-jects brought to the study.


Due to those possibilities caution would be appropri-ate in considering the extension of the multiple reinforcersource procedure to non–human subjects. The extent towhich the present data are a function of the verbal reper-toires and instructional and rule–stating/following histo-ries of human subjects rather than a function of morebasic processes has yet to be determined.

The consistency of results between the within–ses-sion and the between–session comparisons suggests thatthe use of both may be unnecessarily redundant. How-ever, retaining both types of sessions for each subject pro-vides a source and crosscheck for clues to understandingwhatever is discovered in the data. Additional sessionswith each subject, either under the same controlling vari-ables, or under different ones (providing data on historyeffects), can only benefit the fine–tuning and further useof the multi–reinforcer source procedure in the study ofcomplex, especially human, behavior.

Later data may show that the results reported here aretypical of performances only early in the subject’s expo-sure to the contingencies. Given more time, stable, sensi-tive responding might occur even under the single–sourcecondition (though one would still have to ask: Why thenand not earlier?). The relevant questions, though, are stillthese: Which generates more sensitivity to contingencies,the single–source condition or the multiple source condi-tion? And which of these conditions is more analogous tothe contingencies experienced in everyday reality? Onlymore research will tell.

Conclusion

Complex human behavior involves both simultaneousand sequential/alternating response patterns, and bothneed attention from researchers. Even though simulta-neous responses may be more resistant to analysis, theymay also more accurately characterize reality. The mul-tiple reinforcer source procedure reported here maymake possible a research project that replicates basicresearch on fundamental operant processes by extend-ing the study of these processes to more complex, mul-tiple operants. Such a research project can be asystematic and purely inductive investigation and cata-loging of what happens when various basic contingen-cies include complex behaviors.

Before developing that kind of project, replication ofthe present study is needed. This replication should in-clude both variations in the number of selector sources,and other factors (e.g., different rest periods—or none—between the component pairs in a session, other types ofselectors, additional sessions that run dual/multiplesources first instead of single sources first, variations ininstructions, and variations in contingencies—since sen-

sitivity to the maximally different contingencies of and is no guarantee that sensitivity will hold undercontingencies that are more similar). If that replicationshows the multiple reinforcer source procedure to be re-liable, then this procedure might evolve into a more gen-eral multiple selector source procedure, and additionalvariables can be investigated, singly or in combination.The investigation of some of these variables will benefitfrom the continued comparison of single and multipleselector sources; other variables may be addressed ad-equately with only multiple sources. Many antecedentand postcedent variables are worthy of study including(a) establishing operations, (b) stimulus discrimination,(c) generalization, (d) reinforcement schedules, (e) pun-ishment control, (f ) schedule–induced effects, (g) com-peting selectors (e.g., reinforcers and/or punishers ofdifferent magnitudes), and (h) multiple or varying selec-tors (sometimes the same type and sometimes different)for each separate, simultaneously emittable operant.

Most of those additional variables would be worthyof study both with and without the presence of discrimi-native stimuli in the contingencies. With some of thoseadditional variables various selector parameters can alsobe researched. Such parameters could include added andsubtracted (see Ledoux, b) reinforcers and punishers,and primary and secondary reinforcers and punishers, aswell as the latency, duration, and magnitude (a) of one ormore reinforcers and punishers, and (b) of one or moreresponse topographies. And any or all additional variablescan be studied, for instance, (a) with and without in-structions or variations in instructions, (b) with three ormore, rather than two, simultaneously emittable re-sponses, (c) with response–independent selectors (e.g.,playing back non–contingently what the subject just pro-duced contingently), and/or (d) with and without knownor provided or (with younger subjects) short histories.

To answer those questions could take several decades(probably more) of work by many researchers. Addi-tional, more complex or more detailed questions, worthyof attention from candidates or holders of .. and h..degrees, will undoubtedly arise from the data of the basicstudies, as they have even from the present study.

A research project of this type can also provide a levelof research effort that is especially suited to the training ofbehaviorological scientists by involving undergraduate aswell as more advanced students and experienced research-ers. The conceptual and technological levels of the basicresearch program are well within the reach of under-graduate students who are training in behaviorologicalscience. Undergraduates in particular can benefit fromparticipation in this research. They could experience earlyin their training (a) the requirements of study, patience,and careful planning, (b) the thrill of discovery whentheir efforts answer research questions, (c) the satisfaction


of making an original contribution to a growing body ofknowledge about complex, especially human, behaviors,and (d) the further satisfaction when they find ways toapply those answers to concerns in the world at large.These are educational consequences valuable to both thestudent/researcher and the culture at large, expeciallysince simultaneous responses and multiple selectorsources may characterize notable portions of reality andso should be thoroughly analyzed.

At this point, one cannot predict what important dis-coveries await research expansion into the effects of si-multaneous selectors on simultaneously emittablemultiple operants. One can reasonably predict, based onthe beneficial results that have come from previous basicbehaviorological research efforts, that beneficial resultswill also accrue from the research proposed here.�

Endnotes

Parts of this work were presented at the eighth annualconvention of the Association for Behavior Analysis inMilwaukee, , May , and at the ninth annual con-vention of the Association for Behavior Analysis in Mil-waukee, , May , and at the fifth annual conventionof The International behaviorology Association in LittleCompton, , March . The paper was then revisedfor inclusion in Origins and Components of Behaviorology(Ledoux, S.F. []. Canton, : ABCs.).

The author thanks Chris Cherpas, Jack Michael,Alan Poling, Arthur Snapper, and Ken Stephens for col-legial assistance with the research here reported. The au-thor also thanks (a) the poster–session attendants at– (especially Beatrice Barrett and Julie Vargas),(b) Lawrence Fraley, and (c) Carl Cheney and the threeanonymous Behaviorology reviewers, all of whom pro-vided many helpful comments on various versions of thismaterial. Address correspondence regarding this paper tothe author at –, Canton – .�

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Quoted

Lawrence E. FraleyProfessor of Behaviorology (retired)

[This quote originated as the only footnote, and itssource, in Chapter of the author’s General Behaviorol-ogy book (see Fraley, L.E. [2008]. General Behaviorology:The Natural Science of Human Behavior [p. ]. Canton,: ABCs.). That chapter, on graphs and graphing tech-nique, needed a footnote when pointing out the useful-ness of a battery of coordinated graphs. The responses atthe end of this footnote—which are relevant to one ofthe major objectives of the book—have applications incontexts far wider than just this chapter; for this reasonthe footnote and its source are quoted here.—Ed.]

… �t proves easier to tease out the interrelations among thevariables when different kinds of data are graphed in thistime–coordinated way.1 … This example illustrates thatcoordinated graphs afford a more complete and comprehen-sive analytical profile of the situation under investigation bymaking relations among different dependent variables easierto see. Behaviorologically, we would say that the presenta-tion of such an arrangement of graphic stimuli, whichmakes relations among various dependent variables more sa-lient, facilitates those relations acquiring functional controlover certain critical neural body parts of the viewer.________________________1 The reader will note that the text in this chapter, likethat in others, is stylistically written in a combination of(a) common agential language and (b) language craftedto reflect the naturalistic behaviorological perspective.The agential language is comfortably familiar to mostreaders, and its appearances represent a compromise thatfacilitates reading behavior at the expense of technicalcorrectness. The agential language typically appears inpassages where, if uncritically accepted, it may not per-plex the reader. On the other hand, to the extent that itsappearances begin to evoke the critical attention of thereader, the book is succeeding in one of its major objec-tives. For instance, those who may be annoyed by the ex-pressed implication that interrelations revealed in a set ofcoordinated graphs are “teased out” by some kind of pro-active environment–appreciating agent within the viewerare to be congratulated on their maturing scientificsensitivity. They may also enjoy exercising those powerson the preceding acknowledgment of their achievement,and then, in turn, on this invitation to do so.�

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