dialogue on private events

The Analysis ofVerbal Behavior 2004, 20, 111-128

Dialogue on Private Events

David C. Palmer, John Eshleman, Paul Brandon, T. V. Joe Layng,Christopher McDonough, Jack Michael, Ted Schoneberger, Nathan

Stemmer, Ray Weitzman, and Matthew Normand

Smith College, APEX Consulting, Minnesota State University,Headsprout, Inc., Hawthorne Country Day School, Western MichiganUniversity, California State University: Stanislaus, Bar-Ilan University,California State University: Fresno, Florida Institute of Technology

In the fall of 2003, the authors corresponded on the topic of private events on the listserv of the VerbalBehavior Special Interest Group. Extracts from that correspondence raised questions about the role ofresponse amplitude in determining units of analysis, whether private events can be investigated directly,and whether covert behavior differs from other behavior except in amplitude. Most participants took acautious stance, noting not only conceptual pitfalls and empirical difficulties in the study ofprivate events,but doubting the value of interpretive exercises about them. Others argued that despite such obstacles, indomains where experimental analyses cannot be done, interpretation of private events in the light of labo-ratory principles is the best that science can offer. One participant suggested that the notion that privateevents can be behavioral in nature be abandoned entirely; as an alternative, the phenomena should bereinterpreted only as physiological events.

For 19 days in the fall of 2003, the VerbalBehavior Special Interest Group (VBSIG)listserv was the forum for an impromptu dis-cussion about private events among the authors.This paper has been excerpted from that dis-cussion and lightly edited by the first author,who also composed the introductory and con-cluding passages. The remaining authors arelisted according to their chronological entryinto the discussion. Since all entries wereposted with no thought to publication, theywere typically written hastily and informally.No doubt the authors could articulate theirviews more clearly, given the opportunity, andupon reflection, they might prefer to have madedifferent points entirely. Therefore, the readershould recall that this was a spontaneous dia-logue, not a set ofposition papers. The discus-sion revealed that, even among such an intel-lectually homogeneous group, there is no con-sensus about the place of private events in thescience of behavior. Nevertheless, it is note-worthy that the tone ofthe exchange was cour-

Address correspondence to D. C. Palmer, Depart-ment of Psychology, Smith College, Northampton,MA 01063; phone: (413) 585-3905; e-mail:[email protected].

teous and positive throughout; opinions dif-fered, but no points were scored.The informality ofthe dialogue has been re-

tained. Occasional changes have been made tothe text to accommodate the standards of thejournal, and some transitional passages, pre-sumed to be helpful to the reader, have beeninserted and attributed to the relevant author,although these passages did not appear in theoriginal entries. It would have been possible,of course, to mark all such editorial intrusionsorthographically, but the distraction to thereader would not have been repaid by the addedprecision ofattribution. The reader should notethat, in many cases, entries were written in par-allel, a circumstance that necessarily has led tosome incongruities in the dialogue: Entries aresometimes separated from their target by sev-eral other entries to which they make no refer-ence.The "VB" in VBSIG has two meanings.

Broadly speaking, the special interest group isdevoted to the scientific study ofverbal behav-ior as behavior (that is, as distinct from ap-proaches devoted to language as a capacity ofthe mind, or as a set of grammatical rules, oras a hypothetical module in the brain). But thegroup was inspired by Skinner's book VerbalBehavior (1957), which has provided a foun-

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112 DAVID C. PALMER et al.

dation for much of the empirical and concep-tual work in the field. Consequently, Skinner'sviews on private events are familiar to all ofthe participants and foreshadow many of thepoints made in the discussion. It is perhapsuseful to review what Skinner has said.

In Science and Human Behavior (1953),Skinner opened his chapter on private eventswith these lines:

When we say that behavior is a functionof the environment, the term "environ-ment" presumably means any event in theuniverse capable of affecting the organ-ism. But part of the universe is enclosedwithin the organism's own skin.... Withrespect to each individual, in other words,a small part of the universe is private. Weneed not suppose that events which takeplace within an organism's skin have spe-cial properties for that reason. A privateevent may be distinguished by its limitedaccessibility but not, so far as we know,by any special structure or nature. We haveno reason to suppose that the stimulatingeffect of an inflamed tooth is essentiallydifferent from that of, say, a hot stove....But if some of the independent variablesof which behavior is a function are notdirectly accessible, what becomes of afunctional analysis? (pp. 257-258)

Skinner then reviewed ways in which ver-bal behavior under the control ofprivate eventsmight be shaped, but cautioned that some ver-bal responses that appear to be under controlof private events might actually be responsesto public variables (a point emphasized byLayng in the discussion):

Another possibility is that when an indi-vidual appears to describe unemitted be-havior, he is actually describing a historyof variables which would enable an inde-pendent observer to describe the behav-ior in the same way if a knowledge of thevariables were available to him. The ques-tion, "Why did you do that?" is often im-portant to the community, which estab-lishes a repertoire ofresponses based uponthe extemal events ofwhich behavior is afunction. (p. 263)

He distinguished between covert behaviorand other private events:

One important sort of stimulus to which

the individual may possibly be respond-ing when he describes unemitted behav-ior has no parallel among other forms ofprivate stimulation. It arises from the factthat the behavior may actually occur buton such a reduced scale that it cannot beobserved by others-at least without in-strumentation. This is often expressed bysaying that the behavior is "covert." (p.263)

Skinner anticipated other points made in thedialogue. For example, he cautioned that "theappeal to covert or incipient behavior is easilymisused" (p. 264), but he suggested that ad-vances in instrumentation might come to ouraid by moving the boundary of what is pub-licly observable, since "the line between pub-lic and private is not fixed." (p. 282) Regard-ing the matter of parsimony, he remarked,

One is still free, of course, to assume thatthere are events of a nonphysical natureaccessible only to the experiencing organ-ism, therefore wholly private. Sciencedoes not always follow the principle ofOccam's razor, because the simplest ex-planation is in the long run not always themost expedient. (pp. 279-280)

Skinner distinguished between interpretationand experimental analysis in Verbal Behavior(p. 11), but his most extensive discussion ofthe topic is found in his reply to commentatorsin a collection of his canonical papers (Skin-ner, 1988):

[The commentators] have assumed thatbeyond science and technology there liesonly philosophy. I have found somethingelse: interpretation. I would define it asthe use of scientific terms and principlesin talking about facts about which too littleis known to make prediction and controlpossible. The theory of evolution is anexample. It is not philosophy; it is an in-terpretation ofa vast number offacts aboutspecies using terms and principles takenfrom a science of biology based uponmuch more accessible material and uponexperimental analyses and their technicalapplications. The basic principle, repro-duction with variation, can be studiedunder controlled conditions, but its rolein the evolution of existing species is amere interpretation.

Plate tectonics is another example. It is

DIALOGUE ON PRIVATE EVENTS 113

not philosophy but an interpretation ofthepresent state of the crust of the earth, us-ing physical principles governing the be-havior ofmaterial under high temperaturesand pressures established under the con-ditions ofthe laboratory, where predictionand control are possible.

Laboratory analyses of the behavior oforganisms have yielded a good deal ofsuccessful prediction and control, and toextend the terms and principles found ef-fective under such circumstances to theinterpretation of behavior where labora-tory conditions are impossible is feasibleand useful. I do not think it is properlycalled philosophy. The human behaviorwe observe from day to day is unfortu-nately too complex, occurs too sporadi-cally, and is a function of variables toofar out ofreach to permit a rigorous analy-sis. It is nevertheless useful to talk aboutit in the light of instances in which pre-diction and control have proved to be pos-sible. (pp. 207-208)

Skinner remarked that private events are oflittle practical importance in the control of be-havior. Nevertheless he claimed that the radi-cal behaviorist's view of private events is oneof its most important achievements, for it per-mits a monistic science. In that light, his inter-pretation ofprivate events is a landmark in thehistory of science. It is not surprising then thatthe topic should have generated so much dis-cussion on the VBSIG listserv.On October 27 John Eshleman opened the

thread by mentioning five of his "simmeringinterests," one of which was summarized bythe question, "Is amplitude a dimension ofver-bal behavior worthy of further study?"

Paul Brandon (PB): Is amplitude a subcat-egory oftopography, in which case a changein amplitude might define a new response,or is amplitude a measure of a defined be-havior like frequency? In the first case, wewould speak of a verbal response of givenamplitude, with a change in amplitude de-fining a new response. In the second wecould speak of changes in the amplitude ofa given response.

John Eshleman (JE): Both may be correct. Itmay be the case that a change in amplitudedefines a new response, but even ifthis weretrue, amplitude would remain a dimension

of behavior like frequency. Vocalized ver-bal behavior exhibits a wide range of vari-ability in amplitude, only some instancesofwhich make functional differences. Am-plitude is a dimension of any behavior. Inthe case ofsubvocal behavior, it is currentlydifficult to measure; one would presumablyhave to resort to instrumentation that de-tected subtle variability ofthe vocal neuro-muscular system.

But, your question is important: Ifsome-one asks, "When was the Battle ofHastingsfought?" is a hear/shout "1066!" the sameresponse as a hear/subaudibly-vocalized" 1066"? Presumably both are intraverbals.The content or "topography" seems to bethe same. The difference is in amplitude,but this may well vary with the context orother circumstances. Also consider ampli-tude changes within a response. A vocal-ization might start out at one amplitude andchange midstream to a higher amplitude:"HellOOO!" Is what seems to be one re-sponse really two responses?

PB: There is no question that amplitude is adimension on which behavior can be mea-sured. The question is whether a given re-sponse can vary in amplitude, or whether achange in amplitude (beyond some definedrange of variability) always defines a newresponse as indicated by a change in func-tion. Talk to an actor about the functionaldifferences in vocalizations of differentamplitude! Note the way we attempt to in-corporate an amplitude dimension in writ-ten verbal behavior (capitals = SHOUTINGonline). Another area for potential studymight be music, in which response ampli-tude is very functional. Is music verbal be-havior? I think that it fits the definition.

T. V. Joe Layng (JL): Although it is clear tothose with children that amplitude may haveautoclitic effects, we have included ampli-tude as a targeted topography in ourHeadsprout Early Reading program forother reasons. In our user testing we foundthat asking a child to "say it again louder"was critical to reliably establishing goodarticulation of the letter sounds we teach.Children who may (autoclitically?) almostwhisper the response the first time will of-ten shout the response after the response


request. The louder response is usually ac-companied by affective changes as well-sitting up straighter, a smile, or laughter-and it increases the likelihood the next re-sponse, when another stimulus is presentedfor the first time, will be louder. (The per-formance also raises questions about theeffects of reinforcement history and penal-ties for false alarms, which may act to de-crease the amplitude of initial responses.Our findings suggest a paradigm for experi-mentally investigating these processes.)Getting the first response at low amplitudein a largely echoic task, then asking for itlouder helps to firm the articulation of theresponse, which can then be transferred toindependent textual control. Early testsshowed us that without the "say it louder"request (at least in the beginning) firm ar-ticulation was not likely for many children.This investigation, among others in ourlaboratory (N = 250+ children), led to animportant series ofinstructional subroutinesin our speaker-as-own-listener sequences(for which we have been issued a U.S.patent). We found that psychophysical in-dicator response methodology, togetherwith on-going Verbal Behavior analysis,was quite important throughout our R&Deffort, particularly since we need to shapeverbal behavior in the absence of a "true"independent listener.

JE: Amplitude modulation in the reverse di-rection is also of general importance, i.e.teaching learners to go from reading outloud to "silent" reading. The culture gener-ally demands this. (Who would want to sitnext to a passenger on an airplane who readsthe in-flight magazine out loud?)

In Precision Teaching there is a learningstream called "see/think," in which you seesome text and "think" the response. Is see/say different from see/think? Is anintraverbal in which you say the responseout loud the same behavior as an intraverbalin which you "say" the same thing silently?The controlling relation for the differentamplitudes may be the context: See boss,say "idiot." You wouldn't say "idiot" outloud, unless it was your last day at workanyway and you had nothing left to lose.How could research on such questions

be carried out? It would be difficult to

achieve inter-observer reliability. I've re-corded my own see/think frequencies (seefront of card, think response; where think= silent say). I can, with myself as subject,reliably (in the sense of each time) obtainmuch higher response rates with see/thinkthan with see/say (over 100/minute see/think compared to around 60/minute withsee/say, with the same cards). When I doan A-B-A-B design, the rates go down andup accordingly. But in the see/think condi-tion there's no way that an outside observercould tell that I'm doing anything other thanmerely flipping 3 by 5 cards at a high rate.

Christopher McDonough (CM): Can the dif-ference in amplitude alone (i.e., subaudiblevs. audible "say") account for these differ-ences in rate?

PB: We return to basic methodological prob-lems: How do we know the details of thestimulus control of a given individual'stacting of private events? With math prob-lems, when we can specify the precurrentbehaviors necessary to produce a correctsolution, we can infer that they have oc-curred. As a practical matter, sometimes wecan verify that a given treatment packageis effective without being able to tease outthe controlling variables.

JL: The approaches to covert and overt behav-ior must be different. One cannot differen-tiate "thinking" fast from thinking, "I co-vertly said it fast." What I think is fast think-ing may not be so, however firmly I be-lieve it. The problem is not insurmountable,however. One can see if the instruction tosay something (at "low amplitude") pro-duces a change in some indicator that theinstruction to say louder, perhaps in an in-creasing gradient, does not. In addition, onecould look at the effects different establish-ment and practice programs have on thedependent measure under the differentlyinstructed environments as well. In the1950s, Benjamin Bloom at the Universityof Chicago found that while major differ-ences in problem-solving approaches usedby college students might lead to the samesolution, all paths were not equal, nor wereall equally effective. He was able to increasethe amplitude, adjust the "path," and then


decrease the amplitude and maintain theimprovement on the dependent measures.

David Palmer (DP): Regarding the method-ological question of how to study covertverbal behavior, whatever our scruples, thewrong answer is to run away from it. Co-vert behavior is part ofthe domain ofinter-est, and to many people, it is the dominantpart of the domain of interest. I think thesolution is clearly to distinguish interpreta-tion from experimental analysis. We can'tmanipulate or measure phenomena beyondthe range of detection, but we can interpretincomplete data in light of basic principlesthat have been well established in an ex-perimental analysis. This is what Skinnerdoes with such force in Verbal BehaviorMoreover, most of what passes for scien-tific fact is just an interpretation. Newtonanalyzed experimentally the motion ofpen-dulums and rotating buckets of water, buthe offered interpretations of the motion ofplanets, the tides, and a lot of other phe-nomena, interpretations that we take to bescientific fact. But he never achieved ex-perimental control over these phenomena,and neither has anyone else since. Never-theless, we regard the mystery of the tidesas having been solved.So I think we should confidently, with-

out embarrassment, investigate phenomenathat are partly covert, so long as we ac-knowledge that our exercise is interpretive.The purpose of science is not just to masternature but also to resolve mysteries aboutit, and in the latter enterprise interpretationsare often powerful (Skinner, 1957, again).Almost all evolutionary accounts are inter-pretations, but they help us make sense ofnatural phenomena, and they help us resistthe temptation to invent magical solutions.John Eshleman's see/think exercises re-

mind me of a technique used byHeadsprout. Headsprout's program askschildren to speak to the computer (and evenprompts them to speak louder), but the pro-gram has no speech recognition software.The speech of the'child is covert to the pro-gram. Nevertheless the procedure is pow-erful. The point of the procedure is thatchildren can (usually) detect when theyhave matched to a model and when theirbehavior is discrepant from the model. This

permits the automatic reinforcement ofcon-formity to the model and the rapid and effi-cient shaping ofbehavior. It's an ingeniousway of avoiding the need for human super-vision of the student, and in my opinion itis a much more realistic model than ordi-nary ofhow children actually learn in natu-ral settings. It's a good example, becausethe behavior is only covert to one audience(the computer and the people downstreamof the computer); to other audiences (par-ents, visiting consultants, the child), thebehavior is quite observable. If, as I believe,this procedure extends the power of theHeadsprout program, it is possible thatJohn's see/think exercises, and similar ef-forts, might tell us something important.Covert behavior is difficult to study, but thatdoesn't make it less real. As long as we areclear about the interpretive nature of theenterprise, I think it plays a role in our sci-ence.

PB: Since we are talking about covert verbalbehavior, we can distinguish between re-sponses where the only listener is thespeaker (covert), and responses where atleast some listeners are not the speaker(overt). Thus there could be cases where aresponse ofa given topography (amplitude)shifts between the two categories depend-ing upon circumstances (if a tree falls inthe forest where no one is listening, it doesso covertly!); but this is as it should be in asystem of functional definitions.

JL: I think we must make the distinction be-tween private events and covert behavior.The term private event acknowledges thatthere are phenomena that should be inves-tigated for which independent evaluationis currently impossible, whereas covert be-havior assumes these events are of a par-ticular kind, i.e., behavior. But for this wehave no evidence.

I think this area is far more complicatedthan has been generally acknowledged inour literature. Attributing causal or even de-pendent variable status to these events maybe preventing us from a more completeanalysis. My position is to use reports ofprivate events (especially my own) as oc-casions to ask questions about what rein-forcement contingencies and histories might


account for such reports. Is what I reportthe actual private event or simply my ratio-nalization of the changing response prob-abilities shaped, as Skinner has pointed out,by being asked questions for which an overtanswer is required? In writing a sentence, aword may be written and then withdrawn;I may engage in a private dialogue such as,"that is not what I want to say, let me try..."; "no that's not it..."; "that's it ...," etc.Is this covert "trying out words" actuallydescribing covert behavior? Can this sup-posed behavior be used to understand howthe word eventually appears on the paper?Or is it my way of rationalizing the chang-ing response probabilities of historicallyreinforced patterns (a program variable) thatcompete with one another, potentiated bythe current words on the paper, and audi-ence variables, until a response occurs thatprovides an absolute "match to sample" (asopposed to a comparative match) so thatthe written response meets the criteria re-inforced in the past? The private events mayindeed be occurring, but as a by-product,not only of the history responsible for thewritten word, but of the requirement to de-scribe the origin of our behavior. Once areport becomes public, it is an operant un-der the control ofthe reinforcement ofpastcontingencies in its own right. The litera-ture on how the difference in accuracy be-tween spoken and nonspoken indicators,which defines subliminal perception, canbe traced to different consequential histo-ries for each class provides some clear evi-dence of this. All this is to say that whatmay account for an observed behavior andcorrelated private events (not one causingthe other) are consequential contingenciesand their programs. We may have to pay alittle more attention to behavioral develop-ment if we want to understand our privateevents as well as our overt behavior.

CM: I wonder if this won't lead to infinite re-gression. Ifyour rationalization is an inter-pretation of "the changing response prob-abilities," etc., that interpretation is open toa contingency analysis of the same type.Won't we just go around and around?

JL: Yes, and that is one of the problems. Here

is a passage from an earlier paper where Idiscussed this problem (Layng, 1995):

... In essence, they were examples ofwhatKripke (1982) describes as Wittgenstein'sskeptical paradox.... The skeptical para-dox cannot be easily dismissed by thosewho contend that thought causes behav-ior. Even if we were to accept repeatedcongruence of an indicator response to ascore sheet as evidence ofprivate control,how do we or the subject ever know thatwhat the subject describes as governingeither the indicator or the referent behav-ior is indeed the private event that is gov-erning the observable response? (p. 251)

Here is an example, from among severalin the paper:

When the behavior being studied is pri-vate, that is, the event is accessible onlyto the subject and not the experimenter,the question of the validity of the experi-mental subject's description ofthe privateevent as a causal variable is raised. Forexample, a subject, who had no history ofstuttering, and who had been told that hisphysiological reactions to reading aloudcertain passages of text were being mea-sured by electrical leads to his fingers,began stuttering while reading the pas-sages. When asked why he began stutter-ing, he reported that he had become anx-ious having to read aloud and began stut-tering as a result. He reported that the stut-tering slowed down his reading, makinghim even more anxious, which in turn ledto more stuttering. In fact, the experiment-ers (Flanagan, Goldiamond & Azrin,1959) had arranged an avoidance sched-ule in which electric shocks delivered tothe subject's fingers could be postponedby stuttering. The normally fluent subjectstuttered to such an extent that by the sec-ond day almost no shocks were delivered.The shocks became so rare that in the post-experiment interview with an experi-menter the subject denied that shock hadany effect on his verbal behavior. The sub-ject, who never expressed an awarenessof the relation between the shock or theavoidance contingency and his stuttering,and who attributed the stuttering to a sud-den feeling ofanxiousness, was shown tosystematically vary his stuttering withchanges in the shock avoidance contin-gency arranged by the experimenter. (p.256)


Did the subject become anxious? Per-haps. Would counting private instances ofanxiousness have told us anything about thedeterminants ofthe stuttering? Doubtful. Itis more likely that a history of explanationgiving was involved, which may in turnhave led to the subject "feeling, or simplyreporting feeling, and perhaps believing, hewas anxious."

JE: Also see the work ofA. Calkin (2002) re-garding private events, in a recent issue ofThe Behavior Analyst.

In the 60s, 70s, and 80s, some of OgdenLindsley's students studied pregnantwomen counting and charting fetal kicks,which is something that apparatus can de-tect as well. A couple of Og's studentscharted these frequencies on StandardCeleration Charts and published their datain Science (Edwards & Edwards, 1970).They had measures of reliability, obtainedfrom periodic instrument detection and re-cording of the fetal kicks, that showed thatthe women were reliable counters and mea-surers of the behavior that was going oninside them.People can be trained to be reliable

counters and measurers of inner behavior,but that's a separate question from that ofusing amplitude as a dependent variable.Og's students measured frequencies, notamplitude, as a dependent variable. Ampli-tude remains a virtually unstudied, seem-ingly elusive dimension to behavior.

PB: Training is exactly the issue here, and that'swhat makes the above example of internalbehavior different from the usual cases ofprivate/inner/covert responding. Fetal kickscan be detected by both apparatus and by"outside" observers (ask any father). Hencewe can set up reliable training contingen-cies to teach pregnant women to reliablyreport these events.

Jack Michael: I would like to suggest a sharperdistinction between the terms stimuli andresponses. In this case, the pregnant womanis responding to stimuli that are being pro-duced by the fetus. The fetus is respond-ing, but not the woman. If these stimulicontrol some behavior on her part, such as

counting, then the counting behavior is herresponding, and the internal stimuli arefunctioning as possibly discriminativestimuli for a tact ofa private stimulus. I havenoticed in some earlier posts that the term"response" is used when in fact it is the re-sponse product, which is a stimulus, that isrelevant to the issue being discussed. Inverbal behavior this is a common problem,to overcome which the term "responseproduct" was invented. My response to yoursaying "Hello" is not a response to yourresponse but rather to the auditory productofyour vocal response. I think it helps avoidconfusion and unnecessary complexity tohave a very sharp distinction betweenstimulus and response. When "stimulus" isused, it is usually possible to modify it with"visual," "auditory," "olfactory," etc. Whena "response" occurs it is usually possibleto identify a part ofthe body that is respon-sible for the response (a vocal response, amanual response, a head nod), or the re-sponse can be identified in terms of its ef-fect on the environment-a lever press, akey peck, a computer screen touch. In manycases the response product can be taken forgranted, but in this area of private events Ithink unusual clarity is needed. Also, I tendto use the term "covert" as a way of identi-fying a response which cannot be observedby someone else, or that does not have anobservable effect on the environment, orthat is an inferred response. I think covertstimulus is better rendered private stimu-lus. Of course, covert responses may verywell have private response products, whichare stimuli. But I think blending these con-cepts with each other harms rather thanhelps. I realize that there is no reason whymy verbal practices should be universallyadopted, but at least discussing them maylead to less ambiguity.

DP: The skeptical paradox may be unavoid-able, but I think we can live with it, so longas our goal is to offer a unitary and parsi-monious account ofall human behavior. Weinvoke covert behavior, not because some-one reports it and we have faith in his re-port, but because a) it resolves a puzzle thatwould otherwise remain mysterious, and b)it is plausible under prevailing conditions.To return to the example of the tides: For


all Newton knew, the tides might be causedby the respiration of a gigantic sea mon-ster; he never ruled out that possibility. Buthis interpretation appealed to principlesderived from controlled studies, where seamonsters had been ruled out, and therebyoffered a naturalistic explanation for a phe-nomenon that would otherwise remainmysterious. If he had stayed his hand, outof a reluctance to extrapolate, the vacuumwould have been filled with sea monstersand worse things.An appeal to covert behavior is pointless

unless it helps us make sense of a perfor-mance that would otherwise be baffling.The purpose is to show one path that na-ture might take to produce a phenomenon.It helps us lay tentative claim to a domain.Our account need not be right in every de-tail to have that effect. Most of the claimsof evolutionary biology are similarly ten-tative, since the past is largely "covert" tous, but they offer satisfaction nonethelessand fortify us against the temptation to driftinto superstition. So it is with appeals tocovert behavior: For some phenomena, ifwe don't acknowledge the mediating roleof covert behavior, we simply have no ex-planation at all. (I allude, for example, toproblem solving behavior in which thesubject's terminal behavior depends upona pattern ofresponse-produced supplemen-tary stimuli, as in "mental arithmetic.") Ouraccounts must be tentative, as the skepticalparadox insists, but all that is required isthat we have at least one possible explana-tion for a performance that would otherwiseinvite mysticism.

JE: Why must covert behavior "make senseof a performance that would otherwise bebaffling" more than any other behavior?Why not study "covert" behavior in its ownright as behavior, when it is methodologi-cally possible to do so? What controls it?What are its functions? What are its fre-quencies and celerations? How can we dis-tinguish between nonverbal and verbal "co-vert" behaviors? How might "covert" be-haviors chain together in response-responsechains? What amplitude differences can befound with "covert" behavior, and whatwould this range of amplitudes be? Howmight modulations in amplitude of such

behavior be important? Are any such modu-lations related in some way to frequencydifferences (i.e., are the two dimensionscorrelated)?

JL: My problem is not with the privateness ofthe events, but in the assignment of causalstatus. Although such assignment may makea particular phenomenon easier to under-stand, it may lead us to a comfortable ex-planation that masks the real controllingvariables. It also leaves us to account forthe private event itself, which I believe willlead us to contingencies of reinforcement,which in turn will lead us to program vari-ables as the locus of the causal determi-nants. We may find that program variables(which I believe are sorrowfully neglectedby behavior analysts) are responsible forboth overt behaviors and the private eventsthat accompany them. Remember the mostparsimonious account of all, that resolvesall puzzles for many individuals, and is in-deed plausible, even to many noted scien-tists.... "in the beginning there was theWord...."

Ted Schoneberger (TS): Wittgenstein's skep-tical paradox offers a serious challenge tobehavior-analytic explanations ofbehaviorthat attribute causal efficacy to thoughts andfeelings. Interestingly, Chomsky has alsoacknowledged that this paradox offers a se-rious challenge to his linguistic theory.(Those who read Chomsky know that suchadmissions are rare.) Indeed, in KnowledgeofLanguage: Its Nature, Origin, and Use(Chomsky, 1986), he devoted 20 pages to adiscussion of this challenge. QuotingChomsky, "Ofthe various general critiquesthat have been presented over the yearsconcerning the program and conceptualframework ofgenerative grammar, this [i.e.,Wittgenstein's skeptical paradox] seemsmost interesting." (p. 223) Chomsky be-lieves he escapes any destructive implica-tions of the paradox because his(Chomsky's) theory "is a descriptive theoryof... attained or initial competence ... not acausal or dispositional theory." (p. 241)

Returning to the issue of how behavioranalysis responds to the skeptical paradox,I agree with Joe Layng that it cannot be eas-ily dismissed. I also agree with Dave Palmer


that we can live with it. However, pleaselet me qualify my response by saying that Ithink Dave's suggestion that "we invokecovert behavior, not because someone re-ports it and we have faith in his report, butbecause a) it resolves a puzzle that wouldotherwise remain mysterious, and b) it isplausible under prevailing conditions" caneasily lead-if we are not careful-to aform ofinstrumentalism in which "anythinggoes" (a criticism of instrumentalism of-fered, I believe, by Jay Moore). So "livingwith" the paradox, while honoring Joe'sentreaty that it cannot be easily dismissed,suggests, to me, a response to the paradoxthat includes a sophisticated integration intobehavior analytic theory of Wittgenstein'sown response to the paradox, coupled witha neo-pragmatist (i.e., Richard Rorty's) ap-proach to the issue of truth.

PB: The term "causation" itself is ambiguous.(I believe that Aristotle identified five dif-ferent uses ofthe term, and it's only gottenworse since.) Neither Palmer nor Layng(nor any other radical behaviorist that Iknow of) is claiming "hard" (mechanistic)causality for private events. The "party line"is that private events are behaviors, notcauses. The question is: Can we posit thatprivate events, although unobservable toothers, are behaviors in a chain whose endpoints are publicly observable, and can wethen use this hypothesis to account for theend points ofthe chain in a manner consis-tent with the behavior analytic system? Tooversimplify, it looks like Palmer is argu-ing that this approach is pragmatically jus-tified, while Layng is pointing out some ofthe dangers inherent in this approach.

CM: Why is there such a need to explain mys-teries? Or, explain mysteries prematurely?What is a good explanation? One that lastsfor 50 years? 200? 1000? As Dave pointedout, "the vacuum" will be "filled with seamonsters and worse things." Yes, but wouldNewton's vacuum be filled with such ex-planations? It seems to me that it's better toleave things messy than to have thingscleaned up in such a way that you reach forthe bar of soap and end up with the axlegrease. People offer up little explanationsabout phenomena they encounter all the

time; every day; many times a day. Some-times variables are manipulated before ex-planations are offered and sometimes theyaren't. Clearly, we can't live without them.Suppose we were forced to make a choice

right now. Given what we currently know,should we (a) pour all of our collective en-ergy into a unified explanation of verbalbehavior or (b) pour all of our collectiveenergy into verbal behavior experimentsand applications (R&D)? What choiceshould we make?

DP: Whether behavior is covert or overt de-pends on the point ofview of the observer,not on some essential property of the be-havior itself. If you are in the next room,all ofmy behavior is covert to you. If youhave me wired up to an electromyograph,and other such devices (some ofwhich havenot yet been invented, perhaps), you willbe able to detect behavior that even I amunaware of. So there is nothing specialabout covert behavior; it'sjust behavior thatwe aren't at the moment in a position toobserve. Unfortunately, we usually observeonly a small part of the behavior ofany or-ganism. It is perhaps inevitable that muchof the behavior of any organism is effec-tively covert to us, but we should not makethe mistake of assuming that because wehave not measured something, it must notbe there.We are able to experimentally analyze

only a tiny fraction of natural phenomena,be it behavior or anything else. So our un-derstanding of the world will consist of afew islands of experimental facts and prin-ciples amid a great sea of application andinterpretation. (Beyond that lies the endlessfog ofbootless speculation [sea monsters].)I take it as an axiom that this state of affairswill prevail, and that is the reason I arguethat we should offer, without shame, inter-pretations that appeal to covert behavior.That isn't pseudo-science; it's just plainscience. All science is mostly interpretation.

Interpretation isn't just the table scrapsof science; it's the main course. We engagein experimental analysis so that we will beable to interpret the natural phenomenaaround us. It is true that the mastery of na-ture that arises from achieving experimen-tal control leads to wonderful things-

120 DAVID C. PALMER et aL

medicines, vaccines, gadgets of everysort-but the most priceless gift of scienceis the understanding, however tentative, ofhow the world works. Cosmology, geology,evolutionary biology, behavior analysis-almost all of it is interpretation. Sometimeswe will grab the axle grease, not the soap,as Chris so aptly puts it, but nothing canprotect us from such errors. Ifwe are to tryto understand phenomena like continentaldrift, the origin of a species-or problemsolving behavior and memory-we willundoubtedly make mistakes. That's why it'simportant to acknowledge the interpretivenature of our enterprise.

JL: Although much of what we do in an ad-joining room may be covert to others, it isat least open to independent sampling. Ihave always preferred procedural (as op-posed to operational) definitions. All suchdefinitions involve congruence with a scoresheet. That is why I view behavior as therelation of the organism (in the case of be-havior analysis) to its environment as mea-sured by the investigator. Since we are in-terested in consequential relations (amongothers) certain "natural fractures" define theparameters of our measurement systems.However, suggesting that private eventshave properties that somehow function asdoes behavior in direct contact with con-tingencies causes me some concern. Thevery real issue that Jack brought up aside(Is it a stimulus or a response?), the prob-lems that arise seem to me to outweigh thepotential utility of most interpretations.There are so many instances where an ini-tial explanation based upon a reasonableinterpretation ofthe action ofcovert behav-ior has been shown to be highly question-able or dead wrong that one has to questionifany such interpretation can really move ascience of behavior ahead.

But, I have a more fundamental problemthan that. Private events need to be investi-gated in their own right. We should makefew assumptions about the stufffrom whichthey are made (seeing, speaking, hearing)or their role (behavior, stimuli, etc.) Weneed creative "ideas" and experimentsabout their ontogenetic evolution and util-ity (ifany). I agree with Skinner in his standagainst both operational definitions and to

appealing to hypothetical mediating events,but I also agree with his assertion that pri-vate events be studied in their own right.They deserve their own classification andperhaps some new approaches to their pos-sible role in verbal and other behavior.

DP: Paul Brandon summarized the discussionthus: Palmer likes interpretation on prag-matic grounds; Layng notes the dangers ofthis approach; nobody wants to impute ul-timate causal status to private events. Thatsounds right to me.But there is at least a disagreement in

degree of concern. In his recent post, JoeLayng notes that interpretations have sooften been found to be wrong that he won-ders if they can really move a science ofbehavior ahead. He concludes with the sug-gestion that we study private events in theirown right, a suggestion which I believe iscongruent with John Eshleman's position.

Perhaps there is no disagreement after all.Ifa topic is amenable to experimental analy-sis, then by all means it should be investi-gated that way. If past interpretations havebeen proven wrong, as Joe suggests, thenpresumably an experimental analysis wasin fact possible. I agree that if a phenom-enon can be studied, it should be. Armchairinterpretations are the lazy man's enterprise.But I insist that there are many phenom-

ena of interest cannot be experimentallyanalyzed because we do not have access tothe relevant data. I think evolutionary biol-ogy and cosmology offer compelling ex-amples. We have only fragments ofthe rel-evant data, and it is unlikely that we willever have complete data. The viceroy but-terfly looks just like a monarch butterfly.Why? Because God's species stamp gotstuck, and he turned out two species withthe same coloration? Maybe. But the mon-arch is bitter and poisonous, and there ispresumably a selective advantage to look-ing like one. There is a tidy little "just sostory" ofhow the viceroy mimics the mon-arch because of differential predation. It'san interpretation, and the facts are out ofreach. Should we wait until we have a com-plete fossil record that will support the in-terpretation, recognizing that such a recordmight never be available? It depends on thecost of being wrong. Our interpretation of


mimicry might be entirely wrong. Maybeit is the monarch that mimics the viceroyfor reasons that we are unaware of. But Iargue that it doesn't matter if our interpre-tation is wrong. The point ofthe exercise isnot to offer certainty, but to show that thefacts currently at our disposal offer a pos-sible solution ofthe puzzle ofmimicry with-out recourse to mysticism. As long as wehave one plausible natural explanation fora puzzling phenomenon, it displaces occultexplanations. It doesn't matter if it is even-tually displaced by a better and more accu-rate natural account.Moreover, I insist that if we don't offer

interpretations in certain domains, we don'thave any account at all, and that opens thedoor for the spiritualist, the mentalist, andthe mystic. Consider one of my standardexamples, "What is the 10th letter after H?"[Try it.] We can assume that for mostpeople, this is a novel question. Thus, evenifwe were able to look in the subject's his-tory for prior instances of the question andreinforced responses, we wouldn't findthem. But given a minute, most people cananswer the question. Most people twitchtheir lips, twiddle their fingers for a minuteor so, and answer, "R." We interpret thisperformance as follows: the subject is co-vertly reciting the alphabet while simulta-neously ticking off the numbers from oneto ten on his fingers. This interpretationconverts a problem that has no explanationat all in terms of overt behavior into onethat has a perfectly mundane one. Is it plau-sible? Yes: The intraverbal chains ofcount-ing to ten and reciting the alphabet are wellestablished in most adults (and we can testfor them), as is the strategy of lining upobjects and picking out the Nth instance.The latency of the target response leaves awindow for mediating behavior. The twitch-ing of fingers is often overt and supportsthe notion of covert counting.The account might be wrong. Jack

Michael, when posed the problem, took an"educated leap" and landed on a nearby let-ter (or so he reported). Suppose he had got-ten it right and had "leapt" to the right let-ter, in contradiction to our interpretation. Itdoesn't matter. The point of the exercise isto show that behavior analysis can offer atleast one plausible account of a phenom-

enon that might otherwise be left to others.If we can offer an even more compellingexperimental analysis, so much the better.But I am greedy and don't want to leaveanything to mainstream approaches.

CM: Here are a few quotes from Dave's lastpost that I think sum up his position. I'veoffered my opinions after each quote or setof quotes.With respect to butterfly mimicry:

"Should we wait until we have a completefossil record that will support the interpre-tation, recognizing that such a record mightnever be available?"My opinion: I see no reason why we

should not wait. My response to interpreta-tions such as the one offered about butter-fly mimicry is usually something like this:"Interesting. Let's get back to work!"On the consequences of not offering in-

terpretations: "... we don't have any accountat all.... We open the door for the spiritual-ist, the mentalist, and the mystic."My opinion: I can accept not having an

account. I think interpretation is overval-ued. We sometimes talk about changing aperson's worldviews as if that is necessaryin order to change their behavior from mo-ment to moment. I don't think so. Evenparents of young children with languagedelays who have experienced the power ofbehavior analysis directly will frequentlyturn around and say, "Thank God. It's amiracle"; no matter that the therapist is say-ing, "No, it's the systematic application ofbasic principles of human behavior." Theparent can learn to apply the principles weteach them while rejecting our interpreta-tion ofwhy the principles work. I think thisability might get more at the heart ofWittgenstein's rule-following dialectic. (Idon't claim to be one of the dozen or sopeople-in my view-who seem to graspwhat Wittgenstein was saying; so this isreally just a shot in the dark.) The door willalways be open to mystical interpretations.On the value of offering interpretations:

"It depends on the cost of being wrong....The point of the exercise is not to offer

certainty, but to ... offer a possible solution... without recourse to mysticism.... As longas we have one possible natural explana-tion ... it displaces occult explanations."


My opinion: Suppose we "displace oc-cult explanations" of language. How willthings be different? What if Skinner's in-terpretation of verbal behavior (or someneo-Skinnerian interpretation) becamewidely accepted by academics and in thepopular culture alike? Would our lives (mo-ment to moment) be all that different?

JL: There is not much difference of opinion,but there is some. As Dave notes we musthave an analysis ofprivate events. My con-cern is that we offer an account that doesnot simply take something observed andextend it (metaphorically) into the world ofthe unobserved to explain the actions oftheobserved event, and further, assume that theunobserved and the observed belong in thesame categories.The counterexamples to which I have al-

luded have all shown that variables otherthan private events have accounted for thephenomena, and that the reported privateevent, if actually governing or influencingbehavior, would have yielded a differentoutcome.There are indeed many evolutionary "just

so stories" and many such descriptions havecome under increasingly harsh criticism,particularly in the area of behavioral char-acteristics. The generally accepted ones findtheir basis in reference to processes exam-ined under experimental control. Even so,recent assumptions have been turned up-side down by new developmental data thathave shown that comfortable and accepted'interpretations in this area have slowed ourunderstanding of the relations of genes todevelopment. This is a problem for fieldsother than ours as well.Dave's alphabet example is a good one.

What the question "What is the 10th letterafter H?" may occasion is an intraverbaltraining history, which potentiates a privateoccurrence, and a sequence that leads to theanswer R. The question is, how much ofwhat I think the private sequence I'm us-ing is actually the sequence. Is it just mymetaphorical way of describing it, becauseI have no other way of describing it, since Ihave no direct training in this area?Here is a variant I saw somewhere and

have used with students (particularly good

with poor spellers): Write the wordSTRENGTH on the blackboard. Tell thestudents to take out a piece of paper and apencil. Now ask the entire class to stare atthe word. Tell half the class to close theireyes and visualize the word. (As a variant,choose those who claim that they canclearly picture the word with their eyesclosed.) Now tell both groups to write theword, spelling it backwards. One will findthat this is little problem for those lookingat the word, and a more difficult task forthose "clearly picturing" it. What one no-tices is that most ofthe students whose eyesare closed engage in an intraverbal se-quence not unlike what Dave describes, butthe students in the other group do not. Theactual stimulus, and the pictured "stimulus"do not share the same properties. Was therea private event there, or did the studentswhose eyes were closed just think therewas? At least we cannot ascribe to the pri-vate event the same categorical status as thepublic one. Now, if we provide a traininghistory that involves spelling in both direc-tions and repeat the experiment, we mayfind no difference between groups. Are wenow to conclude that the private event actsin the same way as the public? Or, shouldwe say that the differences or similaritiesbetween groups is a function of their pro-gram history, and that the results can be thesame or different as a function of the pro-gram? The private event may or may notoccur. The difference in outcomes is attrib-utable to other variables, and an interpreta-tion that has us overlook those variables iswhat I see as the real problem.A recent NOVA described String Theory,

for which there is no direct or indirect evi-dence, but it explains a lot, and is beauti-fully mathematically consistent. That is, sofar, things we see in the world do not con-tradict it. Now, it is unlikely that Stringswill ever be directly observed, but a wholerange of technologies may indeed be de-veloped as a result of their investigation.Or, it may all be an "ornamental lump."Nonetheless, Strings have their own char-acteristics and functions; they are not sim-ply relations borrowed from the observedworld and used to explain the unobserved.Private events may indeed play a major rolein our ultimate understanding of behavior,


but my concern is that they be treated withcare and that we not assume for the sake ofease in explanation that they are simplyevents (perhaps stimuli and responses) thatact in much the same way, and play the sameroles as do events that are in direct contactwith, and thereby defined by, contingentenvironments.

Nathan Stemmer (NS): I have an alternativeproposal. Newton's hypothesis postulatedthe existence of non-observable gravita-tional forces that explained, among otherthings, the tides. But Newton could havecomplicated his hypothesis. He could haveassumed that in the case of the tides, thegravitational forces had, in addition, mon-strous features, or behavioral features. Butalthough the hypothesis that attributed theseadditional features to the gravitationalforces would also explain the tides, it wouldno longer be the most parsimonious hypoth-esis.Suppose now that a child has appendici-

tis, which among other effects evokes cry-ing behavior. We can offer the normal physi-ological explanation of the behavior. Butwe could also propose a different hypoth-esis, a hypothesis that adds the assumptionthat the inner events that generate the cry-ing behavior had monstrous and/or behav-ioral features. Although the hypothesis thatattributed these additional features to theinner events would also explain the cryingbehavior, it would no longer be the mostparsimonious hypothesis.

Finally, suppose that the child not onlycries but also utters "I am in pain." Whichis now the most parsimonious hypothesis?In my view, it is the hypothesis which, justas in the first case, attributes the behaviorto physiological factors, and the verbal be-havior is explained by attributing it to thefact that the previous learning events-theevents in which the child "learned" the ex-pression "[I am in] pain"-modified thechild's physiological constitution. (Quine,1974, speaks in this connection of the"traces" that the learning events left in thephysiological organism.) Therefore, theappendicitis now operates on a modifiedorganism, and it therefore evokes not onlythe crying but also the verbal behavior. Theassumption that in the present case, the

physiological factors also have covert be-havioral features-e.g., the child subvocallyproduces, say, seven times the subvocalsubstitutes ofthe letters "p" and "n"-doesnot add to the explanation, and is thereforeno longer the most parsimonious hypoth-esis.Notice moreover that, by definition, we

can never know whether the child's innerevents had covert behavioral features-e.g.,whether it also included subvocal substi-tutes of the letters "p" and "n"-becausethe moment we have scientific evidence ofthis covert behavior, the behavior is nolonger covert; it is overt.On the other hand, physiological experi-

ments such as those described in, e.g., Byrne(1987) and Hawkins and Kandel (1984) canindeed increase our knowledge about theneurophysiological factors, and, in particu-lar, about the nature of the physico-chemi-cal features of the neurophysiological ef-fects-the traces-of the verbal learningevents. In short, my proposal is to avoidattributing behavioral features to the innerevents. The addition does not explain morephenomena than the more parsimonious hy-pothesis that restricts itself to neurophysi-ological factors. (See also Stemmer, 1992,1995, 2001, in press.)

PB: Your example could work either way. Itdepends upon what we know about the situ-ation. If we have independent evidence ofappendicitis (tender abdomen, evidence ofinfection) we might assume that an under-lying medical condition is the most likelyexplanation (and parsimony is simply onetool for identifying the most likely expla-nation) of the child's behavior. In otherwords, it would be a relatively uncontami-nated tact. On the other hand, learning his-tories can also be assumed to result inchanges in the state of an organism (we as-sume a neurophysiological basis for behav-ior even if that science has yet to provide auseful account). But neurophysiology hasnot yet developed to the point of meaning-ful control and prediction of behavior.

Analytically, one must distinguish be-tween internal stimuli and covert responses.Both are (potentially) private events. As-signing an event to the stimulus or responsecategory (and it may have both functions)


must be based on our observations of pastand present collateral events.

Ray Weitzman: In behavioral science, it seemsto me that using parsimony as a criterionfor choosing among explanations is highlyundesirable. For example, if one explana-tion claims that environmental variables A,B, C, and D are the functional determinantsof a certain class of behaviors and anotherexplanation claims that just A, B, and C arethe functional determinants of the behav-ior, then according to the "law of parsi-mony," the latter explanation is to be pre-ferred to the former. But only by experi-mental investigation can we really deter-mine which explanation is correct. Select-ing explanations on the basis ofparsimonyseems to cut off scientific investigation ofthe phenomena we are interested in. As faras I can see, parsimony is only useful indealing with formal systems or when theclaimed independent variables are unob-servable. In the latter case, we must thenask ourselves what is the value of decidingamong different explanatory fictions. Par-simony doesn't seem ofmuch value in em-pirical investigations.

In Nathan Stemmer's example of thechild who has appendicitis and cries, neu-roscience might be able to give a descrip-tion of the neurophysiological relationshipbetween the appendicitis and the crying. Ican imagine that such a description wouldbe quite complex. In a primitive society theexplanation might be in terms of evil spir-its inhabiting the child's body and actingin concert, one causing the appendicitis andthe other evoking the crying. This seems tobe a much simpler explanation. However,because the two explanations offered areframed in terms oftotally different domains,the physiological vs. the spiritual, there canbe no basis for really deciding which ismore parsimonious. Only ifthe terms oftheexplanations lie within the same domain canparsimony be useful, but even in this caseits value is highly limited.Why then would we prefer a physiologi-

cal explanation to an evil spirit explanation?Certainly not on the basis ofparsimony. Butcould it possibly be due to our cultural his-tory ofeffective contingencies ofreinforce-ment?

TS: Parsimony is frequently invoked withoutfurther explanation. However, its invoca-tion raises two troubling questions: (1) Bywhat measure are we to determine whichexplanation is more parsimonious? (2) Whyis the more parsimonious explanation pre-ferred? In his post, Ray Weitzman rightly(in my judgment) raises the second, logi-cally prior question. As Elliot Sober (1993)has noted, this topic has not escaped theattention of philosophers of science. Forexample, Quine (1966) argued that simplerexplanations are more probable, while Pop-per (1959) maintained that they are morefalsifiable. For Sober himself, there is noglobaljustification for invoking parsimony;rather, "justification for using parsimony ...depends on assumptions that are specificto the inference problem at hand." (Sober,1993, p. 105)

NS: Brandon admits that we may have knowl-edge ofsome of the biological bases ofbe-havior, but "not yet to the point of mean-ingful control and prediction of behavior."This is certainly true. But this also holds forour knowledge of the behavioral featuresof the covert-behavior events. Our knowl-edge of the behavioral dimension of theseevents-e.g., whether they contain seventimes the subvocal substitutes ofthe letters"p" and "n"-is insufficient for basing onthem our predictions of the child's behav-ior. As Brandon suggests, our predictionswill "be based on our observations of pastand present collateral events." But this isalso the strategy adopted by the physiolo-gists. Our predictions of the child's behav-ior will not be based on our physiologicalknowledge but rather "on our observationsof past and present collateral events." AsQuine observes, "the physiological is thedeepest and most ambitious" level of ourexplanations of behavior ... "and it is theplace for causal explanations." But pres-ently the "behavioral level ... is what wemust settle for." (1975, p. 87) It follows thatphysiologists, too, have at present no alter-native but to look for environmental fac-tors on which to base their predictions ofthe subject's behavior. To formulate myposition in a sharper way: I assume thatBrandon agrees that the covert-behavior


events are physiological events. But hemakes an additional assumption. He as-sumes that these physiological events havealso behavioral features. My argument isthat this additional assumption is superflu-ous, because it does not increase our con-trolling and predictive power. This powercontinues to derive from "our observationsof past and present collateral events."

I agree that Brandon's additional assump-tion may be quite innocent. It does not nec-essarily deviate us from our goal of look-ing for the environmental variables that con-trol the behavior. But there is a disadvan-tage. Eventually, behavior analysts intendto establish a dialogue with other psycholo-gists. This will probably not be an easy task,mainly because most psychologists, eventhose who consider themselves monist ma-terialists, are influenced by mentalist ideas.But one obstacle to such a dialogue can beremoved, namely, the use by behavior ana-lysts of the notion of covert behavior. Thisnotion is so strange, so bizarre, for peoplewho have not been educated in a behavioranalytic environment, that they immediatelyturn away from any position that admitssuch inner events. But this reaction can beavoided because there is no need at all forbehavior analysts to introduce the notionof covert behavior. All relevant phenom-ena can be accounted for by assuming onlypast and present environmental factors. Andif we look for a causal explanation, thenwe add that these environmental factorsoperate on the subject's physiology, and thiscausal factor then generates the relevantbehavior.

PB: I'm not sure that the (implicit) dichotomybetween physiology and behavior is neces-sary. Behavioral events are a particular sub-set of physiological events; covert behav-iors in turn a further subset. Of course notall physiological events are covert nor arethey all behaviors.As for the claim that other psychologists

find the notion of covert behavior bizarre,this has not been my experience. Do yourcognitivist colleagues deny that peoplethink, and that thoughts cannot be observedby others? The main obstacle seems to bethe epistemological one-that thoughts arenot causes of overt behavior.

NS: Paraphrasing Brandon, I hope faithfully:Covert behaviors are inner (covert) physi-ological events, and these events have ad-ditional behavioral features. Ifwe now ap-ply this terminology to the example of thechild who produces the word "pain," wereceive the following conclusion: Thechild's verbal behavior is evoked or occa-sioned by an inner physiological event(probably together with other inner andouter factors), and the inner event has be-havioral features.

In my previous communications, I arguedthat the assumption that the inner event isnot only a physiological event but also hasbehavioral features does not increase ourcapacity for control and prediction of be-havior. I therefore concluded that "this ad-ditional assumption is superfluous." Butmaybe I was mistaken. I therefore raise thefollowing question: (1) Does the attributionof behavioral features to the inner eventincrease our capacity for control and pre-diction ofbehavior?A positive answer sug-gests the further questions: (2) How is theincrease in controlling and predictive ca-pacity achieved? (3) Is there a method thatenables us to establish the physical dimen-sions of the behavioral features of a spe-cific covert-behavior event? For example,can we answer the question ofwhether thecovert behavior, which (perhaps togetherwith other factors) evokes or occasions thechild's utterance of "pain," contains sub-vocal substitutes ofthe letters "p" and "n"?

PB: All behaviors are physiological events, butI'm not sure how a behavior can be said tohave "behavioral features." What does thisstatement add? In your example I don't seea covert behavior, just an internal stimulus.While in practice this stimulus is usuallycovert, such inner physiological events areusually amenable to overt observation (i.e.,medical examination). Thus we are analyz-ing the overt verbal report of private (co-vert) stimuli, a behavior which we assumehas been acquired through the appropriatereinforcement of verbal reports ofpubliclyobserved painful events, and maintained byreinforcement based on the observation ofcollateral events. I would not term the pri-vate event controlling the word "pain" abehavior, as it is not under the control of


either environmental antecedents or conse-quences. Rather, it can serve both functions.In this case it is a discriminative stimulus(the antecedent) for the child's emitting theovert verbal response "it hurts," correlatedwith reinforcement by attention from adults(the consequence), and it might also leadto alleviating the pain (another conse-quence). The parent's response to the child'sverbal behavior might in part be based onthe observation of the respondents elicitedby the same internal event (respondentrather than operant crying).

Matthew Normand: Regarding PaulBrandon's re-statement of"pain" as a stimu-lus and not a behavior, it seems to me thatpainful event would function as a Motivat-ing Operation (MO) rather than an SD, asthings such as parental attention are just asavailable in the absence of the pain as theyare in the presence of pain. That is, "pain"is related to the differential effectiveness ofthe various forms of reinforcement ratherthan the differential availability. The ver-bal response of "pain" (or some other re-sponse that has, in the past, been followedby reduction in pain or parental attention)is then momentarily frequent due to theevocative effect of the MO, and the conse-quence is more effective due to the estab-lishing effect. Various other stimuli orstimulus conditions, such as the presenceofparents or other caregivers, would func-tion as SDS, as they are correlated with thedifferential availability ofrelevant reinforc-ers. (Most people typically do not mand inthe absence of listeners.)

Thus, the "pain," as a Motivating Opera-tion, determines the form of the verbal re-sponse, establishes the effectiveness ofcer-tain consequences, and evokes the types ofbehavior that have in the past producedthose consequences. Perhaps there are sev-eral types ofMOs corresponding to differ-ent aspects of the situation: e.g., parentalattention and pain reduction. Whether or notthe response occurs is controlled by an SD,such as the presence of members of a ver-bal community.

PB: Good point. I'd still say that "pain" couldhave both manding and tacting functions. Iwill agree that in the example as presented

the main function would be manding, andthus the controlling functions of the inter-nal events would be MO's (establishingoperations, to use slightly older terminol-ogy). However, I suspect that there wouldbe tacting functions as well. A response to"Where does it hurt?" would be a tact.

[Following this entry, the forum drifted intoother topics.]

SUMMARY

The discussion ended without consensus,which is not surprising, considering that it wasunstructured and spontaneous, that it was dis-tributed over several weeks, and that its par-ticipants composed their entries in isolation.But most of the disagreements were aboutpolicy and strategy rather than about the placeof private events in the science of behavior.Some participants, notably Eshleman and Bran-don, raised mainly methodological and empiri-cal questions: What is the role of amplitude indetermining units of analysis? Can low ampli-tude responses be studied if measures ofinterobserver reliability cannot be obtained?How does thinking a response differ fromspeaking a response, both conceptually andpractically? These questions set the occasionfor the subsequent discussion, but they werenot answered.

Disagreements arose over the value of inter-pretations that invoke private events. Palmerurged the liberal use of interpretation to layclaim to a subject area, that is, to provide ten-tative explanations for phenomena for whichexperimental analysis is impossible, a positionhe has discussed at greater length elsewhere(Donahoe & Palmer, 1989; Palmer, 1991, 1998,2004). McDonough suggested that such inter-pretations have little force and that our time isbetter spent working on experimental resolu-tions of puzzling questions than on trying topersuade others of the potential scope of a be-havioral analysis. In the same vein, Layng, in-voking Wittgenstein's "skeptical paradox," ar-gued that the virtues of interpretations are of-ten outweighed by the problems they raise. Inparticular, he cautioned against the uncriticalassumption that private events are no differentin kind from their public counterparts and thatthey necessarily play a causal role in the flowofbehavior. He argued that ifmore effort were


devoted to the control ofbehavior by programsof contingencies distributed over time, someofthe pressure for ad hoc interpretations wouldbe dissipated. Accounts that ignore such con-tingencies are likely to be misleading.Schoneberger echoed these reservations andcautioned against a climate in which "anythinggoes." Fortunately, these viewpoints are notmutually exclusive and mainly reflect differ-ences in emphasis or differences in preferences.Michael urged discussants to distinguish

sharply between the terms stimulus, response,and responseproduct. The tendency to attributestimulus control to a response rather than to aresponse product is imprecise.Stemmer suggested that private events be

viewed exclusively as physiological events;endowing them with behavioral properties is agratuitous assumption that adds nothing to theaccount. The physiological account, he argued,is preferred on grounds of parsimony and theextent to which it permits easy dialogue withthose in other fields. But Weitzman andSchoneberger remarked that parsimony, by it-self, is an inadequate criterion for decidingbetween alternative proposals in the behavioralsciences. Once again, the virtues ofexperimen-tal analysis were advanced. Brandon noted thatphysiological accounts are of little use in pre-diction and control. Stemmer asked what useinferences about covert behavior are in predic-tion and control, referring to a hypotheticalexample of a subject reporting pain. Brandonand Normand refined the terms of Stemmer'squestion but left it, in its general form, unan-swered.To bring some closure to the discussion, I

will propose an answer to Stemmer's questionhere. The reason for distinguishing behavioralevents from physiological events is that sci-ence has formulated principles of behaviorfrom tightly controlled laboratory investiga-tions. We can bring these principles to bear onthe interpretation ofbehavioral events, but notother kinds of events. A response of interestmay be unobservable on some occasion, but itis unlikely that all relevant behavioral variablesare equally obscure. We are likely to have ac-cess to relevant discriminative stimuli andmotivational variables, and we may knowsomething ofrelevant historical contingenciesas well. Thus, when we ask a question that re-quires counting letters of the alphabet (e.g.,"What is the 10th letter after H?"), we have

arranged motivational and discriminative vari-ables that potentiate reciting the alphabet as anintraverbal chain. If the matter were of suffi-cient importance, we could even gather dataon the subject's acquisition of that intraverbalchain. Having asked the question, we cannotbe certain that the chain will be emitted, butwe can be confident that it has increased inprobability, for our behavioral principles, de-rived independently, tell us so. If additionalvariables are present that would punish overtresponding (e.g., the instructions to "do it inyour head"), we have objective reasons for pre-dicting that an overt response will not occur.Finally, when a relevant overt response doesoccur (the subject says, "R!"), we can supposethat some relevant discriminative stimulusevoked it. We know from the subject's historythat one such discriminative stimulus is theresponse product of saying "Q," a part of theputative intraverbal chain. Thus, armed withthe data at hand, knowledge of the subject'shistory, and a set of principles of behavior, wecan make predictions about covert responsesand even control them. We cannot do so withcertainty, but neither can we do so with overtbehavior. Ofcourse, we can never confirm ourpredictions or demonstrate our control, but thepurpose of interpretation is not to offer proofbut to make sense of the world.Stemmer is presumably right that eventually

one might offer a parallel account at the levelof physiological processes, appealing to prin-ciples that have emerged from correspondingexperimental analyses. However, the relevantvariables are likely to be as private as the be-havior under investigation. One would presum-ably have to measujre simultaneously the ac-tivity of thousands or millions of neurons, allwithout perturbing the phenomenon understudy. Behavioral principles do not have anyconceptual or empirical superiority to physi-ological principles, but the relevant variablesare usually far more easily measured and ma-nipulated. It was just such practical consider-ations that led Skinner to argue, in the earlyyears of our field, for an independent scienceof behavior.

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