JOURNAL OF APPLIED BEHAVIOR ANALYSIS 1997, 30, 533–544 NUMBER 3(FALL 1997)

BEHAVIORAL CUSPS: A DEVELOPMENTAL AND PRAGMATIC CONCEPT FOR BEHAVIOR ANALYSIS

JESU´ S ROSALES-RUIZ

UNIVERSITY OF NORTH TEXAS

AND

DONALD M. BAER

UNIVERSITY OF KANSAS

Most concepts of development explain certain behavior changes as products or markers of the invariable succession of emerging periods, stages, refinements, or achievements that define and order much of an individual’s life. A different but comparable concept can be derived from the most basic mechanisms of behavior analysis, which are its environmental contingencies, and from its most basic strategy, which is to study behavior as its subject matter. From a behavior-analytic perspective, the most fundamental developmental ques- tions are (a) whether these contingencies vary in any systematic way across the life span, and thus make behavior change in a correspondingly systematic way; and (b) whether some of these contingencies and their changes have more far-reaching consequences than others, in terms of the importance to the organism and others, of the behavior classes they change. Certain behavior changes open the door to especially broad or especially important further behavior change, leading to the concept of the behavioral cusp. A behavioral cusp, then, is any behavior change that brings the organism’s behavior into contact with new contingencies that have even more far-reaching consequences. Of all the environmental contingencies that change or maintain behavior, those that accomplish cusps are developmental. Behavior change remains the fundamental phenomenon of de- velopment for a behavior-analytic view; a cusp is a special instance of behavior change, a change crucial to what can come next. DESCRIPTORS: development, developmental stages, pivotal behaviors, behavior traps, behavior analysis, behavior change

Conceptualizing the development of be- suppose that much behavior develops in havior over the life span has been an endur- obedience to that sequence. And, because ing problem in psychology. Organismic the- the sequence is invariant, it requires an ex- ories postulate an invariable succession of planatory logic, which most often takes the emerging stages, periods, achievements, dif- form of its apparent goal, as if the sequence ferentiations, refinements, or products; they were self-organizing: The individual is seen as traveling epigenetic roads to uniquely The authors are grateful to Sigrid Glenn, Joel Green- adult stages of development, much like a spoon, Hayne Reese, Wendy Roth, and John Wright for train stopping at various stations before it sympathetic, critical, careful, competent, detailed, and constructive argument; but they should not be held re- reaches its final, always scheduled destina- sponsible for the arguments advanced here. The authors tion, or a butterfly passing through the em- are also grateful to the National Institute of Child Health bryo-larva-pupa-imago stages to the inevita- and Human Development for research support (HD 18955). ble fluttering forth (see Overton & Reese, Address correspondence to Jesu´s Rosales-Ruiz at the De- 1973; Reese, 1991; Reese & Overton, 1970; partment of Behavior Analysis, University of North Texas, Spiker, 1966). Whereas the teleological P.O. Box 13438, Denton, Texas 76203 (E-mail: Ro- sequence implied in such approaches is that [email protected]) or to Donald M. Baer at the Depart- ment of Human Development and Family Life, University an embryo is just a butterfly’s way of making of Kansas, Lawrence, Kansas 66045-2133. another butterfly, it is equally plausible to

533 534 JESU´ S ROSALES-RUIZ and DONALD M. BAER argue that a butterfly is just an embryo’s way tant behavior changes have more far-reach- of making another embryo. Perhaps the con- ing consequences than others. Here, we ad- cept of ‘‘development’’ is sometimes a way dress that question by describing the concept to ignore an arbitrary half of the evolution- of developmental ‘‘cusps’’ (Rosales-Ruiz & ary process. Baer, 1996) and suggesting some criteria for Behavior analysis is different; it has no ‘‘far-reaching.’’ comparable guiding metaphor to explain patterns of behavior change throughout the life span. At least, none is intrinsic to its A PRAGMATIC CONCEPT OF present logic. Of course, one or several such DEVELOPMENT FOR metaphors might be added. But that addi- BEHAVIOR ANALYSIS tion would seem apt only if it were done in Consider a cusp as a behavior change that the natural-science style that has guided the has consequences for the organism beyond development of behavior analysis so far. the change itself, some of which may be con- That means it must be more than a meta- sidered important. That requires us to de- phor; the premises justifying it should be velop the criteria of importance. To ap- verifiable. proach those criteria, we must expand the Behavior analysis currently offers its well- definition of cusp: We take as axiomatic that known behavior-shaping contingencies as its any behavior change results from changes in basic analytical processes; and it offers them, the interaction between the organism and its so far, without specifying any distinctive, re- environment. What makes a behavior liable patterning of them over the life span. change a cusp is that it exposes the individ- If a concept of development is to be added, ual’s repertoire to new environments, es- that concept must posit a reliable pattern of pecially new reinforcers and punishers, new how these contingencies are applied over the contingencies, new responses, new stimulus life span. Stated this way, the possibility of controls, and new communities of maintain- a reliable pattern of behavior-change pro- ing or destructive contingencies. When some cesses over the life span becomes a matter of or all of those events happen, the individual’s facts to be determined rather than as a the- repertoire expands; it encounters a differen- ory to be imposed. We can ask whether the tially selective maintenance of the new as application of these contingencies, by nature well as some old repertoires, and perhaps and by people, varies in any systematic way. that leads to some further cusps. We can ask whether the behaviors to which Consider, for example, what can happen they are applied vary in any systematic way, as a result of learning to crawl. The baby and if so, whether that is by nature or by suddenly has increased access to the environ- idiosyncratic societal convention. Discerning ment and its contingencies. Now the baby those kinds of systematic patterns of contin- can get to toys, family, and other things gencies across the life span appears to be an more easily, or can stumble into obstacles, implicit theme of two recent texts that de- all of which produce interactions that will scribe development from a behavior-analytic further shape the baby’s behavior. Some of perspective (Novak, 1996; Schlinger, 1995). these interactions initiate the shaping of oth- These texts are oriented toward undergrad- er behaviors that will soon contribute to uate readers; their mission is to show how walking, others will shape responsiveness to traditional developmental topics are amena- visual cliffs (e.g., Campos, Bertenthal, & ble to a behavior-analytic interpretation. But Kermoian, 1992), and still others will pro- we can also ask whether some of the resul- duce a variety of parental contingencies, BEHAVIORAL CUSPS 535 some delighted, some dismayed, that will accurate, fluent reading is a cusp. Teach a further shape how much more and how child with developmental disabilities gener- much less of the physical and social environ- alized imitation, and future expansion of the ment will be open to the child’s further in- child’s repertoire can suddenly and system- teraction. Thus, if walking, safety, and the atically be as explosive as the social environ- immediate next direction of socialization are ment cares to make it, simply by modeling important for that baby at that time, crawl- new skills, not necessarily intentionally. If ing is a cusp. any of that is important, to the child or to This argument does not deny the devel- those responsible for the child, generalized opment of the many small, sequential skills imitation is a cusp. Teach an infant to dis- that culminate in crawling. Perhaps each of criminate between positive parent attention them is a prerequisite for the next, and thus and disapproving parent attention, and you for crawling. But the important point here end the paradoxical reinforcement of inap- is that none of these skills alone suddenly propriate child behavior, which suddenly open the child’s world to new contingencies and systematically will alter the child’s and that will develop many new, important be- the parents’ futures, especially their joint fu- haviors. Instead, each of them opens the tures. If gentle social guidance is important child’s world only to the next skill. Their end to the child at that time, then coming under point, crawling, is a cusp. the conventional stimulus controls used nat- By contrast, consider a child who has all urally by almost every parent (and almost the prerequisites for walking, yet continues every subsequent teacher) is a cusp. Give to crawl; an early study by Harris, Johnston, young adults the first sizable, dependable, Kelley, and Wolf (1964) dealt with such a disposable income of their lives, and sud- case. They systematically shaped walking in denly, systematically, and enduringly, new a preschool girl who almost always crawled. sources of teaching will emerge that may al- Walking made it possible for her to partici- ter and expand some of their criteria for and pate in the upright, fast-moving games her some of their practice of what constitutes peers played, which was most of their games. food, housing, transportation, entertain- A host of new interactions typically will fol- ment, travel, family, and responsibility. If low from walking. If leg strength and par- any of that is important to the young peo- ticipation in peer socialization were impor- ple, to their society, or to its economy, dis- tant to that girl at that time, walking was a posable income is a cusp. (The parallel ar- cusp for her. Or perhaps it was a cusp for gument for elderly people who can retire her parents and teachers: Perhaps the girl’s with a disposable income is obvious.) behavior showed that walking and peer These examples show that the concept of games had little importance for her at that cusp always depends on the phrase, ‘‘If that time; it was her parents and teachers who is important . . .,’’ as if the audience must believed that leg strength, coordination, and decide if that is important. We suggest that peer participation would have consequences in these arguments, importance most often that would be important to her later. is indeed a social phenomenon. In biology, Teach a child to read accurately and flu- perhaps importance is unquestionably sur- ently, and suddenly and systematically a vast vival. In development, survival is rarely clear, amount of further development, and a new, so importance is very often a matter of drastically more efficient method of teach- something else, usually social validity. A cusp ing, are operative. If any of that is important may unquestionably open new environments to the child or to the child’s future, then for a child, and we may view what those new 536 JESU´ S ROSALES-RUIZ and DONALD M. BAER environments will produce as being impor- cusp that makes them available for that tant; but if we inquire, we often will find shaping. that others do not. More than one preschool The logic of cusps is implicit in earlier teacher has told parents that their child is a discussions by Baer and Wolf (1970) and social isolate and that the teacher can re- Baer, Rowbury, and Goetz (1976), who con- mediate that, only to be told by the parents sidered behavioral ‘‘traps’’ and the responses that they prefer their child to be a social that enter such traps (cf. Martin & Pear, isolate, because the parents think that isola- 1978; Stokes & Baer, 1977). A behavioral tion is important to the child’s artistic, in- trap is a community of reinforcement in the tellectual, or political development. natural environment that could maintain Not all new cusps need be seen as positive and potentially shape much new behavior of or desirable. Introducing a child to an ad- its members. Preschools, universities, and diction is an obvious example of a terrible other social organizations are traps waiting cusp (for the great majority of us); teaching for new members to enter and so, probably, a child that the correct first response to any to be shaped. To the extent that these traps new problem is to seek help rather than to shape behavior beyond the entry responses, persist in independent tries is a more subtle and to the extent that those behaviors are example (for many of us). important to someone at some time, the en- Sometimes changing only one behavior try responses are cusps. For example, a will create a cusp; sometimes it will be nec- child’s rudimentary social skills could be essary to change a class of behaviors. A cusp trapped in the natural community of peers’ may be easy to accomplish, or it may be social reinforcement by reinforcing responses difficult, tedious, subtle, or otherwise prob- that result in proximity to other children. lematic; yet if the cusp is not achieved, little The contingencies practiced by those peers or no further change is possible in its realm on the behavior of anyone in steady contact (and perhaps in several other realms). But, with them will differentiate, discriminate, when the cusp is achieved, a set of subse- schedule, and maintain a much larger, more quent changes, important to someone, sud- refined, and more complex set of social skills denly becomes easy or highly probable. And (e.g., Allen, Hart, Buell, Harris, & Wolf, when that cusp brings the developing organ- 1964). In this example, the cusp is the be- ism into contact with other, subsequent con- havior change of being proximate to the tingencies crucial to further, more complex, group. That is a very small behavior change or more refined development in a thereby and relatively easy to program; but it is also steadily expanding, steadily more interactive a cusp because of the extent and importance realm, that will connote the conventional la- of what happens next. bel of developmental. In traditional theory, Some arguments by the Koegels and their the connotations of increased complexity or colleagues (Koegel & Frea, 1993; Koegel & refinement often are put forward as causal Koegel, 1988; Koegel, Koegel, & Schreib- and explanatory, in a teleological sense. The man, 1991) embody the cusp concept. They cusp explains in a different way. It points out call ‘‘pivotal’’ any behavior changes that ‘‘re- that certain behavior changes cause subse- sult in collateral changes of other behaviors quent broad or important behavior changes, as well’’ (Koegel & Frea, 1993, p. 369). in the sense of making those subsequent They suggest that many children with au- changes available. If we want to explain tism do not persevere in problems as do typ- those subsequent changes, we need to know ically developing children. But programming the contingencies that shape them and the more reinforcement across a variety of prob- BEHAVIORAL CUSPS 537 lem-solving opportunities can remediate changed, not about how it should be that, and thereby increase the children’s rep- changed. That it can be changed by proce- ertoires; when that happens, it widens the dures that are so prevalent in the natural range of situations that evoke teaching from world, and that are so easily open to social the teachers. The result is new and improved intervention, probably reflects great survival skills not specifically targeted by the initial value. program; Koegel and Koegel (1988) cite ty- Thus, cusps are behavior changes, some- ing shoes, buttoning clothes, and restaurant times simple, sometimes complex, that sys- skills as examples. Similarly, Koegel and Frea tematically cause other, further, not formally (1993) report that effectively teaching stu- programmed behavior changes that are sig- dents eye contact and appropriate facial ex- nificant either because of their breadth or pressions may decrease some abnormal be- because of their importance to the organism havior and increase effective conversation. or its species. That importance is seen some- To the extent that these collateral behavior times by the organism, or by parties con- changes prove to be important or introduce cerned for that organism, or by its relevance the organism to new shaping environments to the selection pressures of the environ- that prove to be important, they are cusps ment, or all of those. Cusps often accom- as well as pivotal behaviors. If, for example, plish that kind of extensive or important col- the collateral behavior changes seem to be lateral behavior change because they increase only brief, stereotypic conversations about the organism’s exposure to the relevant very few topics, they remain collateral be- teaching contingencies. havior changes, but their importance to the Restated, the importance of cusps is child or to others seems problematic, and judged by (a) the extent of the behavior thus they may not be cusps. Cusps are be- changes they systematically enable, (b) havior changes that systematically lead to ei- whether they systematically expose behavior ther widespread further changes or to im- to new cusps, and (c) the audience’s view of portant further changes. whether these changes are important for the Again, the criteria for importance are usu- organism, which in turn is often controlled ally situational. Most often, they hinge on by societal norms and expectations of what what the behavior changes are and on what behaviors should develop in children and their consequences are for that organism, when that development should happen. not in their own right, but relative to what Most of that is ultimately judged by survival, that organism wants, what its caretakers, ad- but ‘‘ultimately’’ is a long time and is ex- vocates, and teachers want for it, and what tremely difficult to predict in advance. It is a disinterested audience sees as significant the third criterion, including our guesses for that organism, or for any organism in about survival, that often prompts us to see their society or species. These ‘‘wantings’’ only certain behavior changes as develop- may be pragmatic, or they may reflect an mental. allegiance, even an implicit one, to some The cusp concept is focused on under- theory about what is important to any de- standing the importance of what happens af- veloping organism. Behavior analysis is not ter any behavior change, in order to define such a theory, apart from its usual endorse- development. Other approaches, by contrast, ment of evolution as an inevitable process define development by asking what new lev- and of survival as a near-universal reinforcer el of ability or complexity the behavior of exceptional importance. That is, behavior change represents. Yet, cusps can be simple: analysis is a theory about how behavior is Access to other environments sometimes re- 538 JESU´ S ROSALES-RUIZ and DONALD M. BAER quires only a simple response, like dialing the elements of verbal behavior (e.g., teach- the critical number, or keyboarding the crit- ing the chunking of verbal messages; cf. ical address, or extending the stimulus con- Case, 1987). At the least, it transforms a lis- trol of an existing response. They can also tener from one who must be spoken to with be as complex as the task analysis of conser- slow-paced, one-word messages into one vation, seriation, transitivity, or self-instruc- who can respond correctly to ordinary sen- tion. In other approaches, the ability to read tences, which may not be seen as a very im- might be valued as developmental because of portant change. But, given enough of other the time required to teach it, the extensive related skills—of other cusps passed—it can skill it represents, or the mental functions it also transform that listener into an efficient is inferred to represent. However, if teaching student. reading were to have little effect beyond the Normal children get through many cusps achievement of reading, it would, for this to what follows in their various worlds, usu- behavior-analytic view of development, be ally by extensive if casual teaching (e.g., im- irrelevant to development; it would not be a itation and spoken language), and aided by cusp. It would be typical of modern applied various skills acquired through prior cusps behavior analysts to ask how to repair an that made them increasingly better at self- environment in which reading did not lead teaching (e.g., self-regulation). Less fortu- to broad further changes. (It might be typ- nate, less endowed, less skilled, and less well- ical of near-future applied behavior analysts taught children do not get through as many to ask what behavior change—what media of those cusps and become problems that skill?—is, in that future world, better than attract diagnostic labels and remedial teach- reading for producing those broad further ing. changes.) The point of these examples is that cusps As mentioned, cusps can range from quite can vary in size, particularly in the length or large to quite small behavior changes. An intensity of their teaching programs, yet obvious example of a large cusp is general- have similarly important consequences for ized imitation. An example of a small cusp what can happen next. It is not their man- is seen in an anecdote from a parent rearing agement, their complexity, or the complexity a child with profound retardation: Teaching of the behavior they target but their behav- this child to manipulate the door latches ior-change outcomes that define their im- that separated her from the outside fenced portance. Thus, cusp transcendence is prag- yard transformed her from a child who asked matic, but pragmatics do not change the often all day (and often unsuccessfully) for laws of behavior or the principles of behavior doors to be opened for her into a child who management. However, they may well could manage them herself. The child’s new change management tactics, because the na- skill greatly expanded her opportunities for ture of cusps is that the developing organ- learning and activity from mainly indoor ism’s situation changes in systematically im- ones. It obviously enhanced her control over portant ways. some of her daily life. It transformed her family’s perception of her as an eternal prob- lem to a learner whose skill acquisitions SMALL CONVERGENCES could improve everyone’s life—from some- OF TRADITIONAL AND one to be managed into someone who now BEHAVIOR-ANALYTIC VIEWS could be taught more independence. A cusp Organisms are always doing something whose size is less easy to assess is chaining and are always doing new things; there are BEHAVIORAL CUSPS 539 no holes in the stream of behavior (Bijou & sume and applaud the stage strategy by ask- Baer, 1961; Schoenfeld & Farmer, 1970; ing that it find better tactical criteria. Skinner, 1953; Watson, 1926). The question Some modern theories of development do has always been whether that stream has a not postulate a stage-specific mental struc- structure. Some developmentalists organize ture that explains all developmental phe- it as a progression of stages, often according nomena. Some theorists now see cognitive to what they call the complexity of behavior. development, for example, as highly diverse They describe how behavior increases, not and seamlessly continuous: Individuals use in amount but in complexity, during certain multiple rules, strategies, hypotheses, and so parts of the life span, from early and simple forth, changing them from one kind of to late and complex. In most arguments, problem to the next; these structures range that sequence is predictable and uniform. simultaneously from simple to complex; the Thus, a stage of development is a portion of competence of each one may change at any the organism’s life, qualitatively different time; and each one is more likely to be spe- from the preceding or subsequent stages, cific to a small domain (e.g., speech percep- whose content is often (but not necessarily) tion, reading, arithmetic, language, catego- described as a mental structure that guides rization, or reasoning) rather than to be gen- action and is said to be universal, and is rel- eralized across them all (see Case, 1987; evant to many outcomes, especially emo- Fisher, 1980; Flavell, 1982, 1992; Howe & tional, cognitive, and moral ones. Its timing Pasnak, 1993; and Siegel, 1991, for reviews is seen as modifiable, but only a little; and of this shift in conceptualization). its sequence is seen as even more resistant to The general stage concept is still used, change (e.g., Bickhard, Cooper, & Mace, even so. For example, Flavell postulates de- 1985; Flavell, 1982; Glasersfeld & Kelly, veloping capacities to process information 1982; Lerner, 1986; Overton & Reese, and to resist interference, which, if they ex- 1973; Reese & Overton, 1970; Wohlwill, ist, should allow more complex cognition 1973). across all relevant domains (see Flavell, Stage concepts of development are often 1982). Within a domain, though, it is levels challenged, even within the scientific com- of skill competence rather than stages of munity that generated them. Piaget’s stages qualitative changes that are assumed to pro- of cognitive development (1971), Freud’s ceed in an orderly sequence (Fisher, 1980; stages of psychosexual development (1905), Fisher & Silvern, 1985; Siegler, 1981). Kohlberg’s stages of moral development The thesis that developing an ability or (Kohlberg, Levine, & Hewer, 1983), and Er- competence will open a much larger realm ikson’s stages of psychosocial development to improvement is not new; like most the- (1950)—four prominent examples—have oretical overreaches, it has seen its waves of been criticized on many grounds, most of endorsement and rejection. As the 20th cen- which reflect the vagueness of three sets of tury began, educational psychologists often criteria: those that define a stage; those that supposed that training any specific skill (e.g., tell the theorist how many stages are needed matching colored sticks) would educate the to explain development; and those that de- senses and make them hospitable to many fine the transition from one stage to the next untrained discriminations, just as studying (see Brainerd, 1978, for a heuristic example any small discipline (e.g., Latin, mathemat- of these unresolved questions). These are ics) would improve reasoning in general. criticisms not of the stage strategy but of its Later, that thesis was refined: Not any train- topical tactics. In effect, these criticisms as- ing or study would lead to generalized re- 540 JESU´ S ROSALES-RUIZ and DONALD M. BAER sults; only certain kinds of training or studies the small domain to which these relatively would do that. A specific ability would ben- new cognitive-analysis tactics were applied efit a larger domain (mathematics would im- was admirable. Smaller arenas of analysis al- prove reasoning) only if both contained suf- low a much more intimate interaction be- ficient common elements (see Thorndike, tween research and data and allow more of 1903). That was the logic of transfer (e.g., the data to be experimental. More impor- Grose & Birney, 1963). It automatically rec- tant, smaller domains of analysis allow, and ommended training in larger categories, so almost insure, at least a partial intersection as to sample more of the elements that are of the logic of behavior analysis and cogni- operative in the larger domains to be bene- tive analysis: (a) We all analyze behavior, fited. It also warned the teacher that the ben- even when it is not the fundamental unit of efited domain would be no larger than the our theory; (b) behaviors are readily changed common elements justified. Clearly, the con- by environmental contingencies; and (c) we cept had moved behavior-ward. But it was know any behavior can contact different en- still as vague as any stage theory in offering vironmental contingencies than other behav- criteria for identifying ‘‘common elements.’’ iors do. These three points tell us that dif- Thus, it was not long before a psycholo- ferent behaviors can come under different gist like Ferguson (1954, 1956), apparently control (even though some theories need following Spearman (1927) and Thurstone some very similar behaviors to be under sim- (1938), would see little use in constructs as ilar control). To the extent that even similar general as intelligence. These constructs behaviors do come under different control, could only denote subsets of more real abil- then an overarching stage-like organization ities, which in turn were properties of the of great quantities of behavior is improbable, ultimate reality, behavior. So Ferguson’s con- although not impossible to program. Our re- cept of development was to list the skill mas- search ought to look first for regularity in teries that together would justify the term much smaller domains, then seek experi- ability and to catalog their transfer functions mental control of as much of that regularity (generalizability) at different stages of learn- as proves to be possible (and ethical), and ing and at different ages. The developmental then ask if that control can be extended (ex- question had become: What prior learned perimentally) to a domain large enough to abilities transfer to what untaught abilities, justify a stage concept. and how, and under what conditions? The For behavior analysis, behavior classes as converse question became: What new abili- large as ‘‘intelligence’’ have never seemed ties alter prior abilities, and in what ways? useful, or even real. Response classes have Forty years later, cognitive scientists been defined by the experimenter’s ability to would be asking: What prior abilities, prove that all members of the putative class learned or otherwise, lead to what changes are in fact under the same control (antece- in development? They would answer the dent, consequent, or both) and have been question of how by inferring cognitive me- understood by the experimenter’s ability to diators such as memory access, information make them. Similar response classes that re- organization, inference itself, and strategiz- sult from similar histories of programming ing (Glaser, 1992, p. 249); they would an- then have been seen as possible events in swer the question of under what conditions natural development. by inferring developing levels of function for In behavior analysis, the stage concept those inferred mediators. seems neither essential nor explanatory, but From a behavior-analytic point of view, it is still heuristic. Bijou (1993, p. 46) argues BEHAVIORAL CUSPS 541 that it can guide analysis; he sketches a se- been learned) and a familiar object (one quence of foundational, basic, and societal whose name has been learned). These chil- stages, much as Kantor proposed in 1959 dren typically select the novel object and (see Bijou, 1989, 1993). When the changes thus learn the name of the novel object. Be- described by a stage concept show great gen- fore the age of 2½, children usually select erality across behaviors and contexts, for the object whose name already controls their many children and for a specific period of behavior. However, children as young as 2 the life span, then, and only then, does the years also have demonstrated the disambig- concept of stage become correspondingly uation effect when correction and reinforce- heuristic. ment procedures are used. In behavior anal- But, when a discipline knows, or thinks ysis, this phenomenon has been experimen- it knows, how to diminish or disassemble or tally investigated in persons with mental re- how to create or intensify some of the gen- tardation, with both spoken and visual erality described by the stage concept, and stimuli and with visual stimuli in matching when a discipline can do so by fairly tasks (cf. Dixon, 1977; McIlvane & Stod- straightforward environmental interventions dard, 1981, 1985). It has been demonstrated (as has been done for at least some cases like that learning by exclusion permits an eco- conservation skills, Kuhn, 1974, and gener- nomical way of expanding the repertoire of alized imitation, Baer, Peterson, & Sherman, individuals—a way that the teaching com- 1966), then the concept of stage becomes munity could use to produce almost error- correspondingly more fragile and arbitrary. free behavior changes, even when other Behavior analysis has always at least asked if teaching methods have failed (e.g., de Rose, its processes could create or intensify or di- de Souza, & Hanna, 1996). Learning by ex- minish or disassemble that kind of general- clusion is a cusp that along with other cusps ity, and has succeeded often enough to make may lead us to an understanding of the be- this argument viable. havior changes and the environments that In fact, learning to manage the detailed are required to produce the vocabulary ex- composition of stages may soon prove to be plosion typically seen at around 18 months more interesting than the generalities the of age (Smith, 1926). stages describe. For stage theory, those gen- Studies looking for cusps will eventually eralities are described rather than experimen- produce a long list of organism–environ- tally analyzed. By contrast, the management ment interactions, some of small importance of their components is almost always exper- for what can happen next, others of great imentally analyzed; that is what manage- importance for what can happen next, and ment means in behavior analysis. Then why still others of importance conditional on not shift interest to the often dramatic what other cusps have been attained. Thus changes in behavior that become possible a cusp may be universal, but it need not and with experimental mastery of those compo- rarely will be. Similarly, a cusp may have nents? For example, one way in which chil- wide generality, but need not. One child’s dren expand their vocabularies is the dis- cusp may be another child’s waste of time. ambiguation effect described as part of the In metaphor, cusps often are steps in an mutual-exclusivity bias (Merriman & Bow- orderly path. Perhaps more often they are man, 1989). Around 2½ years of age, most like the branches of a tree: They stem from children begin to learn new words when pre- an earlier branch or trunk, and new branch- sented with a novel name in the presence of es may stem from them, where their struc- a novel object (one whose name has not ture in conjunction with the environment 542 JESU´ S ROSALES-RUIZ and DONALD M. BAER allows for that. But their mutual order, size, cilitation is what it should do to make that and probability of twigs are not very thor- skill reappear. This explanation remained oughly predetermined. Sequences, whether unchallenged for 40 years until Thelen and necessary or merely societal, can be essential Fisher (1982) demonstrated experimentally to this concept; but it is the cusps that need that the disappearance of this reflex was due to be analyzed first. As we come to under- to an increase in the baby’s weight and to stand them, we will then be in a better po- the changing mechanical demands of its pos- sition to learn when their sequences are cru- ture. They restored the stepping reflex by cial or conditional. submerging infants in torso-deep warm wa- As behavior changes that proved to be ter and inhibited it again by adding weights. cusps for one child or another, or many, are Once again, the value of an inferred central listed, any reader is free to chunk that list control had varied inversely with the appli- according to the reader’s criteria, which may cation of experimental analysis. be a predetermined notion of complexity, se- The cusp concept defined here is most quence, or growth. Some readers no doubt powerful when it is limited to those changes will chunk them exactly that way; others will that can be experimentally taught and the find a variety of alternative logics. However, consequences of which can be experimental- a list of cusps, defined as they are here, is a ly verified. Correlational analyses that look list of teachable behaviors, a set of teaching for the sequelae of a cusp will not easily sep- procedures that accomplish them, a shaping arate cause and effect; experimental control community of reinforcement, and a descrip- will be required to meet the definition. A tion of the systematic consequences of doing stage theory may be as unverifiable as the so, including the consequences of the con- theorist wishes; then it can be made to em- sequences. Teachable cusps are susceptible to brace everything the theorist needs to ex- experimental analysis, and experimental plain. By contrast, to the extent that cusp analysis allows us to identify their conse- assessment must be verifiable, cusp-based de- quences. Nonteachable cusps are susceptible velopment will automatically be a set only only to correlational analysis; correlational of already-tested facts and procedures. This analysis allows us to say only what their ac- cusp concept will not embrace everything companiments are. A truly developmental that a developmental theory needs to ex- analysis needs more certainty about what plain, because ethics and practicality bar ex- causes what. An illustrative example of such perimental analysis from many parts of that analysis is the case of the ‘‘disappearing’’ domain. Teaching reading to see its conse- stepping reflex. Newborns held upright with quences fits the cusp concept; awaiting com- their feet on a surface display well-coordi- plete myelinization of the nervous system to nated step-like movements; these responses see its consequences does not. But if myeli- disappear within the first few months and nization should ever become experimentally are seen again towards the end of the first manageable and ethically acceptable to man- year. These changes have been explained as age, it might then be tested for its cusp qual- correlates of the maturation of the voluntary ities. cortical centers. We could suppose that those centers first inhibited subcortical or reflexive REFERENCES movements and later facilitated them at higher levels of control (McGraw, 1943). Af- Allen, K. E., Hart, B. M., Buell, J. C., Harris, F. R. & Wolf, M. M. (1964). Effects of social rein- ter all, inhibition is what a center should do forcement on isolate behavior of a nursery school to make one of its skills disappear, and fa- child. Child Development, 35, 511–518. BEHAVIORAL CUSPS 543

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