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EVALUATION OF FIXED MOMENTARY DRO SCHEDULES UNDERSIGNALED AND UNSIGNALED ARRANGEMENTS

JENNIFER L. HAMMOND AND BRIAN A. IWATA

UNIVERSITY OF FLORIDA

JENNIFER N. FRITZ

UNIVERSITY OF HOUSTON–CLEAR LAKE

AND

CARRIE M. DEMPSEY

CALIFORNIA STATE UNIVERSITY, STANISLAUS

Fixed momentary schedules of differential reinforcement of other behavior (FM DRO) generallyhave been ineffective as treatment for problem behavior. Because most early research on FMDRO included presentation of a signal at the end of the DRO interval, it is unclear whether thelimited effects of FM DRO were due to (a) the momentary response requirement of the scheduleper se or (b) discrimination of the contingency made more salient by the signal. To separate thesetwo potential influences, we compared the effects of signaled versus unsignaled FM DRO with 4individuals with developmental disabilities whose problem behavior was maintained by social-positive reinforcement. During signaled FM DRO, the experimenter presented a visual stimulus3 s prior to the end of the DRO interval and delivered reinforcement contingent on the absenceof problem behavior at the second the interval elapsed. Unsignaled DRO was identical exceptthat interval termination was not signaled. Results indicated that signaled FM DRO was effectivein decreasing 2 subjects’ problem behavior, whereas an unsignaled schedule was required for theremaining 2 subjects. These results suggest that the response requirement per se of FM DROmay not be problematic if it is not easily discriminated.

Key words: differential reinforcement of other behavior, functional analysis, reinforcementschedules

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Differential reinforcement of other behavior(DRO) schedules are used frequently to treat awide range of problem behaviors (Lennox,Miltenberger, Spengler, & Erfanian, 1988;Vollmer & Iwata, 1992). DRO typicallyinvolves delivery of reinforcement contingenton the absence of a response for a specifiedperiod of time. Aside from this commonfeature, a number of procedural variations havebeen reported in the literature, along with somedisparate findings.

The most common variation of DRO isinterval DRO, in which the reinforcer isdelivered at the end of an interval during whichthe target behavior did not occur. Both fixed-interval (FI) and variable-interval (VI) DROschedules have been used extensively and haveshown to be extremely effective in reducingproblem behavior (Lindberg, Iwata, Kahng, &DeLeon, 1999; Vollmer, Iwata, Zarcone,Smith, & Mazaleski, 1993). Several limitationsof interval DRO have been noted, however,including low rates of reinforcement (Vollmeret al., 1993) and extinction-induced side effects(Cowdery, Iwata, & Pace, 1990). Moreover,because accurate implementation of intervalDRO requires continuous monitoring of be-havior, it may prove to be difficult for caregiversto implement with a high degree of accuracy.

Address correspondence to Brian Iwata, PsychologyDepartment, University of Florida, Gainesville, Florida32611 (e-mail: [email protected]).

doi: 10.1901/jaba.2011.44-69

This research was supported in part by a grant from theFlorida Agency for Persons with Disabilities. We thankSarah Bloom for assisting in various aspects of thisresearch.

JOURNAL OF APPLIED BEHAVIOR ANALYSIS 2011, 44, 69–81 NUMBER 1 (SPRING 2011)

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Momentary DRO may represent a conve-nient alternative to interval DRO (Barton,Brulle, & Repp, 1986; Derwas & Jones,1993; Kahng, Abt, & Schonbachler, 2001;Lindberg et al., 1999). The criterion forreinforcement under a momentary DRO con-tingency is the absence of a target response onlyat the precise second the interval times out.Because this contingency does not require thecomplete cessation of problem behaviorthroughout the interval, momentary DROmay (a) circumvent some of the limitations ofinterval DRO and (b) share many of theadvantages of noncontingent reinforcement(NCR; Vollmer et al., 1993) but reduce thelikelihood of adventitious reinforcement thatmay result from the use of NCR (Vollmer,Ringdahl, Roane, & Marcus, 1999).

Previous research on momentary DRO hasproduced mostly negative or mixed results. Someresearchers found momentary DRO to beineffective in reducing problem behavior (Harris& Wolchik, 1979), whereas others reported thatmomentary DRO might be effective when usedas a maintenance procedure (Barton et al., 1986;Repp, Barton, & Brulle, 1983), when pairedwith other procedures such as punishment(Sisson, Van Hasselt, Hersen, & Aurand,1988), or when implemented on a denseschedule (Derwas & Jones, 1993). More recent-ly, research has indicated that momentary-likecontingencies may be effective when functionalreinforcers are delivered under schedules thatreduce the potential for adventitious reinforce-ment. For example, Vollmer et al. (1997) andBritton, Carr, Kellum, Dozier, and Weil (2000)showed that tandem fixed-time (FT) plus 10-sDRO schedules may effectively decrease problembehavior maintained by social-positive reinforce-ment. However, because the tandem schedulesevaluated in these studies included a brief intervalDRO contingency, they did not represent truemomentary DRO arrangements.

One momentary DRO arrangement that hasreceived particular attention is the variable

momentary (VM) schedule, whose inconsistentnature renders the critical moment at whichresponding must be absent less discriminable(Kahng et al., 2001; Lindberg et al., 1999). Forexample, Lindberg et al. compared two para-metric features of DRO, schedule regularity(fixed vs. variable) and the omission contingen-cy (interval vs. momentary) to determinewhether VM DRO would yield effects compa-rable to those achieved under FI and VI DROschedules. Results showed that FI, VI, and VMDRO schedules were equally effective indecreasing three subjects’ self-injurious behavior(SIB) maintained by social-positive reinforce-ment. The authors excluded one variation, fixedmomentary (FM) DRO, from their studybecause most previous research in whichmomentary DRO was found to be relativelyineffective involved the use of fixed schedules.Thus, Lindberg et al. speculated that regularityof the FM DRO schedule might be readilydiscriminated by subjects, thereby rendering itan ineffective procedure.

Several characteristics of early research onmomentary DRO, however, may have contrib-uted to the lack of effects found. First,reinforcers typically delivered were not neces-sarily those that maintained and competed withproblem behavior (Harris & Wolchik, 1979;Repp et al., 1983; Sisson et al., 1988). Second,initial interval lengths often were selectedarbitrarily, and in some cases, the contingencieswere described to the subjects (Conyers,Miltenberger, Romaniuk, Kopp, & Himle,2003; Repp et al., 1983). Finally, and mostrelevant to the present study, the delivery ofreinforcement usually was preceded by thepresentation of a signal, such as prompts orpraise (Harris & Wolchik, 1979), gestures(Repp et al., 1983), or auditory cues includingmusic (Sisson et al., 1988) or tones (Conyers etal., 2003). Harris and Wolchik, for example,compared the effects of momentary DRO,time-out, and overcorrection in reducing self-stimulatory behavior exhibited by four boys

70 JENNIFER L. HAMMOND et al.

with autism. During the DRO condition, theexperimenter either turned away from thesubject to record data (Studies 1 and 2) ordelivered prompts or praise (Study 3) prior tothe delivery of reinforcement, either of whichmay have facilitated discrimination of themomentary requirement of the DRO scheduleby signaling the end of the interval. Repp et al.compared the effects of interval and momentaryDRO on the disruptive behavior of fourchildren in a classroom setting. During alltreatment conditions, the experimenter sat atthe front of the classroom and raised her handas the DRO interval clocked out. In the intervalDRO condition, subjects were told that theywould earn an edible item when the experi-menter raised her hand if they did not engage inany disruptive behavior throughout the 5-mininterval. In the momentary DRO condition,subjects were told that they would earn anedible item if they were not engaging indisruptive behavior when the 5-min intervalelapsed. Thus, the explicit instructions, as wellas the raised hand, may have facilitateddiscrimination of the contingency in effect.

Table 1 summarizes previous research onmomentary DRO. Some commonalities amongstudies in which momentary DRO was found tobe effective include the fact that functionalreinforcers were delivered and impendingreinforcer delivery was not signaled. These

results suggest that the lack of effect oftenreported with FM DRO may not have been dueto the fixed nature of the schedule per se but thefact that the contingency was easily discrimi-nated. If so, it is possible that FM DRO may beeffective when functional reinforcers are deliv-ered under unsignaled arrangements, and thepurpose of this study was to systematicallyexamine the effects of signaling procedures inFM DRO schedules.

METHOD

Subjects and Setting

Four individuals who attended a school forchildren with special needs participated. Allsubjects had been referred for assessment andtreatment of problem behavior and wereselected for inclusion in this study based onresults of their functional analyses. Seth was a 6-year-old boy identified as deaf and learningimpaired whose problem behavior was aggres-sion. Alex was a 14-year-old boy with autismand seizure disorder who engaged in aggression.Curtis was a 13-year-old boy with autism; hisproblem behavior also was aggression. Abby wasa 19-year-old woman with profound mentalretardation, autism, and seizure disorder. Sheengaged in SIB in the form of head hitting.

Sessions were conducted in an unusedclassroom at the school, which contained a

Table 1

Summary of Previous Research on Momentary DRO Schedules

Study Schedule Sr+ Signal Effective?

Harris and Wolchik (1979) fixed arbitrary? turning away; prompts or praise noRepp et al. (1983) fixed arbitrary? gesture no before FI DRO

yes after FI DROBarton et al. (1986) fixed arbitrary? tone yes after FI DROSisson et al. (1988) variable arbitrary? music noDerwas and Jones (1993) fixed arbitrary? none yesMiller and Jones (1997) ? arbitrary? ? yesLindberg et al. (1999) variable functional none yesKahng et al. (2001) variable functional tone yesConyers et al. (2003) variable arbitrary? tone no

Note. Studies are listed in the far left column, followed by the type of schedule used, whether functional reinforcers

were delivered, whether reinforcer delivery was signaled, and whether treatment was effective.

FIXED MOMENTARY DRO 71

table, chairs, and materials that varied accordingto the conditions in effect (see below). Sessionswere 10 min in duration; one to four sessionswere conducted each day, and sessions typicallywere conducted 3 to 5 days per week dependingon the subjects’ schedules.

Response Measurement and Reliability

The primary dependent measures were thenumber of responses per minute of problembehavior and the percentage of programmedreinforcers earned by the subjects during eachDRO condition. Topographies of problembehavior included aggression (Seth, Alex, andCurtis) and head hitting (Abby). Aggressionincluded hitting, kicking, biting, and headbutting (Seth, Alex, and Curtis), as well asthrowing objects within 6 in. of a person (Seth)and scratching (Curtis). Head hitting wasdefined as audible hand-to-head contact.

Data also were collected on several experi-menter behaviors. Attention delivery was definedas the experimenter initiating verbal or physicalinteraction with the subject. A prompt wasdefined as the first (verbal) instruction in athree-step instructional sequence. Escape wasdefined as the experimenter terminating de-mands and turning away from the subject for30 s. Tangible delivery was defined as theexperimenter handing the subject an item orplacing an item directly within reach of thesubject. Signal display was defined as theexperimenter holding the programmed rein-forcer above her head (so as to be visible to thesubject) for 3 s.

Observers used Palm PDAs to recordoccurrences of problem behavior and experi-menter behavior. Data on problem behaviorwere converted to rate measures (responses perminute). Data on experimenter behavior werecalculated by dividing the number of behaviorsrecorded (e.g., reinforcer delivery) by thenumber of minutes in a session. From thesedata, the proportion of available (programmed)reinforcers earned by the subject was calculatedby dividing the number of reinforcers delivered

within a session by the total number ofreinforcers programmed by the schedule ineffect.

A second observer simultaneously but inde-pendently recorded data during a mean of 39%of the functional analysis sessions and 38% oftreatment sessions for all subjects. Interobserveragreement was calculated by dividing sessiontime into consecutive 10-s intervals, dividingthe smaller number of responses by the largernumber of responses in each interval that didnot include zero responses, averaging thosevalues across the session, and multiplying by100%. Mean agreement on problem behaviorduring functional analysis sessions was 97%(range, 91% to 100%), 99.7% (range, 98% to100%), 99% (range, 92% to 100%), and 97%(range, 87% to 100%) for Seth, Alex, Curtis,and Abby, respectively. Mean agreement onproblem behavior during treatment conditionswas 94% (range, 83% to 100%), 97% (range,88% to 100%), 96% (range, 84% to 100%),and 94% (range, 81% to 100%) for Seth, Alex,Curtis, and Abby, respectively. Mean agreementon reinforcer delivery and signal display duringtreatment sessions was 97% (range, 77% to100%) and 98% (range, 75% to 100%) acrossall subjects.

PHASE 1: FUNCTIONAL ANALYSIS

ProcedureFunctional analysis procedures were similar

to those described by Iwata, Dorsey, Slifer,Bauman, and Richman (1982/1994). Test andcontrol conditions were alternated in a multi-element design. An ignore condition was notconducted if the target response was aggression.Specific stimuli (i.e., different experimenters,setting, and colored shirts) were associated witheach condition to enhance discrimination ofconditions.

During the ignore condition, the subject wasin a quiet area of the room without access toleisure items or social interaction. The experi-menter was present but did not deliver anyconsequences for problem behavior or its


absence. The purpose of this condition was todetermine if problem behavior persisted in theabsence of social contingencies, suggesting thatit was maintained by nonsocial (automatic)reinforcement. During the attention condition,the subject was seated at a table with twomoderately preferred items within reach. Theexperimenter directed the subject to play withthe items and then proceeded to do some work.Contingent on the occurrence of problembehavior, the experimenter delivered a brief (3to 5 s) verbal reprimand, a statement ofconcern, and physical contact (e.g., hand onthe shoulder or response blocking in the case ofSIB). The purpose of this condition was todetermine if problem behavior was maintainedby social-positive reinforcement in the form ofattention. During the demand condition, thesubject was seated at a table containing taskmaterials. The experimenter presented academicor vocational tasks on an FT 30-s scheduleusing a graduated, three-step prompting proce-dure (verbal instruction, model prompt, andphysical guidance at 5-s intervals if compliancedid not occur). Contingent on compliance, theexperimenter delivered verbal praise and begana new trial. Contingent on problem behavior,the experimenter removed the materials andturned away from the subject for 30 s. Thepurpose of this condition was to determine ifproblem behavior was maintained by social-negative reinforcement in the form of escapefrom task demands. During the play condition,the subject and experimenter were seated at atable or on the floor. The subject hadcontinuous access to three highly preferreditems that had been identified via a paired-stimulus preference assessment (Fisher et al.,1992) prior to the start of the functionalanalysis. The experimenter initiated friendlyinteraction with the subject approximately every30 s (contingent on a 5-s absence of problembehavior). This condition served as the com-mon control for the other conditions. Finally,during the tangible condition, the subject was

seated at a table and was given approximately90-s free access to highly preferred leisure oredible items immediately prior to session onset.The experimenter removed the items at the startof session and, contingent on the occurrence ofproblem behavior, delivered 30-s access to theleisure items (Seth, Alex, and Curtis) or onesmall edible item (Abby). The purpose of thiscondition was to determine whether problembehavior was maintained by social-positivereinforcement in the form of access to preferreditems.

Results

Figure 1 shows results of each subject’sfunctional analysis. Seth’s aggression was main-tained by multiple sources of social reinforce-ment, including access to attention, escape fromdemands, and preferred items (toys), as evi-denced by high rates of problem behavior in eachof these conditions relative to the play condition.For the purpose of this study, only the tangiblefunction was targeted (attention and escapefunctions were treated separately). Alex engagedin aggression only during the tangible condition,and both Curtis and Abby engaged in problembehavior almost exclusively in the tangiblecondition. Thus, data for all subjects indicatedthat their problem behavior was maintained atleast in part by social-positive reinforcement,which was a prerequisite for participation in thetreatment phases of the study.

PHASE 2: ANALYSIS OF SIGNALED AND

UNSIGNALED FM DRO

Baseline

Baseline consisted of the tangible conditionfrom the functional analysis. Reinforcers in-cluded a toy box (containing various highlypreferred items) for Seth, videotapes (viewed onthe television) for Alex and Curtis, and anedible item for Abby.

FM DRO Contingencies

Two variations of FM DRO were evaluated:signaled and unsignaled. Both schedules shared


Figure 1. Responses per minute of problem behavior during functional analysis conditions.


the following features. All sessions for eachsubject were conducted in the same location bythe same experimenter. The experimenter didnot describe the contingencies at any time priorto or during the session, used a handheld silenttimer to monitor the passage of time, anddelivered the reinforcer (used in baseline)contingent on the absence of problem behaviorat the precise second the interval clocked out.Initial DRO values were based on meaninterresponse times (IRTs) observed duringthe last three baseline sessions. Subsequentvalues increased by 50% (rounded to the nearest5 s) following two consecutive sessions withproblem behavior at or below an 80% reductionfrom mean baseline rates. The terminal goal wasto establish a 5-min DRO interval whilemaintaining low rates of problem behavior.

Signaled FM DRO. The experimenter covert-ly held the reinforcer to ensure that it could bedelivered quickly but that no additionalmovements (e.g., reaching for the reinforcer)might inadvertently signal the end of aninterval. Three seconds prior to the end of aninterval, the experimenter (positioned directlyin front of or next to the subject) signaledimpending reinforcement delivery by holdingthe reinforcer above her head. If no problembehavior was occurring at the precise second theinterval clocked out, the reinforcer (30-s accessto the toy box or video, or one edible item) wasdelivered. If problem behavior was occurring atthat second, the signal was removed, and thereinforcer was withheld until the next scheduledinterval.

Unsignaled FM DRO. This condition wassimilar to the signaled condition, except that theexperimenter did not signal impending rein-forcer delivery. Rather, the experimenter quick-ly delivered the reinforcer contingent on theabsence of problem behavior when the intervalended.

Design

Reversal designs were used to examine theeffects of signaled and unsignaled FM DRO

schedules. Given that the main purpose of thisstudy was to evaluate the effects of signalingprocedures on FM DRO schedules, signaledDRO always was implemented first to eliminatethe potential influence of prior exposure tounsignaled DRO. If signaled DRO proved to beineffective, unsignaled DRO then was imple-mented.

Results

Figure 2 shows Seth’s and Alex’s results.Both subjects exhibited moderate rates ofaggression during the initial baseline. SignaledFM DRO initially was implemented under 20-sand 30-s intervals for Alex and Seth, respec-tively, and was associated with rapid reductionsin aggression. Following a return to baseline,during which both subjects’ aggression in-creased, signaled DRO was reinstated and againwas associated with rapid reductions in aggres-sion. Seth’s and Alex’s aggression generallyremained low as the DRO interval was thinned,eventually reaching the terminal criterion of300 s (5 min). Across all DRO conditions, bothsubjects earned a large proportion of reinforcers,indicating that they typically did not engage inaggression when the DRO interval ended. Theirlow overall rates of aggression, however,indicate that they also refrained from aggressionthroughout the DRO interval and not just at itsconclusion.

Figure 3 shows results obtained for Curtisand Abby. Curtis’s rate of aggression wasmoderate across all baseline phases. Whensignaled FM DRO was implemented initially(with a 20-s interval), his aggression increasedsubstantially during the first several sessions and,because aggression often occurred when theinterval elapsed, he seldom received reinforce-ment. Eventually, however, his aggression de-creased to near zero in the first signaled DROcondition. When signaled FM DRO was imple-mented a second time, however, his aggressiondid not decrease and remained variable acrossmany sessions. Therefore, unsignaled FM DROwas implemented. Aggression decreased to zero


following five sessions in the unsignaled DROcondition, and he earned a large proportionof available reinforcers. Low rates of aggressionand high levels of reinforcement were observedduring two subsequent unsignaled DRO condi-tions, although reductions in aggression weregradual in both conditions. The DRO intervalwas increased to 300 s during his third un-signaled DRO condition. During the last 10sessions of this condition, he engaged in near-zerorates of aggression, and he earned all availablereinforcers.

Abby’s head hitting was variable and showedan increasing trend during her initial baseline. Afurther increase in head hitting was observedunder signaled DRO. Despite this increase, sheearned a large proportion of available reinforc-ers during signaled DRO, suggesting that herhead hitting was under discriminative control ofthe signal (i.e., head hitting ceased when thesignal was presented). Following a return tobaseline, during which Abby’s head hittingcontinued to occur at variable rates, unsignaledDRO was implemented, beginning with a 10-s

Figure 2. Responses per minute of problem behavior (PB) during baseline (BL) and signaled DRO conditions, andpercentage of available reinforcers (Sr+) earned during DRO conditions for Seth and Alex. Numbers above the data path

for problem behavior indicate DRO interval lengths (in seconds) that were in effect during the first and final sessions ofeach phase.


interval. Although variable rates of head hittingwere observed during the first 10 sessions of theunsignaled DRO condition, head hitting even-tually decreased to near zero, and she earned alarge proportion of available reinforcers. Mod-erate rates of head hitting again were observedduring the third baseline. Lower, althoughvariable, rates of head hitting again wereobserved during the second and final unsignaledDRO phase, and a large proportion of availablereinforcers was earned. Abby’s mean rate of

head hitting was 0.4 responses per minuteduring the last 10 unsignaled FM DROsessions, and she earned all available reinforcers.

DISCUSSION

Results of this study showed that FM DROcan be an effective treatment for problembehavior, but that signals correlated withinterval termination may have detrimentaleffects because they facilitate discrimination of

Figure 3. Responses per minute of problem behavior (PB) during baseline (BL) and signaled DRO conditions, and

percentage of available reinforcers (Sr+) earned during DRO conditions for Curtis and Abby. Numbers above the datapath for problem behavior indicate DRO interval lengths (in seconds) that were in effect during the first and finalsessions of each phase.


the momentary nature of the contingency.Although signaled FM DRO produced rapidreductions in the problem behavior of twosubjects (Seth and Alex), it had negligible effectson the other two subjects (Curtis and Abby).

The general results of this study wereconsistent with those of recent research (Kahnget al., 2001; Lindberg et al., 1999) showing thatmomentary DRO may be effective whenfunctional reinforcers are incorporated into thecontingency. This feature may be one determi-nant of the effectiveness of momentary DRO.An obvious difference between these studies andprevious research in which momentary DROwas found to be ineffective (Conyers et al.,2003; Harris & Wolchik, 1979; Repp et al.,1983; Sisson et al., 1988) was the inclusion ofreinforcers that maintained problem behavior.

Results of this study indicate, however, thatthe inclusion of functional reinforcers may notbe sufficient to reduce problem behavior undermomentary DRO schedules because anotherdeterminant of their effectiveness may be thediscriminability of the schedule.1 Lindberg et al.(1999) used VM DRO schedules, which aresomewhat unpredictable due to their irregular-ity. By contrast, the FM DRO schedules used inthis study were highly predictable, and wefacilitated discrimination by signaling the endof the DRO interval. Nevertheless, the problembehavior of two subjects (Seth and Alex)decreased under the signaled FM DRO condi-tion. These subjects apparently failed todiscriminate the actual requirement of thecontingency, such that the liberal reinforcementand extinction components of FM DROdecreased their behavior in a manner similarto what would have been observed under othertypes of DRO schedules.

Curtis and Abby, on the other hand, failed toshow reductions in problem behavior under

signaled FM DRO although they earned a largeproportion of available reinforcers. Thus, itappears that they discriminated the momentarynature of the contingency and respondedaccordingly. This was especially true for Abby,whose problem behavior actually increasedunder signaled FM DRO. Cumulative recordsof her problem behavior during three signaledFM DRO sessions (Figure 4) indicated thatresponding occurred at variable rates through-out most DRO intervals but reliably ceasedwhen the signal was delivered, thereby allowingher to meet the criterion for reinforcement.When the termination of intervals was madeless discriminable by eliminating the signals,reliable decreases were observed in both sub-jects’ problem behavior.

These results have some bearing on thepracticality of implementing various DROschedules. A common criticism of intervalDRO is that it necessitates continuous moni-toring of the client behavior by caregivers.Thus, although interval DRO is a highlyeffective procedure, it may not be very practical,and thinning the DRO schedule does notimprove practicality because continuous obser-vation is still required. Results of this studyindicate that FM DRO, which is less stringentthan interval DRO, can reduce problembehavior maintained by social-positive rein-forcement. These results are consistent withthose of previous studies in which reductions inproblem behavior were observed when differ-ential reinforcement was implemented withless-than-perfect consistency (Vollmer, Roane,Ringdahl, & Marcus, 1999; Worsdell, Iwata,Hanley, Thompson, & Kahng, 2000). Itremains to be shown, however, whether mo-mentary DRO is easier to implement thaninterval DRO or whether momentary DRO islikely to be implemented more consistently.

Related to the above, one limitation of thisstudy is that we did not conduct a comparisonof FM DRO and FI DRO. Because our maininterest was the influence of signals on the

1 Schedule predictability is a problem only withmomentary DRO. Interval schedules (FI DRO and VIDRO) are not affected because, regardless of the predict-ability of the schedule, the requirement for reinforcement iscomplete absence of responding throughout the interval.


effects of FM DRO schedules, and becauseprevious research (Lindberg et al., 1999) alreadyhas shown that momentary DRO may be aseffective as interval DRO, we did not find itnecessary to conduct such a comparison.

However, future research may evaluate whether(a) more rapid effects are obtained undermomentary versus interval DRO schedules,(b) FM DRO is associated with higher ratesof obtained reinforcement, and (c) caregivers

Figure 4. Cumulative number of head hits during three sessions of the signaled DRO condition for Abby. Verticallines indicate delivery of the signal, arrows indicate reinforcer delivery, and open circles indicate instances in whichproblem behavior occurred after the signal. The asterisk above Second 420 in Session 23 indicates that reinforcement was

delivered when it should not have been.


implement momentary DRO with greateraccuracy than interval DRO. For example,should interval DRO produce greater responsesuppression than momentary DRO but care-givers demonstrate greater accuracy with themomentary DRO, an analysis could be con-ducted to determine the relative costs andbenefits of each schedule.

A second limitation of this study is that ouranalysis included only problem behavior main-tained by social-positive reinforcement. Becauseprevious studies on momentary DRO (e.g.,Kahng et al., 2001; Lindberg et al., 1999) andits variants (Borrero, Vollmer, & Wright, 2002;Britton et al., 2000; Vollmer et al., 1997) alsofocused on problem behavior maintained bysocial-positive reinforcement, it remains un-known whether similar effects can be achievedwith problem behavior maintained by social-negative or automatic reinforcement.

A third limitation of this study is that we didnot replicate the negative findings associatedwith signaled DRO for Curtis and Abby. It ispossible that reductions in problem behaviorcould have been achieved had signaled DRObeen implemented a third (Curtis) or second(Abby) time around. However, given theelevated and sustained rates of problem behav-ior shown by both subjects in this condition,replicating the ineffectiveness of signaled DROdid not seem warranted.

Finally, it should be noted that Curtis andAbby required a number of sessions to achievethe terminal criterion under unsignaled mo-mentary DRO. Perhaps more rapid effectscould have been achieved had interval DROfirst been used. Previous research has suggestedthat momentary DRO may be more effectivewhen preceded by interval DRO (Barton et al.,1986; Repp et al., 1983), and future researchcould evaluate this possibility further. Forexample, it is possible that more rapid treatmenteffects could be obtained with momentaryDRO implemented in the natural environmentwhen it is first preceded by interval DRO

implemented by skilled therapists in a clinicsetting.

In summary, this study demonstrated thatFM DRO schedules may be effective inreducing problem behavior maintained bysocial-positive reinforcement, particularly wheninterval termination is not readily discriminat-ed. These results provide further evidence of thebeneficial effects of momentary DRO schedulesand suggest that FM DRO, in particular, maybe a viable treatment for caregivers to imple-ment in natural settings. That aside, however,these data indicate that momentary DROshould be used with caution, because verysubtle therapist responses (e.g., reaching for theprogrammed reinforcer) may function as signalsthat could render FM DRO ineffective.

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Received September 28, 2009Final acceptance June 28, 2010Action Editor, Jennifer Zarcone


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