Martha Pelaez - Contingent and Noncontingent Reinforcement With Maternal Vocal Imitation

8/13/2019 Martha Pelaez - Contingent and Noncontingent Reinforcement With Maternal Vocal Imitation

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277EUROPEAN JOURNAL OF BEHAVIOR ANALYSIS 2011, 12 , 277 - 287

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NUMBER1 (SUMMER 2011)

Infants coordinate their expressive be-havior with the stimulation of adult socialpartners during face-to-face interactions (Lin& Green, 2009). Contingent maternal stimu-

lation can also bring under operant controlprerequisite skills for vocal production. Forinstance, Pelaez-Nogueras et al. (1996) re-ported that contingent maternal touch during

Correspondence concerning this article should be ad-dressed to Javier Virus Ortega, University of Manitoba,Psychology Department, P518 Duff Roblin Bldg, 190 DysartRd MB R3 Winnipeg, Canada. E-mail: javier_virues@ umanitoba.ca

Tis study was presented as part of an oral presentationat the 5 th Conference of the European Association for Behaviour Analysis (Crete, Rethymno, Greece, September 21-24, 2010).

Contingent and NoncontingentReinforcement With Maternal Vocal Imitation

and Motherese Speech:Effects on Infant Vocalizations

Martha Pelaez 1, Javier Virus Ortega 2, and Jacob L. Gewirtz 11Florida International University

2University of Manitoba & St. Amant Research Centre

Tis paper examines the reinforcing effects of two maternal vocal topographies on infant vo-calizations. wo groups of 3- to 8-month-old infants underwent a probe multi-element design

with noncontingent reinforcement (NCR) as control condition, and two forms of contingentreinforcement (CR) as treatment: contingent maternal vocal imitation for the rst group (n =19), and contingent motherese speech for the second group (n = 16). Condition sequence wascomprised of a baseline phase with no programmed consequences followed by CR 1-NCR 1-CR 2-NCR 2. Results revealed that both maternal vocal imitation and motherese speech reinforced infantvocalizations. For the imitation group, frequency of infant vocalizations during NCR 1 was lowerthan CR 1 in all but 5 participants and infant vocalization during NCR 2 was lower than CR 2 inall but 7 participants. For the motherese speech group, frequency of infant vocalizations during

NCR 1 was lower than CR 1 in all but 8 participants and infant vocalizations during NCR 2 waslower than CR 2 in all but 4 participants. Repeated measures ANOVA indicated that infant vocalresponding was signicantly higher during CR as opposed to NCR in both groups. Effect mag-nitudes ranged from moderate to high (Cohensd = 0.33-0.99). Although maternal vocalizationmay have an eliciting effect on infant vocalization, the results of this study support the view thatspecic forms of contingent maternal vocal stimulation can reinforce early infant vocalizationseffectively. Tese ndings may provide a basis for early language acquisition programs in infants

with and without delays.Key words: maternal imitation, infant vocalizations, motherese speech, vocal conditioning,

language acquisition, infant-directed speech.

Authors are indebted to N. M. Mahabir, C. Crdenas, .Calvani, O. J. Paik, M. Otero, and M. E. Giro for collectingdata for this project and assisting with the recruitment ofparticipants. Authors would like to show their appreciationto Dr. C. . Yu (St.Amant Research Centre & University ofManitoba) and oby L. Martin (St.Amant Research Centre)for their comments to an earlier version of this manuscript.


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other behaviors as control condition to showthat contingent maternal vocal imitationreinforces infant vocalizations. Tis literaturesuggests that maternal vocal imitation maybe a practical and effective contribution to

early intervention programs for individuals with developmental delays. Although maternal speech might be a

factor relevant to the development of vocalbehavior in infants, the actual reinforcingvalue of specic forms of adult vocalizationshas yet to be analyzed. Te present study

was designed to determine to what extentmotherese speech and maternal vocal imita-tion could operate as reinforcers of infant

vocalizations.Method

Participants and Settingwo groups of infants and their mothers

participated. Nineteen infants were admit-ted in the vocal imitation group (10 female,average age of 3.94 months [SD = 0.68]).Sixteen infants participated in the motherese

speech group (7 female, average age of 4.56months [SD = 1.21]). Groups did not differsignicantly in age or gender distribution(non-parametric comparisons were non-signicant; WilcoxonW , p > .1). All infants

were healthy at birth and at the time of thestudy. Inclusion criteria were: normal birth

weight, 37 or more weeks of gestational age,no history of medical complications, nophysical disabilities, and an Apgar score of

8 or higher (range 0-10, criteria: skin color,pulse rate, reexes, muscle tone, breath-ing; Apgar, 1953). Mothers were of middlesocioeconomic status and of Hispanic (65%),Caucasian (33%) and African American(2%) ethnicities. Infants and mothers wererecruited through the Dade County BirthRecords within the Greater Miami Metropol-itan Area. Mothers were initially contactedvia mail and subsequently reached by phone.

Mothers were asked to participate voluntar-ily in a study on language development inbabies. Mothers signed an informed consent

form following the Helsinki declarationguidelines. No compensation of any kind

was offered for participation.hirteen additional participants were

initially scheduled to participate but were

nally excluded. Tree mother-infant dyads,one from the vocal imitation group and twofrom the motherese group, dropped outbefore any data were collected; two becauseof the infants excessive crying, and the thirdbecause the mother was unable to followinstructions. In addition, four mother-infantdyads from the vocal imitation group and sixdyads from the motherese group were unableto attend all sessions of the study protocol

(dataset incomplete) and were not part ofthe nal analysis.Te mother-infant dyads were assigned

to either imitation or motherese treatmentgroups using simple randomization. Arandom string of zeros and ones was gener-ated using Microsoft Excel (Microsoft Cor-poration, Redmond, WA) command Rand() and rounding the output to numerals of 0decimals. Simple randomization is robust to

selection bias although it may cause slightlyimbalanced group sizes (Schulz & Grimes,2002).

Te two groups did not differ in languagedevelopment as assessed by the Bzoch-LeagueReceptive-Expressive Emergent LanguageScale Second Edition (REEL-2, Bzoch &League, 1991). A trained graduate studentassistant who did not contribute to other sec-tions of this study administered the REEL-2.

None of the infants demonstrated havingany receptive or expressive delays, nor didthey differ signicantly on their LanguageQuotient (Wilcoxon W , p > .1).

Each mother-infant dyad was studied ina laboratory in a pediatric clinic. Infants satin a baby high chair facing their mothersthroughout the session. wo camcordersinstalled in the room monitored infantand mother behavior concurrently. Next to

the experimental room, mother and infantinteraction was displayed on a video monitorin split-screen format and recorded for later

Infant Vocalizations


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scoring and reliability analysis.Design

Appropriate control strategies are highlyrelevant to this line of research. Bloom(1975) proposed that maternal vocal stimula-

tion may function as unconditioned stimulusfor infant vocalizations (unconditionedresponse). Terefore, maternal vocal stimu-lation needs to be controlled for in order todemonstrate any reinforcing effects. Further-more, extinction baselines (Bloom, 1977) oc-casion interfering emotional responses (e.g.,crying, gazing away) (Pelaez-Nogueras et al.,1996a). Terefore we used noncontingent re-inforcement (NCR) as the control condition

during the present study. Noncontingentreinforcement avoided unwanted emotionalbehaviors often associated with extinctionbaselines, allowed us to control for reinforcerdensity across experimental conditions, andprovided control for the mere presence of themothers vocalization.

wo groups of infants were subjected toa probe multi-element experimental designcomprised of alternating sessions of contin-

gent reinforcement (CR) and NCR usingmother vocal imitation and motherese speechas a reinforcer in each group, respectively. Abaseline probe with no programmed conse-quences preceded CR and NCR phases. Tesequence of conditions for all subjects wasBL-CR 1-NCR 1-CR 2-NCR 2. Each condition

was comprised of a single session.

Procedure

Each session pertaining to each of the 5single-session conditions lasted 2 minutesand they were run sequentially over a totaldata collection period of 12 minutes. Sessions

were separated by 20-second intersessionintervals in which mothers received instruc-tions. A research assistant instructed themother through an earphone from a controlroom, while a second assistant consistentlymonitored mother-infant interactions to

ensure that mothers complied with instruc-tions at all times. When the mother did notfollow the experimenters directions, the

session was discontinued and the mother was re-instructed. wo research assistants were trained in the implementation of thisprotocol and they all established some rap-port with the infants and their mothers at the

beginning of the study. Specic arrangementsfor each study condition are described below:Baseline. Mothers were instructed to

interact with their infant, as they wouldnormally do at home. For the purposes ofreducing the variability of mothers behav-ior in subsequent conditions, mothers werealso instructed to look at their infants witha natural expression and to to refrain fromtouching her infant during the experimental

conditions. No other instructions were given.Contingent Imitation. Immediatelybefore the contingent imitation conditionbegan, mothers were given a short demon-stration on how to imitate infants vocaliza-tions. Mothers were instructed to imitateimmediately and accurately the topographyand duration of each of the infants vocalsounds. Mothers were instructed not toimitate or respond to non-vocal sounds such

as crying, protesting, hiccupping, coughing,fussing and sneezing. Mothers imitative vo-cal responses were coded across conditions toensure that they followed directions properly.

o ensure that mothers were imitatingcorrectly their infants vocalizations, mater-nal vocal responses were routinely checkedacross periods. In addition to the video re-cording, mothers vocal responses were alsoaudiotaped.

Contingent Motherese. Mothers in themotherese group were given a brief demon-stration of motherese speech. Te mother wasinstructed to speak contingently upon eachof her infants vocalizations using a high-pitched voice with exaggerated intonationfor a brief 1- to 2-second period. Mothersin this group were also instructed not torespond to the non-vocal sounds. Mothersmotherese vocal responses were coded across

periods to ensure that they were followinginstructions. Similar to the imitation group,the sessions were audio taped for later use

Martha Pelaez et al.


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during NCR phase.If an infant was fussy, the session was

discontinued and feeding, diaper change, orrocking were used in an attempt to soothethe infant. As soon as the infant was calm,

alert and awake, session was resumed. If theinfant could not be calmed, the session wasterminated. Tis procedure was enforcedduring both CR conditions.

Noncontingent reinforcement . Dur-ing NCR control sessions, both groups ofmothers were instructed to respond in apattern of duration and topography identicalto their earlier pattern under CR. Mothers

were instructed to repeat their own vocal

responses, as they were emitted and recordedunder the rst CR condition (via audio cas-sette recorder). Tese previously emittedvocal responses were heard by the mothersthrough an earphone. Mothers would repeattheir own vocal responses aloud regardless

whatever vocalizations the infant could beemitting at that time. Tis procedure wasreplicated for the second NCR condition.Te density of maternal vocal stimulation

across CR and NCR conditions was thereforethe same.

Measurementswo trained research assistants coded

infants vocalizations. Vocalizations weredened as discrete voice sounds includingcooing and babbling lasting 2 seconds ormore and separated by 1 second, exclud-ing fussing or crying, belching, hiccough-

ing, sneezing, straining sounds, whistling,squawking, loud breathing and whining(Poulson, 1988; Rheingold, Gewirtz &Ross, 1959). For example, vocalizations withno break in time between phonemes werecounted as one (e.g., bababa). Vocaliza-tions were made up of identiable vowelsounds or sequences of consonant and vowelsounds (e.g., mah, geh, ae, ag). Tenumber of occurrences of vocalizations every

2-minute session was obtained for each of the5 conditions of the study. Session duration was split into 30-s bins during coding and

reliability calculations. Observation was as-sisted by a split-screen, which allowed us toobserve infants and mothers at the same time.Each behavior category was coded separately.Periods of access to maternal vocalizations

were not subtracted from sessions duration.Inter-rater Agreement

wo independent observers were traineduntil 90% agreement was reached. Observ-ers coded all study sessions and collectedreliability data. Interobserver agreement

was calculated through the exact count-per-interval method. We divided 30-s intervals

with agreement (same occurrences of be-

havior coded by both observers) by the totalnumber of intervals and multiplied by 100.Secondary observer recordings were availablefor 100% of the sessions of 14 out of the 35participants (40%). Average interobserveragreements across subjects were 87% (range,81% to 100%) and 89% (range, 84% to98%) for infant and mother vocalizations,respectively.

Statistical Analysis A two-factor repeated measures analysisof variance (ANOVA) was used with con-dition as within-subjects factor (BL, CR 1,NCR 1, CR 2, NCR 2) and group (vocal imita-tion, motherese speech) as between-subjectsfactor, respectively. Te number of vocaliza-tions per condition served as the dependentvariable. Mauchlys test for sphericity wasused to test for the homogeneity of co-

variance. Greenhouse-Geisser correction wasimplemented in the event of the sphericityassumption being violated. For the purposesof strengthening the power of the statisticalanalysis, CR 1 and CR 2, and NCR 1 and NCR 2 conditions were aggregated if no differencesin infant responding were found betweenthe original condition and its replication.Pairwise comparisons with Bonferroni cor-rection of condition by group combinations

were conducted. In order to facilitate the in-terpretation of effects magnitude, effect sizes(Cohensd ) for two-term comparisons across



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tions are shown in able 1 for the maternalimitation group, and in able 2 for themotherese speech group. Figure 1 presentsinfant vocalizations across groups and studyconditions with disaggregated and aggregated

CR and NCR phase replication data. For theimitation group, frequency of infant vocaliza-tions during NCR 1 was lower than CR 1 in14 of 19 participants and infant vocalizationduring NCR 2 was lower than CR 2 in 12 of19 participants ( able 1). For the motheresespeech group, frequency of infant vocaliza-tions during NCR 1 was lower than CR 1 in8 of 16 participants and infant vocalizationsduring NCR 2 was lower than CR 2 in 12 of 16

participants ( able 2). Univariate ANOVAindicated no differences in the numberof vocalization across vocal imitation andmotherese speech groups,F (1, 33) = 0.21, p = .886. Mauchlys test indicated that theassumption of sphericity had been violated( = 21.02, p = .013), therefore degrees offreedom for post hoc analyses were correctedusing Greenhouse-Geisser estimates of spher-icity ( = 0.72). Te results showed a main

effect of condition,F (2.90, 95.60) = 6.70, p < .001. Nonetheless, multiple mean pairwisecomparisons by condition with Bonferronicorrection indicated that the difference inthe number of vocalizations during CR 1 and

2

A V E R A G E I N F A N T V O C A L I Z A T I O N S P E

R S E S S I O N

Figure 1. Infant vocalizations emitted duringbaseline, contingent reinforcement (CR 1, CR 2)and noncontingent reinforcement (NCR 1,NCR 2) with maternal vocal imitation andmotherese speech. Error bars represent thestandard error of measurement. CR and NCRconditions have been averaged in the lower graph.* p < .05 (Pairwise comparisons, repeatedmeasures ANOVA)

T 1 M ( S D)

T 2

M ( SD) T 2 T 1 95%CI p

Cohens d

BL CR Vocal Imitation 12.58

(12.78)

20.21

(9.51)

7.63

[1.23, 14.03]

.015 0.57

Motherese Speech 11.69 (7.58)

19.59

(13.52) 7.91

[0.93, 14.88] .022 0.99

BL NCR Vocal Imitation 12.58

(12.78) 14.95

(7.95) 2.37

[ -4.63, 9.36] .999 0.16

Motherese Speech 11.69 (7.58)

14.94

(9.76) 3.25

[ -4.37, 10.87] .870 0.41

NCR CR Vocal Imitation 20.21

(9.51) 14.95

(7.95) 5.26

[0.85, 9.67] .015 0.53

Motherese Speech 19.59

(13.52)

14.94

(9.76)

4.66

[0.15, 9.46]

.060 0.33

Notes . T1 and T 2 refer to the first and second term of the comparison, respectively, as specified in the left column. BL =Baseline; CR = Contingent Reinforcement; NCR = Noncontingent Reinforcement.

able 3. Repeated measures ANOVA, pairwise comparisons by condition and group.



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CR 2, and NCR 1 and NCR 2, respectively, were not signicant ( p = 1.000), thereforedata from the original condition and itsreplication were analyzed jointly. Repeatedmeasures ANOVA with Greenhouse-Geisser

correction ( = 8.50, p = .014, = 0.81) ofthe averaged responding during both CRand NCR conditions indicated again a maineffect of condition,F (1.62, 53.51) = 9.88, p = .001. Responding was distinctively higherduring the CR as opposed to BL or NCRconditions for both groups. Mean differenceand standard error between CR and BL, andCR and NCR were 7.771.88, p = .001, and4.961.29, p = .002, respectively. Tese nd-

ings were sustained when comparisons werereplicated at a group level, with the exceptionof NCR-CR comparison for individuals atthe motherese speech group, for which onlya statistical trend of difference was found,4.661.91, p = .060 ( able 3). Interventioneffect sizes were 0.53 and 0.57 for the vocalimitation group, and 0.99 and 0.33 for themotherese speech group using baseline andNCR as reference condition, respectively

( able 3).Discussion

Overall, the results indicated that: (a)contingent maternal vocalization increasedinfant vocalization over baseline and theeffects were greater than noncontingentmaternal vocalization for both imitationand contingent motherese speech, and (b)

maternal imitation and motherese speech were approximately equally effective in in-creasing infant vocalization. Te magnitudeof the reinforcing effect (effect sizes) obtainedby comparing CR with baseline and NCR

were moderate for maternal vocal imitationand moderate to large for motherese speech(Cohen, 1988). Finally, the present studyprovides a reliable procedure to assess thereinforcing effect of vocalizations in infants

using a group-based design. While there is some evidence indicatingthat motherese speech is a preferred form

of stimulation for infants (Fernald & Kuhl,1987), this study is the rst to analyze thereinforcing effect of multiple maternal vocaltopographies on infant vocalizations. Ourdesign allowed distinguishing the reinforcing

effect of contingent maternal vocal imitationand motherese speech from the eliciting ef-fects of noncontingent presentation of thereinforcing stimuli. Indeed, noncontingentmaternal vocalization resulted in a small,but not signicant, increase over baseline forboth imitation and motherese speech. Tissmall increase may indicate four potentialprocesses. First, the elevated levels of infantvocalization during the NCR conditions rela-

tive to baseline may have carried over fromthe preceding CR conditions. Alternatively,adventitious reinforcement of infant vocal-izations may have occurred during the NCRconditions for some participants. As a thirdexplanation, the mere presence of maternalvocalizations during NCR may have elicitedinfant vocalizations. Finally, vocalizationsmay to some extent be automatically re-inforcing for infants at that age (see for

instance Miguel, Carr & Michael, 2002).More research is needed to determine theextent to which any of these processes maybe mediating the effects of NCR encounteredin the present study.

Our results shall benefit from futurereplications using alternative experimentaldesigns and control procedures. Specically,both forms of intervention (vocal imita-tion, motherese speech) could be compared

directly using single-subject multi-sessiondesigns with longer session durations. Al-though, the design of the study could havebeen strengthened with multiple sessionsper condition and longer session durations,

we chose to use short sessions in order tomaximize the chance that participants willget through the protocol without problembehaviour (e.g., crying). In addition, wefound that mother-infant dyads that required

multiple sessions were likely to drop outthe study. Te limited number of sessionsthat composed the study protocol was in

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part meant to minimize experimental at-at-trition. Nonetheless, the numerous directintersubject replications (Sidman, 1960) inour study are meant to balance the limitednumber of sessions for each participant. It

should be noticed, however, that we wereable to establish reinforcement effects reliably with such brief exposures to the contingen-cies, which provides an indication of therobustness of the effect. Future studies in-corporating longer time-series per participantmay nd even clearer effects.

In addition, the lack of baseline rep-lications may be seen as a design defect.However, NCR provides a stronger meth-

odological control for intervention effectsthan does a no-programmed-consequencesbaseline. Noncontingent reinforcement alsoreduces the probability of emotional behaviorrelated to extinction and equalizes the prob-ability of elicited responses across treatmentand control conditions. Terefore, the initialbaseline condition is minimally relevant tothe study rationale.

Te reinforcing effect on infant vocaliza-

tions of maternal vocal imitation and mothe-rese speech may have practical implications.Several studies have reported a functionalrelation between exposure to maternal vocalstimulation and later verbal competence.For instance, according to Hart and Risley(1995), a high level of exposure to languagein infancy brings about signicant benets inschool age (increased verbal abilities, IQ andperformance at school). More importantly,

infants vocal production and exposure tomotherese speech seem to improve speechsegmentation ability, which is a prerequisitefor successful language acquisition later in life(Newman, Ratner, Jusczyk, Jusczyk & Dow,2006; Tiessen et al., 2005). Te proceduresused in this study could provide a conceptualbasis for language programming for individ-uals and children with developmental and/orlanguage delays. Further research is required

to determine the potential for implementingthese procedures in parent-managed andclinic-based programs in order to foster ver-

bal behavior acquisition in developmentallydelayed and typically developing infants.

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Martha Pelaez - Contingent and Noncontingent Reinforcement With Maternal Vocal Imitation