Gender Differences in Adult-Infant Communication inthe First Months of Life

WHAT’S KNOWN ON THIS SUBJECT: Studies have shown thatreciprocal vocalizations between mother and infant have positiveeffects on language development. It has been shown that girlsacquire vocabulary and language skills earlier than boys.

WHAT THIS STUDY ADDS: Mothers more readily respond to theirinfant’s vocal cues than fathers, and infants show a preferentialvocal response to their mothers in the first months of life.Mothers respond preferentially to infant girls versus boys at birthand 44 weeks.

abstractOBJECTIVES: To evaluate the verbal interactions of parents with theirinfants in the first months of life and to test the hypothesis that recip-rocal vocalizations of mother-infant dyads would be more frequent thanthose of father-infant dyads.

METHODS: This prospective cohort study included 33 late preterm andterm infants. Sixteen-hour language recordings during the birth hospi-talization and in the home at 44 weeks’ postmenstrual age (PMA) and7 months were analyzed for adult word count, infant vocalizations, andconversational exchanges.

RESULTS: Infants were exposed to more female adult speech than maleadult speech from birth through 7 months (P, .0001). Compared withmale adults, female adults responded more frequently to their infant’svocalizations from birth through 7 months (P , .0001). Infants prefer-entially responded to female adult speech compared with male adultspeech (P = .01 at birth, P , .0001 at 44 weeks PMA and 7 months).Mothers responded preferentially to girls versus boys at birth (P = .04)and 44 weeks PMA (P = .0003) with a trend at 7 months (P = .15), andthere were trends for fathers to respond preferentially to boys at 44weeks PMA (P = .10) and 7 months (P = .15).

CONCLUSIONS: Mothers provide the majority of language input andrespond more readily to their infant’s vocal cues than fathers; infantsshow a preferential vocal response to their mothers in the first months.Findings also suggest that parents may also respond preferentially toinfants based on gender. Informing parents of the power of early talk-ing with their young infants is recommended. Pediatrics 2014;134:e1603–e1610

AUTHORS: Katharine Johnson, MD,a Melinda Caskey, MD,b,c

Katherine Rand, BA,d Richard Tucker, BA,c and Betty Vohr,MDb,c

aNeonatal Medicine, Pediatrix Medical Group, San Antonio, Texas;bPediatrics, Alpert Medical School of Brown University,Providence, Rhode Island; cDepartment of Pediatrics, Women &Infants Hospital, Providence, Rhode Island; and dDepartment ofNewborn Medicine, Brigham and Women’s Hospital, HarvardMedical School, Boston, Massachusetts

KEY WORDSlanguage, LENA, late preterm, gender, vocalizations, speech,conversation, mothers, fathers, infant

ABBREVIATIONSAWC—adult word countDLP—digital language processorLENA—Language Environment AnalysisPMA—postmenstrual age

Dr Johnson conceptualized and designed the study, participatedin assessments, and drafted the initial manuscript; Drs Caskey,Vohr, and Rand collaborated in designing the study andreviewing the manuscript; Mr Tucker supervised the databaseand analyzed and reviewed the data; and all authors approvedthe final manuscript.

www.pediatrics.org/cgi/doi/10.1542/peds.2013-4289

doi:10.1542/peds.2013-4289

Accepted for publication Sep 5, 2014

Address correspondence to Betty R. Vohr, MD, Department ofPediatrics, Women & Infants Hospital, 101 Dudley St, Providence,RI 02905. E-mail: bvohr@wihri.org

PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).

Copyright © 2014 by the American Academy of Pediatrics

FINANCIAL DISCLOSURE: The authors have indicated they haveno financial relationships relevant to this article to disclose.

FUNDING: Supported by the Women & Infants HospitalDepartment of Pediatrics, Providence, RI.

POTENTIAL CONFLICT OF INTEREST: The authors have indicatedthey have no potential conflicts of interest to disclose.

PEDIATRICS Volume 134, Number 6, December 2014 e1603

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The importance of parent talk was high-lighted in Hart and Risley’s1 landmark1995 study that showed intelligence andacademic success is directly related toparents’ speech with their children frombirth through age 3 years. Parental speechwas even more important than educa-tion or socioeconomic status to predicta child’s language abilities and IQ.1

Infant vocalization, which is influencedby maternal verbal behavior, is an impor-tant process in language developmentbecause it mimics adult conversationalexchanges.2,3 Mothers are typically theprimary caregivers with the most di-rect interaction with their infants, andstudies have shown that reciprocal vocal-izations between mother and infant havepositive effects on language develop-ment.4,5 Maternal infant-directed speechhas been well described, but there isless research describing the father-infantlanguage relationship. Language struc-ture and speech register for maternaland paternal baby talk may be similar inthe first 3 months of life.6 However,fathers’ talk is often more challengingwith “what” and “where” questions en-couraging toddlers to use amore diversevocabulary and longer utterances.7

Genderdifferenceshavebeen identifiedin infant and child language develop-ment. Girls acquire vocabulary and lan-guage skills earlier than boys.8,9 Girlsalso develop larger vocabularies, displaygreater grammatical complexity, spellbetter, and read sooner than boys,10–12

and girls produce a higher quantity ofverbal communication.13 Data are lim-ited for gender differences in languagedevelopment of preterm infants.

The objective of our study was to eval-uate an infant’s language environmentin the first months of life and to com-pare differences in verbal interactionsbetween parents and infants based onboth adult and infant gender. We hypo-thesized that (1) infants would be ex-posed to more female than male adultspeech in the first months of life, (2)

female caregivers (mothers) and theirinfants would have more reciprocal vo-calizations thanmale caregivers (fathers)and their infants, and (3) female infantswould have more vocalizations and con-versational exchanges than male infants.

METHODS

Study Design

This prospective cohort study includeshealthy late preterm (340/7–366/7 weeks’gestation) and term (370/7–416/7 weeks)infants recruited during their newbornhospitalization (Women & Infants’ Hos-pital, Providence, RI).

Language data were obtained from mul-tiple language recordings of each infantover time by using the language envi-ronment analysis system (LENA ResearchFoundation, Boulder, CO). The LENA sys-tem includes a digital language pro-cessor (DLP) to recordachild’s languageenvironment and software with ad-vanced speech-identification algorithmsto analyze and categorize audio data.LENA is the world’s first automaticspeech monitoring and language envi-ronment analysis system for infants andtoddlers. It reliably identifies both En-glish and Spanish vocalizations and hasbeen validated to have a high degree offidelity in coding when compared withhuman transcribers.14

Each infant wore the DLP in a custom-made vest for up to 16 hours of continuousrecording. Recordings were performedduring thenewbornhospitalizationand inthe child’s natural environment at 44weeks’ postmenstrual age (PMA) and 7months chronologic age for term infantsand corrected age for late preterminfants. During the newborn hospitali-zation, infant recordings took place ineither the NICU or the general newbornunit. The NICU is a single-family-roomunit with private rooms for each infantor twin pair. Infants in the newborn unitroomed-inwith theirmothers. In the homeenvironment, parents were instructed tobegin the recording when the infant

awoke and continue for 16 hours on atypical day when both parents were home.

The DLP records all sounds in an infant’snatural environment. Each segment ofthe recording is categorized as speechor nonspeech. The distinguishable audiothat is used for the reportable languagemeasures is labeled as “meaningfulspeech.” “Distant speech” is languagetypically coming from at least 6 feetaway from the DLP and is less clear todecipher by LENA software. The othernonspeech segments are labeled assilence or background, noise (bumps,rattles, etc), or television (audio fromany electronic device).15

Complete recordings (.10 hours) wereprocessed with LENA software usingalgorithms and statistical modeling toproduce 3 primary language-relatedmeasures: infant vocalization counts,adult word counts (AWCs), and conver-sational turn counts.16 Infant vocalizationestimates include all speech-related childutterances that are bounded by at least300 milliseconds of silence or nonspeechsounds. Cries, other fixed signals, andvegetative sounds from the respiratory ordigestive tract are considered nonspeechsounds, which are filtered and excludedfrom vocalization counts. AWC estimatesthe number of words spoken during therecording. An AWC of 100 words per hourwas our best estimate of presence ofa parent with the infant. This was basedon the predictive ability of 100 words perhour previously reported by using LENA.17

Conversational turn count is a measureof adult-child interaction and estimatesthe number of reciprocal vocalizationsbetween the infant and adult within5 seconds. Human voices overlappingwith another voice, noise, or electronicsound are labeled as overlap by LENAand were not included in our analysis.

Segments of the audio recording con-taining human vocalizations were fur-ther processed with the LENA AdvancedData Extractor and identified as vocali-zation activity blocks.18 Blocks beginwith

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any human vocalization and end whenthere is at least 5 seconds of silence ornonspeech sounds. These blocks arelabeled by 2 criteria: the speaker thatinitiated the language block and re-sponders within the block. Any blockconsisting of only infant or only adultspeech unreciprocated within 5 secondsis labeled as a monologue, and any blockthat contains both infant and adultspeech is considered conversational.The block types used (Fig 1) include (1)infant monologue, (2) infant-initiatedwith adult response, (3) female adultmonologue, (4) female adult–initiatedwith infant response, (5) male adultmonologue, and (6)male adult–initiatedwith infant response.

All language-related measures wereanalyzed tomake comparisonsbasedonboth adult gender and infant gender.Hourly infant vocalization and AWCs de-scribe the quantity of speech, whereasconversational turns and vocalizationactivity blocks describe the languageinteractions between parents and theirinfants.

Demographic informationwascollected.Families were asked to complete logs offeeding times, sleep patterns, family

members or visitors present, and otheractivities throughout the day of the re-cording.

Participants

More than3000hoursofaudiorecordingfrom 81 infants were collected betweenFebruary 2010 and May 2012 as part ofa language study designed to comparedifferences in language outcomes be-tween late preterm and term infants.Thiscohort includeshealthy latepretermand term infants who were medicallystable without congenital anomalies,significant comorbidities, or identifiedhearing impairment.

Within the cohort, 33 of 81 infants metthe inclusion criteria of residing in a2-parent household with full-length re-cordings (.10 hours) at birth, 44weeks’PMA, and 7 months.

During the newborn recording, 8 infantswere cared for in the NICU due to ges-tational age,35 weeks, and 25 infantswere roomed-in with their mothers inthe well-baby unit. At 44 weeks’ PMA and7 months, all 33 infants were recordedat home. The length of recording timewas 16 hours in the newborn hospital-ization, a mean of 15.1 6 0.64 hours

(range 12–16) at 44 weeks, and 15.7 60.93 hours (range 11.9–16) at 7 months.All recordings began between 8 and 10 AM.

Demographic information is shown inTable 1. The mean gestational age was37 6 2 weeks. Fifty-five percent werelate preterm, and 45% were term.Thirty-two mothers and fathers wereincluded because there was 1 set oftwins. Thirty families spoke English asthe primary language, but nearly one-third of families identified their house-holds as bilingual.

The study infants differed from thosenot included for the following charac-teristics: mean gestation (37.7 vs 36.5weeks, P = .01), public insurance (24%vs 71%, P, .0001), maternal age (30 vs27 years, P = .04), and education be-yond high school for both mothers(97% vs 60%, P = .0001) and fathers(72% vs 30%, P = .01).

Statistical Analysis

Analysis of AWC data was done by neg-ative binomial regressionbecauseof thehighly dispersed and nonnormally dis-tributed nature of the counts. Logisticregression was used to analyze theprobability of infant-adult responsesduring conversational blocks. Adjust-ment for multiple measures (blocks)within each individual child was done bygeneralized estimating equations. Allstatistical analyses were calculated us-ing SAS 9.1 (SAS Institute, Inc, Cary, NC).

RESULTS

The language environment findings areshown in Table 2. Infants in the NICUwere exposed to significantly less speechthan those infants rooming-in withtheir mothers. Meaningful speech ex-posure increased after discharge forNICU infants, whereas it decreased fornormal newborn infants. Overall lan-guage exposure (combined distant andmeaningful speech) increased over timefor all infants as theymatured. Additionallongitudinal analysis of the language

FIGURE 1Schematic figure to demonstrate study definitions: vocalization activity blocks.

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environment data revealed no differ-ences between the NICU and newbornnursery groups for percent distantspeech at 44 weeks (17.4% vs 14.7%;P = .23) and 7 months (24.1% vs 25.9%;P = .56) and percent meaningful speechat 44 weeks (15.8% vs 15.2%; P = .77)and 7months (13.8% and 13.7%; P= .94),respectively.

Female adults had significantly highermean hourly AWCs than male adultsduring all recordings (Fig 2). Althoughthere is variance in the number of adultwords spoken per hour, infants, on av-erage, received nearly 3 times as muchlanguage input from their mothers thantheir fathers from birth through 7months of age. To make a best estimate

of a parent’s overall presence with theinfant during the recording, hourlyAWCs for male versus female adultswere compared. Analyses of AWC.100words/hour to reflect parents’ pres-ence with the infant identified an overallaverage of 74% for mothers versus 47%for fathers for all recordings.

Thelanguageinteractionsbetweenmothersand infants compared with fathers andinfants were further explored by ana-lyzing language block data. Infant re-sponse to adult languagewasmeasuredby including all language activity blocksinitiated by female and male adults. Thepercentage infant response was deter-mined by counting the number of adult-initiated blocks with an infant response

comparedwith adult monologue blocks.Figure 3 shows that of all adult-initiatedlanguage blocks, infants vocally re-sponded preferentially to motherscompared with fathers during all 3recording periods. With increasing age,infant response to both parents increased(P, .0001).

Of all infant-initiated language blocks,the percentage of blocks with any adultresponder ranged from 28% during thenewborn recording to 23% by 7months(data not shown). Only the languageblocks initiated by the infant with anadult response (female adult only, maleadult only, or both) were analyzed. Fig-ure 4 shows that mothers were theprimary responders to an infant’s ver-bal cues. During each recording period,infants had relatively few vocal inter-actions with their fathers independentof their mothers. Any male adult re-sponse occurred in 27% to 30% of theblocks compared with any female adultresponse, which occurred in 88% to94% of infant-initiated language blocks(P , .0001).

Table 3 shows infant vocalizations andverbal interactions by infant gender.Vocalization counts did not differ sig-nificantly at any recording period. At 44weeks’ PMA, infant boys had higherhourly conversation turn counts thaninfant girls (24 vs 18, P = .05). Therewere no significant differences for AWCbased on infant gender.

Figure 5 shows adult response rates toinfant vocalizations by adult gender.Female adults had a higher responserate to language blocks initiated byinfant girls than boys during the new-born period and at 44 weeks’ PMA. At7 months, the response rate remainedhigher but did not reach statisticalsignificance. Male adults respondedmore frequently to infant boys thaninfant girls, but the difference did notreach statistical significance.

Analysis of child response by adult gen-der showed few differences. Infant boys

TABLE 1 Characteristics of Study Infants (N = 33a)

Infant Girls Infant Boys P

n 17 16Mean gestational age, wk 37 6 2 37 6 2 37 6 2 .6216Late preterm, % 55 53 56 .8787Male, % 48Twins, % 6 6 6 .9647NICU stay, % 24 24 25 .9215Infant race, %White non-Hispanic 67 59 75 .4279Black non-Hispanic 3 6 0Hispanic 9 6 13Multiracial/other 21 25 13

Maternal age, y 30 6 5 29 6 4 31 6 5 .1810Gravida 1, % 50 47 31 .3530Mother’s education, %Less than high school 0 0 0 .1834High school/partial college 28 35 14College/graduate degree 66 65 86Unknown, n 2 0 2

Father’s education, %Less than high school 3 6 0 .2214High school, partial college 31 47 23College/graduate degree 56 47 77Unknown, n 3 0 3

Bilingual household, % 31 35 25 .5202English as primary language spoken, % 94 94 94 .9647a Thirty-three infants from 32 households (1 set of twins).

TABLE 2 Comparison of Language Environment by Location

NICU Newborn Nursery Home 44 wk Home 7 mo

Background/silence, % 71.9a,b,c 52.3 52.0 46.2Noise, % 4.2a,b 1.1c 1.8c 4.6Television, % 7.4a,b 16.8c 16.0c 10.0Distant speech, % 9.9b,c 10.8b,c 15.3c 25.5Meaningful speech, % 7.6a,b,c 18.8b,c 15.4 13.7

P, .05a: versus newborn nurseryb versus home 44 weeksc versus home 7 mo. % represents percentage of duration of entirerecording.

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and girls had similar response rates tofemale adult-initiated language blocksfor all recordings. Infant boys displayed

a higher response rate than girls tomaleadult–initiated blocks at 7 months (19%vs 15%, P = .02).

DISCUSSION

More than 1500 hours of language re-cordings were analyzed to provide acomprehensive description of languageinput and interactions between infantsand theircaregivers in thefirstmonthsoflife. It is known that early language ex-posure is important for language de-velopment,19 and children with a richlanguage environment, specifically infant-or child-directed speech,20 have betterlanguage and cognitive outcomes.1,21,22

A recent study of preterm infants in theNICU using the same LENA technologyshowed that parental talk in the NICUwas a significant predictor of infantvocalizations and conversational turns,and the AWC in the NICU also correlatedwith improved cognitive and languageoutcomes through 18months of age.17,23

Our study is among the first to assesslanguage environment and languageinteractions longitudinally beginning inthe first days after birth.

The AWC data support our hypothesisthat infants are exposed tomore femalethanmaleadultspeech in thefirstmonthsof life. It also confirms the LENA Nat-ural Language Study that the majority ofthe total talk environment comes frommothers.22 The infants’ total languageexposure increased from birth to 7months as they became more matureand engaging. The finding that the hourlyAWCs from mothers and fathers actuallydecreased over time is explained by thefact that the “meaningful speech” cate-gory, from which AWC estimates aregenerated, decreased over time, whereas“distant speech” increased. The physicalproximity between parent and infant is1 component in a complex Gaussianmixture model that determines if theaudio data are categorized as distantversus meaningful speech. Parents aremore likely to be in closer proximityduring early infancy with more frequentfeeding and holding.

Thefinding thatreciprocal vocalizationsbetween mothers and infants were

FIGURE 2Comparison of female versus male AWC per hour. *P, .0001 comparing female to male adults. Errorbars represent SD.

FIGURE 3Infant response to female and male adult–initiated language blocks. *P , .01 comparing infant re-sponse to female versus male adult.

FIGURE 4Adult response to infant-initiated language blocks. *P , .0001 comparison among 3 categories.

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more frequent than those betweenfathers and infants supports our secondhypothesis.What is striking is not simplythat mothers speak more and have morevocal interaction with their infants, butrather by how much more they speakcompared with fathers. Functional mag-netic resonance imaging has shown thatmothers, but not fathers, have increased

brain cortical activation in specific lan-guage processing areas when listeningto infant-directed speech, suggestingthat mothers have an intent to commu-nicate and the difference in neural pro-cessing is experience-dependent.24 Themothers spoke more to infant girls thanboys inearly infancy.Girlshavebeenshownto have earlier brain maturation, eye

contact, and joint attention, which mayin turn influence greater maternal re-sponsiveness.12,25,26 A significant gap inlanguage input from fathers may havelong-term implications. Recent studieshave shown that fathers’ language in-put and vocabulary spoken to infantsand young children may also be a pre-dictor of child language outcomes.27–29

Our study adds to the literature by de-scribing the relationships betweenadult and infant gender relative to earlyparent-infant communication to betterdescribe the infant early linguistic ex-perience. Early language delays are ofclinical importance, and our study find-ings, which suggest unique gender effectson early communicative interactions be-tweenparentsand their infants, supporta need to explore novel approaches toearly gender-specific intervention.

Much of the literature examining inter-actions of parents with their sons anddaughters has provided inconsistentresults. Some investigators have re-ported that parents converse more andspeak longer to their girls than boys.30,31

Others found that parents of infants andtoddlers used more explanations anddescriptive statements when talking totheir sons than daughters.21,32 Motherstended to give more instructions,30 teachproblem-solving skills, and be more di-rective with their sons,33 and they askedmore questions and made more state-ments about feelings or needs withtheir daughters.30,34 These variationsin communication with children illus-trate differences in both amount andtype of language parents are using.For our study, we did not analyze theactual words but rather the estimatedcount of adult words spoken.

Infant gender differences in vocalizationsand conversational exchanges and therelationship with language skills deservefurther investigation. The gender differ-ences described in the literature show-ing that girls acquire language skillsearlier thanboyswasnot reflected inour

TABLE 3 Infant Vocalizations, Conversational Turns, and AWC per Hour by Infant Gender

Overall Infant boy Infant girl P(n = 33) (n = 16) (n = 17) Boy Versus Girl

Infant vocalizations/hNewborn 36 31 39 .3944 wk 72 85 59 .077 mo 86 95 77 .12

Conversational turns/hNewborn 12 11 13 .6744 wk 21 24 18 .057 mo 23 24 21 .46

AWC/hNewborn 1724 1643 1800 .6444 wk 1295 1391 1204 .377 mo 994 1050 942 .46

FIGURE 5A, Female adult response to infant-initiated language blocks by infant gender. B, Male adult response toinfant-initiated language blocks by infant gender.

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early vocalization and conversationalturn counts. Our findings suggest infantboys are more vocal with more conver-sational turns at 44 weeks’ PMA witha trend for more vocalizations and con-versational turns at 7 months. This mayreflect a difference in emotional ex-pressiveness with infant boys having animmature nervous system and greaterirritability and need for soothing com-pared with girls.12,35 The prelinguisticvocalizations analyzed in this study, how-ever, may be different from the exten-sively studied meaningful speech thatdevelops beyond the first year of life.

Strengths of this study are that (1) it isamong the first longitudinal studies toevaluate an infant’s language environ-ment from the first days of life, (2) it usesa novel research device with analysis ofthousands of hours of natural language

environment data, (3) it analyzes boththe mother’s and the father’s role inearly language exposure, and (4) it an-alyzes the role of infant gender in lan-guage interactions.

A limitation of the study is small sub-group sample size. In addition, LENA hasbeen used to document language en-vironment and vocalization activity ofpreterm infants, but there is no nor-mative LENA data set for infants ,2months of age.23 The findings of femaleand male adult speech reflecting theactualmothers’and fathers’speechwasbased on logs the families kept foreach recording and not by any methodof direct visualization. The actual pres-ence of an individual is confirmed onlyif there are words spoken and in-cluded in the data set. Only infantsresiding in 2-parent households exposed

to both female and male adult speechwere analyzed, and the findings may notbe representative of all home environ-ments.

CONCLUSIONS

Language interactions between femalecaregivers and their infants surpassthoseofmalecaregivers.Mothersprovidethemajority of language input andare theprimary responders to their infant’s vocalcues, and infants show a preferentialvocal response to their mothers. In ad-dition, the data suggest thatmothersmayrespond preferentially to infant girls. Onthe basis of these findings, both mothersand fathers should be informed about theimportant benefits of parent talk anda rich language environment on theirinfant’s language development and lateracademic success.

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DOI: 10.1542/peds.2013-4289 originally published online November 3, 2014; 2014;134;e1603Pediatrics 

Katharine Johnson, Melinda Caskey, Katherine Rand, Richard Tucker and Betty VohrGender Differences in Adult-Infant Communication in the First Months of Life

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DOI: 10.1542/peds.2013-4289 originally published online November 3, 2014; 2014;134;e1603Pediatrics 

Katharine Johnson, Melinda Caskey, Katherine Rand, Richard Tucker and Betty VohrGender Differences in Adult-Infant Communication in the First Months of Life

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