Preterm Infants Exposed to Maternal Voice

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Preterm Infants Exposed to Maternal Voice
Series Title:
Journal of Undergraduate Research
Keller, Lorraine
Krueger, Charlene
Miller, Harriet
Sizemore, Glen
Place of Publication:
Gainesville, Fla.
University of Florida
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The purpose of this pilot study was to evaluate eye movement as an additional component of behavioral observation in preterm infants exposed to maternal voice. Infants received either daily exposure to a CD recording of their mother reciting a rhyme or standard NICU care. Infants exposed to the CD recording opened their eyes by 32 weeks of age when the maternal recording was played. Infants with no prior exposure did not open their eyes when the recording was played. This suggests that inclusion of eye movement observation is warranted in future evaluations of exposure to the maternal voice in preterm infants.

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Preterm Infants Exposed to Maternal Voice

Lorraine Keller et al.*

College of Nursing, University of Florida

The purpose of this pilot study was to evaluate eye movement as an additional component of behavioral observation in preterm infants
exposed to maternal voice. Infants received either daily exposure to a CD recording of their mother reciting a rhyme or standard NICU
care. Infants exposed to the CD recording opened their eyes by 32 weeks of age when the maternal recording was played. Infants with
no prior exposure did not open their eyes when the recording was played. This suggests that inclusion of eye movement observation is
warranted in future evaluations of exposure to the maternal voice in preterm infants.


Neonatal intensive care units subject preterm infants to
an array of auditory stimuli (e.g., routine incubator sounds,
ICU monitoring alarms, speech sounds of health care
teams) from which they are normally sheltered while still
in the womb. At the same time, preterm infants in the
NICU lose significant contact with their mother's voice, an
auditory stimulus they would typically be exposed to if
they were carried to full term.
While there is general theoretical support for the view
that reduced exposure to interactions with one's mother
plays a significant role in a child's growth and develop-
ment (Als et al., 1979; Barnard et. al., 1987; Moon et al.,
2000), very little is known about how exposure to maternal
voice shapes development in the preterm infant. This may
be due, in part, to the unethical nature of conducting stud-
ies that alter normal sensory events in human infants. To
address this issue of altered sensory events in the NICU,
Lickliter and colleagues developed an animal model that
allowed them to alter sound levels and exposure to mater-
nal voice in quail chicks.
Sleigh and Lickliter (1998) did not allow quail chicks to
hear their mother's call during late prenatal development.
Once hatched, they did not walk towards their mother's
voice, an important early, behavioral response. Further,
moving toward or approaching their mother's call was also
interrupted by elevated levels of light (Foushee & Lickliter,
2002) and sound (Reynolds & Lickliter, 2002) prior to
hatching. While not as extreme as the aforementioned ex-
ample, preterm infants similarly lose significant contact
with their mothers' voices late in prenatal development and
are cared for in a hospital environment that necessitates
elevated light and sound levels. Three historical studies
have directly investigated the behavioral response in hu-
man preterm infants to maternal voice (Chapman, 1978,

1979; Malloy, 1979); in each, the behavioral response was
limited to observations of body movement.
Chapman (1978) studied the behavioral effects of mater-
nal voice on preterms exposed to one of three auditory sce-
narios: the incubator's typical auditory stimulation, the
maternal voice or a taped recording of an orchestra playing
Brahms's "Lullaby." Study participants were 28 to 33 post-
conceptional aged infants. Chapman (1978) focused her
observations on gross motor activity. She investigated up-
per and lower limb activity and compared right to left limb
activity, as well as gender differences. While no statistical
differences were found, findings suggested that exposure to
both the maternal voice and music facilitated normal limb
activity development (Chapman, 1978). The gross motor
pattern of laterality (preference for use of one side) devel-
oped earlier in the maternal voice group, and infants did
not require a 24-hour adaptation period for wearing an ac-
celerometer (instrument used to measure gross motor limb
activity), unlike those exposed to music and standard care.
Chapman (1978) noted that infants exposed to music
reached discharge weight faster compared to the control
group, and that female preterms exhibited less motor activ-
ity than males preterms. Chapman repeated her study in
1979 using participants who were 26 to 33 weeks post-
conceptional age and had the same findings.
Similarly, Malloy (1979) compared how the maternal
voice, instrumental music (Brahms's "Lullaby"), and no
planned auditory stimulation affected behavioral response
in 27 to 33 post-conceptional aged infants. Malloy (1979)
used Rosenblith's modified Graham Behavior Scale, which
measures general maturation (limb activity), gross body
movement to audio-visual stimuli, muscle tension, and ir-
ritability. Malloy (1979) found no significant differences in
motor development among the three groups. The maternal
voice and music groups were, however, a younger age at
discharge than the control group (no planned auditory

*Authors: Lorraine Keller, Charlene Krueger, ARNP, PhD, Harriet Miller, MSN (College of Nursing), and Glen Sizemore (Department of Psychology)
This study was funded by the National Institutes of Health (NIH/NINR P20 NR07791, NIH/NCRR M01 RR00082).

University of Florida I Journal of Undergraduate Research I Volume 9, Issue 4 I Summer 2008


stimulation, standard care), suggesting that early exposure
may have affected infant development.
Taking into account the findings discussed above, we
hypothesized that given a history of four weeks' exposure
to maternal voice (using a low decibel level, CD re-
cording), preterm infants would respond with positive be-
havioral changes (body movement). To this we added the
observation of whether the eyes opened, thinking that the
infants would more easily recognize their mother's voice
and thereby reach an attentive state if given a history (4
weeks) of hearing a CD recording of their mothers speak-
ing a rhyme. We believed that the addition of this observa-
tion was essential when studying preterm infant behavioral
development because infants "tend to orient visually to an
attended sound source" (Kemler Nelson, Jusczyk, Mandel,
Myers, Turk & Gerken, 1995, p. 111). Full term infants are
physically capable and mature enough to "learn to maintain
a response (e.g., a head-turn) when motivating stimulation
is contingent on their behavior" (Kemler Nelson et al,
1995, p. 111). Preterm infants, on the other hand, are
physiologically immature which renders them incapable of
turning their heads to attend to sources of sound. There-
fore, eye opening is perhaps an immature attending re-
sponse. Thus, the purpose of this pilot study was to
evaluate eye movement as a component of behavioral ob-
servation in preterm infants exposed to maternal voice. The
study compared the behavioral effects in preterm infants of
daily exposure to a CD recording of mothers reciting a
nursery rhyme, to that of infants receiving standard NICU


Subjects and Setting. Infants in this study participated
in a larger study entitled Heart Rate Variability and
Learning in the Premature. Following parental informed
consent, a convenience sample of 38 infants (admitted to a
NICU in the Southeast) were randomly assigned to 1 of 2
groups. Infants either listened to a nursery rhyme recited
by their mother twice a day, from 28 to 32 weeks postmen-
strual age (Group 1) or did not hear the CD recording
(Group 2). The target age for admission was 27 to 28 post-
menstrual weeks of age. Inclusion criteria consisted of 1)
confirmation of age by Ballard scoring and 2) English as
the parental native language. Exclusion criteria consisted of
the following: 1) abnormal head ultrasound, 2) sensorineu-
ral hearing loss, 3) confirmed prenatally transmitted vi-
ral/bacterial infections, or 4) cardiac abnormalities.
Four low-risk preterm infants from the larger study par-
ticipated in this methodological pilot study. Two infants
(Set A) were randomly assigned to Group 1 and heard the
CD recording from 28 to 32 post-menstrual weeks. Two
infants (Set B) were assigned to Group 2 and did not hear
the CD recording. Both sets were tested at 32 weeks of age:
Set A, using the same CD recording of their mother recit-

ing the rhyme and Set B, using the prerecorded (but never
played) recording of their mother reciting the same rhyme.

Nursery rhyme. A CD recording of one nursery rhyme
was used in this study. The untitled rhyme (Simon &
Schuster, 1985) was nine lines long, took approximately 15
seconds to recite and was not a common verse, making it
unlikely that the infants would be spontaneously exposed
to it. Recordings of the rhyme were made by asking the
mother to use "motherese," a method of speaking that em-
phasizes greater changes in pitch and slower speech (Kap-
lin et al., 1995). To do this, we asked mothers to practice
reciting the rhyme once before creating the recording and
to imagine holding their infants in their arms while reciting
the rhyme. Although the effect of this speaking method on
the fetus (and preterm infant) is unknown, newborns have
been shown to systematically prefer human speech with the
characteristics of "motherese" (Kaplin et al., 1995).
CD recordings consisted of three separate recitations of
the same rhyme, each lasting approximately 15 seconds,
for a total of 45 seconds. The 45-second recording was pre-
sented twice a day over a 12.5-cm speaker positioned 20
cm from the infant's ear. Overall stimulus intensity was 50
to 55 dB (M=53.9; SD=2.35) with background NICU
sound levels just prior to initiation of the stimulus ranging
between 48.6 to 69.2 dB (M=57.90; SD=4.01), using the
A-scale on a Bruel-Kjaer (220SLM) sound level meter.
The decibel level for presentation of the stimulus (50 to 55
dB) was chosen to maintain the decibel level just below
that of human speech (58 to 60 dB) and to stay within rec-
ommended sound levels for the preterm infant (Graven,
2000; Gray, 2000).

Behavioral Coding. Behavioral counts were obtained
from videotaped recordings of the infants. Specific behav-
iors coded were: 1) eyes open or closed, 2) mouth move-
ment present or not, and 3) body movement present or not.
Mouth movement was measured because Standley (2003)
had demonstrated differences in this behavior based on
exposure to music in preterm infants from 24 to 40 weeks
post-menstrual age. Three research assistants were trained
to >95% agreement with a training videotape that demon-
strated the behaviors to be coded. Once trained to >95%,
intra- and inter-rater reliability were maintained at >85%

Procedure. Recordings were presented over a 12.5-cm
speaker positioned 20 cm from the infants' ears. Overall
stimulus intensity was 50-55 dB, using the A-scale of a
Bruel-Kjaer (220SLM) sound level meter. Recordings were
played while the infants remained in their assigned incu-
bator beds, and were initiated at least 15 minutes following
a meal and once the infant was determined to be in an ac-
tive sleep state of the sleep-wake cycle.
Criteria established by Thoman (1990) for use with
preterm infants were employed to control for differences in

University of Florida I Journal of Undergraduate Research I Volume 9, Issue 4 I Summer 2008


behavior secondary to sleep-wake state. Subjects were
determined to be in an active sleep state if: 1) respirations
were irregular, 2) no body movement was present, and 3)
eyes were closed. Interrater reliability in state detection
was maintained at > 90% agreement.
A Sony Hi-8 Digital Camera was used to videotape
subjects' behavioral responses at approximately the same
time of day for each infant (between 10 AM-12 PM)
before, during, and after the CD recording of the rhyme
was played. Videotaping occurred at the same time of day
to control for potential circadian influences on heart rate
patterns and movements (Arduini et al., 1986). Film clips
of the 15-seconds before, during, and after presentation of
the rhyme were then created. These video clips were then
cut into 5-second segments with the audio removed in
preparation for coding the behavioral responses. The 5-
second segments were then randomized prior to behavioral
coding to ensure that no bias would affect the observations.
Researchers viewed the video segments and recorded the
occurrence of three behaviors for each 5-second clip. Be-
havior coded included whether the eyes were open or
closed, the presence or absence of mouthing movements
and the presence or absence of body movements. Move-
ment of the mouth or cheek was considered a mouthing
movement, and any sustained physical movement of the
body (head, arm, fingers, leg, torso, etc.) was considered a
body movement. Twitches and spasms were not considered
body movements in this pilot study.


No consistent changes in body movement were noted
based on exposure to maternal voice for either Set A or B
infants. Mouthing movements were not noted during the 5-
second segments of behavioral observation for Set A or Set
B infants.
The infants exposed to a CD recording of their mother
reciting a nursery rhyme (Set A), however, opened their
eyes when the same CD recording of the rhyme was
played. The infants (Set B) who were not exposed on a
daily basis to the CD recording of their mother reciting a
rhyme did not open their eyes when the rhyme was played.
Subject 025 (a Set B infant) had his eyes open before the
rhyme, and closed his eyes when the rhyme was begun.


A comparison of behavioral responding given a history
of exposure to maternal voice (Set A) and no history of
exposure (Set B) revealed one finding of note. Infants
given a 4-week history of listening to a CD recording of
their mother reciting a rhyme opened their eyes in response
to hearing the CD recording. Infants not exposed to a
regular recording did not open their eyes when their mother
recited the rhyme.

This pilot study adds to historical studies investigating
exposure to maternal voice (Chapman, 1978, 1979; Malloy,
1979) by suggesting the need to add the behavioral obser-
vation of eye movement to studies investigating exposure
to maternal voice. Eye movement (opening) following re-
peated exposure to hearing the maternal voice may be a
crucial first step toward establishing an important mater-
nal-newborn interaction or eye contact between the mother
and infant. Repeated exposure to hearing their mother
speaking a rhyme resulted in only those infants opening
their eyes when the maternal recording was played. The
occurrence of increased body movement was not detected
and no difference in mouthing movements based on expo-
sure to maternal voice was noted.
The small sample used in this pilot study does not allow
for statistical significance to be established, and thus it
cannot confirm or oppose the former research performed
within this field. Pilot findings do, however, suggest an
important methodological change to investigations of the
behavioral response to maternal voice in the preterm infant
(Perry, 2001).

Clinical implications. Preterm infants lose significant
contact with their mothers' voices late in prenatal devel-
opment and are cared for in a hospital environment that
necessitates elevated light and sound levels. All this hap-
pens due to the need for prolonged hospitalization and the
daily care provided within the NICU. Thus, they are not
only deprived of the protective properties of the womb, but
of a possibly critical aspect for normal development-the
mother's voice. Taken together with the fact that these in-
fants are at increased risk for developmental delay (Bhutta
et al., 2002; Colvin et al., 2004; Inder et al., 2005; Perlman,
2001; Therien, 2004), this suggests the need for further
investigation of the relationship between preterm infants'
early altered sensory experiences and developmental out-
Potentially beneficial psychological effects from expo-
sure to maternal voice have been suggested by Latva and
colleagues (2004), who described a correlation between
parental visits during NICU care and emotional/behavioral
development 7 to 8 years later. Moreover, there is substan-
tial literature documenting positive developmental and
long-term outcomes from interventions in which interac-
tions between the mother and her preterm infant were en-
couraged (Als et al., 1986; Als et al., 2003; Als, 2004;
Ashbaugh et al., 1999; Forcada-Guex et al., 2004; Muller-
Nix et al., 2004). While none of these studies specifically
examined exposure to maternal voice and the initiation of
eye contact, taken together with the finding of this study,
they underscore the need for further investigations of the
relationship between exposure to voice and developmental

University of Florida I Journal of Undergraduate Research I Volume 9, Issue 4 I Summer 2008


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University of Florida I Journal of Undergraduate Research I Volume 9, Issue 4 I Summer 2008