The role of the mother's voice in developing mother's ... - FIU Infant Lab

Infant and Child Development
Inf. Child Dev. 14: 29–50 (2005)
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/icd.376
The Role of the Mother’s Voice in
Developing Mother’s Face
Preference: Evidence for Intermodal
Perception at Birth
F. Z. Sai*
Department of Psychology, U.A.E. University, U.A.E.
Four experiments are described which investigated the role of the
mother’s voice in facilitating recognition of the mother’s face at
birth. Experiment 1 replicated our previous findings (Br. J. Dev.
Psychol. 1989; 7: 3–15; The origins of human face perception by
very young infants. Ph.D. Thesis, University of Glasgow, Scotland,
UK, 1990) indicating a preference for the mother’s face
when a control for the mother’s voice and odours was used only
during the testing. A second experiment adopted the same
procedures, but controlled for the mother’s voice from birth
through testing. The neonates were at no time exposed to their
mother’s voice. Under these conditions, no preference was found.
Further, neonates showed only few head turns towards both the
mother and the stranger during the testing. Experiment 3 looked
at the number of head turns under conditions where the newborn
infants were exposed to both the mother’s voice and face from
birth to 5 to 15 min prior to testing. Again, a strong preference for
the mother’s face was demonstrated. Such preference, however,
vanished in Experiment 4, when neonates had no previous
exposure to the mother’s voice–face combination. The conclusion
drawn is that a prior experience with both the mother’s voice and
face is necessary for the development of face recognition, and that
intermodal perception is evident at birth. The neonates’ ability to
recognize the face of the mother is most likely to be rooted in
prenatal learning of the mother’s voice. Copyright # 2004 John
Wiley & Sons, Ltd.
Key words: neonates; mother’s face recognition; intermodal perception
at birth
Increasing evidence suggests that newborn infants can rapidly learn about faces.
Sai (1990), Bushnell et al. (1989), Field et al. (1984) and Pascalis et al. (1995) found
statistically reliable preference for the mother’s face, as opposed to a female
*Correspondence to: Dr. F. Z. Sai, Associate Professor, Department of Psychology, U.A.E.
University, Al-Ain, P.O. Box 17771, U.A.E. E-mail: sai_fz@hotmail.com, f.zohra@uaeu.ac.ae
Copyright # 2004 John Wiley & Sons, Ltd.

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F. Z. Sai
stranger’s face from 4, 12, 72 and 78 h, respectively. Using a high amplitude
sucking (HAS) technique, Walton et al. (1992) reported that infants from 12 h of
age produced more sucking responses to the videotaped image of their mother’s
face than that of a female stranger.
Not only do neonates prefer to look at a composite of previously seen faces
than at a composite of previously unseen faces (Walton and Bower, 1993), but can
recognize a learned face over transformations (Walton et al., 1997), and even learn
an image similar to a composite of the faces they have seen in the first hours of
birth (Slater et al., 1998). Altogether these data suggest a rapid learning about
faces within the first hours of birth, and the establishment of}at least}a
rudimentary representation of faces. Nonetheless the basis of such learning and
what is being learned remains obscure.
There has been more than one interpretation offered to explain the data
suggesting early preference, such that there exists a configurational response in
the neonatal period. Goren et al. (1975) and Dziurawiec (1987) reported that
infants only minutes old oriented their heads to follow a two-dimensional
schematic face-like pattern than either of two patterns consisting of the same
facial features in different arrangements. Johnson and Morton (1991) who
replicated Goren et al.’s study proposed the existence of ‘Conspec’. Consisting of
three dots, the Conspec serves to direct the newborn’s visual attention to faces.
While this proposition seems plausible, there are some data that are not easily
explained (e.g. Turati et al.’s (2002) results). Preference for the mother’s live face
vanished with the slightest orientation, half-profile of that face (Sai, 1990), and
when hair-face line information was masked (Pascalis et al., 1995). Recognition of
the half-profile pose of the mother’s face was, however, possible only at 4–5
weeks from birth (Sai and Bushnell, 1988), and it was only at 10–12 weeks that
infants demonstrated preference for the mother’s face shown in profile (Sai,
1990). Together, these findings seem to favour the learning hypothesis; it Is
possible that the infants had not been sufficiently exposed to the half-profile and
profile poses of their mother’s face. If recognition is based solely on facial
configuration, then infants should have been able to show preference for the
mother’s face since at least some information about facial configuration was still
available, at least in the half-profile pose.
It is fairly clear in retrospect that there were some methodological shortcomings
with the studies that used real faces. For example Field et al.’s (1984)
study failed to take the olfactory information into account. Those which
controlled for discrimination on the basis of olfactory information, implemented
a control over the mother’s and stranger’s odours only during the testing (Sai,
1990; Bushnell et al., 1989) and, so was the mother’s voice. Nevertheless, exposure
to the mother’s voice–face from birth to the time of testing might have facilitated
learning the mother’s visual features. Evidence suggests learning of the mother’s
voice at birth. For example, in a study by DeCasper and Fifer (1980), 2–4-day-old
neonates preferred their mother’s voice. Moon et al. (1991) demonstrated that
with both Spanish and English speaking women, 2-day-old newborns preferred
their mother’s language.
Therefore, the question of controlling for the mother’s voice is, particularly
critical for understanding the mechanism underlying preference for the mother’s
face at birth. The mother’s face, like many other stimuli we experience is
intermodal in that it provides information to more than one sensory modality. For
example, during interaction with the mother, infants are provided with tactile
stimulation, warmth and exposure to the mother’s voice, odours, taste of her
milk and even to the rhythms to her heart beats. This wide range of information
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The Role of the Mother’s Voice 31
may not only play a role in determining the mother’s face recognition, but is
likely to lay ground to early cross-modal learning.
Research has now clearly revealed many interesting intermodal capabilities
in infancy (for review see, Bushnell and Boudreau, 1991, 1993; Lewkowicz
and Lickliter, 1995; Rose and Ruff, 1987). Some of the intermodal relations
are amodal and redundant across the senses. For example, the synchrony
of voice and mouth when a person speaks. Other cues are modality-specific and
arbitrary-related across the senses, such as the pairing of a face and the sound of
the voice.
From birth, newborn infants perceive a wide range of invariant amodal
relations. For example, they reliably co-ordinate visual and auditory space, in
that they turn their heads and eyes in the direction of a sound source, suggesting
that knowledge about spatial location is provided by both visual and auditory
information (e.g. Wertheimer, 1961; Muir and Field, 1979; Clifton et al., 1981;
Butterworth, 1983; Muir and Clifton, 1985). At 5 weeks, infants can recognize a
visual shape (a pacifier) that had been experienced tactually by sucking,
suggesting that the pacifier is coded both tactually and visually (Meltzoff and
Borton, 1979). Twenty week old infants show a sensitivity to temporal synchrony
specified intermodally in that they detect the common rhythm and duration of
tones and flashing lights (Lewkowicz, 1986). Around this age, infants can also
match appropriately the sounds made either by a single unitary element or by a
cluster of smaller elements (Bahrick, 1987, 1988). Together, these findings indicate
that infants from birth perceive amodal relations.
On the other hand, recent evidence suggests that arbitrary intermodal
relations are detected and learned in infancy too. Two-day-old infants can learn
arbitrary visual–auditory associations when familiarized to two alternating
visual stimuli differing in colour and orientation, and when each association
was accompanied by its appropriate sound (Slater et al., 1997). By 14 weeks,
infants were able to learn to associate the sound of their mother’s voice
with the sight of her face (Spelke and Owsley, 1979), and 24 week olds
learned the association between the colour of a container and the taste of the food
it contained (Reardon and Bushnell, 1988). Prior to 12 weeks, infants were not
able to detect the arbitrary pitch colour/shape relations (Bahrick et al., 1996).
Only infants of 28 weeks demonstrated learning of the arbitrary relations
(Bahrick, 1994). If young infants are able to learn the synchrony of voice and mouth
when the person speaks (amodal information), and can learn the pairing of a
stimulus and the sound that stimulus produces (arbitrary information), then learning
about faces would be most likely the outcome of an early intermodal processing.
It is, however, possible that there exists a specific mechanism for learning the
visual features of the mother’s face. If this were the case, then newborn infants
would still prefer their mother’s face to that of a female stranger even when the
mother’s voice is not available to the infants from birth through testing. On the
other hand, preference for the mother’s face might disappear with the
unavailability of a postnatal auditory experience to the mother’s voice. In this
case, the conclusion that would be drawn is that face preference does not solely
depend on visual processing. Instead, we would assume that face preference is
the product of intermodal learning, especially since 2-day-old newborn infants
are able to learn arbitrary visual–auditory associations (Slater et al., 1997) as
mentioned earlier. However, we do not have evidence concerning whether
infants are able to perceive the mother’s face–voice associations and later use
such information in the recognition test. The experiments described here were
designed to determine the role of the mother’s voice in facilitating preference for
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F. Z. Sai
the mother’s face at birth. The infants were, therefore, not exposed to their
mother’s voice from birth through testing.
Some clarification of our understanding of infants’ learning about faces, and
the role of the mother’s face in developing facial processing is likely to emerge
when newborn infants are tested using the same procedures as in our previous
studies (Sai, 1990; Bushnel et al., 1989), with a visual preference task and paired
rather than sequential presentations of the comparison faces. This paper
describes four studies which used non-Caucasian participants.
EXPERIMENT 1
The purpose of the present experiments was to determine the role of experience
with the mother’s voice in facilitating face recognition in the neonatal period.
However, since our previous studies (Sai and Bushnell, 1987; Bushnell et al., 1989;
Sai, 1990) demonstrating recognition of the mother’s face in the neonatal period
tested only Caucasian neonates from the area of Glasgow, Scotland (UK), and the
participants in this research were Malaysians, it was seen advisable to first
replicate these earlier findings on Malaysian neonates.
Before presenting details about the methodology and procedures followed in
these experiments, it is worth pointing out that the newborn infants were
retained on the ward at all times, in bassinets located adjacent to their mother’s
bed. The mothers had continuous responsibility for the care of their infants.
Although the total interactive contact hours involved within each mother–infant
dyad was not assessed, some provisional observations (Sai, 1990) showed that
there was a fairly substantial period of contact within the first 24 h. However,
there was a considerable variability across dyads.
Since our earlier findings had indicated no significant relationship between age
and extent of preference, age was not considered as a potential factor, and was
therefore not included. Similarly, sex factor was not incorporated for the same
reason (see Sai, 1990).
Method
Participants
Fourteen newborn infants, seven males and seven females (M ¼ 3:00 h,
range ¼ 224h;M birth weight ¼ 2:75 kg, range ¼ 2:7022:90) participated in this
study. They all had normal Apgar scores after 5 min (M ¼ 9, range ¼ 8210), and
throughout testing they remained in the behavioural state of alert inactivity
(Ashton, 1973). All the infants in this and subsequent studies were normal,
healthy and full-term infants (37 weeks gestation) with no complications during
delivery. The infants were primarily from middle class and diverse ethnic
backgrounds of Malaysia (Malay, Chinese and Hindou). They were volunteered
by their mothers on the wards of the University Hospital, Kuala Lumpur where
they were born. The data of ten additional infants were discarded from the study:
four for side bias in their looking behaviour (see procedure section for details
regarding criteria for side bias), three for excessive fussiness, two for persistent
sleeping and one because the mother made sounds during the testing.
Stimuli and Apparatus
The stimulus faces for each participant in this experiment were the live face of
the participant’s mother and that of a female stranger. This was another mother
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The Role of the Mother’s Voice 33
from the same maternity ward or, another young woman. To ensure that
preference for the mother’s face was not being forced by an inadvertent bias in
terms of overall brightness of the face or the hair colour, a control over brightness
of the face and hair colour was incorporated. In Field et al.’s study (1984), hair
colour and face brightness cues were randomly varied across participants so that
sometimes the mother’s face should have been brighter and sometimes less
brighter than the stranger’s, and sometimes the hair colour should have been
lighter and sometimes darker. Yet, it could be argued that there might still have
been a systematic bias along these dimensions in favour of the mothers’ faces
since Field et al., used the same small set of comparison faces throughout the
study, and this might have resulted in the demonstrated preferences. Therefore, it
was seen advisable to match each mother on the wards with another female
stranger who was judged to be broadly comparable in terms of hair colour, hair
shape and facial complexion.
The mother and a volunteer female stranger were asked to sit behind a large
white screen (2 2.5 m) into which at head height were cut two apertures
(30 25 cm), one at either side of mid-line and separated by 12 cm. These allowed
a good view of the hair and face of the stimuli from the neonate’s position, with
lighting being provided by two fluorescent tubes above and in front of the faces.
In order to prevent any contamination of the data due to differences in the
clothing of the stimulus faces, they each had white sheet draped around their
necks to effectively mask their clothing. The visible background, a curtain
backcloth, was the same for both stimulus faces (see diagram).
Through a hole, which was made in the middle of this panel, between the two
apertures, a video camera recorded the infant’s face during the whole testing and
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F. Z. Sai
served for later calculation of interobserver reliability. To successfully control for
olfactory information, a strong air-freshener was liberally coated onto the screen
surrounding the faces before the neonate was brought up to the testing room and
immediately before each trial.
Procedure and Design
The method and procedures were identical to those of our previous studies. A
control over the mother’s voice and olfactory information was implemented only
during testing. Neonates were exposed from birth to 5 to 15 min, prior testing, to
their mother’s face, voices and odours. During this period, they all had a first
contact with their mothers immediately after birth, and on average once every
2–4 h. The mothers were encouraged to breastfeed and interact with their infant,
as they would normally do.
All infants were in a state of quiet alertness. Each of them was brought from
the wards of the maternity hospital to an adjacent room where two
experimenters blind as to the identity of the mother and the stranger had set
up the stimulus faces. The participant was held by an Experimenter who sat on
a chair facing the mid-line separating the two apertures from where the
stimulus faces appeared. The Experimenter maintained this optimal state
throughout the testing. A trained white-coated observer who was unaware of
the identity of the mother and the stranger, stood centrally behind the faces,
viewing the infant’s visual fixations through the same aperture as the video
camera, and recording the total duration of these fixations on a pair of buttons
box connected to a lap tope. Whenever the participant looked at the right-hand
stimulus face, the central observer pressed the right-hand switch; similarly, the
left-hand switch was pressed whenever the participant fixated the left-hand
stimulus face. Off-target visual behaviours included closing of eyes and turning
head and eyes away from the stimulus figure. The computer was programmed
to record visual fixations on line, and signal to indicate the trial ending. A
permanent record of the infant’s visual fixations was saved and printed for
later analysis.
There were two trials for each participant. Trials commenced once both
stimulus figures had been satisfactorily instructed to adopt a neutral
expression, to look directly at the neonate’s eyes and to neither move nor
make a sound during the brief test period. At this time, the neonate was
introduced to the stimuli by being brought upright into a seated position at a
point 30 cm from the central point between the two faces; the infant’s head
being supported but free to move in a lateral arc. The first trial began with the
infant’s fixation of either face, and terminated after a 20 s fixation to either or
both faces had been accumulated. After the first trial, the infant was withdrawn
from the apparatus and the two stimulus figures changed seats to counteract
the influence of side bias. The procedure was repeated for the second trial until
a further 20 s fixation had been accumulated. Over the two trials, the mother’s
face was shown once on the left and once on the right, the order being
randomly determined.
Two criteria were established for including the participant’s data. First, it was
required that the two trials must be completed to have sufficient data for
analyses. Second, to ensure that the participant had viewed both faces and had
the opportunity to actively choose between them, neonates were required to
fixate both stimulus faces. The participant’s data were excluded if the infant
spent less than 5 s viewing the least preferred side over the two trials. For each
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The Role of the Mother’s Voice 35
infant, the total fixation time towards either face was based on the live recording
of the central observer, and was then compared to the video recording. For the
test trials of eight infants, the inter-observer reliability was high (Pearson
r ¼ 0:86).
All Malay infants ðn ¼ 12Þ heard the voice of their father’s call for prayer. It
was delivered far from their mothers to prevent any association of voice cues
with the mother’s face. In the Malay culture, this message is given to the
newborn baby soon after birth for 2–3 min to ensure that it will always be heard
and answered.
RESULTS AND DISCUSSION
The data were expressed in terms of percentage of total looking time (PTLT)
infants spent fixating the mother’s face on each trial. Looking percentage for both
trials were averaged for each participant (Table 1). Each newborn infant gave
data for two trials, giving 28 trials for all the 14 participants. From the findings
with both trials included, 12 of the 14 infants looked longer at their mother’s face.
The total visual fixations to the mother and the female stranger accumulated,
respectively, 58.53 and 41.47%. The means preference for the mother on trials 1
and 2 were, respectively, 59.21% (S:D: ¼ 13:3) and 57.85% (S:D: ¼ 9:72). These
preferences are given in Figure 1.
To address the main research question, whether neonates showed significant
preference for the mother’s face over the stranger’s, single-sample t tests were
conducted. The results indicated that the newborn infants showed significant
preference for the mother’s face on trial 1, ðtð13Þ ¼2:59, p50:02), on trial 2,
(tð13Þ ¼3:02, p50:010) and on the combined trials (tð13Þ ¼3:83, p50:002).
The data replicate and extend the earlier findings that though few hours old,
Malaysian newborn infants are able to recognize their mother’s face from that of
a female stranger even when matched closely in terms of hair colour, hair length
and hair form; and when a control over olfactory and auditory cues was
implemented during the testing. However, since the control over the mother’s
Table 1. Experiment 1: Infants’ preference for the mother’s face across trials 1 and 2 and
the combined trials
Infant Sex Trial 1 (T1) Trial 2 (T2) Combined trials (COMTs)
1 M 65 50 57.5
2 M 75 70 72.5
3 M 30 48 39
4 M 50 78 64
5 M 65 70 67.5
6 M 55 59 57
7 M 60 50 55
8 F 65 61 63
9 F 85 48 66.5
10 F 45 64 54.5
11 F 60 51 55.5
12 F 65 60 62.5
13 F 50 52 51
14 F 59 49 54
Mean 59.21 57.85 58.53
S.D. 13.3 9.72 8.34
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F. Z. Sai
Figure 1. Percentage preference for the mother’s face on trials 1, 2 and on the combined
trials.
voice was limited to the testing period, experience with the mother’s voice prior
testing might have facilitated learning of the mother’s visual features.
EXPERIMENT 2
The second experiment was designed to tackle the question of auditory cues by
preventing the infants from hearing their mother’s voice from birth through testing.
All other information was available to the participants from birth to 5 to 15 min
prior testing. The mothers were encouraged to visually interact and play with their
infants without talking or making any kind of sounds. Otherwise a similar design
and test procedures to those used in the first experiment were adopted.
Method
Participants
Participants were 14, six males and eight females (M ¼ 7:35 h, range¼2 –12 h;
M birth weight¼2.91 kg, range¼2.61–3.64; with normal Apgar scores at 5 min
(M ¼ 9, range 7–10), born at the Maternity Department, University Hospital,
Kuala Lumpur, where they were tested. The data of 16 additional infants (nine
males and seven females) were discarded from the final sample because of side
bias in their looking behaviour ðn ¼ 8Þ, or the infants fussed or fell asleep before
the testing was over ðn ¼ 6Þ, or there were technical failures of various kinds
ðn ¼ 4Þ. The subjects were volunteered by their parents who agreed to participate
in the control of voice cues.
Stimuli and Apparatus
The live faces of the mother and that of a female stranger were used, matched
as in the first experiment. The mothers were Malaysians (Malay, Hindou, and
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The Role of the Mother’s Voice 37
Chinese). The mother–stranger pair was judged to be broadly comparable in
terms of hair colour, shape and facial brightness for each infant.
PROCEDURE AND DESIGN
The testing procedure was similar to that in Experiment 1 except a rigorous
control was implemented over the mother’s voice from birth through testing.
Meanwhile all the other cues (visual, olfactory, taste and tactual) were available
to the neonates from birth to 5 to 15 min prior testing. To ensure that the neonates
were at no point exposed to the mother’s voice prior testing, Experimenter 1
attended the delivery of all the neonates and remained with the mothers and
their infants from birth through testing. To successfully control for the mother’s
voice, only one pair (mother–infant) was monitored at a time until the testing was
over.
The infants were retained on the ward at all times in bassinets, located adjacent
to their mothers’ bed. They were positioned in a way that they faced each other,
and could therefore see each other from their bed. The mothers were instructed to
interact with their infant, as they would usually do without using their voice or
making any sound. They were encouraged to establish visual contacts with their
infants at birth, and at least once every 2–4 h during the feeding–soothing
process. There were cases ðn ¼ 4Þ where the mothers made sounds, and the
participants were discarded from the sample before testing.
The routine of the hospital helped in the success of the voice control. The infant
was first kept with the mother in the Intensive Care Unit or in the nursing room
for the first 2 h. Once on the wards, there were sometimes sounds and noises at a
lower level, but far from the infant. Again, the Malay babies ðn ¼ 9Þ heard their
father’s call for prayer far from the mother to prevent any association with the
mother’s face. The interobserver agreement for the test trials of eight infants,
measured as the correlation between the observers’ looking times to both sides,
was high, (Pearson r ¼ 0:87).
Table 2.
Infants’ preference for the mother’s face across Trials in the no voice condition
Infant Sex Age (h) Trial 1 Trial 2 Combined trials
1 M 5 40 60 50
2 M 5.3 80 60 70
3 M 6.55 30 5 17.5
4 M 8 50 55 72.5
5 M 7.3 65 65 65
6 M 6 30 90 60
7 F 5 40 45 42.5
8 F 5.2 60 40 50
9 F 5 60 40 50
10 F 4.27 45 65 55
11 F 7 20 50 35
12 F 3.17 45 65 30
13 F 5.54 10 50 72.5
14 F 12 65 80 72.5
Mean 6.09 45.71 55 53.03
S.D. 2.12 19.3 20.19 17.26
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F. Z. Sai
RESULTS AND DISCUSSION
The data were expressed in terms of PTLT infants spent fixating the mother’s
face on each trial. Looking percentages for both trials were also averaged for each
participant (Table 2).
To assess the role of experience with the mother’s voice in facilitating
recognition of the mother’s face, single-sample t test were conducted on the
PTLTs to the mother’s face on trials 1, 2 and on the combined trials (Trials 1 and
2). As a group, the newborn infants failed to significantly discriminate and
recognize the face of the mother on trial 1 (tð13Þ ¼ 0:83, p ¼ ns), trial 2
(tð13Þ ¼0:92, p ¼ ns), and on the combined trials (tð13Þ ¼0:65, p ¼ ns). Figure 2
displays the means percentage preference for the mother’s face across trials.
Experience with the mother’s voice prior testing seems necessary for mother’s
face recognition. The question how much experience with the mother’s voice–
face is needed for such learning to develop remains however, unanswered.
Further analyses were conducted to determine whether preference for the
mother differed as a function of condition and position of the mother’s face. The
performance of the infants in Experiment 1 was compared to that of infants in
Experiment 2. A mixed factorial design with condition (voice vs no voice) and
side preferences (position of the mother on the right side vs left side) as main
factors revealed no main effects of condition (Fð1; 26Þ ¼3:09, p ¼ ns), side
preferences (Fð1; 26Þ ¼0:001, p ¼ ns) or interaction, condition X side preferences
(Fð1; 26Þ ¼0:099, p ¼ ns). The results indicated that although the newborn infants
showed no significant differences in their preferential behaviour across
conditions, a slight preference for the mother was demonstrated in the voice
condition (Table 3). Further, the infants demonstrated a slight preference for the
mother’s face shown on the left side in the voice experiment. This pattern was
however, reversed in the no-voice experiment. (Figure 3). Perhaps when infants
failed to discriminate between the two faces, they tended to look more to the right
side. This is consistent with early reports suggesting significant head turns
towards the right side in 3 month-old infants (Gesell and Ames, 1947; Turkewitz
et al., 1965). In a study by Bahrick et al. (1996) side preferences was however not
significant at 5 or 8 months.
An interview was conducted with the mother and the female stranger at the
end of the testing of each infant in the no-voice experiment. We asked whether
Figure 2. Percentage preference for the mother’s face across trials in the no voice
condition.
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The Role of the Mother’s Voice 39
Table 3. Preference for the mother’s face across
conditions (voice–no-voice condition)
Voice
No voice
Infant Mother Mother
1 57.5 50
2 72.5 70
3 39 17.5
4 64 72.5
5 67.5 65
6 57 60
7 55 42.5
8 63 50
9 66.5 50
10 54.5 55
11 55.5 35
12 62.5 30
13 51 72.5
14 54 72.5
Mean 58.53 53.03
S.D. 8.34 17.26
Figure 3. Percentage preference for the mother’s face across conditions (voice–no voice).
the infant was attracted to the stimulus faces. For the test trials of eight infants the
agreement that infants were not attracted to the faces was high (Pearson,
r ¼ 0:87).
To conclude, the findings from Experiment 2 indicate that newborn infants are
not able to recognize their mother’s face without a previous experience with the
mother’s voice. The development of face perception in the neonatal period seems
to be, therefore, contingent on a prior exposure to the mother’s voice. It is worth
noting that compared to our previous testing including that of Expt 1, neonates
showed only few head turns towards the stimulus faces in the no-voice
condition. Nevertheless evidence suggests that defense and orientation responses
are present even in uterus. Moreover, quieting characterized by a decreased fetal
heart rate (FHR) and body movements including head orientation are signs of
attention and, perhaps, fetal cognition (Kisilevsky et al., 1998). Thus, since
orientation response is present in the term foetus, then it should be present at
birth. In the present study, the removal of the mother’s voice, as a familiar cue,
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F. Z. Sai
probably did not only hinder the neonates’ ability to learn the amodal relations,
but it also depressed their attention to stimuli around them. Accordingly, a study
designed to investigate the number of infants’ head turns across both the voice
and the no-voice conditions would certainly clarify the role of the mother’s voice
in facilitating recognition of the mother’s face at birth.
EXPERIMENT 3
The role of the mother’s voice in facilitating early mother’s face preference was
further investigated using head turn as a response measure in Experiments 3 and
4. In our previous testing (Sai, 1990; Bushnell et al., 1989; Sai and Bushnell, 1988),
the newborn infants showed a number of head turns towards the stimulus faces.
Such activity disappeared along with the control of the mother’s voice in Exp. 2.
It is however well established that sounds trigger head turns on the part of the
newborn infants. They can shift their eyes and heads in the direction of a sound
quickly and accurately (Field et al., 1980), and that they will make consistent head
turns towards a sound source even when there is no visible stimulus at the sound
locus (Muir and Field, 1979). Moreover, young infants can orient appropriately if
there is a visual pattern at the source of a sound (Castillo and Butterworth, 1981).
However, we do not know whether infants who have never heard their mother’s
voice will orient towards faces, or whether neonates will orient to silent faces
even if one of them is the mother’s face.
Method
Participants
Ten neonates, five males and five females (Mean age¼7.5 h, range¼4–10; Mean
birth weight¼3.40 kg, range 2.80–4.30), with normal Apgar Scores after 5 min
(M ¼ 9:20, range 7–10), born at the Maternity Department, Larbaa Hospital,
Algeria. The data of eight additional infants (five males, three females) were
collected and rejected from the study: four for side bias in their looking
behaviour, three for falling asleep and one for experimenter error.
Procedure and Design
Stimuli, apparatus and procedures were identical to those in Experiment 1,
except that head orientation was used as a dependent variable. Head orientation
research provided reliable results (see Goren et al., 1975; Maurer and Young,
1983). Studies investigating sound localization (Field et al., 1980; Morrongiello
et al., 1990; Muir, 1985) have reported that neonates can shift their eyes and heads
in the direction of a sound quickly and accurately.
Head orientation (head turn) was defined as when the baby oriented both his
eyes and his head towards the stimulus. Therefore, only instances where infants
oriented both the head and eyes towards a stimulus face were live recorded.
When newborn infants oriented towards a face by more than 45 degree relative to
mid-line were not considered as head turns. The reason for this selection was that
infants needed to demonstrate a full head turn so that the stimulus facial features
would be discriminated and perceived. For each head turn, a score of ‘1’ was
recorded. Alternatively, a zero was written down if the infant did not show head
orientation. Each neonate was given a 2 paired stimulus faces (the faces of the
mother and that of a female stranger) preferential looking trials, each continuing
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The Role of the Mother’s Voice 41
until 20 s of head orientation had been accumulated. Stimulus presentations was
in a random order, with the left–right positioning of mother/stranger faces
counterbalanced across neonates. Other details of testing are as described in
Experiment 1.
For each infant, the number of head turns towards the mother and the female
stranger were manually recorded on the recording sheet by the central observer.
For assessment of reliability the scoring of the videotapes of five infants was
performed by two independent coders who were blind as to the identity of the
mother and the stranger. One of them was the primary coder who scored all the
infants’ head turns. Both coders were trained for this task. The interobserver
agreement was high, (rð8Þ ¼0:87).
RESULTS AND DISCUSSION
A repeated measures Anova was conducted on the PTLTs to determine whether
the neonates showed any main effects of trials (T1 and T2) or face (Mother and
Table 4. Number of head turns towards the mother and the stranger across trials in the
voice condition
Infant Sex Age (h) MT1 MT2 MCTS SCTs
1 M 10 3 2 5 2 1
2 M 7 5 4 9 4 2
3 M 4 2 2 4 5 3
4 M 9 4 7 11 6 2
5 M 7 2 4 6 5 3
6 F 6 4 6 10 9 5
7 F 7 5 4 9 8 4
8 F 8 4 3 7 5 2
9 F 9 6 4 10 6 4
10 F 8 3 5 8 4 2
Mean 7.5 3.8 4.1 7.9 5.4 2.8
S.D. 1.71 1.32 1.59 2.33 2.01 1.23
Figure 4. Number of head turns towards the mother and the stranger across trials in the
voice condition.
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42
F. Z. Sai
stranger). Infants showed more head turns towards their mother’s face
(M ¼ 3:95) than towards the female stranger’s face (M ¼ 2:7) and this difference
was significant (Fðl; 9Þ ¼15:4, p ¼ 0:003). Also, neonates turned their heads more
towards the mother on trial 2 (M ¼ 4:1) than on Trial 1 (M ¼ 3:8), and this
difference was significant (Fð1; 9Þ ¼0:018, p ¼ ns), (Table 4). The interaction of
face x trial failed to reach significance (Fðl; 9Þ ¼0:78, p ¼ ns). Preferences for the
mother and the stranger are given in Figure 4.
From the findings with both trials included, newborn infants demonstrated
more head turns towards their mother’s face (M ¼ 7:9) than towards the female
stranger (M ¼ 5:4). Further, head movements were observed but were not
considered as full head turns, as defined above. Preference for the mother’s face
was further replicated in the present study with non-Caucasian faces, and with
head orientation as a response measure. A possible interpretation of the findings
is that since both the mother’s voice and visual cues were available from birth to
the time of testing, neonates might have demonstrated a long-term memory effect
for their mother’s voice–face relations in the recognition test.
EXPERIMENT 4
The purpose of this study was to determine whether the absence of the mother’s
voice, from birth through testing, would result in less head turns towards the
mother’s face.
Method
Participants
There were 15 participants (eight males and seven females) successfully tested
in this experiment while a further 10 infants were eliminated from the sample
because of side bias in their looking behaviour ðn ¼ 4Þ or fell asleep ðn ¼ 6Þ. The
mean age of the sample was 6.31 h (range 2–10), the mean birth weight was
3.30 kg (range 2.98–3.60), the mean Apgar score after 5 min was 9.50 range 7–10).
They were born and tested at the Maternity Department; Larbaa Hospital,
Algeria.
Procedure and Design
The stimuli, apparatus and procedures were identical to those in Experiment 2,
except head orientation was adopted as a dependent variable as in Experiment 3.
Participants were randomly assigned to the testing. A trained observer, unaware
of the subject’s mother, monitored head orientations using video taping. A
second observer monitored head orientations for half of the subjects. Interobserver
reliability was calculated and the correlation between observations of
the primary and secondary observer was high (Pearson r ¼ 0:87).
RESULTS AND DISCUSSION
Head orientations towards the mother and the stranger were calculated as before,
and this information is set out in Table 5. The subjects had almost equal
preferences for the faces of the mother (M ¼ 1:72) and that of the female stranger
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The Role of the Mother’s Voice 43
(M ¼ 1:94). A repeated measure analysis of variance was performed with trials
(trial 1 trial 2) and face (mother, stranger) as within subjects factors. The results
revealed no main effect of face (Fðl; 15Þ ¼1:77, p ¼ ns) with newborn infants
demonstrating no preference for the mother’s face when no previous postnatal
exposure to the mother’s voice was available to them from birth (Figure 5). No
main effects of trials (Fðl; 15Þ ¼0:51, p ¼ ns), or interaction of trials x face
(Fðl; 15Þ ¼0:69, p ¼ ns) were found.
Additional analyses assessed the effects of experience with the mother’s voice
and side preferences across Experiments 3 and 4. A 2 (condition: voice vs no
voice) x 2 (position of the mother: right vs left) mixed factorial design was
Table 5.
Number of head turns towards the mother and the female stranger across trials
Infant Sex Age (h) Mt1 Mt2 MCTs St1 St2 SCTs
1 M 6 1 4 5 2 4 6
2 M 9 3 2 5 3 4 7
3 M 6 3 1 4 2 2 4
4 M 7 1 2 3 1 3 4
5 M 7 1 3 4 3 1 4
6 M 5 2 1 3 1 1 2
7 M 10 1 3 4 1 4 5
8 M 7 2 2 4 1 2 3
9 F 8 2 2 4 3 0 3
10 F 9 0 3 3 2 2 4
11 F 5 2 2 4 3 2 5
12 F 6 2 1 3 2 1 3
13 F 8 0 0 0 2 2 4
14 F 4 1 2 3 3 0 3
15 F 2 2 1 3 1 2 3
16 F 2 1 2 3 1 1 2
Mean 6.31 1.5 1.94 3.43 1.94 1.94 3.87
S.D. 2.33 0.89 0.99 1.15 0.85 1.29 1.36
Figure 5. Number of head turns towards the mother and the stranger across trials in the
no-voice condition.
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44
F. Z. Sai
conducted to determine whether infants showed any main effects of experience
with the mother’s voice or side preferences. The results revealed a significant
main condition effect (Fð1; 24Þ ¼40:42, p ¼ 0:05) with neonates who had
experience their mother’s voice demonstrating more head turns toward the
mother’s face (M ¼ 3:9, S:D: ¼ 0:26) than those who had not been exposed to
their mother’s voice (M ¼ 1:72, S:D: ¼ 0:213). There were no main effects of side
preferences (Fðl; 24Þ ¼0:208, p ¼ ns), or interaction of condition x side preference
Figure 6. Number of total head turns to the mother and the stranger across voice–no-voice
conditions.
Table 6. Number of total head turns towards the mother and the stranger across voice–
no-voice conditions
Voice condition
No-voice condition
Infant MCTS SCTS Infant MCTS SCTS
1 5 2 1 5 6
2 9 4 2 5 7
3 4 5 3 4 4
4 11 6 4 3 4
5 6 5 5 4 4
6 10 9 6 3 2
7 9 8 7 4 5
8 7 5 8 4 3
9 10 6 9 4 3
10 8 4 10 3 4
11 4 5
12 3 3
13 0 4
14 3 3
15 3 3
16 3 2
Mean 7.9 5.4 3.43 3.87
S.D. 2.33 2.01 1.15 1.36
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The Role of the Mother’s Voice 45
for the mother’s face (Fðl; 24Þ ¼0:208, p ¼ ns). The occurrences of head turns
toward the mother’s face in the voice experiment were more frequent than in the
no-voice experiment regardless of the position of the mother (Figure 6). The
number of head turns towards the mother and the stranger were calculated as
before and are displayed in Table 6.
GENERAL DISCUSSION
The findings from these studies show that neonates can visually recognize their
mother’s face only if a postnatal exposure to the mother’s voice–face combination
was available. A common expressed interpretation of the presence of the
mother’s face recognition in the neonatal period is in terms of an innate
perceptual mechanism that detects and responds specifically to faces (Johnson
and Morton, 1991; Meltzoff, 1995; Walton et al., 1997). The present results do not
support this hypothesis. If the CONSPEC mechanism, were the only mediator for
face preference at birth, then infants would have been able to recognize their
mother’s face even when no postnatal exposure to the mother’s voice was
available. As well as showing that at birth there is a preference for some spatial
frequencies that are shared by other stimuli other than face-like pattern, would be
insufficient to claim that there is an innate mechanism specific for faces. The
present findings indicate that preference for the mother’s face is not exclusively
determined by the unique structure of the face. Rather, intermodal structural
properties, which other stimuli possess, would be crucial in determining
newborns’ preferences for the mother’s face.
Thus, the model may be able to explain face preference in older infants,
but it cannot account for the data from studies with real faces which
had been previously associated with voice cues such as the mother’s
voice. Nor can it explain the neonates’ failure to recognize the mother’s
half-profile face where information about the internal configuration was still
available (Sai, 1994).
Given that the infant is born in a multimodal stimulation unit, it is very absurd
to constrain preference for the mother’s face within visual parameters.
Alternatively, an explanation, which takes into account both the auditory and
visual information, would be plausible, especially that young infants are adept
perceivers of multimodal stimulation (Lewkowicz and Lickliter, 1994). They
rapidly turn their heads and eyes in the direction of a sound source (Wertheimer,
1961; Butterworth, 1983; Muir and Clifton, 1985), and they quickly learn arbitrary
visual–auditory associations (Slater et al., 1997). Thus, the amodal information of
temporal synchrony of voice and lips seems likely to facilitate learning the
mother’s voice–face combination. The multimodal stimulation of the mother’s
face–voice could be more powerful than Conspec in attracting newborns’ eye and
head turns.
Learning the mother’s voice–face association might be therefore, initially
triggered by the mother’s voice, a highly familiar stimulus from the time of
uterus. It is then strengthened with exposure to the mother’s voice and face
association. Once this latter has been encoded, the sight of the mother’s face
alone might elicit a visual recognition of the mother’s face as demonstrated in
Exps. 1 and 3.
The particular attractiveness of the mother’s voice has been documented by
several authors (see Andre-Thomas, 1966; Brazelton, 1978). The argument
accounting for this phenomenon could be a postnatal association of the mother’s
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46
F. Z. Sai
voice with positive reinforcers such as the sight of the mother. Conversely,
preference for the mother’s face is likely to be rooted in foetal exposure to the
mother’s speech (Decasper and Spence, 1991; Turkewitz, 1988; Richards et al.,
1992). A growing body of evidence has demonstrated the functioning of foetal
sensory systems during gestation, as well the sequential functional development
of sensory systems (for review, see Lecanuet and Schaal, 1996). The auditory
system develops much earlier than the visual system (Gottlieb, 1971), and healthy
full-term human foetuses respond to a wide variety of sounds and vibrations
originating from outside the womb (Birnholz and Benaceraf, 1983; Kisilevsky and
Muir, 1991; Lecanuet et al., 1986; Serafini and Lindsay, 1984). As well, FHR and
movements to vibroacoustic stimulation were reported in foetuses as early as 26
weeks gestation (Kisilevsky et al., 1992). Data from studies on uterus speech
transmission performed with a hydrophone near the foetal head during delivery,
have revealed a significant better transmission of the maternal voice than of the
external voice (Querleu et al., 1988). We also know that the mother’s voice is the
only auditory stimulus that is transmitted internally via body tissues and bones
(Petitjean, 1989); it also involves diaphragmatic movements generating pressure
changes in the fluid medium of the uterus. Also, prenates of mothers who
listened to ‘soap opera’ theme music during pregnancy showed a preference for
the same music during the postnatal period (Hepper, 1988). The longer the
prenatal exposure of human neonates, living in the Osaka airport neighbourhood,
to airplane noises, the better they slept compared to babies whose mothers
had lived in the area of the airport for shorter times during pregnancy (Ando and
Hattori, 1977). The work of DeCasper and Fifer (1980), DeCasper and Spence
(1986), DeCasper and Prescott (1984) reveals a complexity of bonding and
language processing during the prenatal period. Given that the presence of
potential sensory stimulation in the foetal milieu as well the presence of foetal
sensory sensitivity to acoustic (e.g. Lecanuet et al., 1995) and vibroacoustic (e.g.
Kisilevsky, 1995) stimuli, and the continuity of foetal and newborn response to
sound and vibration, it is, therefore, possible that neonates are born with a longterm
memory for the mother’s voice.
However, the question whether the neonates rapidly associate the mother’s
voice–face at birth, or demonstrate a long-term memory effect for the mother’s
voice learned while the foetus was still in the mother’s womb remains
unanswered. Nevertheless, data from one of our studies in which newborn
infants were exposed to both the mother’s voice and face, among others, show
that mother preference was stronger with shorter delays than with longer delays
between last exposure to the mother and preference testing (Sai, 1990), indicating
that learning the mother’s face is very stable and established as a long-term
memory. The mother’s voice–face association seems, therefore, to take place at
least shortly after the infant’s birth.
These findings replicate and extend our previous research suggesting a rapid
learning of the mother’s face at birth. Such learning, however, vanished when a
previous exposure to the mother’s voice–face combinations (Exps 2 and 4) was
made unavailable to neonates from birth through testing. A prior exposure to the
mother’s voice–face combination remains, therefore, a significant predictor of the
mother’s face recognition at least within the first days of birth. We still do not
know precisely what visual features, the newborns associated to the mother’s
voice in order to make their preferential choices. Nevertheless, the results
strongly suggest an intermodal learning at birth, probably facilitated by a longterm
memory for the mother’s voice learned in the confines of the womb. One
interesting direction for future research concerns the amount of exposure to the
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The Role of the Mother’s Voice 47
mother’s voice–face combination that the newborn infants need to develop
preference for the mother’s face.
Note: A comment made by an anonymous reviewer concerns the use of related
t-tests in present studies and in our previous research (Sai and Bushnell, 1988;
Bushnell et al., 1989; Sai, 1990). The data have been analysed again using singlesample
t tests as suggested by the reviewer, and significant results were obtained,
as is the case in the present studies.
ACKNOWLEDGEMENTS
This research was partly supported by IIU) Malaysia. I gratefully acknowledge
the assistance of Nabila Sai and Sarah Amrani in testing the neonates.
Appreciation is expressed to the parents and infants who participated in the
study, as well as to the nurses and Staff of both Larbaa Hospital, Algeria and of
University Hospital of Kuala Lumpur, Malaysia. I also thank Pr. Darwin Muir,
Dr R. Dillon, Dr C. Moon, an anonymous reviewer and Mohammed Defairi for
their insightful comments on an earlier version of this paper.
Portions of these data were presented at Development, 2000: A conference on
Developmental Psychology, University of Waterloo, Waterloo, Canada, and at the
XII Biennial International Conference on Infant studies, Brighton, UK. July 2000.
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