PERCEPTION OF LINGUISTIC RHYTHM BY NEWBORN INFANTS
Experiment 2: Saltanaj
resynthesized speech
Materials and Method
Stimuli
We used the same sentences as for Experiment 1, but we
resynthesized them in the saltanaj manner described by Ra-
mus and Mehler (1999). For each sentence, the fundamen-
tal frequency (F0) is measured, phonemes are identified and
their duration measured. These parameters can be manipu-
lated at will, and then used as input to the speech synthe-
sizer MBROLA8 (Dutoit, Pagel, Pierret, Bataille, & van der
Vrecken, 1996). The saltanaj manipulation involves reduc-
ing the phonemic inventory of the sentences, by mapping
each phoneme to a single instance of the same manner of
articulation: fricatives are mapped to /s/, vowels to /a/, liq-
uids to /l/, plosives to /t/, nasals to /n/ and glides to /j/. The
exact phoneme durations as well the F0 curve are copied
from the original sentences. Thus, the overall rhythm and
intonation of the sentences are faithfully preserved, together
with broad phonotactic characteristics. However, phonetic
and fine phonotactic differences are eliminated. Obviously,
access to syntax and meaning is blocked as well. Voice
differences are eliminated, since a single synthetic voice is
used; however, prosodic differences between speakers are
preserved. It therefore still makes sense to have a speaker
change in the control condition, where "speakers" refers to
those who produced the original sentences.
Incidentally, resynthesis gives full control over the aver-
age fundamental frequency which, we have noted earlier, was
significantly different between the two languages. We have
thus decided to reduce this difference by multiplying all F0
values by 1.04 for Dutch, and by 0.96 for Japanese. Note that
although this manipulation removes a possible confound, it
is not a very plausible one. Indeed, in Experiment 1, the fact
that Japanese speakers have a higher pitch on average isn’t
sufficient by itself to allow for a discrimination.
Procedure
Hesketh, Christophe, and Dehaene-Lambertz (1997), test-
ing 2-3 month-olds with the non-nutritive sucking procedure,
have improved the habituation paradigm by having each baby
undergo 2 shifts (one of language, one of speakers). Thanks
to the within-subject design, they found that the statistical
power increased, and thus needed fewer subjects to complete
an experiment.
Here we have tried to adapt this 2-shift design to experi-
mentation on newborns. The first two phases of the experi-
ment were run exactly as in Exp. 1. After a baby had under-
gone the first shift and the four-minute test phase, a second
shift was made possible. It was subject to the same habit-
uation criterion, delay and rejection conditions as the first
one. When met, it allowed the baby to undergo a second
four-minute test phase. In that case, the second shift was of
a different kind (language or speaker) to the first one. Babies
who didn’t successfully pass the second shift were neverthe-
less kept for analysis of the first shift.
Thus, this attempt at improving the procedure did not in-
terfere with the collection of the data on the first shift, mak-
ing it possible to independently analyze the results of the two
shifts. Indeed, for all babies, everything was as in Exp. 1 up
until the fourth test minute. Some babies were just allowed
to go on further if they could. This experiment was stopped
as soon as 32 babies successfully passed the first shift.
Participants
Thirty-two babies were successfully tested, 16 males and
16 females, with a mean age of 80 25 hours, a mean ges-
tational age of 39 0; 6 weeks and a mean birth weight of
3508 477 g. Twenty-five came from monolingual French
families, 3 from families where one or several other lan-
guages than French are spoken and 4 from a family where
no French is spoken. The results of 20 additional babies
were rejected for the following reasons: sleeping or insuffi-
cient sucking before the first shift (6), crying or agitation (4),
failure to meet the habituation first criterion (1), sleeping or
insufficient sucking after the first shift (3), loss of the pacifier
after the first shift (6).
Results
First shift
Figure 2 shows the number of HA sucks per minute for
the two groups of babies. There was no significant group
effect on babies’ sucking during the 5 pre-shift minutes
[F (1,31) < 1], neither was there an effect of the habitua-
tion language [F( 1,31) = 1.8, p = 0.19]. An ANCOVA
on the 2 post-shift minutes, controlling for the 2 pre-shift
minutes, showed a significant group effect [F( 1,29) = 6.3,
p = 0.018], indicating that babies in the experimental group
increased their sucking significantly more than those in the
control group. This leads us to the conclusion that the babies
in the experimental group were able to discriminate between
the two languages.
Second shift
Out of 32 babies successfully passing the first shift, only
11 passed the second one. The results of the remaining 21
were discarded due to sleeping or insufficient sucking before
the second shift (7), crying or agitation (2), failure to meet the
second habituation criterion before the 20 minute time limit
(6), sleeping or insufficient sucking after the second shift (4),
loss of the pacifier after the second shift (2). The small pro-
portion of babies able to undergo the second shift already
shows that this procedure, as used on 2-month-olds, is not
viable for newborns: it would lead to discard too much data
(here, a total of41 babies out of 52).
8 MB ROLA is freely available from
http://tcts.fpms.ac.be/synthesis/mbrola.html.